Staying in the loop

The dash for low- and zero-carbon energy prompted by concern about climate change has fuelled rapid growth in the ground source heat pump industry recently. The level of interest in the GeoDrilling 2008 conference was indicative of the market’s buoyancy, with the mix of hydrogeologists, geotechnical engineers, M&E engineers and ground source energy specialists reflecting the unique merging of disciplines which exists in the industry.

The large number of delegates who squeezed into the conference area, in a corner of the main exhibition hall at East of England Showground, Peterborough, prompted the organisers to increase the size of the area for the second day. Elsewhere in the hall, manufacturers of everything from enormous drilling rigs to grouting products displayed their wares.

In the conference area, healthy debate raged: it was clear that there are several issues on which the industry has yet to reach a consensus. The conference opened with an overview of the policy and regulatory framework. Speakers from the Department for Environment, Food and Rural Affairs, E-on and the Micropower Council explained the initiatives set up to promote renewables, such as the carbon emissions reduction target, Low Carbon Buildings Programme, Merton Rule and Code for Sustainable Homes. These provide the industry with a great opportunity in the form of financial and other incentives.

John Aldrick from the Environment Agency gave a regulator’s perspective. This focused principally on open loop systems and left unresolved the ambiguities surrounding the regulation of closed loop systems.

In an inspirational presentation, Dr Robin Curtis of EarthEnergy offered a cautionary tale of ground source energy industries in continental countries that had experienced similar growth to that currently occurring in the UK, followed by collapse because of quality failures. Curtis asserted that there are only three types of ground source heat pump systems: those that don’t work, those that work, and those that work and deliver significant carbon savings. He urged the industry to focus on the third category and bemoaned the level of misinformation circulating about issues such as government support for the technology and the need to balance heating and cooling loads.

The long-term effects of imbalance between heating and cooling energy exchange with the ground was one of the hot topics of the conference. Ryan Law, of Arup, suggested this problem could exist in city centre locations where there may be several ground source energy systems, with a high bias towards cooling, in proximity and isolated from the atmosphere by adjacent buildings. In such cases, he argued, there may be a need to rebalance energy demands by linking adjacent buildings with different load profiles, or heating and cooling the ground by other means.

Guus van Gelder of Groenholland also drew attention to the temperature drift that can occur in the ground over several years of operation of ground source heat pump systems and highlighted the need to model these effects. Several software packages are now available.

Day two of the conference covered topics such as thermal response testing of boreholes, energy piles and lake loop installations. Tony Amis of Cementation Foundations Skanska predicted that 5000 energy piles would be installed during 2008, and described a test in which water at -6°C had been circulated within a pile for four weeks with no undue side-effects on the pile’s bearing capacity.

Professor Lyesse Laloui of the Swiss Federal Institute of Technology, Lausanne, gave a more cautious view of the technology, arguing that the reduced friction around the pile resulting from the thermoplastic nature of soil, along with the changes in load distribution within the heated pile, needed to be accounted for in the design process.

All of the speakers agreed on the necessity for good-quality design and installation practice if the industry is to take advantage of the opportunities available and deliver the carbon savings expected of it. The success of the technology depends on combining best practice in the building environmental and geological fields. Correct analysis of heating and cooling loads and choice of heating and cooling systems is as important as the design of the borehole field and the specification of drilling methodology.