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Furnaces go underground.


The British physicist Lord Kelvin wrote about them in the 1850s. Alabama Power experimented with them in tne 1940s. But it took the energy crunch of the 1970s and its impact on heating-fuel prices to inspire the practical use of electric heat pumps. Since then, heat pumps have grown popular in places where electricity is cheaper than natural gas, bottled gas, and heating oil.

No one disputes the efficiency of heat pumps. Well-designed systems can deliver three units of heat for each unit of electricity they consume --impressive when compared to open-hearth fireplaces, which send 95 percent of their heat up the chimney. Even the most efficient gas furnaces lose a fifth of the energy they create from combustion.

Yet heat pumps have their limitations, the biggest of which is doing their job when outside temperatures fall below freezing. A typical air-source system that works like a charm at 45 degrees will be faltering at 25 and barely delivering at 15. The problem, of course, is that there is simply less available heat in the colder air. Thus, north of the Sunbelt, you can't heat your home solely with an air-source heat pump.

Ground-source heat pumps, however, draw latent heat from soil or ground water instead, which are always warmer than the winter air. Thus, ground-source heat pumps are not the "fair-weather friends' air-source systems are.

James Bose, the director of engineering technology at Oklahoma State University, and his peers are so enthusiastic about the future of geothermal heat pumps they've formed an organization, the International Ground Source Heat Pump Association, to promote the technology. And home heating is one of the major applications for this technology.

A ground-source system connects to a long loop of plastic pipe buried horizontally or vertically in the soil. The loop, filled with a cold antifreeze solution, works like the condensing coil in an air conditioner. As the frigid solution flows through the plastic pipe, it picks up heat from the warmer soil and carries it inside.

Early efforts with ground-source systems were foiled by problems with the plastic pipe. Rigid polyvinyl chloride (PVC) pipe is now usually avoided in favor of flexible polyethylene pipe, which doesn't crack or disjoint with expansion and contraction. Some of the new pipes come with 40-year warranties.

Heat pumps are actually cooling and heating systems rolled into one: in the summer, as air conditioners, they carry heat outside or deposit it into the ground; in the winter, they work in reverse--moving heat into the house. Studies in New York and South Dakota show ground-source heat pumps use 40 percent less energy in winter than do conventional air-source systems with supplemental heat; studies in Mississippi found that ground-source systems also use less energy that air-source systems during the summer months.

Before you run to buy a ground-source system, give consideration to several things. First, consider the relative costs of energy sources in your part of the country. If you live in an area of cheap natural gas, wood, or heating oil, you can probably heat your home less expensively with a conventional furnace or wood stove.

Next, consider the age and efficiency of your present heating system: if it's a 20-year-old energy gobbler, replace it. But a newer furnace will have some energy-saving features, not to mention many years of useful life ahead of it.

Third, remember that heat pumps don't follow the surge-and-ebb pattern of combustion furnaces. The heated air from the ducts, therefore, won't feel as hot. To compensate, you may have to install larger duct-work or increase the number of registers. You'll certainly want to tighten up your home's insulation to improve the new system's efficiency. But by going that far, you may not need a new system.

Fourth, consider the shortage of trained heat-pump contractors. Even in the Southern states, where conventional air-source heat pumps are installed by the tens of thousands, it's difficult to find mechanics who can do the work. Nobody wants a $6,500 system compromised by shabby installation, yet ground-source heat pumps have 1,000 feet of buried plastic pipe that must stay sealed in order to work correctly. If your power company can't recommend a good contractor, maybe you should wait a few years.

The cost of ground-source heat pumps has fallen drastically in the past few years. Units priced at $10,000 a few years ago have dropped as low as $5,000 in some areas.

The advent of ground-source systems means that heat pumps will soon be as successful up North as they've been in the Sunbelt.

Photo: A Vertical Ground Loop Heat Pump System

Geothermal heat pumps use the latent warmth from the ground to help heat our homes. Vertical systems circulate a mixture of water and antifreeze deep down horizontal systems employ more shallowly buried ground loops.
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Title Annotation:geothermal heat pumps for home heating
Author:Ayes, Jack
Publication:Saturday Evening Post
Date:Dec 1, 1987
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