Air Conditioning, the Energy Efficient Way
Don’t lose your head in a war on heat
In the old days, people wore loose clothing, sipped iced tea, and sat in the shade when the temperature rose. If your situation demands a more assertive approach, try the following tactics. They could help you avoid air conditioning, and its associated costs and greenhouse gas emissions, entirely. Or–if you really need to flip the AC switch–they’ll help you save money, fuel, and greenhouse-gas emissions as you enjoy the cool air.
- Reduce your need for air conditioning.The less demand you put on a system, the less energy you’ll squander and the longer your unit will last. There are several ways to do this:
- Avoid overcooling. Unfortunately, many buildings are far chillier than necessary. For most people, 78°F. degrees is perfectly comfortable. Yet many homes and businesses crank the temperature down as far as 65°. You can save a lot of money–and fight global warming–by the simple act of setting your temperature higher. Going upward a single degree, in fact, can reduce your air conditioning bill by 3% to 5%. If you are not going to be home, raise the temperature to 85° or 90°. You can use a timer to automatically bring the temperature down to 78° just before you come back.
- Insulate and tighten up your house. No matter how efficient an air conditioning system is, it can’t perform well in a house with insufficient insulation and poor sealing. Checking for leaky ducts is particularly important. A huge amount of energy–well over $100 a year–can be wasted if they leak. Speaking of leakage, keep doors and windows closed when your air conditioner is on.
- Cool with fans. By circulating air, fans make us feel cooler, yet they use only a fraction of the energy required by air conditioners. Unless it is very humid where you live, a large fan that vents to the outside in the top-floor ceiling may radically reduce your need for air conditioning. Even a good attic fan can cut air conditioning costs up to 30%. Using your bathroom fan can cut your home’s humidity–another way to make you feel cooler.
- Don’t cool unoccupied rooms. If you have room air conditioners, shut them off and shut the doors. With central air conditioning, shut off registers in some of the rooms you are not using. But, be careful. If the thermostat is in the room you have closed off, the system will continue running long after the rest of the home is cool.
- Keep your AC clean. If you have a room air conditioner, remove and rinse off its filter (usually behind the inlet grill) every month. If you have a central air conditioner, have the condenser unit professionally cleaned at least every other year. Clean all registers and air inlets and outlets. This is important not only for efficiency, but to prevent buildup of dust and mold than can harm your respiratory system. Every three years, have a technician add a tune-up and inspection to the cleaning. Among other tasks, the technician will check your refrigerant level. If it’s low, you’re wasting as much as 20% of your air conditioner’s energy. Proper airflow is also critical.
- Buy energy-efficient appliances. All electrical devices give off heat, so consider replacing old refrigerators and incandescent light bulbs. Unplug electronic equipment when it’s not in use.
- When you paint or re-roof, consider “cool” exterior finishes. Light-colored or other “cool” roofing and siding products can reduce peak cooling demand by 10% to 15%.
- Be aware of windows. Close drapes and shutters on windows on the sunny side of the house. If it’s time to replace your windows, get the double-glazed type with a coating that reduces heat coming in from the sun.
- Plant a tree. In the summer, a deciduous tree in front of your window will provide cooling shade. In the winter, after its leaves have fallen, it will allow solar energy to warm your house.
- Plan ahead. If you know your existing air conditioner is on its last legs, think about how you’re going to replace it now. Making quick decisions during the middle of a heat wave rarely leads to prudent purchases.
- Seek out shade. Try to site your air conditioning equipment in shady places so the sun doesn’t heat it up.
When shopping, look for
- An Energy Star. EPA-approved Energy Star air conditioning equipment can save as much as 25% on energy. For window air conditioners, check out the “energy efficiency rating” (EER), which is the products’ Btu ratings divided by their wattage. For example, if a 10,000-Btu air conditioner consumes 1,000 watts, its EER is 10 (10,000 BTU/1,000 watts). Look for window air conditioners with EERs of at least 10. Central air conditioners (and heat pumps) have a slightly more sophisticated rating system called SEER, or “seasonal energy efficiency ratio.” SEER is the total cooling output during the cooling season divided by the total electrical input during the cooling season. Older systems may have SEERs of only 5 or 6, but U.S. law now requires at least 13. High-efficiency models can reach 21.
- R-410. A refrigerant commonly used in air conditioning equipment, freon, depletes Earth’s protective ozone layer. It will be phased out of use in all new AC equipment starting in 2010, but in the meantime its use should be avoided if possible. When you buy a new system, or have refrigerants in an older air conditioner recharged, ask if R-410 refrigerant is available and will work in your system, because it does not damage the ozone layer.
- As air conditioning systems age, they use more energy. If yours is more than 10 or 12 years old, it may need replacing. Also, some new systems are twice as efficient as the old ones ever were. Other signs of old age are inconsistent performance or excessive humidity, dust, or noise.
- If you need a new air conditioner, consider the pros and cons of these six commonsystems:
- Room or window air conditioners. These are designed to cool only a single room. They are less efficient than central air conditioners, but usually cheaper to operate because they draw less power.Smaller room air conditioners that require less than 7.5 amps of electricity can be plugged into any 15- or 20-amp, 115-volt household circuit as long as other major appliances like refrigerators or dishwashers are not plugged into the same circuit. Larger room air conditioners should have their own separate 120-volt circuit. The biggest models require installation of a special 220-volt circuit.A room air conditioner should have a capacity of roughly 20 to 30 Btu per hour for each square foot of floor area. If the room has heavy shade, reduce capacity by 10 percent. If a room gets a lot of sun, increase capacity by 10 percent. If more than two people regularly occupy a room, add 600 Btu for each extra person. If the unit is in a kitchen, increase capacity by 4,000 Btu.If you’re handy, you could install a room air conditioner by yourself. Be sure to seal tightly between the machine and the surrounding frame, and follow the manufacturer’s instructions.
