Renewable energy that is not subject to weather vagaries

Not only do ground-source heat pumps represent an effective way of using renewable energy without storage problems but they also address the issue of rising fossil-fuel prices. As TONY BOWEN explains.A few years ago the ground-source heat pump was little known in the UK. Those in the industry followed progress in USA and Europe, especially Sweden, whilst the UK carried on being besotted by cheap and plentiful gas. More recently, however, the technology has attracted a lot of interest, both in commercial and domestic applications — so let us examine this phenomenon more closely to see why. Every time energy prices increase substantially, there is a flurry of interest in cheaper heating. This has happened over many years, and is certainly happening again now; energy-cost inflation shows every sign of being deep seated. However, in ground-source heat pumps we have a technology with the potential to help us take a longer view. Consider the following. Energy in the ground. The earth beneath our feet is warmed, mostly by the Sun, and retains its heat at a consistent low level. Whereas air temperatures in UK will fluctuate between about 30 and –5°C during a typical year, ground temperature rarely rises above 10°C nor falls below 7°C, except near the surface. Thus there is low-grade energy available to us if it can be successfully accessed. Ground-source heat pumps use ground collectors placed horizontally or vertically, and water/glycol pumped through these collectors in a closed circuit picks up energy from the ground. The Heat Pump. A heat pump is an ‘energy multiplier’, and the GSHP is an excellent example. The low-grade heat from the ground enters the heat pump, energy is extracted from it, and the cooled water returns for another circuit of the collector pipework. Extracted energy is concentrated into, usually, water in a heating system at temperatures useful for heating premises via underfloor heating, radiators or other distribution systems. Heat pumps are also available to heat domestic hot water without supplementary electric heating. The low grade heat is thus multiplied by the heat pump, which uses electricity to power its compressor. Conversion is generally highly efficient, with efficiencies of 400% available depending on the temperatures and complexity of the installation. 1 kW consumed can therefore be transformed into a useful 4 kW produced, a ratio offered by few technologies. Energy and carbon-dioxide emissions. Such efficiencies clearly lead to significant cost savings, providing a strong incentive for using GSHPs. Reductions in carbon-dioxide emissions follow from reduced energy consumption, and actual studies of multiple GSHPs in domestic applications over more than two years show lower carbon-dioxide emissions than from equivalent houses heated by gas. The potential to achieve targeted reductions of carbon dioxide is clearly desirable, and is one of the reasons that GSHPs have been included in the Energy Technology List (Carbon Trust) and recently granted a 5% VAT rate when used in domestic premises. Renewables. GSHP technology is considered a renewable technology and is frequently referred to in relevant guides. However, it has a major advantage compared to many such technologies — it can supply the needs of a building throughout the year. For example there is no dependence on the availability of Sun or wind, and GSHPs do not require a back-up boiler system. Building losses. Building Regulations are about to tighten again, with Part L requirements being yet again revised. This consolidates the move towards lower energy input to buildings and lower installed heating capacity, thus helping to address the problem that heat pumps have traditionally had, i.e. higher capital costs than alternative systems. Maintenance. Once installed, GSHPs have low maintenance requirements and few health-and-safety aspects to worry about. This is becoming a more significant aspect of operation of both commercial and public heating systems. All these factors are increasing awareness of GSHPs, and users, contractors, utilities (notably PowerGen), and trade organisations (Heat Pump Association, Ground Source Heat Pump Club) are working together to develop the industry and its installers in UK. This article has concentrated on heating, but cooling is another competence of heat pumps which will be highlighted by more and more successful applications gaining recognition. Keep a close eye on the GSHP. We will all be seeing a lot more of this growing reality! Tony Bowen is president of the Heat Pump Association, 2 Waltham Court, Milley Lane, Hare Hatch, Reading RG10 9TH.
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