Air Conditioning How Air Conditioners Work. Much like the refrigerator in your kitchen, an air conditioner uses energy to transfer heat from the interior of your home to the relatively warm outside environment.
An air conditioner uses two serpentine tubing coils (usually made of copper) surrounded by aluminum fins and a liquid refrigerant to do the work of cooling your home and dispersing collected heat. A compressor (or pump) forces heat-transferring fluid (refrigerant) through the closed circuit of tubing and fins. The refrigerant flows between a cold indoor coil (called an evaporator) and a hot outdoor coil (called a condenser).
In the evaporator the liquid refrigerant evaporates into a gas, pulling heat out of indoor air, cooling your home. Then, the now heated refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid, giving up its heat to the outside air by flowing over the condenser's metal tubing and fins.
Nearly all air conditioners used to use chlorofluorocarbons (CFCs) as refrigerant. Because these chemicals damaged the Earth's ozone layer, CFC production was stopped in the United States in 1995.
Most air conditioning systems currently employ halogenated chlorofluorocarbons (HCFCs) as refrigerant. These too are being gradually phased out with production and import being totally eliminated by 2030.
Production and import of today's main refrigerant for home air conditioners, HCFC-22 (also called R-22), will be entirely phased out between 2010 and 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 damaging refrigerants are phased out, ozone-safe hydrofluorocarbons (HFCs) are expected to dominate the market, as well as other alternative refrigerants such as ammonia. Common Problems with Air Conditioners. The most common air conditioning problem is improper operation. If your air conditioner is on be sure to close all windows and outside doors. For room air conditioners, isolate the room (or a group of connected rooms) from the rest of your home as much as possible for maximum efficiency.
Common problems with existing air conditioners come 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, which results in impaired performance and efficiency. Unqualified service technicians often fail to find a refrigerant charging problem or even worsen an existing problem by adding refrigerant to an already full system.
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 been tripped; pushing the reset button located in the compressor's access panel will restart the system.
Other common reasons for air conditioner failures are 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. Refrigerant leaks can also be harmful to the environment. 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 may fail prematurely. Electric Control Failure. The compressor and fan controls can wear out, especially when the air conditioner turns on and off frequently. This 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 Problems. Room 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 will 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 Problems. When 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. Central Air Conditioners. Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (openings in the walls, floors, or ceilings covered by grills) carry cool air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home. It then flows back to the central air conditioner through return ducts and registers.
Air conditioners help to dehumidify the incoming air, but in extremely humid climates or in cases where the air conditioner is oversized, it may not achieve a low humidity. Running a dehumidifier in your air conditioned home will increase your energy use, both for the dehumidifier itself and because the air conditioner will require more energy to cool your house. Two types of Central Air Conditioning Units: Split-system and Packaged. Split-system Unit. In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners this indoor cabinet also contains a furnace or the indoor part of a heat pump. The air conditioner's evaporator coil is installed in the cabinet or main supply duct of this furnace or heat pump. If your home already has a furnace but no air conditioner, a split-system is the most economical central air conditioner to install. Packaged Unit. In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner is also used in small commercial buildings. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors. Tips For Choosing or Upgrading Your Central Air Conditioner. Central air conditioners are more efficient than room air conditioners. Additionally, they are out of the way, quiet, and convenient to operate. To save energy and money you should try to buy an energy-efficient air conditioner and reduce your central air conditioner's energy use. In an average air-conditioned home, air conditioning consumes more than 2000 kilowatt-hours of electricity per year, causing power plants to emit about 3500 pounds of carbon dioxide and 31 pounds of sulfur dioxide.
If you are considering adding central air conditioning to your home, the deciding factor may be the need for ductwork. See section on limitations when replacing existing systems for more information.
If you have an older central air conditioner, you might choose to replace the outdoor compressor with a modern, high-efficiency unit. If you do so, consult a local heating and cooling contractor to assure that the new compressor is properly matched to the indoor unit. However, considering recent changes in refrigerants and air conditioning designs, it might be wise to replace the entire system. Energy Usage. Today's best air conditioners use 30%–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%–40% of your cooling energy costs by replacing it with a newer, more efficient model. SEER Rating. Central air conditioners are rated according to their Seasonal Energy Efficiency Ratio (SEER). SEER indicates the relative amount of energy needed to provide a specific cooling output.
Air conditioners manufactured after January 26, 2006 must achieve a minimum SEER of 13. SEER 13 is 30% more efficient than the previous minimum SEER of 10. Equipment with a rating less than SEER 13 manufactured before this date may still be sold and installed. Many older systems have SEER ratings of 6 or less.
Look for the ENERGY STAR label for central air conditioners with a SEER rating of 13 or greater. You should consider using air conditioning equipment with the highest SEER ratings available for the greatest savings.
The standards do not require you to change your existing central air conditioning units so the average homeowner will be unaffected by this standard change. As the "lifespan" of a central air conditioner is about 15 to 20 years, replacement parts and services should continue be available for your systems. Manufacturers typically continue to support existing equipment by making replacement parts available and honoring maintenance contracts even after the new standard goes into effect.
Unit Size and Installation. 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 attain a comfortable temperature on the hottest days. Improper unit location, lack of insulation, and improper duct installation can greatly diminish efficiency. Other Features to Look For When Buying an Air Conditioner: • Thermal expansion valve and high-temperature rating (EER) greater than 11.6, for high-efficiency operation when the weather is at its hottest
• Variable speed air handler for new ventilation systems
• Unit that operates quietly
• Fan-only switch so you can use the unit for nighttime ventilation to substantially reduce air-conditioning costs
• Filter check light to remind you to check the filter after a predetermined number of operating hours
• Automatic-delay fan switch to turn off the fan a few minutes after the compressor turns off. Installation and Location of Air Conditioners. If your air conditioner is installed correctly or if major installation problems are found and fixed your unit will perform efficiently for many years with minor routine maintenance. However, many air conditioners are not installed correctly. As result, modern energy-efficient air conditioners can perform almost as poorly as older inefficient models.
Be sure that your contractor performs the following procedures when installing a new central air conditioning system:
• Allow adequate indoor space for the installation, maintenance, and repair of the new system, and installs an access door in the furnace or duct to provide a way to clean the evaporator coil.
• Use a duct-sizing methodology such as the Air Conditioning Contractors of America (ACCA) Manual D.
• Ensure there are enough supply registers to deliver cool air and enough return air registers to carry warm house air back to the air conditioner.
• Install duct work within the conditioned space, not in the attic, wherever possible.
• Seal all ducts with duct mastic and heavily insulates attic ducts.
• Locate the condensing unit where its noise will not keep you or your neighbors awake at night, if possible.
• Locate the condensing unit where no nearby objects will block the flow of air to it.
• Place the condensing unit in a shady spot, if possible, which can reduce your air conditioning costs by 1%–2%.
• Verify that the newly installed air conditioner has the exact refrigerant charge and airflow rate specified by the manufacturer.
• Locates the thermostat away from heat sources, such as windows or supply registers.
If you are replacing an older or failed split system, be sure that the evaporator coil is replaced with a new one that exactly matches the condenser coil in the new condensing unit. (The air conditioner's efficiency will likely not improve if the existing evaporator coil is left in place. In fact, the old coil could cause the new compressor to fail prematurely.)
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