KMD–7302 Roof Top Unit Controller
Contents
1. 230 NOT COOLING STAGE 1 AND NOT COOLING STAGE 2 THEN COOLING STAGE 1 amp 2 0 240 IF COOLING STAGE 1 THEN COOLING STAGE 1 amp 2 50 250 IF COOLING STAGE 2 THEN COOLING STAGE 1 amp 2 100 260 IF NOT HEATING STAGE 1 AND NOT HEATING STAGE 2 THEN HEATING STAGE 1 amp 2 0 270 IF HEATING STAGE 1 THEN HEATING STAG 280 IF HEATING STAGE 2 THEN HEATING STAG 1 amp 2 50 1 amp 2 100 290 END Program 3 ECONOMIZER 30 REM ECONOMIZER CYCLE 40 IF NOT ECONOMIZER OPERATION THEN END 50 IF NOT OCCUPANCY STATUS THEN END 60 OUTSIDE RET DAMPER CON3 70 IF OUTSIDE RET DAMPER lt MIN DAMPER POSITION THEN OUTSIDE RET DAMPER MIN DAMPER POSITION 80 END AN0404H 3 153 KMD 7302 Roof Top Unit Controller Application drawings KMC Controls Application drawings KMD 7302 FROM PREV DEVICE A FROM PREV DEVICE B o2. TO NEXT DEVICE A LS TO NEXT DEVICE B qu K A GND GND GND T TRIAC T2 A 2 TRIAC T3A T3 B RET RET 24VAC I 120VAC NS 24VAC n Bly FAN 2avac 6 Q AIR 5112 HEATSTG 1 H1 STE 5112 10 O MEP 1222 iia HEATSTG2 H2 F STE 5200 SERIES COoLSTG 1 c1 GND IN1 IN2 GND THERMOSTAT OPTION ceases le ER OUTSIDE F DIS an AIR fno t se TS RTU CONTROL PANEL X 24VAC CIRCUITS STE 1214 ROOF TOP UNIT STE 52XX Illustration 4 Rooftop unit with two stage heat and cool and optional economizer ANO0404H 3 154
3. Auto 25 Percent MIN DMPR 404 3 151 KMD 7302 Roof Top Unit Controller WinControl settings 3 152 Table 5 Tables Table 1 Unused Table 2 Unused Table 3 Unused 1 0 0 0 86 0 54 2 0 0 0 71 85 0 05 54 3 0 0 1 07 80 0 538 58 4 0 0 1 38 75 0 939 62 5 0 0 1 67 70 1 27 66 6 0 0 1 91 65 1 42 68 7 0 0 2 1 60 1 56 70 8 0 0 2 23 56 1 68 72 9 0 0 3 55 1 8 74 10 0 0 5 55 1 91 76 11 0 0 0 0 2 01 78 12 O 0 0 0 2 2 82 13 0 0 0 0 2 36 86 14 0 0 0 0 2 5 90 15 0 0 0 0 3 90 Table 6 Control Basic listing PRG Description On Manual Label 1 SET POINTS YES Auto 2 FAN HEAT COOL YES Auto 3 ECONOMIZER NO Auto 4 NO Auto 5 USER PROGRAMMING NO Auto Program 1 SET POINTS 30 REM DETERMINING ACTIVE SETPOINTS BAS 50 IF NOT VAR22 THEN VAR25 VAR26 60 IF VAR22 THEN VAR25 70 IF VAR22 THEN VAR28 VAR28 100 REM Outside Damper Operation VAR32 110 IF VAR22 THEN OUT4 300 END IN2 VAR27 2 IN2 VAR27 2 kkk ELSE OUT4 ED ON OCCUPANCY MODE 0 Controls AN0404H KMD 7302 Top Unit Controller Digital Designer s Guide WinControl settings Program 2 FAN HEAT COOL 30 REM FAN Control 40 IF OCCUPANCY STATUS OR COOLING STAGE 1 amp 2 gt 50 OR HEATING STAGE 1 amp 2 gt 50 THEN START FAN 50 IF NOT OCCUPANCY STATUS AND TIME OFF HEATING STAGE 1 gt FAN DELAY AND TIME OFF COOLING STAGE 1
4. a fixed set point simply write a line of code in Program 5 such as 70 IF OCCUPIED THEN HEATSSPT 72 COOLSSPT 74 Different numbers or reference variables can substitute the numbers 72 and 74 Also note the KMC supplied sequence defines the unoccupied heating and cooling set points by referencing setback variables These too can be modified if necessary or the cooling and heating set points can be set directly as shown below 80 IF NOT OCCUPIED THEN HEATSSPT 66 COOLSSPT 76 A NetSensor can be used to bring values into the controller without using any physical input To add a NetSensor and use the factory programming in the KMD 7302 simply change the PID controllers 1 and 2 in label from IN1 to the variable mapped to the NetSensor s onboard temperature sensor Change SETPTSTP in line 60 and line 70 of program1 to a variable mapped to button 2 on the NetSensor One of the biggest features of any KMC digital DDC Controller is the inherent programming ease and flexibility available in each and every unit If the KMC supplied sequences do not satisfy the application at hand they may be turned off or edited and the entire control strategy can be manipulated The KMDC digital Technical Operator s Manual provides help and examples for programming Control Basic ANO0404H Digital Designer s Guide WinControl settings KMD 7302 Roof Top Unit Controller WinControl settings The following tables display the WinCon
