Carrier AQUAZONE PSV - Manual (Page 44)

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NOTE: Scheduling can either be controlled via the unit or the
BAS, but not both.
INDOOR FAN — The indoor fan will operate in any one of
three modes depending on the user configuration selected.
Fan mode can be selected as Auto, Continuous, or Always
On. In Auto mode, the fan is in intermittent operation during
both occupied and unoccupied periods. Continuous fan mode
is intermittent during unoccupied periods and continuous dur-
ing occupied periods. Always On mode operates the fan con-
tinuously during both occupied and unoccupied periods. In the
default mode, Continuous, the fan will be turned on whenever
any one of the following is true:
• The unit is in occupied mode as determined by its occu-
pancy status.
• There is a demand for cooling or heating in the unoccu-
pied mode.
• There is a call for dehumidification (optional).
When power is reapplied after a power outage, there will be
a configured time delay of 5 to 600 seconds before starting the
fan. There are also configured fan delays for Fan On and Fan
Off. The Fan On delay defines the delay time (0 to 30 seconds;
default 10) before the fan begins to operate after heating or
cooling is started while the Fan Off delay defines the delay
time (0 to 180 seconds; default 45) the fan will continue to op-
erate after heating or cooling is stopped. The fan will continue
to run as long as the compressors, heating stages, or the dehu-
midification relays are on. If the SPT failure alarm or conden-
sate overflow alarm is active; the fan will be shut down imme-
diately regardless of occupancy state or demand.
Automatic Fan Speed Control — The WSHP Open controller
is capable of controlling up to three fan speeds using the ECM
(electronically commutated motor). The motor will operate at
the lowest speed possible to provide quiet and efficient fan op-
eration with the best latent capability. The motor will increase
speed if additional cooling or heating is required to obtain the
desired space temperature set point. The control increases the
motor's speed as the space temperature rises above the cooling
or below the heating set point. The amount of space tempera-
ture increase above or below the set point required to increase
the fan speed is user configurable in the set point. Also, the
control will increase the fan speed as the supply-air tempera-
ture approaches the configured minimum or maximum limits.
Fan Speed Control (During Heating) — Whenever heat is re-
quired and active, the control continuously monitors the sup-
ply-air temperature to verify it does not rise above the config-
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
°