Combined heat and power (CHP) and GCHP systems

A challenge with a GHX in extreme climates is the imbalance between heating and cooling loads. Unbalanced energy loads require a larger GHX. They cost more to build. They require more space between boreholes or trenches. They don't work as efficiently because the fluid temperature to the heat pumps approaches the upper or lower limits of heat pumps connected to them. The additional construction cost combined with lower operating efficiency makes these projects more difficult to justify to a client. 

In colder climates there can be significant advantages to integrating a GCHP system with a combined heat and power (CHP) plant. Depending on the type of power plant, only 25% to 40% of the energy used by the power plant is converted to electricity. A similar percentage of the fuel used by the power plant is converted to heat that can be captured and used to provide space heating or domestic hot water.

The problem with a conventional CHP system is that not all of the projects that can use the waste heat can make use of it when it's available...much of the waste heat is truly "wasted" to the outside air. 

Integrating a CHP system with a GHX and a GCHP system provides a storage medium for the waste heat. In spring, summer and fall, waste heat from the CHP system that would normally be wasted to the atmosphere can be rejected into the GHX, gradually increasing the temperature of the soil and rock around the buried pipe. As the temperature drops in fall and winter, energy stored in the ground can be pulled out by homes and businesses connected to it. 

The waste energy stored in the GHX has an enormous impact on the size of the GHX needed for the system compared to a conventional GCHP system that relies only on the ground. An example of a project appropriate for this approach is found in this paper presented at the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE)/uploads/2/2/3/6/22361732/paper_9101_manuscript_rev.pdf.