40 RENEWA B L E E N E R G I E S Proven, eco-friendly and cost-effective Chris Stammers, product marketing director for Dimplex, draws on the manufacturer’s latest CPD module to consider the technical considerations that installers must make before With a greater understanding of the benefits and continued support from incentive schemes like the Renewable Heat Incentive, more and more homeowners are turning to renewable energy. One such technology helping to make a big difference for the right households is a ground source heat pump (GSHP) system – a proven, eco-friendly and cost-effective solution to deliver lower heating bills, particularly for rural homes where outdoor space is not so much of a premium. By getting the necessary accreditation and tapping into the opportunities provided by heat pumps, installers can generate business and drive down bills for their customers – a win-win situation. But what do you need to know? Going green A GSHP system comprises of three elements; a ground heat exchanger which collects energy from the ground, a ‘brine’ to water heat pump, which raises the heat from the ground collector to a useful temperature and transfers it to the heat emitters and a heat distribution system which provides heat to the property. There are some considerations that must be taken into account – and installers must be aware of the implications on their system. Ground source heat pumps can be used to feed individual properties, or as part of a communal heat pump system feeding multiple properties from one, larger heat pump. The required energy consumption of all receiving properties will have a bearing on the size and location of the GSHP system, together with extraction rate and design of the collector. Building energy profiles, for example, determining the balance of cooling/heating loads, is important. Once modelled in the various software packages available, the number of boreholes could be reduced – and with costs of around £45 per metre for a bore drilled to 100 metres deep, fewer boreholes can mean substantial savings for customers. Geology Depending on the geology of the development site and amount of available land, collectors can be laid either horizontally or via boreholes. A British Geological Survey report can provide many of the answers surrounding geology, while a Thermal Response Test can establish whether more or less boreholes are needed once the geology is known – and create potential for further cost savings. Ground temperature Energy is extracted from the ground using one of a number of different types of collector and transferred to the heat pump system. As the heat is extracted, the ground temperature will drop, so it is important to make sure that the brine outlet temperature does not fall below 0º. Types of collector system The most common type of system in the UK is an indirect closed loop system, where a water/glycol mix is circulated through the collector, transferring the energy from the ground to the refrigerant via the internal plate heat exchanger of the heat pump. Other systems – although less common – include a direct closed loop, direct open loop and indirect open loop. Horizontal collectors Horizontal collectors are typical to low capacity systems because of the land area required, but can be incorporated into new housing development sites at an early stage in the build. One of the most common applications in the UK, a horizontal collector is a closed pressurised system comprising of a header pipe connected to individual loops. Each loop, which requires balancing valves or “reverse return” connections to ensure an equal flow rate, will be buried in trenches at approximately 1.5 metres deep and 0.75 metres apart. Boreholes If boreholes are deemed the most suitable option, they are typically drilled to 100 metres depth, although they can be drilled up to 200 metres. Each borehole will consist of a single or double U tube (electro-fusion welded), a sacrificial head (weight) and a tremie pipe (to pump bentonite grout mixture to seal the borehole). Consideration should be given to spacing (minimum six metres) and the direction of ground water flow (re-charging). planning a ground source heat pump installation www.hpmmag.com August 2016 enquiry number 129 A ground source heat pump in-situ A ground source heat pump system is fitted Top tips Dimplex gives its top four tips for installers when specifying a ground source heat pump solution: 1) Make sure you have the necessary accreditation, including Microgeneration Certification Scheme approval. Many customers will look to approved installer networks or contact the Ground Source Heat Pump Association to find an installer, so it’s important to be involved. 2) Speak with your manufacturer of choice for advice. They can help your installer to understand the product limitations and benefits, including any safety features, so you can communicate to customers. 3) Choose proven technology. Like any technology, cheap imports are available, but it is important to understand the impact that a low efficiency GSHP system will have on running costs for homeowners. 4) For open loop systems use intermediary heat exchangers with glycol (antifreeze) wherever possible. Ruptured heat exchangers in the product will ruin the entire unit.
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