Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: TUESDAY, July 5, 1994 TAG: 9407050133
SECTION: EXTRA PAGE: EXTRA6 EDITION: METRO
SOURCE: David Butler
DATELINE: LENGTH: Medium
A: Multispeed heating and cooling has been around for years. The air handler has a two- or three-speed blower motor so it can more closely match the current demand for heat or air-conditioning. If your house is well insulated, a multispeed system will operate on low most of the time, delivering additional capacity only when you need it. A single-speed system, on the other hand, is either on or off.
For optimum efficiency and overall system balance, multiple-speed blower motors are usually combined with multistage energy sources. Otherwise, the reduced airflow during low-speed operation could cause through the air handler to overheat or freeze up. For example, a multispeed gas furnace typically has a two-stage burner and a two-speed compressor, allowing the entire system to operate in tandem. This same strategy is used by multispeed heat pumps.
Multispeed systems offer improved comfort by maintaining a more consistent temperature, usually within one degree. Furthermore, since they run at their lowest speed more than half the time, you'll spend less for energy and maintenance. If you live in a humid climate, you can save even more. When an air conditioner runs slower, it does a better job removing moisture, allowing you to raise the thermostat without sacrificing comfort.
Recent advances in electric motor controls have led to a new generation of continuously variable blowers and compressors. Although still relatively expensive, variable-speed systems deliver the same benefits as multispeed, only to a greater extent. With a seasonal energy efficiency ratio (SEER) of up to 16.9 (cooling) and a heating seasonal performance factor (HSPF) up to 9.5 (heat pumps), you can recover the extra cost in just a few years.
Unlike two-speed models, a variable-speed system rarely turns off, leading to further operational efficiencies and even better humidity control. For heat pumps this means no more cool air blast every time the system turns on. And you'll appreciate the continuous super-quiet operation of a variable-speed system.
Using rebates and other incentives, many utilities are aggressively promoting variable-speed and other high-efficiency air conditioners and heat pumps. Gas utilities have something to be excited about as well - the first natural gas heat pump. Using variable-speed technology, it achieves an annual fuel utilization efficiency (AFUE) of 126 percent, more than 30 percent higher than the most efficient gas furnace! Later this year, a gas furnace with a continuously variable burner will be introduced.
Variable-speed technology also offers some unexpected benefits. With today's super-tight homes, fresh-air ventilation has become increasingly important. Since variable-speed blowers run constantly, they make the perfect companion for a heat-recovery ventilation system. Variable-speed is also well-suited for automatic damper systems. The blower slows down as more dampers close, eliminating the need for a bypass duct.
To receive a list of multispeed and variable-speed furnaces, air-conditioners and heat pumps, please send $1.50 and a self-addressed envelope to David Butler F-251, Department TWN, 14713 Pleasant Hill Road, Charlotte, N.C. 28278-7927. It includes toll-free phone numbers and a description of each system. You'll also receive information on the first natural gas heat pump.
Reader tip: Rather than wait for my aging heating and cooling system to fail, I went ahead and sought advice from several local contractors so I'll be ready when it finally gives out. Since this is one of the most expensive repairs a homeowner is likely to face, a snap decision under duress can only lead to regrets.
by CNB