Gas vs Reverse Cycle Heating

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Re: Gas vs Reverse Cycle Heating

Postby mrtechguy » Mon Oct 21, 2013 11:20 pm

Thanks for the clarification there.
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Re: Gas vs Reverse Cycle Heating

Postby PeterC » Tue Oct 22, 2013 10:15 am

Since you are building a house, the first thing, before concerning yourself about which way to heat, is to ensure that you don't need very much heating (or cooling) of any kind.
I live in Canberra which gets pretty cold in winter. Our house had reasonable solar orientation with large north-facing windows. Since retrofitting much better insulation to the walls and roof and under part of the floor, double-glazing and better draft exclusion, our annual heating cost is under $100 and we don't need summer cooling. Plan to be able to close doors so you don't need to heat all or nothing.
Only after dealing with good house design, I would say to use the electric heat pump option since Tassie has a high proportion of hydro rather than fossil fuel electricity. For whatever residue of electricity is not from hydro, you can pay a little extra for accredited Greenpower-if you designed your house properly, you won't need much.
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Re: Gas vs Reverse Cycle Heating

Postby Quokka2 » Sun Dec 08, 2013 12:05 pm

Smurf1976 wrote:As a general rule, the smallest systems have the highest COP's due to engineering factors.


Can only agree with nearly all of Smurf's longer contribution above this one, except I wouldn't bother with any kind of ducted system. Apart from the cost, your overall COP is generally lower, not only due to the "engineering factors" (I've never understood why that was so) but because you loose heat from ductwork usually installed in non-conditioned spaces. This gets worse as they age and the seals start to break down and the spiders get in.

Gas is just too inefficient to consider these days. Personally, I'd buy small split systems and just put on the ones you need depending on where you are in the house. I wouldn't buy expensive brands because there is likely to be better technology around by the time you have to replace the cheap ones anyway - I have an old Daikin (which I have had problems with) which has never worked as well as my two newer Fujitsus.
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Re: Gas vs Reverse Cycle Heating

Postby bpratt » Sun Dec 08, 2013 1:47 pm

Quokka2 wrote:[
Can only agree with nearly all of Smurf's longer contribution above this one, except I wouldn't bother with any kind of ducted system. Apart from the cost, your overall COP is generally lower, not only due to the "engineering factors" (I've never understood why that was so) but because you loose heat from ductwork usually installed in non-conditioned spaces. This gets worse as they age and the seals start to break down and the spiders get in.


Add on to that ducted systems draw the air from the one place, usually the hallway in around the middle of the house, so if you're running it of a night time whilst asleep or worse yet through the hot day for a shiftworker in bed sleeping, you would be drawing in hot air all the time, whilst pulling the cooler air from the floor of that bedroom in to the hallway to be recycled.

Yes, there are ducted systems with different zones that you can turn on or off, but they all still suck their air supply from the one place.


Split system inverter a/c's are a far superior way to cool the areas that you are using at the time.
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Re: Gas vs Reverse Cycle Heating

Postby davidg » Sun Dec 08, 2013 5:37 pm

bpratt wrote:Yes, there are ducted systems with different zones that you can turn on or off, but they all still suck their air supply from the one place.


They may suck by default from one place, however it's not always true ours draws from two places in the building and distributes accordingly, we have 2 distinct main areas in our house. It was 15+ years it was installed, if you turn off the back of the building then the intake also turns off there as well, so it can be done, it's just not done very often.

As for reverse cycle AC it might be one of the better options now a days.

If you have enough thermal mass and enough insulation you should not need the AC in the first place. 8-)

I went to a lot of design effort to ensure our new house, still to be built had both in it, along with a way of cooling in this case the slab (Thermal mass) so we should not need AC at all just ceiling fans to move the air across the floor so it can absorb heat, which is then taken away by the hydronic in slab water piping system, of course all driven by 100% solar. The slab is thermally broken from the rest of the surrounding ground, so we don't loose or absorb heat into or out of the sides of the slab.

If you are building a house how to heat and cool is a thing well worth spending time on, it will save a fortune in charges of one from or another over the following of the decades. Being solar only cooling and heating the amount of power required will be minimal apart from which the whole house is off-grid anyway.
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Re: Gas vs Reverse Cycle Heating

Postby Tracker » Sun Dec 08, 2013 5:57 pm

mrtechguy wrote:....... one of the blocks of land that I am looking at has the stipulation that I must use gas for my hot water and heating. ....

I know this is old, but I am intrigued at the STIPULATION .....
What gives them the right to demand...

The real issue to me is the service charges.. and especially down there, I would think that if you can tolerate heat pump heat (dry)... then I would have nothing to do with gas.

Given that they are selling it at a kWH rate and that a heat pump should be three times more efficient COP.. then where is the attraction to add another service charge..

I have disconnected from town gas and gone to LPG, and so far am ahead.. and given the dire warnings about how gas in total will rise in cost, then as it rises, they could likely reduce their margin on sale price and make all their money on service charges..

LPG has just jumped to over 90c a Ltr. Whilst that is likely seasonal, I suspect that it does reflect what will happen to all gas products..

The further we get into selling off our CSG potential, the more that producers will demand that gas be exported, and not sold locally... ie.. if they are to sell locally, it will be massively priced...

Anyway - I'm off my soap box..

