Geothermal Heat Pumps
An Alternative for Heating your Home

Last week I watched Al Gore's film called the "Inconvenient Truth," which just recently won an Academy Award for best documentary. In short, it detailed how the perceived threat of destruction caused by global warming will grow into reality in less than two decades. The film points out that one of the biggest causes attributed to global warming is the burning of both fossil and wood-based fuels which pour carbon dioxide-heavy emissions into the atmosphere.

This adds to the “greenhouse effect” which directs heat back into the earth's atmosphere. Even electric heat is suspect because, in many areas, to generate enough electricity for home heating generally takes power in the form of oil, gas or coal. This negates the advantages. What is needed is an alternative way of heating and cooling that does not require the generation of carbon dioxide. Heat pumps can be a good choice for stemming the tide of carbon monoxide emissions because the only power needed is for the mechanics. In many cases this low-energy requirement that can be generated by alternative sources such as solar and wind energy.
The name 'heat pump” does not aptly describe the process. Heat is not “pumped” but rather transported. For you engineering types “the second law of thermodynamics” states that heat cannot spontaneously flow from a cold to a hot area. Work is required to achieve this. A heat pump allows energy to be directed from a hot source to a cold one, extracting heat from this action in the process. The outdoor coil of the heat pump absorbs heat from the outside air, even at relatively low temperatures, and transfers it to your home. In hot weather the heat pump operates in reverse to provide cooling. It transfers heat from within your home to the outdoors.
The pump and motor of heat pumps are made of cast-iron with alloys of nickel, molybdenum and magnesium to avoid corrosion. The other parts are usually stainless steel with aluminum or, in some cases where consistency is critical, copper tubing. The fluid used to transfer energy from one heat source to the other used to be chlorofluorocarbons or (CFC's), a substance found to cause harm to the environment and ozone layer. In recent times the use of water, hydrocarbons and ammonia are implemented although the efficiency is less than the CFC's.
The fluid, in its gaseous state, is pressurized by a compressor and circulated through the system. On the discharge side of the compressor, the now hot and highly-pressurized gas is cooled in a heat exchanger called a condenser which renders it into a high-pressure, moderate-temperature liquid. The condensed refrigerant then passes through a pressure-lowering device like an expansion valve. Diagram compliments of B.C. Hydro.
The low-pressure, barely liquid (saturated liquid) refrigerant now enters another heat exchanger, the evaporator, where the refrigerant evaporates into a gas via heat absorption. The refrigerant then returns to the compressor and the cycle is repeated.
Most heat pumps in service are the air-to-air, or air-source, type. These units rely on outside air for their heat, but there is a problem with this: outside coils can form ice. So, periodically, this ice has to be melted and to do this the unit switches back to air conditioner mode which defrosts the coils. To prevent the house from cooling down during the process back-up burners or electric strip heaters are initiated during this process. This is the expensive process because the house is now heated by either electricity or fossil fuels at this time. Once the melting is completed the heaters shut off and the heat pump takes over again.
What is needed for sustained efficiency is a constant temperature to avoid this energy drain. Geothermal heat pumps extract heat from the ground or from water, either in a pond or well and, because the temperatures beneath the ground and water are a constant 7° - 13° C (45°-55° F) year-round.
This type of system has lesser temperature fluctuations and is therefore more efficient. There are two basic types of geothermal systems, open loop and closed loop. An open loop system uses a conventional well as its heat source but the water is discarded after the circuit has been made and the heat or, in summer, cold is extracted. Open loop systems are subject to disposal laws in certain areas. Diagram compliments of B.C. Hydro.
Closed loop systems consist of a system of buried or submerged piping in either a horizontal or vertical placing. In horizontal systems the pipe is laid 2.4 meters (six to eight feet) deep in trenches. In a water-based system the pipe is fixed below the winter ice level in pond or lake, or below low tide level in the ocean. In vertical systems, the pipe is put down from 45 to 60 meters (150-200 feet) deep in bored holes with U-shaped loops of piping. These are used in areas where space is limited. Diagram compliments of B.C. Hydro.

Geothermal heat pumps have made such an impact on heating costs that the EPA now touts the high efficiency and low operating costs of the units. According to the agency, geothermal heat pumps can offer homeowners from as much as 30 percent to 70 percent savings on heating and from 20 percent to 50 percent on cooling over traditional systems. A poll of builders who monitor these units shows a heating and cooling savings of between $358 and $1,475 over the course of a year.

And as technology advances more we should be seeing a potpourri of compact and efficient geothermal systems with the ability to heat and cool homes using only a small space in your back yard and utilizing solar energy to power the mechanics.

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