Product data

53
Cooling — The WSHP Open controller will operate one
or two stages of compression to maintain the desired cool-
ing set point. The compressor outputs are controlled by
the PI (proportional-integral) cooling loop and cooling stag-
es capacity algorithm. They will be used to calculate the de-
sired number of stages needed to satisfy the space by com-
paring the space temperature (SPT) to the appropriate
cooling set point. The water side economizer, if applicable,
will be used for first stage cooling in addition to the com-
pressor(s). The following conditions must be true in order
for the cooling algorithm to run:
• Cooling is set to Enable.
• Heating mode is not active and the compressor time
guard has expired.
• Condensate overflow input is normal.
• If occupied, the SPT is greater than the occupied cool-
ing set point.
• Space temperature reading is valid.
• If unoccupied, the SPT is greater than the unoccupied
cooling set point.
• If economizer cooling is available and active and the
economizer alone is insufficient to provide enough
cooling.
• OAT (if available) is greater than the cooling lockout
temperature.
If all the above conditions are met, the compressors will
be energized as required, otherwise they will be deener-
gized. If cooling is active and should the SAT approach the
minimum SAT limit, the fan will be indexed to the next
higher speed. Should this be insufficient and if the SAT falls
further (equal to the minimum SAT limit), the fan will be in-
dexed to the maximum speed. If the SAT continues to fall
5° F below the minimum SAT limit, all cooling stages will
be disabled.
During Cooling mode, the reversing valve output will be
held in the cooling position (either B or O type as config-
ured) even after the compressor is stopped. The valve will
not switch position until the Heating mode is required.
The configuration screens contain the minimum SAT
parameter as well as cooling lockout based on outdoor-air
temperature (OAT). Both can be adjusted to meet various
specifications.
There is a 5-minute off time for the compressor as well
as a 5-minute time delay when staging up to allow the SAT
to achieve a stable temperature before energizing a second
stage of capacity. Likewise, a 45-second delay is used
when staging down.
After a compressor is staged off, it may be restarted
again after a normal time-guard period of 5 minutes and if
the supply-air temperature has increase above the mini-
mum supply-air temperature limit.
The WSHP Open controller provides a status input to
monitor the compressor operation. The status is moni-
tored to determine if the compressor status matches the
commanded state. This input is used to determine if a re-
frigerant safety switch or other safety device has tripped
and caused the compressor to stop operating normally. If
this should occur, an alarm will be generated to indicate the
faulted compressor condition.
Heating — The WSHP Open controller will operate one
or two stages of compression to maintain the desired heat-
ing set point. The compressor outputs are controlled by
the heating PI (proportional-integral) loop and heating
stages capacity algorithm. They will be used to calculate
the desired number of stages needed to satisfy the space by
comparing the space temperature (SPT) to the appropriate
heating set point. The following conditions must be true in
order for the heating algorithm to run:
• Heating is set to Enable.
• Cooling mode is not active and the compressor time
guard has expired.
• Condensate overflow input is normal.
• If occupied, the SPT is less than the occupied heating
set point.
• Space temperature reading is valid.
• If unoccupied, the SPT is less than the unoccupied heat-
ing set point.
• OAT (if available) is less than the heating lockout
temperature.
If all the above conditions are met, the heating outputs
will be energized as required, otherwise they will be deener-
gized. If the heating is active and should the SAT approach
the maximum SAT limit, the fan will be indexed to the next
higher speed. Should this be insufficient, and the SAT rises
further reaching the maximum heating SAT limit, the fan
will be indexed to the maximum speed. If the SAT still con-
tinues to rise 5 F above the maximum limit, all heating
stages will be disabled.
During Heating mode, the reversing valve output will be
held in the heating position (either B or O type as config-
ured) even after the compressor is stopped. The valve will
not switch position until the Cooling mode is required.
The configuration screens contain the maximum SAT
parameter as well as heating lockout based on outdoor-air
temperature (OAT); both can be adjusted to meet various
specifications.
There is a 5-minute off time for the compressor as well
as a 5-minute time delay when staging up to allow the SAT
to achieve a stable temperature before energizing a second
stage of capacity. Likewise, a 45-second delay is used
when staging down.
After a compressor is staged off, it may be restarted
again after a normal time-guard period of 5 minutes and if
the supply-air temperature has fallen below the maximum
supply air temperature limit.
The WSHP Open controller provides a status input to
monitor the compressor operation. The status is moni-
tored to determine if the compressor status matches the
commanded state. This input is used to determine if a re-
frigerant safety switch or other safety device has tripped
and caused the compressor to stop operating normally. If
this should occur, an alarm will be generated to indicate the
faulted compressor condition. Also, if auxiliary heat is
available (see below), the auxiliary heat will operate to re-
place the reverse cycle heating and maintain the space
temperature as required.
Auxiliary heat — The WSHP Open controller can con-
trol a two-position, modulating water, or steam valve
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