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2. - HVAC Education Australia

1. Z iia arad UNOS SSE En st 2 AE et See as ES As shown opposite a Velometer can also be used to measure velocity and y therefore calculate total air volume N A A eonen a ka 4 kal e E A ARA fenna 6 6 6 4 ERA e N AE aU oN HA e gt WR Ke d ii Traverse across filters CO Pn IA e SR oa Sometimes we must use an alternate location for e measuring total N PERETE raw air volume The lt a Ze same methods i ee covered previously eT g Y Y ES can be used to De os E A measure total air volume at the filter location ae N t wk G Ea sats Y ater The balancer is taking a reading across the filter to determine ve locity using a velome ter 111 Traverse in main duct A third alternative for measuring total air volume is in the main discharge duct Measurements must be made in a straight section of duct approximately ten duct diameters dounstream from an elbow or fan and between two and five duct diameters upstream from an elbow on take off A Velometer fitted with a duct jet may be used to traverse the duct and this is the preferred instrument when the duct velocity is below 5 m s When the duct velocity is above 5 m s then the pitot tube is generally used to calculate the total air flow a Quickly removable plug inst
2. Question 14 With the aid of a drawing describe three different duct layout systens A sent B AS 5 C Question 15 What is an abrupt expansion and how can some of the resistance created by them be overcome pete Siria atte Sipinen 6 Question 16 Describe spot cooling and give an application S A aAA naaa o o Question 17 What regulates the amount of cooling that can be obtained from the use of Evaporative cooling te A ae eee ten A E TT reacio Question 18 Although Evaporative cooling is cheaper to run what other requirements of Evaporative coolers Ay By G LEARNING OUTCOME 3 Assessment Practical exercise student report Performance a State the application of several different ductwork components b Select from an installation specification all duct work component items required to install the system C List what installation equipment would be needed to carry out the installation in part b FANS FILTERS Classifications and types Impurities in air Construction materials Particle size Applications Types of filters Service requirements Applications Operating characteristics Service maintenance requirements Identification Odour removal Bearings and shafts Absolute filters Power consumption Service schedules Balancing Problems arising
3. nn AR EEES SST OOO ODO DO OO O CONO Question 7 How is odour generally filtered out of the air in an air conditioning system LT NT NN EAST reserpine airs rrr tities ra rl to Question 8 What do you expect to happen to a Direct Expansion coil if the filters are A Removed from the system for a reasonable period of time A a A ALA B Allowed to clogg up LEARNING OUTCOME 4 Assessment Performance TEST EQUIPMENT Practicality Types available Usage and care Calibration Flow characteristics Appropriate formulas Units of measurements Application Use of information gathered Permanently installed portable Expected results Suggested teaching time 4 hours Short answer practical exercise Briefly describe the correct operating procedures for a range of test equipment commonly used on ventilation equipment and state how the information gathered could be used Use the most appropriate items of test equipment to take the following measurements air Volume air Velocity air Pressure sound power level from various points on a ventilation air conditioning system Whilst carrying out the above procedures the student will explain to his her lecturer how they have arrived at their measurements what they consider to be the most appropriate units to use and how the above measurements are related NOISE VIBRATION Source of noise Nature of sound
4. Wiis v RA ES E E ES 5 Z 7 E Weenies Z a ES Z a EIA Z E ES SEE E E A Y S A Sirisa ALCULATIONS apponi Question 9 What is meant by the term surge as applied in fan terminology and how can it be corrected a s e o e o y s o G 9 y 9 A y S o M M MG IG a 2 20 02o0ox2b 0 2 2 0 Po o 4 Hd gt e gt o o o b U gt S gt 9 gt gt o o o t o lv oo y 06 0 H H HT T H s OoOO O 2 0 0ox0b0 as a N e gt o o l o TH TH o H H HL H H H H 1 1 1111 x gt gt gt e e e a a e e e 19 60 04 e e A 6 8 R ER AIR CLEANING ASSEMBLIES La ER One of the concepts of air conditioning is that the air introduced into the zone should be clean Some of the advantages of air being cleaned is that dirt removed by the filter keeps the inside of the building cleaner and clean air passing over a dehumidifying coil prevents the moisture and dust forming a muddy coating on the coil reducing its het exchange efficiency and increasing its pressure drop Increase pressure drop will result in less air flow again reducing the heat e chang
5. o o e a k e s o k o G F A G O G e L 4 gt L L e o a s gt e L L e 02 20 0O lt 0O _ e ee e e e ae ee ae e e 6 a e e e e e e eK 6 E o 2 2 1 8 2 2 0 o0 0o 0o _ e 2 ee 2 2 o AO gt gt C es a eee sea ee e e e a e a a e e ee 4666 6 KK 6 E 6 0 o o o 2 2 2x2020202 20 2 eo 2 s o o a a o e amp amp o o o 6 0 S o e oe 80 O o e p 6 aae Bits e o 9 e 6 060 06 6 a e x amp o 8 eo L o L o o o a e e s e o o e vra mr L Question Give the formula and state the definition which explains what happens to the pressure in a constant duct system if the air flow is varied s a a amp e e o gt gt amp y k o oy s o o s lo e o d 60 US55PsA OO s L s e L e L gt s o 6 o 9 e 9 S 9 g s a o p o L e e e e gt a 4 2 e gt e L L a e L e s t e e 6 6 e oe 6 e s o o o a e e gt e 4 amp e o 9 y y G gt G 4 6 y E F o 9 L a e gt L e e L L L L a L oe gt o KKK o g
6. 1 2 3 5 6 7 8 9 0 mal The irritation caused by noise depends unon frequency and loudness The unit used for sound measurement is the Decibel dB scale is a logarithmic scale which results in a small range of numbers to cover the audible range of the human ear The decibel It ts to be noted that decibels cannot be added or subtracted by ordinary arithmetic For each frequency band noises as experienced by the human ear have been ascertained and the noise rating N R curves established N R curves are in S I units the older N C curves are not Both curves are interchangeable SOUND PRESSURE LEVEL dB The N R curves are used to determine the noise present in a situation N R ratings above 85 can cause temporary or permanent hearing damage OCTAVE BAND CENTRE FREQUENCIES o L P Ln O gt 3 O D O S A C TT AA ls j CL HT Z ZZ S tit TAT fo 0 O a g ASS T gt Z a X A L XN INS N 10 i eas ee Ld ex 9 T 15 LL ISSN 31 5 2000 8000 125 500 OCTAVE BAND CENTRE FREQUENCIES NR CURVES NR CURVE NUMBERS ene da puras Table Recommended noise ratings Typical application Concert halis opera halls sound studios large theatres Lecture rooms small theatres cathedrals Living rooms board rooms offices conferences small lecture rooms Hotel rooms hospital wards small offices Restaurants bars night clubs departmental
7. A combined induction ammeter and voltmeter is generally used for current measurement This does not have to be wired into the circuit it is easy to use and has an accuracy of 3 full scale The trigger operated jaws of the ammeter is placed around the conductor at any convenient point and the induced current in the ammeter is indicated as the actual current flow in the conductor Insulation does not affect the reading but the instrument will only work on a Single conductor not a twin cable With three phase motors take readinos on each of the three wires and average the results The instrument described can also be used for measuring voltage although in practice measurements are not often required induction Ammeter SOUND LEVEL Noise and vibration caused by fans pumos compressors etc may produce sound Noise is simply undesirable sound The frequency range of human hearing varies from person to person and age reduces ability to hear higher frequencies The audzo frequency range for humans is generally 20 Ez to 20 000 Hz The audio frequency range is divided into 10 groups octave bands The centre frequency geometric mean frequency of each band is half that of the next higher band High frequency will be heard as high pitched sound Table Band Frequency limits Centre frequency number Hz Hz 20 50 50 78 78 200 200 312 312 800 800 1 250 1 250 3 200 3 200 5 000 5 000 12 800 12 800 20 000
8. EU AANS LEARNING OUTCOME 1 Assessment Short answer practical exercise Performance a List the general distribution requirements for ventilation air conditioning system applications b Inspect two different ventilation systems and state how they do or do not meet the above requirement REQUIREMENTS Basic Human Comfort Duct Work Construction Site Work Necessary Skills How to Install new buildings existing buildings Spot Cooling heating Return Air Evaporative Systems Refrigerated Systems Basic layout of system and compatibility with other mechanical services Suggested teaching time 4 hours VENTILATION NR13 LEARNING OUTCOME 1 THE PROCESSES OF AIR CONDITIONING Different levels of comfort for occupants of buildings can be achieved by processes varying from the opening of windows to the full air conditioning by mechanical processes This chapter deals with the principles of natural and mechanical ventilation evaporative cooling and full air conditioning whilst the remainder of the text deals in detail with the mechanical processes most extensively used by Australian engineers Discomfort results from extremes of temperature for which the only solution is heating or cooling and from stuffy conditions which can result from poor air movement high humidity and concentration of odours or smoke Ventilation can usually provide the remedy NATURAL VENTILATION The prime purp
9. vi Variable pitch pulleys not adjusted so each groove has same pitch diameter Vil Misaligned pulleys viii Worn belts ix Motor motor base or fan not securely anchored X Belts oily or dirty xi Incorrect drive selection Es _Bearing PROBABLE CAUSE 1 Defective bearing 11 Needs lubrication iii Loose on bearing support iv Seals misaligned VY Worn bearing vi Corrosion between inner race and shaft d Shaft Seal Squeal PROBABLE CAUSE 1 Needs lubrication 11 Misaligned e Impeller PROBABLE CAUSE 1 Loose on shaft 11 Unbalanced Shaft PROBABLE CAUSE 1 Bent 11 If more than two bearings are on a shaft they must be properly aligned High Air Velocity PROBABLE CAUSE 1 Ductwork too small for application 11 Fan selection too small for application ill Registers or grilles too small for application iv Heating or cooling coil with insufficient face area for application Rattles Rumbles or Whistles PROBABLE CAUSE 1 Dampers 11 Registers 111 Grilles iv Sharp elbows v Sudden expansion in ductwork vi Sudden contraction in ductwork vii Turning vanes viii Leaks in ductwork 1X Fins on coils X Vibrating ductwork xi Vibrating cabinet sections xii Vibrating parts not isolated from building Pulsation or Surge PROBABLE CAUSE Restricted system causing fan to operate at poor point of ratings 11 Fan too large for application lil Ducts vibrate at some frequency as
10. windows Larger but similar units may be installed on roofs with air ducted to required rooms Nair WATER DISTRIBUTOR TROUGH BLEED OFF ADJUSTMENT y TROUGH FILTER MOTOR SPLASH PLATE AD RACK ESE WATER TRAY a Y Z Y L Q G WATER PUMP LC OVERFLOW PIPE ASSY BLOWER WHEEL pd BALL VALVE ASSEMBLY WATER PUMP STRAINER Typical evaporative cooler Evaporative air conditioning is cheaper than mechani ition nical air conditioning but requir acceptance by the user that E equires a The temperature achieved depends upon the outside air humidity rather than temperature b All air brought into the space by the unit must be exhausted at the same rate c The higher air volume needed may result in higher noise levels and draughts Figure 19 21 shows relative requirements of conditioned and evaporative cooler air requirements Limited air mwana around window doors etc is returned Controlled fresh air intake wy A Uu a Air conditioners need a closed system for recirculation Ceilin ri 7 Windows ASUS b Evaporative coolers need large open areas for air release Fig 19 21 Evaporative cooler requirements e SR o a rne E rc marp 7 l FILTER J f L E A SPRAYED COOLING COIL LONE HEATER i E SUPPLY a FAN SILENCER Quaid awe ees eR room EXTRACT FA
11. Filter Coil Area Location Design m s System Actual nm Ge CU Gare agus l 0 1 ll Area sq M X Average Velocity m s Air Volume m s j 8g M X m s K m s Area Average Velocity Air Volume S Instrument By orogen eg o ae e A ty asemene or w o a e a S d _ BARBER COLMAN COMPANY e Rockford Illinois U S A Dra gt E A K ea af ea T lt ena edeg A ne e lt A L sot Brest A NS E Barber Colmen Company Air Distribution Division GATITO AIR BALANCING WORK SHEET 1300 Rack Street WENN BB Rockford IL 61101 TT ws Duct Velocity Traverse DUCT VELOCITIES m s Traverse Date Test No Traverse Job Name Points Location AT System AAA l i a eee ee Duet S120 AAA A A ae are Duct Area _A _AA lt gt A AAA LA 2 Fo ae e Design m 5 MA T J o ooo ooo ee Actual m Is oe a o T EJ NORIA AO NAO TENES PEE E DE E AA A 7 L OURAN O SM O nf tot of tot pe jut tt Y ae Volume Instrument By 4 Determining the correct nroportion of outside to total air is basic to the proper balancing of any system The most practical method of setting outside air proportional dampers is the mixed atr temperature method Tmix OA x Toa RA x Tra where Tmix Temperature of air mixture Toa Temperature of outdoor air Tra Temperature of return air SOA Percentage of outdo
12. It is actually a comparative location description with respect to the tubular centrifugal which is mounted directly in the ductwork In this latter instance the fan housing is tube shaped and the fan is turned so that the air enters axially After passing through the fan the air is discharged toward the side of the housing and must be redirected 90 back to the axial direction The intent is to conserve floor space It must be recognised that velocities are often high to keep size down and installation conditions at inlet and outlet as well as internal design provisions are extremely important to prevent excessive losses and noise It is possible as in the case of the axial fans that incorrect installation can practically destroy the effectiveness of the fan by excessive local pressure losses CENTRIFUGAL FANS The centrifugal fan comprises an impeller which rotates in a casing shaped like a scroll as illustrated in figure 2 1 The impeller has a number of blades or plates around its periphery similar to a water wheel or the paddle wheel of some shallow draught river steamers The casing has an inlet on the axis of the wheel and an outlet at right angle to it When the impeller rotates the blades at its periphery throw off air centrifugally in a direction following the rotation The air thrown off into the scroll is forced out of the outlet as more and more leaves the blades At the same time air is sucked into the inlet to replace that
13. stores lobbies post offices reception areas shops Cafeterias canteens supermarkets Swimming pools bowling clubs laundry rooms kitchens computer rooms accounting machine rooms Justifiable in factories Recommended noise rating curve NR 50 and above seeds To arrive at the noise level of say a supplv air fan involves measuring sound pressure level at different frequency bands These valves are then used in conjunction with the N R curves and Ed recommended noise ratings to determine if the sound level is accept i able Either a Sound Level Meter or a Frequency Analyzer can be used Both instruments work on the same principle MICROPHONE AMPLIFIER INDICATING OR METER AMPLIFIER WITH FREQUENCY ANALYSER The microphone picks up and converts the sound impulses into electronic impulses These are amplified and passed on to the indicating meter E which gives sound pressure readings in dB The sound level meter consists of a microphone an amplifier and an indicating meter The frequency analyzer consists of a microphone an amplifier with frequency analyzer and an indicating meter In the sound level meter there are three scales scale A is used for low noise intensity levels 55 dB and below scale B for medium noise intensity levels 55 dB to 85 dB and scale C for high noise 85 dB and above In the frequency analyzer the sound pressure levels in each of the octave bands can be obt
14. 2 where Pv Velocity Pressure Pascals Pa Density kq m3 Velocity metres second m s lt l H Py 0 6 V V m Hv Velocity head in mm of water a Assume density of air as 1 2 kg m b The manometer is graduated in Pascals Pa ey Pv 2 where Pv Velocity pressure Pascals Pa Density ka m gt V Velocity metres second m s 2 ez Pvy m 1 2 xV 2 4 Py 0 6 VUZ 2 Pv oe Oe Pv v j 0 6 These formulas are essential in testing and balancing because with instruments and procedures covered later the velocity pressure Pv in a duct can be measured and then the velocity can be calculated using these formulas 4 Air velocity in a duct determines the volume of air flowing in the duct as found by Volume m 5 Velocity m s x Area m 5 Duct sizes are given in millimetres therefore rea a For a round duct e 2 Area m a or 1 where D Diameter of duct in millimetres r Radius of duct in millimetres 2 Il Dmm ye II je oe XL MM een E 1000 1900 4 b Tor a square or rectangular duct Area m Length L x Depth d 2 _ Imm drm BNE Amd gag 1000 EXAMPLES 1 Duct size 450mm x 350mm Velocity 7 5 mS What 1s the volume in m gt s Solution Velocity m s x Area m7 450 350 1000 1000 U Volume m s V TeS X V 1 18 m s approx A G piir Errn 2 Specified Air flow 1 0
15. 334 2 800 018 OTH PAT PEND bu REMOVE THIS COVER FOR ACCESS TO BATTERIES USE ONLY LEARPROOF BATTERIES FOR ALPLACE MENT The instrument is also provided with temperature be read by selecting the correct button also be measured on some instruments if the proper vrobe is supplied with the instrument scales that can Static pressure can i i The probe of the hot wire ane mometer is quite directional and must be used in the precise location recommended by the outlet manufacturer Probe Measuring positive static pressure Measuring air velocity in neck of a round diffuser q l Measuring grille Measuring negative static pressure face velocity a t i a l m at ia k s s e e A ET ES MS PE e a o ER Y ur x C J Je Fe A E AAR TERK VY ESTE e TO a w e y e xo x a 5 amp e 6 a oct A x gt a A L BA A pan E K La 7 a p K L p H C ee be PE i iaia A lt dd e F LTE Stee tg OOE RZ r a WYRE F a 3 4 P P PZ 4 x e e os a SA a S l A A An j E A K L SR ep at fee ENG e E LA ee ie D ont veg Fed XL 0 ae ded Tad y os po a we a Pe N e w A eD TRS L E ts z gt gt lt F L sh a d Q ERA deso a oe gt Typical applications of the hot wire anernometer to air flow measurements e Variable Area FLouncter The anemometer shown is classified as a variable area flowmete
16. backward inclined blade fan must be selected closer to free delivery therefore it does not have as great a range of high efficiency operation as does the backward curved blade fan Manufacture of an inclined blade is understandably a simpler operation ALA KILLS AIRFOR INCLINEN d e PS ADVANTAGES 1 pA 5 More efficient Horsepower curve has a flat peak so that the motor may be sized to cover the complete range of operation from zero to 100 air flow for a single speed Non overloading Pressure curve is generally steeper than that of the forward curved fan This results in a smaller change in air volume for any variation in system pressure for selections at comparable percentages of free delivery Point of maximum efficiency is to the right of the pressure peak allowing efficient fan selection with a built in pressure reserve Quieter than other types RADIAL BLADE FAN The radial blade fan has efficiency speed and capacity characteristics that are midway between the forward curved and backward curved blade fans Itis seldom used in air conditioning application because it lacks an optimum characteristic Typical performance of a radial straight blade fan is shown in Figure 5 1 The pressure characteristic is continuous at all capacities Horsepower rises with increasing air quantity in an almost directly proportional relation Thus with this type of fan the motor may be overloaded as free air delivery is a
