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Heat Pumps
A heat pump can save as much as 30% to 40%
of the electricity you use for heating.
Why Buy An Energy Efficient Heat
Pump?
If you use electricity to heat your
home, consider installing an energy-efficient heat pump system. Heat pumps are
the most efficient form of electric heating in mild and moderate climates,
providing two to three times more heating than the equivalent amount of energy
they consume in electricity.
Air source heat pumps are recommended
for mild and moderate climate regions, where the winter temperatures usually
remain above 30°F. Ground source (also known as geothermal) heat pumps are
more efficient and economical to operate when compared to conventional air
source heat pumps, especially in climates with similar heating and cooling
loads.
About Heat Pump Efficiency
Three types of heat pumps are typically
available for residences: (1) air-to-air, (2) water source, and (3) ground
source. Heat pumps collect heat from the air, water, or ground outside your
home and concentrate it for use inside. Heat pumps operate in reverse to cool
your home by collecting the heat inside your house and effectively pumping it
outside.
Heat pumps have both heating and cooling
ratings-both in terms of capacity and efficiency. Capacity ratings are
generally in British thermal unit (Btu) per hour or tons (one ton equals
12,000 Btu/hr). Heating efficiency for air source heat pumps is indicated by
the heating season performance factor (HSPF). The HSPF tells you the ratio of
the seasonal heating output in Btu's divided by the seasonal power consumption
in Watt-hours. A heat pump can supply 2 to 3 times as much heat as it consumes
in electricity because it moves energy from ouside to inside (or vice versa).
Heat pump efficiency varies with outdoor temperature. The performance of an
air source heat pump in heating mode decreases with the drop in outside air
temperature. The actual seasonal efficiency (as opposed to the rating) is
therefore higher in a mild climate than in a severe cold climate.
In the cooling mode, a heat pump
operates exactly like a central air conditioner. The seasonal energy
efficiency ratio (SEER) is analogous to the HSPF but tells you the seasonal
cooling performance.
Federal efficiency standards require
that conventional heat pumps have an HSPF rating of at least 6.8 and a SEER
rating of at least 10.0. The most efficient air source heat pumps have an HSPF
rating between 9.0 and 10.0 and a SEER above 14 or so.
Tips for Buying a New Heat Pump
- Heat pumps must be sized and
installed properly to work efficiently. Heat pumps are sized for either
the heating demand or cooling demand, depending on which implies the
larger unit (almost always cooling). However, heat pumps do not perform
well over extended periods of sub-freezing temperature and it may not be
cost effective to meet all your heating needs with an air-source heat
pump.
- Ground source heat pumps (GSHPs) are
more efficient and less noisy than conventional air-source heat pumps.
Though GSHPs are more expensive to install, the dramatic improvement in
efficiency can yield attractive life cycle cost savings. However, the
appropriatenes of a GSHP depends on the size of your lot, the conditions
of the subsoil and landscape, and sometimes the relative magnitudes of
summer cooling and winter heating requirements.
- Select a heat pump with a higher HSPF.
For units with comparable HSPF ratings, check their steady-state rating at
-8.3°C, the low temperature setting. The unit with the higher rating will
be more efficient.
- Select a heat pump with a
demand-defrost control. This will minimize the defrost cycles thereby
reducing supplementary and heat pump energy use.
- Select a heat pump with an outdoor
sound rating of 7.6 bels or lower. The lower the value, the less noisy the
outdoor unit.
- If installing a heat pump in an
existing home without an existing heat pump or air conditioner, ductwork
may need to be enlarged. Heat pump systems generally require larger duct
sizes than other central heating systems. For proper heat pump operation,
air flow should be 50 to 60 liters per second per kilowatt-hour or 400 to
500 cubic foot per minute per ton of cooling capacity.
- If a heat pump is added to an
electric furnace, the heat pump coil can usually be placed on the cold
(upstream) side of the furnace for greatest efficiency.
- Fans and compressors make noise.
Locate the outdoor unit away from windows and adjacent buildings. Some
units also make noise when they vibrate. You can reduce this noise by
selecting quiet equipment or by mounting the unit on a noise-absorbing
base.
Tips for Lowering Your Heat
Pump's Energy Usage
- Do not manually set back a heat
pump's thermostat at night. Without a thermostat specifically designed for
heat pump set-back, the electric resistance backup heat will engage when
the thermostat is raised in the morning, resulting in much higher energy
consumption.
- Continuous indoor fan operation can
degrade heat pump performance unless a high-efficiency, variable-speed fan
motor is used. Operate the system on the "auto" fan setting on
the thermostat.
- Clean or change filters once a month
or as needed, and maintain the system according to manufacturer's
instructions. Filter and coil maintenance have a dramatic impact on system
performance and service life. Dirty filters, coils, and fans reduce
airflow through the system. Reduced airflow decreases system performance
and can lead to compressor damage if it continues for an extended period.
- Clean and lubricate the fan motor
annually to ensure the required airflow is provided for proper operation.
The fan speed should be checked at the same time. Incorrect pulley
settings, loose fan belts, or incorrect motor speeds can all contribute to
poor performance.
- Outdoor units should be protected
from high winds. High winds may reduce efficiency by causing defrost
problems. However, outdoor units should not be placed in restricted areas
that will result in recirculation of air over the coil.
U.S. Department of Energy
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Pumps
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