Heat Pump Operation - Carrier RTU Open v5 Integration Manual


The unit has a valid Supply Air Temperature input

The unit is configured for gas or electric heat

The Outdoor Air Temperature is less than the Minimum Cooling SAT

The current operation mode is either Fan Only, IAQ Override,or Pre-occ Purge

The fan status is True (if configured for the fan status option)

The supply air temperature falls below the configured SA Vent / Temper Setpoint
When the algorithm preconditions above have been met, the first stage of heating is energized. The heating
operates to maintain the desired SA Vent / Tempering Setpoint subject to the minimum on timer and anti-recycle
timer to protect the equipment from short-cycling and ensure minimum burn time for gas heat. There are fixed
one-minute minimum on and off times for the heating output.

Heat Pump operation

The RTU Open can control heat pumps HP O/B and Y1/W1.
HP O/B provides a separate output (BO-7) to control a reversing valve. The reversing valve control may be
configured to be energized with a call for heating (B), or energized with a call for cooling (O).
The sequence of operations are as previously described for heating and cooling except that the Y1 and Y2 outputs
are compressor outputs, energizing mechanical heating or cooling, depending on the state of the reversing valve.
W1 and W2 are used for auxiliary heat. Up to 2 stages are available.
For heat pumps configured as HP O/B, the RTU Open provides a reverse cycle lockout that prevents reverse cycle
operation when the OAT falls below the configured HP Rev Cycle Lockout Temp. Whenever the OA temperature is
below this value, the RTU Open will immediately operate the auxiliary heat and disable the compressor operation
whenever heating is required.
Select Y1/W1 for heat pumps that do not require a O terminal to energize the reversing valve. The sequences of
operations are as described for Heating and Cooling. The reversing valve output is not used in this application. W2
is used for auxiliary heat. Up to 2 stages are available.
For all heat pump types, the RTU Open will prevent auxiliary heat operation whenever the OA temp is greater than
the configured HP Aux Heat Lockout Temp. This allows the RTU Open to utilize the more efficient heating from the
reverse cycle operation and prevents the operation of the auxiliary heat source.
IMPORTANT! All heat pump unit types (HP O/B and Y1/W1) require a valid OA Temperature value. This value may
be a local sensor connected to the RTU Open or a value received from the network.
RTU Open v5
Integration Guide
29
Sequence of Operation
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