Installing an A/C System Everyone is Cool With Takes a Pro

It Takes a Pro to Put In an AC System Everyone's Cool With
By Tim Carter
Saturday July 21, 2007
WashingtonPost.com

Q: DEAR TIM: The air conditioning in my home has never seemed to work well.
My recent promotion and transfer has me moving to home that is in the early stages of construction. What can I do to ensure that the new home has a central air-conditioning system that keeps all rooms comfortable no matter the outdoor temperature? Is it possible to have all rooms nearly the same temperature? My existing home's second floor feels like an oven.-- Julie

A: DEAR JULIE: I can think of many reasons why the central air conditioning in your existing home does not cool properly. Some of the problems might have been corrected with a simple service call from an expert at air-conditioning troubleshooting. It's also possible that you have had serious air-conditioning-system design flaws that would have cost thousands of dollars to correct.
The central air-conditioning system, plus the heating system, is one of the most important parts of a home, after a sound roof and indoor plumbing. The systems create an artificial climate.
It is realistic to expect this climate to be the same in each room. In my home, each room, no matter the outdoor temperature or time of day (this is very important), can be within one or two degrees of any other room. That keeps my family and me comfortable.
It is unrealistic to expect your home to be a certain temperature no matter what the outdoor temperature is. In other words, if the outdoor temperature is 115 degrees, I would not expect you to be able to cool your home to 72 degrees without considerable discomfort on days when the temperature is, say, 85.
Central air-conditioning systems are designed to operate in a given range of temperatures. For example, the range in your part of the country may be 20 degrees. This means there is only a 20-degree difference between the outdoor temperature and the lowest temperature the system can maintain indoors. It is possible to create a wider temperature spread, but oversizing an air-conditioning system can result in short-cycling when the air conditioner has little work to do.
If an oversize air-conditioning system short-cycles, or has to drop the temperature only a few degrees, it does not run long enough to remove humidity from the air. When this happens, the temperature inside the home gets to the desired level, but you feel cold and clammy. Properly designed central air-conditioning systems run for 10 or 15 minutes at a time, which allows them to extract humidity as the air flows across the cooling coils in the air handler.
The key to getting a central air-conditioning system to work properly is to have a professional size the equipment and install a duct system that delivers the right quantity of air to each room of the house. Each room must also have a return-air duct that vacuums hot air from the ceiling and returns it to the central system to be cooled once more.
A professional air-conditioning technician can analyze your new-home plans with computer software to determine the heat gain and loss for each room. This same exercise can be done on existing homes. With this data, the technician can ensure that the proper size equipment is bought and that the ductwork is sized correctly.
Tim Carter can be contacted via his Web site, http://www.askthebuilder.com/printer_Submit_Question.shtml