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Combined Heat and Power

There is lots of talk about condensing boilers as a green solution with forecasts of over 30% saving on a conventional boiler. Many gas utility companies will offer cheap installation costs and certainly if you’re moving house it should be something you look for in your new home.

Meanwhile you will all have seen those pictures of 'pollution' coming from our large power station with great white plumes over large parts of them? Unfortunately this is mainly scaremongering by the wilder side of the Environmentalist debate as they are generally plumes of condensing water vapor from the cooling towers, otherwise manifest as simple clouds in the sky. What they ignore is to ask why they are there at all; the clue is in the name ‘cooling’ towers. To generate electricity you need high-pressure steam to drive turbines but then you need to cool the spent low-pressure steam before discharging to the atmosphere. Power stations generate lots of load grade heat, about 60 degree C to 70 degree C that is generally wasted in the plumes you see from the cooling tower. That’s why power stations are so energy inefficient at less than 45% (then you lose another 20% in transmission to your house but that’s another story!)

It is uneconomic on a large scale to recovery this but starting to think small scale. Why can’t you Combine Heat generation with Power (electricity) generation? The answer is you can if you are prepared to think differently. Domestic CHP unit are now becoming available and are simply gas-fired engines (modified Sterling Engines for the engineers out there). Think car engines generating electricity for the battery and a radiator to cool themselves. The Sterling engine uses natural gas just like your central heating boiler to produce electricity and then the waste energy to heat your water. It sounds simple but the maths can be complicated, as you need to very closely balance your electricity requirement with your hot water load, as you can’t have one without the other. The best plan is to size it for how much hot water you want and then export or import the difference of the electricity. So that means discussions with your utility supplier. Then the units are bigger and not totally silent than the equivalent combi boiler (don’t confuse combi, which means hot water and central heating, with CHP) so location in the house or building is important. Also strictly speaking these are not renewable as they use gas just more efficient in energy use, so don’t qualify for ROCs (yet another story) but are a 24/7 energy supply unlike most renewables. They are also better for larger establishments or small business

As a result they not be your solution but with the correct advice we’ll soon tell you and, if you go ahead, with the correct specification the issues can easily be overcome.

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