5. been satisfied A built in differential prevents the fan from cycling on and off due to minor temperature variations LE Note The triac outputs for heating and cooling are staged The first stage must be on when the second stage is on In the heating mode VAR24 is OFF cooling stages are disabled Controller 2 controls staging of the heat If the controller is above 50 and the cooling has been off for the stage delay VAR30 period the first stage of heat will be turned ON If the controller gets above 90 The space continues to be too cold and the stage delay VAR30 for the first stage has timed out the second stage of heating is started The second stage will remain on until the controller falls below 50 Both stages will be off once the controller output is below 10 In the cooling mode VAR24 is ON Heating stages are disabled Controller 1 controls staging of the cooling If the controller is above 50 and the heating has been off for the stage delay VAR30 period the first stage of cooling will be turned ON If the controller gets above 90 The space continues to be too warm and the stage delay VAR30 for the first stage has timed out the second stage of cooling is started The second stage will remain on until the controller falls below 50 Both stages will be off once the controller output is below 10 Note The user must determine Heating and Cooling Mode VAR24 The default mode is CO
6. gt FAN DELAY THEN STOP FAN 60 REM Cooling Heating 70 IF HEAT COOL MODE THEN 160 REM Heat mode skips over cooling sequence 80 REM COOLING MODE 90 STOP HEATING STAGE 1 STOP HEATING STAGE 2 REM TURN OFF HEATING 100 IF CON2 lt 10 THEN STOP COOLING STAGE 1 STOP COOLING STAGE 2 110 IF CON2 gt 50 AND TIME OFF HEATING STAGE 1 gt STAGE THEN START COOLING STAGE 1 120 IF CON2 gt 90 AND TIME ON COOLING STAGE 1 gt STAGE DELAY THEN START COOLING STAGE 2 130 IF CON2 lt 50 THEN STOP COOLING STAGE 2 140 IF NOT COOLING STAGE 1 THEN STOP COOLING STAGE 2 150 GOTO 230 T ELAY 160 REM HEATING MODE 170 STOP COOLING STAGE 1 STOP COOLING STAGE 2 REM TURN OFF COOLING 180 IF CON1 lt 10 THEN STOP HEATING STAGE 1 STOP HEATING STAGE 2 190 IF CON1 gt 50 AND TIME OFF COOLING STAGE 1 gt STAGE DELAY THEN START HEATING STAGE 1 200 IF CON1 gt 90 AND TIME ON HEATING STAGE 1 gt STAGE I THEN START HEATING STAGE 2 210 IF CON1 lt 50 THEN STOP HEATING STAGE 2 220 IF NOT HEATING STAGE 1 THEN STOP HEATING STAG oO ELAY 2
7. temperature set points for cooling and heating that the unit will maintain In an unoccupied condition these values become the appropriate setback temperature settings VAR26 and VAR29 In the occupied mode these values are calculated based on the BASE SET POINT IN2 and THERMOSTAT DEADBAND VAR 27 The set points are calculated in Program 1 Variable 26 and 29 SETBACK TEMPERATURE SET POINTS For cooling and heating respectively These variables are fixed values entered by the user Variable 27 THERMOSTAT DEADBAND Our method of determining set points for cooling and heating insures a neutral range or deadband exists between set points Variable 30 STAGE DELAY This variable establishes the minimum time the first stage of heating or cooling must run before the second is allowed to start It also sets the minimum time between heating and cooling changeover Variable 31 FAN DELAY This is the minimum time the fan must run after the heating or cooling stages have been shut off Variable 32 MINIMUM DAMPER POSITION This variable allows easy access to changing the minimum damper position in an occupied mode as requested by the control sequence The Default value is 25 outside air In the unoccupied mode the damper output goes to 0 Configuring controllers PID loops KMC digital products feature built in full function PID Proportional Integral and Derivative controllers In the KMD 7302 Controller 1 is set up as a d
8. Digital Designer s Guide Application Note AN0404H Related materials Introduction KMD 7302 Roof Top Unit Controller This application note describes methods and programming to use the KMD 7302 as a roof top unit controller with two stage heating and cooling and includes optional economizer operation In addition to the material presented in this installation and operation guide review and have available the following reference materials Installation and operation guides for KMD 7302 MEP 1222 and STE 5100 series or STE 5200 series sensors WinControl XL Plus User s Manual Hardware Configuration Manager reference guide System plans with controller addresses The KMD 7302 Roof Top Unit Controller is a four input four output DDC Controller specifically designed for operating small air handling units with two stage heating and cooling This device has been pre programmed with a KMC supplied control sequence to operate a fan two stages of heating and two stages of cooling to maintain the desired space temperature An optional economizer sequence is included for units with modulating outside and return air dampers In addition to the basic control sequence this device will determine active and setback temperature set points as well as primary outside damper positioning based on occupancy status If you do not want to use any of the factory setup and programming options send a panel file with your own setup para
