Heating and cooling: Could I live with just Solar thermal Panels and a Wood burning Stove.

1 to 30 of 35

- CommentAuthorHairlocks
- CommentTimeNov 28th 2009
Does anyone use a wood burning stove, the decorative type that goes in the living room and ET solar as the only means to heat their home?

I currently designing with an architect and new build house, that is going to be about 160m2, detached, have 4 bedrooms with 5.5 acres of land (with have lots of wood available). I would like to know if my plans on heating the house are going to be realistic.

I have told my architect to design with floor, roof and walls U-Values of 0.1 W/mK as an aim, will and air change test result thing of 1. According to my calculations on a cold winters day (-3) this will give a heat loss of 1.2 kW through the floor,roof and walls. A loss of about 8.2 kW through air infiltration/escape (10% of test value target) and of about 0.7 due to MHVR at 90% efficiency. This gives a total heat loss of 10.2 kW, therefore the heating demand will be about 244kWh for the day. Hence I calculate I would need a 15 kW Stove running for 16 hours to meet this and a thermal store of 81kWh to last 8 hours without the stove (e.g. over night). This would be a Thermal store of 1550 litres with a temperature drop from 85C to 40C. Do all these values look to be in the right ball park? Or can someone correct my false assumptions them apart? I know I haven't included hot water needs.

Running the Log burning Stove like this would be a bit onerous, but we could cope for a few very cold days at a time. Would this be possible or would I need to need to design another room to house a gasification wood boiler? I guess I am going to need to increase the thermal store size to the next available and try to fit in a 2000 litre one. With this in mind, what sort of area of solar tubes should I install to try an reduce the amount of wood wee burning the autumn and spring. What would be the best orientation for these tubes to maximize the heat gain in the autumn and spring, and to reduce the heat gain in the summer. Plus what would be the best form of heat dump during the summer?

Any comments on the above welcome:)

Hairlocks
- CommentAuthorHairlocks
- CommentTimeNov 28th 2009
Just to add, I do have a spreadsheet of all my calculations, but it is a mess and needs to be organised for anyone else to understand it.
- CommentAuthorTerry
- CommentTimeNov 28th 2009 edited
Most of your aims seem to be around passive house levels, in which case a 15kW stove will have you overheating in a big way
I think you may have gone wrong with your figures somewhere, but I suspect someone will be along shortly to give you a more technical explanation.

Have you had a look at passive house details? Does your architect have experience of these levels of insulation and airtightness? Detail is all important so familiarise yourself with what is required and dont just leave it up to the professionals unless they have a proven track record with real low energy construction.

That said, you are aiming in the right ball park so good luck.
- CommentAuthorHairlocks
- CommentTimeNov 28th 2009
My Architect was chosen for more than one reason, but he did say the rights things, and seems interested about going for a sustainable homes, unlike some Architects. Did exhibit at http://www.ecostrust.org.uk/h4g/visitors_organisers.html and seems quite pro warmcel.

For all my calculations, I used a U value of 0.15 and a air change of 1.5 on the assumption, may target will not be quite reached. I have found on mistake, I forgot to half the volume of the attic to account for a pitched roof, but it still leaves it at

For my Air infiltration I used I used this formula from a website somewhere (can find it now)

Heat Loss caused by Infiltration
Hi = cp Ï n V (ti - to)Â Â Â Â Â Â Â Â (8)
where
Hi = heat loss infiltration (W)
cp = specific heat capacity of air (J/kg/K)
Ï = density of air (kg/m3)
n = number of air shifts, how many times the air is replaced in the room per second (1/s) (0.5 1/hr = 1.4 10-4 1/s as a rule of thumb)
V = volume of room (m3)
ti = inside air temperature (oC)
to = outside air temperature (oC)

And I used the following values

cp = 1158 ( via google)
Ï = 1.2 ( via google)
n = 1.5/3600 = 0.00041666667
V = 615 m3 ( Whole house
ti = 20
to = -3

This still gives me a value of 6.8 kW, that still seems a lot more that any other means of heat loss?
- CommentAuthorHairlocks
- CommentTimeNov 28th 2009
I try to never leave anything up to the professionals (well on intelligence based stuff). I always try to work it out for myself, and then get them to explain why I am wrong if I am. When it comes to skill like plastering, then that when I just leave it to the professionals.
- CommentAuthorGotanewlife
- CommentTimeNov 28th 2009
Well Hairlocks, something doesn't seem quite right and I can't say what because I have not needed to get into air changes and Heat Recovery - and when I say not right, either you will be too hot or I am going to be too cold!!!!

