Overview:
Dehumidification Sequence of Events for Voyager II and Precedent units.
Process:
Dehumidification with hot gas reheat
Factory installed hot gas reheat allows application of dehumidification. Initiation of reheat is performed by an input to the RTOM module from either a relative humidity sensor or a humidi-stat type device. These connections are made through the low voltage terminal strip located in the unit control panel. Actuation of the reheat is accomplished by energizing a valve that allows refrigerant hot gas to flow through the hot gas reheat coil.
Dehumidification is allowed only when the outside air temperature is above 40F or below 100F. Dehumidification is not allowed if there is an active call for heating . If, during a dehumidification cycle, there is a call for heating, the dehumidification cycle is terminated. The economizer outside air damper is also driven to minimum position during dehumidification.
In the absence of a zone humidity sensor input, an on/off input from a zone humidistat is used to initiate or terminate the dehumidification cycle. A relative humidity sensor takes priority over a humidistat .
Dehumidification takes priority over a single call for cooling on dual compressor units. Cooling takes priority over dehumidification on single compressor units.
Heating or 2nd stage cooling takes priority over dehumidification.
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 minimum compressor on and off times are still active during compressor operation.
On certain units the use of a two speed condenser fan motor is required to maintain proper airflow. For those applications, if the unit is in the reheat mode, and the outside air temperature is below 70 degrees, the motor changes to low speed. Once the reheat mode is terminated, or the temperature goes above 75 degrees, the condenser motor will revert back to high speed. This speed variation is only functional during the reheat mode.
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, as well as turning 2nd stage compressor back on. The three-minute minimum on and off times are still active during compressor operation. In other words, 2nd stage cooling take priority over a call for dehumidification.
In addition to the normal sequence of events, there is a purge sequence in the ReliaTel RTRM module that changes the state of the refrigeration cycle. During a cooling or dehumidification cycle, if the given cycle remains in that state for 90 accumulated minutes without changing to the other state, a purge time algorithm in the RTRM, will force the system to switch to the other state for three minutes.
If during the the 90 minute period the refrigeration cycle changes from one state to the other based on a call from a temperature controller or humidity sensor, the timer is reset and starts counting again.
Refer to appropriate unit wiring diagrams for control connections.
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.