What makes GCHP systems different than conventional HVAC systems

Inside the building a GCHP system is very similar to a conventional heating and cooling system. They both use the same kinds of distribution systems...either a forced air and/or hot and chilled water distribution systems. They're both controlled with a thermostat. They can both keep you very comfortable if they are well designed and installed. So what makes a GCHP system different?

Most conventional systems are connected to an external energy source. A gas line. An electric grid. An oil or propane delivery service. As long you pay the bill you have access to, for all intents and purposes, an infinite energy source. A GCHP system, however, is connected to a relatively finite mass of dirt. It's possible, if you take enough energy from the ground heat exchanger (GHX) the heat pump is connected to, you can completely discharge your GHX. 

Think of it as a battery. Even a weak battery will power a flashlight for a little while...but if you want to read a whole novel by flashlight, you'll need a fully charged battery. If you expect to heat your home or building with a GHX all winter, you'll need to make sure it's fully charged or it can get too cold for the heat pump to extract heat from it efficiently. It may even quit working altogether.  Likewise, if you live in a hot climate with a GCHP system, it's possible to overcharge the ground. It can get too hot for the heat pump to work efficiently. 

The mass of dirt the GHX touches, the type of rock or soil it's installed in, how deep it's buried, the ground temperature, moisture content and ground water flow, and a bunch of other factors all have to be considered when designing a GHX for your system. The design of your home or building and how it's used can have a huge impact on how much energy you have to extract from the ground to heat it and how much energy you have to take from it to keep it cool. 

In upcoming posts we'll look in greater detail at some of the factors you have control of, and some of the factors you have little control over and what you can do to deal with them.