17. conditions do you need to use metal braid hose LEARNING OUTCOME 5 Assessment Student report practical exercises Performance a Develop an appropriate checklist with all information formulas etc needed to carry out an air balance to a given specification b Using the above checklist and all other required equipment air balance a ventilation air conditioning system that has several fixed volume supply registers ATR BALANCE Specifications Methods of ratio Application of test equipment Rules of thumb Checklists Equipment required New installations existing installations Fault Finding Adjustment methods Pitfalls Suggested teaching time 4 hours a e d DEFINITION OF BASIC TERMINOLOGY Volume of Ar Volume of atr flowing in a system is the flow rate produced by the fan independent of the density of the air expressed as 1 Cubic metres per second handled by a fan at any density m s ii Litres per second handled by a fan at any density 1 s Outlet Velocity This is the theoretical velocity of the air as it leaves a fan or air distribution outlet and is calculated by dividing the air volume in m s by the fan or outlet nett area in m and is expressed as Metres per second m s Laminar and Turbulent Flow When air flows throuch a duct system at low velocities the particles follow paths free from eddy currents or swirls The flow i
18. is required for timing or with a built in automatic stop watch Engaging Lever zero Reset Lever Rotating vane anemometer atts Where remote readinos or pulsating flows may be encountered an instrument with electrical remote transmission is generally employed wt 6 ax Sn EAT nK E ayrat L t mee t x PA e on we ee de v P La Z TARET Vane Anemometer with electrical remote transmission The rotating vane anemometer ts used both with fixed stationary readings and travelling averaging time readings Both give the same accuracy b Deflecting Vane Anemometer This instrument is commonly known and referred to as a Velometer The deflecting vane anemometer consists of a pivoted vane enclosed in a case Air exerts a pressure on the vane as it passes through the instrument from an ubstream to o downstream opening The movement of the vane is resisted by a hair spring and dampening magnet The instrument gives instantaneous readings of directional velocities on an indicating scale The instrument can be used with various types of remote connected measuring tips or jets each of which must be tndividually caltbrated with tts individual instrument and tubing Air Flowmeter 087 l Selector Pitot Tube Probe Static Pressure 7 Probe Probe for use with diffusers Low Velocity Probe Deflecting vane anemometer Lg Af Measuring Grafts or other low air
19. m s Duct size 375mm diameter round duct What should the velocity be at the specified air flow Solution Volume m gt s Velocity m s x Area m Volume m3 s Area me Velocity m s 2 2 _ ff D Area m for round duct 1000 gt 2 R m2 _ H x 375 oe 1000 4 2 2 Area m 0 11 m abprox a gt 2 velocity m s Oil Velocity m s 9 1 approx 3 Specified Air flow 1 8 m s Maximum duct velocity 10 m s What is the minimum length of a rectangular duct if depth is to be 300mm Solution il Volume m s Velocity m s x Area i 3 24 _ Volume m s NS Velocity m s 3 _ 1 8 m s eS O l s 2 Area 0 18 m 2 Length width meee 1000 1000 Length _ Area m 1000 width 1000 E A The various techniques for measuring the air flow in duct systems and at terminal devices are controversial and none is universally accepted It is difficult to measure air velocities and flow rates in the field All methods are subjected to the ability of the balancer Proper balancing is time consuming and requires expertize and diligence At present no one established procedure can be considered as applicable to all systems However there is one point of agreement atr systems should be balanced before the hydronic steam and refrigerant systems l The minimum instruments necessary for air balancing are a Incline manometer cali
20. mark is made on the vulley and the stroboscope adjusted until the mark appears to be stationary when the pulley is rotating The frequency setting on the stroboscope may however be a multiple or sub multiple of the actual shaft speed and such errors of harmonics need to be eliminated to assess the correct speed The stroboscope ts normally used on stte only when tt ts tmposstble to use a mechanical tachometer Y Stroboscope 2 PRESSURE MEASURING INSTRUMENTS For in duct measurements a pitot tube with an adjustable manometer will give the most reliable results These need no calibration and are consistent In practice the lower pressure readability on the manometer is about 10 Pa 4 m s or 1 0 mm a U Tube Manometer This type of manometer is a simple and useful instrument for the measuring of partial vacuums and pressures both for air and hydronic systems In its simplest form the manometer consists of a U shaped glass or plastic tube partially filled with liquid C Levels above scale 2ero A Levels at zero of scale B Levels below scale zero Reading the U tube manometer A difference in height of the two fluid columns denotes a difference in pressure in the two legs When reading a U tube manometer observe that the liquid level in one leg falls while the liquid in the other leg rises The pressure h is the sum of the readings at these two levels b Well Type Manometer 7 As descr
21. power for the fan at the correct flow rate SHOW ALL FORMULA AND CALCULATIONS eee e 4 o 4 a e ee y v k e 8 6 K 6 a a amp e e ee o gt gt ae e y e k o KKK o o o o o gt eo o O v k o o O e y a oe e a Qee e o s 4 s o a o k 0 o k 9 O k G y a a G y S A e S G 8 amp 8 G amp e ber a s o o o o o h o GA o o gt 4 4 l GG e gt e a e e e o 9 o S e 9 8 amp e e amp e e o a e e o gt o o gt R gt gt 8 o o K 9 8 9 9 k gt o 2 2020 h o o 6 o ee a 6 e eee e e e o amp o gt a 9 9 gt o K amp R O KK gt S KK k h o 8 o y e o o e oe a ge e amp o s gt 0 o K amp R 9 9 amp o amp a a 6 o k o k o l o e o gt k 9 k gt eso 4 a h 9 8 o e 9 Oo k gt O gt o o o S LH gerrea arrea E ES Eg E EA pera E 9 ES S N E Ed A Ed H x T Z ET TR
22. readinas average the measurements and record the average reading To measure fan motor voltage and current drawn use a volt amp meter Connect the volt amp meter to the nower input terminals to read voltage Record the readings Connect the meter in the ot t a U b KRSR AE SUS D b 4 A r t Q rs JP A a e AA t r y CS ee fe wa saat VA ST tas K YU a ed Lu NL LA w power line and read current drawn Record the reading Compare the fan R P M voltage and current drawn with those on the motor nameplate Readings should not exceed the nameplate ratings of the motor The balancer is check ing the rotation speed of the fan C To measure total air flow use a Velometer or stonwatch and Rotating Anemometer Three alternate methods are commonly used 1 Velocity traverse across the coolina or heating coils For best results wnen using the Anemometer and stopwatch measurements must be made on the downstream side of the coil Position the Anemometer about 25mm from the coil surface Before beginning divide the coil into equal sections ana calculate the area of each section in m Multiply the velocity in m s by the area in m for each section and total all section volumes to arrive at the Total Volume The balancer is taking a reading across the coils to determine ve ER locity using a rotating a fe a a y oa E vane anemometer D
23. surfaces A common form of curved blade has the concave side facing the direction of rotation Blades of this type are shallow as multi vane or multi blade The blades are mounted between side rings mounted on the arms of a spider or on a solid plate mounted on the shaft A typical design 1s shown in figure 3 1 The forward curve blade has a scoop effect on the air As shown in figure 13 b the velocity of air leaving this type is greater than with others Asa result this design moves more air than others for a given impeller diameter and speed In other words for a given capacity the forward curve fan is smaller and runs at a lower speed PERCENT OF SHUTOFF STATIC PRESSURE HORSEPOWER STATIC EFFICIENCY PERCENT OF FREE DELIVERY CAPACITY Figure 3 2 Forward Curved Blade Fan Performance The variation of volume with pressure for forward curve fans The rise of horse power towards maximum volume is even more marked with this type paddle blades This factory considerably affects the rating of the fan drive required ADVANTAGES L Runs at relatively low speed compared to other types for same capacity 2 Smaller fan for given duty excellent for fan coil units BACKWARD CURVE FANS The highest efficiencies in centrifugal fans are achieved with backward curve blades These have the convex side facing the direction of rotation This form improves air flow through the blades by reducing shock and eddy losses These fan
24. the Trunk duct system This system is quite complicated but when properly designed ad installed provides good control of separate air streams and uses a minimum of sheet metal N K ann J A AS Y gt a a a Z E Trunk Duct System b c Another solution to the same system is the Exrended Plenum duct system The main feature being that the trunk duct does not vary in size even after branch ducts have been taken off Careful measurements of varied shapes of trunk ducts are eliminated The location of branch ducts can be installed after the extended plenum has been installed A greater amount of sheet metal will be used in the extended plenum than in the trunk duct with its reducing sections Often the labour savings more than compensates for the material costs pa Pm mn an ly Extended Plenum Duct System A third common duct system which could be used is the Box Plenum The box plenum differs from the extended plenum in the size of the plenum The plenum box is quite large and air from the conditioner is delivered to this large box where the initial air velocity is considerably reduced From this box the air is distributed to the various branch ducts The advantage of the box plenum system over the trunk duct system is simplicity in construction and reduced manufacturing labour costs A Box Plenum Duct System Any duct system is a compromise between the resistance created by air fl
25. the air stream parallel to the direction of flow and with the openings always pointed upstream The inner tube facing into the air stream conveys the impact or total pressure The outer tube has a number of small radial holes in its wall and the annular svace between the two tubes conveys the statte pressure 5 e 16D 2 m 8D qe Y A T PREETHI EE dds ax 5 wa I TTT LL LLL LL 16 t 5 Rad Di 32 8 Holes 0 04 Dia equally spaced Nose shall be free Free from Burrs from nicks and burrs o e 90 1 SECTION A A Note other sizes of pitot tubes when required may be built using the same geometric proportions with the exception that the static orifices on sizes larger than standard may not exceed 04 in diameter The minimum pitot tube stem diameter recognized under this code shall be 10 In no case shall the stern diameter INNER TUBING Approx exceed 1 30 of the test duct diameter a Nos a ot k N gt t a STATIC PRESSURE OUTER TUBING 5 16 O D x Approx 18 BL S Ga Phd H aa LKK OS TOTAL PRESSURE Pts TOTAL PRE TOTAL PRESS STATIC PRESS VEL PRESS SHOWS SEPARATE STATIC AND TOTAL PRESSURT TUBES FOR MEASURING VELOCITY PRESSURE TYPES OF PRESSURE MEASUREMENTS PITOT TUBE SECTION EMARGEO 10 SHOW DETAR PITOT TUBE SENSES TOTAL AND STATIC PRESSURES MANOMETER MEASURES VELOCITY PRESSURE DIFFERENCE BETWEEN TOTAL AND STATIC PRESSURES Pitot tub
26. the basic information regarding fans and their operation the fan laws are presented here with illustrations for their use Further examples will be presented in the chapter concerning trouble shooting system malfunctions TYPES OF FANS A fan basically consists of a number of blades on an axle or shaft which together rotate in a housing designed to minimise the internal losses and to maximise the available pressure and air flow at the consumed horsepower The motor may be directly connected to the fan shaft or may drive the fan through a pulley and belt arrangement which is more flexible The belt and pulley arrangement is generally more desirable from the standpoint of equipment safety since the belts can break or slip under overload conditions with less chance of damage to motor or fan Fans are manufactured in all shapes and sizes Many are designed for a specific application or piece of equipment However fans used in environmental systems fall into two general categories centrifugal and axial flow The centrifugal flow fan is so named since it produces air flow along or in the same _ direction as the length of the fan shaft or axially In both cases the term axial is derived from the direction of the centreline of the axle or shaft Centrifugal fans are classified according to the blades on the impeller frame or wheel They are forward curved backward curved or radial straight Modifications of these basic categories produce si
27. traps are cleaned all drainage lines are to be flushed wees ae eq pr Drainage Liquid Discharges Always a source of problems not designed correctly not installed correctly nil or limited access Plug Tee pieces should be used S trap water seals too small allow double static provisions to keep S trap seal from drying out sized for required when Coil Cleaning Condensate Trays t No pools or puddling permitted Slime build ups must be removed as microbes and fungi would be present Probably not Legionnaires as temperatures are too low to support growth even in winter cycle Make trays large enough in plan area to carry over watch design velocities 500 F M 2 5 M S Negative fall to drain connection Pipe connection to tray must not stand proud ie full drainage is restricted NB Pipework and bottom of trays on cooling coils Air On side should be treated to stop condensation oils Any cooling or heating coil accumulation dust organic material obviously has an inadequate filtration system upstream Coils which have a spray cycle for dew point control or other reasons act as an efficient air filter therefore require more maintenance and servicing than a Normal coil Whilst working downstream of the cooling coil when the system is operating don t forget your own safety and wear a mask Outside Air intakes Exhaust Outlets Return Air Grilles Legionella may travel over 1 km under cert
28. velocites as at exhaust hoods Measuring velocities inside of Gucts Measuring SES PIO air velocity static pressures at plating tank Measuring air velocities at supply openings Typical applications of deflecting vane anemometer c Direct Reading Anemometer Florite and Bridled Similar to the already described vane anemometer however these include a calibrated scale built into the instrument The Florite type shown below is limited in use because of the scale limitations sr ego S R L a wa d HZ P ad eit sm ca Side Wall Register Floor Register OS ws Sarg u F P ba U ER Y Y po 7 AAN r y Baseboard Dittuser Hi Fee so e E Refrigeration Grille Pocket type deflecting vane anemometer and typical applications The Bridled vane anemometer shown below is often used with special attachments that direct air through the instrument 4 The Bridled anemometer is also often used with an extension handle to reach high side or ceiling outlets and is provided with a scale lock which locks the indicator in place once the reading is made B View showing vane A View Bridled vane anemometer showing scale 1900590 e n 58 Measuring grille velocity use of handle minimizes interference with le me ar stream Used overhead string operates scale lock rm eee s e f TAS ILE 569956
29. 0000 M0 SE S gt o mW e 8 we we 2 T 1 A gt 8 ee c a A Ue e e a MA li EERTSE 6ops Lor L P 4 S Bridled vane anemometer with air scoop housing used to measure diffuser outlet velocity Bridled vane anemometer Both the Florite and Bridled vane anemometers require considerable judgement to obtain average velocities especially when recording at right angles to the atr flow d Hot Wine Anemometer This instrument utilizes the principle that resistance of a heated wire will change with temperature A probe with a wire element energized by batteries is connected to the instrument As the air flows over the element in the probe the temperature of the element is changed from that which exists for still air an this change is indicated as a velocity on the scale of the instrument EA L Z sip 3 4 Z Z q on b gt c E ER ant 6 eee el gt x z lt 6 Y 2 Ms a w HG s OEA 2 LG tifa ee P E S s EL lt d A e ex Poe ow vl TT pa L a j b A AS i egt E Nr we PJ EA 2 A E TE 2 11 4 le wh d SN Ye re A Y ia se te s pr y de r er E ER P CURRENT ADJUSTMENT ANEMOTHERM AIR METER auteestay paosucts sivisies ted SYRAMKS CORPORATION OF ABL REA staacwo T SCRANTOR PA AM SA U S PATENTS 2 377 804 l 2 388 615 E 2 012 047 2 648
30. ERCENT OF FREE DELIVERY CAPACITY Figure 6 1 2 Axial Flow Fan Performance PROPELLER FANS Propeller fans serve a very wide field of applications where resistance to air flow is low As a rule they are used where there is no duct system or where the length of duct is short In a majority of cases they move air through a hole in a wall Their inherent attribute is that they enable large volumes of air to be handled economically and entail low capital costs Consequently they are extensively used all over the work for general ventilation purposes The term exhaust fan is often applied to propeller fans because they are so widely used for exhausting air from buildings That description however is not a correct one since the fans may be used for fresh air input and for many other purposes such as for unit heaters coolers etc These fans have an impeller with two or more blades usually of sheet steel set at an angle to the hub somewhat in the manner of a ship s propeller In some cases the blades follow the shape of aircraft propellers but sheet steel blades of the type shown in Figure 6 2 1 are widely used The propulsive effect of the blades varies according to their shape A fan with broad curved blades will move more air and is quieter than one with flat and narrow blades of the same diameter running at equal speed Air enters a propeller fan from all directions and is discharged mainly axially but there is also some radical
31. Find i ii 21 c and Tmix 24 C The temperature of the mixed air stream that will result from the correct outside air return air ratio Discuss correction procedures if they are required Show all caleulations ma 5 Bala ncing Procedures AJUST ALL REGISTERS IN THE SYSTEM TO WIDE OPEN a SAE LA DIFFUSER HEIGHT C m mm A mm 75 too 125 150 200 250 300 450 400 Determine the average face AB 0 10 1 47 velocity from the corrected 200 09 13 ee 23 T TTT Anemometer reading 250 12 18 24 30 42 55 Determine net core area 300 14 21 29 37 52 67 8 from Table EIA 17 J 26 34 43 6l 19 Determine air volume ae LR 7 as follows 226 SSS Zil Average face velocity ME 9 Portion of in m s x net core area feet a table showing in sq m x diffuser Ys Le net core area O factor volume in m HA grilles side wall eaa Typical instructions tor round diffuser Place the Anemometer Probe in four equally spaced positions around the 8 Cone as shown Record and average these four velocity readings The flow rate in m factor x average velocity One suggested procedure is to first check the furthest outlet in each branch If the outlet is below design velocity leave the damper fully open and move onto the next upstream outlet If the outlet velocity is above design then throttle before moving to the next upstream ou
