Industrial & commercial heating Combined heat & power
> or already-installed infrastructure, alongside high water loads, which help to make CHP a cost-effective solution. However, when considering long-term ‘life-cycle’ costs, CHP may be economically less attractive for large-scale district heating systems for existing small towns or larger communities, which can require a great deal of investment in new infrastructure. There is also the question, here, of the potentially huge social disruption arising from the construction work that may be needed for such district heating installations. Having said that, with appropriate planning and integration, DHSs are being successfully installed in Britain – one example being a scheme in Sheffield that serves around 130 buildings in and around the city centre. One could say it comes down to ‘horses for courses’: if the capital costs can be borne, the infrastructure is successfully developed, and the loads are appropriate, CHP can be an ideal solution for district heating.
Micro-CHP In recent years, micro- and mini-CHP has entered the marketplace. Mini-CHP based on, for example, Stirling Engines or microturbines, can provide small (up to 5kWe) systems for use directly in homes and small commercial applications. Larger mini-CHP systems (up to 50 kWe) typically use gas-fired reciprocating engines for bigger installations such as residential schools, hotels and leisure centres. However, these developments are still small in number, and it will be some time before the efficacy of these
can be assessed in terms of performance, cost and efficient use of energy.
Conclusion CHP systems are being widely applied, from industrial factories to homes. There are also various combinations of mixed users, local communities and major developments. It seems that the challenge for engineers and specifiers of CHP is to design a system where the application is using up as much heat as possible when it is generating electricity. This would suggest that the bigger and more diverse the ‘basket’ of users of the CHP installation, the more ‘flat’ the thermal load will be compared with the electricity load. Sometimes there is pressure to use a CHP or CCHP
system to satisfy planning requirements. It is important that this is done while taking full account of the engineering requirements, as it is possible to install a CHP system to meet ‘low carbon’ targets and find that the operating profile undermines the ‘low carbon’ performance. The extent to which designers will be able to undertake a full design evaluation of a new CHP installation will often depend on the time and resources available – which will sometimes be down to how much the client or end-user is prepared to pay or listen. Ideally, though, designers should be in a position where they are able to stand back and undertake a proper engineering appraisal of a CHP’s efficacy and appropriateness for the scheme or development they are involved with. l
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44
CIBSE Journal February 2011
www.cibsejournal.com
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