Ground Source Heat Pumps

This Video Explains About ground source heat pumps (Geo Exchange – Heating and Cooling System

About Ground Source Heat Pumps

Ground Source Heat Pumps (GSHP’s) use the earth's relatively constant temperature between 16 - 24^oC at a depth of 20 feet to provide heating, cooling, and hot water for homes and commercial buildings. GSHP harvests heat absorbed at the Earth's surface from solar energy. The temperature in the ground below 6 metres (20 ft) is roughly equal to the mean annual air temperature at that latitude at the surface. It uses the earth as a heat source (in the winter) or a heat sink (in the summer).

Working Principle of GSHP

The basic principle on which the GSHP works is "refrigeration cycle". The refrigerant carries the heat from one "space" to another. The heat pump's process can be reversed. The earth is the main source and sink of heat. In winters, it provides heat and summers it takes the heat.

The common two types of GHPs in use are

• Earth-couple (closed loop) system that uses sealed pipes/tubes-placed vertically or horizontally, through water or a mixer of water and antifreeze circulates transferring heat to and from the earth and
• Water source (open loop) system where water from the underground aquifer pumps water to the heat exchanger.

Between the two, earth coupled GHPs are very popular because they are very adoptable.

Efficiency of GSHP

The GSHP is one of the most efficient residential heating and cooling systems available today, with heating efficiencies 50 to 70% higher than other heating systems and cooling efficiencies 40 to 50% higher than available air conditioners.

Use of GSHP’s in India

GHP is effective in all kind of climate zones or can be deployed anywhere in India on 24 x 7 basis.

• Heating: Earth's heat (the difference between the earth's temperature and the colder temperature of the air) is transferred through the buried pipes into the circulating liquid and then transferred again into the building.
• Cooling: During hot weather, the continually circulating fluid in the pipes 'picks up' heat from the building - thus helping to cool it - and transfers it into the earth.

Use of GSHP can bring down substantially consumption of expensive electricity cost which is in the range of Rs 8-10 per unit at present.

Land requirement and Capital cost of GSHP

Trenches should be at least two meters deep to harness a consistent year-round heat source. Trenches will need 50-80 meters of pipe per kilowatt (kW), or 10 meters of ‘slinky’ coiled pipe per kW, with at least 5 meter distance between trenches with coils. So a typical 8kW heat pump requires around 400 m² of ground area for slinky coils. Note, however, that this will depend on a number of factors, including ground conditions.

Boreholes need 20-50 meters of pipe per kW, and will usually be 100-150 meters deep. You may need 2-4 pipes per borehole, or more than one borehole. The Pipe diameter should be 20 to 40mm for best performance.

Cost of the GSHP is site specific for normal soil it cost’s around Rs 1 Lakhs to 1.5 Lakhs per Tones but if the rock is encountered during boring then cost get increased.

Pay back period of GSHP

The payback period varies significantly, as geothermal systems are customized to individual homes. Factors that influence the payback period include:

• New home vs. retrofit (existing) home
• Cost of the geothermal heat pump system
• Size of home
• Energy efficiency of the home and the age/type of heating/cooling system the geothermal heat pump is replacing.

Roughly the estimated payback period of Geothermal Heat Pump is 2 to 3 Years.

Source : MNRE

Related Resources

1. FAQs on Geothermal energy
2. Geothermal Bulletin