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Installation
Indoor air quality (IAQ) and demand control ventilation (DCV)
If the optional indoor air quality sensor is installed, or the System Space AQ network input point is used, the
WSHP Open maintains indoor air quality with a modulating OA damper, which provides demand-controlled
ventilation. The control operates the modulating OA damper during occupied periods, monitors the CO2 level,
compares it to the configured setpoints, and adjusts the ventilation rate, as required. The control provides
proportional ventilation to meet the requirements of ASHRAE specifications by providing a base ventilation rate
and then increasing the rate as the CO2 level increases. The control proportionally increases ventilation when the
CO2 level rises above the start ventilation setpoint and reaches the full ventilation rate when the CO2 level is at or
above the maximum setpoint. You can configure a minimum damper position to ensure that proper base
ventilation is delivered when occupants are not present. Access the IAQ configurations through the Configuration
screen.
The following conditions must be true in order for this algorithm to run:
•
Damper Control is configured for DCV
•
The Fire/Smoke Input and Shutdown modes are inactive
•
Fan Status is True (if option is enabled)
•
The unit is in an occupied mode
•
IAQ sensor reading is greater than the DCV Start CTRL Setpoint
The control has the following 4 adjustable setpoints:
•
DCV Start Ctrl Setpoint
•
DCV Max Ctrl Setpoint
•
Minimum Dmpr Pos
•
DCV Max Vent Damper Pos
NOTE In order for the damper to maintain proper base ventilation, you must configure the fan as Continuous or
Always On.
2-position OA Damper - You can configure the control to operate as a ventilation damper in a 2-position
ventilation mode to provide the minimum ventilation requirements during occupied periods.
Dehumidification
The WSHP Open provides occupied and unoccupied dehumidification only on units that are equipped with the
modulating hot water reheat option (HWR). This function requires an accessory space relative humidity sensor.
When using a relative humidity sensor to control dehumidification during occupied or unoccupied times, the
dehumidification setpoints are used accordingly. Also, you may use the network input point System Space RH in
place of the hard-wired RH sensor.
When the indoor relative humidity becomes greater then the dehumidification setpoint, a dehumidification
demand is acknowledged. Once acknowledged, the dehumidification output is energized, bringing on the supply
fan (medium speed), mechanical cooling, and the integral hot water reheat coil. The controls engage cooling mode
and the waste heat from the compressor cooling cycle is returned to the reheat coil simultaneously, meaning that
the reversing valve causes the compressor to operate in the cooling mode.
NOTE During cooling mode, the unit cools and dehumidifies, and disables the HWR coil. However, once the call
for cooling has been satisfied and there is still a call for dehumidification, the unit continues to operate in the
reheat mode and HWR coil.
18
WSHP Open v3
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