Pushing Part L under the floor

underfloor heating
By using the floor as a large heat emitter with a low surface temperature, underfloor heating works effectively with low flow temperatures — enabling the energy-efficiency benefits of condensing boilers and heat pumps to be fully exploited.
Underfloor heating has always been a highly effective method of delivering comfort, especially in large spaces. Changes in the last two editions of the Building Regulations have so improved its cost basis that the benefits can be more widely enjoyed.Underfloor heating and the trend in recent editions of the Building Regulations to reduce the energy consumption of buildings go hand in hand. As Chris Pritchard, managing director of Giacomini Sales in the UK, explains, high levels of insulation under the floors of buildings are essential for the effective and economic operation of underfloor heating. However, until the October 2001 update of Part L of the Building Regulations the cost of thermal insulation under the floor screed had to be carried by the underfloor heating system. Removing that financial burden at a stroke approximately halves the cost of installing an underfloor heating system — explains Chris Pritchard. Economically viable Suddenly it becomes economically viable to exploit the characteristics of underfloor heating that complement the philosophy of the latest Building Regulations to maximise the application of technologies such as condensing boilers and alternative and renewable energy. The fact that the surface temperature of the floor should not exceed 29°C implies that the flow temperature of the water through the pipework embedded in the floor should not exceed around 60°C. With a temperature difference of 20 K between flow and return temperatures, a condensing boiler will be operating so deeply into condensing mode that it will be very efficient indeed. If a heat pump is used to generate the hot water for circulating through the pipe loops, those low flow and return temperatures will enable a very high COP to be achieved, especially with ground-source heat pumps. A high COP can be achieved with a flow temperature of 40 to 45°C combined with pipework loops that are more closely space. Enabling condensing boilers to deliver their energy-efficiency potential requires that the system be appropriately designed. Chris Pritchard explains that two approaches are in common use. One is to supply water to the distribution manifolds at a constant high temperature of, say, 80°C and blend this water with lower-temperature return water to achieve the desired flow temperature to the pipework that is embedded in the floor. The other approach is to supply hot water at a temperature that permits condensing operation at all times. The space-heating requirements are then met by controlling flowrate and adjusting the spacing of the pipework at design and installation stage. Of these two approaches, Chris Pritchard says that it is far better to go for a lower flow temperature off the boiler itself. System design While the efficient use of fuel is an important benefit of underfloor heating, careful consideration needs to be given to system design to deliver that heat effectively. It is self-evident that the temperature of water in the pipes falls off between the exit and return of the manifold. To avoid some parts of the heated area receiving more heat than others, Chris Pritchard advocates laying the underfloor pipes in a snail pattern. That configuration puts pipes carrying the coolest water near those carrying the hottest. In delivering energy-efficient space heating, underfloor heating comes into its own in large, high spaces. Not only is heat delivered evenly across the whole space but it is also concentrated in the occupied zone — up to 2.5 m above the floor — rather than heating the entire building interior. ‘There is little convection with underfloor heating, so it is very well suited to high spaces,’ says Chris Pritchard. The comfort delivered by underfloor heating is focused in the area above a pipe circuit, so a large, open space can be zoned effectively — with control provided by simple room thermostats. Likewise, the higher heating requirement of perimeter areas or those near full-height glazing can be met by laying the pipes closer together. Strong growth The capabilities of underfloor heating and developments in the Building Regulations have both contributed to strong growth since 2001. Much of that growth is client led, says Chris Pritchard. But why stop at heating? If a ground-source heat pump serves a system, why not circulate cool water to provide 30 to 40 kW/m2 of cooling in the summer — with little addition to capital cost. And since Building Regulations are increasingly part of the response to climate change underfloor heating becomes even more appropriate. Giacomini is at Unit 3, Goodrich Close, Westerleigh Business Park, Yate, BS37 5YS.
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