last updated 12th January 06
by 4ecotips.com

A winning formula

For the first time for more than a generation the UK has became a net importer of gas and oil. The result is a new urgency on the part of house builders and buyers to reduce the dependency on fossil fuels. Rex Ingram, managing director of Osma Underfloor Heating believes that geothermal energy could be the answer.

In the past twelve months the price of a barrel of oil has risen by more than 50% to over $65 per barrel and gas prices, on average, have risen by 30%. And yet most of our buildings, including the new ones, still have heating systems that are dependent on fossil fuels. Even those heated or cooled by electricity are still reliant on fossil fuels as this is the staple power for most of our power stations.

Many architects and developers agree that the economic life of new buildings is between 60 and 100 years. However, when asked about the affordability of fossil fuels over the same period, some are prepared to predict that they will be affordable for only another 10 years. Others believe that even this may be optimistic.

Self-builders have traditionally been more prepared to use alternative heating methods and have been at the forefront of installing underfloor heating instead of traditional radiator systems. UFH requires water temperatures of approximately 35-55 OC , depending on the conductivity of the floor structure, whereas radiators need water at approximately 70 OC. With much lower temperatures required for UFH, it will always be possible to generate water at this temperature whether by solar panels, by heat pumps or from waste heat from a small CHP unit.

There are two types of heat pumps that can be used; air-to-water pumps, which transfer energy from/to the air around a building, or water-to-water heat pumps that transfer energy from/to water pipes.

Air-to-water heat pumps are most suitable for use within a metropolitan urban environment, particularly city centres where ambient air temperatures are rarely below freezing. This type of pump is ideal for recycling and harnessing waste energy from kitchens, traffic or industrial processes. The system can be incorporated into ventilation systems to capture energy in the air before being drawn out of a building, they are ideal where the density of houses is very high.

Water-to-water heat pumps have two main advantages. Firstly, they can remain efficient even when ambient temperature is below freezing, secondly they are much quieter. There is however one major disadvantage, when you take into account the amount of water pipe work that has to be included in the ground. If there is insufficient space underground, it is possible for the heat pump to take too much out of the ground causing a tundra-like permafrost condition. Most system designs are aware of this risk and ensure sufficient ground is used to prevent this from happening.

In Germany, Wavin Plastics has developed a way of minimising the external area required. Instead of cutting trenches and setting the geothermal pipe into these, the process involves stripping and removing the ground to a depth of 1.2 metres, and then covering the sub-ground with an impermeable membrane.

In the future, geothermal heating and cooling systems are likely to be a combination of surface heating and cooling within a building. The systems will be powered by water-to-water heat pumps with geothermal pipes set into wet ground that is re-hydrated as part of the rainwater management system, linking gutters, down pipes and storm water tanks.

In addition the ground can become a potential thermal store, with any excess energy from solar panels, for example, that are being used to heat the hot water system being piped into the ground to increase the efficiency of the heat pump.