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The Different Types of Ground Source Heat Pumps

  • 01-11-2014 12:19pm
    #1
    murphaph
    Registered Users, Registered Users 2 Posts: 19,050 ✭✭✭✭


    We're in the final stages of buying a site for a 200m² including heated cellar new build here in Berlin, low energy house (not quite passiv but getting there) with high air tightness (will have blower door test performed to verify), UFH throughout and mechanical ventilation with heat recovery.

    We also intend installing Photovoltaic. Not sure of the size yet, but the feed in tariff here is now just 9c falls a bit every month (though they guarantee the feed in tariff at the rate you first connect at for 20 years) it is more economical to use the energy yourself if at all possible, rather than feeding in at 9c and buying back at 29c (electricity is expensive here).

    As we are 100 metres from the nearest gas main and it would be very expensive to get it connected, plus, well, we want to move away from fossils as much as we can and do our bit, even if a high efficiency condensing boiler would actually work out cheaper over its lifetime than a heat pump.

    So...
    We have made the decision for PV + HP (of some kind). I've been reading up on the different kinds of heat pumps and well, my head is in a bit of a spin. So many variants. I haven't yet discounted an air source heat pump either. I think they operate more efficiently in our climate here than in Ireland (fewer defrost cycles as in winter it just gets cold and stays cold, rather than hovering up and down around the freezing point, causing icing)

    So far I have identified:
    -Water/Groundwater based (two wells, one source and one return)
    -Water/Brine based with ground loop collector
    -Water/Brine based with 100m deep borehole
    -Direct Exchange (no brine or water-the refrigerant itself is passed around the collector loops via a manifold)

    In our area the groundwater is high. At it's lowest (around September) it's 2.65m below ground level, according to site investigation. I don't have any information (yet) about the water quality. I believe iron and manganese are of particular concern when using groundwater as they lead to rapid corrosion of the heat exchanger and rust filling up the return well.

    I believe the direct exchange method is extremely popular in France for some reason. It is seldom offered in Germany.

    Regardless of system, we want to be able to run the heat pump in reverse (using PV) to cool the house in summer on the days it gets really hot (we get days here over 30 degrees every summer and it is not pleasant when you can't escape the heat). We'd aim to run the heat pump (using PV) in the afternoons when we're at work to produce hot water for bathing during summer and in winter for both heating and bathing.

    Would anyone (who knows what they are talking about) care to comment on the pros and cons of each system (or just one system if you are only familiar with that...it's unlikely people will be genuinely familiar with all of them).

    I'm open minded at this stage, as I said, haven't even ruled out air source, even with the lower COP. I THINK some air source heat pumps offer a further advantage that you can run them as "true" air conditioners, not just passive coolers, which I think ground source systems are limited to, but stand open to correction on that!


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