©2008 by  Raymond Alexander Kukkee

Heat Pumps:  Pump Free Heat from the Earth

Modern and efficient geothermal heating systems that harvest free heat from the earth are becoming increasingly popular as a method of providing domestic heating. Vast amounts of heat from the sun is stored in the earth at all times, waiting to be tapped as a ready source of free, clean, and renewable energy.   Geothermal heat is extracted from the earth by essentially the same mechanical process used in any domestic refrigerator or freezer. In a home appliance, the circulation of refrigerant absorbs heat from the food storage compartment and the heat is moved outside of the appliance. In a geothermal heating system, heat energy is absorbed from the earth and transferred into the residence.

Operating a geothermal system involves pumping a liquid, usually an alcohol/water mixture, through pipes buried in the earth. The liquid absorbs ground heat, which is then subsequently extracted by a "heat pump" and heat exchanger system that uses common mechanical refrigeration equipment including a separate refrigerant loop, a compressor, condenser, and a heat exchanger similar to a common radiator. The "ground heat" is extracted from the circulating coolant and transferred by a heat exchanger to the refrigerant loop. The heat is then transferred to a water or hot air exchanger, and distributed throughout the residence by forced air or circulated hot water.

Domestic potable hot water may be heated and is usually available with the installation of a heat pump system. Highly efficient residential air conditioning is also offered using the same equipment, simply by reversing the process and sending heat from the building back into the earth.

Geothermal Heat is Free

With the average temperature of the soil approximately 40 degrees at depth and remaining relatively constant, a virtually endless supply of heat is accessed . Modern heat pump systems are highly efficient and are being continuously improved. At the date of writing, with some systems, for every 1,000 watts of energy used to operate the system, heat energy returned is 4,000 watts or greater, for an effective C.O.P. (Coefficient of Performance) efficiency rating of 4:1 or even higher.

  Efficiency and high energy return of a geothermal home heating system make a geothermal heat pump system an attractive heating option, simply because the heat drawn from the ground is absolutely free. The only energy consumed is the minimal power needed to circulate the heat-collecting fluid, and the power to operate the heat pump compressor and associated equipment to effect the extraction and distribution of the heat.  

Mechanics of the System

  A system of specialized, flexible, seamless, pipe, normally 1-1/4 to 1-1/2" diameter,  durable polyethylene or equivalent pipe -is usually buried horizontally in a soil trench at an average depth of 5 to 6 feet in trenches conveniently located for the application. One or more lines may typically be placed in a single, continuous trench, or in a more compact configuration of shorter trenches 10-20 feet apart. The pipe is carefully bedded in rock-free soil at a constant depth and the trench may be insulated where traffic will drive over it, or where the desired soil depth is not achievable because bedrock or other obstructions exist. Alternative ground pipe system designs may include sinking a continuous coil of pipe into a pond, burying a large coil of pipe in a smaller, compact, wet area, or installing sealed vertical pipe loops in one or more vertical wells as required, with all loops interconnected to optimize circulation and maximize heat transfer from groundwater to the circulating fluid in the pipes.   Inside the building, the circulating fluid is routed through high-pressure pipes, connected directly to the circulating pump station and to the mechanical heat pump. The heat pump is controlled by a solid state circuit board and a suitably-located programmable thermostat system.          *This modern heat pump is  smaller than an average-sized domestic refrigerator.    

  The physical length of earth pipe required for any installation depends upon the soil conditions available and the size, condition, age and type of home construction. The type of windows, geographical location and other mitigating factors all affect the technical analysis of the home. Heat loss is calculated, and the correct size of equipment is recommended by qualified heating contractors. The rating of the actual heat pump unit required and the capacity of circulating pumps required for the installation is based upon the calculations. As an example, a modern, well-insulated 1500 square foot home may be found to require, upon calculation, 2,000 linear feet of pipe with a circulation rate of 9-10 gallons of ground fluid per minute, and a mechanical heat pump unit rated at 3.5 tons*. (* Heat pump equipment is rated using the same system that air conditioning equipment is rated with. One "ton" equals 12,000 BTU's ( British Thermal Units) , the cooling equivalent of one ton of ice. A single B.T.U. equals the amount of heat required to raise one pound of water one degree Fahrenheit. )   Various models of heat pumps are designed and available to heat air for forced air systems, or heat water,- for circulated-water hydronic systems. Both types of systems may also provide domestic hot water as an added bonus. The correctly-sized mechanical heat pump unit is installed with high-quality connections to suitable electrical circuits and to existing hot and cold air plenums if an existing forced-air distribution system is used.

A separate potable water circuit may also connected to provide pre-heating of the existing domestic hot-water tank system if the domestic hot water option is desired. Considering that 50% or more of the electricity used in an average home may be used for heating potable water, the geothermal domestic hot-water option can be a substantial benefit and a good choice for most homeowners. A suitably sized electrical heating coil is usually included in the heat pump unit, and is designed to provide backup electrical heat in the event of compressor failure, or for assistance under sudden changes in severe weather conditions. Under normal conditions, however, if the system is correctly sized and designed, the electrical heating coil will very seldom be required except under the most extreme weather conditions.   After the ground pipe installation is completed, the ground loop is pressure-tested and if deemed leak-free, it is charged with environmentally-friendly denatured alcohol/water mixture ( 50:50) and all entrained air is removed from the system by circulation and bleeding of air from the system. Antioxidant chemical is also introduced into the ground loop liquid system to eliminate corrosion. After commissioning and testing the equipment and controls for operation and efficiency, the system is set into operation and the system will operate automatically. Modern programmable thermostats are capable of keeping the building temperature within one-half of one degree, maintaining any set temperature range desired, switching back and forth to air conditioning mode automatically, and lowering the room temperature at night in various zones if the heat distribution system has been designed to do so.  

"Can I retrofit a Geothermal system to my older home?" is a common question asked.

Upgrading to Geothermal Home Heating

Retrofitting a geothermal heating system to an existing, older home is commonly done. A heat pump system can be adaptable to many situations, and to minimize cost, the process usually involves tying the mechanical heat pump to the existing heat distribution system, whether it be for hot air or hot water distribution.

Heat may be distributed anywhere in the home by using one of several methods, including forced air, circulating of hot water to various separately valved zones, through existing registers, or by circulating hot water through specialized pipe networks placed in the floors or ceiling of the building. Hybrid adaptations involving both air and water systems are common.

Modern geothermal home heating is a good choice if you are considering changing or upgrading your heating system. Geothermal heating systems are clean, efficient, and may be qualified for home improvement grants available under energy conservation programs in some jurisdictions if the home meets program criteria. If you need to upgrade your home  a geothermal home heating system, do contact your local geothermal heat pump dealers for details and make the decision to keep your home warm the efficient, clean, geothermal way. ##

Is that Incoming I hear?