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:
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:
In my blog I'll be expressing my opinions about what I've the learned about ground coupled heat pump (GCHP) systems over the last 30 years. I've been very fortunate to work with many interesting people who are passionate about this technology...engineers, geologists, mechanical contractors, drillers, excavation contractors...in different parts of the world. I've learned a lot from them and will be using this forum to pass on some of the things I've learned and feel are important. Please feel free to use this information if you feel it's worthwhile...hopefully you can avoid some of the same mistakes I've learned from.
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