Boreholes for Cooling
Ground source cooling can be used to cool buildings. This approach is less expensive than air conditioning which provides cooling by heat exchange with external air – often hot air. Ground source cooling is a mechanism of allowing the excess heat within a building to escape to cold ground. This natural process is cheaper than using electricity to force heat out into hot air. The process of releasing heat to the ground also provides the useful function of heating the ground in preparation for using ground source energy the following winter to return the heat to the building from which it came
Modern buildings are designed with a much higher level of insulation – in order to retain heat in winter and save heating costs and carbon emissions. Partly as a result of this winter efficiency there is a strong tendency for well insulated buildings to overheat in summer. The standard answer to overheating is to provide air conditioning to cool buildings in summer.
However, air conditioning is very unattractive from an economic point of view (it is expensive to install and it costs a lot to run every year) and from an environmental point of view (it emits lots of carbon dioxide to the atmosphere). It also fights a fundamental principle of physics: heat naturally moves from hot places to colder places in the same way that water naturally flows down hill – if given the chance.
Water can only be moved uphill with an input of energy. In the same way heat will only move to a hotter place if energy is used to force it to move in that direction.
Air conditioning is used in summer when the inside of buildings become uncomfortably hot. It is likely that when cooling is required inside, the outside temperature will be even hotter. For this reason energy has to be expended to force the heat out of the building: air conditioning works against nature and is based on the principle of "wasting" heat.
Luckily there is now an alternative means of providing cooling to buildings which is much more natural – less expensive because it requires less energy and free from the need to emit carbon.
The new system is called ground source heating and cooling – "GSHC" – and works by releasing heat from the building in summer down to the cold borehole field in the ground (in order to allow heat to escape from the building naturally).
When the building gets too hot in summer, water is circulated through underfloor piping in the building down to the cold borehole field in the ground. This allows heat from the building to escape naturally to the ground. This type of natural cooling is also called "Free Cooling" as the only cost is the cost of a circulation pump to circulate water in a closed loop from the underfloor piping down to the borehole field in the ground.
If a more aggressive form of cooling is needed then a heat pump can be used in reverse to reject heat to the ground more quickly. But it will always be cheaper to reject heat to the cold ground than trying to reject heat to warm external air using chillers.
- Circulation: The above-ground heat pump moves water or another fluid through a series of buried pipes or ground loops.
- Heat absorption: As the fluid passes through the ground loop, it absorbs heat from the warmer soil, rock, or ground water around it.
- Heat exchange and use: The heated fluid returns to the building where it used for useful purposes, such as space or water heating. The system uses a heat exchanger to transfer heat into the building’s existing air handling, distribution, and ventilation system, or with the addition of a desuperheater it can also heat domestic water.
- Recirculation: Once the fluid transfers its heat to the building, it returns at a lower temperature to the ground loop to be heated again. This process is repeated, moving heat from one point to another for the user’s benefit and comfort.