Gas vs Reverse Cycle Heating

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Re: Gas vs Reverse Cycle Heating

Postby Quokka2 » Sat Jan 04, 2014 11:30 am

We lived in Melbourne 30 years ago and installed RC split systems because there was a lot of talk at the time about gas prices being brought into parity with electricity prices :lol:

Although flued gas heaters can be very efficient, they still suck air out of your room (10x the volume of gas burnt), and that has to be replaced by cold air leaking in from the outside. Also bear in mind that you may need an air conditioner to keep your cool in Summer, so the cost of gas is in a way an incremental expense if one or the other is going to be unused for half the year.

Give me electric air-con any day!
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Re: Gas vs Reverse Cycle Heating

Postby Warpspeed » Sat Jan 04, 2014 12:07 pm

Quokka2 wrote:Although flued gas heaters can be very efficient, they still suck air out of your room (10x the volume of gas burnt), and that has to be replaced by cold air leaking in from the outside.


That is not how they work.
There is a coaxial flue, the hot exhaust going up the centre pipe out to atmosphere.
Combustion air is drawn in through the outer flue casing, pre warming the combusion air, all the combustion air is drawn from OUTSIDE. Almost all the heat is extracted from the flue gas and returned to the burner via the combustion air. Heat extraction is almost total, the final expelled flue gas is barely warm.
The constant combustion air volume is controlled by a small centrifgal air blower.

http://www.bfm-europe.com/pages/high-ef ... fires.html

This has two advantages, fist the air pressure at the flue outlet and combustion air inlet are identical as they are located very close together. In very gusty windy conditions with huge sudden changes in air pressure, the burner sees no sudden corresponding change in airflow.
Room air is totally isolated from combustion air by a pair of stainless steel heat exchangers.
You could completely hermetically seal a room, and the heater will run perfectly.

In a warmer climate I would definitely agree with you, airconditioning takes on a much greater significance.
In Melbourne we require pretty constant heating over several months, airconditioning on only a few really exceptionally hot days.
For us in Melbourne, heating costs vastly outweigh airconditioning costs, so economics dictate gas is cheaper to run, even though you need to double up with an airconditioner as well.
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Re: Gas vs Reverse Cycle Heating

Postby Quokka2 » Sat Jan 04, 2014 10:07 pm

Whoops - I'm obviously a bit out of date :oops: Gas heating has obviously come a long way since I last looked at it (haven't had any nat gas since we left Melbourne) Never too old to keep learning, though!
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Re: Gas vs Reverse Cycle Heating

Postby dmaunder » Sat Jan 04, 2014 10:30 pm

Warpspeed wrote:The tariffs here in Victoria appear to be very different to Tassie.

Electricity 370 kWh costs me $171.71, that includes service cost as well as the power itself.
Net cost 47.75 cents per kWh.

Natural gas 15,785 Mj costs me $262.39, that is both usage and suppy cost.
Works out to 1.662 cents per Mj.
Converting that to kWh, would be 4384.7 kWh at 5.98 cents per kWh.



My costs in Melbourne (United Energy / Momentum) for Electricity and AGL for gas are somewhat different to yours:

Gas is 2c per MJ, which is around 7c per kWH (1kWH is 3.6MJ). But ducted gas heating is only around 70% efficient so that means my gas heating is around 10c per kwH.

Peak electricity is 28c per kWH, but with a COP of 5, a heat pump is therefore 5.6c per kWh
Offpeak at 15c per kWH, but with a COP of 5, a heat pump is 3c per kwH (this includes all weekend)
If using solar PV, and therefore forfeiting the 8c FIT, effective cost is 1.6c per kwH.

We currently export quite a bit so every kWH that we use instead of export will increase the value of the PV. s

I am hoping to save a fair bit this winter using a heat pump for heating our main living area. In addition, my son now has a heat pump in the upstairs bedroom instead of an electric resistance heater, so that will definitely save quite a bit. Plus gas costs are likely to rise faster than electricity.