My house is 300m2 with 3m ceilings, solid stone walls, huge amounts of single pane glass incl 4x very high double patio doors all glazed, roof is insulated now but no other insulation anywhere. I calculated I needed 25Kw to heat my house and I have put in a 2000 ltr TS fed by a 40KW wood gasification boiler and 5 x FPs at 2m2 each feeding a coil in the TOP of the TS. (I live in Italy and expect 8.5-9 months solar only DHW but given the 25Kw heating load negligible assistance to space heating in the other 4 months ie when we need space heating). I am confident my figures add up and the boiler will be fired up for the first time on Tuesday (I hope!!). So you see instinctively your new build figures seem high to me........that is all yout figures add up for a poorly insulated house like yours.

BTW I absolutely agree with your last post - for me, and I am guessing most of us on this Forum NOT as part of our everyday business, this Forum is all about becoming an intelligent customer (in a give and take way) and if you're not an intelligent customer you're a sheep!!!

As for wood - it is a way of life; it will be part of your life, 3 burns a day when it is really cold - embrace it now or get a biomass boiler! Suggest finishing your wood store before you lay the foundations for your house - then fill it asap......then you might get away with only buying the 1st year's wood
- CommentAuthorjemhayward
- CommentTimeNov 28th 2009
Without resorting to calculations, we heat a 500yr old stone and thatch cottage of about 150m2 on two floors with plenty of lost insulation, some leaky double glazing, and a few draughts with a 4.5 kw Hwam woodburner, for all but the coldest month of the year (we also have a storage radiator). Water heated electrically at present, but solar thermal will be on stream by the spring. We won't be totally free of electricity, but hope to cut the summer consumption by 50% min. The house has huge thermal mass, and so the wood burner keeps us happy.
- CommentAuthorHairlocks
- CommentTimeNov 28th 2009 edited
Thanks for the comments so far. It does seem like a small wood burning stove will work for us. I just can't do the calculations yet, so should probably get a smaller wood burning stove.

I have now found this article http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/94/940111.html that says I should divide the pressure test by 20 not 10 (and it seems I didn't even mange to divide by 10 in the first place.)

This now gives me the following

1.2 kW through Walls, floor and roof
0.35 kW through infiltration/escape ( is this now too low?)
0.62 kW through the MHVR

I now only need 52 kWh a day in the cold (this seems much more realistic to me) a 3.2kW stove, and a Thermal store of 331 litres.

Currently I am going to have to clear down some trees, so I can get at the crumbling farm house, so a wood store cut this winter ready for next winter should be no problem.

The next question is how much wood will I use per year?
- CommentAuthorRachel
- CommentTimeNov 30th 2009
I run a 2/3 storey house ( strawbale) with one clearview stove and back boiler, plus ET solar ... all is good.
- CommentAuthormike7
- CommentTimeDec 1st 2009
Posted By: Hairlocks

The next question is how much wood will I use per year?

Dry wood should generate 3kWh per kilo or a bit more if you're lucky. Suppose you needed your 52 kWh per day for 120 days per year, then that means about 2000kg of dry wood/yr, or 3000kg unseasoned. All very ball-park, but hope it gives you some idea.
- CommentAuthorBenpointer
- CommentTimeDec 2nd 2009
Re: "Suppose you needed your 52 kWh per day for 120 days per year, then that means about 2000kg of dry wood/yr, or 3000kg unseasoned."

.... I thought 52kWh was for a -3deg day... ? We're not likely to have 120 of those a year
- CommentAuthorGotanewlife
- CommentTimeDec 2nd 2009 edited
I can't rember the sums I used to get there but for our house (calculated at 18Kw heating demand after insulating the roof - now done) I worked out I would need 1250 Kg of wood for 5 months, 5 months is heating season where I live in Italy but (I promise you!) we have the same temps as the avg in the UK for these 5 months.
- CommentAuthormrswhitecat
- CommentTimeDec 4th 2009
What's 1250 kg of wood actually look like - I don't think my executive log store is going to be big enough ...
- CommentAuthormike7
- CommentTimeDec 4th 2009 edited
Roughly, 1250kg of executive logs would make a stack about 3 cubic metres. I like my executive logs cut down to 50cm long (even shorter if they're banking executive logs) and stacked about 1.5m high, which makes a row 4 m long. A bit less if they're well stacked or dense. Insert obvious joke here.
- CommentAuthorGotanewlife
- CommentTimeDec 5th 2009
Oh drat, missed of a pesky nought! that's 12.5 tonnes not 1.25! Surprised somone didn't guess you lot usually being so sharp!!

