A GHX is not an energy source....it's a storage system

A GHX is not an energy source...it's not like a gas or power line, or even delivered oil or propane. These fuels are delivered to the building and are essentially an infinite energy supply (as long as someone pays the bill). A GHX is very much a storage tank that can be discharged and recharged depending on what is going on in the building it's connected to. When the building is being cooled, the GHX is being recharged with energy...when the building needs heat, the GHX is being discharged. The storage capacity of the GHX is...

dependent of the thermal characteristics of the soil or rock it is built in and the design and configuration of the heat exchanger buried in it. Some types of rock or soil hold more energy than others, and heat moves through some soils and rock more quickly than through others. 

The GHX can be a fairly leaky storage tank. It's influenced by:

• How near the pipe is to the surface of the ground. As rainfall filters through the soil it carries energy to the pipe or can drag it away, depending on the relative temperature of the soil and rain. Cold winter temperatures can cool a warm horizontal GHX and also have some influence on the top 30-50' (9-16 m) of soil above a vertical GHX.
• The ambient temperature of the earth around the GHX field. In warmer climates the temperature of the soil can be as warm as 75-80°F (24-28°C). In colder climates the soil temperature can be as low as 43°F (7°C), and in the far north the ground can be permanently frozen (barring global warming). Temperature differences created by changes in the temperature of the soil around the GHX causes energy to migrate to or from the soil in the far field. 
• Ground water moving in the soil will influence the temperature of the earth around GHX piping. 

The greatest influence in the temperature of the GHX field, however, is the energy transferred to and from the building to the soil. When energy is continually pushed into the GHX field, the soil warms over time...it can't dissipate to the atmosphere or to the soil in the far field around the GHX. If energy is continually removed, the soil around the pipe can actually freeze in extreme cases. If energy can't transfer quickly enough from the far field or from earth warmed by the sun and rain in summer, it can continue to cool over a number of years and eventually freeze. 

A GHX designer can prevent the soil from gradually over heating or cooling too much by ensuring the energy transferred to the ground in summer, when the building is being cooled, is approximately equal to the amount of energy removed in winter. If the energy loads can't be balanced within the building, there are a few options:

• Increasing the size of the GHX by increasing the depth of the boreholes and spacing between boreholes facilitates more energy transfer to and from the soil surrounding the GHX field and from the surface.
• Using other devices to either add energy to the system or to dissipate energy from the GHX field. This can include fluid coolers, boilers, waste energy from combined heat and power plants, solar thermal panels, snow melt systems, etc. Controls become a bit more sophisticated, but the size of the GHX field can be substantially reduced...reducing the cost of the system and improving the return on the owner's investment.