COMBINING NATURE€™S HEAT SOURCES

	Friday May 11 Combining renewable technologies such as solar thermal and biomass — can be a great way to get an efficient heating solution all- year round. Simon Holden, from biomass solutions provider Euroheat, explains how these two technologies fit together. Biomass is very well suited to being combined with a solar thermal system. In the summer months, when no central heating is required, solar thermal is an adequate arid energy efficient solution for water heating, allowing end-users to replenish their wood stock, ready for the colder season (or optimum efficiency, as wood must be split and left to dry for at least 18 months). Modern biomass systems Euroheat Chairman Simon Holden are set up to run in this way, with control options designed to accommodate multiple heating circuits, hot water stores, remote heating networks and additional heat sources such as solar pumps or gas boilers. Weather compensation can also be included to further increase efficiency. The crucial element of a system such as this, or in fact any heating system where more hot water than needed is generated, is a vessel to store this water, such as an accumulator, buffer tank or thermal store. Most models of accumulator/buffer can include at least one thermal solar coil. Some models offer two coils — an upper and lower. If this is the case, a dual-channel solar controller is utilised which prioritises the upper coil. Once the upper area is heated it switches to the lower solar coil, offering an ideal solution for solar as the volume of the accumulator/ buffer can far exceed the production of the solar panels, ensuring all possible heated water is collected. Accumulators The accumulator absorbs energy, which in the case of wood boilers and solar thermal systems is heated water. In correctly specified log boiler installations the aim is to fuel and light the boiler once a day in cold weather conditions or once every two to three days in warmer weather. This is possible, not because it takes a long time for the wood to burn, but because the energy is collected and stored in the accumulator until it is needed. The same goes for solar thermal — on hot sunny days more hot water than is needed will be produced. By accumulating it, end-users are ensured of accessing this, whatever the weather. The accumulator is highly insulated so the heated water can be used days later. Buffer tanks Buffers are generally smaller than accumulators, although in practice they have the same constructional design. They can include temperature stratification systems, hot water production, thermal solar coils and connection positions for electrical heating elements. A temperature sensor between the heat source and the heating circuit detects when temperature drops to a preset levels, activating the boiler to reheat the buffer. If no demand exists, the water remains heated, with high level-s of insulation maintaining its temperature. This prevents the boiler from cycling, which in-turn limits undue wear and tear reduces emissions and fuel consumption. All our automatic HDG boilers monitor the current heat stored, ignite, produce heat and switch off when not required, in conjunction with a buffer. This greatly increases the overall annual efficiency, reduces fuel consumption, reduces environmental emissions, servicing costs and extends the boiler’s life. Thermal stores A thermal store is slightly different to a buffer tank — it is best described as a small buffer undertaking many duties. These include buffering, some accumulation (though this is limited due to the size), hot water production through internal transfer coils or via external heat exchangers. As with accumulators and buffers, thermal stores can include additional coils for thermal solar input and electrical heating elements. Due to the limited size, normally 200-300 litres, its use is only advised in very small property applications with low energy demands. Stratification The aim of any accumulator/buffer is to remain stratified. This means the hotter water is at the top and cooler water at the bottom. Water returning to the accumulator from a heating system is cooler than the water at the top of the accumulator. If the return water enters the accumulator slowly it will sink to the bottom. If, however it returns to the accumulator at high velocity it will stir the water in the accumulator with temperature dropping evenly from top to bottom. To prevent this occurring, either the speed at which the water enters the accumulator is reduced by increasing the connection size based on the system kW demand, or return water is introduced through a neutral area — a stratification tube of the correct size to suit the output of the flow talc. We have already seen interest in wood biomass boom thanks to the commercial arm of the Renewable Heat Incentive (RHI) and this is only set to increase when the domestic arm is (hopefully) bought in, making this combination of technologies an attractive proposition for many of Britain’s homes —as storage of water is key, properties in the country with space to store associated equipment, not to mention the wood fuel, are ideal.

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