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OPERATION
Power Up Mode
The unit will not operate until all the inputs, terminals and safety
controls are checked for normal operation.
NOTE: The compressor will have a 5-minute anti-short cycle
upon power up.
Unit Protection Module (UPM)
Figure 39 shows the UPM sequence of operations for unit safeties.
All 50PC units are equipped with a UPM.
Units with Better B, Complete C, or
Deluxe D Controls
STANDBY
Y and W terminals are not active in Standby mode; however, the
O and G terminals may be active, depending on the application.
The compressor will be off.
COOLING
Y and O terminals are active in Cooling mode. After power up, the
first call to the compressor will initiate a 270 to 300 second random
start delay and a 5-minute anti-short cycle protection time delay.
After both delays are complete, the compressor is energized.
NOTE: On all subsequent compressor calls the random start delay
is omitted.
HEATING STAGE 1
Terminal Y is active in heating stage 1. After power up, the first
call to the compressor will initiate a 270 to 300 second random
start delay and a 5-minute anti-short cycle protection time delay.
After both delays are complete, the compressor is energized.
NOTE: On all subsequent compressor calls the random start delay
is omitted.
HOT GAS REHEAT (OPTIONAL FOR COMPLETE C OR
DELUXE D CONTROLS)
Terminal H is active in dehumidification mode with hot gas
reheat. After a call for H, the reversing valve (O), compressor (Y),
and fan (G) are also enabled.
NOTE: Any call for cooling (Y), heating (Y or W), or reversing
valve (O) will override dehumidification mode (H).
WATERSIDE ECONOMIZER (OPTIONAL FOR COMPLETE
C OR DELUXE D CONTROLS)
Y and O terminals are active in Cooling mode. When the entering
water temperature drops below the entering water temperature set
point on the waterside economizer Aquastat, the compressor and
reversing valve are disabled and the waterside economizer is
enabled. The waterside economizer three way control valve will
divert water to the economizer coil for free cooling. When the
entering water temperature rises above the Aquastat set point, the
waterside economizer is disabled and the compressor and
reversing valve are enabled.
TWO WAY WATER FLOW CONTROL VALVE (OPTIONAL)
The two way water flow control valve is enabled anytime there is
a call for cooling (Y), heating (Y), or dehumidification (H) and
allows water to flow through the unit. When there is no call for
cooling, heating, or dehumidification, the water flow control valve
is disabled, stopping flow through the unit.
BOILERLESS HEAT (DELUXE D ONLY)
When the entering water temperature is below the boilerless heat
Aquastat entering water temperature set point and there is a call
for heating (Y), the compressor is disabled and the auxiliary heat
output is enabled. When the entering water temperature is above
the Aquastat set point, the auxiliary heat output is disabled and the
compressor is enabled.
PUMP/VALVE RELAY (DELUXE D ONLY)
The pump/valve relay is enabled anytime there is a call for cool-
ing (Y), heating (Y), or dehumidification (H) and can be used to
enable/disable field installed flow control valves or circulator
pumps. When there is no call for cooling, heating, or
dehumidification, pump/valve relay is disabled.
Units with WSHP Open Controls
Units with WSHP Open still feature a UPM board for unit
operation, so the operation will be similar to the sequence for
the other control packages. WSHP Open does feature advanced
functionality, such as automatic fan speed control and intelli-
gent alarming, which will differ from the other control packag-
es. Below is an overview of the different features for the
WSHP Open controls. For more details of the WHSP Open op-
eration, please refer to the WSHP Open Integration Guide and
the WSHP Points/Properties Manual. See Fig. 40 for WSHP
Open Control Board overview.
COOLING
The control will operate one or two stages of compression to
maintain
the
desired
dehumidification and reduce noise, the control operates the fan at
the lowest speed possible to satisfy the load conditions. 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 in-
sufficient and if the SAT falls further (equal to the minimum SAT
limit), the fan will be indexed to the maximum speed. If the SAT
still continues to falls 5 degrees below the minimum SAT limit, all
cooling stages will be disabled.
During Cooling, 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
opposite mode is required.
REVERSE CYCLE HEATING
The control will operate one or two stages of compression to
maintain the desired heating set point. To reduce noise, the control
operates the fan at the lowest speed possible. 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, then if the SAT rises further and reaches 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, 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
opposite mode is required.
TWO POSITION OA DAMPER
The control can be configured to operate a 2-position ventilation
damper to provide the minimum ventilation requirements during
occupied periods.
MODULATING OA DAMPER WITH DCV
The control can be configured to operate a modulating ventilation
damper during occupied periods that responds to changing CO
levels from an optional sensor. The control monitors the CO
and compares it to the configured set points and adjusts the
ventilation rate as required. The control provides proportional
ventilation to meet the requirements of ASHRAE specifications
by providing a base ventilation rate and then increasing the rate as
the CO
level increases. The control has three user adjustable set
2
points; start ventilation maximum ventilation and maximum
damper position. The control will begin to proportionally increase
ventilation when the CO
point and will reach the full ventilation rate (maximum damper
position) when the CO
point. A user configurable minimum damper position ensures that
proper base ventilation is delivered when occupants are not
present.
51
cooling
set
point. To
level rises above the start ventilation set
2
level is at or above the maximum set
2
improve
2
level
2
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