Save Energy — Air Conditioning

Not so long ago homes were not air conditioned. Open windows served as the only means of summer relief. In many parts of the country, this was not sufficient. Summer heat and humidity was just too much. Air conditioning has become quite common in homes. Whether through window units or central systems summer comfort became a reality. Unfortunately these units use large amounts of energy. This comfort has come with peaking summer electric bills.

Your Home Energy Living Plan

  • Keep thermostat set at the highest temperature you can be comfortable.
  • Keep system properly maintained.
  • Closed blinds or shades to block sunlight.
  • Reduce infiltration and increase insulation. Most energy saving actions reducing the cooling requirement.
Impact of Your Energy Saving Actions

Space cooling accounts for 11% of the average US home’s annual utility bill. This percent is an average across the United States. This percent is much larger in southern locations. Energy saving actions to your home can reduce the amount of cooling significantly. Due to the high cost of air conditioning systems, it is better to complete all energy saving actions before replacing air conditioner. You may be able to downsize your air conditioner. If you have accomplished many energy saving actions, then require the cooling contractor to calculate the proper size of air conditioner. The contractor will charge more for this but it insures you are getting the most efficient size. If the contractor says it is not necessary, then find another contractor. (While not uniformly enforced, building codes require heating/cooling load calculations.)

How Energy is Lost

Heat always flows from hot to cold. During the summer, the hot outside temperature is driving heat into your home. You can not directly remove this heat. A mechanical device is needed to create the situation to draw heat out of your home and dump it outside. This is done by using a fluid called a refrigerant. The air conditioning system causes the refrigerant to get cold (this is done by lowering its pressure), then it flows through the coil inside your home. This cold coil absorbs heat from your house. Then the system increases the pressure so the refrigerant becomes hot. This hot refrigerant flows through the outside coil, dumping the heat. The air conditioner is simply a way to change the pressure and route the refrigerant through the system. To do this a compressor is used, not much different than the air compressor in your garage or shop.

Air Conditioning Characteristics

The compressor is the main energy user of the air conditioner. It accounts for about 85% to 90% of the energy. Although the compressor uses a large amount of energy, the system will remove more heat energy than that used by the compressor. The purpose of the compressor is to change the pressure of the refrigerant. The movement of heat occurs naturally. The air conditioner will help the process by using fans.

The energy used by the air conditioner can vary drastically depending upon operating conditions. As the outside temperature rises, the refrigerant must be pushed to a higher pressure which is more work for the compressor. Also the capacity of the compressor will decrease. So as it gets hotter outside the air conditioner cools less and uses more energy. There will be a point when the air conditioner can no longer meet the cooling load and your indoor temperature will rise.

Why not just put in an air conditioner big enough to handle extremely hot days? Although it is bigger and uses more electricity, it runs only when needed. While quite uncomfortable, these hot days are few. Most of the time the air conditioner is trying to cool when the temperature is not at its peak value. The unit will turn on and off if the cooling needed is less than its capacity. This is very inefficient for the unit and also causes wear on the unit. It is more efficient to have a smaller unit run for a longer time, than a larger unit run for a shorter time.

Because of the loss of capacity and the increase in energy, proper maintenance is important. You may want to consider paying for a maintenance program by you local residential heating and cooling contractor. Have them explain how their program saves you energy.

Energy Solutions Explained

The lower the setting on your thermostat, the more cooling is needed. Move up the temperature setting to the point just before you become uncomfortable. If you are not home for more than a few hours, then raise the temperature a little more. Since night temperatures are lower, moving up the thermostat during summer nights is little help.

A Heating and Cooling Maintenance/Service contract is the best way to insure proper maintenance is being done. But there are a few things you can do. Look at your outdoor unit. It should be free of obstruction and debris like leaves and grass. (Do not wash the unit from the outside of the unit, it will drive dirt deeper into the coil.) Keep unit clear of surrounding shrubs. Listen to the unit run. Call for service if you hear any clanking or screeching. Feel over the fan to check if air is flowing strongly, the air will be warm to hot. (This air has all of the heat from your home.) Go inside to the indoor unit. Replace the air filter regularly. One inch filters should be replaced every month. Four inch filters can go three to four months before replacing. Dirty filters block airflow which reduces capacity and increases energy use. Look at the copper lines. The smaller line will feel warm and the larger one will feel cold. If there is ice on the larger line, then call for service. You have a refrigerant leak or major obstruction or both. By the way, if you are not certified to do so, it is against federal law to open any valve or cut into a line on the refrigerant system. See air distribution for more tips.

You can save energy by preventing the heat from getting into the house. Solar gain from the sun can add a large amount of heat to you home. Closing shades and blinds can reflect some of that heat back out the window. Energy saving actions like replacing windows, adding insulation, weather stripping, etc all save energy by reducing the run time of the air conditioner.

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