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 Air Conditioner units are more efficient than window or through-the-wall units resulting in fewer environmentally harmful emissions while saving you money. They are also out of the way, quiet, and convenient to operate.

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 warmer seasons and 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 13 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 must consider a SEER of 13 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 13.0.
• 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 78ºF or higher. Each degree setting below 78ºF 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.

Source: U.S. Department of Energy