Guidelines for Air Conditioning a Room with a Window Unit | |
In southern and southwestern parts of the country central air conditioning is standard equipment in new homes. But in the majority of existing homes a high efficiency room air conditioner is the best way to take the sizzle out of hot summer weather. This type of unit is self-contained and easy to install in any structurally sound window. It allows you to selectively cool only the lived-in areas of your house. A window air conditioner transfers heat from inside the room to the outside. The unit seems complicated but the process is rather simple. An electric compressor circulates a liquid refrigerant through the closed system. The refrigerant absorbs heat as it expands into a gas in the evaporator coil inside the room and then releases the heat as it turns back into a liquid in the outside condenser coil. The change from liquid to gas continues as long as the compressor pump runs. A fan inside the unit circulates the warm room air through the cold evaporator coil where it is cooled and dehumidified and then blows it back into the room. Purchasing the Right Unit Window air conditioners come in a variety of sizes, shapes and efficiency levels. The cooling capacity is rated in British Thermal Units (BTUs). Room air conditioners from 5000 to over 20,000 BTU cooling capacity are available for window mounting. For an air conditioner to operate at peak efficiency it must be sized to fit the area it's expected to cool. In addition to the room size other factors to consider are the number of people who will use the area and whether or not it's located on the south side of the building. Obviously if the unit is undersized it will not cool the room but if it is oversized it will cool the area so quickly that it won't run long enough for the evaporator coil to properly dehumidify the air. Using a room air conditioner that's over capacity is inefficient and can cause the unit to short cycle. This constant on-and-off cycle may prematurely wear out the compressor. Units in the 5000 to 7000 BTU range will usually cool an average sized bedroom. Kitchens with heat producing appliances like the oven and busy family rooms with lots of people activity require more cooling power. Before you purchase a unit check your electrical power. Window units under 12,000 BTU capacity require a 120 volt 20 amp electrical circuit. Smaller units of 5000 BTU may run on a 15 amp circuit. In both cases neither will work reliably if it has to share the circuit with another high amperage appliance like a refrigerator. Larger units require a dedicated 240 volt circuit. Ask the salesperson about the power requirements for any of the room units under consideration. In addition to proper sizing, buy an energy efficient unit which will save money in the long run. The Energy Efficiency Ratio (EER), the ratio of the amount of electricity the air conditioner uses to produce one BTU of cooling, is the most readily available gauge. This number is published on a yellow label affixed to the unit. The higher the EER, the more efficient the unit. Units with EERs over 7 are considered efficient but real energy savings can be realized by purchasing units with EERs over 9. Evaporative Coolers an Option for Some If you live in a dry climate like the southwest consider buying an evaporative cooler instead of a conventional air conditioner. This unit uses the energy transfer during water evaporation to cool the air. The physical property has been known for centuries because historical records reveal the use of wet mats that were hung in doorways of tents and in bedroom doorways to help cool the space. This type of cooler is effective and economical to run because it does not require a compressor. An evaporator belt, pad or drum is bathed in a water reservoir. A fan blows air over the wet evaporator medium which is usually thin plastic foam. The hot dry air causes the water to evaporate and in changing from liquid to vapor heat is absorbed from the air. Evaporator coolers do not dehumidify like an air conditioner and require very low relative humidity to be effective. Evaporative coolers come in window and whole house sizes and they're rated by the capacity of the fan in cubic feet per minute. When considering your cooling needs ask the salesman if it is feasible to install an evaporative cooling unit in your area. He'll be able to help determine the proper size. Placement Most window air conditioners are manufactured to fit into double hung windows. There are, however, models that can be installed in casement and sliding windows or installed directly through the wall. Before you install any unit check out the location. Air conditioners collect moisture from inside the house and deposit it outside. Look below the area where you plan to install the unit. Will dripping water cause problems? For example, if the unit is located on the second floor above a patio or deck then the run off may be a nuisance. If it presents a problem consider ways to route a section of drainage tubing from the air conditioner to a more convenient drainage point. If this is not possible then look for a unit that recycles the condensation by splashing it on the condenser coil to help cool it. These units usually don't drip condensation. If you plan to mount the air conditioner through the wall check that there are no plumbing pipes or electrical lines running through the wall in the area where the opening for the air conditioner will be made. Choose a location where the unit is not blocked by a door that's constantly opened and closed. Try to place the unit in a window or through the wall directly across from the door. The air conditioner blower will then force a good portion of the cool air out the open door into the adjoining area. Don't locate the unit in a dead end corner of the room. Analyzing the