Can Varitrac do hot gas reheat for dehumidification?

Issue:

Can Varitrac do hot gas reheat for dehumidification?

Resolution:

Yes, the only issue is that the CCP won't display the setpoint, that needs to be set in the rooftop, or show what the humidity is. Temperature control will work fine.

When connected to the CCP, the Reliatel will only go into dehumidification when it is not in slave mode, namely when the CCP is not controlling it to heat or to cool (discharge air temperature is higher than the heating setpoint but lower than the cooling setpoint) and the space humidity is higher than the setpoint (as controlled through the setpoint potentiometer). When in dehumidification, the Reliatel will turn on all cooling stages and enable hot-gas reheat. It does not use a space or discharge-air temperature sensor to decide when to reheat. If the supply air gets to hot during this mode, the CCP will tell tell it to go into cooling again and dehumidification will be disabled.

Sequence of Events

Single compressor units

On a call for dehumidification, the reheat valve is energized and the compressor is turned on. When the humidity control setpoint is satisfied, the valve is de-energized and the compressor is turned off. If there is a call for cooling from the space temperature controller, i.e. zone sensor or thermostat, while in reheat, the reheat valve is de-energized and the compressor continues to run. The three minute compressor on and off times are still active during compressor operation.

Dual Compressor units

On a call for dehumidification, the reheat valve is energized and both compressors are turned on. When the humidity control setpoint is satisfied, the valve is de-energized and both compressors are turned off. If there is a call for 1st stage cooling while in the dehumidification mode, no action takes place. If there is a call for 2nd stage cooling, the reheat valve is de-energized, and the unit reverts to the cooling mode. If 2nd stage cooling is satisfied and there is still a call for dehumidification, the reheat valve will once again be energized. The three minute compressor on and off times are still active during compressor operation.

Can we see the Humidity Setpoint?

The Precedent unit (Comm3 and Comm4) with ReliaTel controls has the ReliaTel Options Module (RTOM) which has the potentiometer for the return air humidity setpoint and input terminals for the humidity sensor. There is nothing in the data packet for the Comm3 or Comm4 Voyager or Precedent with ReliaTel controls that includes this humidity information to allow us to read it in Tracer Summit. LCI-R provides the only option. The Precedent with dehumidification option will provide the functionality; we just cannot view or control this on a Comm3 or Comm4 link.

 

Notes:

This applies to CCP III. CCP II completely controls the rooftop unit and will disable the dehumidification cycle of the ReliaTel system.

Changes:

 

Other Question/Problem/Cause Statements:

• Can Varitrac do hot gas reheat for dehumidification?
• How does dehumidification work on a VariTrac system?
• Does the precedent support dehumidification when used in conjunction with a CCP3?
• Can a CCP work with a Voyager using Reliatel controls equipped with dehumidification?
• Has a Comm3 Precedent unit, wants to use its hot gas reheat for dehumidification purposes.

Facts:

• CCP3, Precedent, Reliatel
• Tracker BMTK
• CCPIII
• Reliatel
• VOYAGER/PRECEDENT
• Voyager/Precedent

Original wave: wave11584