OPINION
system will be at least 8C, assuming an average ‘round trip’ of 8 km out of its 16 km network. Given that the operating temperatures are 95C fl ow/55C return, this means that (ignoring the pumping losses) at least 20% of the heat is wasted to the ground (and probably considerably more than this at low fl ow). Since the heat network is more than 85% fed by conventional, natural gas-fi red boilers, one wonders on what basis the operators claim this to be a ‘low carbon’ heating network. I would suggest that the signifi cant
heat loss from the district heating pipework is a good reason why heat networks are unlikely to be the future for us, as Prof Courtney suggests (particularly if the heat sources are more than 50km away). The answer to future (zero carbon) urban heat supply is heat pump technology (using air- source, ground-source or even waste- water source), with biogas as the fuel of choice for the rare situation where insuffi cient heat sources are available. James Thonger
Counting carbon does count David Fisk might be right to question the justifi cation for seeking a single grid carbon emission factor (Letter, October Journal, page 19), but in the hard-pressed marketplace where equipment manufacturers are jostling for every advantage, variations in grid emissions certainly do count. Because the regulators have chosen
to provide fi scal support in the form of feed-in tariffs for more-expensive but less-effective technologies, combined heat and power (CHP) has to depend on its superior carbon and energy saving credentials to stay in pole position. Every increase in grid emission
factors deliver more carbon savings from CHP – and that matters, not least because it gives the designer the option of reducing the CHP size, so improving overall performance and delivering better payback. If there is a chance that the current
range of grid emission factors in general use is skewing results, clarifi cation is certainly needed.
Prof Fisk’s suggestion that it could be 0.5 to 0.6 is a bit cavalier, but if it were to be 0.6 the CHP industry would be delighted! David Shaw Baxi-SenerTec UK
Every
increase in the grid emission factor delivers more carbon savings from CHP – and that matters
Trusting heat pump accreditation One year on from the Energy Saving Trust’s (EST) report, air-water heat pumps can live up to the claims of energy effi ciency (‘Hot prospect?’, October Journal, page 50). It is widely recognised that most of the heat pumps in the EST fi eld trial were installed prior to the introduction of the Microgeneration Certifi cation Scheme (MCS). The next logical step is for the industry to continue to work with the government and industry associations such as the EST to support initiatives which improve knowledge and understanding within the UK heat pump market such as the development of skills and ‘best practice’ for heat pump installations. Andrew Crown Daikin UK
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