Sustainability – must do better

However, we could do better if UK buildings were connected to district heating systems, rather than using individual boilers or electricity. CHP/district heating power stations can produce twice the energy for sale as electricity-only power stations for similar fuel consumption and carbon emissions. At the same time significant carbon emissions from building heating systems are avoided. In Denmark, about 60% of dwellings are heated via utility scale chp/district heating schemes. Adopting utility-scale chp/district heating systems would save energy and also reduce carbon emissions.

The present UK community energy schemes are arguably good so far as they go, but they are relatively minor in extent, and are unlikely to affect plans to double the number of gas-fired power stations. Of course, to introduce utility scale chp/district heating, CIBSE members would have a significant role to play in advising government, in adapting Scandinavian best practice to UK conditions and in designing and installing appropriate m&e engineering systems. However, besides introducing Scandinavian style chp/district heating, CIBSE members have other fences to mend.

The seasonal efficiency of conventional UK heating system design is generally much lower than commonly assumed. With three-port valve control, boiler water recirculation to provide back-end temperature control, and no adequate control of water flow through hot water radiators, more water than necessary is circulated, and return water temperatures can approach supply water temperatures for much of the year. Condensing boilers are not fully condensing unless return water temperatures are below about 50°C, and most small-scale chp systems shutdown, or dump heat, if return water temperatures exceed about 70°C. With variable flow/wide temperature difference heating systems using say Danish best practice, we could provide substantial water distribution capital and running cost savings and we could also make condensing boilers and small-scale chp systems work properly.

UK building air distribution systems generally use more electricity than aimed for in energy consumption guides. Air distribution installations are inefficient as installed because ductwork is adapted to fit cramped above ceiling spaces and service ducts. Inefficient fans with poorly designed and installed fan drive systems are too often found. Air handling units are often constructed to fit the space available, rather than being supplied as properly designed and type-tested complete units, which are inefficient as a result. Bulky and power absorbing noise attenuators are provided rather than noise cancelling.

The technical changes described above could significantly reduce UK energy consumption associated with buildings, and If CIBSE members do not take the lead in these matters, who else will? The government seems to be in dire need of authoritative advice, the privatised BSRIA and BRE need all the support they can get, the new design methods need to be developed and proved, and somehow architects, consulting engineers and contractors need to find ways to ensure that buildings are built and perform as efficiently as intended and required.

John Amos CEng, MCIBSE