Ground Source Heating & Cooling Systems

Maximising the performance of ground source systems

Ground source heating and cooling systems offers a very efficient means of using electricity to heat and cool buildings.

The key to understanding the benefits of this approach lie not only with the technology itself but with an accurate analysis of how much heating and cooling is required for a given building.

Perpetual Energy is a specialist in energy consumption analysis, a fact which is crucial to designing truly cost effective and energy efficient ground source systems.

Our own sophisticated building heating and cooling model enables us to recommend systems that are sized for optimum carbon benefits, and return on investment. And it is a model that can be used for any building anywhere in the world. Having established a heating and cooling demand profile a system can be designed that uses the ground in the most efficient way.

Well-designed and installed ground source systems require little maintenance and have a long service life. The extent of carbon savings depends on whether 'brown' or 'green' electricity is used to power the system, and on the design of the ground collector. Experience and know-how are crucial in getting all the variables right, as an incorrectly sized collector loop can result in higher carbon emissions than if conventional fossil systems were used.

Perpetual Energy offers feasibility analysis, detailed design and construction of efficient and reliable ground source systems, for new and existing buildings.

Our desk-based feasibility service allows you to:

• Understand the costs/benefits and risks of using closed and open loop systems
• Understand the relationship between system size (and the size of back-up systems), return on investment and carbon savings
• Determine whether the ground conditions beneath the location are suitable for open or closed loop systems, and what conditions may be required by the Environment Agency
• Assess the extent to which existing power distribution systems need to be strengthened;
• Establish the compatibility of ground source systems to existing building heating/cooling systems, and the potential costs of modification. The service can also define how best to configure heating/cooling systems for new buildings
• Understand influences on the timescale for construction, and how to minimise drilling costs.

With this thorough feasibility work complete, you will be in control of the facts and able to make the right decisions.

Perpetual Energy will then undertake detailed design, and with our construction partners Balfour Beatty, progress the project right through construction, commissioning and into a maintenance programme.

Ground source technology: how it works

The temperature at around 50 metres underground is the same as the regional average outside air temperature - in the UK this is around 10°C.

During the winter this is mostly warmer than the air temperature, and during the summer it is cooler. Thus, the ground can be used as a source of energy for heating and cooling. In order to heat a building, the temperature difference between the ground and the building must be enhanced by a device known as a heat pump. Cooling can often be achieved without a heat pump by utilising the temperature of the ground directly.

Ground source systems can collect energy from hard rocky ground, or from ground under which there is an aquifer. In hard ground energy is collected by drilling holes up to 120 metres deep and setting pipes in them, through which a liquid is circulated in a closed loop. Where an aquifer exists, water may be directly extracted to the surface and subsequently returned. The water is returned to the ground with either heat taken out when in heating mode, or with heat put in when in cooling mode.

Heat put into the aquifer in the summer contributes to the energy output in the winter and vice versa - effectively the aquifer can be used as an energy store. Much care must be taken with aquifer systems to understand the properties of the aquifer - flow can enhance heating and cooling only systems, but reduce the effectiveness of heating and cooling systems. The presence of certain compounds in the water can also be detrimental to performance. Regulation and permitting considerations must be addressed in both approaches.

Where constant cooling loads exist the ground may need to be cooled during the winter by means of the cooler air temperatures. To achieve this, the water/liquid is passed through a heat exchanger and cool air is blown over it.

The performance of ground source systems is directly affected by how the heating and cooling systems are designed in the building. The greatest efficiencies are achieved via minimised temperature difference between ground and the temperature at which the heat or coolth is emitted (by air handling units for example). For new build projects the extra cost of designing emitters that are optimised for ground source systems is negligible, whereas in existing buildings this work is an additional cost to installing the ground source system.