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How an Air Conditioner Works

 

What you need to know about air conditioning!

 

Air conditioning does more than cool the air. It truly "conditions" it by removing dust and dirt as the air is drawn through a filter. Air conditioning also lowers the humidity, making the air more comfortable at any temperature. These benefits, however, can be costly. Depending on your region of the country, it is estimated that air conditioning can account for anywhere from 5 to 40% of your household budget. Because an air conditioner is such a sizable investment, you can save money and energy by carefully purchasing and operating your air conditioner.

When shopping for an air conditioner, first consider what system best suits your needs - central air conditioning or room air conditioning. Central air conditioners are usually mounted on concrete slabs exterior of your home/building, but they cool the entire interior either by blowing cold air through ducts positioned in each room, or by circulating cooled water through pipes to each room where fans blow air across the pipes. Room air conditioners work in the same way, but have a smaller capacity and therefore only cool the immediate area.

Central air conditioners generally provide the greatest comfort but they also cost more than room units. If several rooms need to be cooled, however, a central system is probably the best buy. Central systems generally are not cost-effective as an addition to an existing home unless the existing ductwork can be used.   My experience is that room air units usually save energy, because we tend to just cool the one room that we stay in the most, and with central we are cooling every room, all the time.  When a bedroom is cooled by a window or wall unit, the air conditioning energy expense is for that room only, whereas with central the entire home is still being cooled.

Room air conditioners are mounted in windows or built into an external wall. Room units are less expensive than central units; however, they only cool the general space in which they are located. There are four types of room units; window models can be installed in most windows; casement window models, used in narrow, vertical windows, usually require the removal of a window panel for installation; and built-in models which are encased in a sleeve installed in the wall. The fourth type of air conditioner is the portable air conditioner, which has grown immensely in popularity.  Portables have many advantages to them:

  1.  Roll room to room as needed.
  2. Affordable (costs have declined dramatically over the last five years
  3. Easy to install in double hung windows and sliding glass doors
  4. Can be converted, as needed, into just a dehumidifier by a simple push of the button on the remote  control
  5. Can be installed flush to a building line, and maintain low exterior visibility, so as to maintain the beauty in appearance of a home.

Size determining which BTU to purchase

After selecting the optimum unit type, consider unit size. A bigger unit is not necessarily better, because a unit that is too large will not cool an area uniformly. Also, an oversized unit will cool an area too quickly, causing the air conditioner to frequently turn on and off. This wastes electricity and money. In addition, a unit that is too large will not run long enough to reduce humidity and, instead of feeling comfortable, the air will feel cold and clammy at the normal thermostat setting.

On the other hand, you should avoid purchasing too small a unit. An insufficiently sized unit will run constantly on hot days and still not be able to cool the area adequately.

In sizing an air conditioner for your home, consider the dimensions of the area to be cooled and how the area is used. Based on size alone, an air conditioner commonly needs 20 Btu for each square foot of living space. For instance, to air condition a room that is 15 feet wide and 20 feet long, you would calculate: 15 x 20 x 20(Btu) = 6,000. Thus, an air conditioner with a 6,000 Btu capacity would be required.

Calculating Btu requirements becomes more complicated when you consider an area's use. For instance, if you use passive cooling techniques such as shading, ventilation or vegetation, your Btu estimate can be lowered. Likewise, your Btu needs are increased by factors such as the size of the household, frequent use of heat-producing appliances, or summer humidity levels. An appliance dealer will use these factors to adjust your estimated Btu requirement. For most efficient cooling, purchase a unit, with a capacity within 5% of this estimate.

If you'd prefer to calculate your own capacity needs, you may send away for a "Cooling Load Estimation Form" from:

The Association of Home Appliance, Manufacturers 20 North Wacker Drive, Chicago, Illinois 60606


Efficiency  Look for the E STAR Label

When choosing between units with similar prices, capacities and features, energy efficiency should be the deciding factor. Even though an energy efficient unit may be higher priced, it may be the best buy. High efficiency appliances cost less to operate and can pay back the extra initial cost many times over during their lifetimes. Many utilities are offering rebates on E STAR air conditioners, which makes the difference in E STAR versus non-E STAR very similar in cost.

All room air conditioners bear bright yellow Energy Guide labels which provide information on energy efficiency. Energy Guide labels are mandated by Congress as part of the Energy Policy and Conservation Act of 1975. The label displays an energy efficiency rating (EER) in large black numbers. The higher the energy efficiency number rating, the more efficient the appliance, and the less energy it will consume. Units with an EER of 9.0 or above are considered very efficient. To help you compare units, a range for competing air room conditioners of the same cooling capacity is printed on the Energy Guide label below the EER.

The label also provides a cost/use chart to calculate the cost of operating the appliance based on local electricity rates and expected hours of use. If your utility is in the 12 cents to 16 cents KWH range, it almost always pays to buy an E STAR unit.  700 hours a year is the basis of the cost to run an air conditioner.  If you use an air conditioner year round, then once again, it certainly would pay to only buy an E STAR model.

Central air conditioners are rated according to their Seasonal Energy Efficiency Ratio (SEER). Like the EER, the higher the SEER, the more efficient the system. To compare the efficiency of two units with equal cooling capacity, take the difference in SEER's and divide by the large SEER. For example, if system A has a SEER of 6, and system, B has a SEER of 8, system B will provide the same amount of cooling as system A while consuming 25% less energy(8 - 6 =2; 2/8 = .25).

Finally, compare warranties and maintenance agreements when buying an air conditioner.

