Gas vs Reverse Cycle Heating

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Gas vs Reverse Cycle Heating

Postby mrtechguy » Tue Oct 15, 2013 12:36 am

Hi All,
I am looking at building a house and 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 am happy to use gas for my hot water but am not entirely sure on using it for heating.

I am in Tasmania so we have rather cold winters. The property has gas "on tap" through TasGas and here are the numbers
Gas: 10.78c /khw
21.31c /day (standing charge)
Electric: 17.075c/ kwh
19.431c /day (standing charge)

I also read that I can get gas through Aurora (for slightly cheaper), but I might leave that for now considering that Aurora is being sold off etc.

I also understand the gas heating can be less efficient in comparison to heat pumps.

Considering that I am building I am considering the options of ducted (for both systems) as opposed to non-ducted.

Is there anyone who would be able to provide me with a bit of information from a non-trying-to-sell-me-a-product perspective.

I am also guessing that if I go with gas heating I will not need the HydroHeat connection and therefore won't have to pay the standing charge for it, is this correct?

Any additional information one could provide would be much appreciated.

Thanks in advance,
mtg
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Re: Gas vs Reverse Cycle Heating

Postby davidg » Tue Oct 15, 2013 1:15 am

Isn't gas done in "mj" mega joules of energy? It sure is in Vic.

What is it your trying to achieve?
Are you just trying to figure out which would be "cheaper" to run?
Or maybe something else?
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Re: Gas vs Reverse Cycle Heating

Postby mrtechguy » Tue Oct 15, 2013 1:34 am

In Tasmania is it billed on the KWhr basis.

I wish to heat the whole house (but that said currently we have two heat pumps in the current house which seems to do the job reasonably well).

I am trying to figure out which is the cheapest to run, and whether I will even need to had a "HydroHeat" tariff connected if I go with gas heating (and therefore just not have that tariff connected saving 17c a day).

The numbers can be found here http://www.auroraenergy.com.au/your-hom ... ison-table

I suppose at the end of the day it comes to what gets me more heat per unit of energy.
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Re: Gas vs Reverse Cycle Heating

Postby Tracker » Tue Oct 15, 2013 8:38 am

davidg wrote:Isn't gas done in "mj" mega joules of energy? It sure is in Vic.?


GORDON, went through that for me some time back, converting MJ to kWh.. ie equivalent energy.

Given the advice to me that energy would eventually (sooner than later) be priced at energy value, it's good to be able to compare real COST... MJ - what does that mean to anyone..?

I too, was procrastinating over disconnecting town gas, knowing their intention to sell ENERGY, and paying multiple service charges was not logical.

TODAY, the figures come up well for the GAS, but what will happen tomorrow, as the world demand for transportable energy ramps up... you can't economically bottle Hydro-Power and ship it to China.

So, how much of a gambler are you..? .. ;)
..
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Re: Gas vs Reverse Cycle Heating

Postby Smurf1976 » Sun Oct 20, 2013 8:47 pm

Happy to help (I'm in Tas).

For space heating I'm assuming that you would be installing a non-ducted system as the "default" option (given that ducted heating is pretty uncommon in Tas).

If you use heat pumps for heating then in practice with modern units of a good quality brand (Daikin or Mitsubishi are the ones to consider in my opinion) you should achieve a COP of close to 4 assuming we're talking about somewhere around Hobart (COP will be lower for Launceston due to the colder winters there).

So your heat pump will put heat into the house at around 4.3 cents / kWh in practice. Even if you bought a cheap and nasty one, it will still have a COP around 3 and produce heat around 5.7 cents / kWh.

Gas? Assuming the gas heater to be 80% efficient which is typical, it will produce heat at about 13.5 cents / kWh which is 3 times the cost of running a good quality heat pump.

But there's more to it than just the energy cost for heating the main living area.

Typically, homes in Tas have a main heater (of whatever type) in the lounge room and that's it apart from some power-guzzling (28.283 cents / kWh !) fan heaters in the bedrooms and heat lamps in the bathroom. That's the basic arrangement in probably 90% of houses in the state. In Victoria it is common to have central heating but that certainly isn't common in Tas.

But if you go for gas then quite likely you could afford to install ducted heating and thus heat the entire house with the one system. You'll be paying more for heating the main living area that is true, but not having fan heaters etc will partly offset that. And apart from the cost, it's simply nicer to heat the place properly.

