Combining the benefits of central boilers with individual heating and hot-water systems

The alternative to individual boilers — Lars Fabricius.
Lars Fabricius of SAV Modules explains how new heat-exchange technology can bring the benefits of their own combi boiler to dwellings served by central boilers.The UK is in the throes of a total change in the way it views and uses energy. Politically, the driving force is an altruistic desire to cut carbon emissions and thus reduce the threat to our planet from global warming. All well and good, but a more cynical observer might point to the total failure of successive Governments to establish anything like a cohesive energy policy. As a result, with our nuclear power stations reaching the end of the lives, the coal industry reduced to a shadow and North Sea oil and gas supplies dwindling fast, we are becoming dependent on imported gas — and, moreover, gas imported from sources that could hardly be described as reliable. We have to save energy, because we don not exactly know where it is coming from! I speak as a Dane, who’s own country reached exactly the same conclusions three decades ago. We switched to energy saving because we had to. For whatever reason, energy reduction is the order of the day. With Britain’s buildings accounting for 40% of its total carbon emissions, the building-services industry is a natural priority. As a result there is change in every aspect of the way we maintain the indoor environment. Some of those changes may be simple. Not setting the clocks back in Autumn could save millions of tonnes of carbon dioxide. Some will be technical. All will be far reaching. One of the first changes will be consigning the indirect cylinder to the museum. UK homes have enjoyed the option of the combi boiler for some time — an option that saves energy by making it possible to switch the same heat source from space heating to hot water on demand. Standing losses are eliminated and there is a space-saving bonus into the bargain. It is not an option that has been available to the larger, multiple-dwelling project such as apartment blocks, social housing units, residential care centres etc. Providing combi boilers for individual flats has been regarded as too expensive. Like so many things, this situation has now changed. The swing to central boiler plant has in turn created a demand for compact heat-exchange technology that combines the benefits of the combi with the economies of scale offered by a large, shared energy source. Central boiler plant is not only more efficient than individual boilers in each dwelling, it is also far easier to combine with renewable energy sources such as biomass fuels and solar panels (and the Government currently targets to generate 10 to 15% of UK energy from renewables by 2020). Used with localised heat exchangers, central boiler plant is equally at home with underfloor heating or radiator systems. Using a single energy source for both space heating and hot water also makes energy metering — and billing — far easier. Designers and system operators can meet all requirements for users to have access to accurate records of their energy usage. CIBSE's TM 39 published in 2006 gives a practical guide to establishing sub-metering in non-commercial buildings. Why? Because in the guide’s own words, ‘Action taken as a result of using meters can achieve quantifiable energy savings.’ The meters themselves may not save energy, but taking action as a result of what they show will. CIBSE believes that 5 to 10% of the energy being metered can be saved —sometimes more. New heat-exchange technology The new heat-exchange technology we use to maximise the potential of central boilers is based on Danish experience. As I mentioned, Denmark came early to energy saving. With no natural energy resources (until recent finds of oil and gas) the Danish government established its first energy plan back in the mid 1970s. As a result Denmark now leads Europe, and perhaps the world, in putting energy to best use. The new AquaCon series of heat-exchange modules has been developed for UK requirements around technology from the district-heating division of Danfoss A/S. It combines experience and expertise from home and abroad to create a perfect complement to the modular solutions now offered for building services distribution and control.

Heat-exchange modules for UK requirements — the AquaCon range from SAV Modules.

Available in a range of sizes from 35 to 220 kW, these modules are particularly suited to multi-dwelling applications served by a common boiler plant. Apartment blocks, prisons, hospitals etc. can all have ample supplies of hot water — with energy metering where required. The comprehensive range of design options — with flows from 12.5 to 32.3 l/min — means a solution is available for virtually any application. Models are available for both direct and indirect systems. In the direct application, hot water from the central plant is distributed straight into the unit served by the AquaCon module. Indirect versions have a second heat-exchange module, which acts as an interface between the main supply of hot water from the boiler and the circuit in the dwelling. In this way heat energy can be taken efficiently from the central boiler, while maintaining a ‘sealed system’ for the individual apartment. Energy automatically diverted When a variation in pressure is detected as a result of an opening tap the thermostatically controlled system ensures an instant supply of domestic hot water. Energy is also automatically diverted via the heat exchanger from the heating circuits to the hot water supply — reverting to the original setting when demand ceases. The system is designed to run smoothly, with no wild fluctuations in temperature or pressure on either heating or hot water circuits. Diverting energy to hot-water supply is much more efficient, especially at times of peak demand, and also ensures a low return-water temperature so that condensing boilers are kept in maximum efficiency deep condensing mode for much longer. Moreover, constant modulating control can ensure that energy is directed in exact proportion to demand — from a single tap in the kitchen to simultaneous use of two bathrooms. Specifiers may opt for modules with a built in differential-pressure-control valve (DPCV). The DPCV maintains optimum pressure conditions in the hot water and heating circuits — maximising the energy exchange at times of hot-water demand and enabling better individual room control via thermostatic radiator valves, or actuators at the manifold in the case of an underfloor heating system. So efficient is the heat-exchange process that a combined flow from an 80°C heating circuit and a 10°C cold water connection is converted into a 15°C return. Moreover, constant modulating control ensures energy is directed in exact proportion to demand — from a single tap in the kitchen to simultaneous use of two bathrooms. Safety Safety is also a major design feature. Hydraulic regulation ensures that the DHW supply valve in the module closes immediately demand ceases — largely preventing the formation of both bacteria and lime scale. The cold water connection also incorporates a dual function ball valve and non-return valve plus safety valves, so that backflow cannot occur. Lars Fabricius is managing director of SAV Modules.
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