24 October 2016

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

| mtrax
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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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chrisi said :

I got rid of gas 3 years ago and I’ve saved hundreds of dollars.
No more gas bills during the warmer months were the service/access charges were more than the actual use!

I have a Daikin ducted reverse cycle and love it! There are comments in this thread saying they never get to -6… which is puzzling because I distinctly remember a few -6 nights this past winter. The Daikin didn’t miss a beat. We have young children and have the heater on pretty much 24/7 during winter to ensure a comfortable inside temp during the night for them.

Induction cooking is also far superior btw. I haven’t missed gas at all.

Running 24/7 is why you won’t have much issue with freezing. If you were to turn it off or down really low overnight then in the morning when you turn it on it would have to work extra hard to warm up, which in turn would lead to freezing of the coil and the subsequent freeze/defrost cycles.

By keeping it constant when it is running it won’t be running as hard, meaning the coil won’t get as cold and it won’t freeze as easily. And if (when) it did you wouldn’t notice it as much anyway.

I got rid of gas 3 years ago and I’ve saved hundreds of dollars.
No more gas bills during the warmer months were the service/access charges were more than the actual use!

I have a Daikin ducted reverse cycle and love it! There are comments in this thread saying they never get to -6… which is puzzling because I distinctly remember a few -6 nights this past winter. The Daikin didn’t miss a beat. We have young children and have the heater on pretty much 24/7 during winter to ensure a comfortable inside temp during the night for them.

Induction cooking is also far superior btw. I haven’t missed gas at all.

Good point. It totally depends on the unit you are getting and how you get it done. I have early morning shifts and have to take my kids with me. They are 3 and 2 so you can imagine what a nightmare that would be if the temperature was freezing. I get up at 4 usually and turn it on before a shower, and once im back in like 15 minutes, it is well heated. I have no complaints. You should probably speak to whoever you are getting it done by, else you can go to Nick from Southern aircon. That is where I got it done. They did a great job-
Here is his number- 0401 317 694 and his website – https://southernaircon.com.au Highly recommend their work.

JimCharles said :

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.

ns said :

I had Daikin reverse cycles put in about 7 years back and my only regret is that I didn’t invest in them earlier. I found them to be both cost-effective, efficient and a huge improvement over the ancient electric systems in my house which barely heated the place up. The ability to control the temperature for different rooms was also a plus.

I don’t know if I’m missing something, but I’ve never heard of a de-icing issue. Have I just been lucky? I’ve always been diligent with cleaning filters and regular servicing and have never had an issue either during below freezing temperatures or on insanely hot Canberra days.

Even though I had 4 units put in (3 smaller units for each of the bedrooms and a larger unit for the living space), I only had one outdoor unit. It can be done if you get a clever and creative installer. I had every Daikin rep come out to give me a quote and only one came up with the goods (and at a cheaper quote to everyone else) – Bell-Air. I’d recommend them unreservedly (if only for their can-do attitude and creativity).

I was originally set on ducted, but had a mate who installs ducted systems for a living nix the idea because I have a two-storey townhouse. He said I’d always struggle with getting the right temperature balance across the two levels. His advice was that ducted worked better on single level homes.

I also had Daikins installed about 7 years ago ( or was it 10 ? ) anyway have a larger machine for the family room, and a smaller one for the bedroom. Both work very well in the winter and summer. Have had no problems with this ‘freezing up’ business that some have mentioned.

I picked Daikin ’cause on my walks up to the shops ( and back by a different track) most of the houses with an a/c unit outside were Daikin. So I thought good for the goose ..

ns said :

I don’t know if I’m missing something, but I’ve never heard of a de-icing issue. Have I just been lucky? I’ve always been diligent with cleaning filters and regular servicing and have never had an issue either during below freezing temperatures or on insanely hot Canberra days.

It is nothing to do with cleaning or servicing. Essentially the way reverse cycle works is it extracts what ever heat is in the air and transfers that inside. The side effect is the outdoor unit coil gets really cold and starts to freeze up. They get to a point where the coil gets so frozen that the unit needs to stop so it can defrost. Depending upon the unit when it is defrosting the indoor unit may be running, so you will get cold air coming in, or it may not run, in which case the coil in the indoor unit will get cold, but maybe not feel it. But it won’t be heating either.

The tell tale sign of defrosting is a pool of water near the outdoor unit. Whilst good practice not many outdoor units have their drains connected to plumbing.

The magic figure in Canberra is around the 5 degree mark. If the temps are at 5, the coil will most likely be below 0 and subject to freezing. As someone mentioned above if is humid it will freeze over quicker. When this happens it takes longer to heat the house as it goes through constant heat, stop, heat stop cycles.

So I would be very surprised if your unit doesn’t do it. Maybe you just don’t notice. I don’t notice my ducted system inside, but do see the tell tale sign of water on the concrete pad and the ground around the pad from the thawing.

I had Daikin reverse cycles put in about 7 years back and my only regret is that I didn’t invest in them earlier. I found them to be both cost-effective, efficient and a huge improvement over the ancient electric systems in my house which barely heated the place up. The ability to control the temperature for different rooms was also a plus.

I don’t know if I’m missing something, but I’ve never heard of a de-icing issue. Have I just been lucky? I’ve always been diligent with cleaning filters and regular servicing and have never had an issue either during below freezing temperatures or on insanely hot Canberra days.

Even though I had 4 units put in (3 smaller units for each of the bedrooms and a larger unit for the living space), I only had one outdoor unit. It can be done if you get a clever and creative installer. I had every Daikin rep come out to give me a quote and only one came up with the goods (and at a cheaper quote to everyone else) – Bell-Air. I’d recommend them unreservedly (if only for their can-do attitude and creativity).

I was originally set on ducted, but had a mate who installs ducted systems for a living nix the idea because I have a two-storey townhouse. He said I’d always struggle with getting the right temperature balance across the two levels. His advice was that ducted worked better on single level homes.

Comment here. I accept this discussion is about existing houses, but if anyone is planning to build a new house, build it correctly and you won’t need to bother with any of this. You won’t need any air-conditioning and the rare times a heater is wanted, a small fan heater in the evening will be enough. On low temperature setting too, once it has warmed the air.

Anyone taken it a step further and using a heat exchanger boiler for hydronic/in-slab heating (units such as Daikin Altherna, Sanden etc…) If so, do they cope with the -6deg mornings?

mtrax said :

I was thinking of getting a ducted reverse cycle system, or is better to get 3 smaller systems?

It depends.

Ducted is the nicer solution. It’s more aesthetically pleasing with only ducts inside and only one outdoor unit, more even air distribution, and the convenience of one controller. However it’s also usually more expensive to install than equivalent split systems, and will be more costly to run due to lower efficiency units and ducting losses.

Splits are uglier, but cheaper and more efficient, especially if you only use them to heat/cool just the part of the house you’re in. They also give you built in redundancy, whereby if one breaks down, you still won’t be totally without heating.

So it’s kind of a personal choice.

I was thinking of getting a ducted reverse cycle system, or is better to get 3 smaller systems?

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.

But far more vulnerable to high prices due to global market demand. In fact one of the reasons reverse cycle electric is now actually cheaper than gas is because our gas prices have gone through the roof as they are now set to global prices. End result we are paying far more for it than we did previously.

dungfungus said :

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.

You peddle the liberal party line no matter what. Did you not read the report about the issue in SA?

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.

Leon Arundell4:23 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.

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.

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

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.

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.

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

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.

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.

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.

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.

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

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?

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.

Sanitair Canberra North9:33 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

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.

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. 🙂

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.

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.

wildturkeycanoe6:43 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.

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