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'Heat Pump' Doubles as an Air Conditioner

August 01, 1993|JAMES DULLEY | Dulley is a Cincinnati-based engineering consultant

QUESTION: I need a new central air conditioner. I've heard of special ground-source heat pumps that can produce $4 of free heat for each $1 on my utility bills. Are they also super-efficient for air-conditioning?

ANSWER: The correct name is "geothermal heat pump" and they are also super-efficient central air conditioners in the summer. Replacing a 10-year-old central air conditioner with a geothermal heat pump can cut your air-conditioning bills by up to 50%. The steady high-cooling capacity insures comfort even on the hottest days.

Even if you have a gas furnace, it may be economical to add on a geothermal heat pump. With some of the new geothermal units, you pay only 20 cents on your electric bill for each $1 of heat you get in the winter.

Another advantage of geothermal heat pump is free hot water in the summer. With a geothermal unit, the waste heat removed from your house runs through a special heat exchanger. This transfers the heat to your water heater, so you get free hot water all summer. It can also heat water in the winter less expensively than an electric water heater.

A geothermal heat pump is very efficient for heating and cooling because it uses the earth as a source for heat in the winter and a sink to exhaust heat in the summer. Since a condenser fan is not needed, the entire system (in a soundproof cabinet) is located inside your utility room or basement. Since it is indoors, there is little maintenance and risk of damage.

In the summer, ground temperatures several feet deep can be 30 degrees cooler than the outdoor air. This makes it easier for the heat pump to exhaust heat from your house. In the winter, the ground can be 40 to 50 degrees warmer than the air, so it is easier to draw out the free heat.

A closed-loop geothermal heat pump system circulates a water/antifreeze solution in a small plastic pipe buried in the ground. This long pipe can be laid horizontally in a very narrow, several-feet deep trench. Another closed-loop system uses a long vertical pipe in a hole drilled in the ground. An open-loop system can use water from ponds or wells.

There are several design variations that effective the efficiency. One manufacturer has a two-speed compressor. It runs in the super-efficient slow speed 80% of the time. It switches to high-speed only during very hot or cold weather. Many models now use new low-maintenance scroll or inertia compressors. Other models have multispeed blowers for comfort.

Another design runs the refrigerant through the pipes in the ground. This eliminates one of the heat exchangers and therefore increases efficiency. A vertical "fence" configuration of pipes is used in a narrow trench.

You can write to me for Utility Bills Update No. 595 showing a buyer's guide of geothermal heat pump manufacturers listing maximum cooling and heating outputs, efficiency levels, types of compressors, prices and special features. Please include $1.50 and a self-addressed business-size envelope. Send your requests to James Dulley, c/o Los Angeles Times, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.

Does Electric Lawn Mower Waste Energy?

Q: My gasoline lawn mower quit yesterday and I am considering an electric one. Does an electric lawn mower use more energy?

A: An electric lawn mower is more energy-efficient than a gasoline mower. Small gasoline engines are inefficient, require expensive tune-ups, are noisy and severely pollute the air.

A typical electric lawn mower has a motor that draws about 11 amperes. At an electric rate of 9 cent per kilowatt-hour, for example, it costs about 12 cents per hour's use.

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