3000 kgs properly stacked takes up 5.75m3.

Mrs Whitecat: From my first post here:

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=2853&page=6#Item_11

you can see what 3000 kgs actually looks like and on the last page of that discussion what 12.5 tonnes looks like.
- CommentAuthormybarnconversion
- CommentTimeJan 2nd 2010
Solar thermal panels & wood burning work for me in my 140ish sqm conversion with high but not passivhaus levels of insulation.

The one gap is when we're away over the winter and the house isn't occupied - I'll be posting that as a new question shortly...
- CommentAuthorludite
- CommentTimeJan 2nd 2010
One things for sure, u will not be able to generate enough of your own wood on only 5 acres - especially if u want to use it for other green activities like your own chickens or veggies. Not one to boast, but we have considerably more land/mature trees/dead wood than that, and now my husband is having nightmares we might run out and have to buy in. . . in which case, where will we store it. . . . . .

As gotanewlife states, wood becomes a way of life - my husband can't pass a tree now without wishing he had his chainsaw handy. . . . . .
- CommentAuthorsipman
- CommentTimeJan 2nd 2010
Hairlocks

has been done, and provided you have no problem with using a stove,will work very well

http://www.claysllp.co.uk/Eco-Self-Build-House-at-Oakworth,-Keighley-development/11506

http://www.claysllp.co.uk/SIPS-Energy-Efficient-Cottage-development/11434

http://www.claysllp.co.uk/Passive-House,-Clayton-le-Moors-SIPS-Development-development/10773

Sipman
- CommentAuthorwookey
- CommentTimeJan 5th 2010
We almost do that here in a nondescript 1960s detached house. Heating is almost entirely woodburner. Hot water is almost entirely soalr thermal. Gas boiler gets turned on maybe 10 times/yr, mostly to fill in winter hot water gaps (our woodburner is not connected to hot water)

This does require you to be reasonably hardy in a normal house. It should be absolutely fine in a passive-ish house, and of course works much better if the wood burner can do hot water too.

Your 52kWh/day looks a lot more like the right answer than your earlier numbers. You will have to get a lot of detailing right to actually achieve those numbers thought.
- CommentAuthorHairlocks
- CommentTimeJan 6th 2010
Thanks for all the replies, looks like we will go for the way of life change and good for it. I am concerned about what ludite says though. I was under the impression that a coppice of 1 hectare would be enough for the average house, not sure where that came from though.

We are also now thinking of a wood burning range cooker, but am concerned it may overheat the house in the autumn/spring. can the heat output into the room be low enough, with still a good cooking temperature? My parents have a gas aga which is great for cooking on (bad eco though) so I am currently thinking about either an esse or a rayburn, any opinions? currently I am thinking of one with a boiler the heat the hot water as well.
- CommentAuthorJohnh
- CommentTimeJan 6th 2010
Hairlocks - we've had an Esse W23 for nearly 3 years and it's a great cooker, provides plenty of hot water and heats a few rads.
- CommentAuthorludite
- CommentTimeJan 7th 2010
You need enough area to grow/coppice your wood, then an area to cut it and leave it to dry, and you need to allow enough time for the crop to grow back. . . . . At the moment we are using between 6-8 trug buckets of wood a day (the 36 litre size).
Of course, everyone will use different amounts of fuel depending on their lifestyle and the insulation and size of their house.

I'd be interested to know how much wood (in trug buckets) others are using. . . . .
- CommentAuthorGotanewlife
- CommentTimeJan 7th 2010
Ha! Trug buckets to you too! I am using one wheel barrow load (rounded but still good for bumping up steps) per day. How many trug buckets to a wheel barrow?

I use one load every 36 hrs in mild conditions. But my wood is excellent: oak, very well seasoned, stored under cover and off the ground, and stacked to allow air to flow around.
- CommentAuthorBenj
- CommentTimeJan 7th 2010
The productivity of your patch of land will depend on the state of the soil, its aspect etc. Have you thought about passive solar gain in the design of the house?
- CommentAuthorludite
- CommentTimeJan 8th 2010
But how big is your barrow? We have a brilliant builders barrow thats twice the size of the 'ladies girls barrows' with rusty holes in the bottom.

