Q: With these crazy gasoline prices, we stay home more now. Therefore we use the air conditioner more. My old central air conditioner costs a lot to operate. What type of replacement unit will be cheapest to run?
A: I think everyone is feeling the budget pinch from high gasoline costs. Other than driving less or buying a hybrid, there is not much you can do about the cost. Fortunately, installing a new super-efficient air conditioner unit costs a lot less than a new car and it will save money and improve your family's comfort.
Many new super-high-efficiency central air conditioners are available, and many use Earth-friendly (ozone-safe) R410A refrigerant. Assuming your old air conditioner is of typical efficiency, installing a new one with the highest SEER (seasonal energy efficiency ratio) of 21 will consume less than 50 percent as much electricity as your old one. The newer outdoor compressor/condenser unit also operates more quietly than old ones.
The payback period from the savings on utility bills depends upon your climate and the efficiency of your house. Particularly if your house is not energy-efficient (old windows, little insulation, leaky ductwork, etc.), the 50 percent savings can provide an excellent return on your investment. It also helps the environment.
Since you want a new central air conditioner with the lowest operating cost, have your heating/cooling contractor provide a quote on a two-stage model with a variable-speed ECM blower motor and matching thermostat. This setup can cost several thousand dollars more than the cheapest single-stage model.
If you go this route, your contractor will likely recommend you also install a new two-stage or modulating furnace at the same time. This is because the furnace and central air conditioner use the same controls, thermostat and blower motor. Even if you do not install a new furnace, you will have to install a new indoor cooling coil to attain the high efficiency.
A two-stage model operates at a low-cooling-output level about 80 percent of the time. This uses less electricity and provides more even cooling. With the newest communicating thermostats, the indoor air temperature varies less than one-half degree from the setting. This allows you to set the thermostat a degree or two higher for more savings without sacrificing comfort. With a TAM or SAM (telephone or system access module), you can change the setting remotely.
Even though it costs a little more, install a variable-speed blower motor. This allows the cooling system to constantly vary the air flow for maximum cooling or maximum dehumidification or any combination you like. This also lowers the indoor noise level from the air flowing through the ducts. With the soft-start motor speed, it is barely noticeable when it comes on each time.
James Dulley is a mechanical engineer and do-it-yourselfer. Send questions to James Dulley, The Sensible Home, St. Petersburg Times, 6906 Royalgreen Drive, Cincinnati, OH 45244. Go to his Web site at www.dulley.com to tour his energy-efficient home, post questions for other readers and find other information.