Heat Pumps Pay Their Own Way - Carrier PREMIER 52P SERIES Architects And Engineers' Manual

PRODUCT FEATURES AND BENEFITS (cont)
HEAT PUMPS PAY THEIR
OWN WAY
Heat pump models are available at a nominal addi-
tional cost. In many locales, the payback is realized in
just a few months. Cost and payback details are pro-
vided on the next page.
Special Features
Two-Stage Indoor Thermostat:
The indoor thermostat senses the indoor temperature
and automatically turns on the electric heat to warm
the room quickly. After the desired temperature condi-
tions have been satisfied, the thermostat automatically
switches to heat pump mode. If compressor failure
occurs, the thermostat will provide backup electric
heat automatically.
Outdoor Thermostat:
During the heating cycle, the outdoor thermostat
senses outdoor coil temperature. It switches the unit to
electric heat mode when the outdoor coil temperature
is 20 F or below (approximately 35 F outdoor-air tem-
perature). The thermostat switches the unit back to
heat pump mode when the outdoor coil temperature
rises above 40 F, which is enough to provide heat
to meet demand. The entire operation is completely
automatic.
Reversing Valve:
The reversing valve provides quiet refrigerant flow
after the unit shuts off. The valve controls the direction
of refrigerant flow for both heating and cooling func-
tions and remains energized as long as the controls are
in the heat position. When the cooling controls are
activated, the valve automatically reverses to the cool-
ing position.
Manual Compressor Override Switch:
This switch completely locks out the compressor. Note
that the compressor and heater do not operate at the
same time, thus conserving energy.
How The Heat Pump Works
In Hot Weather:
Carrier's PTAC units provide indoor comfort in the
same manner as conventional air conditioners, remov-
ing heat and humidity from indoor air. The heat and
humidity is released to the outdoors. Carrier's high-
efficiency design saves energy and reduces cooling
costs.
In Cool Weather:
When the outdoor coil temperature is above 20 F
(approximately 35 F outdoor-air temperature), the
heat pump draws heat from outdoor air and uses it to
heat indoor air. Since heat is transferred and not pro-
duced, Carrier's heat pump uses less electricity and
reduces energy costs significantly.
In Sub-Freezing Weather:
When the outdoor coil temperature falls below 20 F
(approximately 35 F outdoor-air temperature), the
unit automatically switches on a built-in electric
heater. The compressor stops and a blower circulates
warm air produced by the heater. When the outdoor
coil temperature rises above 40 F, heat pump operation
resumes automatically.
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