I am ignoring the service charges in the above, but they just help me with the move to all-electric. If we find we can totally stop using the gas heating, at some stage the gas HWS will die and be replaced with a heat-pump or solar unit (hard call but advice seems to lean to heat pump for Vic) and then it is an easy change to swap the hotplates from gas to induction, and then we can disconnect the gas and save the service charge altogether.
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Re: Gas vs Reverse Cycle Heating

Postby Smurf1976 » Sat Jan 04, 2014 10:50 pm

Warpspeed wrote:The tariffs here in Victoria appear to be very different to Tassie.

Electricity 370 kWh costs me $171.71, that includes service cost as well as the power itself.
Net cost 47.75 cents per kWh.

Natural gas 15,785 Mj costs me $262.39, that is both usage and suppy cost.
Works out to 1.662 cents per Mj.
Converting that to kWh, would be 4384.7 kWh at 5.98 cents per kWh.

Definitely a difference in costs between states and also in common usage.

To be fair you should really be looking at usage charges certainly for electricity, and likewise for gas unless you'd actually disconnect the gas if you didn't use it for heating. You're going to pay the fixed supply charges regardless of how much electricity you actually use, likewise gas if you also have it for cooking or hot water.
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Re: Gas vs Reverse Cycle Heating

Postby dmaunder » Sat Jan 04, 2014 10:53 pm

Smurf1976 wrote:[
To be fair you should really be looking at usage charges certainly for electricity, and likewise for gas unless you'd actually disconnect the gas if you didn't use it for heating. You're going to pay the fixed supply charges regardless of how much electricity you actually use, likewise gas if you also have it for cooking or hot water.


I disagree. At this point, I am going to pay both service charges anyway. So they don't have any affect on whether it is more cost effective to use gas or electricity to heat the house.
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Re: Gas vs Reverse Cycle Heating

Postby Warpspeed » Sun Jan 05, 2014 7:06 am

I dont see how you can ignore service charges when costing relative energy sources.

Gas appears to be flat rate, but electricity is a bit more complicated with different tariffs and a sliding scale depending on total usage.
I suppose if I consumed a lot more electricity, it could work out much cheaper per kWh, but at the end of the billing quarter it is only the final dollar figure that really matters.

There is also the rather contentious issue of "special deals" offered by the various utilities.
Two neighbours using the exact same energy utilities may be charged (ripped off ?) at rather different rates.
You can lock yourself into special energy deals over long periods with the potential of horrendous penalty charges if you break their contract. The whole energy provider system is rather suspect to put it mildly.

Most of my energy consumption goes towards heating.
That is, hot water, cooking, and space heating. I could do all of that with either gas or electicity, but gas seems to be a much cheaper source of raw heat energy, and has a far more reliable history of uninterrupted supply.

Another project in slow progress here is the total rebuild of an old 5 kVa Wisconsin standby power generator with a few unique Warpspeed modifications.
It now has electric start and a natural gas carburettor and special super quiet exhaust system.
Next time the power goes off (five outages here in 2013) I can go out to the garage and just push a button....
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Re: Gas vs Reverse Cycle Heating

Postby davidg » Sun Jan 05, 2014 8:42 am

Warpspeed wrote:I dont see how you can ignore service charges when costing relative energy sources.

Can't, service charges have become in most cases a decent part of the bill (domestic), nowadays. just having a service connected such as Electricity in Vic will run you at least $400.00 p.a without using any power at all.
Warpspeed wrote:Gas appears to be flat rate, but electricity is a bit more complicated with different tariffs and a sliding scale depending on total usage.

Not completely anymore, there is an increase in charges per MJ once you use more than a certain amount and the rate charge is being increased upwards that will drive cost of Gas to pretty much match that of Electricity. The expected increase in charges over the couple of years upto 50% increases, who knows from there, 2016 original state contracts for Gas supply apparently expire and then we'll see something ugly occur I suspect, all under the some excuse or another.
Warpspeed wrote:You can lock yourself into special energy deals over long periods with the potential of horrendous penalty charges if you break their contract. The whole energy provider system is rather suspect to put it mildly.

