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19
Heat Pumps and Energy
Savings
• GE Zoneline Heat Pumps are designed to provide cost
efficient heat pump operation while monitoring room
conditions to maintain comfort.
The units employ a logic system monitoring both outdoor
and indoor temperatures to determine the heat source, thus
increasing energy savings by operating longer in the heat
pump mode.
Heat pumps save energy and cost less to operate than units
with electric resistance heaters as the only heat source. Just
as the EER of an air conditioner is an indication of the
efficiency of the unit, COP (Coefficient of Performance) is
the indication of the efficiency of the heat pump. This
relative efficiency of a heat pump compares the unit to
electric resistance heat. If a unit has a COP of 3.0, it means
the unit will produce three times as much heat at rating
conditions for the same electrical input wattage used for
electric resistance heat.
The compressor is used in heat pump operation just as in air
conditioning operation. In heat pump operation, the hot
refrigerant gas is directed to the indoor coil rather than to
the outdoor coil. Room air that circulates over the indoor
coil gains heat from the coil rather than losing heat to the
coil as during cooling operation.
As the outdoor temperature falls, the heat pump is able to
extract less heat from the outdoor air to raise the
temperature of the indoor air. For this reason, all packaged
terminal heat pumps also have electric resistance heaters as
backup to heat pump operation. At some point, the heat
pump is unable to provide sufficient heat to adequately
warm the room. Many Packaged Terminal Heat Pumps cease
heat pump operation and change to more expensive
resistance heat at some pre-determined outdoor
temperature to compensate for the inability of the heat
pump to maintain room temperature. This point, called the
“switchover point”, is usually at an outdoor temperature
where savings from heat pump operation may still be
realized, if the unit is designed to maintain room comfort at
the lower outdoor temperatures.
Balance Point
An important consideration of the selection of a heat pump
unit is the “balance point” of the installation. Virtually every
room is unique - with different insulation - different sizes
and types of windows - different types of construction -
different directional exposures. All of these variables, as well
as geographical location, must be considered in order to
determine the balance point, the point at which the heat
pump is unable to produce enough heat to compensate for
the heat loss of the room or area being heated. For these
reasons a consulting engineer should be engaged to
calculate the heat loss and specify the heat pump unit
required.
GE offers two series of Zoneline Heat Pump units - the 3500
Series with Standard Microprocessor controls and the 5500
Series with Highly Featured Microprocessor controls - and
both series react to the indoor temperature as well as the
outdoor temperature in determining the heat source to
provide comfortable room conditions and energy savings.
This determination of the heat source based on the indoor
temperature helps provide a more comfortable room.
• Heat Pump Operation - Zoneline 3500 Series
Switchover to resistance heat is determined by indoor
temperature differential and outdoor coil temperature
The Zoneline 3500 Series heat pumps are Standard
Microprocessor controlled units. A solid state thermostat
control is used to measure the room temperature and
compare it to the temperature selected with the “TEMP”
control knob. A temperature sensor is in contact with the
outdoor coil to monitor the outdoor coil temperature
during heat pump operation.
The switchover point of the 3500 Series heat pump is
determined by the outdoor coil temperature or the indoor
air temperature. When the outdoor coil temperature is
above 9°F. (which corresponds to approximately 25°F.
outdoor air temperature), the unit attempts to provide
sufficient heat through heat pump operation to satisfy the
selected temperature setting.
The microprocessor monitors the indoor room temperature
and determines if the heat pump output is adequate to
maintain comfort conditions. As long as the heat pump
output maintains the room temperature within 2.7°F of the
set point, the unit will operate in the heat pump mode. If
the room temperature continues to decline with the heat
pump operating, heat pump operation will terminate and
the unit will switch over to electric resistance heat to warm
the room. This heat source logic allows the heat pump to
operate to lower outdoor temperatures, increasing the
savings from heat pump operation, while providing the
ability to use resistance heat only when necessary. The heat
pump and the electric resistance heaters never operate
simultaneously on the Zoneline 3500 Series Units.
A heat pump override switch is provided in the auxiliary
controls to allow the unit to operate only in resistance heat.
The use of this option significantly increases the cost for
heating.
Heat pump defrost - Zoneline 3500 Series
If the outdoor coil drops below 9°F. (which corresponds to
approximately 25°F. outdoor air temperature), the unit
employs a passive defrost system. A “passive defrost system”
prevents heat pump operation until outdoor temperatures
rise sufficiently to enable economical heat pump operation
to resume. During the defrost mode, the indoor
temperature is maintained by the electric resistance heater.
The defrost cycle terminates when the outdoor coil
temperature rises above 36°F., at which point the
microprocessor will allow the unit to return to economical
heat pump operation.
Heat pump condensate
See page 34 for information on heat pump condensate. The
Zoneline 3500 Series heat pumps may be ordered with a
factory installed Internal Condensate Removal (ICR) system
to minimize the amount of condensate water draining from
the unit during heat pump operation. The ICR system has
proven to be an effective means of minimizing the amount
of heat pump condensate dripping from the unit. However,
if the requirements of a particular installation will allow no
dripping of condensate water from the wall case, the
installation of an internal or external drain system is
recommended.
Units with ICR may not be installed in seacoast or corrosive
environment applications.
2020 Data Manual 2002 11/7/02 3:19 PM Page 19
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