Space and water heating

[Anonymous]

I've been asking questions in the electric heating topic but I think I'm in danger of subverting the thread completely, I notice that there are a lot of diverging views here on the topic of heating, from my reading the ideal scenario seems to depend on super insulation and a combination of technologies, I'd like to propose here a hypothetical case, would you agree with my solution?

Project:
New build with plenty of land around it, not gas connected, potential to plant a small coppiced woodland

Proposal:
Solar water heating
Wind turbine (subject to consent)
Ground heat pump
Wood fired stove/boiler
Some kind of heat store

I'd imagine the above scheme would be quite viable (in terms of hot water provision) but what about the cost? It'd be 10000s of punds wouldn't it? And the wood burnt in the stove until the first coppiced wood is harvested would have travelled a fair distance.

How does one assess the viability of such projects and and how big a part should financial considerations play?

[Anonymous]

I'm not an expert in this area, but I'd say your scheme there is overspecified. If the insulation of a house has been well designed and installed, it shouldn't need more than a wood burning stove, especially if there's a rammed earth wall or two to provide thermal mass. I spent last New Year's Eve in a beautiful new straw bale house in France, which had an underfloor heating system installed, which wasn't yet operational. The people who designed it, built it and live in it were regretting having done the underfloor system at all, as they thought in retrospect it just wasn't necessary. We were still up talking at 5am, in T shirts, the only heat having come from the wood-burning stove which had been used to cook the dinner and had gone out about 10pm. I was amazed – it made me realise just how badly built 'normal' buildings which lose all their heat within an hour or two really are.

[Anonymous]

After a little chat with Nick Grant I'm coming to the same conclusion as you Dan. I'll let you all know what we end up with (eventually)

[Anonymous]

Wouldn't a chip/pellet burner be able to fulfil those needs? Especially if placed next to a rammed earth wall quite centrally in the house? Or does the design not allow for that?

[Anonymous]

I'm no expert on this, I've never fitted a pellet burner. But I certainly think the technology can meet those requirements. The question is, is it more efficient overall, if gas pipes are already in place and require mimimal energy to extend them? The ideal situation would be buildings in or near woodland which could supply a direct local source of chips from coppiced wood. Failing that, pellets are, I believe, wonderfully efficient and carbon neutral, but the question mark is over the distribution network and how developed and efficient it is. Have a look at this:

http://www.woodenergyltd.co.uk/

[David Olivier]

Mention of my house (experimental and – yes – designed to need no space heating energy in a southern English winter) prompts me to comment on this thread, starting with woodstoves. Why burn wood locally, with the attendant pollution problems, when a house can be sufficiently well-designed and -built to need only a tiny input of gas or (out in the sticks) LPG?

Germany for instance now has 4000 buildings using (generally) gas for heating and cooking at a rate of less than 15 kWh/m2.annum. See http://www.passiv.de. Switzerland and Austria between them have another 1000, the rest of the EU has at a guess 3-500, mostly in Scandinavia and the Low Countries.

Planting a few cherry or maple trees could be sufficient to offset the CO2 emissions due to such a low level of fossil fuel usage.

I will exclude from the following discussion the health effects of the exhaust emissions from burning solid fuel (coal or wood). These include some very nasty chemicals and potentially more particulates than a diesel car.

Well, excluding emissions, the other problem is that most wood heating systems are severely dysfunctional if they're applied to ultra low-energy houses – almost certainly the proposed Silver Standard, and without any doubt the Gold Standard.

Take a 150 m2 house meeting the proposed Silver Standard whose space heating load varies from 0 to 3 kW (maximum) and back to 0 kW between (typically) November & April. The space taken up by wood storage and plant would be excessive; the money to be spent on that would arguably be better devoted to an even better thermal envelope. Also the heat output is too inflexible. We know from years of experience with low-energy homes that they need heating systems which automatically turn off as soon as the sun comes up after a cold night (or a cold morning). All solid fuel systems fail this test.

In the USA, condensing gas water heaters have sometimes been used to heat very low-energy homes (a logical step, because the space heating load is lower than the water heating load). This hasn't happened here yet, but it probably will.

[Anonymous]

Good point about the pollution created by solid fuel combustion

[Nick Grant]

Just to pick up on the part load issue, I'm not convinced this needs to be an issue with a well insulated house with even a little thermal mass (think plasterboard and skim) and a reasonable size hot water store (good idea to make use of solar).

We run our winter space heating using a simple Clearview stove. Even at full pelt we dont suddenly overheat as the walls and ceiling absorb the output. Stove goes out (we dont turn it right down so it would smoulder) and next morning the house is a pleasant temperature.

Same could apply to gas, perhaps with very simple underfloor heating. Put in x kW from smallest boiler for say 30 mins, 1hour then turn off?

Rather like the boost and coast of motor mileage marathon vehicles where an oversize engine is used intermitently because tiny engines are less efficient.

I can imagine a problem with rads and trv where one rad is on and boiler cycles because it can't loose the heat quick enough.

I have never lived in a house with gas so may be talking bollocks.

[Author]

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