Geothermal heating is the direct use of geothermal power for heating applications. Humans have taken advantage of geothermal heat this way since the paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004. As of 2007, 28 GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption. Thermal efficiency is high since no energy conversion is needed, but capacity factors tend to be low (around 20%) since the heat is mostly needed in the winter.
Geothermal energy originates from the heat retained within the Earth's core since the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. Most high temperature geothermal heat is harvested in regions close to tectonic plate boundaries where volcanic activity rises close to the surface of the Earth. In these areas, ground and groundwater can be found with temperatures higher than the target temperature of the application. However, even cold ground contains heat, and it may be extracted with a geothermal heat pump. Due to recent advances in heat pump performance, this is now a rapidly growing market.
Ground source heat pumps work in a similar manner as air source heat pumps, minus the high cost. Atypical household can save $2500 a year or more. This can give most systems a payback period of three to five years. GSHP's are more than three times as efficient as the most efficient fossil fuel furnace. By moving heat that already exists in the earth, instead of burning a combustible fuel, GSHP's deliver three units of energy for every one unit used to power the heat-pump system.
The principle action of a heat pump moves heat from lower temperature location to a higher temperature location. This principle can be witnessed in an air conditioning window unit, or air source heat pump, where cold air is blown into the house and warm air is released out of the back of the unit. A ground source heat pump works in a similar manner, except that its heat source is the warmth of the earth. The process of elevating low-temperature heat to over 100 degrees F and transferring it indoors involves a cycle of evaporation, compression, condensation and expansion. A refrigerant, like freon, is used as a heat-transfer medium which circulates within the heat pump.
The cycle starts as the cold, liquid refrigerant passes through a heat exchanger (evaporator)
The ductwork is no different than that of a conventional forced-air system. The difference is found in the temperature of the air flowing from the registers in the winter. With a conventional air source heat pump, the air flow is seldom warmer than 80 degrees. But because water transfers a greater volume of heat than air, the Ground source heat pump is able to deliver warmer air, typically about 110 degrees F.
Another benefit of a ground source heat pump can be found when teamed with a desuperheater. This component skims residual warmth from the compressor to heat water. Which means that in the summer, when the system is working to get rid of heat, the desuperheater can provide practically free hot water. And since most systems are oversized, there is usually enough warmth left over for low cost hot water in the winter too.
http://www.geoprodesign.com/
http://www.geoprodesign.com/
