COMBINED HEAT AND POWER 2 CIBSE GUIDE
based predominantly around the Stirling engine (a heat-driven engine) which, while having lower efficiency than a spark- ignition engine, is well suited to the small outputs of an individual-dwelling CHP system with around 1 kWe output. The fuel cell-driven CHP system is promoted as having the potential for a higher electrical efficiency than other types of CHP, and hence better CO2 and cost savings; but AM12 notes that there are continuing challenges to their deployment, including initial costs, the short life of the fuel cell stack, and the sheer physical size of the system.
Renewables and thermal storage Reflecting a shift in the marketplace since the 1999 edition, AM12 now has a separate section on ‘Renewable Fuels and CHP’. Although relatively brief, it covers solid and
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liquid biofuels and their application as an energy source for CHP. This also includes a succinct review of the opportunity for integration of other renewable technologies (solar thermal, photovoltaics, wind) with CHP systems. This edition also includes an enhanced
section on thermal storage being applied as a means of increasing the utilisation of CHP systems. The guide explains that stored heat can reduce the use of associated boiler systems, while increasing the useful and efficient peak load CHP running hours. The extra heat resource can be used both
at times of low demand (when it would not be efficient to operate the CHP engine) and during periods when the load is beyond the maximum CHP capacity. Some guidance is given on the sizing, design and installation of a complementary thermal store.
December 2011 CIBSE Journal 35
Smaller, domestic CHP applications that avoid the need for the cost of some form of district heating are available
Dimplex
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