At a site in south Buckinghamshire, open-loop ground source heat pumps use water from the chalk aquifer to provide the renewable heat for the heating and hot water systems. H.D. Drilling Ltd has been a member of the Well Drillers Association since 1988 and H. D. Services Ltd is an MCS accredited company that install, commission and service open-loop ground source heat pump installations. The water can also be used for domestic consumption (subject to analyses and suitable filtration) and as a grey water supply.
The company were approached in 2011 by Acanthus Developments and asked to tender for the installation of three water supply boreholes to serve each of three prestige properties. Closed loop ground source heating was being considered, however the availability of a reliable ground water supply from the chalk aquifer resulted in the installation of three open-loop heat pumps. The development went on to win a Green Apple award in recognition of the Sustainable Nature of the development and the Architectural Design Excellence of the properties.
Using the postcode of the site to assess the hydro-geology, a quotation was submitted for the construction of both the water supply borehole and soak away at each location. The deal was that both the water supply borehole and soakaway were constructed and water pumped from one to the other to prove the worthiness of both before and payment was requested. It was several months later, once the construction of the properties had been completed that the heat pumps could be installed and commissioned. Each installation is covered by a 5 year workmanship warranty and annual maintenance contracts have been offered.
Working from building plans and SAP reports, the quote allowed for the supply and installation of Soleco three-phase heat pumps; two 18-kW and one 26-kW. The boreholes were drilled using a cable-percussion rig – the method preferred by the Environment Agency when drilling into the chalk aquifer. Borehole logs were submitted to both the British Geological Survey and Environment Agency to protect the abstractions from derogation by a third party.
An advantage of open-loop ground source heat pump installations is that the discharge water can feed a harvesting tank, from where it can be pumped for garden irrigation or other ‘grey-water’ uses. Harvesting tanks that are only connected to a rainwater system will quickly run dry during a prolonged dry spell, whereas a harvesting tank fed from a heat pump will replenish whenever the heat pump is in operation.
Work commenced in early 2012 and the boreholes were drilled just after the original buildings had been demolished. The borehole pumps were left in-situ to provide build-water until the houses had been erected, after which the heat pumps were installed and commissioned.
From the experience gained on the contract, plumbing and electrical guides were designed and are handed to the client for distribution to their contractor. These have been written by a fully qualified professional and in conjunction with the heat pump manufacturer, they inform the heating distribution system installers of both the plumbing requirements and the electrical requirements of the heat pump. This ensures that while work is continuing on the build, those on site have the information to hand regarding system requirements which provides confidence that all required connections are in the correct location making the installation and commissioning of the heat pump a straightforward process.
Work was completed in late 2012 and all three of the heat pump installations were commissioned successfully. Although the whole job, from quotation to commissioning, took over a year we worked closely with the client to ensure that the process was as straightforward as possible.