Huge hot water cylinder heating more water than needed

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  • markinmarkin Forumite
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    Section62 said:
    markin said:
    Sunamp also has very low heat loss it keeps the heat for months.


    Standard water tank is in the range of 1.3 - 1.6KW /24h

    Months?

    Back of a fag packet, a loss of 0.48 kWh per 24 hours would drain 3.5kWh in 7.3 days or with the larger 12kwh unit with a loss rate of 0.84 kWh/24h all stored heat would be gone in about 14 days, surely?  Presumably the rate of heat loss will vary a bit depending on total heat remaining, but for practical purposes I'd suggest the useful heat energy remaining is more important.

    Essentially by installing one of these the OP would be spending a fair amount of money replacing one form of heat store (which they consider to be excessively sized) with a different form of heat store (with the same issue of getting the capacity right for different use patterns).

    Adding more insulation to the existing HWC should still be the first consideration for seeking out the best return for investment.
    Its 'W' not 'KW'
     
  • edited 9 April at 12:09PM
    QrizBQrizB Forumite
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    edited 9 April at 12:09PM
    markin said:
    Section62 said:
    markin said:
    Sunamp also has very low heat loss it keeps the heat for months.


    Standard water tank is in the range of 1.3 - 1.6KW /24h

    Months?

    Back of a fag packet, a loss of 0.48 kWh per 24 hours would drain 3.5kWh in 7.3 days or with the larger 12kwh unit with a loss rate of 0.84 kWh/24h all stored heat would be gone in about 14 days, surely?  Presumably the rate of heat loss will vary a bit depending on total heat remaining, but for practical purposes I'd suggest the useful heat energy remaining is more important.

    Essentially by installing one of these the OP would be spending a fair amount of money replacing one form of heat store (which they consider to be excessively sized) with a different form of heat store (with the same issue of getting the capacity right for different use patterns).

    Adding more insulation to the existing HWC should still be the first consideration for seeking out the best return for investment.
    Its 'W' not 'KW'
    Yes, from page 9 of the brochure "kWh/24h" is 0.48 and "[W]" is [20].
    A constant loss of 20W over 24h is 0.48kWh.
    That's roughly 1/3rd of the heast loss from a standard HW tank, but still significant.
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  • boxofpawsboxofpaws Forumite
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    We are also just 2 of us in a 4 bed house. We recently replaced our boiler and cylinder with a combi boiler. There is plenty of capacity for heating AND hot water even with guests staying but I’m not sure it’s saving us any more. On the contrary, I’m starting to suspect it’s going to increase our bills. 
    Debt Jan 2017 = £42k
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  • markinmarkin Forumite
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    QrizB said:
    markin said:
    Section62 said:
    markin said:
    Sunamp also has very low heat loss it keeps the heat for months.


    Standard water tank is in the range of 1.3 - 1.6KW /24h

    Months?

    Back of a fag packet, a loss of 0.48 kWh per 24 hours would drain 3.5kWh in 7.3 days or with the larger 12kwh unit with a loss rate of 0.84 kWh/24h all stored heat would be gone in about 14 days, surely?  Presumably the rate of heat loss will vary a bit depending on total heat remaining, but for practical purposes I'd suggest the useful heat energy remaining is more important.

    Essentially by installing one of these the OP would be spending a fair amount of money replacing one form of heat store (which they consider to be excessively sized) with a different form of heat store (with the same issue of getting the capacity right for different use patterns).

    Adding more insulation to the existing HWC should still be the first consideration for seeking out the best return for investment.
    Its 'W' not 'KW'
    Yes, from page 9 of the brochure "kWh/24h" is 0.48 and "[W]" is [20].
    A constant loss of 20W over 24h is 0.48kWh.
    That's roughly 1/3rd of the heast loss from a standard HW tank, but still significant.
    Thanks, was miss reading it. I presumed the gell was staying static until activated and turning from a liquid to solid, has anyone tested heat loss from the pipes?



     
  • Section62Section62 Forumite
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    markin said:
    Section62 said:
    markin said:
    Sunamp also has very low heat loss it keeps the heat for months.


    Standard water tank is in the range of 1.3 - 1.6KW /24h

    Months?

    Back of a fag packet, a loss of 0.48 kWh per 24 hours would drain 3.5kWh in 7.3 days or with the larger 12kwh unit with a loss rate of 0.84 kWh/24h all stored heat would be gone in about 14 days, surely?  Presumably the rate of heat loss will vary a bit depending on total heat remaining, but for practical purposes I'd suggest the useful heat energy remaining is more important.

