Industrial and commercial cooling Boreholes
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borne out by actual performance to date – are that the store will save nearly 900 tonnes CO2 equivalent per year, compared to standard air-cooled refrigeration and gas-fired boiler systems; this is 300 tonnes CO2e more that the alternative renewable technologies considered prior to the refurbishment. Under the terms of the installation at the site, the
specialist installer not only assumes the installation risks, but owns and operates the system and is responsible for ongoing maintenance throughout its 20-year installed life. The benefit to the client lies in the fact that ‘specialists’ are operating the system, leaving local store personnel free to focus on their core business activities. The system incorporates continual monitoring,
showing actual energy savings achieved compared with original forecasts. Since September the store’s energy performance has been on target – that is, in line with the initial energy modelling predictions – and in the four months since its installation, the client is happy with the results. While commercial details of costs and savings
are confidential, the fully financed structure of the agreement is such that real-terms payback to the client is achieved from the first year of operation. Moreover, the agreement includes built-in incentives for both parties to keep working together to achieve continuing improvements in energy reductions. The store is also meeting the wider environmental
targets for it set by Sainsbury’s. These targets are: • Zero increase in operational carbon emissions (energy and refrigerant gas);
• Zero use of gas for heating and hot water; Digging deep for earthly energy
The 200m-deep boreholes are drilled at angles away from the surface location to ensure sub- surface separation. This ensures that there is no thermal interference for the majority of the length of each borehole. At surface, all that can be seen are
15 manhole covers within a small area of the car park. The borehole array at surface extends under about 30 car- parking spaces, out of a total of 700. Coaxial borehole design rather
than traditional U-tube is employed, with steel used as the heat exchange interface between the working fluid and the ground. Steel has a high conductivity to readily transfer energy between the fluid and the ground, increasing the rate at which energy can be transferred to/from the ground compared to plastic. The geology for the area is
predominantly chalk. Although chalk has one of the lowest thermal conductivities, our design process ensured this proved no hindrance in this application, both in terms of drilling/implementation and ongoing long-term thermal performance. There is a significant aquifer below
the site, through which some of the boreholes extend, which changes the thermal reaction of these parts of the system. This can be detected through monitoring of system performance, and can be controlled to optimise for these conditions in conjunction with the building’s actual demand requirements. The drilling programme was reviewed in consultation with the Environment Agency and Thames Water, to ensure no environmental risk at any stage, either during installation or in operating the system. Kevin Stickney
The borehole array lies beneath 15 manhole covers in the car park
• 60% reduction in electricity demand from the national grid versus a standard store in 2005-06;
• 30% of energy demand met from on-site renewable energy;
• 50% reduction in mains water usage per sq ft sales area versus the standard store; and
• Minimum 90% reduction in construction waste to landfill. These have been achieved by the store’s range of
environmental features, which include high levels of insulation, rainwater harvesting, LED lighting and sun pipes, and automatic light dimming. There were many challenges in bringing this project
to life – integration of hitherto very discrete disciplines (borehole construction, commercial, refrigeration and M&E), adoption of a new technology on a flagship retail store under very tight time frames, and adoption of a business model not normally associated with this technology. Sainsbury’s were willing to break down traditional barriers and embrace an integrated system that addresses, and actively manages, all of their thermal energy needs to provide guaranteed energy and carbon savings over the life of the installation. It’s early days, certainly, but not only is the system hitting year-one targets for energy saving (despite the coldest December on record), there are strong mutual incentives to make year-on-year energy reductions, over and above initial targets, to ensure it keeps benefiting both the end-user, the supplier and ultimately the environment. l
Kevin Stickney is technical director of Greenfield Energy
www.greenfieldenergy.co.uk
48
CIBSE Journal February 2011
www.cibsejournal.com
Greenfield Energy
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