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Central Air
Conditioners
The indoor coil in your air conditioner
acts as a magnet for dust because it is constantly wetted during the cooling
season. Dirt build-up on the indoor coil is the single most common cause of poor
efficiency.
Why Buy An Energy
Efficient Central Air Conditioner?
- Central A/C units are more efficient
than window or through-the-wall units. They are also out of the way,
quiet, and convenient to operate.
- High-efficiency A/C units save money
on your utility bills.
- High-efficiency A/C units result in
fewer environmentally harmful emissions.
In an average air conditioned home, air
conditioning consumes more than 2000 kilowatt-hours of electricity per year,
causing about 3,500 pounds of carbon dioxide and 31 pounds of sulfur dioxide
to be emitted at the power plant and, at average electricity prices, costs you
about $150. In high-cooling climates those numbers can be doubled or even
higher.
About Central Air Conditioner
Efficiency
Central air conditioners use electric
energy to pump heat out of your home and dump it outside. They distribute
cooled air throughout your house and remove moisture from the indoor air.
The efficiency of Central A/C units is
governed by U.S. law and regulated by the U.S. Department of Energy. Every A/C
unit is assigned an efficiency rating known as its seasonal energy efficiency
ratio (SEER). The SEER is defined as the total cooling output (in Btu-British
thermal units) provided by the unit during its normal annual usage period
divided by its total energy input (in Watt-hours) during the same period.
The SEER is displayed on a yellow label
affixed to the A/C unit. Higher SEERs are better. The minimum SEER allowed by
law for a central A/C is 10 for a split system or 9.7 for a single-package
unit. The best available SEER is about 18, while many older units have SEER
ratings of 6 or less. Most consumers should look for a SEER of 12 or higher
when buying a new A/C system.
Tips for Buying a New Central
Air Conditioner
- The type and size of air conditioner
you need depends on your climate and cooling loads. Evaporative coolers
are practical in hot, arid regions such as the southwest. For other
regions, compressor-driven air-conditioning systems are the only choice.
- When you are shopping for a central
air conditioner, look for a SEER rating higher than 12.0.
- If you already have a forced-air
heating system, you may be able to tie an air conditioner into existing
ducts, depending on their size and your home's relative heating and
cooling loads. A good HVAC contractor can do the calculations for you.
- Proper sizing and installation are
key elements in determining air conditioner efficiency. Too large a unit
will not adequately remove humidity. Too small a unit will not be able to
maintain a comfortable temperature on the hottest days. Improper unit
location, lack of duct insulation, improper duct sealing, and incorrect
refrigerant charge can greatly diminish efficiency
- When buying a central air
conditioner, look for a system with a fan-only switch so you can use the
unit for nighttime ventilation to substantially reduce air-conditioning
costs; a filter check light to remind you to check the filter after a
predetermined number of operating hours; and an automatic-delay fan switch
to turn off the fan a few minutes after the compressor turns off.
- Look for a unit with quiet operation.
- If you need or want to replace your
existing air conditioner's outdoor (compressor) unit, make sure the indoor
(blower coil) unit is compatible with the new outdoor unit. A highly
efficient outdoor unit will not achieve its rated efficiency if paired
with an older blower coil.
Tips for Lowering Your Central
Air Conditioner's Energy Usage
- Set your thermostat at 78 F or
higher. Each degree setting below 78 F will increase energy consumption by
approximately 8%. Be careful, however, that if you're A/C is oversized the
diminished run-time from raising the thermostat setting may result in
too-high indoor humidity in some locations.
- Use bath and kitchen fans sparingly
when the air conditioner is operating to avoid pulling warm, moist air
into your home.
- Inspect and clean both the indoor and
outdoor coils. The indoor coil in your air conditioner acts as a magnet
for dust because it is constantly wetted during the cooling season. Dirt
build-up on the indoor coil is the single most common cause of poor
efficiency. The outdoor coil must also be checked periodically for dirt
build-up and cleaned if necessary.
- Check the refrigerant charge. The
circulating fluid in your air conditioner is a special refrigerant gas
that is put in when the system is installed. If the system is overcharged
or undercharged with refrigerant, it will not work properly. You will need
a service contractor to check the fluid and adjust it appropriately.
- Reduce the cooling load by using
cost-effective conservation measures. For example, effectively shade east
and west windows. When possible, delay heat-generating activities, such as
cooking and dishwashing, until evening on hot days.
- Over most of the cooling season, keep
the house closed tight during the day. Don't let in unwanted heat and
humidity. Ventilate at night either naturally or with fans.
U.S. Department of Energy
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Home Information>Central
Air Conditioners
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