32. Frequency Acceptable levels Measurement Transmission _ Controlling noise vibration Attenuation Absorption Fault finding Suggested teaching time 4 hours lt Eo E ES ATR BALANCING INSTRUMENTS Before you can attempt to balance an air stream you must have accurate reliable instruments All instruments witn the exception of the pitot tube and manometer need to be recalibrated at intervals of not more than Stx months If an instrument is dropped or otherwise damaged it should be recalibrated If there is any doubt about the accuracy of an instrument it should be checked against another instrument measuring the same quantity and be recalibrated if the answers do not agree kach instruments should carry a calibration record Read the manufacturer s instructions and become familiar with your air testing instruments before using them on an actual job 1 ROTATIONAL SPEED MEASURING INSTRUMENTS Measurement of rotational speed will be required to determine whether a fan is working as specified Mechanical tachometers are normally _ used where the shaft of the fan or motor is accessible Where it is dangerous or not possible to use a mechanical tachometer a stroboscope is usually employed a Revolution Counter Speed Indicator A small inexpensive hand held counting device that is pressed to the centre of a rotating shaft for a timed period It requires the use of a stop watch and cannot usually be reset t
33. N UA VENTILATION NR13 LEARNING OUTCOME 1 STUDENT WORKSHEET 1 1 Question 1 Name the two most common types of ventilation in use today aS SS tren eServices Question 2 Why do we require proper ventilation LTA TST eA TET ATS A A Question 3 What is the major disadvantage of natural ventilation aA TRA A A rE asi rr Wn tpt SPS Question 4 How was the first attempt at mechanical ventilation achieved and what was it called A a a O Question 5 What is meant by the term induced ventilation 2 Question 6 How is forced ventilation achieve Question 7 List four 4 applications where ventilation is required and the type of ventilation Question 8 There are six 6 considerations to be aware of when using ventilation name four 4 Question 9 What is the difference between ventilation fans and circulation fans 3 Question 10 What does the term climate controlled conditions relate to and what does it apply to Question 11 What are the five 5 factors to be controlled in the air conditioning process Question 11 What do you need to control to obtain desirable indoor conditions Question 12 What air velocities are required for HEATING COOLING Office workers Restaurants Dancing 4 Question 13 Comfort depends upon WHAT conditions
34. N HEATING COOLING COMFORT SYSTEMS 3 Edition Business News Publishing Company Birmingham Michigan VARIOUS MANUFACTURERS INSTALLATIONS START UP SERVICE MANUALS AND BULLETINS and many other publications ayra VENTILATION NR13 Learning Outcome 3 Student Worksheet 3 1 Question 1 The maximum pressure a fan can develop occurs when the ductwork connected to the fan is a open to atmosphere or b closed off and all openings sealed lt 2 eoo0 0 00U80 0 N0 666 Re e S e e 6 O U ee K amp R E E R 8 e Question 2 a In an air conditioning installation where would you most expect to come across a radial blade centrifugal fan ee gt o o eae a ee amp s o a o e e e ae a e e e K 6 e a o amp 8 amp o amp e eo a o o S amp KKR Question 3 Describe and show by means of a sketch the difference between a tube axial and vane axial fan e o
35. OFF STATIC PRESSURE HORSEPOWER STATIC EFFICIENCY eT A a ie EE PERCENT OF FREE CELIVERY CAPACITY Figure 2 2 Propeller Fan Performance FAN CONSTRUCTION In addition to the physical variations required by the types of fans themselves there are requirements imposed upon the construction as a result of system pressures The Air Moving and Conditioning Association AMCA has established construction classification standards for the industry which though not mandatory are followed by most centrifugal fan manufacturers Formerly the operating limits were specified by the total pressure which a fan must be able to develop on at least one point of its performance curve for a given class of construction The performance limits were then determined by the maximum impeller speed for that construction and then catalogued using this criteria The requirements were Class 1 95 2mm total pressure Class II 171 4mm total pressure Class I 311mm total pressure Class IV Aobe 311mm total pressure This method of classifying construction was a source of much confusion in the industry Later AMCA standards define the minimum outlet velocity versus static pressure limits necessary for Class I II and III construction The curves in figure 7 1 illustrate these requirements for single width backward curved blade fans Similar information for other fan types may be obtained by referring to the AMCA standards The classifications are based on a mean b
36. Velocity Pressure Pv is the pressure which air in a duct exerts due to its motion ii Static Pressure Ps is the pressure within a duct which tends to burst the duct iii Total Pressure Pt is the sum of the static pressure Ps and the velocity pressure Pu Pt Ps Po The static velocity and total pressures should not be measured in mm of water or any other liguid as the unit of pressure is the Pascal or Pa When these pressures are however measured in mm of water they should be termed static velocity and total heads respectively The head in mm of water must be multiplied by 2 81 to obtain the pressure in Pa Multiply by 10 is close enough for practical purposes THE SIGNIFICANCE OF STATIC PRESSURE Ps Static Pressure Ps is a measure of the resistance that a duct system presents to the flow of air Just as a given value of static pressure will push the liguid in a manometer column as shown on following page so it has the ability to push air through a duct eS merenn State pressure connection to duct Tube with open end facing air stream Manometer To umum fan A Static pressure B Static pressure greater than less than atmospheric atmospheric pressure pressure Measuring static pressure Fans are rated on the basis of the amount of static pressure Ps they can develop as an indication of the amount of duct resistance they can overcome A difference i
37. adjustment Proceed to Outlet No 4 and adjust to obtain agreement between R4 and R3 within 10 percent After all outlets on Branch No l are provortionally balanced to each other proceed to Branch No 2 etc The alternative proportional balance differs as follows Start regulating outlets on a branch which has a high percentage of design flow after adjusting supply fan for design flow rate branch could be the closest or farthest or anywhere in between from the fan Flow rate should not be above 30 of the design figure Use branch dampers to correct if required Branches with less than 70 of design flow are left until the high percentage outlets are regulated This will force air into the low flow rate outlets On the selected branch locate the outlet with the least percentage of the design rate the lowest value of measured flow design flow Generally it is the last outlet in the branch If not adjust damper in the last terminal until it is working with the same percentage ratio as the one previously measured The last terminal ts then used as an index agatnst which the ratios from other outlets in the group are compared yeso pri oriente Measure the flow from the outlet next to the index and calculate the percentage ratio Adjust damper to bring percentage ratio within required tolerance of index outlet Repeat procedure for next downstream outlet again comparing it with the index outlet When all the outlets have b
38. ain conditions There is a lot of commonsense involved here as understandably the rules have a wide base Dirty air exhaust systems toilets car parks kitchen cooling towers etc must be located downwind of the prevailing weather pattern Consider separate high efficiency filtration to fresh air systems booster fan Keep filter media moisture free to minimise bacteria growth Return air grilles and ductwork are an ideal place for bacteria sporing to occur especially in high population smoking areas A constant temperature and organic material is supplied all year for such growth as in restaurants Similar but to a lesser degree occurs with paper dust lint etc Cigarette nicotine adheres to the duct lining building up with organic food etc Access panels in ductwork and fans for cleaning are most important but just as important are good lighting and safe access Again wear a mask Filters Legionella is only 3 micrometres Microns long by 1 Micron in diameter however it joins to Protozoa 5 100 Microns dust 1 100 Microns or Microbes The filter then needs to remove a much larger particle than the virus itself Test Dust No 2 Particles in 3 10 Micron range are ccllected dirt and droplet particles however it is no good for viruses say 0 03 to 0 8 Microns Some examples of viral infections are Smallpox Chickenpox Measles Mumps Influenza and the common cold The common cold are produced during sneezing
39. ained Therefore the frequency analyzer gives more complete results These instruments are compact and can be held in the hand while taking readings many being battery operated The instrument must be held at a height of 1 5m above the floor level and at least 1 0m away from the sources o the noise SECTION 1 WORKSHOP ASSESSMENT SHEET Manometers and Velometers are both used in air balancing a One measures pressure What does the other instrument measure b Which instrument measures pressure c Give the unit or units of measurement for each instrument Manometer Velometer Could more information be found by using a Hot Wire Anemometer than a Rotating Vane Anemometer Fully explain your answer With which instrument or combination of instruments would you use the following formula b H J Pv rms If using the formula in Cuestion 3 then in what units of measurement would you be recording Obtain a Rotating Vane Anemometer from the store and on the register nominated by the teacher find the average air flow in l s Give a full description of the proce re you followed The formula Pv Pt Ps is very important because we need to find Pv in duct systems a Why do we not just measure Pv directly b Why is Pv so important ewe Te Sketch and label how you would fin
40. are provided make sure both top and bottom openings are a used o Where possible incline windows for downward deflection of air in summer and upward deflection in winter e Do not use screens or heavy curtains o When using ventilation fans open the bottom windows or door to admit air at low level e Regularly clean any air supply and exhaust air grilles o Do not run ventilating fans with doors and windows shut Circulating fans may be used but they will not provide ventilating air o Leave ventilating fans on overnight in hot weather to cool the building ready for the next day ATR CONDITIONING DEFINED Air conditioning is often referred to as a science The Science of Supplying and Maintaining a Desirable Internal Condition Regardless of External Conditions This may be incorporated in a machine which heats cools cleans and circulates air and controls the moisture content in simultaneous processes all year round Complete air conditioning is sometimes referred to as Climate controlled Conditions and is generally applied to large offices and public buildings This type of conditioning provides a high level of control of all the requirements for human comfort Very few of the systems used to provide the fully conditioned air are identical because of the particular design of each building While the refrigerating and heating plants may be the same the methods used to distribute cool or heated air differ because of the require
41. ation inclined vertical manometer NOTE In most commercial tnstrwnents the fluid used ts a light oil normally with a specific gravity of 0 83 It ts important that only the correct fluta ts used in each instrument as the scale is corrected for the designated specific gravity ra amp N Z 8 2 set e Portable Air Pressure Gauges Dry Tvne Manometers have the disadvantage of containing liquid which can be spilled or contaminated and they must be accurately levelled Dry type draft gauges overcome these problems One such operates on a bellows that actuates a helix which in turn moves a pointer across a printed scale Others operate by weight or blade displacement Generally dry gauges are not as accurate as a liquid filled U tube and frequently do not stand up to rough handling Several instruments are recuired to cover the normal ranges encountered in average air condition ing jobs There are approximately 30 available pressure ranges in this instrument INCHES OF WATER 20 30 VO uwin 70 AA Dry type draft gage PITOT TUBE The Pitot tube named after the Frenchman Pitot who designed it is an instrument for measuring Static Veloctty and Total pressure in a stream of air or gas It consists of two concentric tubes usually L shaped for convenient handling and which ends in two separate outlets for connection to a manometer The instrument is inserted into
42. brated in no less than lmm divisions 10 Pa b Combination inclined and vertical manometer 0 250mm 0 2500 Pa is generally the most useful c Pitot tubes usually 450mm and 1200mm long tubes cover most balancing requirements d A tachometer which should be of the high quality direct contact self timing type e Clamp on ampere meter with voltage scales Deflecting vane anemometer g Rotating vane anemometer nh Thermal type hot wire anemometer i Dial and glass stem thermometers 2 Before beginning to balance the system eliminate every possible air flow restriction Open all air valves fire dampers and volume controls in both supply and return ducts Adjust outside air dampers for minimum and maximum positions and adjust return air dampers for maximum flow Set adjustable pattern ceiling diffusers for horizontal air discharge patterns whenever possible 3 Before any system can be balanced properly the supply fan must develop enough static pressure Ps for the system and the air volume handled by the fan must be adequate for the system Therefore after ensuring that all related fans supply return exhaust are operating measure and compare with specifications a System Static Pressure b Fan RPM voltage at fan motor and current drawn c Total air volume A Contrary to what may be supposed fan static pressure is not simply the difference between outlet static pressure and inlet s
43. cause misalignment and unexpected unreasonable wear to belts bearings and other components In some instances where the building construction is light or where a resonant condition might ann ancre Wig amplify the vibration the isolation system must protect against what may be called sympathetic resonance in the construction At times the result can be worse than having no isolators at all The four common types of isolators are steel coil springs double rubber in shear single rubber in shear and cork in order of decreasing efficiency and cost These materials are often used alone in combination with each other and in various types of load distributing and supporting rails frames and bases For further information refer to the later chapter regarding this subject By proper use of vibration isolation equipment a large portion of the noise normally generated by fans and other equipment may be prevented or reduced to acceptable levels However there are other sources of undesirable sound Fans generate noise in the process of pumping air and air generate noise from velocity and turbulence while moving through the system Any fitting outlet damper air valve straight piece of duct or other sources of undesirable sound Fans generate noise in the process of pumping air and air generates noise from velocity and turbulence while moving through the system Any fitting outlet damper air valve straight piece of duct or other sy
44. ction All systems are to be cleaned at three montly intervals Approval to extend the three monthly cleaning interval may in individual cases be given by the Director General of the NSW Health Department t e If a cooling tower system is operated on a seasonal basis it is to be drained as soon as practicable after shut down Where it is incapable of being shut down water treatment shall be maintained e Cooling towers operating on a seasonal basis are to be inspected and any necessary maintenance work carried out prior to recommissioning HOT AND WARM WATER SYSTEMS Hot water systems operate at temperature of 60 C and above measured at the outlet Warm water bathing system which are designed to prevent scalding operate at a temperature of 35 to 43 5 C measured at the outlet These temperatures are conducive of the growth of Legionella and other micro organisms The warm water may be generated instantaneously with the aid of approved fail safe type thermostatically controlled hot and cold water mixing valves These systems are widely used in health care facilities such as hospitals and nursing homes Stratification of water temperature can occur in water heaters and warm and hot water Storage tanks The temperature within the vessels can result in Legionella proliferating Water Treatment Because hot warm and cold water are classified as potable water fit for drinking there are limits to the water treatment that can be app
45. cupier for maintenance contractor responsible for the plant shall make a written record of the date and nature of the work performed and the name of the employer The maintenance record is to be signed by the person who actually performs the work o An occupier or maintenance contractor who fails to make a written record is guilty of an offence o Any person who removes maintenance records from premises within 12 months after the record is made is guilty of an offence ka An authorised officer may enter any regulated premises and inspect the records AFE WORKING PRACTICE Chemicals used in operating maintenance and cleaning procedures must be treated with caution Legionellosis is of course also a potential health hazard for people who work around systems harbouring the bacteria Safe working practices are vital and it is important that safety measures are instituted as soon as possible Safety measures must be observed by all whether they are a maintenance worker a building inspector or someone taking a sample from the system The risk is from contaminated aerosols and spray mists as well as the obvious hazards of working with chemicals and around structures with difficult or inadequate access New installations must be designed and constructed to provide safe access while existing installations must be made safe without delay Protective measures must be taken during maintenance and inspections of air handling and water cooling s