    Essentially by installing one of these the OP would be spending a fair amount of money replacing one form of heat store (which they consider to be excessively sized) with a different form of heat store (with the same issue of getting the capacity right for different use patterns).

    Adding more insulation to the existing HWC should still be the first consideration for seeking out the best return for investment.
    Its 'W' not 'KW'
    As QrizB says, there's two figures quoted and the first is kWh/24hours. It is a bit of a strange way to quote specs in literature intended for consumers though.

    It would be great if there was a domestic-scale and domestic-budget device that could store heat for months, but I fear that's entering similar territory to perpetual motion.
  • doodlingdoodling Forumite
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    Hi,

    The Sunamp things are not magic, they work by having something hot in them which transfers heat to water flowing through the pipes inside. The only difference to a traditional hot water cylinder is terms of heat retention is that in the Sunamp the material used can store more heat than water for a given volume, therefore the box can smaller and in turn it is easier to more effectively insulate it.

    Adding more layers of insulation to an existing hot water cylinder (and connected pipework) will get you to the same heat retention performance as the Sunamp, albeit taking up more space.
  • ZandoniZandoni Forumite
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    Fit a time switch to your immersion heater and experiment with the amount of time it is on.
  • StarfrogStarfrog Forumite
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    Im considering getting a Sunamp to replace my Hot water tank as that is heated by my Oil boiler (Scottish Highlands so no Gas) and I have a solar array with battery storage to help offset the increase in cost for heating from Electric alone (as well as the surplus solar). My question and one that I cant find from the Sunamp information is when it goes through the phase change, does it do it for the entire unit ? eg its all changed and from that point its an ever dwindling heated water resource until charged again ? and do i have to fully recharge it or can i just apply a bit of power and it will give me the same amount of capacity in hot water back ? I agree that they are quite expensive but when you take into account that I can use my solar panels, and that there are no service and expansion tanks etc to worry about it seems to fit the bill ? 
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  • Reed_RichardsReed_Richards Forumite
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    If you have a hot water tank with an immersion heater you can heat it with your solar array.  If it does not have an immersion heater it might be a lot cheaper to get one inserted than to replace it with a Sunamp unit.  If you get a Sunamp unit, get the type that can either be heated electrically or from your oil boiler so you can choose whichever option is the cheaper on days when the sun does not shine enough.

    Bits of the "stuff" inside the Sunamp box can be in one phase and bits in the other.  I imagine you would want to keep it fully charged, it will get partially discharged as you use hot water and then you'll charge it back up again at an appropriate time. 
    Reed
  • edited 10 April at 1:09PM
    StarfrogStarfrog Forumite
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    edited 10 April at 1:09PM
    If you have a hot water tank with an immersion heater you can heat it with your solar array.  If it does not have an immersion heater it might be a lot cheaper to get one inserted than to replace it with a Sunamp unit.  If you get a Sunamp unit, get the type that can either be heated electrically or from your oil boiler so you can choose whichever option is the cheaper on days when the sun does not shine enough.

    Bits of the "stuff" inside the Sunamp box can be in one phase and bits in the other.  I imagine you would want to keep it fully charged, it will get partially discharged as you use hot water and then you'll charge it back up again at an appropriate time. 
    Thank you for the response and agreed I can heat it with my solar array and use an Eddi ? But its fairly old and I think the method of heating water with an immersion is not as efficient as I think i can have it. It does use the Oil boiler as well. Its about time for it to be replaced and I think the Sunamp would be the most efficient way to provide hot water for the odd bath and kitchen hot water that we use. We currently use an electric shower so that takes its 9kWh each time its used which is in excess of what my solar and battery store can provide so there’s always a draw from the grid when i use the shower so replacing that well be useful as well. Knowing that the Sunamp can be topped up during the day with solar is a good option and as soon as i get a smart meter (been waiting two years !!) then I can utilise cheaper top up of my battery storage at night. The Sunamp seems to be the way to go for low maintenance and electric/solar driven so its one lest item using Oil which I will eventually get rid of that ether with an airsource heatpump with underfloor heating or just electric radiators and more PV panels. 
    ——-
    12 x JASolar 455w Panels (5.46kWp south facing array) Enphase Microinverters IQ7+, Lux AC ESS 3.6kW, 5 x 2.4kwh = 12kWh Plyontech US2000C Battery storage, Lochinver far North, west coast of Scotland 
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