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Sizing a cooling systemPosted Friday, April 22, 2011, at 12:11 PM
Most central cooling systems that are installed in today's homes are oversized. By some estimates, as many as 80% of air conditioners and heat pumps that are in use today are too large in their capacity for the homes in which they have been put into use.
To the home owner this presents several undesirable conditions. Not only are the larger units more expensive to purchase but they require (and waste) more costly energy. In addition to that, "short cycling" (when the cooling unit operates for only short periods) will reduce the life of the unit and will fail to remove humidity from the home that is being cooled. Reducing the temperature in the home without sufficiently removing humidity can be conducive to mold growth.
There are certain formulas that trained heating and cooling specialists use for calculating the specific needs for a home and while the amount of the conditioned area in square feet is an important factor, it is only a part of what goes into those formulas.
When determining the proper size for the cooling unit the type and placement of the distribution ducts and vents, the placement and number of return air vents, the amount of insulation in walls and ceiling, the direction in which the home is facing, the types and numbers of windows, the color of the roof, attic venting, the amount of shading from nearby trees and many other variables also need to be considered. Failure to take all of these factors into consideration will result in waste, discomfort or both, and it is almost impossible to calculate these needs without taking the time to acquire the required data and model the home with the assistance of a computer program.
Select a heating, ventilating and air conditioning professional who uses "Manual J" and/or "Manual F" calculations to determine the proper cooling system for your home. You will be assured of increased comfort for the least expense while paying for less energy to cool your home this summer.
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James H. Bushart is a Building Analyst who is certified by the Building Performance Institute (BPI) and is also a Certified Missouri Home Energy Auditor by the State of Missouri Department of Natural Resources. He has performed home performance analyses (aka "energy audits") for homes of all types throughout the states of Missouri and Arkansas. He has also performed over a thousand inspections of Missouri homes and commercial buildings and holds various certifications and licenses in residential building inspections.
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