Combined heat & power
CHP makes commercial sense
Sizing CHP units correctly also goes for other commercial businesses where it is gaining increased popularity for its multitude of energy efficiency, water conservation and pollution reduction benefits. Paul Wilson, national sales manager for CHP at Remeha, explains in our second feature on CHP sizing
W
asted heat is a widespread problem within the UK’s energy supply chain. Forty per cent of the
UK’s energy is used to generate heat energy, and heat wasted from buildings accounts for half of total energy emissions. In addition, 54 per cent of energy used to produce electricity is being wasted via conventional power production at a cost of £9.5 billion per year. However, by moving to decentralised
production, using CHP technology, businesses can become highly efficient in several ways.
Buildings that using electricity from the grid will experience transition losses. CHP not only negates this issue, but on-site production also costs three to four times less. Further efficiency savings are provided by the generation of heat. The heat created by on-site CHP can be used in the hot water and heating systems, therefore reducing waste. Whether CHP is part of a heat network or an independent heating system, it can achieve carbon reduction, especially when it is the lead heat source. With an energy cost ratio of around
3.5/1, the savings are calculated using the cost of energy input to the unit (natural gas), the value of the heat output (thermal) and the electricity produced. Overall, it means CHP can be approximately 30 per cent more efficient than traditional electricity4. Typical payback periods are around seven to 10 years. The perfect scenario is that all the hot water and electricity produced by a CHP system is used inside the building, as that is the most cost and carbon efficient result.
18 July 2017
Also, there is no government subsidy available for selling CHP-generated electricity back to the grid – so sizing and designing the system to suit the building it serves is paramount. Specifiers must assess heat and hot water requirements and average usage levels when sizing, in order to achieve maximum savings. Building Regulations state that CHP must be sized to provide ‘not less than 45 per cent of the annual total heating demand’, which includes space heating and domestic hot water. Unfortunately, there is still a tendency to ‘size up’ during specification, with some professionals applying the old adage ‘add ten per cent for luck’ when it comes to calculating the size of a unit. But, by fitting an oversized CHP, not only is the capital expenditure increased unnecessarily, but the unit will operate less efficiently too. Oversized CHP units will not run if the heat demand is not present. As a result, the anticipated electricity will not be generated, leaving building owners with higher operating costs and ultimately disappointed with the performance of their equipment. The rule of thumb for sizing CHP is to use the smallest sized unit possible, to cover baseload heating requirements. If additional heat and/or hot water is needed at peak times, consider an energy-efficient condensing boiler to supplement supply rather than an oversized CHP unit. A cascade arrangement can be a way to meet fluctuating demands, as this can respond quickly to changes in usage patterns. This approach ensures that the unit is running constantly and, as such, is
Paul Wilson, the national sales manager for CHP at Remeha
generating low cost, low carbon electricity as a by-product of producing base load heating. Sourcing both the boiler and the CHP unit from the same manufacturer has a number of benefits in terms of compatibility and assistance with system design. Indeed, Remeha offers a comprehensive commissioning service, based upon extensive experience of both technologies. To run continuously, the CHP unit stores hot water generated during low-demand periods in storage cylinders, to supplement supply during peak times. As soon as the
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