Reverse Cycle Heating - Carrier WSHP Open v3 Integration Manual

Sequence of Operation
If all of the above conditions are met, the compressors' relays are energized as required. Otherwise, they will be
de-energized. If cooling is active and if the SAT approaches the minimum SAT limit, the fan will be indexed to the
next higher speed. If this is insufficient, and if the SAT falls further (equal to the minimum SAT limit), the fan will be
indexed to the maximum speed. If the SAT still continues to falls 5°F below the minimum SAT limit, all cooling
stages will be disabled.
During Cooling, the reversing valve output is held in the cooling position (either B or O type, as configured), even
after the compressor is stopped. The valve does not switch position until the heating mode is required.
The configuration screens contain the Min SAT parameter as well as Cooling Lockout based on outdoor air
temperature (OAT). Both can be adjusted to meet various specifications.
There is a 5-minute off-time for the compressor, as well as a 5-minute time delay, when staging up to allow the
SAT to achieve a stable temperature, before energizing a second stage of capacity. Likewise, there is a 45 second
delay when staging down.
After a compressor is staged off, it may be restarted again after a normal time-guard period of 5 minutes and if
the supply air temperature has increased above the minimum supply air temperature limit.
The WSHP Open provides a status input to monitor the compressor operation. The status is monitored to
determine if the compressor status matches the commanded state. This input is used to determine if a refrigerant
safety switch or other safety device has tripped and caused the compressor to stop operating normally. If this
occurs, an alarm is generated to indicate the faulted compressor condition.

Reverse cycle heating

The WSHP Open operates 1 or 2 stages of compression to maintain the desired cooling setpoint. The compressor
outputs are controlled by the heating PI (Proportional-integral) loop and heating stages capacity algorithm. The
algorithm calculates the desired number of stages needed to satisfy the space by comparing the space
temperature (SPT or ZS) to the appropriate heating setpoint.
The following conditions must be true for the heating algorithm to run:
•
Heating is set to Enable
•
The Fire/Smoke Input and Shutdown modes are inactive
•
Cool mode is not active and the compressor time guard has expired
•
Condensate Overflow input in Normal
•
Fan Status is True (if option is enabled)
•
If occupied, the SPT or ZS is less than the occupied heating setpoint
•
Space Temperature reading is valid
•
If unoccupied, the SPT or ZS is less then the unoccupied heating setpoint
•
OAT > Heating Lockout Temperature if OAT is available
•
Source Water Pump is on (if Source Water Linkage active)
If all the above conditions are met, the heating outputs are energized as required, otherwise they are de-
energized. If the heating is active and the SAT approaches the maximum SAT limit, the fan is indexed to the next
higher speed. If this is insufficient, and if the SAT rises further and reaches the Maximum Heating SAT limit, the
fan is indexed to the maximum speed. If the SAT still continues to rise 5° F above the maximum limit, all heating
stages are disabled.
WSHP Open v3
Integration Guide
26
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