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Advice wanted on variable speed ground source heat pumps

  • 05-03-2017 9:16pm
    #1
    Ging Ging
    Registered Users, Registered Users 2 Posts: 268 ✭✭


    I'll be building a new house shortly. First I was going with an air to water system and then I switched to looking at ground source for more stable operating COP. On closer inspection and talking to suppliers I am struggling to find ground source units with variable speed compressors. Does anybody have the reasons why? 
    It is now the standard for ASHP to be inverter driven with variable kW ouput to suit given load. Its turning me back off ground source that I can't find many of them with this. I'm worried about high starting current causing more wear and tear on the  fixed speed compressor than a variable version and loss of efficiency due the miss-match between at heat pump operating at full output and a reduced load requiring open loops and/or buffer tank.
    My house will be new build, A rated by provisional BER with 4 kW space heating and 4kW hot water load, concrete construction with UFH up and down and MHRV throughout. Electric connection to single phase supply.


Comments

  • #2
    murphaph
    Registered Users, Registered Users 2 Posts: 19,050 ✭✭✭✭murphaph


    I guess it makes more sense to employ inverter tech on ASHPs than GSHPs as the energy source fluctuates in energy content much more. Having said that, I know Thermia/Danfoss makes a modulating GSHP now (Diplomat Inverter). No idea how well respected it is however.


  • #3
    soundskin
    Registered Users, Registered Users 2 Posts: 64 ✭✭soundskin


    The fall off in geo installs over the last 5 years is the reason for the lack of info. Nibe, Thermia and IVT all have inverter driven geo units. I've only ever seen a handful of inverter Geo units.

    I'd be much happier with a properly sized (fixed speed) geo, a 100litre heating buffer and plenty open circuits in your house. The price of inverter geo units are very high.

    Much like the air to water inverter units, spare parts are very expensive.


  • #4
    ShanE90
    Registered Users, Registered Users 2 Posts: 239 ✭✭ShanE90


    Most, if not all fixed speed speed GSHPs have a soft starter for the compressor to bring it online slowly and reduce the starting current.

    As said already a correctly sized fixed speed system running on night rate with a buffer tank and open loops will be just as efficient if not more than an inverter system. The complicated electronics behind the inverter drive compressor are far more expensive and likely to fail than a soft starter on a fixed speed.

    The water circulation pump on the heating side on many GSHP units is speed driven this is possibly as close as you'll get to variable output!


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