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Waterside economizer
The WSHP Open can provide modulating, or 2-position water economizer operation (for a field-installed
economizer coil mounted to the entering return air side of the unit and connected to the condenser water loop), in
order to provide free cooling or preheating, when water conditions are optimal. Water economizer settings can be
accessed on Properties > Equipment > Status.
The following conditions must be true for economizer operation:
•
SAT reading is available
•
EWT reading is available
•
If occupied, the SPT is greater than the occupied cooling setpoint or less than the occupied heating setpoint
and the condenser water is suitable
•
Space temperature reading is valid
•
If unoccupied, the SPT is greater than the unoccupied cooling setpoint, or less than the unoccupied heating
setpoint, and the condenser water is suitable
Modulating water/2-Position water economizer control - modulates a water valve to control condenser water
flowing through a coil on the entering air side of the unit
•
Cooling - Provides an economizer cooling function by using the water loop when the entering water loop
temperature is at least 5°F below space temperature. If the water loop conditions are suitable, the valve
modulates open to maintain a Supply Air Temperature that meets the load conditions. If the economizer coil
capacity alone is insufficient for a period greater than 5 minutes, or if a high humidity condition occurs, then
the compressor starts, in order to satisfy the load. If the SAT approaches the Minimum Cooling SAT limit
(HOME > CONFIG > UNIT), the economizer valve modulates closed during compressor operation.
•
Heating - In addition, the control modulates the water valve if the entering condenser water loop temperature
is suitable for heating (at least 5°F above space temperature) and heat is required. The valve is controlled in
a similar manner, except to satisfy the heating requirement. If the coil capacity alone is insufficient to satisfy
the space load conditions for more than 5 minutes, then the compressor starts in order to satisfy the load. If
the SAT approaches the Maximum Heating SAT limit, the economizer valve modulates closed during
compressor operation.
2-position water economizer control - has the capability to control a NO or NC, 2-position water valve to control
condenser water flow through a coil on the entering air side of the unit.
•
Cooling - The purpose is to provide a cooling economizer function directly from the condenser water loop
when the entering water loop temperature is at least 5° F below space temperature. If the optional coil is
provided and the water loop conditions are suitable, then the valve opens to provide cooling to the space,
when required. If the capacity is insufficient for a period greater than 5 minutes, or if a high humidity
condition occurs, the compressor is started in order to satisfy the load. If the SAT reaches the Minimum
Cooling SAT limit, the economizer valve closes during compressor operation.
•
Heating - In addition, the economizer control opens the water valve, if the entering water loop temperature is
suitable for heating (at least 5° F above space temperature) and heat is required. The valve is controlled in a
similar manner, except to satisfy the heating requirement. If the coil capacity is insufficient to satisfy the
space load for more than 5 minutes, then the compressor is started to satisfy the load. If the SAT reaches the
Maximum Heating SAT limit, the economizer valve closes during compressor operation.
WSHP Open v3
19
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