Energy Assessment: kWh for wood(biomass) burning

1 to 26 of 26

- CommentAuthorjamesingram
- CommentTimeOct 1st 2012 edited
This has been discussed elsewhere but thought it might be of interest under it's own heading

So got this figure for wood from steamytea 4.5kWh/kg
and this 4.2kw/kg for seasoned wood from http://www.nottenergy.com/energy_cost_comparison/
also seen estimate for kWh/m3 but can find it .
Ok I know it's a bit of a best guess area , but if you're interested in logging your energy use to compare to other forms of heating energy whats the best option ?

How about ,; I've a 5kW stoves, so if it's on for an hour, that's 5kWh used , is that to simplistic ?
- CommentAuthorSteamyTea
- CommentTimeOct 2nd 2012
Probably too simplistic.
The 5 kW figure for the stove is probably a peak. You could throw a lighted match in ever few seconds for an hour and it probably would not register on a heat meter.
No, the best way is to weight the timber you typically put in.
- CommentAuthorSeret
- CommentTimeOct 2nd 2012
Hmm, maybe a set of bathroom scales that you sit your bucket of wood on when you bring it in, then log the weights?
- CommentAuthorfinny
- CommentTimeOct 2nd 2012
How accurate do you want?
You can determine how much available energy goes into a stove in the form of dry weight of wood, subtracting the moisture percentage. You will have to consider available energy from combustion, which depends on that moisture content..ie higher moisture, cooler, less efficient combustion. Then you look at your installation.. not just the stove, but the flue, how efficient is your system at extracting available energy..also usage patterns, most manufacturers will tell you what a typical burn cycle is for your stove, but in practice people tend to ignore that and do their own thing..everyone knows best when it comes to fire! If you still have over 50% of the initial available energy coming into your house you are lucky
- CommentAuthorSteamyTea
- CommentTimeOct 2nd 2012
Posted By: finny50% of the initial available energy coming into your house you are lucky

Too true.

Thinking about it I have a 2 kWp fan heater, not often on for more than about 4 hours on the coldest days and even then it is at the 1 kWp level. So that will be about 2kg of CO2.

A 5 kWp stove/fire probably kicks out half that because of ramping up and ramping down, so that will be 2 kg of wood, as most of the timber is carbon that will be about 5 kg of CO2 before any sequestration (lets not get into that silly definition).
- CommentAuthorBeau
- CommentTimeOct 2nd 2012 edited
Last winter I did a comparison of first heating our house with just wood and then just our GSHP I recorded amounts of wood burnt per day and temperature difference between outside and inside. I have all the figures somewhere but my basic conclusion was wood burners are much better than predicted or GSHP are much less efficient than claimed.

If others are interested I will try and dig out the numbers.
- CommentAuthorjoe90
- CommentTimeOct 2nd 2012
Beau,

Your conclusion does not suprise me, let Steamy Tea have the figures and he will produce a graph (hes good at that)
- CommentAuthorfinny
- CommentTimeOct 2nd 2012
Would be interested in the figures too.. am all too often in competition with heat pump guys who confidently throw around data! am actually doing the 2 day BPEC heatpumps course this month to get a better handle on that..
- CommentAuthorSteamyTea
- CommentTimeOct 2nd 2012
Yes, post the numbers up and your location and I shall see if I can get some weather data too.
- CommentAuthorRobinB
- CommentTimeOct 2nd 2012
But I have a 5kw rated stove. It feels like it chucks out far more than three fan heaters on full blast. I don't think I'm overloading?
- CommentAuthorfostertom
- CommentTimeOct 2nd 2012
Posted By: SteamyTea5 kg of CO2 before any sequestration
How cd sequestration come into it? - burning is the antithesis.
- CommentAuthorSeret
- CommentTimeOct 2nd 2012
Posted By: fostertomHow cd sequestration come into it? - burning is the antithesis.

Because carbon that's in the carbon cycle is different from carbon taken out of geological sequestration. Or isn't, depending on your point of view.
- CommentAuthorfostertom
- CommentTimeOct 2nd 2012
Posted By: Seretcarbon taken out of geological sequestration
Wot, you're talking about burning coal in the 5 kWp stove/fire? Surely this is red-herringsville.
- CommentAuthorBeau
- CommentTimeOct 2nd 2012
I will try and post up the figures this evening.
- CommentAuthorSeret
- CommentTimeOct 2nd 2012
Posted By: fostertomWot, you're talking about burning coal in the 5 kWp stove/fire? Surely this is red-herringsville.

No, ST was talking about comparing carbon from wood (which is carbon in the carbon cycle) with the carbon in grid electricity (which is carbon from geological sequestration).

Don't really want to get into the different points of view on that, as it's OT will likely derail what could otherwise be a useful thread.
- CommentAuthorfinny
- CommentTimeOct 2nd 2012
I agree..
if we didn't know Tom better, we might suspect him of deliberate sabotage there..
- CommentAuthorBeau
- CommentTimeOct 2nd 2012 edited
I have found the figures.

