Eon green grant-Daikin ASHP with heat store?

C_Mababejive Posts: 11,645
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edited 23 January at 2:36PM in Heat pumps
Today i happend to spot a mobile exhibition trailer run by Eon /Daikin so stopped to have a chat. The guy told me all about the green energy grant upto 10k and showed me and told me about the daikin ASHP and heat store cylinder set up. The HS cylinder is an unvented cylinder complete with immersion heaters. Simply put, the ASHP heats the water in the heat store. A max temp of 50c was mentioned.  The heating circuit is heated via a heat exchanger from the heatstore cylinder and hot water is drawn direct from the cylinder.

I dont have any data on heat store temp with respect to differing outside air temps and how often the immersion heater(s) might have to come on to top up.

Also we talked about radiators and i was assured that the system could feed existing rads or i could have them replaced.

The other thing of course is the running time for the ASHP. Is it going to run 24/7? If not, how much off time would it have?

I currently run a 40 year old "zombie" boiler which is fully pumped ,range rated down to circa 10 Kw and it provides all our heating and HW needs. The house is well insulated and has DG and cavity wall insulation plus plenty of deep loft insulation.

I was told that the grant would cover full cost and there would be nothing to pay.

Can anyone see any drawbacks?

Am i going to end up paying more in electricity?
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  • For your hot water you need a minimum temperature of around 45 C so your stored hot water needs to be heated to 45 C or more.  If you have radiators you need the input water temperature to be at least 45 C when its cold outside (or you need radiators with a huge surface area).  But when it's spring or autumn and you don't need so much heat you might be able to use a lower input water temperature and thereby operate your heat pump at higher efficiency.  It would seem to me that the heat store cylinder would prevent you from doing that so it's basically a means of preventing you from running your heat pump as efficiently as you might do otherwise.

    The system could certainly feed existing radiators but you would not get enough heat out of them to keep your house warm in winter.  Anyone who tells you otherwise is not being honest.

    An ASHP, correctly sized with correctly sized radiators, will not need to run 24/7.  Mine is off at night and for varying intervals during the day.

    If your current boiler is electric then an ASHP would greatly reduce your electricity bills.           
  • Verdigris
    Verdigris Posts: 1,725
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    Am i going to end up paying more in electricity?

    There'll be a catch. I suspect they'll recoup the difference between the RHI payments and the installation costs by sticking on your electricity unit price and you'll be tied to Eon until you've paid it off.

  • rp1974
    rp1974 Posts: 723
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    Not head of that old saying,there's no such thing as a free heat pump?.
    Something for nothing doesn't really work in practice,you'll likely pay for it,somehow,somewhere.

    Might be better taking a look in this section for more detailed information:https://forums.moneysavingexpert.com/categories/lpg-heating-oil-solid-other-fuels.

    Dont wish to pour cold water on it,but highly suspect that Eon are doing this to benefit themselves,not their customers.
    I know little about the whole heat pump set up,the alarm bells start ringing when suggesting that you keep existing radiators,the majority of people have them replaced.

    Eon might have "Green Washing" targets to meet,or incentives to do so but more than likely will view this as a fit and forget type thing,once it's fitted you'll not see them for dust provided you keep paying them probably inflated prices for however many years.
    By all means look into it in greater detail,though do be certain that it suits you and not Eon before committing to anything.
  • Reed_Richards
    Reed_Richards Posts: 3,987
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    edited 6 November 2021 at 9:07AM
    When it comes to alarm bells
    I dont have any data on heat store temp with respect to differing outside air temps and how often the immersion heater(s) might have to come on to top up.

    Also we talked about radiators and i was assured that the system could feed existing rads or i could have them replaced.

    Mention of using immersion heater(s) should ring alarm bells.  Mine comes on once a week for one hour to raise the cylinder temperature to 60 C as a precaution against Legionella.  Any more use is liable to become expensive.

    And you will not be able to keep your existing radiators except by adding greatly to the running cost and even then probably not.

    Not to mention the whole Heat Store thing.  Heat pumps do not play nicely with Heat Stores.   
  • matelodave
    matelodave Posts: 8,573
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    edited 6 November 2021 at 12:09PM
    I'm guessing that Heat Store is just a buffer tank rather than the generally accepted concept of a heat store that gets heated up to 80-90d egrees.

    As Reed_Richards rightly says a normal heatpump can get up to 50-55 degrees and then needs an immersion heater to raise the water temp any higher.

    If you existing radiators were correctly sized for a gas boiler running at around 75 degrees and you now only shove water round at 50-55 dgrees then you'll only get about 50% of the heat output from them, thats why you need suitable, properly sized, low temperature radiators. (even then, running a heatpump at 55degrres is way outside its optimum efficiency parameters)

    That why there are so many people who are dissatisfied with their heat pump installions when it's just been the boiler thats been replaced. They crank up the heat output which dramatically increases their energy costs and they probably still wot be warm enough

    Whatever anyone says, gas still costs 4-5 times less than leccy and a heat pump properly configured, commisioned and operated might acheive a COP of around 3 which means it'll still cost around 50% more to run than gas (and a lot more if its not set up or operated correctly)

    In my opinion you'll only save money (as opposed to saving energy)  with a heatpump if you heat with electricty (storage heaters or panel rads etc) or LPG. Oil is about on a par and mains gas is still a lot cheaper.
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