This week I thought I would try and explain a little about our new biomass boiler system. Ok, so, on the face of it possibly not the most interesting topic, but, I think it is actually one of the more exciting parts of the project here at Swan Barn Farm.
The basecamp used to have its heating and hot water supplied by electric stroage heaters and an electric immersion hot water cylinder. It was a really difficult system to work with , the heating only warmed up over night so you couldn’t just turn it on when you wanted it. This meant it had to be left on much more than it was needed just to keep the place habitable, and it used massive ammounts of electricity, all in all about as ungreen as you could get. As part of the project here we were all keen to see that change. The question of what to use for fuel was obvious for us. The team here manage over a thousand acres of beautiful countryside around Haslemere, much of that being woodland. We manage the woodland for the benefit of the local wildlife and public access. Much of this woodland is coppiced, a very sustainable form of woodland management, where areas of trees are felled and then regrow on a cyclical basis from the cut stumps. regular readers will have heard me banging on about coppice on many occassions, it is very productive, both for wildlife and for producing useful timber, and there is scope for much more coppicing in the woodlands in this part of the world.
All of this means we have an abundant supply of wood, making it the obvious choice for our fuel supply. It is sustainable, renewable and by helping provide an end use for our coppiced timber has a direct positive effect on local wildlife.
This is the patch of coppice woodland where we felled the trees used to make the frame for our building, this photo was taken about 6 months after the area was cleared and you can clearly see the cut stools regrowing strongly. As well as providing the timbers for the frame it also provided some of the wood we made into shingles for the roof, our bale spikes and stair spindles, handrails and gutter mounting boards and the laths for our internal walls. On top of all that it provided the posts for several miles of fencing. In 20 years or so it will have regrown, absorbing carbon dioxide all the time and will be ready to harvest all over again. What was left over you can see piled up in the foreground, but it will not go to waste, it will provide fuel for our new boiler.
Here you can see our new boiler, with a stack of coppiced sweet chestnut next to it ready for loading. Its a log batch boiler, we went for a log fired system as it means the fuel has the minimum of processing and machinery involved in its production.
When you open up the front of the boiler you can see it has three doors in it.
The top one is where the logs are loaded, the middle is for lighting (although it also has an automatic ignition system) and the bottom one is the gassification chamber, this clever bit is an area where all of the smoke and products of combustion are circulated and re ignited to make the boiler extremely efficient. Below you can see inside the firebox where the remains of the last burn are still smouldering.
Heres how it works. A batch of logs is loaded into the boiler and lit. The boiler self regulates the flow of air to ensure the most efficient combustion possible and heats water in a heat exchanger at the back of the big red box. This hot water is the stored in two big super insulated thermal stores (tanks to you and me). You can see one of these tanks on the right in the picture below, its the big grey thing next to the doorway (the other one is hiding behind it).
These tanks store the thermal energy from the boiler from where it can be used over the next day or two. A system of pipework and heat exchangers take the heat from the stores and distribute it to our radiators throughout the basecamp and Speckled Wood, as well as to all the taps, baths and showers.
The thermal stores also have a second feed in to them, from the basecamp roof.
Where as well as photovoltaic panels generating electricity we also have solar hot water panels. They are the 6 panels towards the bottom of the roof that look like massive iphones. On a decent day in the summer they should keep the thermal stores topped up without the need to burn any wood, and during the rest of the year they reduce the need to feed the boiler.
Its a really clever system, the pipework alone looks like something from the space programme. It has all of the controls and functions you would expect from any modern heating system, you can set times and temperatures and all of the rest of it, but, it is being run on logs produced in our coppice just half a mile down the road rather than on fossil fuels. It has made these two buildings self sufficient in terms of their heating and hot water energy needs.
The volunteers who live here will be helping us to manage the woodlands, and the product of those woods will be used to keep them warm. Its a nicely circular system, something we are quite proud of. Its only been up and running for a couple of weeks, but it has transformed the basecamp already. To be honest it used to be a bit cold and unwelcoming on a cold winters day. But now it is cosy and warm. Hopefully the people who come and stay here in the future will appreciate the change.
