(Almost) Carbon Neutral Central Heating

For many people, Portugal conjures up images of sun, sand and sea. But the reality of this central region of the country is that winters are cold, very cold. We often get frost between October and March, with temperatures sometimes as low as minus 6-8??C at night. Thick stone walls help to keep the cold at bay, but once winter really sets in the stones cool down and it feels as if they are sucking heat out of the rooms after dark. So a good heating system is essential for there to be any kind of comfort during the colder months. But what kind of heating?

Well, we started off with a wood burning stove in the kitchen. Despite its failings (it's a rather inefficient local design with a very poor flue), it got us through our first winter. But by autumn of 2007 we were hoping to get some kind of central heating. The pipework was already in place, so really it was simply a question of paying for radiators and choosing a boiler. But what kind of boiler? Was there any way we could reduce our carbon dioxide emissions?

Gas is a simple, low maintenance choice. But we would be contributing to global warming and also at the mercy of future price rises. Wood is logistically awkward for us because (a) we don't have our own supply and (b) we didn't design the house to have a conveniently located wood-fired boiler. So we'd have to purchase wood. And firing the boiler would probably entail running downstairs and out to the 'boiler room' every hour or so. Not ideal

In the end we decided on a wood-pellet boiler. Wood pellets are a form of biomass derived from forest waste, sawdust or cut wood. They are formed under pressure, using the natural oils in the wood as a binder. They are reasonably convenient to handle, and boilers offer the advantage of having auto-ignition (using an electric igniter) and regulated pellet feed, so they can be run on a timer and controlled with a thermostat. Here's the boiler we chose in action:

We have to fill the unit with pellets and clean out the ash (once a day or every couple of days), but aside from that there's almost nothing to do. After more than one season of use, I can say we are pretty happy with it.

Does it make our heating carbon neutral? Well no, not quite. The pellets cost energy to produce ?Eprobably electricity. Then they have to be transported here, though fortunately we have now found a local producer so they only have to come about 10km. Then, most importantly, the boiler requires electricity. When running, it consumes something under 100W to run the hot water pump, the draft fan, and the electronic circuitry. With an output of 25kW, this is a fairly small amount of electricity in comparison. But it is certainly not negligible. It would feel good to have a solar system capable of supplying this power in the future...

We use, currently, about 15kg (one sack) of pellets per day (and that amount will rise when we start operating the Japanese bath from this heat source). That means we have to store quite a lot of pellets. So, I had to build a store for them...

Here we go... "Sakuragi-an" under construction:

Quite a lot of firsts in there (for me). I've never really built any kind of structure before; previously the closest I got was the wood store. Certainly I've never made a tiled roof. (We used tiles removed from the old roof of the house.) Nor fitted doors and windows (also re-used from the original house). Rendering the interior was also fun :). Yet to do is the exterior rendering; I'll probably get around to that once the bath is finished.

Our next heating question is what to do about the wood burner. It's good looking, but has some serious problems. Currently we are considering ?\ with the help of friends ?\ the possibility of designing and building some kind of tile/masonry stove. Our ideal would be something that burns super-efficiently (which means fast-burning, hot fires), provides immediate heat (such as when we come in later in the evening), stores some heat (so it doesn't have to be fired continually) and offers the possibility of heating water or food while burning. This could be a tall order and some compromise is going to be needed. But we should be able to come up with something better than what we have now. More news in future ?\ perhaps in time for next winter.