Grid Ref SX531715

The weather was fairly steady throughout the test, mainly cloudy and warm. The house was not noticeably affected by solar gain (we don,t get much direct sun in the winter months as the barn runs north south)

Using the wood burning stove, this is not connected to a wet heating system.
I took temperature readings throughout the house and averaged them but the variation from room to room was rarely more than 3C

The logs are hardwood at 20-22% moisture content.
The flue is internal in room to roof so good for squeezing every last bit of heat out.

Date 17/1/12
Inside temperature through the day 20.69c 21.175c 21.525c
Outside temperature through the day 3.6c 8.4c 8.3c
Wood used 19.6Kg

18/1/12
20.65c 18.6c 21.35c
9.9c 11.3c 10.1c
21Kg

19/1/12
20.55c 20.725c 21.775c
10.4c 9.1c 6c
21.8Kg

20/1/12
20c 21.875c 21.475c
7.4c 10.9c 9.6c
19.9Kg

GSHP figures to follow
- CommentAuthorBeau
- CommentTimeOct 2nd 2012 edited
Second time lucky as I just lost this once.

The GSHP also does our hot water so some adjustments to the figures need to be made. I estimate the circulation pump uses 1.68Kwh per day and long term test suggest that the hot water uses 2.26Kwh per day. The temperture lift from the ground loop to the UFH was around 27c

The GSHP heats through UFH so I left it on for a few days to allow for this to come up to temperature.

23/1/12
21.35c 20.85c 20.925c
8.5c 9.8c 8.3c
Meter reading
787Kwh 791Kwh 796Kwh
- CommentAuthorBeau
- CommentTimeOct 2nd 2012 edited
Sorry having internet problems

24/1/12
20.925c 21.075c 21.45c
7.9c 7.9c 8.6c
808Kwh 811Kwh 820Kwh

25/1/12
21.025c 21.475c 21.05c
2.5c 10.2c 0c
828Kwh 834Kwh 842Kwh

I am not 100% sure I have got the dates right but the drop in temperature at the end of the test should fit in with any weather data ST might find.
- CommentAuthorfostertom
- CommentTimeOct 2nd 2012
Posted By: finnyif we didn't know Tom better, we might suspect him of deliberate sabotage there
No no, I see it now.
- CommentAuthorSteamyTea
- CommentTimeOct 2nd 2012
Beau
I have weather data for your area. Shall get the data in the morning.
- CommentAuthorWillInAberdeen
- CommentTimeOct 2nd 2012 edited
Posted By: SteamyTea

Thinking about it I have a 2 kWp fan heater, not often on for more than about 4 hours on the coldest days and even then it is at the 1 kWp level. So that will be about 2kg of CO2.

A 5 kWp stove/fire probably kicks out half that because of ramping up and ramping down, so that will be 2 kg of wood, as most of the timber is carbon that will be about 5 kg of CO2 before any sequestration (lets not get into that silly definition).

Don't think its that bad. AIUI wood is mostly carbohydrates (lignin and cellulose) and water. Carbohydrate is about half carbon by weight, half oxygen, with a dash of hydrogen.

So 2kg of wood would give a fair bit less than 5kg of co2, maybe 2 or 3 kg.
- CommentAuthorSteamyTea
- CommentTimeOct 3rd 2012
I will bow to much superior knowledge about plants as I kill them them with kindness in my garden. So would it be fair to say that it is comparable with electricity. I think we had a thread about this somewhere a while back.
- CommentAuthorSteamyTea
- CommentTimeOct 3rd 2012
Had a look at your data and there really is not enough to use, sorry (and I think the dates are not right too).
Do you have any more?
- CommentAuthorSteamyTea
- CommentTimeOct 4th 2012
Bit in this months grown up comic about using wood as a fuel.
They made a little mistake with kWh typed as kW/h and not checked the figures.

"He estimates that at an average value of 22t per hectare per year, the amount of energy produced by woodchips would be 77,000kW/h per year. This is equivalent to 45 oil barrels or to 23 photovoltaic roof systems each producing 1.8kw from solar power."

Shall look at that later.

1 Barrel of oil is 1628.2 kWh
- CommentAuthorArchmoco
- CommentTimeMar 31st 2014
hot water and heating for my house is via wood burning stove and solar. The boiler in the stove is rated at 16kw, I'm lucky if I get 8kw, but I'm working on that. A flue thermostat will give you parameters for your burning. I've a mixture of wood depending on what I'm trying to achieve. I've expensive kiln dried birch which gives out a good heat very quickly, and Ash which is not giving out the higher temp. If I need a quick high temp burn to get the heat in the accumulator tank up I use the birch. If I'm burning just for some background heat then I'll use the Ash. It also takes time for the stove to get up to temperature and also it will lose the efficiency when re-loading.

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