Carrier AQUAZONE PSV - Manual (Page 45)

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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 config-
urable). The heat will be controlled so the SAT will not exceed
the maximum heating SAT limit.
Auxiliary Modulating Hot Water/Steam Heating Reheat
— The control can modulate a hot water or steam valve con-
nected to a coil on the discharge side of the unit and supplied
by a boiler in order to maintain the desired heating set point
should the compressor capacity be insufficient or a compressor
failure occurs. Unless a compressor fault condition exists, the
valve 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 valve will be con-
trolled so the SAT will not exceed the maximum heating SAT
limit.
Two-Position Hot Water/Steam Heating Reheat — The con-
trol can operate a two-position, NO or NC, hot water or steam
valve connected to a coil on the discharge side of the unit and
supplied by a boiler in order to maintain the desired heating set
point should the compressor capacity be insufficient or a com-
pressor failure occurs. Unless a compressor fault condition ex-
ists, the valve will only open to supplement the heat provided
by the compressor if the space temperature falls more than one
degree below the desired heating set point. The valve will be
controlled so the SAT will not exceed the maximum heating
SAT limit. The heat stage will also be subject to a 2-minute
minimum OFF time to prevent excessive valve cycling.
Single Stage Electric Auxiliary Heat — The control can op-
erate a field-installed single stage of electric heat installed on
the discharge side of the unit in order to maintain the desired
heating set point should the compressor capacity be insufficient
or a compressor failure occurs. Unless a compressor fault con-
dition exists, the heat stage 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
heat stage will be controlled so the SAT will not exceed the
maximum heating SAT limit. The heat stage will also be sub-
ject to a 2-minute minimum OFF time to prevent excessive
cycling.
INDOOR AIR QUALITY (IAQ) AND DEMAND CON-
TROLLED VENTILATION (DCV) — If the optional in-
door air quality sensor is installed, the WSHP Open controller
can maintain indoor air quality via a modulating OA damper
providing demand controlled ventilation. The control operates
the modulating OA damper during occupied periods. The con-
trol monitors the CO
2
level and compares it to the configured
set points, adjusting the ventilation rate as required. The control
provides proportional ventilation to meet the requirements of
ASHRAE (American Society of Heating, Refrigerating and
Air Conditioning Engineers) specifications by providing a base
ventilation rate and then increasing the rate as the CO
2
level in-
creases. The control will begin to proportionally increase venti-
lation when the CO
2
level rises above the start ventilation set
point and will reach the full ventilation rate when the CO
2
level
is at or above the maximum set point. A user-configurable min-
imum damper position ensures that proper base ventilation is
delivered when occupants are not present. The IAQ configura-
tions can be accessed through the configuration screen. The
following conditions must be true in order for this algorithm to
run:
• Damper control is configured for DCV.
• The unit is in an occupied mode.
• The IAQ sensor reading is greater than the DCV start
control set point.
The control has four user adjustable set points: DCV start
control set point, DCV maximum control set point, minimum
damper position, and DCV maximum damper position.
Two-Position OA Damper — The control can be configured
to operate a ventilation damper in a two-position ventilation
mode to provide the minimum ventilation requirements during
occupied periods.
DEHUMIDIFCATION — The WSHP Open controller will
provide occupied and unoccupied dehumidification only on
units that are equipped with the modulating hot water reheat
(HWR) option. This function requires an accessory space rela-
tive humidity sensor. When using a relative humidity sensor to
control dehumidification during occupied or unoccupied times,
the dehumidification set points are used accordingly. When the
indoor relative humidity becomes greater than the dehumidifi-
cation set point, a dehumidification demand will be acknowl-
edged. Once acknowledged, the dehumidification output will
be energized, bringing on the supply fan (medium speed), me-
chanical cooling, and the integral hot water reheat coil. The
controls will engage Cooling mode and waste heat from the
compressor cooling cycle will be returned to the reheat coil si-
multaneously, meaning that the reversing valve is causing the
compressor to operate in the Cooling mode. During Cooling
mode, the unit cools, dehumidifies, and disables the HWR coil;
however, once the call for cooling has been satisfied and there
is still a call for dehumidification, the unit will continue to op-
erate using the Reheat mode and HWR coil.
WATERSIDE ECONOMIZER — The WSHP Open control-
ler has the capability of providing modulating or two-position
water economizer operation (for a field-installed economizer
coil mounted to the entering air side of the unit and connected
to the condenser water loop) in order to provide free cooling
(or preheating) when water conditions are optimal. Water econ-
omizer settings can be accessed through the equipment status
°