The penalty for breaking them in Vic is capped, checking this morning, I could only find maybe $40.00 worst case, I could be wrong. For any user of power in Vic that's almost irrelevant, less than 1/2 of a quarters service charges and there so called fixed contracts mean nothing anyway, as they all have clauses that say they can change the rate with appropriate notice, which like you say is a con if I ever saw one eg a contract that states "rate freeze" but we may vary any and all charges, we will give you notice so you know though, what sort of rate freeze is that, complete garbage.
Warpspeed wrote:It now has electric start and a natural gas carburettor and special super quiet exhaust system. Next time the power goes off (five outages here in 2013) I can go out to the garage and just push a button....

An Auto Gas (LPG) conversion, you can use off the shelf parts for that, traditional Auto Gas systems will function with town gas perfectly in fact they will work with home made "biogas" (a combination of methane + CO2) as well, the trick with biogas is making & storing enough of it to make it useable and producing it at a rate that makes it easy to compress for storage, not something, I suggest should be done in built-up a area.

Why not go a step further and make it full autostart and incorporate an ATS (Automatic Transfer Switch) linked in. You would be required to put in at a minimum a manual Transfer Switch anyway under AS3000 & several other STD's, to ensure you there is no chance of "back" feeding the grid.
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Re: Gas vs Reverse Cycle Heating

Postby Warpspeed » Sun Jan 05, 2014 10:51 am

An Auto Gas (LPG) conversion, you can use off the shelf parts for that, traditional Auto Gas systems will function with town gas perfectly.

Yes indeed...
I purchased a proper commercial low pressure natural gas demand regulator, and plumbed that into the carb venturi.
Used a good quality exhaust gas analyser to set it all up.

Much easier starting, and now an inexhaustibe fuel supply, and no need to store flammable liquid fuel that deteriorates over time.
But the best part is the natural gas should cost about 1/12 the running cost of of petrol last time I worked it out.
Running it should (in theory) be even cheaper than grid power, but noise, neighbours, and the high rate of mechanical wear and tear makes that option less than attractive.

If I was doing it all over again totally from scratch, I would prefer a small four cylinder water cooled car engine running at 1,500 rpm rather than a single cylinder air cooled engine running at 3000 rpm.
For the hopefully very infrequent use planned for it, it probably does not really matter.
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Re: Gas vs Reverse Cycle Heating

Postby Smurf1976 » Sun Jan 05, 2014 11:14 am

If you are trying to compare the cost of heating then you should only be looking at that cost.

If you already have electricity connected, and would keep it connected regardless of what form of heating you use, then the fixed charge is irrelevant so far as comparing heating methods is concerned. You're going to pay that fixed charge no matter how you heat the place.

Same with gas. If you're going to have gas connected for hot water, cooking or some other use then you'll be paying that gas fixed supply charge regardless of how you heat the place. It's only relevant if deciding to not use gas for heating means that you will actually disconnect the gas supply completely.

I'm assuming here that few if any people would actually disconnect their electricity supply if it wasn't being used for heating, since electricity has a large number of other uses. Someone might, but most wouldn't. 99%+ of people are going to pay the supply charge no matter how they heat the place thus making it an irrelevant factor in the choice of heating in all states except Tasmania.

With gas however, some people do only use it for heating and would thus disconnect the gas if they switched to non-gas heating. In that case the supply charge is a relevant factor certainly. But it's not of you'd keep the gas connection for other uses.

As with most energy things, there's an exception with Tasmania. An extra $67.22 a year in fixed charges if you want an electric heating meter. But this is offset by the energy charge on that meter being 16.167 cents / kWh versus the standard rate of 26.807 cents. There's a break even point at 631 kWh per annum - and very few people would manage to heat the place with that so for most people it's a definite cost saving. Note that this rate is for 24 hour supply, not off-peak.
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