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The following conditions must be true in order for the cooling
algorithm to run in the OAT control mode:
•
A valid Outdoor Air Temperature is present.
•
Control Mode Selection is set to OAT.
•
Cool Enable is set to Enable.
•
Unit is occupied (see Occupancy Section above).
•
The OAT is greater than the Cooling lockout temperature
setpoint.
•
Heat mode is not active and the compressor time guard has
expired.
•
The Changeover time guard has elapsed.
•
Load water temp is above the Chilled Water Supply
Setpoint.
SPT
Configuring the Control Mode Selection for SPT sets the control
to change modes between heating and cooling based on the Space
Temperature sensor located in the space or return air plenum
(SPT). The control will compare the SPT to the configured
lockout temperatures for heating and cooling and select the
appropriate operating mode. A valid space temperature reading
(hardware or network) is required for this mode. Once enabled,
equipment control is as described for heating and cooling.
When conditions require cooling, the module will operate as
described in the Cooling section. The Outdoor Air and Relative
Humidity Cooling setpoint reset functions are available provided
their associated preconditions (described previously) are met.
The following conditions must be true in order for the cooling
algorithm to run in the SPT control mode:
•
A valid SPT is present.
•
Control Mode Selection is set to SPT.
•
Cool Enable is set to Enable.
•
Unit is occupied (see Occupancy Section above).
•
The SPT is greater than the Cooling lockout temperature
setpoint.
•
Heat mode is not active and the compressor time guard has
expired.
•
The Changeover time guard has elapsed.
•
Load water temp is above the Chilled Water Supply
Setpoint.
System T1 Temp
Configuring the Control Mode Selection for System T1 Temp sets
the control to change modes between heating and cooling based
on a network temperature. The control will compare the network
temperature to the configured lockout temperatures for heating
and cooling and select the appropriate operating mode. The
System T1 Temperature network input object must be addressed
to read the desired temperature and communicating for this mode.
Once enabled, equipment control is as described for heating and
cooling.
When conditions require cooling, the module will operate as
described in the Cooling section. The Outdoor Air and Relative
Humidity Cooling setpoint reset functions are available provided
their associated preconditions (described previously) are met.
The following conditions must be true in order for the cooling
algorithm to run in the T1 control mode:
•
A valid network T1 Temperature is present.
•
Control Mode Selection is set to T1.
•
Cool Enable is set to Enable.
•
Unit is occupied (see Occupancy Section above).
•
The T1 Temperature is greater than the Cooling lockout
temperature Setpoint.
•
Heat mode is not active and the compressor time guard has
expired.
•
The Changeover time guard has elapsed.
•
Load water temp is above the Chilled Water Supply
Setpoint.
HEATING (SINGLE MODULE)
When configured for "Single/Secondary Unit" operation, The
W2W control will operate up to four stages of compression to
maintain the desired hot water supply setpoint. The control point
can be selected by setting the "Control Type" to either the leaving
water temperature sensor (default) or the entering water tempera-
ture sensor. While in the heating mode, the compressor outputs are
controlled by the PI (Proportional-integral) heating loop and
heating stages capacity algorithm. The algorithms calculate the
desired number of stages needed to satisfy the load water setpoint
by comparing the actual water temperature sensor value to the hot
water supply setpoint.
Additionally, an independent leaving load water temperature
safety check is included to verify that sufficient load water flow is
provided. Regardless of the control type, as the leaving load water
temperature exceeds the configured "Hot Water Supply Setpoint,
the compressor stages will start to be reduced as required.
The following conditions must be true in order for the heating
algorithm to run:
•
Unit is occupied (see Occupancy Section above).
•
The lockout temperature (OAT, SPT, or T1) is less than the
Heating lockout temperature setpoint.
•
Heat Enable is set to Enable.
•
Cool mode is not active and the compressor time guard has
expired.
•
The Changeover time guard has elapsed.
•
Load water temp is below the Hot Water Supply Setpoint.
If all the above conditions are met, the compressors will be
energized as required to satisfy the heating requirements. While
heating, the reversing valve output will be held in the heating
position (either B or O type as configured) even after compression
is stopped. The valve will not switch position until the cooling
mode is required.
During heating operation, the control employs a 5 minute time
delay before each subsequent stage of compression to allow the
leaving water temperature (LWT) to achieve a stable temperature
and avoid overshoot. Once energized, a stage of compression will
have to run for at least 180 seconds before being staged off to
avoid short-cycling.
Once a compressor is staged off, it may not be restarted again until
a five minute time guard delay period expires.
The module provides three (binary) compressor status inputs to
monitor compressor operation. These inputs are monitored to
determine if the compressor status matches its commanded state.
These inputs are used to determine if a refrigerant safety switch or
other safety device has tripped and have caused the compressor to
stop operating normally. If this should occur, an alarm will be
generated to indicate the faulted compressor condition. The
Compressor Status Alarms include a 6 minute delay to avoid
nuisance alarms.
ADDITIONAL HEATING FUNCTIONS
Heating Setpoint OA Reset
The W2W control may be configured to reset the hot water supply
setpoint proportionally based upon OAT. The amount of reset and
the reset range are both user configurable. This feature can provide
energy savings by operating the unit at a lower load water
temperature setpoint when the maximum hot water supply
temperature is not required. It also can be used to better match the
hot water temperature to the heating load requirements.
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