46. d air distribution components are used the correct zone velocities and ir movement are as important as the correct cooling and heating system The activity of the people in the controlled zone should be taken into account when deciding upon acceptable velocities The relationship of air velocity and air temperature difference between supply air and zone air is shown as a percentage of zone occupants who will complain in the graph on the following page y S l NECK REGION LE LAAT 14 f v4 FEELING OF 3 2 i AIR VELOCITY o s AIR VELOCITY m s TEMPERATURE DIFFERENCE TEMPERATURE DIFFERENCE Percentage of Room Occupants Objecting to draughts EXAMPLE For the neck region a velocity of 0 3m s at a temperature of 0 5 K below zone temperature will be acceptable to 80 of the occupants The accepted velocities measured at head height for both heating and cooling is shown in the following table O Heavier work in war Dancing cooking heavier 0 45 0 3 manufacturing Air velocities below 0 075m s give a feeling of stagnation Activity Application Long sitting Office work The rate at which a body will dissipate heat by convection and evaporation depends upon the air velocity Air movement is required to ensure uniform temperature but velocities must be kept within limits or occupants will feel draughts Maximum air velocity within a zone is usually assumed as 0 21m s while a mini
47. d only one final in duct measurement of total air flow is needed at the supply fan at the end of the balancing process Consider the branch duct shown below The volume of air delivered by each outlet represents a percentage of the total flow in the duct Unless the outlet dampers are altered the percentage proportion will remain the same whatever the flow rate in the duct ta Sub branch flow 1 0 m s tb Sub branch flow 2 0m s Basis of proportional balancing Although thc flow to the system is altered the percentage share of each terminal remains the same At the present time there are two procedures used for balancing the outlets in the proportional or ratio method 1 The farthest outlet on the farthest branch from the supply fan will be Outlet No l on Branch No l Number all outlets consecutively working back towards the fan Number the outlets similarly on the test report sheet It is imvortant that the outlets be numbered tested and adjusted in this seguence If the sequence is not followed the procedure will not be valid Determine that Outlet No l on Branch No l has enough air being delivered to give measurable readings If not adjust fan speed etc as required Measure velocities at Outlet No l on Branch No l the outlet farthest from fan Determine average velocities at outlet No l and tabulate Hee norig In the following the designation Vm will mean measured velocity and Vd will indicate de
48. d the velocity of air following in a duct using a Pitot tube and show all pressures and indicate direction of air flow a When the teacher is satisfied with the answer to Question 7 obtain required instrument or instruments from the store and where indicated by the teacher find the average air flow in 1 s and m s in a duct Give a full description of the procedure you adopted a Obtain from the store a Deflecting Vane Anemometer and using the same register as nominated by the teacher in Question 5 find the average air flow in 1 s Give a full description of the procedure you followed Y S L M H M G Os ps a Q T 0 O H W ha N B S Qu y 2 What are the two volumes am i Rotating Vane ii Deflecting Vane yene Saan d Were the instruments both checked for calibration PA 10 a A duct 600mm square when connected to a water manometer gives a reading of l2mm 3 Find air volume flowing in the duct in 1 s and m s Show all calculations Sara Sae b A duct 500mm x 225mm should have a volume flow rate of 944 1 s What should be the reading in Velocity Head mm on a water manometer Show all caleulattons and convert the answer Hv into Pv Pa VENTILATION NR 13 Student worksheet 13 4 2 To answer the following questions you will need to obtain from the inst
49. dication Remedy vit High humidity due to warmer coit Indication re RN CY viii Draughts due to overblow of outlets Indication END OF SECTION II Additional and more detailed information pertaining to Section II will be found in the following A S H R A E SYSTEMS VOLUME 1980 CHAPTER 40 A S H R A E 345 East 47th Street New York N Y 10017 TESTING BALANCING AND ADJUSTING OF ENVIRONMENTAL SYSTEMS William G Eads P E SMACCNA 8224 Old Courthouse Road Tysons Corner Vienna Virginia 22180 AIR CONDITIONING TESTING AND BALANCING John Gladstone Van Nostrand Reinhold Company New York Cincinnati Toronto London Melbourne MANUAL FOR THE BALANCING AND ADJUSTMENT OF AIR DISTRIBUTION SYSTEMS First Edition 1967 SMAACCNA P O Box 3506 Washington D C 20007 START TEST AND BALANCE MECHANICAL EQUIPMENT SERVICE MANUAL First Edition 1976 NJS PAC Printed in the United States of America MANUAL FOR REGULATING AIR CONDITIONING INSTALLATIONS Application Guide 1 75 B S R I A Old Bracknell Lane Bracknell Berkshire RG124AH TPC TRAINING SYSTEMS Volume 7 A Dun and Bradstreet Company 1301 South Grove Avenue Barrington Illinois 60010 U S A VARIOUS MANUFACTURERS INSTALLATION START UP AND SERVICE MANUALS AND BULLETINS and many other publications afer daea SECTION II HORKSHEET ASSESSMENT SHEET Using the Low Velocity Fan Un
50. discharge When resistance is imposed the air tends to flow back through the impeller Because of this propeller fans are not suitable for working against any substantial resistance Their particular field is air movement under condition of free intake and discharge or at static pressures not exceeding 0 5 in wg For applications of this kind they are usually the most practical and most economical choice The power loading of a propeller fan increases with the resistance against which it works When working against excessive resistance the power input may rise very considerably until the motor over heats and eventually burns out As a safeguard the motors should be generously rated As a general rule a propeller fan with sheet steel blades gives maximum volume under free air flow conditions when the straight training edge of the blades that is the discharge edge is flush with the mounting ring as shown in Figure 6 2 1 Maximum pressure is obtained by projection permits centrifugal discharge from the blade tips reduces losses through backflow and thereby enables the fan to develop its maximum pressure Ample space should be allowed at the blade tips for centrifugal discharge If a fan is mounted in a circular duct the best performance will be obtained when the duct is not less than 25 larger than the impeller diameter and the fan is mounted on a diaphragm plate with the blades projected through the orifice prose PERCENT OF SHUT
51. e efficiency and causes more power to be absorbed by the f lt motor s Airborne particles are measured in microns a unit of measurement which is defined as one millionth of a metre For comparison consider the following Smallest Size Particle To Be Seen With The Naked Eye 20 Microns Dia Human Blood Corpuscle Tobacco 10 Micron Dia Smoke 1 4 Micro Dia Greatly Magnified View Showing Relative Particle Size Operating characteristics and the performance of an air filter are described or stated by a number of parameters a Rated Capacity is expressed in cubic metres per second m s 15 the recommended maximum rate at which air should be passed through a filter in service Rated face velocity expressed in metres per second m s is an alternative method of deriving capacity Capacities are sometimes expressed in litres per second 1 s 1000 1 s 1 m s b Resistance expressed in Pascals Pa is the pressure drop developed across the filter as air passes through it In most types of filters the resistance is also a function of the amount of dirt in the filter As the filter Zoaze up with dust the resistance increases It is normal to quote the ciem resistance for fixed panel type filters but for automatic self cleaning filters the averace operating resistance is generally used Bee c Dust Holding Capacity is the mass of dirt in the filter which will increase the resistance at rated capacity either t
52. e hook ups are shown in the following figures It can be seen from these figures that whatever the condition the hook up for reading velocity pressure remains unchanged the impact total tube goes to the high pressure side and the static tubes goes to the low pressure side QC ean Air Flow 4 af gt K UW UST DUCT TOTAL PRESSURE 15 Ate ncn ian Sp L p U aa N V i e Y 5 E E E a POSITIVE SUPPLY DUCT TOTAL PRESSURE IS POSITIVE DETERMINATION OF FLOW VOLUME The object of an actual test usually is not only to determine the flow velocity at a certain voint but to determine the volume of air flowing through a duct EXAMPLE From a 10 point traverse of a 300mm round duct the velocity pressures are tabulated and corresponding velocities found and also tabulated as shown in the following table the average velocity being found as the average of all velocities Horizontal Vertical O P Ln GO Y 0 0 KA Hm L L O 00 C O D w 00 L 09 L 0 LA KA PM L WW IN HH L CO C0 G G On GO 3 Gn G 4 e e o e L L La O On SS d On On Ln Pa L e L 6 L LE LO Gn d d d d GO Pa D L Cn P 000 yO Y O 1 1 2 2 3 de 3 2 1 1 Average 60 6 m s It ts necessary to convert each velocity pressure reading into velocity and then to average these velocities An incorrect answer will be obtained if velocity pressures a
53. een balanced on a branch each outlet will be running with an equal percentage of the design flow within the allowable tolerances steered K To balance the branches select an outlet well within the tolerance limits it does not have to be the index terminal used in the outlet balance for each branch Find the branch with the least air when comparing measured flow design flow If it is not the branch farthest from the fan then adjust branch dampers until it becomes the least favoured and therefore the index to which other branches are referred Starting with the branch next to last compare percentage of design flow between reference outlets in this branch and the reference outlet in the branch Adjust duct damvers until the two percentage figures agree within the tolerances usually 5 for branches Repeat the procedure with the next upstream branch again comparina the flow at the selected branch reference outlet with the reference outlet in the index branch The balancing of the branches in the technique described in Section C t differs in that each branch is proportionately balanced to the preceeding branch and not to an index branch as per Section C 11 as is as follows Select a typical outlet on Branch Nos 1 and 2 branches farthest from supply fan Calculate R ratios for each outlet Adjust branch splitter or volume dampers until the selected outlets are within 5 percent of each other The two branch ducts are n
54. fan pulsations LOW VOLUME PROBABLE CAUSE i ii 111 iv V V1 Vil Vill Forward curved impeller installed backwards Fan running backwards Fan speed to low Actual system is more resistance to flow than calculated Dampers closed Registers closed Leaks in supply duct Insulating duct liner loose 1X Filters dirty or clogged X Coils dirty or clogged xi Obstructed fan inlet xii No straight duct at fan outlet HIGH VOLUME PROBABLE CAUSE i Oversized ductwork 11 Access door s open 111 Registers or grilles not installed iv Dampers set to by pass coils v Filters not in place STATIC PRESSURE LOW VOLUME HIGH PROBABLE CAUSES i System has less resistance than calculated This is a common occurrence Fan speed may be reduced to obtain desired flow rate This will also reduce absorbed power 11 Fan speed to high STATIC PRESSURE HIGH VOLUME LOW PROBABLE CAUSES 1 Obstruction in system 11 Dirty filters 111 Dirty coils 1V System too restricted ABSORBED POWER HIGH PROBABLE CAUSES Backward inclined impeller installed backwards 11 Fan speed to high 111 Oversized ductwork iv Face and by pass dampers oriented so dampers are open at same time by pass dampers are open V Filters left out vi Access door s open viii Fan not operating at efficient point of rating Fan size or type may not be best for application FAN DOES NOT OPERATE ELECTRICAL OR MECHANICAL Mechanical and elec
55. form wt Loken NUS 1 Mini Wi H SYSTEM NO lomo es leal erval IIe ba pozz 239 los 17 E se7 GEH 2 3 277 203 029 99 72 2 se hele wo 23 asra 23193 ee eT ela ols 1991258 eoor ee see ello ro 2 3 1s7l239 07 Typical outlet report on system balancing MP 6 EI PR P R PA gomiti Note that in the form the column is filled in to show the velocity corresponding to design volume Therefore rea ings in m s are entered and adjustment is determined by whether measured velocity is greater or less than 10 per cent of design velocity Continue to balance progressively upstream from the supply fan until all outlets have been adjusted Make one or more additional passes until an acceptable balance is achieved If all outlets on one branch are high on air flow tt may be required to install an additional volume damer in order to avotd excessive noise generated at the outlets by closing the outlet damper down too much When a satisfactory balance is obtained calculate and tabulate the actual final volume Compare to system design volume and make any adjustments as indicated by results tabulated c The technique of Proporttonal Balancing is generally recognized as the simplest way to regulate an air distribution system Its greatest advantage is once a damper has been set tt never needs to be altered It is not necessary to work with actual design air flow rates to balance outlets or branches an
56. ibed previously the U tube manometer requires two readings The well type manometer requires only that one reading be taken The scale is corrected to compensate for the change in reservoir liquid level so that the well does not have to be excessive ly large Pressure T 41 A Equal pressure atmospheric B Pressure imposed on well 1 on both legs l Well type manometer Ty c Inclined Manometer Draft Gauge a The inclined manometer is often called a draft gauge because of its use in measuring the draft in boilers The inclined manometer is a variation of the well type but the indicator leg is placed in a slopina position rather than vertical The purpose of this is to improve accuracy in reading the scale For the same pressure the distance of the incline scale ts considerably greater than the vertical scale Pressure The inclined manometer is A Equal pressure atmospheric B Pressure imposed on inclined commonly used for measuring on both legs leg low pressures of 50mm 500 Pa or less ae zero Leveling Adjustment 7 Screw Knob C Typical incined manometer inclined manometer ET d Combination Inclined Vertical Manometers Many U and well tyve manometers may also be used as vertical manometers This allows for reading both high and low pressures on the same instrument Level 0 ARACENA AA et Leveling Adjustment Screw Knob Combin
57. iesiadacs Filters utiliza t statically charced bodies are at to be cleaned is first passed tn wad e orinciple that unlike electro cies to each other The air ch a unit called the or3ser which consists of a series of earthed electrodes having fine tungsten wires lt spaced centrally E L between them When a high voltage D C supply is connected between the earthed conector t electrodes and the wires a very high voltage gradient is E ot produced around the os wire and a vast number of ions are generated in the intervening space e tra rou jOMIZER Principle of operat cn of lonitren ereciroic ar titer As the airborne dust particles pass through this highly ionised space they are given a specific electrostatic charae The Charged particles then pass through a collector cell where an electrostatic field between charged plates forces them towards a plate of opposite polarity where they adhere An adhesive is applied to the plates to ensure retention The unit is cleaned by flushing away the adhesive and precipitated dirt with water Fresh adhesive is then applied before placing the filter back in service Direct Current at high voltage 13 kV for the wires and earthed plates and 6 5 kV for the collector cells parallel plates which are alternatively earthed is supplied from a 240 volt 50 cycle single phase power pack supply A variation of the electronic filter is the Jonitron Agolomerator An aggl
58. ir path The second major consideration is that of sound The axial tube fan can be selected to produce high volumes of air in a relatively small piece of equipment but the noise level becomes high In locations where background noise is already high or unimportant this may not be serious consideration However when noise is a factor special care must be taken in the fan selection In many cases sound attenuators either ahead or after the fan or both may become an absolute must L Vanes Propeller Tube Axial Vane Axial Figure 6 1 Axial Fan Diagrams AXIAL FLOW FANS The tubeaxial fan is a common axial flow fan in a tubular housing but without inlet or outlet guide vanes The blade shape may be flat or curved of single or double thickness The axial flow fan has become particularly associated with the vaneaxial type which has guide vanes before or after the fan wheel To make more effective use of the guide vanes the fan wheel usually has curved blades of single or double thickness Figure 6 1 l is a sectional view of the vaneaxial fan The curved stationary diffuser vanes are the type most frequently used when higher efficiency vaneaxial fans are desired The purpose of these vanes is to recover a portion of the energy of the tangentially accelerated air Typical performance of an axial flow fan is shown in Figure 6 1 2 STRAIGHT AIR HORSEPOWER PERCENT OF SHUTOFF STATIC STATIC EFFICIENCY PRESSURE A E O P
59. it in the air conditioning laboratory find the supply air volume as follows a In the supply duct upstream of the fan b Traverse across the filter bank Fill in and complete the Duct Velocity and Filter coil velocity traverse worksheets on the following pages Using the Low Velocity Fan Unit find a The static pressure across the fan Show all calculations and describe the procedure BARBER a pr Ao e Hi eT dy jr L ODED Engineered pen etn AIR BALANCING WORK SHEET COLMAN Filter Coil Velocity Traverse Dee Ke U Cate E IN Pee ite IA Filter Coil Size Dbtte Test Nj __ e Job Name Filter Coil Area Location Design m 1s System eS TT Area Sq m X Average Velocity m s Air Volume m5 Is sq m X m Area Average Velocity Instrument 2 m s Air Volume By o EL BARBER COLMAN COMPANY Rockford lllinols U S A Ernie AOS wee Date Job Name Location System Duct Size Duct Area Design m s Actual m c Layout tt Instrument By yf BARBER N WU BB bo de le de dE Test No S R zr AIR BALANCING WORK SHEET Duct Velocity Traverse Barber Colman Company Air Distribution Division 1300 Rock Street Rockford iL 61101 DUCT VELOCITIES m s raverse T Traverse Points Average Velocity Duct Area Total m3i s nct b Having found the sta
60. lancing system anpear to work Balance the same system using the Balance from the fan out method Which method is the quickest Describe how you would arrive at the required mixture temperature when balancing an air conditioning system a If using a water manometer and it is calibrated in Pascals how would you convert the manometer reading to a velocity reading in m s Encina b c Assuming the reading in a is 12 Pa what is the duct velocity in m s Show formula and all calculations usina Pa What would be readina b if the manometer is calibrated in mm What is the duct velocity in m s Show formula and all caleulations using mm NOTE This section has been SATISFACTORILY completed DATE a INSTRUCTOR S Student mark for this section is 60 70 20 90 100 THE MARK FOR THIS UNIT IS l AAA NASA PRA e CANANARNAN PIAR X Por VENTILATION NR13 Learning Outcome 6 AIR HANDLING SYSTEMS In order to comply with Sections 45 and 46 of the Public Health Act 199 L in respect of the installation and maintenance of air handling systems the following requirements must be met All drainage and liquid discharges are to be dicharged into a waste water system or otherwise disposed of as approved by the relevant public authorities Suppl
