Closed loop HVAC systems are becoming increasingly important in the quest for improved energy savings and safety.
For optimum function, the quality of borehole construction is a key consideration. WB+AD Morgan’s experience of drilling boreholes, and their emphasis on quality control and environmental care, will be a key factor in a fully successful outcome.
Borehole cooling and heat pumps extract the heat in the ground or water and transfer it to a building for space and water heating. To cool the building in hot weather, heat is returned to the ground or water.
Why renewable energy?
- Energy costs continue to rise, and there is an ethical move to reduce the use of carbon-based fuels
- Legislation is helping drive things forward, Part L of the Building Regulations sets higher standards for energy conservation
- Renewable energy can bring attractive economic benefits – ground source heating and cooling bring the promise of ‘something for nothing’, often delivering four times more heat than the electric energy used
Ground source heating is proven technology, and systems have been successfully and extensively used worldwide for many years, and the benefits demonstrated.These include environmental and economic factors due to very low operating costs compared to fossil fuel systems. CO2emissions are reduced.The ground can be used either as a source of heat or for ‘coolth’ to provide cooling. Underground temperature is constant, so air temperature has no effect on a system’s efficiency. Either way, heat is taken from or disposed of into the ground via boreholes.Heat is made available to the building using a heat pump. Configurations range from simple under floor heating and domestic hot water, to reverse cycle pumps for heating and cooling; and sophisticated systems for simultaneous heating and cooling.
Vertical closed loop systems incorporate one or more boreholes with a single U-shaped HDPE plastic pipe loop that circulates water with an antifreeze, usually brine.The finished borehole is sealed with special heat-conductive grout from top to bottom.The solution extracts heat from the borehole and delivers heat to the heat pump. Heat is extracted from the water before returning it to the ground.
Vertical open loop systems abstract groundwater which is circulated directly through the heat pump. Due to the conductive nature and specific heat capacity of groundwater, an open loop system can deliver a large amount of energy from a single well.Water is abstracted from the borehole, passed through a heat exchanger/pump system, and then either used as part of a greywater supply system or discharged to a surface water system, or back underground.A second borehole may be required if discharge to groundwater is used. Both abstraction and discharge require consents and licences.
A borehole producing 10 cubic metres/hour can supply 80kW. Sometimes energy loadings in excess of 500kW are possible.
What is a heat pump?
Think of it like a fridge, but in reverse—it takes the heat out of groundwater and concentrates it for use in the building. The opposite of a fridge which takes heat out of the appliance and dumps it into the air.
The use of the ground as a source of heating or cooling has inherent risks. With closed loop systems, in major schemes the largest risk is excessive heating or cooling of the ground around the boreholes. This can occur if they are too close together, or too heavy a demand is put on the system. This would affect system efficiency—but is most unlikely to be a problem with domestic and smaller scale projects under 50kW.
In open loop systems, demanding too high a volume of water from a borehole can exhaust its supply. Otherwise, thermal breakthrough can occur, where the intake pulls warmed water back in. Then there are thermal plume migration issues too—an impact on other boreholes, or the surrounding environment.
For open loop schemes, and closed loop schemes over 50kW, specialist advice should be sought.
While existing buildings can often be successfully adapted to use ground source energy, the most efficient systems are designed into the building from the start. Liaison between building and systems designers, hydrogeologists and thermogeologists will ensure that any risk factors are taken fully into account and eliminated.
Something for nothing is always appealing, and having paid for the installation, you’ll reap the benefit of low-priced heat for years to come.