You could get a ducted heat pump system of course. But the odds are that you won't since that's the usual situation on account of the cost. It's a great option - if you can afford to install it in the first place.

Alternatively you might choose to install a radiant type gas heater with a nice warm glow in the living room or even one of those gas "log fires". Either of those on a cold Winter night sure beats a plastic box on the wall (a heat pump) blowing out warm air in terms of ambiance etc.

But then there's Summer. I don't know if last Summer was a freak one-off event or if it's likely to be repeated due to climate change. But if it happens again then I think it's fair to say that the ability of a heat pump to also cool the place on a hot day is a definite advantage compared to heating with gas (or wood). At least it is for those who don't like or aren't used to the heat.

So all that can really be said with certainty is that producing a unit of heat from an electric heat pump is considerably cheaper than doing it with gas. But gas does have advantages in terms of actually heating the place, will be cheaper up front if you want a ducted system and has the option of log fires etc too which electric can't really do.

As for the hot water, well hot water is hot water regardless of how its' heated. And gas will be cheaper than a standard electric system would be. Gas will cost more to run than solar however.

Cooking - it may not be "required" but if you've got gas available to the house then you'd be crazy to not connect the cooktop to gas. Much better than electric in terms of performance etc.

Supply charges - you are correct in assuming that you will not have to pay the HydroHeat supply charge if you don't have a HydroHeat meter installed.

Personally, I'd be happy to go along with it. Put in gas ducted heating, gas hot water, gas cooktop (use electric for the oven - it's better). Then, if you feel the need after living there a while, you could always add a split system air-conditioner installed in the main living area and have Aurora enable the HydroHeat output on the meter (modern meters can record two tariffs on the one physical unit so it's just some minor wiring work etc) to run it from.

But then a lack of gas wouldn't bother me either. Heat pump for space heating, solar hot water with electric boost (installing an ordinary electric HWS in 2013 is bordering on crazy in my opinion - outdated and just too expensive to run), LPG for the cooktop, everything else electric.
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Re: Gas vs Reverse Cycle Heating

Postby jimbo » Mon Oct 21, 2013 11:22 am

What is the COP when it is under 5 degrees outside?
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Re: Gas vs Reverse Cycle Heating

Postby mrtechguy » Mon Oct 21, 2013 7:24 pm

Yeah, I am in Launceston. I have chosen another block of land because of some of the conditions on that block of land. Now I have to make the choice between ducted and a single heat pump unit (which of course depends on what the budget says)

I did think about the cooling and that is another reason I was thinking to avoid the gas is to have one unit that can do all.


Thanks for the in depth discussion.
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Re: Gas vs Reverse Cycle Heating

Postby Smurf1976 » Mon Oct 21, 2013 10:49 pm

jimbo wrote:What is the COP when it is under 5 degrees outside?


Assuming we're talking about good quality brands, and by that I mean Daikin, Mitsubishi Heavy Industries or equivalent quality, then at 5 degrees it will still be up around 4.

If it gets down to zero degrees then you'll see a COP somewhere around 3, perhaps even in the high 2's at the worst. But for typical usage, the overall COP should be pretty close to the nominal rating of 4+

The market for reverse cycle A/C is substantially different in Tas to that in the rest of the country. Specifically because in 99% of cases they are installed as an energy saving device (to the point that many wonder why there is no government rebate to install A/C*) rather than simply because someone wants A/C as such. That being so, it's economics 101 - no point buying a cheap and nasty system that breaks before the energy cost savings have repaid the cost.

Heating performance is the other big one. Any system will work at 7 degrees but it's a different story when there's ice on the ground outside. Daikin and Mitsubishi work well but with anything else it's a gamble unless you research the specific model very carefully.

As with practically all things energy related, the situation with air-conditioning in Tas is the reverse of that in the rest of Australia.
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Re: Gas vs Reverse Cycle Heating

Postby mrtechguy » Mon Oct 21, 2013 10:59 pm

Also please excuse my ignorance but what is CoP?
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Re: Gas vs Reverse Cycle Heating

Postby Smurf1976 » Mon Oct 21, 2013 11:16 pm

Co-efficient Of Performance.

It's the ratio of output heat to input energy. Eg you use 1kW of electricity and produce (say) 3.9 kW of heat output. So that's a COP of 3.9 in that example.

As a general rule, the smallest systems have the highest COP's due to engineering factors. But as a general rule, assume that it will be 3 or higher when comparing heat pumps with gas, wood etc.
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