Installation

An improperly installed unit, even one with a very high efficiency rating, will waste energy. Whether you install the unit yourself or hire a professional, the following installation tips should be followed. Remember that each unit has specific installation requirements. Therefore, follow the manufacturer's instructions carefully. In addition, it is important to install the unit in a shaded spot on the house's north side or east side because direct sunshine on the unit's outdoor heat exchanger decreases efficiency. If your system is already exposed to the sun, a shading device such as an awning will protect the unit. Also, do not try to hide the unit's external part behind shrubbery. The shrubbery reduces the unit's ability to exhaust air and lowers its efficiency. Plenty of air circulation is mandatory. Room air conditioners must be installed on a flat, even surface so that the inside drainage system and other mechanisms operate efficiently.

The room air conditioner should fit snugly inside the sleeve. Make sure the unit's front and rear filter plates, top and side flanges and the gaskets/jacketing, on all four sides are waterproofed. Also, provide for effective storm water drainage.

Finally, verify that your home's electrical system can meet the unit's power requirements. Room units operate on 115-volt or 230-volt circuits. The standard household receptacle is a connection for a 115-volt branch circuit. Large room units rated at 115 volts may require a dedicated circuit and room units rated at 230 volts may require installation of a special circuit. If in doubt about your wiring, consult an electrician or electric utility. An HVAC contractor should install your central air conditioner.

Maintaining your air conditioner

A dusty filter reduces air flow, and costs you more money to operate. Examine your unit's air filters once a month and clean or replace filters when necessary. Keeping your filters clean can cut energy consumption 5 to 15%. Most room air conditioners have lifetime filters but central units require replacement of filters.

Room units should be covered or removed and stored in the winter.

Clogged drain channels prevent a unit from reducing humidity and the resulting excess moisture may discolor walls and carpet. Channels usually can be cleaned by passing a stiff wire through them.

Holes in the seal between the air conditioner and the window frame allow cool air to escape from your home. Moisture can damage this seal so inspect it annually to see that it makes contact with the unit's metal case.

Coils can become clogged with dust. To clean room air conditioner coils, first unplug the unit. Use a vacuum cleaner to remove dust from the interior heat exchanger; the exterior heat exchanger may be cleaned using water from a garden hose.

You may wish to install a timer. When leaving home, you can set the timer so that the unit turns on a half hour before you return. This should be enough time to cool the room. Before purchasing a timer, you must make sure that it can handle the electrical load; otherwise, the timer could be a fire hazard. For central air conditioners, a programmable thermostat will control the unit. Many units today have electronic controls with a timer, built right into the unit.

For a central air conditioning unit, make sure the ducts are properly insulated, especially those that pass through the attic or any other unconditioned areas.

Make sure furniture does not obstruct air conditioning vents. Close off unused rooms and close vents in those rooms.

Weather-strip all doors and windows.

Close all unnecessary openings such as fireplace dampers, doors and windows.

Set the thermostat to 780 F. Setting the thermostat down to 720 F would increase your cooling costs 12 to 47%, depending on where you live.

Do not set the thermostat lower than the desired temperature when you first turn it on. It will not cool faster; it mill only cool to a lower temperature than necessary and waste energy.

Set the fan speed on high except in very humid weather. When it's humid, set the speed on low; you will get less cooling but more from the air which will make it feel cooler.

Do not position heat-producing appliances, such as televisions or lamps, near the thermostat. The heat they produce "fools" the thermostat and causes the unit to run longer than necessary.

Keep out sun with louvers or awnings on the outside of your windows, or draw draperies, blinds, or shades indoors. Keep storm windows closed.

Limit heat and humidity producing tasks like cooking and laundering to early morning or late evening.

Use kitchen and bathroom exhaust fans sparingly.

Alternatives

Good conservation habits also help hold down electric bills. For instance, only use your unit when the temperature is above 78 degrees F. Close windows and draw drapes and shades during the day to keep out the heat. At night, open the windows and turn on window or attic fans to draw in the cooler air. In addition, passive cooling techniques such as shading, ventilation, and vegetation can reduce your cooling needs.

A heat pump can be an alternative to the conventional air conditioner. In its cooling mode, an air-to-air heat pump works like an ordinary air conditioner. But unlike an air conditioner, the heat pump can reverse during cold weather, absorbing heat from the outdoor air and transferring it indoors. Though air-to-air is the most common type of heat pump, water-to-air and ground-to-air heat pumps are also available. Water-to-air heat pumps exchange heat with either ground surface or well water.

Ground-to-air heat pumps are most cost effective when included in a new home's design rather than as an addition to an existing home.

Fans can also help cool your home. While fans cannot replace air conditioners, they can provide supplemental cooling, especially on mild summer days. Substituting fans for air conditioners can save 60% or more in energy.

Evaporative coolers, or "swamp coolers" also can cool your home. An evaporative cooler works on the principle that it takes heat to evaporate water. An evaporative cooler uses the outside air's heat to evaporate water that is held by pads inside the cooler. The heat is drawn out of the air through this process and 'the cooled air is blown into your home by the cooler's fan.

An evaporative cooler costs less than an air conditioner and it also requires only about a quarter of the electricity it would take to run a regular air conditioner. Due to the humidity they add to the air, however, evaporative coolers are only effective in hot, dry regions such as the southwestern United States. An evaporative cooler are also requires a large amount of water. This may be a problem for areas where water has to be conserved. Also, the evaporate cooler requires more maintenance than an air conditioner.