Carrier AQUAZONE 50PTH - Manual (Page 40)

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ured maximum heating SAT limit (110 F default). As the SAT
approaches this value, the control will increase the fan speed as
required to ensure the SAT will remain within the limit. This
feature provides the most quiet and efficient operation by oper-
ating the fan at the lowest speed possible.
Fan Speed Control (During Cooling) — Whenever mechani-
cal cooling is required and active, the control continuously
monitors the supply-air temperature to verify it does not fall be-
low the configured minimum cooling SAT limit (50 F default).
As the SAT approaches this value, the control will increase the
fan speed as required to ensure the SAT will remain within the
limit. The fan will operate at lowest speed to maximize latent
capacity during cooling.
COOLING — The WSHP Open controller will operate one or
two stages of compression to maintain the desired cooling set
point. The compressor outputs are controlled by the PI (propor-
tional-integral) cooling loop and cooling stages capacity algo-
rithm. They will be used to calculate the desired number of
stages needed to satisfy the space by comparing the space tem-
perature (SPT) to the appropriate cooling set point. The water
side economizer, if applicable, will be used for first stage cool-
ing in addition to the compressor(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 cooling
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 cool-
ing.
• 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 deenergized. 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 indexed to the maxi-
mum speed. If the SAT continues to fall 5 F below the mini-
mum 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 configured)
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 sup-
ply-air temperature has increased above the minimum supply-
air temperature limit.
The WSHP Open controller provides a status input to moni-
tor the compressor operation. The status is monitored to deter-
mine if the compressor status matches the commanded state.
This input is used to determine if a refrigerant 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 heating set
point. The compressor outputs are controlled by the heating PI
(proportional-integral) loop and heating stages capacity algo-
rithm. They will be used to calculate the desired number of
stages needed to satisfy the space by comparing the space tem-
perature (SPT) to the appropriate heating set point. The follow-
ing 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 deenergized. If
the heating is active and should the SAT approach the maxi-
mum 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 continues 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 configured)
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 sup-
ply-air temperature has fallen below the maximum supply air
temperature limit.
The WSHP Open controller provides a status input to moni-
tor the compressor operation. The status is monitored to deter-
mine if the compressor status matches the commanded state.
This input is used to determine if a refrigerant 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 replace 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 connect-
ed to a coil on the discharge side of the unit and supplied by a
boiler or a single-stage ducted electric heater in order to main-
tain the desired heating set point. Should the compressor capac-
ity be insufficient or a compressor failure occurs, the auxiliary
heat will be used. Unless the compressor fails, the auxiliary
heat will only operate to supplement the heat provided by the
compressor if the space temperature falls more than one degree
below the desired heating set point (the amount is configu-
rable). The heat will be controlled so the SAT will not exceed
the maximum heating SAT limit.
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