9. N START H C MOD 50 IF ECONOMIZ OR OAT lt 55 THEN STOP H C MODE 3 149 KMD 7302 Roof Top Unit Controller Fan proof Fan proof Temperature setpoints Using the NetSensor Other options 3 150 KMC Controls This example uses the economizer variable to determine when the outside air is no longer suitable for cooling as a means of enabling mechanical cooling ECONOMIZE VAR23 is off when the damper is allowed to modulate past minimum position VAR32 The fourth input INA is available for some type of fan proof device This may be an airflow switch current transducer or an auxiliary starter contact to show the fan has started You can prohibit the heating and cooling from operating without the fan by adding a line of code in Program 5 such as 60 IF NOT FANSSTAT THEN COOLSSTG 0 HEATSSTG 0 Where FANSSTAT is proof the fan is running IN4 Setting COOL STG and HEATSSTG to 0 will keep all stages from operating until the fan has started This model has been pre programmed assuming a set point potentiometer is connected to Input 2 In some cases it may be desirable to provide a fixed set point in the software to free up the input for another purpose or have a standardized set point for the whole building The KMC supplied sequence determines the heating and cooling set points in an occupied mode as half the deadband below and above IN2 set point respectively To change this to
10. OL ANO0404H SEP Note Variables 18 19 20 and 21 are the cooling and heating flags As long as Program 2 is running these variables can be used to monitor the staging sequence They can also be used to indirectly set the value of the outputs You may find it easier to view and work with these variables ON and OFF units than the output points that have units in percentage Program 3 ECONOMIZER If this program is set to run and the economizer cycle is enabled VAR23 ON the outside air damper will be positioned according to Controller 3 but not less than the minimum damper position specified in Variable 32 The Controller 3 compares mixed air temperature IN3 to the mixed air set point as defined in Variable 17 The damper is controlled as a direct acting cooling device If the mixed air temperature falls below the set point the damper will be modulated closed to bring the temperature back to set point Program 4 and 5 Available for user programming Program areas 4 and 5 are typically used to customize the control sequences for each particular application The following sections discuss some of the most common options used with this model The user will need to set values for OCCUPANCY MODE ECONOMIZER MODE and HEAT COOL MODE in a program It may also be necessary to 3 147 KMD 7302 Roof Top Unit Controller Custom tables Custom tables 3 148 KMC Controls establish fan status here before runn
11. dit Erase Cancel Panel A1 Status Idle Illustration 3 Control Basic listing Program 1 SET POINTS The first part of this program serves to define the active temperature set points for use by the control routine In the occupied VAR22 is ON mode the heating set point is calculated by subtracting half of the deadband value VAR27 from the set point indicated on the thermostat dial IN2 Similarly the cooling set point is found by adding half of the deadband to the thermostat setting In the unoccupied mode VAR22 is OFF the cooling and heating set points simply assume the setback values defined in Variables 26 and 29 respectively Note User programming will be required to change occupancy modes The KMC supplied sequence simply defaults to an occupied mode on initial start up This program also contains the basic sequence for the outside air damper The damper is opened to minimum position VAR32 in the occupied mode and is fully closed in the unoccupied mode Additional damper control is available using the optional economizer program PRG3 AN0404H Digital Designer s Guide KMD 7302 Roof Top Unit Controller Setting up with WinControl Program 2 FAN HEAT COOL The fan is called to operate continuously in the occupied mode In the unoccupied mode if the controllers call for either heating or cooling to maintain the setback temperatures the fan will run until the space temperature has
