Refrigerating air for comfort inside the home, (called air conditioning) is far more complicated than heating. Instead of using energy to create heat, air conditioners use energy to remove heat. The most common air conditioning systems use what is known as a vapor-compression cycle similar to the one used by a refrigerator. The primary difference is a refrigerator moves heat out of its interior and releases it to the surroundings, (usually the kitchen), while air conditioners take heat from inside the house and release it to the outside environment.
Air conditioners use about 5% of all the electricity produced in the United States, at a cost of over $11 billion to homeowners. As a result, roughly 100 million tons of carbon dioxide are released into the air each year – an average of about two tons for each home with an air conditioner. Switching to high-efficiency air conditioners and taking other actions to keep your home cool could reduce this energy use by 20-50%. See also air conditioning.
How it works
An air conditioner cools your 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. This tubing is usually made of copper.
A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils.
The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling your home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid, giving up its heat to the outside air flowing over the condenser's metal tubing and fins.
Throughout the second half of the 20th century, nearly all air conditioners used chlorofluorocarbons (CFCs) as their refrigerant, but because these chemicals are damaging to Earth's ozone layer, CFC production stopped in the United States in 1995. Nearly all air conditioning systems now employ halogenated chlorofluorocarbons (HCFCs) as a refrigerant, but these are also being gradually phased out, with most production and importing stopped by 2020 and all production and importing stopped by 2030.
Production and importing of today's main refrigerant for home air conditioners, HCFC-22 (also called R-22), will begin to be phased out in 2010 and will stop entirely by 2020. However, HCFC-22 is expected to be available for many years as it is recovered from old systems that are taken out of service. As these refrigerants are phased out, ozone-safe hydrofluorocarbons (HFCs) are expected to dominate the market, as well as alternative refrigerants such as ammonia.
MaintenanceAn 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 filtersThe 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. Keeping the filter clean can lower your air conditioner's energy consumption by 5-15%.
For central air conditioners, filters are generally located somewhere along the return duct's length. Common filter locations are in walls, ceilings, furnaces, or in the air conditioner itself. Room air conditioners have a filter mounted in the grill that faces into the room.
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 coilsThe 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, reducing its ability to absorb heat. To avoid this problem, check your evaporator coil every year and clean it 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 finsThe 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.
Condensate drainsOccasionally pass a stiff wire through the unit's drain channels. Clogged drain channels prevent a unit from reducing humidity, and the resulting excess moisture may discolor walls or carpet.
Window seals for room air conditionersAt the start of each cooling season, inspect the seal between the air conditioner and the window frame to ensure it makes contact with the unit's metal case. Moisture can damage this seal, allowing cool air to escape from your house.
Preparing for winterIn the winter, either cover your room air conditioner or remove and store it. Covering the outdoor unit of a central air conditioner will protect the unit from winter weather and debris.
Common problems with air conditionersOne 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. For room air conditioners, isolate the room or a group of connected rooms as much as possible from the rest of your home.
Other common problems with existing air conditioners result from faulty installation, poor service procedures, and inadequate maintenance. Improper installation of a central air conditioner can result in leaky ducts and low airflow. 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. Unqualified 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, begin by checking any fuses or circuit breakers. Let the unit cool down for about five minutes before resetting any breakers. If a central air conditioner's compressor stops on a hot day, the high-pressure limit switch may have tripped; reset it by pushing the button, located in the compressor's access panel. Other common reasons for air conditioner failures are listed below.
Refrigerant leaksIf 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. Refrigerant leaks can also be harmful to the environment.
Inadequate maintenanceIf 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 failureThe 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.
Sensor problemsRoom air conditioners feature a thermostat sensor, located behind the control panel, which measures the temperature of air coming into the evaporative coil. If the sensor is knocked out of position, the air conditioner could cycle constantly or behave erratically. The sensor should be near the coil but not touching it; adjust its position by carefully bending the wire that holds it in place.
Drainage problemsWhen it's humid outside, check the condensate drain to make sure it isn't clogged and is draining properly. Room air conditioners may not drain properly if not mounted level.
Types of air conditioner
Central air conditionerA central air conditioner circulates conditioned air throughout the various rooms of a building via a system of supply and return ducts. A central air conditioner is either a split-system unit or a packaged unit.
Window air conditionerA window air conditioner, or room air conditioner, fits into a standard size window opening and is used to condition the air in a single room rather than an entire home or business. Because they provide cooling only where needed, window air conditioners are less expensive to operate than central units, although their efficiency is generally lower.
Portable air conditionerA portable air conditioner is a relatively small unit that stands inside a room and has a hose to convey heated air, through an opening in an exterior wall, to the outside.
Related category• COOLING, REFRIGERATION, AND AIR CONDITIONING
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