Harvest Hot Water

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Yes, they do! If you have a reverse cycle air conditioner and it works, then yes, a heat pump will work too. It’s exactly the same technology.

It’s also important not to over-state the severity of Canberra’s climate. Even in the depths of winter, the afternoon temperature is usually over 10 degrees, and that’s the best time to run a heat pump:

Mean temperatures by month in Canberra

Time of day \ MonthMarchAprilMayJuneJulyAugustSeptemberOctober
Mean 3 pm temperature (℃)23.519.114.911.410.612.615.118.3

In fact, recognizing that use of heat pumps in cold climates was becoming a normal practice, Standards Australia introduced a new climate zone in 2011 specifically to cover heat pumps designed for cold climates. Canberra was designated the representative location for that zone. The Clean Energy Regulator’s 2017 register of heat pump water heaters listed 171 models which had passed the testing and modeling requirements for cold climate operation.

The modeling undertaken to certify the Midea heat pumps against the Australian Standard established that in Canberra, the HP170 would result in 28 MWh or 28,000 kWh less electricity over a 10 year period than a standard electric hot water system, while the HP280 would use 26 MWh less electricity.

Midea heat pump cold climate features

The Midea heat pumpshave several features which ensure smooth cold climate operation. Firstly, the refrigerant used in our heat pumps (R134a) boils at -260C. This means that even at very low temperatures it will boil, thus extracting warmth that exists in the air even at low temperatures.

Secondly theMideas have a frost protection function which ensures that in the event that the evaporator becoming frosted during cold weather operation, the heat pump will de-frost automatically. This process takes 5-15 minutes, after which normal operations resume.

Thirdly, when the ambient temperature falls below 5 degrees, the HP170 automatically switches to electric boost mode. This is a sensible shift that avoids placing pressure on the heat pump during the infrequent occasions when it would be operating at low temperatures. As for the HP280, when the ambient temperature falls below 20C, it switches to combined heat pump and electric booster operation.

Finally, the timers on both the HP170 and the HP280 allow selection of the optimum time to run them. Here some scope exists for optimising their operation to match a particular household’s needs. For smaller households who typically have showers in the morning, it makes sense to set the heat pump to run during the afternoon when the air temperature is highest. It may only need an hour or two to restore the tank temperature. For larger families longer operation will be needed, but even then this can be set for the optimum time of day. And while this means the heat pump use daytime electricity, they don’t use too much of that. If you have a rooftop solar system, even in winter you will be able to power most of your usage from your rooftop.

But my plumber says heat pumps don’t work in Canberra

Yes, well … Canberra does have a dark history on that front. Back in 2009 and 2010 when generous rebates were available, a large number of heat pumps that were poorly made or were otherwise unsuitable for use in Canberra were installed here. From product reviews we’ve seen, the electronic controllers were unreliable, the units leaked water, they were noisy and they did not withstand frosty conditions particularly well.

But that is not to say that heat pumps don’t work. Certainly poor quality products and those which have not been designed to operate in cold climates will fail, but better quality products will work perfectly well.

You might have heard your plumber say `don’t buy a heat pump. They don’t work!’ There’s something in that. During the rebate-driven boom in 2009 a lot of dodgy heat pumps were installed. And they were provided by two of the best-known hot water system companies! They failed because many of these had no frost protection mechanism, and in some cases they were poorly installed.

Surely it’s too cold for a heat pump to work in Canberra, especially in winter?

It’s true that the warmer the air is (that is, the ambient temperature), the more efficiently can heat pumps work. It stands to reason: the more warmth there is in the air, the more warmth the heat pump can extract to heat up your water. But the refrigerant used in our heat pumps boils at – 26℃, so even on the coldest winter day in Canberra – say it’s -5℃, there is still enough heat energy in the air to make the refrigerant boil.

But most of the time the heat pump doesn’t need to operate during very low temperatures. By the middle of the day, even in mid-winter, the temperature is usually over 10 degrees, as you can see from this table:

Time of day \ MonthMarchAprilMayJuneJulyAugustSeptemberOctober
Mean 9 am temperature (℃)16.312.18.35.13.95.99.813.3
Mean 3 pm temperature (℃)23.519.114.911.410.612.615.118.3

So it’s a simple matter of setting the timer so that the heat pump only runs from say 11 am to 5 pm each day. That works for most people, but heavy water users might need a slightly longer timespan. The great thing is that if you have solar panels on your roof, even in winter the heat pump will be mostly powered from your roof.