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Hot water tank size / heat pump

  • 18-02-2020 9:14pm
    #1
    Registered Users Posts: 404 ✭✭ ec_pc


    All, quick question for some advice regarding hot water tank size.

    Heat pump being installed, under floor heating, air tight etc. 6 people, 2 power showers and a bath. Likely to be 4-5 showers each night and 1-2 in the morning. What size hot water tank would people recommend from professional or personal experience? Remember the heat source is a heat pump.

    Concern is to have enough hot water for showers. Part L recommendation is 300 but installer wants to put in smaller unit.


Comments

  • Registered Users Posts: 10,926 ✭✭✭✭ Calahonda52


    What temperature do you expect the heat pump to heat the water to?
    What is the net usable hot water in a 300 L cylinder?
    What is the heating capacity of the coil in the HW cylinder
    Can you post a link to the Prt L doc where you did the sizing?
    .
    https://steps.ie/cmspages/getfile.aspx?guid=b410fe27-2f49-4a47-9a16-7065752f18f4&forceattachment=1
    shows how to do the math, assuming HW temp, cold water temp and shower temp.

    for 60/10/40 5 ten minute showers will require 250 litres of HW.

    IMO the HP alone will not do the job all year round


  • Registered Users Posts: 404 ✭✭ ec_pc


    What temperature do you expect the heat pump to heat the water to?
    What is the net usable hot water in a 300 L cylinder?
    What is the heating capacity of the coil in the HW cylinder
    Can you post a link to the Prt L doc where you did the sizing?
    .
    https://steps.ie/cmspages/getfile.aspx?guid=b410fe27-2f49-4a47-9a16-7065752f18f4&forceattachment=1
    shows how to do the math, assuming HW temp, cold water temp and shower temp.

    for 60/10/40 5 ten minute showers will require 250 litres of HW.

    IMO the HP alone will not do the job all year round



    I've been told that the water will be at 60 degrees in the tank which will be 220 litres which equates to approx 300 at the tap at 40 degrees.

    I don't know the heating capacity of the coil (I don't understand this stuff really). Part L stated 300 L tank based.


  • Registered Users Posts: 10,926 ✭✭✭✭ Calahonda52


    Whats the spec on the heat pump, can you share it?
    .
    Can you please find the 300L reference in Part L and tell us what page it is on in what document?
    .
    You may have hot water at 60 but it wont all come from the HP, especially in winter.
    Most of them have an elec element which is used to maintain the 60 output.
    .
    So you might have a 9 kW element in the heat pump to take up the slack.
    A better idea is to use the HP to bring it so far, maybe UFH temp and then have a night rate immersion in the HW cylinder .

    as for 220 at 60 yielding 300 at the tap does not make sense if you look at the link I sent last night.
    15 at the shower is c 9 hot and 6 cold
    Its closer to 370 which suggest that its not based on 60/10


  • Registered Users Posts: 125 ✭✭ selfbuild17


    300-400 litre tank seems to be the norm now for any decent sized house. It would be madness pushing a HP to produce water at 60 deg. just to allow you to have a smaller tank


  • Registered Users Posts: 55 ✭✭ Ning


    Our heat pump (joule samsung) heats water up to 48 degrees. When the temperature drops under 43 degrees in the tank, the hp starts to "top up" the water temperature in summer months (top up happens as soon temperature drops under 48 degree if the hp is already on heating rest of house in winter months). So the total available hot water is technically greater than the size of the tank as the hp is topping it up as soon as needed, and not once a day.


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  • Registered Users Posts: 4 RikKav


    Hi Ning - Just wondering how you find your Joule HP. I am looking to instal one soon. Thanks.



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