61. lied to control any growth of Legionella Routine disinfection by chlorination to maintain a low level of free residual chlorine is one of the few proven methods The method must be accurate automatic and filtration may be a prerequisite So far other methods for application in large warm water systems have shown to be unreliable and unacceptable Other Water Treatments Microbial growth in warm water systems can be controlled by various non chemical treatments However the efficacy of these treatments has not been fully determined in the field under varying conditions such as water quality temperature of storage volume of water use and system design queen telat Two methods of microbial control in warm water system which have potential application are using the effects of heat and ultra violet irradiation Ultra violet light treatment of warm water systems which have potential application are using the effect of heat and ultra violet irradiation Ultra violet light treatment of warm water appears at this stage to have limited application t EVAPORATIVE AIR COOLERS Evaporative air coolers operate by utilising the physical phenomenon of cooling air entering the building by evaporation of water These systems will only work satisfactorily in dry climates as a high level of humidity prohibits an adequate rate of evaporation They are used in large numbers in areas remote from the coast for instance in western NSW At this s
62. low rate where static pressure cuts the fan curve or it may surge between them FAN LAWS It is often necessary to operate a fan at a speed other than the manufacturers tabulated capacities due to the actual required volume of air The following is confined to those laws of most common use in air conditioning For a given Fan Size Duct System and Air density 1 The volume varies proportional to the fan speed Ql NI 02 N2 11 The developed pressure is proportional to the square of the fan speed N1 A ili The power absorbed is proportional to the cube of the fan speed WI N1 g W2 N2 where O Volume flow rate m s P Pressure Pa normally static but it can be velocity or total pressure W Watts not installed but what is absorbed N Revolutions per minute Revs s EXAMPLE A fan delivers 7 3 m s of air against a static pressure of 383 Pa when rotating at 600 RPM 10 Rev s and absorbs 3 9 kW If the fan speed is decreased to 400 RPM 6 7 Rev s find a the new volume b the new static pressure c the new absorbed power Perea QU rai ig Fiennes SOLUTION I a Volume m s Q2 N2 Q Qi Uni Q 7 3 00 Q2 4 87 m s Pl Static Pressure Pa P2 P2 PI N2 P2 383 600 P2 170 2 Pa l bo Power absorbed kW lt W2 Wi NI W2 W2 1 16 kW PROBLEMS A fan running at 350 RPM 5 83 Rev s supplies 6 2 m s
63. m uses the effect of Latent Heat to cool the air as it passes over a water soaked porous material The materials vary from plastic compositions to pads of cotton covered straw and heat is removed absorbed from the air in changing some of the water to a vapour The amount of cooling of the air depends entirely upon the amount of moisture already in the air in changing some of the water to a vapour The amount of cooling of the air depends entirely upon the amount of moisture already in the air Thus with dry air in inland areas the temperature can be reduced by up to 15 C The system is less effective near the coast because during this heat transfer process the incoming air will absorb even more moisture depending upon the original condition of air entering the machine Therefore if the entering air is close to saturated very little cooling by evaporation will occur and temperature reductions may be offset by the increased humidity within the space Because of the increase in relative humidity as air is cooled and moisture added air should never be recirculated through an evaporative cooler To be effective only fresh outside air should be brought through to cooler and be exhausted out through the other sides of the conditioned space The systems described earlier and a great many are sold for domestic and small commercial applications Figure 19 20 shows an exploded diagram of a typical unit designed for installation in
64. ments of the buildings The main types of buildings requiring complete air conditioning are o High rise apartment buildings o High rise office blocks e Multi storey departmental shops e Theatres and entertainment centres o Large shopping complexes e Hospitals saon The applications of the air conditioning process are more wide ranging than most people realise Two extreme applications for comparison could be air conditioning of astronauts space suits for life preservation and the climate controlled conditions for mushroom cultivation Other processes will become apparent as you learn more about this industry We will now investigate the factors to be controlled in an air conditioning process These are Control of Air Temperature Control of Air Humidity Control of Air Cleanliness Control of Air Purity Control of Air Distribution To achieve complete air conditioning equipment must be provided together with the necessary controllers to achieve the desired internal conditions under all prevailing external internal loads Equipment to achieve full air conditioning must therefore provide for the Heating Cooling Humidifying Dehumidifying Filtering Purifying and Distributing of air supplied to the occupied areas of the building We will now look at the methods employed to produce these effects AIR HANDLING AND DISTRIBUTION SYSTEM In any air conditioning system where duct work an
65. mum velocity of 0 127m s is necessary to ensure distribution of temperature through the zone seres Capertee P pomo The degree of comfort experienced by the individual will depend upon a The dry bulb temperature C b The wet bulb temperature C c The relative humidity d The velocity m s The measure of comfort taking these factors into account is known as the Effective Temperature This can be defined as the temperature of saturated still air which gives the same feeling of warmth or coolness as the condition under consideration e l 32 o yO tle A vet y la We ES Q 265 Wr DUAB TEMPARATORI IO 5 5 21 265 32 275 PRY BULB TEMPERATURE es e SS COMPORT ZEE FOR NORMALLY eef PEOPLE SEDENTREYT of IGT RETIWE AIR VELOCITY 0 127 m s The effective temperature graph shows what has been determined as the comfort zone For office workers if all occupants are to feel comfortable the dry bulb temperature must be between 22 5 C and 25 C What these lines also tell us is that at 23 C and 55 R H and 24 C and 40 R H we have the same effective temperature of 21 C That is the feeling of comfort or discomfort would be the same at these two conditions TYPICAL AIR CONDITIONING SYSTEM The ducted air conditioning system incorporating a spray humidifier is shown in the following diagrammatic sketch peering Dotted Lines Represent Duct System To Be Installed a One system of duct layout is
66. n static pressure Ps between that at the fan and that at the far end of the duct results in flow of air in the duct TOTAL PRESSURE PT A tube often called an impact tube is placed so as to face h Total pressure directly into the air strean reading In this position the pressure transmitted to the manometer will be the total of the velocity pressure Pv plus the Static pressure Pv in the duct ha one Measuring total pressure THE SIGNIFICANCE OF VELOCITY PRESSURE PV Velocity Pressure Pv is an important fiqure because it enables us to calculate the volume of air flowina in a duct Velocity pressure Pv cannot be measured directly but is found as the difference between the total pressure Pt and the static pressure Ps Pv Pt Ps This can be done by taking sevarate pressure readings and then subtracting one reading from the other Normally velocity pressure Pv is found directly by using the connections shown below Static pressure connection h Total pressure minus static pressure equals velocity Tube with pressure reading open end facing air steam a Measuring velocity pressure Duct The greater the velocity the greater will be the velocity pressure Pv If we measure the velocity pressure Pv we can calculate the corresponding velocity as follows a Assume density of air as 1 2 kg m b The manometer is graduated in millimetres of water y D Py
67. nd the air flow rate The mass retained by 9 the filter is the mass fed multiplied by the gravimetric efficiency The filter life com be calculated from this figure and the filters Cust hol ince capaci v Often when long periods of time between servicing or when dirt concentration is high filter life can be increased by decreasing the rate of air flow through the filter US 4 Althougn there are many different types of filters available they al fit into one or a combination of three basic categories la Day Anmmestance filters remove dust particles from the air stream by trapping them between the fibres of a t filter mat which may be of cellulose cloth felt glass paper or specially developed synthetic materials Dry arrestance filters are available in both the fixed panel shown below or roll types shown opposite 3 im TIT Lulu yee Oy The mecia texture necessary for high efficiency requires low surface velocity to keep the resistance low To obtain this low velocity the area of the filter can be increased within the filter frame either by pleating or forming it in corrugations or by sharing and sewing it into a sermi supporting basket This increases the depth of S the filter and also increases a Pyracube deep bes filter the effective surface area up to four times the filter face area depending on the configuration All the dry media filter mentioned so far can be clean ed by vacuum cleaning wa
68. ngle width single inlet SWSD double width double inlet DWDD floor mounted in line and tubular centrifugal among others The basic blade configurations and their modifications are indicated in figure 1 2 1 The backward curved air foil and backward inclined blades illustrated in figure 1 2 1 are all in the backward curved family the difference in each case being the blade shape i FORWARDO CURVED RADIAL a b ALA N BACKWARD CURVEO C LL AL BACKWARD AIRFOIL INCLINED d e Figure 2 1 Basic Fan Blade Configurations The SWSI and DWDI fans may be designed with any of the blade arrangements on the wheel The basic difference in each case is the shape Each is built with the wheel enclosed in a housing called a scroll which is designed to produce the most efficient airflow within the fan from inlet to outlet discharge The single width fan provides one path for air to flow from the single side inlet through the wheel and scroll and out the discharge Because of the need to provide maximum air distribution across the width of the wheel and blades increase of size and capacity is accomplished mainly by increasing height since an increase in width would produce an ineffective portion of the blade and wheel on the blind side opposite the inlet The double inlet fan with inlets on both sides provides the means for air to reach this difficult area Hence the comparison by name of single and double width For the
69. o leak out through doors and windows b Induced ventilation where a fan mounted either in the ceiling or high on a wall exhausts air outside allowing fresh air to enter via doors and windows c Combined forced induced ventilation with inlet and outlet fans Applications usually requiring ventilation are a Buildings and rooms occupied by people at work b Machine and plant rooms where heat is generated c Process plants requiring quick cooling of foods confectionery print etc d Areas where toxic or unpleasant fumes can accumulate Figure 19 5 shows an application of ventilation to large public buildings such as halls schools workshops and offices Similar ventilation may be applied to any room where ad heat is generated but induced ventilation is generally preferred to forced ventilation where heat and fumes could be blown back over occupants Laboratories handling particularly toxic or radio active materials often required specially designed fume cupboards made of non corrodible plastic and special glass covers on all sides Comfort of the workers is usually a secondary consideration in industrial processes with safety the prime objective However when people are involved consideration must be given to e High air noise levels e Draughts o Air turbulence o Temperature o Moisture content o The purity of the circulated air DO S AND DON TS WITH VENTILATION o Where only windows
70. o be generous in the original selection The propeller fan is also a relatively low speed fan Increased capacity means increased fan diameter and resulting high blade tip speed which also limit the capacity performance Vaneaxial and tubeaxial fans are specially designed propeller types fans although their operating characteristics with external resistance are greatly improved The basic difference between the two may include blade configuration but is mainly the fact that tubeaxial fans do not employ guide vanes before or after the impeller and the vaneaxial fans do The vanes are arranged in such a way as to improve the internal air flow pattern reduce the internal resistance and thus to increase the efficiency and performance of the fan The blade and vane configuration may be flat or curved single or double thick the selection being determined in the design to produce best performance at lowest cost Two critical items must be considered in the selection and application of axial fans One is similar to the tubular centrifugal The outlet and especially the inlet air flow pattern is extreme importance Some axial fans may be applied without inlet and outlet cones but this refinement usually improves operation and in many cases is the difference between success and failure The streamlining effect of the cones is similar to that of a venturi meter where the axial fan casing is the centuri and the fan is placed at the narrowest point in the a
71. o or through a pre determined valve of resistance and this 15 a more significant figure than clean resistance The dust holding capacity is normally given in grams Velocity also affects dust holding capacity d Efficiencu or more correctly arrestance efficiency is generally defined as the amount of matter retained by the filter expressed as a percentage of the amount entering it Both atmospheric air and test dusts are used in filter testing standards As to the measurement of the amow t of dirt retained by the filter there are a number of ways in which this can be assessed 1 Gravimetric or mass test the amount of dust is determined by weighing the dust and the filter collecting it ii Dust spet blackness or discolouration test all meaning the amount of dust being measured by assessing the soiling of filter papers through which the air has been passed iii Count tests in which the number of particles is counted by samplino microscopic examination or by automatic particle counters iv Opacity test in which the opacity of an air stream containing dust in suspension is assessed le Filter ide or the time a filter will operate without attention is a function of four parameters UE CORS 1 Dust holding capacity ii Gravimetric efficiency 111 Dust concentration in air being filtered iv Rate of air throuoh filter The mass of dust being fed to the filter is the product of the dust concentration a
72. o zero j poene B A stop watch should be used for timing when reading RPM with speed indcator Speed indicator NF Ho t 16 D L AS where RPM Shaft sveed revoluttons per mnute No Original reading Nf Final reading t Time interval minutes REE b Dial Tachometer Centrifugal Type A hand held instrument that directly indicates the instantaneous speed on the face of a dial Envira Tachometer with single speed range Tachometer with multiple speed ranges c Chromometric Tachometer i o A han held instrument that a combines a precision stop watch Lad M and a revolution counter in an Tip to be instrument The scale is ey inserted in calibrated so that after 6 seconds 4 countersunk eet the instrument stops accumulating o non revolutions Each actual gt revolution of the instrument li indicates 10 revolutions on the to start dial so that readings are directly in R P M Repeatedly pressing the activating button wtthout contact J with a rotating shaft on allowing the timer to run down will damage this instrument Chronometric tachometer Always keep tachometer and Reading shaft speed all anachments incase when notin Complete tachometer set use with extra tips and case d Stroboscone This instrument is a source of variable frequency light and the technique in using it is to match the light frequency to the Siete rotational speed A chalk
73. omerator combines an ioniser and cell fed with high voltage direct current from a power pack but the cells are not coated with adhesive In addition there is a dirt storage section immediately following the collector cells Prnc ple of cperation of lon tron aaglomerator type electronic air filter The ionised dust is precipitated onto the cell plates and here it coctomersies into large particles and as there is no adhesive ace de gets blown off again The large agglomerated particles are then carried into the dirt storage section where because of their large size they are effectively 100 trapped js NOTE Any maintenance or repair of eLectronic ain filters must be done with the power CFF Do not attempt ZC bypass any of the electrical saseguards installed 5 Since the effectiveness of an air conditioning system is dependent on the amount of air flowing care should be taken to ensure that the resistance of the system does not materially increase Draught gauges installed across the filter will provide a continuous reading of the filter resistance The point at which service is required alters depending on system or manufacturers recommendations AS a genera rule filters should be serviced before the total air flow in the Fi drops by 10 and or the pressure drop across the filter rises da TAN a s ie L rn In some locations the odour of air may need to be controlled as well as the cleanliness Activated Car
74. or air to total air SRA Percentage of return air to total air The formula may be restated as Tra Tmx S OA Tra Toa Example A system designed for 7 0 m gt s total air The minimum setting for the outside air damper calls for 1 1 m3 s Determine the correct setting of the outdoor air damper STEP 1 Using the pitot tube traverse at the proper point of the supply duct set the fan speed to deliver 7 m gt s STEP 2 Insert a set of calibrated thermometers at strategic voints to measure the temperature of the outdoor air return air and mixed air Assume that these read 33 C outside 24 C return air and 24 5 C mixture STEP 3 Find the design percentage of outdoor air eet 9 157 7 0 STEP 4 Calculate the air mixture temperature required to give 15 7 outdoor air by using the formula Tris 0 157 x 33 0 843 24 25 4 C STEP 5 Since the recorded mixture temperature is 24 5 C and the required mixture temperature is 25 4 C the system is obviously short of outdoor air by formula 5 6 therefore open the outdoor damper slightly to allow more outdoor air and close the return air damper slightly to decrease return air keeping the supply volume at 7 0 m s until the air mixture temperature rises to 25 4 C rn E 4 BBN GN PROBLEM Supply air quantity 4 72 m s Specified minimum outside air quantity 940 l s From actual measurements Toa 32 C Tra
