Residential Geothermal Basics: Basic Ground Source Heat Pump Process

April 30, 2009 - PRLog -- Residential Geothermal Basics

Ground source heat pumps (GSHPs) are electrically powered systems that tap the stored energy of the greatest solar collector in existence: the earth. These systems use the earth's relatively constant temperature to provide heating, cooling, and hot water for homes and commercial buildings.

1. How Geothermal Energy works

The heat pump system uses solar energy stored in the earths crust. Energy is transferred to and from the earths surface by solar radiation, wind and rainfall. As a consequence of this solar energy, the earths temperature at depths greater than 10 meters remains constant, and is comparable to the annual average air temperature. Between the surface and a depth of 2.5 meters (maximum depth for a horizontal loop) the ground temperature will swing above and below the annual average air temperature , depending on the geographic location, soil type an moisture levels.

Because of its own insulation, the earth's soil temperature is more moderate year round than outside air.

3. How a heat pump works

Ground sourced heat pumps simply move energy from one place to another. The process of which is explained on the image below:

  1. An Evaporator (ground loop heat exchanger) transfers the heat from the ground into the fluid circulating in the loop.
  2. At this point the energy in the ground loop transfers through the evaporator within the heat pump and into a CFC free refrigerant.
  3. A compressor increases the pressure of the working fluid, which causes the temperature to rise.
  4. This energy is transferred over the condenser and into the distribution circuits, where hot water is circulated through the under floor circuits and in turn heating the property.
  5. The refrigerant now passes through an expansion valve and the process starts again

4. Types of Ground Loop

Ground source heat pumps can be categorized as having closed or open loops, and those loops can be installed in three ways: horizontally, vertically, or in a pond/lake. The type chosen depends on the available land areas and the soil and rock type at the installation site. These factors will help determine the most economical choice for installation of the ground loop.

For closed loop systems, water or antifreeze solution is circulated through plastic pipes buried beneath the earth's surface. During the winter, the fluid collects heat from the earth and carries it through the system and into the building. During the summer, the system reverses itself to cool the building by pulling heat from the building, carrying it through the system and placing it in the ground. This process creates free hot water in the summer and delivers substantial hot water savings in the winter.

5. Overall Concept

The closed loop portion of a ground sourced heat pump system consists of a long plastic pipe buried below the earth's surface. This plastic pipe is buried in the ground, or ground coupled, to allow heat transfer between fluid in the pipe and the earth. The heat pump transfers thermal energy to and from the closed, buried pipe and the buildings thermal load. The system consists of the closed-loop buried pipe, a water-sourced heat pump and an energy distribution system. In some cases the heat pump can provide domestic hot water (DHW).

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