Groundwateraquifer cooling and warming

Alternatives to full air conditioning with chillers that make heavy demands on electricity and fossil fuel for space heating are coming increasingly into prominence. One option is

Outside air

Dampers

Dampers

To ventilation plant

Dampers

Thermal ground store

Figure 3.1 Ground source air cooling (courtesy of Building Research Establishment (BRE))

Process

Free cooling

Production well

Heat exchanger

Open cooling tower

Heat exchanger

Injection well

Production well

Heat exchanger

Heat exchanger

Injection well

Figure 3.2 Aquifer cold water/warm water storage system (courtesy of Caddet)

Outside

Figure 3.2 Aquifer cold water/warm water storage system (courtesy of Caddet)

aquifer thermal energy storage (ATES). This uses water from an underground well to cool either a building or an industrial process. Once the water has taken up the heat from the building etc., it can be returned to a second warm well and used to pre-heat ventilation air in winter.

Two boreholes are drilled to a depth of between 30 and 150 metres. The wells should be between 100 and 150 m apart.

Where there is no movement of groundwater ATES uses layers of water for cold and heat storage. In summer cool groundwater passes through a heat exchanger where it cools the water system of the building which, in turn, cools incoming air in an air-handling unit.

The groundwater, having absorbed the building's heat, is injected into the warm well. During the winter the system is put into reverse.

It is estimated that ATES can achieve 60-80% energy savings compared with conventional air conditioning. It has quite a short payback time to recover the extra investment of 2-8 years (see Fig. 3.2).

In situations where there is groundwater movement the system can be used as a heat source or sink for a heat pump (see below).

In the UK the extraction and use of groundwater is subject to approval by the Environment Agency.

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