Application Note: Enable De-humidification on units with Hot Gas Re-Heat that requiere a simultaneous Cool call

Use Case:

As you may know by now, 75F has a built in sequence of operation to control the humidity on units with that capability. This gives the customer an advantage over a standalone humidistat since they can have visibility of the humidity in their building and control the operation of the units dehumidifier option when installed.

Problem:

On some units it is required that the controller enables the compressor at the same time as the the dehumidification because the units Hot Gas Re-Heat does not trigger the compressor natively which is required in order for the dehumidification sequence to work.

Solution:

There are two options to achieve this:

1. With an external isolation relay the cooling call can be enabled at the same time as the dehumidification so the Hot Gas Re-Heat can achieve dehumidification. No additional configuration is needed. You can do this with either the CCU or the HyperStat.

2. You can use one of the available relays on the CCU with some re-wiring and configuration to command the compressor on when the dehumidification is on.

Result:

We can activate the refrigerant flow in the system as required to be able to bypass some of the hot refrigerant to a coil downstream of the cooling coil for the removal of the humidity in the airstream that serves supply air to the conditioned space.

Notes:

Requires a CCU or a HyperStat to control the units cooling and de-humidification.
With the first option: Requires a SPDT relay like a Functional Devices RIBU1C and no additional configuration is needed.
With the second option: the CCU will require some rewiring and the configuration of Relay 7.
See diagrams below for terminations:

HyperStat with Pilot Relay to enable Cooling with a De-humidification call