The two main components of a geoexchange system are the:
- Ground Source Heat Pump or geothermal heat pump which provides the mechanical component of the system (Click here to learn more about Ground Source Heat Pumps or Visit our product range).
- Ground loop or Ground Heat Exchanger provides the passive component of the system.
The Ground Heat Exchanger is the component that extracts the heat from the ground in winter or returns it to the ground in summer. They are classified as either closed loops or open loops depending on how they utilise the water flowing through the system. In some instances can be coupled to conventional chillers/boilers as a hybrid system.
Closed loops are constructed of polyethylene (PE) pipe and continuously circulate the same water for many decades. They can be either a vertical (borehole) or a horizontal (trench) configuration and some are even located in surface water bodies such as dams and harbours.
The loop fluid is simply circulated through the ground loop and returned to the Ground Source Heat Pump. In accordance with the Zero Law of Thermodynamics, the loop fluid and the ground will endeavour to reach a thermal equilibrium.
Thus during its passage through the ground, the loop fluid is equilibrating with the stable ground temperatures either by extracting heat from the ground (winter) or rejecting heat to the ground (summer). The extent of this equilibration is determined by the residence time in the ground, the temperature differential between the loop fluid and the ground and other ground properties such as thermal conductivity and thermal diffusivity.
Some important points to note regarding closed loop systems:
- Closed loop systems should be installed using only high-density polyethylene or polybutylene pipe. They have a chemical half life of ~250 years, are inert to chemicals normally found in soil and properly installed would be expected to last well beyond the life expectancy of your home. PVC or copper pipe should not be used.
- Pipe sections are joined by thermal fusion. Thermal fusion involves heating the pipe connections and then fusing them together to form a join that’s stronger than the original pipe. This technique creates a secure connection to protect from leakage and contamination.
- An earth loop will not affect your lawn or landscape. Research has proven that loops have no adverse effect on grass, trees, or shrubs. There will initially be temporary bare areas, but they can easily be restored with grass seed or sod. Vertical loops require little space and result in minimal lawn damage.
Horizontal Ground Heat Exchanger
Horizontal closed loops are installed when there is sufficient land area available and that soil depth permits excavation to an approximate depth of 1.5m.
There can be multiple pipes within the trench and the total length of the trench is a function of the heating / cooling load.
Vertical Ground Heat Exchanger
Vertical closed loops are installed when land area or shallow rock does not permit the installation of a horizontal loop.
The boreholes are drilled to depths from 50 to 120 m. The depth of the boreholes, the number of boreholes and their spacing is a function of the heating / cooling load.
Closed Water Loop Heat Exhanger
The only thing cooler than heating / cooling your home from the ground is using your dam, pond or lake. Either polythylene coils or stainless steel plate heat exchangers are installed in the dam to provide a low cost an dhighly efficient system.
A minimum of 1.8 meters in depth at its lowest level during the year is needed for a pond to be considered as suitable.
The surface area required depends on the heating and cooling load of the home.
Open loops utilise ground or surface water directly, pass it through a heat exchanger and then return the water to either its origin or a secondary application such as irrigation, industrial water etc. Open loop sources are varied and include groundwater, rivers, oceans, dams and treated effluent.
Some important points to note regarding open loop systems:
- The water requirement of a specific model is usually expressed in litres per second (l/s) and is listed in the unit’s specifications. Generally, the average system will use 0.07 l/s per kilowatt of capacity while operating. However, the exact volume of water required depends on the size of the unit and the manufacturer’s specifications. Your contractor should be able to provide this information.
- Your well and pump combination should be large enough to supply the water needed by the heat pump in addition to your domestic water requirements. You probably will need to enlarge your pressure tank or modify your plumbing to supply adequate water to the heat pump.
- There are a number of ways to dispose of water after it has passed through the heat pump:
- The open discharge method is the easiest and least expensive. Open discharge simply involves releasing the water into a stream, river, lake, pond, ditch or drainage tile (if permitted in your local area). Obviously, one of these alternatives must be readily available and have the capacity to accept the amount of water used by the heat pump before open discharge is feasible.
- A second means of water discharge is the return well. A return well is a second well that returns the water to the aquifer. A return well must have enough capacity to dispose of the water passed through the heat pump. A new return well should be installed by a qualified well driller. Likewise, a professional should test the capacity of an existing well before it is used as a return.
- All or part of the installation may be subject to local codes and licensing requirements. Check with local authorities to determine if any restrictions apply in your area.
- An open loop system is pollution free. The heat pump merely removes or adds heat to the water. No pollutants are added. The only change in the water returned to the environment is a slight increase or decrease in temperature. Systems are designed to ensure this does not result in heating or cooling of the aquifer.
- You cannot reclaim heat from your septic system disposal field. An earth loop may reach temperatures below freezing during extreme conditions and this may freeze your septic system. Such usage is banned in many areas.
- Poor water quality can cause serious problems in open loop systems. Your water should be tested for hardness, acidity and iron content before a heat pump is installed. Your contractor or equipment manufacturer can tell you what level of water is acceptable. Mineral deposits can build up inside the heat pump’s heat exchanger. Sometimes a periodic cleaning with a mild acid solution is all that’s needed to remove the build-up. Impurities, particularly iron, can eventually clog a return well. If your water has high iron content, make sure that the discharge water is not aerated before it’s injected into a return well.
Open Groundwater Heat Exchanger
An open loop system uses groundwater from an ordinary well or water bore. The groundwater is pumped into the heat pump unit where heat is extracted and the water is disposed of in an environmentally safe manner.
Because groundwater is a relatively constant temperature year-round, this is an excellent heat source.