12. ing the cooling or heating For complete details on writing your own custom logic in Control Basic Language refer to the WinControl manual Custom tables allow the user to create unique ranges to be used by inputs or other special applications The most often used application of these custom tables is to establish a correlation between a potentiometer setting a voltage and a temperature value such as the dial setting on a thermostat The KMD 7000 Series Controllers allow user access to all 3 tables These tables have been defined for the following applications in the KMD 7302 Table1 Available for user programming Table 2 Correlates slider position of STE 5200 Series Thermostat into degrees F Table 3 Correlates the dial setting of STE 5000 Series Thermostat Sensor to degrees F These tables use nominal values for correlation Due to component tolerances and the resistance of field wiring these values may need correction on an individual basis If the value read is too low enter a positive calibration in the input column labeled cal If the value read is high a negative calibration can be entered If necessary reconfigure Table 2 and or Table 3 The complete Table 2 and Table 3 from the factory are shown If the tables have been reconfigured and the user wants the factory configuration for Table 2 and Table 3 it will be necessary to use Clear Panel or re enter the values TE Note Using Clear Panel wi
13. irect acting cooling thermostat It compares SPACE TEMPERATURE IN1 to the ACTIVE COOLING SETPT VAR25 to operate the cooling stages OUTS Controller 2 defines a reverse acting heating thermostat It compares SPACE TEMPERATURE IN1 to the ACTIVE HEATING SETPT VAR28 to operate the heating stages OUT2 Controller 3 compares mixed air temperature IN3 to the MIXED AIR SET POINT VAR17 for operation of the outside air damper in the economizer cycle All parameters may be modified as necessary 3 145 KMD 7302 Roof Top Unit Controller Setting up with WinControl KMC Controls Control Basic programs Program areas 1 through 4 have specific KMC supplied programming burned into the controller at the factory If none of sequence fits the required application simply edit the programs or send blank programs to the controller and replace any of the factory programs The factory programs can be retrieved if necessary The original factory programs can be re installed again by using the Clear Panel function in the System Setup Menu 3 146 Caution This will erase any programming changes that have been made to the controller Clear Panel does not affect changes made with HCM or panel type The following explanations are provided for the KMC supplied programs in the KMD 7302 X Control BASIC Programs Description 1 SET POINTS 2 FAN HEAT COOL 3 ECONOMIZER 5 USER PROGRAMMING Auto Load E
14. is variable ON will also force the first stage of heating on Variable 21 HEATING STAGE 2 This variable is ON when the second stage of heating is required the first and second heating triacs are energized Manually turning this variable ON will also force the first and second stages of heating on Variable 22 OCCUPANCY STATUS This variable can be toggled to indicate occupied unoccupied status by user programming It is used to start the fan in occupied times or when cooling or heating are needed in unoccupied mode The Default is OCCUPIED The user must determine the state Variable 23 ECONOMIZER OPERATION This variable can be easily toggled to enable or disable operation of the economizer control sequence It should be set to ON when the outside air is suitable for cooling The Default is DISABLED The user must determine the state Variable 24 HEAT COOL MODE Determines if the Roof Top Unit is in the heating or cooling mode The default is COOL MODE If this variable is off only heating will take place when required by the space conditions Cooling will be inoperable When this variable is ON the cooling mode is on and only cooling will take place when required by the space conditions Heating is disabled in COOL MODE The user must determine the state AN0404H Digital Designer s Guide AN0404H KMD 7302 Roof Top Unit Controller Setting up with WinControl Variable 25 and 28 ACTIVE TEMPERATURE SET POINTS These variables are the
