Combustion vs Reverse Cycle heating

General tips, questions and answers about going green in your home and business. Achieve a more environmentally friendly lifestyle!

Combustion vs Reverse Cycle heating

Postby Mazbo » Wed Nov 02, 2011 3:03 pm

I have pondered the impact of the 2 forms of heating we have available in our house regarding least impact on the environment for some time. We have a very efficient combustion heater that we feed with recycled, dead or grown on our property timber, and a 3 phase reverse cycle airconditioner.

Question 1. Is it a more efficient use of the stored energy in the raw material (timber vs coal) by burning timber in the combustion heater with the resulting heat generated directly into the home OR by burning coal at a remote power station with all the power transmission losses and effeciency losses in the air con system.

Question 2. Which of above methods will put the most CO2 into the atmosphere for a given unit of heat energy output in our home?

We're in Adelaide, so electricity comes from power stations at Port Adelaide and Port Augusta (300km), some wind and some solar (during daylight). I assume most is still coal powered.
Mazbo
Solar Supporter
Solar Supporter
 
Posts: 6
Joined: Wed Nov 02, 2011 2:28 pm

Re: Combustion vs Reverse Cycle heating

Postby bpratt » Wed Nov 02, 2011 11:50 pm

I've always been under the impression that the most efficient form of heating is the reverse cycle inverter air conditioners.

The fact that unless you're cutting up the wood with an axe or log splitter manually, you're running a chainsaw that's generally a two stroker, therefore adding to greenhouse emissions.
Kaco 6600
26 x Trina Honey 250w panels. (wish I could work out how to upload to pvoutput.org)

New house build :-
http://bandlnewhomebuild.blogspot.com

My weather station :-
http://jimboombaweather.com
bpratt
Solar Crusader
Solar Crusader
 
Posts: 935
Joined: Wed Oct 14, 2009 11:09 am
Location: Jimboomba, Queensland - Energex and Origin

Re: Combustion vs Reverse Cycle heating

Postby Tracker » Thu Nov 03, 2011 12:19 pm

.
I can see two issues..

First ANY electricity is generally generated,using FOSSIL fuels to create the energy. and for all intents and purposes, that CO2 can never (realistically) go back to the original fuel
Second - Using a Combustion-Stove is burning timber that will eventually rot anyway and return the carbon to the air to be recycled into more trees, cannot be viewed as worsening any CO2 issues (not that there are any anyway)

I think that I would use a combustion stove for any heating, and then an RAC for other times...
..
.
Tracker
Solar Crusader
Solar Crusader
 
Posts: 5067
Joined: Wed Sep 23, 2009 5:54 am
Location: SYDNEY --- EA - Network, Retailer - EA

Re: Combustion vs Reverse Cycle heating

Postby Mazbo » Thu Nov 03, 2011 12:29 pm

Thanks bpratt, I hadn't factored in the chainsaw. I always thought reverse cycle with inverter was meant to be one of the more efficient methods of heating, but it doesn't make sense that if I burn a chunk of coal 300km away, convert the heat to steam, drive a turbine, produce and transmit the electricity through hundreds of km of transmision lines, use that electricity to drive compressors and fans in the aircon unit,and incur heat losses through air con ducting, that with all the energy losses through this system, will give me anywhere near the heat energy output if this same piece of coal was burnt directly in my combustion heater in the room where the heat is required.

In my case I'm burning a piece of renewable or recycled timber, but I'm concerned about the best use of the limited supply of energy as stored in carbon. Also if much more coal needs to be burnt to produce a given unit of heat energy in my lounge room than if I burn timber in my lounge room, I would have thought more greenhouse gasses will be produced at the powerstation, as compared to my fireplace, for the same amount of heat energy.

I'm interested in any views on this, or if anyone with appropriate skills has done some figures/calculations on these issues.
Mazbo
Solar Supporter
Solar Supporter
 
Posts: 6
Joined: Wed Nov 02, 2011 2:28 pm

Re: Combustion vs Reverse Cycle heating

Postby Mazbo » Thu Nov 03, 2011 12:35 pm

Thanks Tracker,
Also I hadn't factored in the carbon used and emmissions at the coal mines and transport to get the coal to the power station. Combustion heater is looking like best option.
Mazbo
Solar Supporter
Solar Supporter
 
Posts: 6
Joined: Wed Nov 02, 2011 2:28 pm

Re: Combustion vs Reverse Cycle heating

Postby Gordon-Loomberah » Thu Nov 03, 2011 12:46 pm

3ph AC implies it is quite a large unit, and from looking through the specs of various machines, the larger ones seem to be less efficient, although I dont know why. Emails I've sent to a couple of companies with this question, and how COP varies with ambient temperature for their machines, were not replied to.
To accurately calculate which is the most efficient in terms of CO2 emissions and net energy extracted from a certain amount of fuel, the specific characteristics of the wood would need to be known- there is a fair range involved with firewood. Also the COP of the AC under the relevant conditions would need to be known- it's going to be less efficient in colder weather.

