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EDN Europe's Editor Graham Prophet posts a selection of comments and insights prompted by the many items of industry news and rumour that cross the editorial desk or are gathered on his frequent travels to interviews, press conferences and events around Europe - and further afield - and somehow never find their way to the magazine or the web site, recovering some of the information otherwise lost in the noise level...

Tuesday, March 18, 2008

What’s wrong with this picture?

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The following thought was triggered by a news item in an entirely different context to EDN Europe, in which operating domestic air-conditioning was depicted as a most shocking environmental extravagance (here at latitude 51.5 north, at any rate).
Simultaneously (bear with me on this) I get very many press releases from power semiconductor makers who are going to save the planet – or at least, marginally postpone its demise – by making all of the world’s electric motors run more efficiently. And included in those motors are all the compressor- and fan-drivers in air conditioning units.

Now, deep in the recesses of my memory, there is a vague recollection (this must have been in a school or college physics class) of working through a calculation on the theoretical thermodynamic efficiency of heat pumps. The figure that comes to mind is a multiplier of four to six; that is, and putting into electrical terms, 1 kWh of energy used to drive a heat pump will move 4-6 kWh of heat compared to (obviously) generating just 1 kWh if used for resistive heating.

So, why are we not heating our homes with air conditioners running in reverse?

I can think of a few possible reasons.
The air conditioner/heat pump may get nowhere near that theoretical efficiency – can we not contribute to raising its efficiency with all of the sophisticated power electronics those press releases keep telling me about?
The most immediate domestic heating competitor is not, mostly, resistive dissipation of the same electrical supply, but on-site combustion of hydrocarbon fuel (most often, gas). Domestic heating installations appear to recover energy from burning gas with moderate efficiency; by contrast, following the electrical supply back to hydrocarbon fuel leaves you with a big efficiency hill to climb; the fuel gets burnt in a power station with thirty-something percent efficiency, and then gets to you via a transmission system with highly-variable but significant losses.

It looks like it could be a good market for those motor-control MOSFETs, if the numbers could be made to add up – is there anyone out there who knows what the scope for improving the domestic air-conditioner is? Or, of course, that vague recollection of mine from a long-ago physics class may be plain wrong……

Related entries in: Power Management |

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