15. ll erase any programming changes that have been made to the controller Clear Panel does not affect changes made with HCM or panel type AN0404H Digital Designer s Guide Occupancy status Economizer Heating cooling mode AN0404H KMD 7302 Roof Top Unit Controller Occupancy status For simplicity a system variable VAR22 has already been defined as an occupied status indication The KMC supplied routines do not define what constitutes an occupied status However the KMC supplied routines do reference the status of this variable when determining room set points or for outside air damper operations Typically the occupancy status is determined by reference to a time schedule by writing a line of code in Program 5 such as 10 IF WSl THEN START VAR22 ELSE STOP VAR22 Where WS1 is weekly schedule 1 as defined in the KMD 7302 panel Scheduled times are assigned with up to four ON and four OFF times per day for each day of the week See the WinControl manual If you choose to use the KMC supplied economizer routine it will be necessary to determine when an economizer cycle can be allowed An efficient method to do this is to compare outside and inside enthalpy Operation of the economizer is then based on where the air handler can get the least expensive cooling The lower the enthalpy is the lower the heat content of the air If the enthalpy is lower outside then the economizer is enabled If the enthalpy is lo
16. meters and programming to the controller This will remove all of the factory configurations allowing you to program any desired sequence This feature allows the user to custom tailor the control sequence to match specific applications The following paragraphs explain the pre programmed control sequence in detail and offer suggestions for user programming to customize operation of the controllers 3 141 KMD 7302 Roof Top Unit Controller Hardware Configuration Manager HCM KMC Controls Hardware Configuration Manager HCM Setting up with WinControl 3 142 For networked operation use the HCM software to configure the address baud and last panel setting Each controller requires a distinct panel address and a common baud rate to reside on a network The unit with the highest address must be designated as LAST PANEL Before running the HCM software to set these parameters flip the network isolation switch located near the terminal strip See the Operators Manual for details on HCM and networking controllers Table 1 Default Configuration for KMD 7302 Panel Number 124 Network Baud Rate 38400 Last Panel Unchecked Phone compensation No Panel Type 18 This section covers the set up requirements to activate any of the pre programmed options available in this device At this point communications should have been established with the unit A Master password is available to sign on to each controller Other sec
17. trol XL Plus settings for this applications note Table 2 Inputs Description Manual Value Units Average Label 1 SPACE TEMPERATURE Auto 236 483 Deg F KMC10K Type II 64 SPACESTP 2 BASE SET POINT Auto 55 Table 2 64 SETPT TP 3 MIXED AIR TEMP Auto 184 042 Deg F KMC10K Type II 64 MIXED TP 4 Auto 0 Unused 64 Table 3 Output Description Manual Value Units 0 100 Security Delay Label 1 FAN Auto On Off On 0 FAN 2 HEATINGSTAGE1 amp 2 Auto 0 100 0 0 10 0 5 3 COOLINGSTAGE1 amp 2 Auto 0 100 0 0 10 0 COOL STG 4 OUTSIDE RET DAMPER Auto 25 0 100 2 0 10 0 OUT DMPR Table 4 Variables Description Manual Value Units Label 1 16 Available for user programs Auto 0 17 MIXED AIR SET POINT Auto 55 Degrees Fahrenheit MIXD SPT 18 COOLING STAGE 1 Auto Off Off On COOLSTG1 19 COOLING STAGE 2 Auto Off Off On COOLSTG2 20 HEATING STAGE 1 Auto Off Off On HEATSTG1 21 HEATING STAGE 2 Auto Off Off On HEATSTG2 22 OCCUPANCY STATUS Auto Occupied Unocc Occ OCCUPIED 23 ECONOMIZER OPERATION Auto Disabled Dis Enabled ECONOMIZ 24 HEAT COOL MODE Auto Cool Cool Heat H C MODE 25 ACTIVE COOLING SETPT Auto 57 Degrees Fahrenheit COOL SPT 26 SETBACK COOL SETPT Auto 80 Degrees Fahrenheit C SETBK 27 T STAT DEADBAND Auto 4 Degrees Fahrenheit DEADBAND 28 ACTIVE HEATING SETPT Auto 53 Degrees Fahrenheit HEAT SPT 29 SETBACK HEAT SETPT Auto 62 Degrees Fahrenheit H SETBK 30 STAGE DELAY Auto 0 03 00 Time STAGEDEL 31 FAN DELAY Auto 0 03 00 Time FANDELAY 32 MIN DAMPER POSITION
18. turns off below 70 Output 3 COOLING STAGE 1 amp 2 Default settings select 0 to 100 range The first cooling triac turns on above 40 and off below 30 The second cooling triac turns on when the output is above 80 and turns off below 70 Output 4 OUTSIDE RET DAMPER his output configuration is set up to modulate an outdoor damper actuator from 2 to 10 volts 0 100 open Configuring variables A total of thirty two system variables are available to perform various functions such as set points limits and modes variables can be changed or modified to suit the specific application The following have been pre defined for use in the KMC supplied control sequences Variable 17 MIXED AIR SET POINT This is the temperature that Controller 3 CONS will maintain at the mixed air sensor IN3 by adjusting the OUTSIDE RET DAMPER OUT4 Variable 18 COOLING STAGE 1 This variable is ON when the first stage of cooling is required the first cooling triac is energized Manually turning this variable ON will also force the first stage of cooling on Variable 19 COOLING STAGE 2 This variable is ON when the second stage of cooling is required the first and second cooling triacs are energized Manually turning this variable ON will also force the first and second stages of cooling on Variable 20 HEATING STAGE 1 This variable is ON when the first stage of heating is required the first heating triac is energized Manually turning th
