Geothermal Heat Pump Systems

A geothermal heat pump is HVAC equipment that can heat or cool a building by tapping into the earth, utilizing a stable source of renewable energy such as the ground or a lake.

Geothermal or “ground-source” heat pumps heat or cool a building by coupling to the earth in several ways. These are sometimes referred to as “ground-coupled systems.” They transfer energy to borefields using a closed loop heat exchanger installed in vertical bore holes or in horizontal trenches.

The ground source heat pump can use the ground as a “thermal battery,” storing energy into the ground when the building is cooling (energy charge) and extracting energy from the ground to provide heat to a building (energy discharge). 

The geothermal heat pump transfers energy from the ground or lake to heat or cool a building. Additionally, the geothermal heat pump may also recover excess heat from within the building eg. people, computers, lighting. That heat is then transferred to other parts of the building or into the ground or lake for later use.

A central geothermal system consists of one or more chillers or heat pump chillers centrally located in a single mechanical room, coupled with a geothermal loop. The chiller/heaters provide heated and cooled fluid to hydronic heating and cooling air handlers throughout the building.

Ground source geothermal uses the ground as a form of energy storage. Energy is stored in the ground when the building is cooling (energy charge). Energy is extracted from the ground to provide heat to a building (energy discharge).

Ground source geothermal couples heat pumps to the earth utilizing borefields. The borefields refer to a closed loop heat exchanger installed in vertical bore holes or in horizontal trenches. Heat pumps inside the building transfer energy from borefields to the spaces that need heating and cooling.

Both distributed and central geothermal systems offer unique benefits beyond their geothermal function. As with any system, what one person views as an advantage, another person may view as a disadvantage.

Distributed systems use multiple small geothermal heat pumps located throughout a building, allowing for individualized zone control and built-in redundancy. However, they require maintenance at many locations and can generate more noise in occupied spaces due to nearby compressors.

The Central Geothermal System combines the energy efficiency of a traditional geothermal heat-pump system with the benefits of centralized heating, cooling and air handling to provide an even more efficient and comfortable geothermal system. Significant benefits include centralized maintenance, reduced noise, improved air cleaning and greater flexibility in equipment selection within the system.

One of the most critical elements in the design is the selection and layout of the ground heat exchanger. For example, the choice between horizontal and vertical heat exchangers is driven by available land, project budget, and capacity requirements.

Another major consideration is the configuration and control strategy of the heat pump equipment. Designers must decide between distributed systems and central systems. Each of these systems provides distinct benefits and drawbacks.

Lastly, system designers must evaluate maintenance of long-term ground temperatures and manage energy balance to the borefield to avoid situations of the borefield getting too warm or cold.