Auxiliary Heat - Carrier WSHP Open v3 Integration Manual

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.
During Heating, the reversing valve output is held in the heating position (either B or O-type, as configured), even
after the compressor is stopped. The valve does not switch position until the cooling mode is required.
The configuration screens contain the Max SAT parameter as well as heating 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, a 45 second delay is
used 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 fallen below the maximum 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. Also, if auxiliary heat is available (see
below), the auxiliary heat replaces the reverse cycle heating and maintains the space temperature as required.

Auxiliary heat

The WSHP Open can control a 2-position or modulating water or steam valve, connected to a coil on the discharge
side of the unit and supplied by a boiler, or a single stage ducted electric heater, in order to maintain the desired
heating setpoint. If the compressor capacity is insufficient, or a compressor failure occurs, the auxiliary heat is
used. Unless the compressor fails, the auxiliary heat only operates to supplement the heat provided by the
compressor, if the space temperature falls more than 1° F below the desired heating setpoint. (This amount is
configurable.) The heat is controlled so the SAT does not exceed the Maximum Heating SAT limit.
The same conditions required for Reverse Cycle Heating must be true in order for the Auxiliary Heat algorithm to
run.
Auxiliary Modulating Hot Water / Steam Heating Reheat - The control can modulate a hot water or steam valve
connected to a coil on the discharge side of the unit, and supplied by a boiler in order to maintain the desired
heating setpoint, if the compressor capacity is insufficient, or a compressor failure occurs. Unless a compressor
fault condition exists, the valve only operates to supplement the heat provided by the compressor if the space
temperature falls more than 1° F below the desired heating setpoint. The valve is controlled so the SAT does not
exceed the Maximum Heating SAT limit.
2- Position Hot Water / Steam Heating Reheat - The control can operate a 2-position, NO or NC, hot water or
steam valve, connected to a coil on the discharge side of the unit and supplied by a boiler, in order to maintain the
desired heating setpoint, if the compressor capacity is insufficient or a compressor failure occurs. Unless a
compressor fault condition exists, the valve only opens to supplement the heat provided by the compressor, if the
space temperature falls more than 1° F below the desired heating setpoint. The valve is controlled so the SAT
does not exceed the Maximum Heating SAT limit and is subject to a 2-minute minimum OFF-time to prevent
excessive valve cycling.
Single Stage Electric Auxiliary Heat – The control can operate a field-installed single stage of electric heat that is
installed on the discharge side of the unit, in order to maintain the desired heating setpoint, if the compressor
capacity is insufficient or a compressor failure occurs. Unless a compressor fault condition exists, the heat stage
only operates to supplement the heat provided by the compressor if the space temperature falls more than 1° F
below the desired heating setpoint. The heat stage is controlled so the SAT does not exceed the Maximum
Heating SAT limit and is subject to a 2-minute minimum OFF-time to prevent excessive cycling.
WSHP Open v3 17