Sequence of Operation
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WSHP-SVX13C-EN
Entering water temperature (EWT)
sampling
The controller will sample the entering water temperature
to determine proper control action for all units that utilize
a hard-wired entering water temperature indication. If the
entering water temperature is communicated to the
controller via a BAS system, then no sampling will be
required.When the EWT sampling function is invoked, the
isolation valve output will be driven open for 3 minutes
and the EWT reading is taken at that time.
EWT sampling will not occur automatically at power up,
only when all of the following conditions are met:
•
EWT is not communicated via BAS system
•
There is a new request for compressor operation.
•
The isolation valve is not OPEN.
•
It has been more than an hour since the last time that
the isolation valve was opened.
After the 3-minute EWT sampling time period expires, the
isolation valve will remain open for compressor operation.
Isolation Valve “OFF” Control
The isolation valve output will be de-energized (controlled
closed) when there is no longer a request for compressor
operation and the 10 minute minimum on time has expired
or the manual output override test has driven it closed.
Reversing Valve Operation
For normal unit operation, the reversing valve output is
energized when the unit is in cooling mode and de-
energized in heating mode. Under normal operating
modes, the reversing valve does not change states until
the compressor is energized and reaches its startup speed.
Cooling and Heating Operation
For normal cooling and heating operation, the unit cooling
or heating capacity will modulate and cycle based on a PI
algorithm in order to meet the active space setpoint. The
following fan and compressor actions are based on the
required unit capacity:
•
When no unit capacity is required, the compressor
output(s) will be OFF.
•
When the required unit capacity is less than the
compressor can provide at its minimum speed, the unit
will operate in a duty cycle scheme based on a required
ON/OFF time in order to meet the space demand.
•
When the required unit capacity is greater than the
minimum capacity for the unit, the unit will operate the
compressor and fan between minimum and maximum
capacity in order to meet the space demand.
Unoccupied Cooling and Heating
Operation
The unit will control the zone temperature to the active
unoccupied setpoints during unoccupied periods.
Demand Limit Operation
The controller supports a communicated request for
demand limiting operation of the compressor and supply
fan outputs. Demand limiting operates as follows: If the
point is placed into the active state, the unit limits the
compressor capacity output to 50% for all unit modes
(cooling and heating). During this period, the supply fan
tracks the compressor as normal and is limited by the user-
selected minimum and maximum fan speeds. Demand
limit requests do not override compressor startup and
shutdown sequences or unit protection modes.
