Combustion vs Reverse Cycle heating

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Re: Combustion vs Reverse Cycle heating

Postby bpratt » Fri Nov 04, 2011 9:35 am

I have no idea how big your property is, but eventually you are going to run out of already fallen timber, then you'll have to start cutting down live trees, which unless they are allowed to fully dry out, will burn quicker requiring more wood to burn.

Whilst you have the timber that's great, as you're using something that was otherwise going to waste.


I dare say that lump of coal being burnt at the power station, is probably being more efficiently burnt than the equivalent lump of 'coal' that you would be burning at home, particulary if you are using a chainsaw to chop it up. :)
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Re: Combustion vs Reverse Cycle heating

Postby Smurf1976 » Fri Nov 04, 2011 10:11 pm

bpratt wrote:II dare say that lump of coal being burnt at the power station, is probably being more efficiently burnt than the equivalent lump of 'coal' that you would be burning at home, particulary if you are using a chainsaw to chop it up. :)

Absolutely agreed in terms of combustion and thermal efficiency.

But you can plant more trees whereas you can't easily grow more coal... OK, so cuttign the wood uses some petrol for the chainsaw but then there's that truly huge train that hauls coal hundreds of km from Leigh Creek to the Port Augusta power stations so I'd say it balances out somewhat.

Most estimates I've seen put CO2 emissions from purchased (cut and delivered) firewood at 0.06 kg / kWh of heat delivered assuming it's wood that otherwise goes to waste or that trees cut are replaced with new ones. I'm personally not that keen on wood heating due to the hassle it involves, but it does seem somewhat more sustainable than digging up coal (and in the specific case of SA there's not a lot of easily accessible coal left at Leigh Creek - it's a case of either dig much deeper or close the mine a few years from now (and it's the only coal mine in SA...)).
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Re: Combustion vs Reverse Cycle heating

Postby bpratt » Fri Nov 04, 2011 10:27 pm

Don't want to sound too negative here, but to plant more trees to cut down for firewood in years to come implies that you have sufficient land to grow them on whilst still chopping others up. :)

If you already have plenty of land with lots of trees ready to be cut down, and likewise a combustion stove or fireplace to burn them in, they clearly it is worthwhile to heat the house with that, rather than a/c for heating.


Personally the lazy side of me shows up and sooner use a/c for heating, rather than having to chop up wood all through winter. ;)
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Re: Combustion vs Reverse Cycle heating

Postby Smurf1976 » Sat Nov 05, 2011 4:14 pm

bpratt wrote:Personally the lazy side of me shows up and sooner use a/c for heating, rather than having to chop up wood all through winter. ;)

I have both wood and electric heat. The end result is that I use the combustion heater on the weekends but can't be bothered with it during the week.
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Re: Combustion vs Reverse Cycle heating

Postby draffonue » Tue Nov 08, 2011 1:59 pm

From a greenhouse gas emissions perspective: According to the National Greenhouse Accounts (NGA) Factors, dry wood produces 16.2 GigaJoules of energy per tonne and creates 0 kg of carbon dioxide, 1.3 kg of methane and 19.4 kg of nitrous oxide per tonne. On the other hand, black coal produces 27 GigaJoules of energy per tonne and creates 2,381 kg of carbon dioxide, 0.81 kg of methane and 5.4 kg of nitrous oxide. The reason for the zero carbon dioxide emission is that firewood is considered to be a renewable fuel source. Even when efficiencies are taken into account, burning wood is far more greenhouse friendly than burning coal. Of course I am not talking about other pollution such as particulate matter.
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Re: Combustion vs Reverse Cycle heating

Postby Nifty » Wed Nov 09, 2011 8:04 am

One thing that never seems to be considered is the environmental cost of the device producing heat! A simple steel firebox with brick liner (like a combustion heater) with an operating life of many decades has to be compared with the complex manufacturing requirements of something made of plastic, rubber, aluminium, copper, steel, lead, fibre and god knows what else, requiring some grease or oil, and charged with gas which will probably escape at some stage. I suppose the life of an aircon unit is about ten years. There are also, for me, undeniable advantages inherent in using our old Rayburn wood stove: it heats the house continuously, is always available for cooking, and produces radiant heat as well as convective and conductive, which means everything gets warm (floor, walls, furniture etc). It runs from abut Easter til November. Zero noise, and no draughts. A/C systems blow air around, with the hot air blown in up top cooling as it comes in contact with cold windows and walls, and then returning across the floor as a cold draught only to be reheated once more. I think efficient wood heating is better on all counts, as long as you have access to wood, but I appreciate of course that it's not much of a solution for people living in high-rise apartments
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Re: Combustion vs Reverse Cycle heating

Postby Mazbo » Wed Nov 09, 2011 2:38 pm

We have a large suburban block, with many trees (too many) and gather some wood from our block each year, but having a chainsaw I find there are always dead tree, fallen limbs or industrial timber on offer somewhere each year to satisfy our requirements.
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Re: Combustion vs Reverse Cycle heating

Postby lad » Wed Jan 25, 2012 11:01 am

draffonue wrote: According to the National Greenhouse Accounts (NGA) Factors, dry wood produces 16.2 GigaJoules of energy per tonne and creates 0 kg of carbon dioxide,


assuming equal replanting and successful regrowth of course.

I looked into the best heating solution with regard to environmental/comfort/efficiency and decided to go with wood heating from a boiler and hydronic radiators.

A very small amount of chainsaw fuel goes a long way when cutting the wood (if the chain is kept sharp), similarly a small amount of fuel is required to transport a trailer load (collected from the block). Intelligent design of the boiler (firebox fully encased in water) sees the extracted heat efficiently moved away to the radiators, heating the home and keeping the firebox "cool" even with extremely hot burning woods like black wattle, often treated as a pest species and burnt in open piles.

I understand that the majority cannot go down this path, but for those of us with enough land and trees, the effort is tiny for the reduction of our environmental impact.
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Re: Combustion vs Reverse Cycle heating

Postby debe » Wed Jan 25, 2012 2:33 pm

As a pensioner the cost of heating in SA is very relavent. My lounge room has a 1.5Hp rev cycle AC @ a slow combustion heater in one corner of the room which also heats the wall in the center of the house. The rev cycle unit warms the room rather well but when its switched off there is no residual heat & it cost mutch more to run than my chainsaw. The wood heater keeps the house mutch warmer & for longer & mutch cheaper. The house is a large stone building with insulated ceiling & full veranda around the house. Sofar this year the inside temperature for the summer hasnt risen above 26Deg C even when it was above 40Deg C for several days. So the AC unit hasnt been needed for cooling.
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Re: Combustion vs Reverse Cycle heating

Postby Tracker » Sat Jan 28, 2012 10:10 am

.
Sat Jan 28th.. Sydney News..

The NSW Govt. recommends a TAX on wood-burning heaters and on WOOD as a heating fuel, as a means to control the pollution caused by the use of wood-burning heaters, in urban areas.

Now won't that P'off the environmentally conscious, who accept that burning wood for heating etc. is carbon-neutral..
I suppose it does not matter what medical ailments might result, for all others in the valley..

So, when comparing the two forms of heating, it might be good to include consideration of a Wood-Tax.. :(

PS - Interesting - The NSW GREENS are supporting the proposal..
And there you were thinking that the GREENS were keen on ALTERNATIVE energy and lowering Carbon Emmissions..
Well, only when it suits, I guess.. :lol:
..
.
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