75. ose of ventilation is to remove objectionable air and to replace it with fresh air When outside air is more acceptable than room air the simplest way to improve comfort is to open doors or windows but the degree of relief will depend upon a number of factors a The size and type of windows b The location of the openings c The velocity and direction of the prevailing wind d Window treatments such as fly wire curtains and blinds DURAS rera 7 ES Fig 19 1 Natural air flow induced by double hung sash windows Other windows are more effective when they can be turned into the direction of the breeze such as side hinged casements Side pivoting windows and louvres as shown in Figure 19 2 are most effective when used as shown for summer and winter use General air flow pattern for pivoting windows summer ventilation General air flow pattern for pivoting windows winter ventilation Fig 19 2 LOCATION OF THE OPENING Efficient ventilation requires openings on opposite sides of a building where a maximum use can be made of the prevailing breezes and the high and low pressures which result on the windward and lee sides of the building because of the wind forces Little effective movement is possible when the openings are on one side with openings on adjacent walls only marginally better Figure 19 3 shows the direction of air movement due to wind VELOCITY AND DIRECTION OF THE PREVAILING WIND The
76. ow and the cross sectional area of the duct in which the air 1s flowing To keep the resistance as low as practical for any given installation some thought must be given to the resistance created by bends contractions expansions etc in the duct system Typical bends contractions and enlargements are shown below and on the following page oes RCR DED AR AOT One tas EPO eee l BOUNDED OUTER Different ways of making a 90 degree bend Some involve greater pressure losses than others Pressure losses occur with abrupt reducing fittings To overcome some of the resistance created by abrupt expansions on contractions these fittings are usually made angular as shown in the following figures EA tevi PELO 1008 Abrupt expansion results in excessive pressure losses ll 19 gertrniiotory raen T ERN H LLL UT f For sudden contraction in transformation piece with an included angle of approximately 60 is a reasonable compromise and for sudden enlargements an included angle of between 10 and 20 is frequently used Where space limitation requires greater included angles then splitters similar to those used in bend may be installed Using Splitters To Reduce Expansion Angle To summarise therefore the main items contributing towards greater resistance in a duct system are a High air velocities b Small cross sectional duct areas c Large air volumes d Long duct lengths e Changes in di
77. ow proportionately balanced Proceed to obtain proportionate balance between branches 2 and 3 3 and 4 etc Regardless of which proportioning system ts used always work towards the fan from the end outlet of a sub branch the end sub branch duct and the end branch on a main duct When all branches etc are proportionately balanced check i the total air flow at the fan Adjust fan speed or fan dampers to obtain design flow The ratio R Vm Vd Om 0d at the fan will now be 1 0 since the system will be approximately 1 0 and the flow from each outlet will be design air flow rate a The baste steps outlined form the foundation for balancing anu system There are however a number of varrattons to the conventional system t e Dual Duct Multt Zone Variable Volwne and Inductton Systems etc and these where applicable will be covered by individial worksheets e Service to overcome air supply variations are often required because of the following faults and can be corrected as indicated 4 ii Dirty fitters on coils Indication Remedy Fan speed too Low Indication enaze iv Belt slipping Indication Remedy Dampers onr outhets closed Indication Remedy mr uz Restrrccted ductwork Indication Remedy Abnormal temperature drop across the cooling cork In
78. pproached a TARRO GEA AR A PERCENT OF FREE DELIVERY CAPACITY HIRO KAN PERCENT OF SHUTOFF STATIC PRESSURE HORSEPOWER STATIC EFFICIENCY Figure 3 1 Radial Blade Fan Performance ADVANTAGES 1 Ze Self cleaning Can be designed for high structural strength to achieve high speeds and pressures AXIAL FLOW FANS Axial flow fans are classified as propeller tube axial and vanaxial see figure 6 1 All may be belt driven or directly connected to the motor The most commonly recognised is the propeller fan which may be a small household version a pedestal model a kitchen wall exhaust fan or one of the many other adoptions available This style is also the least expensive to produce The blades are often stamped metal and in many cases little consideration is given to desirable features such as entering air pattern and tip shrouds which can greatly improve performance It may be seen from examination of the curves later in this chapter that the static pressure characteristics of this type of fan are comparatively poor which leads to the correct conclusion that restrictions such as ductwork louvers screens and dampers have a serious effect on performance In fact it is not generally good practice to apply this type of fan where ductwork is required and other restrictions should be kept to an absolute minimum Some fan designs provide ratings at low external resistance figures but it is still prudent t
79. proliferation of Legionella and other bacteria The aerosol drift from a contaminated tower may cause an infection in nearby susceptible people The correct operation and regular routine maintenance including cleaning are important to ensure the desired performance and acceptable hygienic conditions of all components of the air conditioning system Water Treatment A water treatment program is essential for a condenser water cooling system to inhibit corrosion the build up of scale and the development of any microbial contamination Corrosion and scale development can cause fouling of the condenser tubes and the panas pipework distribution system resulting in poor system efficiency and premature failure These factors can also provide an environment which promotes the colonisation and growth of organisms such as Legionella Specialist water treatment companies will be able to advise on the appropriate regimen whether it is a chemical or non chemical process or a combination of water treatment processes These companies should also be familiar with any legislation applicable to the particular products or processes they offer _ E Biocides Water treatment biocides are used to control the growth of bacteria algae protozoa and fungi in the condenser water These micro organisms may provide nutrients for growth of Legionella The effectiveness of biocides may be reduced by the presence of organic and inorganic materials such as sand di
80. r Air flowing from the probe enters the bottom of the meter where it impinges against the bottom of a small ball This causes the ball to rise in a tube which is tapered so that the flow area increases at the rises The height to which the ball rises is proportional to the air velocity which can be read directly in metres per second on an appropriately graduated scale The probe the instrument tube and connecting tubing comprise a calibrated instrument It is therefore important to use the proper probe and that the length of the connecting tube not be changed When using a suitable probe the instrument can be used to measure static pressure sete Z ES ES NR e Ra OS STAN Tar SSE Sasa DNS ANTES Z 4 L E e t Measuring grille velocity k Noe B oo R N MA AIR VRLOCITV2LOW RA a Al B IILIAIIITIALITIEA el S e e L AA w d N bad Kd t 4 pe 5 w Aar V AR LE A L lt L BID age ct APT om Ano te Am wye ha Se o E ER ISSN Gek 4 E x o er Eme iT Nar YA 5 h iiA E a SUEY yer Flowmeter kit with probes accessories and case Variable area flowmeter 5 AIR TEMPERATURE AND RELATTUE HUMIDITY To get a simultaneous readina of wet and dry bulb temperatures a wet and dry bulb thermometer are mounted side by side on a frame fitted per w by which the two thermomete
81. rake horsepower per square metre of outlet area concept and more nearly represent the actual structural limitations of the centrifugal fan designs A centrifugal fan in one of these classifications must be physically capable of performing over the entire class range From the user s point of view the limit lines represent minimum performance For example the Class II fan in the chart must now be capable of providing 216mm of static pressure at 15 24 metres per second outlet velocity By comparison the old standard merely required that the Class II fan be capable of operation up to 171mm of total pressure at one point on its performance curve Another AMCA classification 1s especially for cabinet fans These are Class A to 76mm wg Class B to 139 wg Class C above 139mm weg FAN INSTALLATION MOUNTING Supporting a fan is not merely a matter of strategically placed steel and concrete The fan motor and drive together became a complex system of dynamic components all connected together by moving in different directions at different relative speeds The composite assembly must be tamed by the proper application of supports and isolation Isolation of the fan motor and drive from the connecting ductwork is generally accomplished by means of a suitable flexible connection The connection must be long enough so that the rigid duct and the moving equipment do not touch The differences between the position in motion must be taken into accoun
82. re averaged and the result converted to velocity Having found the average velocity the volume of air flowing can be calculated as follows Duct size 300mm round Duct Area 0 0707 m approx Velocity 60 6 m s Volume Velocity x Area 60 6 x_ 0 0707 4 28 m3 s cs 4 ANEMOMETERS Critical to the proper use of any anemometer is the determination and application of the correction factor which will convert the anemometer reading into a reasonable accurate velocity or volume measurement It is absolutely essential that the correction factor be used for each instrument e The manufacturer tests each type of supply outlet and return inlet to determine the X factors for all of the different types of instruments The manufacturer also determines the location on the face for making measurements a Rotating Vane Propeller Anemometer The propeller or rotating vane anemometer consists of a light weight wind driven wheel connected through a gear train to a set of recording dials that read the linear metres of air passing through the wheel in a measured time The instrument is made in various sizes 75mm 100mm and 150mm diameter sizes being the most common Each instrument requires individual calibration Most of these instruments are not sensitive for use below 1 0 m s Their useful range being from 1 0 m s to 10 m s The instrument is available aS a manual timed type in which a watch or stop watch
83. rection of air flow f Contractions in the air stream g Expansions in the air stream TYPICAL AIR CONDITIONING SYSTEMS SINGLE UNIT LOW VELOCITY SYSTEM Automatic Exnaust Damper x Rein Air Ex aust Y a Air N Return Y Automatic Return Supply as Air Damper NNS to room LCE as Outside air ome MIOS ee E D l Supply 7 E Fan Automatic Finer Pre neat Reneat O A Dampers Co Coil Cootng Coil Air handing syste r single zone with return air fan and economizer control This is a simple system with the addition of economiser control which allows use of outside air for cooling Note the two outside air dampers The two dampers will supply 100 outside air to the system The minimum O A damper will supply required ventilation normally 10 to 20 of total supply air The maximum O A damper is usually controlled by thermostat and opens gradually to admit outside air when it is cool enough for use in the system Provision must be made to exhaust used O A and this exhaust damper must be automatically co ordinate with the return air and maximum outside air dampers The economiser control can be used with other types of systems This is a constant volume system with no individual room control The activity of the occupant also contributes to the particular method used to produce the desired result For example the proportional mixing of fresh and recirculated air is quite acceptable in an office b
84. rs can be whirled through the air A TT A AAN nE ete at Gy A Al k Sn gt s AA TLI ee 10 EZ gt ote 1 ath Z 0 5 Eon et T x PA Y TETAS O EA E LA D ast Sling psychrometer with wet bulb and dry bulb stems and handle to whirl the instrument until che wer bulb settles The whirling is stopped from time to time and readings taken until the temperature veading of the wet bulb thermometer starts to rise the lowest reading beina taken as the wet bulb thermometer A mercury in class thermometer may be needed to check whether air density corrections should be made at the final stage in measuring total volume flow from the fan s A high degree of accuracy is unnecessary Electric thermometers may also be used and these are usually one of two types One is the thermocouple type in which the thermocouple generates an electrical current when temperature varies between the hot and cold junction of dissimilar metals By reading the amount of current generated an indication of temperature is given The other type of electric thermometer is the resistance thermometer the type generally known as the Hot Wrre Anemometer see Page 23 covered elsewhere since it also is used as an air velocity measuring instrument gues VOLTAGE AND CURRENT It ts important to check all motor current at the beginning of balancing to see if tt ts within design range
85. rt and other particulate matter Biocides must never be allowed to discharge into surface draining systems or other water courses Approval for discharge in sewage reticulation systems must be obtained from the relevant authority Filter and Separators The use of a correctly designed system of either mainstream or sidestream filtration and or centrifugal separation can significantly reduce fouling of cooling water systems with particulate matter This cleansing process allows the biocide or other treatment process to be more effective Routine Cleaning The regular cleaning of cooling towers and any associated condenser water system 1s important in a well maintained system Such cleaning also reduce the nutrients and microbial populations which may aid in the growth of Legionella Stagnation of water must be avoided as this can be conducive to the growth of Legionella Legal Requirements In order to comply with sections 45 and 46 of the Public Health Act 1991 in respect of the installation and maintenance of cooling towers the following requirements must be met ka All drainage and liquid discharges are to be discharged into a waste water system or otherwise disposed of as approved by the relevant public authorities dEms ka All cooling tower systems are to be inspected monthly o All maintenance work found to be necessary as a result of the inspection is to be carried out within a reasonable time prior to the next inspe
86. ructor the NEEB Environmental systems books 3 Question 1 Name the two areas where sound tests are required Question 2 Identify three scoures of noise that are common in most offices Question 3 What are some methods that can be used to reduce outdoor noise levels from entering a building List and explain three 3 Question 4 List four 4 types noise that could come from the Air Conditioning and air handling system 2 Question 5 How are vibrations transmitted through a building Question 6 What are the major sources of vibration in Air Conditioning systems List seven 7 scoures S Question 7 How is equal deflection under unequal loads achieved Question 8 Apart from mechanical equipment what other types of equipment should have isolators fitted am 3 Question 9 l Describe the construction of the open exposed spring type isolator Question 10 l With the aid of a diagram explain the operation and possible problems of this type of isolator Question 11 On what of equipment may Neoprene Pads be used Question 12 What type isolation mount could be used to support pipework and explain it s operation LAL rg 4 Question 13 With the aid of a diagram explain how ductwork should be connected to a fan plenum Question 14 l When fitting vibration eliminators to pipework under what
87. rument test port EQUAL CONCENTRIC PITOT TUBE STATIONS INDICATED BY O AREAS Regardless of the instrument used the drawing _opposite sii illustrates the method of 9773 Tu arriving at sensing points across the duct cross section n DUCT RECTANGULAR DUCT TRAVERSE ON ROUND ANO SQUARE DUCT AREAS For traversing square or rectangular ducts at least 16 and up to 64 are required depending on duct size For traverses of less than 64 sensing points the minimum distance between centres should not exceed 150mm All the material covered in Section 11 discusses preliminary air balancing and must be fully documented Final air balancing depends on the kind of sustem to be balanced A sample of revort sheets are shown on the following pages If supply fan volume is not within plus or minus 10 percent of design volume adjust fan speed to obtain approximate design air volume Barber Colman Company COLMAN AIR BALANCING WORK SHEET hoakiora S110 a INEA i 1 ws Air Moving Equipment Date Test No Job Name Location System PC A AA YA A I S i MANI ZII IPN ARI Ima volume eave o IE e e N A e SVR Me Discharge S P E RDA E AIR E RS O ps YA pm peee YC UCI ION A E H By Operating Conditions hag rE COLMAN a N t TN Sy tor HEET Ps TOLON AIR BALANCING WORK S Filter Coil Velocity Troverse Filter Coil Size_________ Date Peat Na Job Name e
88. s operate at higher speeds than other types of centrifugal fans The blades are longer radially than the forward curve type and usually heavier while the impellczs are strongly reinforced with stiffening rings and larger section shafts are required The air output for a given wheel diameter is less than with forward curve fans The efficiency however can be substantially higher Special types may develop very high pressures for example forced draught fans for boilers The pressure volume characteristics of backward curve fans are shown in figure 4 1 In this case the maximum horse power occurs within the normal working range PERCENT oF SHUTOFF STATIC PRESSURE HORSEPOWER STATIC EFFICIENCY PERCENT OF FREE DELIVERY CAPACITY Figure 4 1 Backward curved blade fan performance Figure 4 2 Backward curve impellers Two modifications of the backward curved blade fan are the air foil and backward inclined blade fans These are illustrated in Figure d and e Both are non overloading types The airfoil blade fan is a high efficiency fan because its aerodynamically shaped blades permit smoother air flow through the wheel It is normally used for high capacity high pressure applications where power savings may outweigh its higher cost Since the efficiency characteristic of an airfoil blade fan usually peaks more sharply than those of other types greater care is required in its selection and application to a particular duty The