See the photos of our fireplace in another thread (looked like a fresian cow before we painted it?) well, 24hrs worth of wood fills each side of the fireplace right to the top. . . .

Point taken about your 'excellent' wood gotanewlife!
- CommentAuthortimevans2000
- CommentTimeJan 8th 2010
Hairlocks, why do you think you need a thermal store? If you bank your log burning stove down at night and during the day when you are out, the stove will still kick out a kw or so. It should bank down for 10 hours or more on good dry wood. If you design your house with lots of thermal mass within the insulated envelope you will have a thermal store inherantly within your design.
My house is constructed in this way with log burning stoves connected to radiators and the hot water cylinder. I do not have the benifit of a purpose built house with very low heatloss like you. My house is a 270 year old barn. It was -9 degC at night earlier this week but our house never dropped below 17 degC by the time I got out of bed in the morning. I calculated my house had a heat loss of 12kw at -3 degC outside for an internal temperatire of 21 degC.
- CommentAuthorludite
- CommentTimeJan 8th 2010
Just done a count up. Thats 6 trug buckets of wood stacked around the fire and one in front - so you can see the delightful 'recycled pink' colour and size

Which means, you need to create a wood store that will hold at least 600 times that amount of wood (because it needs time to season and dry out before you use it)

And then you need enough land to grow enough wood to keep you going as you harvest. . . . . . . that si, if you want to be independent. . . . . .
- CommentAuthorrhys
- CommentTimeJan 8th 2010
Hairlocks - remember that wood burning stoves, unless room sealed and getting their combusion air from outside, will need unobstructed ventilation to meet Part J of the building regs. This will greatly affect you ventilation heat loss calculations.
There are a number of WBS's suitable for use in house designed to Passive Haus standards on the market.
I have yet to find any Wood Fired Range Cookers that have an external supply air provision.
- CommentAuthorgarypcook
- CommentTimeJan 8th 2010
Ludite,

That's a scary photo! It can't be good to stack your wood so tight around the woodburner. Apart from the obvious fire risk of having wood in contact with the hot sides of the stove, building regs require a 6inch space all around the stove. This would also almost certainly invalidate any house insurance should you have a fire!

what is more, this will also considerably reduce the efficiency of the stove - without the free space around the sides of the stove it will not be able to radiate heat efficiently, and you will end up burning more wood to provide heat into the room.

Hope you reconsider stacking your wood so close!

Regards,

Gary
- CommentAuthorMartin Jenkins
- CommentTimeJan 8th 2010 edited
Nicely painted fireplace - it seemed to have a fresian cow effect last time you posted it I think.

We only have a wood burning stove, and an electric immersion. Solar panels may follow if I feel flush one day, but spending Â£3,000 or something like that seems a LOAD when the electric hardly costs anything. Maybe my (2 adults, 2 children) family don't wash enough!!

We get through 1 stacked up wheelbarrow of wood per day right now, in the coldest of cold times.

In light times (November, early December), a third that was workable.

I've built 6 bays now of wood store (see http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2853&page=4), which are made with a 4in x 4in x 2.4m square fence post at each corner, then 1.2m baton down each side, then 2.4m baton along each front bit, then a 2.4m square roof, which is "fenced" with old sheep fencing, then with a 3.5m x 5m tarp roped to the top. Three of the sides of the wood bays are fenced with sheep fencing as well. Cost about 25 quid per bay in wood I think. From Mole Valley.

ANYHOW It seems to take 4 - 6 weeks in the coldest times to get through a wood bay, so for me I think 6 bays should be enough; 3 = 12-18 weeks, which should get us through the winter, and double that for two years.

I may add a couple just for contingency.

Re the stacking wood close - well, I do the same nearly (again see http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2853&page=4) - the sides of the wood stove aren't very hot at all, and the air paths to the stove are all completely clear - there is a big hole in the wall behind the stove, and the air then goes underneath the stove to the air intake below it.

1 to 30 of 35



	Site Map \| Home \| View Cart \| Pressroom \| Business \| Links	Contact Us
Logout
© Green Building Press

Green Building Forum

Categories

Feeds

Heating and cooling: Could I live with just Solar thermal Panels and a Wood burning Stove.