Quality (IAQ) section of the Economizer Operation section above for more details on Demand Control Ventilation (DCV).
Economizer Operation for Units Equipped with Return Air CO2 Sensor Only
When the CO2 sensor detects a CO2 level or IAQ Level (Inputs→AIR.Q→IAQ) below the AQ Differential Low (Configuration→AIR.Q→AQD.L) value the MP.25, MP.50, MP.75 and MP.MX points will be recalculated to new values for MP.25, MP.50, MP.75 based on the Econ Min IAQ Position (Configuration→AIR.Q→AQ.MN). The economizer outside air damper will close and reduce the amount of outside air CFM to the conditioned space based on the lower IAQ sensor readings and indoor fan speed. The economizer outside air damper will continue to close and reduce the amount of outside air CFM to the conditioned space until the damper reaches user configurable Econ Min IAQ Position (Configuration→AIR.Q→AQ.MN). This will
happen when the Commanded Fan Speed (Outputs→FANS→F.SPD) is at the Supply Fan Maximum Speed (Configuration→UNIT→FS.MX). When the Commanded Fan Speed (Outputs→FANS→F.SPD) is between Supply Fan Maximum Speed (Configuration→UNIT→FS.MX) and the Supply Fan Minimum Speed (Configuration→UNIT→FS.MN) the damper will operate in the shaded area of Figure 8 based on the IAQ Level (Inputs→AIR.Q→IAQ).
Economizer Operation for Units Equipped with Return Air CO2 Sensor and outside air CO2 Sensor
The Economizer will operate similar to Economizer Operation for Units Equipped with Return Air CO2 Sensor Only but the IAQ Level (Inputs→AIR.Q→IAQ) will be determined by actual outside air CO2 measurements instead of the 400 ppm CO2 default value for OAQ.
Cooling Mode Using Space Temperature Sensor T55, T56, T58 or T59 and Humidistat (HL38MG029 or TSTATCCPLH01-B)
Enhanced dehumidifying will be provided when a humidistat (HL38MG029 or TSTATCCPLH01-B) is connected the PD unit terminal strip across the R and W2 terminals (since the PD unit does not support the use of conventional thermostat inputs the W2 terminal is reconfigured for humidity input) and Space Humidity Switch (Configuration→UNIT→RH.SW) configuration variable is set to 1 (Normally Open-no call to dehumidify). Relative humidity set point is set by adjusting the dial on the HL38MG029 or TSTATCCPLH01-B device. When the humidistat contacts close and provide 24VAC to the W2 terminal the PD unit will reset the Supply Air Control Point (Run Status→COOL→SA.CP) by one degree F lower than the Supply Air Set Point (Setpoint→SASP) or the current control point if the Supply Air Set Point (Setpoint→SASP) has already been modified. After 5 minutes if the humidistat contacts are still closed and 24 VAC is being supplied to the W2 terminal the PD unit will reset the Supply Air Control Point (Run Status→COOL→SA.CP) lower by one more degree F. This reset cycle will continue to lower the supply air temperature every 5 minutes until the Supply Air Control Point (Run Status→COOL→SA.CP) is equal to the Supply Air Set Point (Setpoint→SASP) + SASP Maximum Reset Down (Configuration→COOL→SAT→SA.MD). The unit will continue to operate at this reduced supply air temperature control point until the humidistat contacts open and 24VAC is no longer supplied to the W2 terminal. When 24VAC is no longer supplied to the W2 terminal the supply air control point will be reset higher by one degree F. After 3 minutes if the humidistat contacts are still open and 24VAC is not being supplied to the W2 terminal PD unit will reset the Supply Air Control Point (Run Status→COOL→SA.CP) higher by one more degree F. This reset cycle will continue to raise the Supply Air Control Point (Run Status→COOL→SA.CP) every 3 minutes until the Supply Air Control Point (Run Status→COOL→SA.CP) is equal to the Supply Air Set Point (Setpoint→SASP) or the supply air control point if reset was being
applied due to cooling requirements that reset the Supply Air Set Point (Setpoint→SASP). Whenever Relative Humidity Reset is applied the space temperature is controlled by modulating the fan speed even if the fan was locked at 100% due to (Setpoint→SASP) reset.
Cooling Mode Using Space Temperature Sensor T55, T56, or T58 and Humidity Sensor (HL39ZZ007 or 33ZCSENRH-01)
Enhanced dehumidifying will be provided when a humidly sensor (HL39ZZ007 or 33ZCSENRH-01) 4 to 20 ma control is connected the PD unit terminal strip across the TB1-J10 pin 3 and 4, power to humidity sensor is connected to R and C, the RH Sensor on OAQ Input (Configuration→UNIT→RH.S) is set to
YES and Space Humidity Switch (Configuration→UNIT→RH.SW) configuration variable is set to
0.Relative humidity set point is set by changing the value of Space RH Set point (Setpoint→RH.SP). When the relative humidity in the space is above the Space RH Set point (Setpoint→RH.SP) the PD unit controls will reset the supply air temperature by one degree F lower than the Supply Air Set Point (Setpoint→SASP) or the current control point if the Supply Air Set Point (Setpoint→SASP) has already been modified. After 5 minutes the PD unit will reset the Supply Air Control Point (Run Status→COOL→SA.CP) lower by one more degree F. This reset cycle will continue to lower the Supply Air Control Point (Run Status→COOL→SA.CP) every 5 minutes until the Supply Air Control Point (Run Status→COOL→SA.CP) is equal to the Supply Air Set Point (Setpoint→SASP) + SASP Maximum Reset Down (Configuration→COOL→ SAT→SA.MD). When the relative humidity in the space goes below the Space RH Set Point (Setpoint→RH.SP) - the Space RH Deadband (Setpoint→RH.DB) the supply air control point will be reset higher by one degree F. After 3 minutes if the humidity sensor reading is still below the Space RH Set Point (Setpoint→RH.SP) - the Space RH Deadband (Setpoint→RH.DB), the PD unit will
reset the Supply Air Control Point (Run Status→COOL→SA.CP) higher by one more degree F. This reset cycle will continue to raise the Supply Air Control Point (Run Status→COOL→SA.CP) every 3 minutes until the supply air temperature control point is equal to the Supply Air Set Point (Setpoint→SASP) or the supply air control point if reset was being applied due to cooling requirements that reset the Supply Air Set Point (Setpoint→SASP).
Heating Modes
Gas Heating Mode Using Space Temperature Sensor T55, T56, or T58 (48PD Units Only)
For gas units, the Type of Heat Installed (Configuration→HEAT→HT.TY) will be factory set to a value of 1.
Heat will not operate if the outdoor temperature is greater than the value configured for the Heating Lockout Temperature (Configuration→HEAT→HT.LO), Heat Minimum On Time (Configuration→HEAT→MRT.H) and Heat Minimum Off Time (Configuration→HEAT→MOT.H). Timeguards apply to both stages of heating. Factory defaults values are 2 minute s ON and 2 minutes OFF. The Integrated Gas Controller (IGC) minimum on-time of 1 minute will be followed even if Heat Minimum On Time (Configuration→HEAT→MRT.H) is lower and during Service Test.
If the indoor fan control is configured to cycle with the heating demand by setting Fan ON When Occupied Heat Minimum On Time (Configuration→UNIT→OC.FN) to NO, the fan will stop after a delay configured by Fan-off Delay, Gas Heat (Configuration→HEAT→FOD.G). The factory default for Fan-off Delay, Gas Heat (Configuration→HEAT→FOD.G) is 45 seconds. If the IGC temperature limit switch opens within 10 minutes of the end of the gas heat cycle, the next fan off delay will