I would think however, that adding some more insulation to the house if possible, putting more clothes on when it is cold, and chopping wood from your own place (and replanting to replace it) to burn would be the best overall by a fair margin.
http://gunagulla.com Loomberah weather and astronomy including live solar radiation intensity and UV + Gunagulla aquaponics, organic eggs and cherries
User avatar
Gordon-Loomberah
Community Moderator
 
Posts: 5396
Joined: Thu Sep 24, 2009 9:41 pm
Location: Loomberah NSW Australia

Re: Combustion vs Reverse Cycle heating

Postby Tracker » Thu Nov 03, 2011 3:08 pm

Gordon-Loomberah wrote:3ph AC implies it is quite a large unit....... the larger ones seem to be less efficient, although I dont know why.

I think that IF one was looking for efficiency, then you would buy multiple SMALL units for individual room cooling, rather than a large "Area" device. Then, just use what is needed for the family needs.
I am also not convinced that the "Inverter" technology is that effective.. I can't convince myself, but I just think that it is better to have a smaller unit running at peak/optimum capacity, than to have a larger one, ramping the power up and down to control the power consumption.
I would be convinced, if I could see practical figures for a large room with both an Inverter and a normal device..
ie KwH for Mj figures.. for 1 Vs the other for cooling for a day (same conditions)

Also the COP of the AC under the relevant conditions would need to be known- it's going to be less efficient in colder weather.

Remember that I have a Heat-Pump HWS, and with just the two of us, know that the daily cost in 50% more in WINTER.. This is because of the COP..
..
.
Tracker
Solar Crusader
Solar Crusader
 
Posts: 5067
Joined: Wed Sep 23, 2009 5:54 am
Location: SYDNEY --- EA - Network, Retailer - EA

Re: Combustion vs Reverse Cycle heating

Postby Mazbo » Thu Nov 03, 2011 4:19 pm

Thanks Gordon & Tracker,
It seems that the combustion heater will have least impact, even if I can't quantify it. Maybe I'll have a go when I have some research time. I've only had a gut feeling that this is so, but now that I am more aware of our daily usage with our Solar PV installation (Energy Matters - 4kW SMA Inverter & Suntech panels) I am starting to get a real feeling for where our usage is and can act accordingly.

Thanks for your comments.
Mazbo
Solar Supporter
Solar Supporter
 
Posts: 6
Joined: Wed Nov 02, 2011 2:28 pm

Re: Combustion vs Reverse Cycle heating

Postby Smurf1976 » Thu Nov 03, 2011 9:36 pm

If the wood that is burnt is wood that would otherwise be left to rot (or be burnt in the open to get rid of it) then the combustion stove isn't really using any additional fuel at all apart from the chainsaw and transporting the wood (which is still far less fossil fuel than using electricity).

On the other hand, if someone's clear felling an old growth forest to get the wood to burn then that adds an entirely new dimension to it...

One thing about efficiency, is that it really only matters if the resource itself is limited. For example, nobody cares about using sunlight or sea water efficiently because there's plenty of them. Likewise if you're using waste wood, then it really doesn't matter how efficient it is compared to electric heating since it's always going to be better to use an otherwise wasted wood resource than to take coal from the ground. That would be true no matter what the actual efficiency of the wood stove is.

For the record, a few "facts and figures".

Wood heater efficiency = 60% would be a typical figure.

Reverse cycle A/C = 80 - 100% after allowing for losses at the power station and in transmission.

Now, the reverse cycle A/C is more efficient. But it's more efficient at using coal (non-renewable) than the wood stove is at using wood. If that's waste wood then using it does stack up a lot better in terms of resource use than using coal / electricity.

For the record, electricity in SA is about 50% from the power stations in metropolitan Adelaide (Torrens Island, Osbourne and Pelican Point (Outer Harbour) account for the majority of production), about one third from the power stations at Port Augusta and about one sixth from wind. There is a small amount from solar and various other peaking / backup power stations at Snuggery, Port Lincoln, Lonsdale (Adelaide), Dry Creek (Adelaide), Mintaro etc. That's excluding transfer to/from Victoria although that hasn't amounted to overly much in recent times (some years ago fully one third of SA electricity was coming from Vic. And if you go back even further, 30 years or so, then Torrens Island power station was itself supplying two thirds of the entire state's power - that plant had a lot of very hard running for many years but it's rarely cranked up to full output these days as production from the newer stations has substantially displaced it (though it still runs flat out during a heatwave)).
Smurf1976
Solar Crusader
Solar Crusader
 
Posts: 1035
Joined: Mon Oct 26, 2009 11:56 am

Re: Combustion vs Reverse Cycle heating

Postby Mazbo » Thu Nov 03, 2011 9:48 pm

Smurf1976, thanks for excellent info re elec supply breakdown in Adelaide. We do burn waste wood or timber thats fallen around the house. I can now feel warm and cozy around my fire while feeling warm and fuzzy that I'm doing the right thing!
Mazbo
Solar Supporter
Solar Supporter
 
Posts: 6
Joined: Wed Nov 02, 2011 2:28 pm

Next

Return to Living Green

Who is online

Users browsing this forum: No registered users and 2 guests

new solar power specials