location for an air conditioner is ~especially important if you hope to cool more than one room with the unit so spend time looking at all the options. Efficient Operation Purchasing an air conditioner with a high EER assures you that the unit will function efficiently but how you operate it will make a greater difference in your utility bill. Power company studies discovered that people who purchase energy efficient air conditioners tended to turn the thermostat to a lower setting and run the unit more often which negates their energy savings. Perhaps they felt that since the unit is efficient they can operate it more often for the same cost as operating a less efficient unit for a shorter time or at a higher setting. As a rule of thumb which varies depending on the orientation of your house to the sun and the condition of your house, you can expect to lower your cooling bill by about 2% to 3% for every degree you turn up the thermostat. Keeping a room at 80 degrees uses roughly 10% more energy than maintaining the same area at 85 degrees. If you are away from the house during the day for extended periods of time you can save substantially if you install a timer to turn the unit 'off' when you're away and back 'on' an hour or so before you return. Multi-cycle timers can be programmed to fit just about any schedule. Unlike light timers, air conditioner timers are heavy duty units capable of carrying high amp. loads. Check the current requirements of your air conditioner. The amp draw or watts capacity is listed on a plate attached to the front of the unit usually under the front grill. Purchase a timer that is rated higher than the amp capacity of your unit and check that the plug will fit the unit. Some timers have standard three prong grounded receptacles, others have receptacles that fit 240v plugs. The busy comings and going of an active family can affect the amount of energy you use to keep cool. Every time the patio door opens letting hot air inside you're putting more demand on the cooling system. Routine Maintenance Another factor influencing the efficiency of an air conditioner is how well it is maintained. A dirty filter chokes the air flow through the unit effectivity reducing its capacity to cool. An air conditioner with a clogged filter has to run much longer wasting considerable electricity to cool the same area. In addition to simply washing the filter at least once a month clean the cooling fins of accumulated lint and dust annually. Use a soft brush to remove the dirt then straighten any bent fins to keep the unit working as efficiently as possible. Air Conditioner Aids Ceiling fans, whole house fans and proper attic ventilation will help make an air conditioner more efficient. Moving air feels cooler so with the installation of a ceiling fan it's possible to set the air conditioner to maintain a higher temperature and still remain comfortable. With a ceiling fan installed in the bedroom you can frequently turn off an air conditioner during the night and remain cool and comfortable because of the constant air movement. Ceiling fans also make sense in areas where the family congregates. Moving air helps evaporate moisture faster off your skin so the same temperature air feels cooler to the skin than still air. This will allow you to put off starting up the air conditioner on many warm days. Ceiling fans are most effective if mounted at least a foot or more below the ceiling. They come with special mounting adapters for very height or low ceilings. If you have ceilings under 8 feet high check with the building department to find out the minimum headroom required between the fan and floor. Another old standby is a whole house fan. This type of fan is mounted in the ceiling below the attic and draws air through the house and exhausts it into the attic. The fan is very effective in the evening or at night when the outside air is cooler than inside the house. This type of fan is less expensive to operate than central air conditioning. Its only disadvantage is that during hot and very humid periods a whole house fan will draw in outside air that is cool but very humid and moist. The air conditioner then has to remove the moisture during the day. Whole house fans should have sufficient capacity to change the air in the house at least every couple of minutes. A large 20 inch window fan with a capacity of about 3850 cubic feet per minute (CFM) can cool several rooms. An attic fan with 1/4 to a 1/3 horse power (HP) can handle the average size house. The attic fan moves a lot of air and which has to get out of the attic. If you are installing a fan or already have one it will operate much more efficiently if you provide adequate vents in the attic. ~ In almost every case the attic vent area should be increased if you install a whole house fan. Fan manufacturers have recommendations about the amount of net free vent area their units require. Even without a whole house fan most houses do not have adequate attic ventilation which causes the air in the attic to become very hot. On a hot sunny day the air in an unvented attic can reach 150 degrees. The larger the difference between temperatures on either side of an insulated wall or ceiling, the faster the flow of energy through that wall or ceiling. Simply venting this hot air to reduce the attic temperature will cut your cooling costs. There are many types of attic venting systems, some use the natural movement of heated air to vent and other vents incorporate a fan. Convection systems are the most economical to operate since they don't use a fan but in many cases it is difficult to install enough additional vent area for this type of system to be effective. A power vent moves more air through a smaller opening and is usually easier to install in a retrofit project. written by Gene and Katie Hamilton Copyright HouseNet, Inc. |