The biomass boiler

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.

Getting plastered

The last of our flakey earth plaster came off the walls this week.

And with that I think we have marked a bit of a new beginning. The atmosphere is lifting and things are moving on. It really feels like we made the right decision. We decided that lime plaster was the way forward, and that has been the main task of the week.

We are very fortunate that Dylan from Ben Law’s Roundwood Timber Framing Company has come back to help us on site for a couple of weeks. He did a lot of the lime plastering on our straw bale walls, and we needed his help to make sure we got it right. He was here throughout the the main part of the build last year, and its been great having him back.

I’m not quite sure why we decided to start at opposite ends of the panels in the picture above, but I’m hoping the one I did turns out as well as his.

The first part of the process is to wet the laths with water, this prevents the wood from sucking the moisture too quickly out of the plaster. Then the first coat of lime plaster is applied. The first coat has animal hair mixed in with it, this helps to bind the plaster together to make a solid base. Once this has dried the right amount it is scratched all over to create a key for the top coat to bind on to.

A top coat of plaster is then applied. This will be left until it is almost dry, it will then be rubbed down with a damp sponge to create an even surface before we apply several coats of limewash. The limewash provides a breathable protective skin for the lime plaster as well as being decorative. Lime has been used for centuries in construction. It uses far less energy than cement in its production and absorbs CO2 as it sets. Its breathable properties should mean that it works well with the timber frame and wooden panels it sits within.

The laths are starting to dissappear again under their new coating, we are hoping that within a week or two we will have the plastering pretty much finished and will be able to start moving on to some of the other jobs that are remaining.

In the picture above you can see the progress we are making, and if you look closely above the tie beam in between the roundwood joists you can make out the last remaining internal panels of earth plaster. These small panels seem to have worked out allright, so we are keeping them. They will be a reminder of the time we spent wading around in mud.

The earth plaster walls (and why Dave went quiet for a while)

Hi everyone, sorry to have been so quiet for the last month or so, I think the whole project was starting to wear me down a bit towards the end of last year, and we have had quite a lot of problems with our internal walls. Between that and christmas I’m afraid I couldn’t really face the blog.

But, the decorations have come down, its a new year, and I think its about time I told everyone what has been going on at Speckled Wood.

The internal partition walls of the building are of a lath and plaster construction. The plan (and and awful lot of work went into it) was to use earth plaster on these walls.

I remember, as it turned out rather foolishly, a remark being made just before we started plastering over our hand cleaved chestnut laths. It was something along the lines of not expecting them to see the light of day again for about a hundred years or so.

As it turned out nothing could have been further from the truth. The laths were visible again all too soon.

We have been really lucky that so many people have been prepared to come and help on the project, that is part of the reason I have been dreading having to write this post. I don’t know how many people helped us with the earth plaster, but there were a lot.

It was mucky work, but everyone got stuck in, and for a while it looked like it was going really well. But soon we started to have problems. The plaster was crazing, cracking and starting to delaminate from the laths. Every week we put in at least two days work filling cracks, wetting the plaster down, putting on extra slip coats, and readhering it onto the laths.

You can see some of this process taking place in the picture above. Several times chunks of plaster were so much on the verge of falling away we had to tear them off and patch in with new clay.

We all put so much effort into it but the cracks kept on appearing…

We managed to get to a stage where they were getting smaller over time, but still we were having problems getting it to adhere properly to the walls. We put a heap of work in just before christmas, had some time off to recover and then came back in early January to see what on earth we were going to do.

I tore off a couple of the worst chunks to have a look at what was going on underneath, so that we could make an informed decision.

Underneath it was bad news. We really wanted to stick at it, give it a few more weeks, presevere and make it work. But I was worried. We were going to have to re patch so much of it we wouldn’t be back to where we were for a month or so at least. It just takes for ever to dry, and you have to be carefull not to let it dry to quick or the cracking gets worse. Then came the final, and biggest worry. After all that extra work we were considering putting in, was there any guarantee we would manage to finally get it working? In the end I realised, we could put in a solid months work and still fail. We had to call it a day, cut our losses, and find a different way forward. The earth plaster had to go.

It was funny really, I had been dreading it for ages, and fealt absolutely awful about it (very much feeling I have let people down by not getting it right) but when the decision was made I just knew it was for the best. We are now in the process of tearing off all of the clay and we will be lime plastering the internal walls instead.

One thing is for sure, it certainly comes off a lot easier than it goes on.

I know some of you reading this are probably far more expert in these things than me, and some of you probably know where we went wrong. I think I know some of the reasons, and am sure 3 or 4 mistakes conspired together so that in the end we were fighting a losing battle. I am pretty gutted about the whole thing, it was one of the aspects of the build I really wanted us to get right. But, I also know that we are building a house, and can hardly call it that until it is in a fit state for someone to live in. The time really has come to get back to the bigger picture and stop staring at cracked mud.

Lime plaster should work fine as a replacement, in terms of the history of architecture you could probably argue we have taken an evolutionary step forwards! I know it is the right choice for us, with what we have learnt I wouldn’t be afraid to try it again, but it would be on a much smaller scale, and only for feature areas, I have been converted to the joys of lime.

I guess I was wrong about how soon those laths would be on display again, lets hope next time they are covered over its for good.

Its been quite cathartic writing this, I really hope nobody out there is too dissapointed with our decision. I really hope it means I can get back into the blog, as well as back into the project, there is so much there that is going well, hopefully I will be bringing you news of some of that over the next few weeks. Happy New Year!