Honeywell PC8900A Manual page 36

Heat Pump Recovery
In Mild Weather
When outdoor temperature is mild; for example 50°F (10°C),
the recovery from energy savings is handled completely by
the heat pump, without the need for auxiliary heat. The heat
pump starts only after the setpoint has risen above the sensed
temperature and is locked on until the comfort setpoint is
reached. See Fig. 36.
COMPRESSOR:
AUXILIARY HEAT:
Fig. 36. Adaptive Intelligent Recovery™ ramp for
a heat pump in mild weather (50°F).
In Moderate Weather
When outdoor temperature is close to the balance point of the
heat pump, the heat pump runs continuously during the
recovery period and auxiliary heat cycles if necessary.
See Fig. 37.
COMPRESSOR:
AUXILIARY HEAT:
Fig. 37. Adaptive Intelligent Recovery™ ramp for
a heat pump in moderate weather (20°F).
In Severe Weather
When the outdoor temperature is below the balance point of
the heat pump, the heat pump and auxiliary heat run
continuously in the recovery period. See Fig. 38.
68-0173—3
COMPRESSOR
SETPOINT
AUXILIARY
HEAT SETPOINT
ROOM
TEMPERATURE
WAKE
ON
OFF
ON
OFF
M6187
COMPRESSOR
SETPOINT
AUXILIARY
HEAT SETPOINT
ROOM
TEMPERATURE
WAKE
ON
OFF
ON
OFF
M6188
COMPRESSOR:
AUXILIARY
HEAT:
M6189
Fig. 38. Adaptive Intelligent Recovery™ ramp for
a heat pump in severe weather (0°F).
Comfort Period
In mild weather, the heat pump cycles continuously to
maintain the sensed temperature within 1°F of the setpoint. In
moderate weather, the heat pump cycles longer, minimizing
the need for auxiliary heat. The heat pump runs the majority of
the time in severe weather and only shuts off for brief periods
using auxiliary heat to maintain temperature within 1°F of
setpoint. See Fig. 36 through 38.
THERMAL PERFORMANCE
During severe weather, the PC8900A actually controls closer
to the setpoint than a conventional control. This is because
the heat anticipator is replaced by two electronic control
strategies—cycling by heat anticipation and proportional plus
integral (P+I) control.
Electronic cycling by heat anticipation acts like a traditional
heat anticipator except that it never needs adjusting for
various control circuit load currents. It cycles off the heating
system slightly before the room temperature reaches the
setpoint to keep heat that remains in the ductwork from
overheating the room.
In severe weather, a conventional control with a heat
anticipator tends to turn off the system too soon so the
effective setpoint is somewhat below the setpoint. In very cold
weather, the difference between setpoint and effective control
point can be 5°F or 6°F (2°C or 3°C) with a conventional
control. This phenomenon is called droop .
Proportional plus integral action eliminates droop by adjusting
the on time of the stage until the control point matches the
setpoint. The PC8900A maintains the space temperature
within 1°F of the setpoint when the temperature has stabilized
after an energy saving period.
This zero droop performance provides improved occupant
comfort and energy savings. Occupants do not need to
continually adjust thermostat settings to maintain desired
temperature, even during severe weather.
Remote Communications
Adding the CM8900A Communications Module and the
W8735B Telephone Access Module gives the PC8900A/
W8900A-C remote communications. Users are able to control
36
COMPRESSOR
SETPOINT
AUXILIARY
HEAT SETPOINT
ROOM
TEMPERATURE
WAKE
ON
OFF
ON
OFF