89. s then said to be Laminar As the velocity increases the characteristics of the flow changes eddy currents form and the air becomes swirly This type of flow is known as Turbulent flow Laminar flow produces less friction losses considerably less system noise but also extremely poor heat transfer coefficients A special case of laminar flow called strattjteation which is the result of different densities mixing of return and outside air can raise problems in air systems Turbulent flow produces higher friction losses reduced chance of stratification and excellent heat transfer In general turbulent flow is more desirable for the overall system Pressure Chassrsication 04 Ducts Classification of duct systems by pressure and or velocity is quite arbitrary The SHEET METAL and AIR CONDITIONING CONTRACTORS NATIONAL ASSOCIATION INC SMACNA is developing duct construction standards established the following breakdown i Low Velocity Up to 10 m s and up to 50mm 500 Pa static pressure e ii High Velocity Above 10 m s a Medium Pressure unm to 150mm 1500 Pa static pressure b High Pressure Over 150mm 1500 Pa static pressure Up to 250mm 2500 Pa static pressure NOTE Medium and high pressure duct systems should be tested for leaks because performance of systems having such ductwork is affected by air leaks to a much greater extent than low velocity systems Velocity Static and Total Pressure i
90. same capacity a single inlet fan is about 30 taller but only about 70 as wide as a double inlet The DWDI fan can therefore be extremely useful where physical installation height is limited Sirenas PEN Outlet Coil or Casing Double Width ingle Width PAN Inlet Double Inlet SWSI DWD Figure 1 2 Fan Inlet Conditions In either case SWSI or DWDI successful operation of the fan is critically dependent upon the space conditions afforded the air at the fan inlet see figure 1 2 1 The absolute minimum for proper operation is that the distance from casing to the fan inlet be equal to the entrance opening diameter Preferably the distance should be 1 4 times this diameter or greater It can be seen then that the DWDI fan requires a considerable plenum width to provide adequate inlet space for satisfactory operation Furthermore the DWDI fan location must usually be in a plenum where the SWSI fan can be located outside the plenum with the inlet connected to an opening in the side of the casing which must be there to accommodate discharge ductwork connection Furthermore the DWDI fan will commonly have its motor and drive in the air stream which will increase heat gain in the air stream and possibly increase maintenance to belts pulleys bearings and motor The floor mounted category referred to does not intend to eliminate the installation of this type of fan on platforms roofs or elsewhere other than the floor itself
91. shing Or some other method However a dry media filter which is never cleaned is the 4beciute or FIP Hiah Efficiency Particulate Air filter immerse and agitate in bath of warm or cold water with Getergent mcr These use a glass paper media and have an efficiency of i 99 97 The paper is arranged in an extreme concerting arrangement separated by pieces of corrugated material cenerally aluminium The filter pack of paper and separators are sealed in a strong frame generally made of metal Pan of anabsolute HEPA filler pack showing corrugated separators dies A Pr Gea be stt rac tty L 4 tab Fans elevo OUT IN TIEN H L et RETT HH H PT A d die hgn e hen v fiter b Viscous All the dry media filters with the exception of the EFRPA filters can be impregnated with an adhesive normally a gel or light oil to increase their efficiency Generally medias impregnated with an adhesive cannot be satisfactorily cleaned Metal viscous oi filters are available as simple fixed panel filters or as automatic types which provide for the panels to be cleaned and re oiled by passing them through an oi bath in the base of the filter frame The filters are normally constructed from aluminium Section of filter media approx actual size Cross section of filter media showing airflow pattern pure qaa A e ma e o ap ee e a aw Te TEASER A te Eleco
92. sign velocity For outlet No l calculate ratio of measured to design velocity as Vm R 7 POEA Call this Ratio R for Outlet No l EXAMPLE J Vm 3 0 m s Vd 2 5 m s Vm Ry va _ 3 0 o oe Ry Toa Proceed to Outlet No 2 Measure flow and determine average velocity Vm for this outlet Calculate Ratio R for Outlet No 2 vm gt 3 0 m s e Ro Vm gt VO 2 3 0 S a R gt 0 732 Compare Ry and R If the ratios are not within 10 per cent adjust outlet No 2 to bring ratios into closer agreement Do not adjust Outlet No 1 wee ii 10 Ri Lee 10 1 32 1 08 10 and Ra 0 732 Wie 0 805 0 69 Measure Vm for both outlets and calculate new values for Ri and Rj Continue re adiustino Outlet ho 2 re measuring and calculating R and R until R and R3 are within 10 percent of each other and record Although neither of the two outlets may have design velocity or volume they are now proportionately balanced one to the other Proceed to Outlet No 3 Measure and determine average velocity Vm for Outlet No 3 and calculate Ratio R3 for this outlet If necessary adjust Outlet No 3 to bring R3 within 10 percent of Rj Do not adjust Outlets Nos 1 and 2 Adjust of Outlet No 3 automatically changes the ratios of Outlets 2 and 1 The ratio for these outlets approaches the same values For this reason once the outlet has been adjusted correctly it never requires further
93. ssure up to 250mm 2500 Pa swg static pressure Note Medium and high pressure ducts should be tested for leaks because performance of systems having such ductwork is affected by air leaks to a greater extent than low pressure systems In parts 18 19 and 20 we covered the definitions of a volume of air handled b outlet velocity c total static and velocity pressures We are now going to look at Static Pressure Ps as it effects fan performance Consider a complete air distribution system which may include heat exchangers coils filters grilles dampers and duct work If air is forced through the system at a given rate of flow a certain static pressure will result If air is forced through the same system at a different flow rate a different static pressure will exist Most air distribution systems are turbulent flow systems in which the static pressure varies as the square of the air flow rate Ps A Q where Ps STATIC PRESSURE Pa A CONSTANT Q VOLUME FLOW RATE m s The graph constructed from this equation is called THE SYSTEM CHARACTERISTIC CURVE Field problems often will required that both a fan performance curve and a system curve be used Ifa fan curve is available a system curve can be drawn directly on it Where manufacturers data is in a multi rating table form it is possible to draw a fan curve based on these tables EXAMPLE A test on a forward curved centrifugal fan gave the following re
94. st be of a sufficient height above the ground or surrounding rod to minimise the intake of dust and detritus Cooling towers must not be located near exhaust discharges from kitchens or other areas where nutrients conveyed in these systems could assist in the growth of Legionella When considering the relocation or repositioning of duckwork in a building care should be taken to ensure that the duct work is designed and installed to minimise the ingress and accumulation of moisture This includes grading ductwork to prevent water collection As an added precaution all ductwork must be cleaned before the air handling system is commissioned Locations near occupied areas pedestrian thoroughfares air intakes and building openings should be avoided
95. stem device including sound attenuators deadeners and traps may generate noise under some conditions Fans generate sound in a relatively narrow and predictable range of frequencies dependent upon the rotational speed and the number of individual impeller blades CONCLUSION The following information concerning the characteristics of the various fan types will assist in determining the fan selection providing the previous considerations are satisfied or are not determining factors CENTRIFUGAL Forward curved blade fan As system static pressure falls off the horsepower increases immediately and continues to increase For the illustration the motor would begin to overload immediately although small increases may remain within the service factor Backward curved blade fan Horsepower has been selected at the maximum requirement at any point on the horsepower curve and neither increasing nor decreasing system static pressure will increase horsepower requirement or cause motor overload Radial blade fan Operation is similar to the forward curved blade fan with the same results Propeller fan Horsepower requirements are relatively constant throughout the range but decreasing system pressure could cause overload if the motor is initially selected too close to name plate rating or within the service factor PRINCIPLES OF AIR FLOW For large air conditioning systems and package air conditioners which serve several zones the trea
96. sults with the fan running at 480 RPM volume ars Jo fro 2 3 la s e 7 The fan supplies air to a system for which the static pressure loss is calculated to be 615 Pa when the volume flow rate is 4 3 m s Using the graph below plot the fan and system curves SOLUTION Ps A Q 615 A 4 3 A 615 33 3 4 3 For selected volume flow rates find the corresponding static pressure losses Rt SYSTEM S CURVE 70 is n m o o dun E AGA ps ae 30 y 40 PRESSURE Pa gt VOLUME FLOW K s The fan characteristics volume flow rate versus static pressure and system characteristics are now drawn on the graph The condition at which the fan operates is given by the point at which the two characteristics intersect 4 4 m s 630 Pa Approximate Volume Approximate Static Pressure When the fan is actually tested on start up it is found that the actual flow rate is only 2 25 m s and the measured static pressure is 557 Pa The obvious solution is to increase the fan speed however if the fan is operating in the unstable or surge area the static pressure must be reduced or another fan substituted To find the actual system characteristic Ps A Q A 557 2 25 110 Prese Tn zars ao oars 990 15015 Plot the actual system capacity on the graph and you can see that the static pressure cuts the fan curve in more than one place Therefore the fan may settle down to any f
97. t y y e e a a bo U l gt a e e e L e L lt gt e a e E E E o o E o o o o E a o o o E E o a e e e e E e e e ee ee ee ew a a Question 6 If when starting a fan on a new system the flow rate was found to be high and the static pressure lower than calculated would this be common or an uncommon occurrence Give reasons for your answer A E RS A Se E A E AAA A E O A ae Ss es ce UE ee E ROR E E L E E RE TE EA SU A ee A Om a A AE AE ES IE EA SA CERO EE E EE ER E EE A AA AA TORD E A E TS RR E AO DES TE TER LR E E SE O A R TRT RR RN ee Question 7 Explain fully what is meant by the term system characteristic curve as used in fan applications e gt o e gt cwxy 0c e l o o o a o D G O l H RR Gl KK e e a o k o o o o k gt k k 8 o o h G h h 8 9 k amp 8 amp 8 9 H 8 9 Question 8 A fan is required to supply 8 5 m s when operating at 650 RPM against a static pressure of 850 Pa On start up the capacity is found to be 9 75 m s and the static pressure is measured to be 565 Pa A 4 5 kW motor is installed and the absorbed power of the fan is 4 7 kW i How would you fix the problem 11 What would be the static pressure for the fan at the correct flow rate 111 Does the motor need to be changed once the flow rate is corrected iV What is the absorbed
98. t velocity is the theoretical velocity of air as it leaves the fan outlet and is calculated by dividing the air volume in m s by the fan outlet area in m Because of the variations in velocity across the fan outlet velocity readings taken across a fan outlet mean very little Readings sheuid be taken across a fan outlet mean very little Readings should be taken further down stream of the discharge duct to allow air flow to become reasonably uniform EOE Outlet velocity is normally associated with centrifugal fan and Tip Speed is often quoted for axial fans although both terms can be applied to either form of fan design SYSTEM PRESSURES a Static Pressure P is the pressure within a duct which tends to burst the duct b Velocity Pressure P is the pressure which air in a duct exerts due to its motion C Pressure P7 is the sum of the static pressure P and the velocity pressure v Pr P Py PRESSURE CLASSIFICATION OF DUCTS Classification of duct systems by pressure and or velocity are quite arbitrary The SHEET METAL and AIR CONDITIONING CONTRACTORS NATIONAL ASSOCIATION INC SMACNA in developing duct construction standards established the following breakdown a Low velocity Up to 10 0 metres second and up to 50mm 500 Pa swg static pressure b High velocity Above 10 metres second 1 Medium Pressure Up to 150mm 1500 Pa swg static pressure il High Pressure Over 150mm 1500 Pa swg static pre
99. t when the initial installation is made Even the difference in position caused by the static loading of the fan isolators must be accounted for Too often the installation is made from a straight line drawing which does not account for the variations of misalignment torque and statice and dynamic deflection of bases and isolators Then the duct and equipment contact negating the purpose of the flexible connection and transmitting vibration up and down stream of the equipment i Even though the direct equipment vibration may be isolated by the flexible connection in the duct the air in the system because of velocities and pressures or because of fittings may generate motion in the ducts At times it is necessary to use vibration isolators on the duct hangers to overcome these disturbances Motion of the fan motor and drive mass may be reduced in magnitude or amplitude by adding weight to the system A common example is the use of a concrete and steel base At other times the mass is not added and the isolators are selected to operate at the fan and motor system amplitude In almost every case isolation is required and the type will depend on the application The means of isolation selected must isolate the vibration at the generated frequencies and most also adequately support the system The isolators must never be allowed to over compress or bottom out so that they short circuit They must never be so flexible that the system will warp and
100. tage they have not been implicated in any outbreak of Legionnaires disease although Legionella bacteria have been found in such systems Evaporative air coolers required regular attention and manufacturer s instructions for operation must be followed Minimising Contamination g Before switching the unit off the fan should be allowed to dry the filter pads Evaporative coolers should be fitted with a bleed off system This is essential to prevent excessive accumulations of dissolved solids and other impurities within the unit Maintenance of Systems All systems shall comply with the following general maintenance requirements Procedures to be Taken During Maintenance If maintenance of a regulated system is being carried out on the premises on which it is installed the contractor or employee carrying out the maintenance is guilty of an offence if appropriate measures are not take to e help prevent or minimise adjoining areas and the ambient environment from being contaminated by aerosols or the generation of dust or particulate matter and e prevent public access to the area in which the maintenance is being carried out Maintenance Records 0 Whether a maintenance inspection of a regulated system is carried out the occupier or maintenance contractor responsible for that plant shall make a written record of the date and details of the inspection e Whenever maintenance work is carried out on a regulated system the oc
101. tatic pressure By definition fan static pressure is equal to pe the rise in total pressure across the fan minus the velocity pressure created by the fan Fan Ps static pressure Fan Pto outlet total pressure Fan Pti inlet total pressure Fan Pvo outlet velocity pressure Since Pt Pv Ps Outlet Pt Outlet Ps Outlet Pv and insertina this for Outlet Pt in the above formula we have Fan Ps Outlet Ps Outlet Pv Inlet Pt Outlet Pv and as Outlet Pv cancel out negative and positive we are left with l Fan Ps Fan Pso outlet Fan Pti inlet 5 To measure System Static Pressure which is also the Fan Static Pressure either two separate readings or two pitot tubes must be used as shown opposite when ducted fans are installed pressure is not measurable and is taken as zero Therefore amp l Inlet Total Pressure ts equal S to Inlet Statte Pressure and FAN SP gt DISCHARGE SP INLET TP E Where fans are installed in plenum chambers inlet velocity TP TAP Fan Ps Fan Pso outlet Fan Pst inlet Fan Static Pressure Ducted Fans j A i 3 ES gt Se ASSUME INLET VELOCITY PRESSURE NEGLIGIBLE HORIZONTAL UNIT VERTICAL UNIT Fan Static Pressure With Non Ducted Fans Static Pressure Measurements Draw Thru Air Handling Units B To measure fan R P M use a tachometer Hold the tachometer in contact with the fan shaft make several
102. ted air must be conveyed through ducts Air flows through a duct because the pressure existing at one point is higher or lower than the pressure at another point of the same duct The direction of pressure increase of decrease decides the direction of air flow ie that is towards the lower pressure t Highest pressure Lowestpressurs Open m system at PAYS end tan discharge T of ouct fan suction Air Flow t B i K Oper end O duct Pressure Pressure decreases decreases trom Ate B trom Dio C Fan creates a ditterence in pressure Causing arr to flow in duct The difference in pressure is created by the fan The air does not normally move along in a placid stream it moves in either turbulent or laminar flow LAMINAR OR TURBULENT FLOW When air flows through a duct at low velocities the particles follow paths free from eddy currents of swirls The flow is then said to be LAMINAR As the velocity increases the characteristics of flow change eddy currents form and the air becomes swirly This type of flow is known as TURBULENT flow While laminar flow develops less resistance than turbulent flow it can sometimes cause problems of stratification The volume of air handled by a fan is the flow rate produced by a fan independent of the density of the air normally expressed as Cubit metres per second handled by a fan at any density m or Litres per second handled by a fan at any density l s OUTLET VELOCITY Outle
103. ted and automated equipment Fans of varying shape and size were driven via a shaft by such methods as water flow over paddle wheels by large clock mechanisms or by pre loaded weights which when permitted to unwind which would drive a gear and eccentric which was attached to a moveable blade Unfortunately all these alternatives where rather cumbersome and required various alteration to the building or large amounts of time and energy to operate However these early attempts did fulfil their purpose and today we use the same principle of moving air to effect personal comfort convenience or safety Now air is moved mainly by means of electric motors which drive propeller or centrifugal fans a Induced ventilation Fresh air entry to room is at high level above occupant height mainly Fresh air entry 1s forced down and mixed with room air at occupant level b Induced ventilation with circulation fans AN it Air release through door H DA grilles windows etc Mo wo c Forced ventilation system pressurised air supply to all points Fig 19 5 Examples of mechanical ventilation are found in buildings used for every day activities where toxic fumes are not a problem Mithat aerea parent Ad Mechanical ventilation may take several forms today depending upon the application Generally these systems may be classified as a Forced ventilation where air is forced into the room by a fan and allowed t
