Friday, July 9, 2010

Is your AC working efficiently?

Summer is in full swing and air conditioners are working overtime. Here are some ways to make sure your AC is running at its optimum.

Size matters.
A window unit that is too big will cool the room too quickly, then turn off, then turn back on when the temperature rises. This cycle will be repeated over and over, meaning that you are using more electricity than you need to. A unit that is too big also won’t get the humidity out of the air, since it won’t be running long enough at a time. A too-small unit will also overwork, running constantly to keep up with the demand to cool the area.

To pick the size of the AC unit you need, use this equation: 20 Btu for every 1 square foot of living space. For example: your living room is 15 x 15. The calculation is 15 (feet) x 15 (feet) x 20 (Btus) = 4,500. You need an air conditioner with 4,500 Btus to cool the living room.

Now, of course, it can’t be as simple as all this, right? There are other factors to consider. Is your house shaded by trees? Do you use a whole-house fan too? Do you use the oven a lot (even in July and August)? Answering “yes” to any of these questions can impact cooling capabilities an average of about 5 percent. So, when you go to buy a unit, you may need to increase or decrease the Btus by 5 percent to accommodate how your household actually runs.

Efficiency is key.
Room AC units have an EnergyGuide label on them, which gives you an energy-efficiency rating (the higher the rating, the more efficient the unit). They also come with a comparison of similar models and a chart to calculate the cost of operating the unit based on usage.

Central air conditioning units are rated by Seasonal Energy Efficiency Ratio. The higher the ratio, the more efficient the system is.

Install it properly.
There’s no sense in buying an energy-saving model if you put it in the wrong place. Window AC units should be installed on the north or east side of the house in the shade to prevent direct sunlight from decreasing their efficiency. If there’s no other spot to put a window unit than in the sun, put an awning or some other shading device over it. Make sure, though, that the unit has enough room to exhaust air. This holds true for plants, too. Don’t hide the unit with trees or shrubs that are planted too close, because they’ll impede air circulation and decrease efficiency.

Make sure that you install room air conditioners levelly in a window or wall cutout. Units must be on a flat surface so that mechanicals, including the inside drainage system, operate efficiently.

The AC unit should also fit snugly inside its sleeve. There should be no gaps between it and the window.

And, of course, make sure that your house’s electrical system can meet the unit's power requirements. Room units operate on either 115-volt or 230-volt circuits. Standard household receptacles accommodate 115-volt branch circuits, so if you have a large unit, you may need a dedicated circuit. Room units rated at 230 volts may require a special circuit to be installed. If in doubt, consult an electrician. Also, don’t try to install central air yourself; have an HVAC contractor do it.

Boost energy efficiency.
Install a timer on room units. Central AC should be tied into your programmable thermostat. Set the timer to have the unit kick on a half-hour before you come home, that way the room is cool for you but you aren’t wasting energy and money by running the unit all day in an empty house. Just make sure that the timer you buy can handle the electrical load; you don’t want a fire.

Keep it maintained.
To keep your cool, follow this routine periodically.
  • Examine air filters once a month and clean or replace them when necessary. Clean filters can cut energy consumption up to 15 percent.
  • Remove window units for the winter. If they are permanently installed, such as in a wall, then cover and double-check weatherproofing.
  • For central AC, make sure all ducts are properly insulated, especially those that pass through the garage, attic or any other uninsulated areas.
  • Check drain channels for clogs, which can prevent the unit from reducing humidity. The build-up of excess moisture may drip and ruin walls and carpet. Clean channels by running a stiff wire through them.
  • Inspect the seal between the air conditioner and the window frame to make sure there is good contact with the metal casing. Moisture can create gaps that allow cool air to escape from your home, making the unit run less efficiently.
  • Clean the coils, which can get clogged with dust. For a room AC, unplug the unit and use a vacuum to remove dust from the interior heat exchanger. Use a garden hose to hit up the exterior heat exchanger.