The following sections describe the operation details.
Cooling
Cooling calls are handled the same way as non-heat pump cooling units with one exception.
The H1 output to the reversing valve remains energized between calls for cooling. If a heating call arises, the H1 output turns off.
Heating - thermostat inputs
All available compressor outputs are energized.
If there is a first stage call for heating, all available compressors stage on with a 30 second delay between compressors. In the zone sensor mode heating stages turn on as the demand requires.
The cooling fan on delay and cooling fan off delay are used for the first stage of heat pump heating.
During a first stage of heating, the H1 output reversing valve turns off and remain off between heat calls.
If there is a second stage call for heating, the H2 or AUX output energizes the emergency/aux heating.
If a thermostat calls for W2 only, only the H2 output energizes. The heating fan on delay and heating fan off delay are used.
Heating – space temperature inputs
In two stage units, compressors are treated as two stages of heating.
Auxiliary heat is treated as a third stage.
Defrost
The heat pump defrost cycle only applies during compressor heating operation. In heating mode, the H1 output is de-energized, the C1 and/or C2 outputs are (and possibly H2) energized and the CN-FAN output is energized.
At the initiation of the defrost cycle these are the outputs that occur, the H1 output energizes, the H2 output energizes or remains energized, the C1 and/or C2 output remain energized and the CN-FAN output is de-energized.
Defrost cycle initiation
Demand defrost
Number of refrigeration systems (#RefrigSys) is set to 1.
- Defrost curve selection 1, 2, 3 or 4 - 40 minutes have elapsed since the previous defrost cycle or UCB boot-up
- Defrost curve selection 5 - 60 minutes have elapsed since the previous defrost cycle or UCB bootup
- Defrost curve selection 6 - 30 minutes have elapsed since the previous defrost cycle or UCB bootup
Number of refrigeration systems (#RefrigSys) is set to 2 or more.
When the intersection of the operational outdoor air temperature (OprOAT) and either the condenser coil temperature 1 (CC1) or the condenser coil temperature 2 (CC2) remain in the demand defrost region for 4½ minutes, the defrost cycle initiates based on the same conditions as if the number of refrigeration systems is set to 1.
Forced defrost
Number of refrigeration systems (#RefrigSys) is set to 1.
- Defrost curve selection 1, 2, 3, 4, 5 or 6 - 6 hours have elapsed since the previous defrost cycle or UCB boot-up
Number of refrigeration systems (#RefrigSys) is set to 2 or more
- Defrost curve selection 1, 2, 3, 4, 5 or 6 - 6 hours have elapsed since the previous defrost cycle or UCB boot-up
Defrost cycle termination
- Defrost curve selection 1, 2, 3, 4 or 5: the condenser coil temperature 1 (CC1) reaches the 40°F defrost termination temperature or 8 minutes have elapsed since the initiation of the defrost cycle.
- Defrost Curve selection 6: the condenser coil temperature 1 (CC1) reaches the 50°F defrost termination temperature or 10 minutes have elapsed since the initiation of the defrost cycle - pinked due to possible production variation.
- Defrost curve selection 1, 2, 3, 4 or 5: both the condenser coil temperature 1
(CC1) and the condenser coil temperature 2
(CC2) reach the 40°F defrost termination
temperature or 8 minutes have elapsed since the initiation of the defrost
cycle.
Within the 8-minute period; if either CC1 or CC2 is above the 40°F defrost termination temperature and the remaining CC input has not reached 40°F, the CC input above 40°F holds the corresponding C output on until that CC input reaches the 50°F defrost cutout temperature. If the remaining CC input has not reached 40°F and the other CC input reaches 50°F, the CC input above the 50°F defrost cutout temperature turns off the corresponding C output for the remainder of the defrost cycle. The C output that was turned off due to defrost cutout temperature can resume compressor heating operation once the defrost cycle terminates and that C output ASCD expires.
- Defrost Curve selection 6 - both Condenser Coil Temperature 1
(CC1) and Condenser Coil Temperature 2
(CC2) reach the 50°F defrost termination
temperature or 10 minutes have elapsed since the initiation of the defrost
cycle.
Within the 10-minute period; if either CC1 or CC2 are above the 50°F defrost termination temperature and the remaining CC input has not reached 50°F, the CC input above 50°F holds the corresponding C output on until that CC input reaches the 60°F defrost cutout temperature. If the remaining CC input has not reached 50°F and the other CC input reaches the 60°F defrost cutout temperature, the CC input above 60°F turns off the corresponding C output for the remainder of the defrost cycle. The C output that was turned off due to defrost cutout temperature can resume compressor heating operation once the defrost cycle terminates and that C output ASCD expires.
The heat pump heating operation according to the demand resumes when the defrost cycle terminates.
Initiation of the defrost cycle is prevented by temperature sensor input in the following cases:
- If the operational outdoor air temperature (OprOAT) is less than -25°F ±1°F or greater than 50°F ±1°F.
- If the CC1 and CC2 condenser coil temperatures are both greater than 40°F ±1°F.
Within the boundaries of the operational outdoor air temperature (OprOAT) greater than -25°F ±1°F or less than 50°F ±1°F and the condenser coil temperature (CC1 and CC2) less than 40°F ±1°F, demand defrost and forced defrost regions for defrost cycle initiation are determined by the defrost curve selection, see the following figures.