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Our advice on using a 3 in 1 heat pump for heating / cooling and hot water

08 Jan
Our advice on using a 3 in 1 heat pump for heating / cooling and hot water

Can I use my heating & cooling heat pump to make hot water also?

Technically, you can use your heating & cooling heat pump to make hot water but Siddons Solar Hydronics suggests you go with two separate heat pumps if you have the space for the following reasons:

No Cost Difference
There is no real cost difference in Australia of adding a second, smaller heat pump dedicated making hot water. This is because you receive rebates of approximately $1,000 for your hot water heat pump so. You will also require a three-way valve and a special storage tank with a large stainless steel internal coil to separate the treated hydronic water with mould inhibitor from your potable fresh water supply. The rebate and the cost saving of the simpler set-up with standard storage tank add to about the cost of an additional dedicated hot water heat pump.

Optimal Performance
The refrigerant used in a heating and cooling heat pump is different to a hot water heat pump. The former is optimised to do both heating and cooling tasks and typically uses R410a, commonly found in reverse cycle air conditioners also.  The hot water heat pump typically uses R134a refrigerant or similar and is optimised for heating hot water to 60 deg C but not for cooling. 

R410a boils at a much lower temperature of minus 48 deg C so is better at making heat in sub zero conditions such as providing hydronic heating in very chilly winter mornings with sub temperatures outside. R134a boils at minus 26 deg C so is better set to run in the afternoons for a few hours (it only runs for about 3 hours per day) when the air temperature is hopefully above zero.

Also, the critical temperature of R134a is 101 deg C (when the refrigerant will no longer condense no matter what the pressure is) so reaching 60 deg C (for legionella bacteria control) is easier using this refrigerant. The critical temperature of R410a is 72 deg C so reaching 60 deg C is more difficult using this refrigerant. 

A hot water heat pump only uses about 3kWh per day so can easily be run using your own solar power during the day or will cost about $280 per year to provide hot water using power at 26 cents per kWh.

Run Two Tasks Independently
With two machines, you can run two separate tasks at the same time, heating/cooling and hot water. The hot water heat pump will be set to run 365 days of the year. The heating and cooling heat pump will normally operate during the heating and cooling seasons for 6 to 9 months per year and then turned off during the temperate months. 

Simpler System
The other benefit is that you have a simpler system to maintain over the life of the machines. Any issues with hot water will not affect your heating and cooling and vice versa. The KISS principle is always good.

Check out our heat pump range by clicking here.

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