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Heating and cooling: Air source used along side combi boiler

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    Hi all, I have got a gas combi boiler running hot water and central heating upstairs in my property. I am just wondering if it would be possible to run underfloor heating downstairs using a small air source heat pump say 3KW as a stand alone system. Would we require a water cylinder as we don't have much room for one? Any comments much appreciated. Thanks
    • CommentAuthorringi
    • CommentTimeNov 25th 2016
     
    Why, what problem are you trying to solve?
  3.  
    I am looking for the most economical solution to heating. We are on lpg gas and air source is supposed to be much cheaper. We work from home and would have the ufh on downstairs all day and just run the rads upstairs for an hour or two in the morning and at night. It is possible to buy small heat pumps for less than £1000 (we aren't too fussed about claiming rhi) so don't need to buy a more expensive mcs accredited pump. Hopefully in the future we will get solar panels or a small wind turbine to contribute towards the running costs. I am just asking the question to see if it is a possible solution and if the system would work without a water cylinder, and as usual I am over-thinking things. Thanks
    • CommentAuthorDarylP
    • CommentTimeNov 25th 2016
     
    @barnconverter, you can buy cheap non-MCS, non-PCDF air source heat pumps for less than £1k.
    Connect it to a decent TS/buffer, and then to your UFH.

    How much do you pay for LPG, compared to grid electricity....?
    Cheers
    :smile:
    • CommentAuthorringi
    • CommentTimeNov 25th 2016 edited
     
    Is the UFH already installed?

    How well insulated is the floor?

    How old is your boiler and is it a condenser boiler?
  6.  
    Ufh not installed yet. Will have 100mm insulation below, pipes in 60mm screed, flagstones to finish. Lpg costs approx 30% more than mains gas, so according to my calcs, gas will cost 7p per kwh and electric 14p per kwh. House will be insulated to current building regs.
  7.  
    @DarylP please can you explain what a TS buffer is? Thanks
  8.  
    Boiler is new condensing.
    • CommentAuthorDarylP
    • CommentTimeNov 25th 2016
     
    @barnconverter
    TS - thermal store, buffer - buffer tank to 'smooth ' the output from the HP...
    At a CoP 3.00, a HP will cost circa 5p kWh from grid electricity......?:smile:
    • CommentAuthorowlman
    • CommentTimeNov 25th 2016
     
    I understand it is possible to get hybrid air/water heat pumps to run alongside your normal gas boiler, switching in and out as required and as outside air temps dictate. I doubt that they are cheap though.
    I'm looking at air/air pumps at the moment ( not what you're proposing, I know) but from my experience you'll find that good air pump engineers will want to slightly oversize your system, (3kW seems very small), to avoid customer disappointment.
    The TS, Thermal store/buffer tank, that Daryl mentioned would be a pre-requisite for what you have in mind otherwise how do you propose to even out water temps in the system.
    • CommentAuthorJonG
    • CommentTimeNov 25th 2016
     
    You could either set up a hybrid linking it to the gas combi to do both systems, or the heat pump could do the UFH alone.

    Most units need a minimum flow volume, and smallest are around 5kw, you would need to check the manufacturers recommendation but usually it is 10-20 litres per kw (lowest ramp down) so whatever the unit will modulate down to times the litres.

    With a set-up like that we would generally calculate the volume of the fluid in the loops and then make it up with a small buffer in the return.
    • CommentAuthorringi
    • CommentTimeNov 25th 2016
     
    Personally I don't think you are putting in enough floor insinuation for UFH. I would be more inclined to use a A2A heat pump along with some radiators on the boiler for when it is too cold for the heat pump alone.

    If the boiler was coming to the end of its life, then a hyped boiler/heap pump would be an option.
  13.  
    @JonG I would be running the ufh/ashp separately to the combi. So am I correct in thinking that we wouldn't need a large thermal store as the combi would provide DHW. Would a small buffer tank approx 50 litres be okay instead of a thermal store? Obviously I would have it sized to suit our system by the manufacturer /installer.
    @ringi I will be using 100mm PIR insulation not polystyrene.
    Thanks to everyone who's replied so far 😁
    • CommentAuthorringi
    • CommentTimeNov 25th 2016
     
    Posted By: barnconverterWould a small buffer tank approx 50 litres be okay instead of a thermal store?


    Personally I would have a DHW coil to preheat before your combi if the pipe layout works.
    • CommentAuthorcjard
    • CommentTimeNov 25th 2016 edited
     
    I think you'll spend a lot and see little benefit, to be honest, especially if you're building to regs..

    If your combi is struggling to cope with the heating demand (I.e. Chewing through so much gas, it's making you squeak) just wait til you get the electricity bill for running an ASHP..
  16.  
    Thanks everyone 😀

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