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Cold weather performance of air sourced heat pumps

FlyWheel
Any heat pump experts on here? I’m looking at air sourced heat pump performance for a friend’s installation. They have NIBE F2040’s for the house, and Waterco Ultra 31’s for pool. Both use same R410A refrigerant, but that seem to be perhaps the only thing in common. NIBE (made in Sweden) twin rotary variable speed compressors are inverter controlled as standard (I guess vector or torque type drives), whilst the Waterco units are direct on line, capacitor start induction motors (I thought that technology went out long ago), with no soft start options.
 I’m interested in COP performance in the colder weather, the Ultra 31’s are specified as generally for use in ambient greater than 10 degrees C, although they do rate this particular model down to zero, BUT do not provide COP performance below 5 ambient, but enquiries suggest a COP of around 1 (perhaps even lower, ie, less power out than in!). The NIBE manufactures claim very much better, performance down to at least -25 ambient, with COP of around 2 even at this low temperature (is that even possible?).
Anyway, any thoughts on the subject, much appreciated.

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    re-reading my post that the last bit may have come over as a bit condescending.

    That was not the intention.  It was really to say 'this  is not so simple, and the school explanation is not really good enough' .

    And if ever it gets so cold or over pressure that the pump sucks in liquid instead of gas, then  it has had it !


    (Note that most of the modern refrigerant gasses are blends and have a range of temperature over which liquefaction/ evaporation occurs - rather as plumbers solder goes through a phase of being a bit pasty in between fully solid and fully liquid, - the exact gas blend 'slides' so that on expansion  the vapour is slightly richer  in the more volatile part, and in compression the liquid has more of the less volatile)

    Assuming the designers have done their stuff there is no need to worry about that.
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  • 0
    re-reading my post that the last bit may have come over as a bit condescending.

    That was not the intention.  It was really to say 'this  is not so simple, and the school explanation is not really good enough' .

    And if ever it gets so cold or over pressure that the pump sucks in liquid instead of gas, then  it has had it !


    (Note that most of the modern refrigerant gasses are blends and have a range of temperature over which liquefaction/ evaporation occurs - rather as plumbers solder goes through a phase of being a bit pasty in between fully solid and fully liquid, - the exact gas blend 'slides' so that on expansion  the vapour is slightly richer  in the more volatile part, and in compression the liquid has more of the less volatile)

    Assuming the designers have done their stuff there is no need to worry about that.
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