the friend online
19 January 2007


Green living may not be so simple – or is it? - preview

Andrew Hughes Nind, an energy consultant from Reading MM, responds to suggestions in the issue of 5 January on reducing our energy footprints

A number of websites for heat pumps make the claim that they are 300-400 per cent efficient, at least three to four times as efficient as conventional boilers
  • The claim is a little suspect, because it doesn't compare like with like
  • A heat pump transfers heat (from outside to inside or vice versa) whereas a boiler produces heat by burning fuel
  • The figure quoted by heat pump manufacturers is not really an efficiency – to a physicist or engineer, nothing can be more than 100 per cent efficient – but it is nonetheless useful to compare costs of various ways of heating one's home
  • Cost is a good guide here, because it takes account of the fact that to produce one unit of electrical energy for the heat pump in the home requires (roughly) three units of primary energy at the power station source
  • That is because power station turbine efficiencies are generally in the range thirty to fifty per cent and about ten per cent of electricity generated is lost (as waste heat) in its transmission and distribution

  • Andrew Hughes Nind

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