Modulating Re-Heat Valve; Filter; Heating And Cooling - (1 And 2 Compressor Stages) - FHP 641-224 User Manual

Modulating Re-Heat Valve:

This valve is an analog device and has the capability to modulate the amount of hot gas that is
allowed through the re-heat coil, thus allowing control of the discharge air temperature to a user
defined setpoint.
The operation is similar to the on/off control except once the space temperature is satisfied the
controller will monitor the space humidity if the value is greater than the setpoint the controller
will modulate the valve to meet a particular a desired discharge air temperature on zone
applications only.
A typical application of modulating re heat valves can be seen on Discharge Air Control systems
where the unit is required to maintain a particular value of supply air temperature (neutral air).
For this particular type of units the unit will only discharge air to meet the specific setpoint, this
operation is done via a reverse acting PID closed loop, and its sequence of operation is
described in detail under the Discharge air section of this document.

Filter:

Based on fan runtime, a filter alarm message is generated after a user definable amount (adj.
factory default 2000 hours) or can be enabled by an optional differential pressure switch.
Heating and Cooling – (1 and 2 Compressor Stages):
The controller will measure the zone temperature and stage the compressor(s) to maintain its
setpoint. To prevent short cycling, there will be a 5 minute delay between compressor stages (if
equipped with 2 compressors). Additionally, there will be a 1 minute delay when transitioning
between heat and cool modes. The compressor will run subject to internal safeties and controls
provided by UPM board.
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