IMHO... Were I living in Tasy, then I would think that it's better in the long term to use electricity, as gas will be always imported/exported..
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Re: Gas vs Reverse Cycle Heating

Postby Quokka2 » Sun Dec 08, 2013 6:05 pm

davidg wrote:If you are building a house how to heat and cool is a thing well worth spending time on, it will save a fortune in charges of one from or another over the following of the decades

How true. Unfortunately most people building homes these days are short of cash because of the crazy land prices. They end up with a nice-looking home from a project builder and later find that retro-fitting all the bits cut out of the spec is a nightmare, or impossible. We just need to drip on the stone until we get more sensible houses (put the eaves back, for a start).
We asked our project builder in Melbourne to insulate the walls of our brick veneer home in the early 80's; he couldn't see any sense in that and preferred to install a bigger gas heater. We insulated the walls ourselves before the Gyprock went in, and deleted the gas heater in favour of two split systems. I got transferred to Brisbane before the house was finished and the builder moved in under lease. All the houses he has built since have had wall insulation as standard; I believe he was the first in Melbourne to do that. ;)
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Re: Gas vs Reverse Cycle Heating

Postby mrtechguy » Mon Dec 09, 2013 12:39 am

Thanks for all the replies. The stipulation was built into the covenant on the land, so was unfortunately legally binding, since then I have found another block that was $20k cheaper without such stipulations. The house I am building has good insulation floor, walls and ceiling and also double glazed windows, all of which will help. I have decided to go with a reverse cycle, considering I have only just signed the contract for the building I haven't had the time to decide on more specifics than that, but the display home for the builder had a single system in it and was very warm (the display home was standard with a few extras which they pointed out at the time).

I thought the thread was long dead and was pleasantly surprised to find it was still quite active.

We have a Daikin at home and it seems to do the job quite well, that said I haven't really seen much to compare it to. At the end of the day I am going to say that it probably comes down to personal preference and what works for the budget and space.

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Re: Gas vs Reverse Cycle Heating

Postby Smurf1976 » Fri Dec 13, 2013 8:25 pm

In 1992 the price of LPG here in Tasmania was 7.3 cents / kWh and electricity was about 10 cents.

21 years later the price of LPG is 19.7 cents and electricity for heating is a bit over 17 cents and over 28 cents on the general tariff. 6 years ago when I bought a new oven, I went electric oven and LPG cooktop with the general electricity tariff being cheaper than LPG at the time. Not now....

And of course we all know the ups and downs of solar feed-in tariffs over a relatively short timeframe in most states.

There's a valid reason why businesses generally demand a very high rate of return on investments into fuel switching. If projected savings don't cover the cost of conversion within 2 years then it's usually not considered a priority, and if not within 5 years then most won't even consider it. The reason is simple - predicting the relative prices of competing energy sources is fraught with risk. Plenty have tried and failed at this game over the years, hence most aren't willing to take a gamble unless the payback is exceptionally high for this reason.

I take a similar approach myself these days. Energy efficiency is generally a "safe" investment since, apart from Tasmania during the mid-1990's, there aren't too many precedents for sharp falls in energy prices to consumers. But choosing one fuel versus another is pretty much a gamble since relative prices can and do change.

In terms of the general consensus, natural gas prices are likely to go up that seems fairly certain. But as for electricity and LPG - that's anyone's guess to be honest.

The only fuel that tends to be reasonably price consistent is firewood if it's locally sourced. It basically just goes up in line with general inflation / wages.

But then there's things like wood pellets - they were $400 a tonne in the mid-2000's but the last lot I bought cost $1050 per tonne which is a huge increase. Anyone who switched from electric or gas to wood pellets in the hope of saving money won't likely be too happy with the outcome. Just like the many before them who have switched from one fuel to another and ended up with a financial loss.

Don't assume that current fuel price relativities will last more than 2 years into the future. Beyond that, it's a gamble and the best defence is energy efficiency regardless of what fuel is being used.
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Re: Gas vs Reverse Cycle Heating

Postby Warpspeed » Sat Jan 04, 2014 7:39 am

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.

A heat pump in Melbourne would probably have to have a COP of at least 7.98 to be of benefit.

That may not all be strictly true, because the actual energy costs are distorted by the added on service charges.
But the bottom line is that gas heating is vastly cheaper than electrical heating in Melbourne, even with an off peak tariff.
Replacing my very old poorly insulated off peak electric hot water heater with a natural gas hot water, almost halved my electrical power consumption.

In my case energy efficient gas space heaters in each room allow me to just heat the occupied areas.
This is likely the optimum for an individual or a retired couple.
A fairly large family might benefit from whole house ducted heating, but mainly more for convenience than any cost saving.
For us, the optimunm solution is individual Rinnai energy saver forced flue gas space heaters.
These have a very efficient heat exchanger that pulls over 80% of the heat out of the flue gas, almost all the heat goes into the room. These have a 4.5 energy star rating, which is not bad.

I now have six of these heaters installed around the house. Only two would heat the entire house if given sufficient time to do so, but two heaters would be running flat out all day in mid winter.

As it is now, each room is now massively overpowered, so heats up very rapidly, and we only heat the rooms we are actually using. I suspect it is vastly cheaper to run than fully ducted whole house heating.
Plenty to think about when planning home heating.

Heating individual rooms with very powerful individual heaters hardly seems to have changed my total gas consumption, which has been a very welcome surprise, as the comfort level has actually increased, especially very early first thing on a frosty morning.

These Rinnai heaters are pretty expensive to buy new, about roughly $2.4K each, but older now obsolete models that work just as well can be bought typically for $50 to $100 on e-bay.
The older ones don't have a remote control, digital displays, or multiple programmable timers, but the burner and heat exchanger design has never changed over the last twenty years, and they heat the house just as efficiently as a mega dollar brand new one.

I also agree that insulation installed at the time of building will be of huge benefit. One curious aspect is the reflective aluminium building foil that is invariably used.
The highly reflective side reflects infrared extremely well, the blue side does not. Should the reflective side face inward or outward ??
That depends on what is more important, reflecting the long wavelength infrared radient heat in or out. And that might depend on the climate, or even which way a particular wall is facing.....

Very few builders are clued up on these small but very important details, and it can make a surprising difference.
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