- Central air conditioners. Room air conditioners may be adequate and cost effective for a small house or mobile home. But for a larger house where most rooms are frequently occupied, central air conditioners will probably do the best job. They usually have two main parts, an evaporative unit inside, commonly installed in conjunction with furnace ducts, and a condensing unit that is usually outside the house on a cement base. It is important to size a central air conditioning unit properly. Ask if your contractor uses the Manual J® residential load calculation procedure, which includes measures of your home’s insulation, air leakage, building layout, window type, number, and location, shade, and the condition of duct systems–as well as the efficiency rating of the equipment itself. This is the best way to figure out the proper size system.
- High velocity air conditioners. If your house doesn’t already have ducts for air conditioning, you might want to consider a high velocity air conditioner. It’s less efficient than a central conditioner, but perhaps worth the tradeoff if ducts would be difficult to install.
- Heat pumps. Also called heat exchangers, these devices can provide both heating and cooling, eliminating the need for a conventional furnace. If you already have a fairly new furnace, it may not pay to buy one. If you have an old furnace that needs to be replaced, however, a heat pump might be worth considering. “Air-source” heat pumps are most cost- and energy-efficient in warm climates that need a lot of air conditioning and little heating. (They use large amounts of energy when it gets very cold.) “Ground-source” heat pumpscan work well in larger homes that need a lot of heating and cooling in equal measure. Neither system makes sense inhomes where little or no air conditioning is needed. For more information, see our heat pump article.
- Evaporative coolers. Also called swamp coolers, these are efficient alternatives for hot, dry climates like the Southwest. They cool the air by forcing it through moist pads. But they don’t work well in humid climates because they rely on the cooling power of evaporation and humid air can’t absorb much additional moisture
- Hydronic (floor or baseboard) systems. Hydronic systems can also provide both heating and cooling. They send either cooled or heated fluid through pipes embedded in a concrete floor or positioned directly under other types of floors. They can also be enclosed in baseboards, or in panels on ceilings. Like central air conditioners, hydronic coolers have outdoor and indoor units. But with hydronic systems, no ductwork is required and each room or area can have its own comfort level. These floor or baseboard systems are much more effective in heating than cooling, because heat rises and cold sinks. In humid areas, condensation of moisture on the cool floor can also be a problem.
- The up-front cost of these devices varies widely. At the low end, if you just want to cool a room, a swamp cooler or window-mounted room air conditioner will run anywhere from $100 to $800. In a 2,000 square-foot house, central air conditioning can cost anywhere from $3,500 to $8,000, depending on whether you can use existing ducts. An air-source heat pump can cost about the same as or less than central air conditioning, but a ground-source heat pump will cost considerably more. Also at the high end are hydronic floor systems. But in all cases, don’t forget to factor in operating costs. For hydronic systems, they are very low.
…to your health
Every year there are news reports of illness and even death brought on by excessive heat. A reliable air conditioning system is sound prevention. Also, most folks are simply not as happy, sociable, or productive in extreme heat.
…to your wallet
You can save hundreds of dollars every year by having a highly efficient, well-maintained air conditioning system and taking the steps listed above to reduce your energy demand and prolong your air conditioning system’s life.
…to the Earth
Home air conditioning consumes almost 5% of all the electricity produced for home consumption in the United States. Generating this much power pumps roughly 140 million tons of carbon dioxide into the air each year, which increases the speed of global warming. Mining and burning coal, oil, and natural gas to generate all this power has many negative effects on the environment, from emissions of toxic chemicals such as mercury to water and air pollution and destruction of wildlife habitat from mining and drilling for oil and gas. Efficient, well-maintained, and moderately used air conditioning system can significantly reduce all these serious environmental threats.
Supersizing your system. Bigger is not better. If air conditioners and air conditioning systems are too big, they can cost more, use more electricity, increase humidity, and turn on and off more frequently, which wears them out faster. All installations should be carefully sized to fit the dimensions and conditions of your house. Among the factors to consider in addition to square footage: types of windows, shading, insulation, and the system’s efficiency, as measured by its Energy Efficiency Ratio (EER) or Seasonal Energy Efficiency Ratio (SEER)–the higher the number the better. Don’t necessarily get the same size system you had before. It may have been wrong in the first place.
- Ask about rebates. Check www.dsire.org for state, local, utility, and federal rebates and other incentives for energy efficient air conditioning systems.
- With the exception of a window model, an air conditioner should be installed by a licensed contractor. Your safest bet is to hire a contractor who is a member of the Air Conditioning Contractors of America or the Sheet Metal and Air Conditioning Contractors’ National Association. Contractors certified by North American Technician Excellence are trained in the latest techniques. Some other tips for dealing with air conditioning contractors:
- Don’t hire a company over the phone that won’t send a technician to your home for an on-site review.
- Don’t use any company that tries to sell older equipment or seems to be dumping equipment by offering big discounts.
- Ask the contractor to estimate the annual energy costs for the equipment they are proposing.
- Ask for a bid in writing that specifies the equipment to be installed, the work to be done, and the total price, including labor costs.
- Get more than one bid, and don’t jump at the lowest price. Better contractors may charge more, but if they do a better job with a better system, you will save in the long run. Be wary of ultra- low bids, especially if they omit routine services and warranties, or even worse, seem to be an attempt to dump inferior or outmoded equipment.
- Ask if your contractor uses the Manual J® residential load calculation procedure, which considers your home’s insulation levels; air leakage; building layout; window type, number, and location; shade; and condition of duct systems–as well as the efficiency rating of the equipment itself. This is the best way to figure out the proper size for your system.