Climate control is an important part of everyday life in most parts of the country and an essential one in areas that get very hot at certain times of year. Of course, air conditioners use energy, and during the cooling season they can represent a huge portion of the owner's electric bills. While every air conditioner will cost the owner some money on a monthly basis, that cost can vary widely depending on the location, the size of the home, the type and arrangement of air conditioners and many other factors.
How do Air Conditioners Work?
To understand why air conditioners use energy, it is important to first understand how these appliances work. An air conditioner uses the same cooling technology as a refrigerator: A heat pump and a circuit of tubes make up the cooling system. The serpentine tubing, usually made from copper, curls into evaporator and condenser coils. During cooling, the indoor evaporator coil blows cool air into the room while the outdoor condenser coil releases heat outside. When the air conditioner is running properly, a great deal of heat is expelled as a natural result of operation.
Air conditioners use pumps known as compressors to transfer heat between these components. The compressor pumps refrigerant fluid through the tubing and fins surrounding the evaporator and condenser coils; when the fluid hits the indoor coil, it evaporates, taking heat with it that cools the air that will be pumped inside. The pump then moves the gaseous refrigerant over to the outdoor coil where it condenses, transferring that heat to the air that will be expelled from the building. To keep these pumps running throughout the day, the air conditioner needs a substantial amount of energy.
Of these components, the one that uses the most energy is the compressor. Because it has to move fluid, the compressor requires a great deal of power to take care of the air conditioner's "heavy lifting." Spinning the fan also requires a significant amount of energy, but because the fan's job is to move air rather than fluid, it uses much less during normal operation.
Energy Efficiency Ratings
An air conditioner's capacity is measured in British Thermal Units (BTU), a measure of the amount of heat the machine can remove from the home per hour. One ton is equal to 12,000 BTU. Manufacturers divide the BTU rating by the machine's energy consumption in watts per hour to find the energy efficiency rating (EER); higher numbers denote a more energy-efficient machine. For both heating and cooling equipment, this is typically expressed as a nominal seasonal energy efficiency rating (SEER). The Energy Guide gives a SEER rating for every model that typically ranges from 13 to 17.
Although the nominal SEER rating can be useful to compare different systems, the actual energy efficiency ratio depends on many factors that are independent of the air conditioner itself. While the nominal SEER is based on standard conditions, the real SEER can change depending on the other equipment installed in a home, the size and layout of the building and other individual conditions. Only a licensed dealer can conduct a full inspection to determine how energy-efficient a given air conditioner will be in a given home, and that estimate is the only way to know precisely how much energy an air conditioner will use.
Depending on these unique factors, a ton of air conditioning may cool as few as 300 or as many as 800 square feet. The amount of energy consumed, then, is a function of the size of the home in square feet, the amount of BTU required to cool all of those square feet and the energy efficiency of the air conditioning equipment. Climate control for a very small, efficient home may require only a few hundred watts hourly, while larger buildings with less efficient layouts may need thousands.
Reducing Energy Consumption
For large and small buildings alike, however, there are ways to reduce the amount of energy air conditioners use without sacrificing climate control. First, it is important to note that the HVAC industry has made great strides in energy efficiency over time. Systems used today are up to 50 percent more efficient than equipment used as recently as the 1970s, and manufacturers are constantly looking for ways to improve efficiency even further. Upgrading to a newer air conditioner can lead to improved SEER and thus less energy consumption; for many homeowners, the monthly savings on energy bills are more than enough to offset the cost of the upgrade.
Another way to reduce an air conditioner's energy consumption is to take steps to reduce the workload on climate control equipment. Using drapes to prevent sunlight from entering the house, for instance, can lower temperatures at no cost and thus reduce the need for air conditioning. Consider investing in a programmable thermostat that can turn down the air conditioning while no one is at home; because air conditioners can cool a space down fairly quickly, they only need to be turned on while the building is occupied to be effective. Taking these steps to reduce the strain on an air conditioner will not only lower energy costs but also extend the life span of the equipment.
Routine maintenance also impacts the energy efficiency of air conditioning systems. Over time, an air conditioner will accumulate dust and debris that force the fan and compressor to work harder, which leads to less effective cooling and less efficient operation. If any component of the machine is damaged or malfunctioning, the energy consumption can also be affected. Frequent maintenance checks can identify and deal with these issues before they start to appear on energy bills or lead to an equipment failure; again, keeping an air conditioner well-maintained extends its working life in addition to improving its efficiency.
Certain home maintenance steps, such as replacing or cleaning the air filters monthly, also have some effect on an air conditioner's energy consumption. By making their home environments as easy on their AC equipment as possible, knowledgeable homeowners can keep their energy consumption down to manageable levels.