Wednesday 26 November 2014

Renewable Heat for Community Buildings

Acomb - the story so far
What do you do when your boiler is very old and you know that the next time the gas man comes to fix it, it might not recover? Most people would replace it with a more efficient new gas boiler, but the issue is: given that fuel prices are on a steady upward curve with the expectation that this will only get worse over the next 20-30 years, why lock yourself in to an old technology and high bills?
For Acomb Methodist Church, the answer is obvious: power the new boiler with renewable heat. Work is still in the early stages of getting prices, but I thought it would help to summarise the story so far.
One option is to install a standard electric boiler using renewable electricity, but this There are two main sources of renewable heating other than electricity (which costs more per unit than gas unless you generate it all yourself!). You can get heat direct from the sun ie pumping water through tubes on the roof to be warmed by the sun or via a heat pump. 
So what's a heat pump? 
Remembering the 2nd law of thermodynamics (see Flanders and Swan's comedy song if you weren't listening in physics), heat normally goes from hot objects to cold ones, unless you put energy ("work") in. Your fridge works on exactly the same principle: a pump uses a small amount of energy to extract a lot of heat from a refrigerant and pump it out into your room instead.
So a heat pump needs something at a reasonably constant temperature that it can extract heat from when it's cold outside. Good sources include: large bodies of water (eg a lake), the ground or the air (least efficient option, as its temperature varies a lot, and unfortunately you need more heating when the air outside is coldest!)
For Acomb, we have no convenient lakes nearby, so we have looked at using the air or the ground. In fact we've looked at three ways of using the ground:
(1) With shallow pipes laid under the grass. This is not the preferred option for Acomb because for large buildings the horizontal heat pipes cover too large an area, and we don't have a big enough lawn!
(2) By installing deep pipes vertically in a borehole and either circulating water through them (a closed loop system) or by extracting water at a constant temperature from one borehole from the sandstone aquifer at 40m depth and re-injecting into another borehole further away (an open loop system). The BGS (British Geological Survey) have done some great research into deciding which aquifers are suitable or not for open loop systems!
The open loop system is currently looking to be the best option as there is enough space to keep the source and outlet sufficiently far apart that they don't affect each other and there's no requirement to add antifreeze (which could leak leading to pollution). 

Grants and Funding
Once we have established our method, the next challenge is paying for it. The drilling and installation operation costs around £100,000 for a large building like Acomb but the Renewable Heat Incentive (RHI) will pay a feed in tariff for every unit of fossil fuels saved, which will pay £250,000 over about 7 years. The equivalent figures from the Energy Saving Trust for domestic properties using the pipes-in-the-lawn option are in the region of £11,000 to £15,000 with typical RHI payments of £2000 to £3000 per year (plus a big saving on your bills!)
Why renewable heat matters
There's a good reason why the Renewable Heat Incentive is pretty generous: Heating currently produces a third (32%) of UK greenhouse gas emissions, but a recent report by the WWF in Scotland found that only 2% of our current heating demand is being met from low-carbon sources. This has to change, and quickly, for us to keep our promise to developing countries to reduce our emissions by 20% in the next 5 years to 2020! My church are doing our bit - now it's over to you...

See also: 

No comments:

Post a Comment