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Discussion in 'Renewable Energy' started by ambrosia, Sep 17, 2016.

Discuss wiring in the Renewable Energy area at

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  1. ambrosia

    ambrosia Plumber GSR

    if a system has a heat pump as the primary heat source for both hot water and underfloor heating, and a gas boiler as a back-up if the heat pump becomes overwhelmed, how do you wire it all together so the boiler only kicks in when the heat pump isnt coping

    Also i probably need to talk to the manufactures, but what kw should I be expecting on the compresser, i'm guessing they normally need a dedicated breaker on the consumer unit, please tell me theyre not normally 3 phase
  2. MC_Bob

    MC_Bob Member

    What have u been fitted manufacturer wise?
    We done an ecodan system and was told it'd be perfect for the job but was quite dissapointed with its functions.
  3. leesparkykent

    leesparkykent S. Mod

  4. Worcester

    Worcester Plumber

    That'll work, though there's all sorts of parameters to consider with bivalent, also the hydraulic considerations.

    Heat wise - what flow temperature is needed for the designed outdoor temp?
    Does the ufh have blending stats/ valves ?
    Is the boiler going to supplement or take over completely?
    Buffer tank or low loss header?

    Once you've done the heat loss calculations and you know the heat output curve of the heat pump - it deceases with outdoor temperature, so a 12kw A7/W35 Heat Pump is typically 8 kW at A-2/W45 when you now both of those then you can calculate the bivalent point.

    Most of the heatpump manufacturers have a bi-valent controller, (just don't buy a Dream, Husky or a few others I could name )

    Max size single phase heatpump you'll get is one that will output 12kW at -15, most 16kW heat pumps won't do that.

    Some need single supplies, some twin and some triple, the manufacturer will supply the 'fuse' ratings for the supplies - remember that the compressor supply will need a Type C MCB

    Simples really :)

    p.s. Only attempt this is you understand the above, else you'll spend a shed load of time and money trying to DiY and getting it well wrong, when if you paid a professional the government will give you a grant to put it in :)
    • Like Like x 5
  5. quality

    quality Plumber GSR

    as above very easy to get this wrong
  6. ambrosia

    ambrosia Plumber GSR

    its a low loss header, which currently has 3 potterton suprima 70L attached, one has blown-up

    underfloor heating has standard manifold with blending valve, but only on ground floor, normal rads upstairs

    unvented tank only has one coil

    customer says current gas bill is £5k a year. its a reasonably modern insultated mansion with 2 people, 2 kids and a maid so not high hot water usage. customer wants to reduce that £5k

    understood 20% of the above post, if customer goes for it could be a steep learning curve.
    heat pumps havent really taken off in London yet, but think they might so good to learn for the future
  7. leesparkykent

    leesparkykent S. Mod

    I could wire the lot for you if you needed someone to.
  8. Worcester

    Worcester Plumber

    Maybe not the right job to do that steep learning curve on; massive amount to learn for a job like that, and very easy to get it sooo wrong.
  9. Chalked

    Chalked Plumber GSR

    £5k on gas, if I'm reading your post right for 3 x 70l suprima's They are 26kw each, so 72kw. They ate old boilers now and are only 78% efficient. So £5k a year it's that bad.
    If you changed the boilers to quality condensing ones, theres a possible saving of 18%. That's £900 a year.

    Getting that output without a large outdoor space and plant room , might be difficult with a heat pump.
  10. Worcester

    Worcester Plumber

    Sometimes the wrong solutions are sought for the wrong reasons.

    “So in war, the way is to avoid what is strong, and strike at what is weak.”
    ― Sun Tzu, The Art of War

    Gas is strong - simple to install, cheap to buy
    Weak - Old inefficient boilers
  11. Sparkgap

    Sparkgap Active Member

    So are they looking at having a heatpump for the main source? Air or ground source?
    You could have a heatpump for the UFH and do that direct without having the blending valve, though middle of winter with outside temps near freezing it would be a more expensive way of heating if you've already got a gas system.

    I would look at improving the controls to reduce the bills as I can see them spending a load on heat pumps and finding their electric bills exceed their old gas bill!
  12. Sparkgap

    Sparkgap Active Member

    Why am I getting double postings?
    Last edited: Jan 26, 2017
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