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Energy Efficient Air-Conditioning

Summary: This section will provide you with information on how to make your air-conditioning system more energy efficient. Are you considering buying a new air-conditioner? Or, are you dissatisfied with the operation of your current air-conditioner? Are you unsure whether to fix or replace it? Are you concerned about high summer utility bills? If you answered yes to any of these questions, this section can help. With it, you can learn about various types of air-conditioning systems and how to maintain your air-conditioner, hire professional air-conditioning services, select a new air-conditioner, and ensure that your new air-conditioner is properly installed.

Understanding Air-conditioners: Many people buy or use air-conditioners without understanding their designs, components, and operating principles. Proper sizing, selection, installation, maintenance, and correct use are keys to cost-effective operation and lower overall costs.

Maintaining Existing Air-conditioners: Older air-conditioners may still be able to offer years of relatively efficient use. However, making your older air-conditioner last requires you to perform proper operation and maintenance.

Air-conditioning Problems: One of the most common air-conditioning problems is improper operation. If your air-conditioner is on, be sure to close your home's windows and outside doors. Other common problems with existing air-conditioners result from faulty installation, poor service procedures, and inadequate maintenance. Improper installation of your air-conditioner can result in leaky ducts and low air flow. Many times, the refrigerant charge (the amount of refrigerant in the system) does not match the manufacturer's specifications. If proper refrigerant charging is not performed during installation, the performance and efficiency of the unit is impaired. Service technicians often fail to find refrigerant charging problems or even worsen existing problems by adding refrigerant to a system that is already full. Air-conditioner manufacturers generally make rugged, high quality products. If your air-conditioner fails, it is usually for one of the common reasons listed below:

Refrigerant leaks. If your air-conditioner is low on refrigerant, either it was undercharged at installation, or it leaks. If it leaks, simply adding refrigerant is not a solution. A trained technician should fix any leak, test the repair, and then charge the system with the correct amount of refrigerant. Remember that the performance and efficiency of your air-conditioner is greatest when the refrigerant charge exactly matches the manufacturer's specification, and is neither undercharged nor overcharged.

Inadequate maintenance. If you allow filters and air-conditioning coils to become dirty, the air-conditioner will not work properly, and the compressor or fans are likely to fail prematurely.

Electric control failure. The compressor and fan controls can wear out, especially when the air-conditioner turns on and off frequently, as is common when a system is oversized. Because corrosion of wire and terminals is also a problem in many systems, electrical connections and contacts should be checked during a professional service call.

Regular Maintenance: An air-conditioner's filters, coils, and fins require regular maintenance for the unit to function effectively and efficiently throughout its years of service. Neglecting necessary maintenance ensures a steady decline in air-conditioning performance while energy use steadily increases.

Air-conditioner Filters: The most important maintenance task that will ensure the efficiency of your air-conditioner is to routinely replace or clean its filters. Clogged, dirty filters block normal air flow and reduce a system's efficiency significantly. With normal air flow obstructed, air that bypasses the filter may carry dirt directly into the evaporator coil and impair the coil's heat-absorbing capacity. Filters are located somewhere along the return duct's length. Common filter locations are in walls, ceilings, furnaces, or in the air-conditioner itself. Some types of filters are reusable; others must be replaced. They are available in a variety of types and efficiencies. Clean or replace your air-conditioning system's filter or filters every month or two during the cooling season. Filters may need more frequent attention if the air-conditioner is in constant use, is subjected to dusty conditions, or you have fur-bearing pets in the house.

Air-conditioner Coils: The air-conditioner's evaporator coil and condenser coil collect dirt over their months and years of service. A clean filter prevents the evaporator coil from soiling quickly. In time, however, the evaporator coil will still collect dirt. This dirt reduces air flow and insulates the coil which reduces its ability to absorb heat. Therefore, your evaporator coil should be checked every year and cleaned as necessary. Outdoor condenser coils can also become very dirty if the outdoor environment is dusty or if there is foliage nearby. You can easily see the condenser coil and notice if dirt is collecting on its fins. You should minimize dirt and debris near the condenser unit. Your dryer vents, falling leaves, and lawn mower are all potential sources of dirt and debris. Cleaning the area around the coil, removing any debris, and trimming foliage back at least 2 feet (0.6 meters) allow for adequate air flow around the condenser.

Coil Fins: The aluminum fins on evaporator and condenser coils are easily bent and can block air flow through the coil. Air-conditioning wholesalers sell a tool called a "fin comb" that will comb these fins back into nearly original condition.

Sealing and Insulating Air Ducts: An enormous waste of energy occurs when cooled air escapes from supply ducts or when hot attic air leaks into return ducts. Recent studies indicate that 10% to 30% of the conditioned air in an average central air-conditioning system escapes from the ducts. For central air-conditioning to be efficient, ducts must be airtight. Hiring a competent professional service technician to detect and correct duct leaks is a good investment, since leaky ducts may be difficult to find without experience and test equipment. Ducts must be sealed with duct "mastic." The old standby of duct tape is ineffective for sealing ducts. See section Ductwork.

Obstructions can impair the efficiency of a duct system almost as much as leaks. You should be careful not to obstruct the flow of air from supply or return registers with furniture, drapes, or tightly fitted interior doors. Dirty filters and clogged evaporator coils can also be major obstructions to air flow.

The large temperature difference between attics and ducts makes heat conduction through ducts almost as big a problem as air leakage and obstructions. Ducts in attics should be insulated heavily in addition to being made airtight.

Buying New Air-conditioners: 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. See section How To Buy Energy Efficient Central Air-Conditioners.

Sizing Air-conditioners: 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. See section Sizing Heating And Air-Conditioning Systems.

  • How big should your air-conditioner be? The size of an air-conditioner depends on:

  • How large your home is and how many windows it has;

  • How much shade is on your home's windows, walls, and roof;

  • How much insulation is in your home's ceiling and walls;

  • How much air leaks into your home from the outside; and

  • How much heat the occupants and appliances in your home generate.

An air-conditioner's efficiency, performance, durability, and initial cost depend on matching its size to the above factors. Make sure you buy the correct size of air-conditioner. Two groups-the Air-conditioning Contractors of America (ACCA) and the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE)-publish calculation procedures for sizing central air-conditioners. Reputable air-conditioning contractors will use one of these procedures, often performed with the aid of a computer, to size your new central air-conditioner. Be aware that a large air-conditioner will not provide the best cooling. Buying an oversized air-conditioner penalizes you in the following ways:

  • It costs more to buy a larger air-conditioner than you need.

  • The larger-than-necessary air-conditioner cycles on and off more frequently, reducing its efficiency. Frequent cycling makes indoor temperatures fluctuate more and results in a less comfortable environment. Frequent cycling also inhibits moisture removal. In humid climates, removing moisture is essential for acceptable comfort. In addition, this cycling wears out the compressor and electrical parts more rapidly.

  • A larger air-conditioner uses more electricity and creates added demands on electrical generation and delivery systems.

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