19. urity codes can be entered to control access to the system If you do not want to use any of the factory setup and programming options send a panel file with your own setup parameters and programming to the controller This will remove all of the factory programming allowing you to program any desired sequence The first step after signing on to the controller is to Load Descriptors One or Load Descriptors All Many of the descriptions have been pre defined for Inputs Outputs and Variables to aid in configuring the options To use a program or programs for a specific application go to the Control Basic programs screen and turn ON the appropriate program AN0404H KMD 7302 Roof Top Unit Controller Digital Designer s Guide Setting up with WinControl Configuring inputs All inputs on the KMD Controllers can be selected through software for either analog or digital ranges The pre programmed sequences assume the following input configuration Inputs Description Manual Value Label SPACE TEMPERATURE JW 72 Deg F XL SPACESTP w EE BASE SET POINT M 72 Unused Table2 SETPTSTP i I MIXED AIR TEMP t F1 55 PR MDED P 000 Unused mb Panel Al uto Load Mode 6 Illustration 1 Input configuration in WinControl XL Input 1 SPACE TEMPERATURE Default selects a KMC 10k ohm thermistor as used in all of KMC s STE Series sensors Inp
20. ut 2 BASE SET POINT Default range selects Table 2 which has been pre defined to correlate slider position of the STE 5200 Series Thermostats into degrees F This input is used to determine the active set points for heating and cooling Input 3 MIXED AIR TEMP Default selects standard KMC 10K ohm thermistor in degrees F This input is required for operation of the outside air damper with optional economizer programming routine For STE 1200 series sensors use range 2 or 3 Input 4 Unused Configuring outputs The KMD 7302 Roof Top Unit Controller features five on board triac relays Digital only and one universal output analog or digital set in software The KMC supplied control routines have been written to use the following output configuration Description Value On Off On HEATING STAGE 1 amp 2 COOLING STAGE 1 amp 2 OUTSIDE RET DAMPER Panel Al Status Idle Illustration 2 Output configuration in WinControl XL Output 1 FAN This output uses 1 amp zero crossing triac with optical isolation It is intended to switch a 24 VAC starter circuit to energize the fan motor AN0404H 3 143 KMD 7302 Roof Top Unit Controller Setting up with WinControl 3 144 KMC Controls Output 2 HEATING STAGE 1 amp 2 Default settings select 0 to 100 range The first heating triac turns on above 40 and off below 30 The second heating triac turns on when the output is above 80 and
21. wer inside the economizer is disabled Here is an example of programming to make this comparison 20 IF OUT ENTH lt IN ENTH 1 THEN ENABLE VAR23 30 IF OUT ENTH gt IN ENTH THEN DISABLE VAR23 In this example OUT ENTH is the calculated outdoor enthalpy and IN ENTH is the calculated indoor enthalpy To make these calculations it is necessary to have outside temperature and humidity sensors as well as space or return air humidity and temperature sensors A more simplistic approach to enabling the economizer is to look at outside air temperature The following example looks at outside air and the cooling demand based on the controller output to the cooling valve 20 IF CON1 gt 5 AND OAT lt 65 THEN ENABLE VAR23 30 IF CON1 lt 1 OR OAT gt 67 THEN DISABLE VAR23 This example requires a cooling demand CON1 of greater than 5 and an outside air temperature OAT of less than 65 degrees before economizer operation is allowed Once enabled the economizer cycle will be disabled if either the demand for cooling falls off or the outside air temperature rises above 67 degrees The KMC supplied program 2 uses Variable 24 to lockout cooling when heating is required and to lock out heating when cooling is required The mode can be selected based on factors such as outside air temperature and space temperature 40 IF NOT ECONOMIZ AND OAT gt 58 THE
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