104. the droplet nuclear are 4 Micron approx The better the filter efficiency the better for the occupiers For correct maintenance and installation edge and face sealing is critical Always seal on the air on side even if an access panel is required Ensure that all moisture is eradicated from filters and ductwork as bacteria moulds fungus and other micro organisms rely on moisture for their survival and growth They are aquatic life forms Humidifiers More prevalent overseas not so much in our climate However when used in industry eg printing works textile factories and woodworking shops there is an abundance of food for Microbes cellulose material Steam is preferred and clean steam free of chemicals is best Conditioner and ductwork condensate trapping access for ease of cleaning chemical disinfection to be carried out after manual clean if slimes etc present Water type whilst more economical and simpler to install for smaller systems etc computer rooms have problems of solids chemicals and other matter remaining The end of main seasonal usage ie Winter these systems require vigorous and intensive service and clean up WATER COOLING SYSTEMS The excess heat energy extracted from a building by an air conditioning system is released into the atmosphere via a cooling tower Because of the temperature of the water and the presence of sludge algae and so on the water cooling system may aid the
105. through lack of Fan laws service Correct installation Suggested teaching time 4 hours Suggested teaching time 4 hours mareo onne Learning outcome 3 NR13 FANS INTRODUCTION A fan is a pump having a specific purpose of producing sufficient pressure to overcome system resistance at the required flow rate A fan pumping air must have a relatively high compressibility of the air By proper use of fan manufacturers published catalogue data based on tests the tables or preferably curves make it possible to select a specific fan for a particular application Tables are most readily available because they are easily obtained from direct computer printout However complete curves supply information which tables cannot Curves can be developed from the tables but the curves will be incomplete since it is common to tabulate only the useable portions of the curves In addition to the tables and curves a set of mathematical relationships exists which make it possible to predict reasonably well the operating conditions other than those of the original selection and installation These are commonly called the fan laws With these formulae it is possible to determine required new physical conditions such as speed and horsepower based on field measurements The formulae minimise the guess work which would otherwise be required to change the fan operation in the event of unexpected field conditions In addition to the presentation of
106. tic pressure across the fan how do you use this to find the fan volume c How do you check the volume flow rate found in b e 3 On a system nominated by your teacher find the volume flow rate from l any three 3 outlets a What instruments did you use b How did you calculate the flow from each outlet Show all calculations detail any information you feel must be supplied before calculations can be assumed as correct ESO Prosa c _ FAN DATA RPM Fill in the worksheet section following for the three outlets INSTRUMENTS A o CFM SP MOTOR AMPS ot VOLTAGE 4 6 4 i Supply Desi Design E Measured K esign Outlet Average Velocity Air Flow REMARKS Raruto Air Flow 1 velocity Reading m s m s Size L s Close off one outlet and then re calculate the flow rate of all three Evaluate the results Using the Low Velocity Fan Unit you will be given a system sketch for the air distribution system The teacher will reduce the air flow rate by closing the main covl damper omen LOR 4 gt Z 7 3 3 mana L mwan ES L 2 ES A A El S 2 m K mm 2 A x 4 R E Z 2 L a Reas Kaea E Adjust all registers and diffusers using a proportional balancing method Open the main coil damper to bring supply air up to actual requirements c From your own observations does the nroportional ba
107. tiow factor tables Probe locations for several instrument types RETURN INLET core H L RvA 45 a o a T 700 T 800 T 8000 Flow rate in m 5 Factor x Core area x Average velocity Measuring flow through grilles using deflecting vane anemometer and other instruments ial give spot readings en rc As the adjustment of one outlet affects the others it will be necessary to repeat the above procedure one or more times making finer adjustments each time x e an te ind e gt This sidewall grille is being checked for mys deliv ery with an anemometer The velometer is being used to take a reading at a light troffer Note location of the probe b A second proce ure often used is referred to as the Balancing from fan out method This method is similar to that previously described and begins by each branch being adjusted using splitter or manual volume dampers until an approximate balance between branches is achieved This branch balance must also be reached before proceeding ZZ L the individual outlet correction previously discussed in Section S a Proceed with balancing individual outlets Begin by measurina the flow through the outlet nearest the supply fan Reduce excessive flow by partially closing the volume control damner at the outlet Move to next downstream outlet from the supply fan and repeat as per outlet number one Record the measurements on a suitable
108. tlet It ts tmportant that the balancer refers to the manufacturer s data for the proper K factor to use in conjunction with the tnstrument used It ts also important to note that the manufacturer will destgnate various locations for taking readings on different models of outlets diffuser factors EY da aM diflusers Corrected Ane mometer Veloc Reading in S _ Cones Up cena Down Factor Factor SEL a table of flow factors Note that if cones are adjustable factor varies with position of cones sor ica Y ds EET HE a he 1 L de yo at POS ve x y L L gt gt Measuring flow from supply grille with deflecting vane anemometer Note spacer accessory to maintain correct spacing of probe from grille face POMAR A Te p o 4 Y DEE Measuring flow into return or exhaust grille with deflecting vane anemometer 6 Velometer Jet No 2225 or Determine net core area from Table No 3930 Determine air volume as follows Average face velocity in ai m s x net core area in sq m volume in m s Placing the probe when air flows into grille ga j 2220A elometer Jet Jet No 2220 No 2220A Dyer or No 3920 ae 2225 Jea Correct placement of anemometer probe for Supply sunny Retum one type of grille k SUPPLY OUTLETS DEFLECTION ALNOR i 0 83 CORES ACCESSORY Examples of
109. ton which is a special form of carbon is normally used for odour control Activated carbon is capable of soaking w or adsorbino gases and vapours just as silica gel adsorbs moisture The air is passed through beds of activated carbon when the carbon is saturated it can be rejuvenated by heating Es to 540 There is nothing to prevent the installation of different types of filters in series in the one air duct An example is the use of a panel type dry fabric filter as a pre filter to remove the larger particle of dust leaving a HEPA filter to collect only the finer material A second example is the installation of an after filter in an electrostatice precipitator again normally a dry fabric panel type in case of power failure VENTILATION NR 13 LEARNING OUTCOME 3 STUDENT WORKSHEET 3 2 Question 1 List the three categories of filters A B C A _ __ _______ Question 2 Which filter is the most efficient and what type of media does it use A A A o CE rt aranan nnn TA O O O O ODO DO Question 3 How many types of electric filters are there TT Ta EE e A rs Question 4 How would you check if a filter required cleaning or replacing IO EEEE E O e DONANT nnn Treena Question 5 What metal is used in the manufacture of Metal Oil Filters _ A O OO OD OO O DI oaran pta E 2 2 Question 6 What precaution must be observed before working on any electronic type filter
110. trical provlems are usually straight forward and are analysed in a routine manner by service personnel In this category are blow fuses broken belts looses pulleys electricity burned off impeller touching scroll and motor too small and overload protector has broken circuit BEARING REPLACEMENT If a fan shows an increase in vibration it generally indicates that the bearings require replacing or servicing When bearings are to be replaced they should be removed from the shaft with a bearing puller and the same tool can by relocating the jack nut be used on site to install the bearing Always check the fan shaft for wear before replacing the bearing and if the shaft is worn it too must be replaced After replacement of bearings run the fan without a load for a short period to allow new components to bed in PIPE ON INNER RACE ONLY Driving a bearing onto a shaft bearing puller Using 8 Alte iranian END OF SECTION 2 Additional and more detailed information pertaining to SECTION 2 will be found in the following AIR CONDITIONING ENGINEERING 2ND EDITION S I UNITS Whitstable Litho Ltd Whitstable Kent T P C TRAINING SYSTEMS Air Handling Systems Technical Publishing Company Barrington Illinois ASHRAE SYSTEMS AND EQUIPMENT 1967 American Society of Heating Refrigerating and Air Conditioning Engineers Inc New York START TEST AND BALANCE National Joint Steamfitters Pipefitters HOW TO DESIG
111. ts e Check passages between inlets impeller blades and housing for damage from corrosion or foreign matter trapped in impeller f Check ductwork for loose insulation sheet metal paper etc g Check conditions of coils filters etc If dirty clean h On fan equipped with inlet vane or damper control check visually that the vane damper position agrees with the position of the control arm For double width fans check that both inlet vane dampers are synchronised With unbalance flow between inlets the thrust on the bearings is also unbalanced and it often leads also to surge conditions in the fan 1 After completing the system check list put the fan back into operation j Inspect the entire system including the fan fan plenum and all ductwork for leaks Leaks may be detected by sound smoke feel soap solution etc Common leak sources are access doors coils duct seams fan outlet connection etc which must be sealed pa eh gritar TROUBLESHOOTING CHART NOISE a Impeller Hitting Inlet Ring PROBABLE CAUSE i Impeller not centred in inlet ring 11 Inlet ring damaged 111 Crooked or damaged impeller iv Shaft loose on bearings v Impeller loose on bearings vi Bearing loose on bearing support b Drive PROBABLE CAUSE pe i Pulley not tight on shaft motor and or fan ji Belts too loose iii Belts too tight iv Belts wrong cross section v Belts not matched in length on multi belt drive
112. uilding but most undesirable in a hospital where germs and bacteria may be transmitted from patient to patient Similarly in a laboratory where air purity is critical during drug manufacture or testing of materials a specific air condition maybe required to overcome possible variations in measuring devices On the other hand largely recirculated air with some fresh air conditioned to an average comfort level would be acceptable throughout a department store or dry goods shop spent L 7 Total Climate Control by air conditioning is a very costly exercise and may be neither feasible nor necessary Imagine a situation where the worker in a very large factory requires improved environment for health and production efficiency Personal relief in this case may be achieved by Spot Cooling Unit supplying fresh air or air conditioned by mechanical or evaporative systems H Wx J IY Air Supply Duct dn Pet Fig 19 6 Spot cooling Figure 19 6 shows a factory worker exposed to an air supply which is cool fresh or conditioned by either of the alternatives suggested in the sketch This air is not returned to the plant as it is diluted and expelled with the existing factory air However it does offer a considerable amount of relief to those for whom it is designed Spot cooling is used extensively in environmental hostile situations such as smelters and welding booths EVAPORATIVE COOLING This syste
113. value of openings in opposite walls has been stated but the effect of increased velocity of the wind is such that constant regulation of the size of the opening is necessary to prevent excessive draughts and even damage inside the room Changes to wind direction can result in an acceptable level of ventilation becoming unacceptable or draughty Figure 19 3 shows how the wind force causes good ventilation with windows on windward and lee sides WINDOW TREATMENTS Because the changes in air pressure are very small any resistance to free air movement greatly reduces the air flow Thus the effect of flywire and heavy drapes will be to greatly reduce movement unless the wind pressure can overcome this resistance The major disadvantage of natural ventilation then is that it is unreliable being subject to weather wind and the normal requirements of building design ar ee a a Infiltration Exfiltration Fig 19 3 Effect of wind forces on a low building ares MECHANICAL VENTILATION Early methods to provide ventilation in an attempt to make life more bearable during oppressive weather conditions may seem humorous today however the punka as used in India moved air by displacement as shown in Figure 19 4 It consisted of a large manually operated fan generally hung from the ceiling with movement was achieved by pulling a rope Fig 19 4 Various other mechanical methods were quickly followed by more sophistica
114. when the static pressure is 187 Pa and absorbs 2 25 kW If the speed of the fan is increased to 480 RPM 8 Rev s find 1 the new air volume li the new static pressure 111 the new absorbed power A fan is required to supply 700 1 s When it is started it is found to have a capacity of 572 1 s when rotating at 400 RPM 6 7 Rev s and a static pressure of 478 Pa The drive motor installed is rated at 1 5 kW and the absorbed power is 850 Watts Find 1 the required RPM il the new static pressure 111 the required absorbed power iv Would the existing motor still be suitable when the required air flow is achieved INSPECTION AND PROCEDURES Before checking the fan and during inspection the fan must be electrically isolated and all disconnected switches locked in the OFF position Where these are remote from the fan prominent DO NOT START signs should be installed SYSTEM CHECKLIST a A impeller comes to rest check if rotation is correct b See impeller is not installed backwards NOTE Fan rotation for centrifugal fans is clockwise or counter clockwise when viewing the drive side and for axial fans when viewing the inlet C For belt driven fans check alignment of motor and fan pulleys d Check belt tension to the manufacturers recommendations excessive tension will shorten fan and motor bearing life Belt should be re adjusted after the first 48 hours of operation Check condition of pulleys and bel
115. which is discharged radially The purpose of the scroll is to covert the high velocity pressure at the blade tips into static pressure Fig 2 1 General arrangement of centrifugal fan The three different types of blades used are shown in Figure 2 2 a Straight radial blade b Forward curved c Backward curved Types of centrifugal fan blades The shape of the blades influences for force exerted on the air and the proportion of energy imparted in the form of velocity The velocity of air leaving the impeller is proportional to the length of the arrows in figure 2 2 The efficiency of centrifugal fans suffers from the fact that the air handled must turn through 90 This causes losses of energy due to shock and eddies Moreover the aerodynamic efficiency of the scroll or volute as it is called is generally rather low The fan efficiencies are usually between 45 and 75 according to type APPLICATIONS The centrifugal fan is used in most comfort applications because of its wide range of quiet efficient operation at comparatively high pressures In addition the centrifugal fan inlet can be readily attached to an apparatus of large cross section while the discharge is easily connected to relatively small ducts Air flow can be varied to match air Ran distribution system requirements by simple adjustments to the fan drive or control devices FORWARD CURVE FANS Higher efficiencies are obtained when the blades have curved
116. y air filters shall be installed on air handling systems see Appendix 6 for minimum standard On completion of installation and before being brought into service the system is to be cleaned Outside air intakes and exhaust outlets must be inspected montly Any maintenance work found to be necessary as a result of the monthly inspection of air intakes and exhaust outlets is to be carried out prior to the next inspection Line strainers valves sparge pipes spray nozzles and components discharging moisture into the airstream within humidifiers are to be inspected monthly and any necessary maintenance work is to be carried out prior to the next inspection Tanks trays and discharge devices within humidifiers are to be inspected monthly and any necessary maintenance work is to be carried out prior to the next inspection If an air handling system or a component of an air handling system is shut down on a seasonal basis it is to be inspected immediately after the shut down and any necessary maintenance work is to be carried out within a reasonable time prior to the next inspection The following parts of an air handling system are to be inspected annually and cleaned if the inspection discloses this to be necessary coils trays and sumps condensate drains tundishes and traps duct work in the vicinity of moisture producing equipment and at access points in the vicinity of fire dampers After condensate drains tundishes or
117. ystems to reduce the risk of inhalation of spray mists or exposure to toxic chemicals Respirators must comply with AS1716 and be used in accordance with AS1715 The minimum respiratory protection shall be provided by a Class M half facepiece particulate filter The location of the system must be taken into consideration to ensure that maintenance and cleaning activities do not put any persons or adjoining premises at risk AS2645 gives guidance to precautions to be observed when working in confined spaces such as cooling towers or storage tanks Anyone taking a sample from a system particularly during a suspected outbreak must also take protective measures If possible the system should be turned off before a sample is taken A Class L particulate filter is not acceptable as adequate protection against contaminated aerosols In all other respects Table Al of Appendix A of AS3666 can be considered as the minimum requirement for personal protective equipment during maintenance of air handling and water systems BUILDIN NSTRUCTION AND MODIFICATIONS Fresh air intakes must be located away from cooling towers and exhaust discharges from air handling system to avoid cross contamination from the same or nearby buildings Prevailing wind directions should also be considered Air intakes must be designed and installed to minimise the entry of rainwater and prevent the entry of birds rodents and windblown material such as leaves and paper They mu

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