Central Air Conditioners
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Introduction
Cooling residential and commercial buildings in California typically draws 30% of the state's peak summer energy demand. Heating and cooling can account for more than 40% of a homeowner’s or business' annual energy bill. By installing a new central air conditioner in your home or business, you can dramatically reduce your annual cooling costs, save electricity and reduce smog-causing emissions.
Technology Options
Air conditioners employ the same operating principles and basic components as a home refrigerator. An air conditioner cools a home with a cold indoor coil called the evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and condenser coils are serpentine tubing surrounded by aluminum fins. The tubing is usually made of copper. A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser by forcing the liquid refrigerant through the circuit of tubing and fins in the coils. The refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling the home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid and gives up its heat to the air flowing over the condenser's metal tubing and fins.
As an air conditioner cools the air, it also dehumidifies the air, because warm air passing over the indoor evaporator coil cannot hold as much moisture as it carried at a higher temperature, before it was cooled. The extra moisture condenses on the outside of the coils and is carried away through a drain.
There are two general types of central air conditioners: split systems and packaged systems.
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High-Efficiency Improvements
High-efficiency air conditioners usually contain one or more of the following technical improvements: High-efficiency compressors use less energy than traditional models to move the refrigerant; variable-speed fans can cycle between high speed (when cooling is most needed) and a lower speed for maintaining that cooling (this reduces on/off cycling, a major electrical draw); high-efficiency motors operate the fan using less electricity; and improved heat exchangers extract more heat out of the air that is drawn into the unit.
Efficiency Ratings
Air conditioners are rated by the number of British Thermal Units (Btu) of heat they can remove per hour. Another common rating term for air conditioning size is the "ton," which is 12,000 Btu per hour. Each air conditioner has an energy efficiency rating that lists how many Btu per hour are removed for each watt of power it draws. For central air conditioners, this is called the Energy Efficiency Ratio (EER) or the Seasonal Energy Efficiency Ratio (SEER), which is adjusted for a representative residential cooling load during the cooling season. The higher the EER/SEER, the more efficient the central air conditioner is.These ratings are posted on an EnergyGuide Label, which should be conspicuously attached to all new air conditioners.
National minimum standards for central air conditioners require a SEER of 13, but there is a wide selection of units with SEERs reaching up to 23.
Before 1979, the SEERs of central air conditioners ranged from 4.5 to 8.0. Replacing a 1970s-era central air conditioner having a SEER of 6 with a new unit having a SEER of 13 or better may cut your air conditioning costs in half.
ENERGY STAR publishes guides to the most energy-efficient appliances. Visit its Central Air Conditioning page for more information and efficiency ratings.
Efficiency Benefits
Central air conditioners that are in the top 25% of efficient models may carry the 'ENERGY STAR', label. To qualify, they must have a minimum SEER efficiency level of 14. Additionally, Energy Star® models must also have a minimum Energy Efficiency Ratio (EER) of at least 11.5 for split systems, and of at least 11.0 for single-package models. Air conditioners that bear the Energy Star® label may be twice as efficient as some existing systems. Today's best air conditioners use 30 to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20 to 40% of your cooling energy costs by replacing it with a newer, more efficient model. A new central air conditioner may also perform more quietly and provide better humidity control than your old model.
The Federal Energy Management Program (FEMP) of the U.S. Department of Energy (DOE) provides a cost-effectiveness calculator which you can use to calculate your projected savings. Below is an example comparing air conditioning units that meet the federal minimum standard, the ENERGY STAR standard and the best available efficiency product, for a home in San Diego. The values are based on a 3 ton central air conditioner with a 36,000 Btu/hour capacity, San Diego averages for cooling loads and California average electricity prices ($.12/kWh). Actual savings and energy use will vary with climate and usage.
Cost Comparison of Standard and ENERGY STAR Qualified Central Air Conditioners | |||
Performance | Federal Minimum | ENERGY STAR Minimum | Best Available |
SEER | 13.0 | 14.0 | 23.0 |
Annual Energy Cost | $470 | $436 | $266 |
Lifetime Energy Cost | $6,091 | $5,829 | $4,025 |
Lifetime Energy Cost Savings | - | $262 | $2,066 |
Use ENERGY STAR's central air conditioner calculator to estimate how much money and energy you can save with a highly efficient unit.
Manufacturers
York, Bryant, Carrier and Trane are some of the manufacturers of ENERGY STAR qualified central air conditioners. For a complete list, visit the ENERGY STAR website.
Purchasing Tips
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