Ask RiotACT: Do reverse cycle heating units work ok in Canberra?

mtrax 24 October 2016 32
Ask RiotACT

I’m looking to switch to all electric ie disconnect my gas, so looking for pros and cons of reverse cycle heating systems.

I hear some systems go into a de-icing cycle often when temperature goes below zero, but not sure if that’s indicative of all systems?

Also the efficiency drops with the temperature but does this mean they are still efficient averaged over the winter?


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32 Responses to Ask RiotACT: Do reverse cycle heating units work ok in Canberra?
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wildturkeycanoe wildturkeycanoe 6:43 am 27 Oct 16

We put reverse cycle AC in after our first winter gas bill and had paid off the purchase with our first year’s energy savings. They work fine, are cheap to run and cool as well as heat. Sure it defrosts occasionally but you won’t suffer a bout of icy air while it does so. At least with r/c a/c you can offset costs with solar power, gas just drains your bank account.

dungfungus dungfungus 8:45 am 27 Oct 16

I agree with wildturkeycanoe comments.

Within 10 years, domestic-solar battery arrays will allow you to be permanently “off-grid” so it makes sense to have everything electric and that includes heat-pump hot water which will work well in Canberra with the de-icing chip.

Ensure you have reverse cycle (cooling) with the heat-pump heating unit.

Anyhow, with the CSIRO and the BOM both hitting the headlines today about impending doom because Australia’s temperature has risen 1 degree in the past 100 years the matter of heating the home becomes academic.

darkmilk darkmilk 9:42 am 27 Oct 16

Yes they work OK here but all of them have to do de-icing cycles to work when it’s near 0. When it gets to -6 the ones I’ve used struggle but do still heat a bit between long de-ice cycles.

Some brands/models come in tropical versions and non-tropical which affects whether they’re rated to work below 0, make sure you’re getting one that is able to do de-icing.

Deref Deref 11:21 am 27 Oct 16

Our ducted Fujutsu unit has been brilliant. Warms the place nicely in winter and cools it delightfully in summer. One of the best investments I’ve ever made. 🙂

Lurker2913 Lurker2913 7:55 pm 27 Oct 16

darkmilk said :

When it gets to -6 the ones I’ve used struggle but do still heat a bit between long de-ice cycles.

When does it get to negative six degrees in Canberra? If it got that cold and the air conditioning stopped, I think I would set something on fire.

Sanitair Canberra North Sanitair Canberra North 9:33 pm 27 Oct 16

I spoke with a client recently who has gas heating and split systems for cooling. He advised he now runs the split systems all year due to the saving he gained from not using the gas system for heating.

I hope this helps

dungfungus dungfungus 8:10 am 28 Oct 16

Lurker2913 said :

darkmilk said :

When it gets to -6 the ones I’ve used struggle but do still heat a bit between long de-ice cycles.

When does it get to negative six degrees in Canberra? If it got that cold and the air conditioning stopped, I think I would set something on fire.

I think that should be +6 actually. That’s when my system ices up and then defrosts. It’s not a problem.

Nilrem Nilrem 12:25 pm 28 Oct 16

Sanitair Canberra North said :

I spoke with a client recently who has gas heating and split systems for cooling. He advised he now runs the split systems all year due to the saving he gained from not using the gas system for heating.

I hope this helps

Does anyone know if a split cycle electric system can use existing gas ducts?

mtrax mtrax 1:08 pm 28 Oct 16

Nilrem said :

Sanitair Canberra North said :

I spoke with a client recently who has gas heating and split systems for cooling. He advised he now runs the split systems all year due to the saving he gained from not using the gas system for heating.

I hope this helps

Does anyone know if a split cycle electric system can use existing gas ducts?

I believe it can, but may need to be cut slightly bigger in places, however the ducting might need to be replaced to handle heating/cooling

mtrax mtrax 1:17 pm 28 Oct 16

thanks for the feedback, we have cut our GAS line so will take the plunge, just need to look at what brands and models would be best suited to the Canberra climate.

As the the question about -6 didn’t we get a -7 in Jun last year, so I definitely don’t want my heating to struggle when temps drop below zero.

montana montana 1:43 pm 28 Oct 16

im surprised that the comments are saying reverse AC will work fine in Canberra during Winter. Ive found that it struggles for that 1 month in Winter or so when temps reach anywhere below 3 degrees in the mornings. Some mornings when it is -3 outside, it’s not even worth switching it on because all you will get is coldish air coming out before it freezes up. By the time you go to work, the house has barely warmed up by 1 degree. In the evenings you need to set the timer to switch on about 90 minutes before you get home otherwise your house wont be warm enough. Whilst reverse cycle works in the winter evenings, it works very slowly. Also there’s no way you can get your house above 23 degrees during Winter. It’s real a strange concept that a heater doesnt work well when it gets too cold but that is the reality of reverse cycle.

mtrax mtrax 2:57 pm 28 Oct 16

just curious if you start RC earlier in morning will it work? and are some RC units better than others as there seems to be some mixed opinion.

Masquara Masquara 4:03 pm 28 Oct 16

Are you sure it is wise to disconnect from the gas? During the SA blackout , people with gas could still cook and shower… The gas supply is far less vulnerable to disasters.

montana montana 4:14 pm 28 Oct 16

Even if you start it earlier in the morning, it wont make any difference. Lets say its minus 3 outside, the AC will run, but the air going into the house wont be sufficiently warm enough to heat your house. Then after 15 minutes the AC will freeze up and enter the defrosting mode. It will take at least another 15 minutes for the AC to de-ice and start running again, which by then the house has lost any heat it built up and also the air coming out will be cold again anyways. The only way to wake up to a warm house is to leave the AC running all night and it might manage to keep the temps up (though ive never tried this) On cold winter mornings the best you can do is just wait for the sun to come out and the fog to clear before even bothering to turning the reverse AC on. Even the manual says when it’s really cold, the reverse AC will be inefficent and it suggests using a different heater instead, (such as electric fan, element or oil column heater)

if we lived in sydney the reverse AC would work just fine as it doesn’t get that cold at night.

im not sure if theres much difference between brands, as they all work on the same heat pump principle

arescarti42 arescarti42 8:17 pm 28 Oct 16

A modern, good quality, correctly sized and installed reverse cycle AC/heater will have no problem in any temperature you’ll experience in Canberra. Daikin, Panasonic and Mitsubishi are good brands, others can be a bit hit and miss.

Most units will need to de-ice from time to time when it gets really cold, but if the unit is correctly sized it won’t be a problem.

Efficiency will drop with temperature, but will still be cost effective compared to gas, particularly if you’re not paying for a gas connection.

dungfungus dungfungus 8:59 pm 28 Oct 16

Masquara said :

Are you sure it is wise to disconnect from the gas? During the SA blackout , people with gas could still cook and shower… The gas supply is far less vulnerable to disasters.

Good point, and as the ACT will soon be relying on 100% renewables for electricity supply it would also be a good idea to stock up on candles.

mtrax mtrax 8:10 am 29 Oct 16

Masquara said :

Are you sure it is wise to disconnect from the gas? During the SA blackout , people with gas could still cook and shower… The gas supply is far less vulnerable to disasters.

We only have gas heating, nothing else

JimCharles JimCharles 1:22 pm 29 Oct 16

montana said :

Even if you start it earlier in the morning, it wont make any difference. Lets say its minus 3 outside, the AC will run, but the air going into the house wont be sufficiently warm enough to heat your house. Then after 15 minutes the AC will freeze up and enter the defrosting mode. It will take at least another 15 minutes for the AC to de-ice and start running again, which by then the house has lost any heat it built up and also the air coming out will be cold again anyways. The only way to wake up to a warm house is to leave the AC running all night and it might manage to keep the temps up (though ive never tried this) On cold winter mornings the best you can do is just wait for the sun to come out and the fog to clear before even bothering to turning the reverse AC on. Even the manual says when it’s really cold, the reverse AC will be inefficent and it suggests using a different heater instead, (such as electric fan, element or oil column heater)

if we lived in sydney the reverse AC would work just fine as it doesn’t get that cold at night.

im not sure if theres much difference between brands, as they all work on the same heat pump principle

I disagree with this. Our house gets down to about 8 degrees inside when it’s well below freezing outside in mid-winter.
We have two split systems at either end of the house, we set the timer to come on at 6am and the thermostat to 18 which it reaches in about 10 minutes without fail; certainly warm enough to have breakfast, get ready for work and get out.
Surely it depends on the efficiency of the unit, how old it is, and how long your house can hold the heat for?
We were very sceptical about using these hot air blowers for heating after coming from a country with gas-powered hydronic central heating radiators in every house, but’s been a lot better than we expected in winter.

Leon Arundell Leon Arundell 4:23 pm 29 Oct 16

I did a Masters project on reverse cycle units, and I’ve been using them in my Canberra house for 30 years.
You can save money by insulating as much of your house as is reasonably possible (ceiling, walls, underfloor) before you buy the reverse cycle unit. That way you will get good performance from a smaller, cheaper unit.
They typically use less than half the electricity of a conventional electric resistance heater.
They become progressively less efficient as the temperature drops. You can compensate by closing off parts of the house that don’t need heating, putting on warmer clothes, or using a gas heater or a conventional electric heater.
They start to de-ice below about +5 degrees C when the air is humid. When the air gets really really cold it becomes less humid and the unit doesn’t need to de-ice as often.
Yes, it does get to -6 degrees C once or twice in a typical Canberra winter. That’s usually some time between midnight and 5am when an electric blanket will warm you more efficiently than a reverse cycle unit (because the electric blanket is just heating you, and is not trying to heat the whole room).
For best comfort on winter mornings, set the unit to start heating an hour or two before you get up.

JC JC 6:24 pm 29 Oct 16

dungfungus said :

Lurker2913 said :

darkmilk said :

When it gets to -6 the ones I’ve used struggle but do still heat a bit between long de-ice cycles.

When does it get to negative six degrees in Canberra? If it got that cold and the air conditioning stopped, I think I would set something on fire.

I think that should be +6 actually. That’s when my system ices up and then defrosts. It’s not a problem.

You are most correct. The reason being the coil on the outdoor unit will be colder then the ambient temperature. The magic figure is around the 5 degree mark which is when outdoor units can start regularly so they can deice.

Once you get below about -5 thats when their deice times can become so long they start to become useless.

Just means they can take longer to heat up inside than say a gas unit or oil heater, electric blower heaters etc. Still very efficient though.

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