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Thermal Store required for UFH ?

  • 07-04-2019 9:54pm
    #1
    Turner
    Moderators, Society & Culture Moderators Posts: 3,931 Mod ✭✭✭✭


    Current setup

    Air to water heat pump for our UFH, our heatpump does not heat our hot water, max temp of water produced from the heatpump is 45 degrees.

    We have one array of solar tube panel for hot water feeding into 250L tank which is topped up by electric heating element at night.

    In sunny weather like today (and since early march) our solar panels are heating water to 50 degrees all day, but this hot water is just been fed into our 250L tank which is probably already at 65 degrees from being heated from the night before by electricity.

    We have a night meter so generally heat the water for 2 hours a night. Coupled with the solar tubes we always have 250L of 65 degree hot water.

    I think though that there is a lot of hot water being produced from the solar panel that could be kept in reserve for use at night for the UFH, instead of using the heatpump.

    Is it possible to use my setup including a thermal store to store water for the UFH. What i mean is that the solar tubes feed hot water into our 250L tank and a thermal store for later use in the UFH system.

    Anybody have experience of this or could recommend a company (by PM) that could advise on this type of setup.

    Thanks in advance


Comments

  • #2
    froshtyv
    Registered Users Posts: 225 ✭✭froshtyv


    Turner wrote: »
    Current setup

    Air to water heat pump for our UFH, our heatpump does not heat our hot water, max temp of water produced from the heatpump is 45 degrees.

    We have one array of solar tube panel for hot water feeding into 250L tank which is topped up by electric heating element at night.

    In sunny weather like today (and since early march) our solar panels are heating water to 50 degrees all day, but this hot water is just been fed into our 250L tank which is probably already at 65 degrees from being heated from the night before by electricity.

    We have a night meter so generally heat the water for 2 hours a night. Coupled with the solar tubes we always have 250L of 65 degree hot water.

    I think though that there is a lot of hot water being produced from the solar panel that could be kept in reserve for use at night for the UFH, instead of using the heatpump.

    Is it possible to use my setup including a thermal store to store water for the UFH. What i mean is that the solar tubes feed hot water into our 250L tank and a thermal store for later use in the UFH system.

    Anybody have experience of this or could recommend a company (by PM) that could advise on this type of setup.

    Thanks in advance

    Do you have a thermal store at the moment?

    Controls is your biggest issue here. You would need a differential temperature controller that would divert a three port valve to a thermal store once your hot water cylinder has gotten to a set temperature.
    Sensor in your cylinder, sensor in your buffer tank and a three port valve.

    You are then going to have to put a mixing valve on your underfloor heating circuit as you cant control the temperature of the thermal store once you connect solar to it.

    Depending on your current setup there will be a few thousand to get the installed correctly.
    Buffer tank, differential temperature controller, diverting valve, UFH mixing valve. Competent electrician and plumber.

    If your hot water cylinder is being heated to 65 at night time, your solar panels at 50 will do nothing.
    Your panels would need to be at least 7 degrees higher than what is in your hot water cylinder, otherwise you will just cool your cylinder.


  • #3
    John.G
    Registered Users Posts: 3,464 ✭✭✭John.G


    Turner wrote: »
    Current setup

    Air to water heat pump for our UFH, our heatpump does not heat our hot water, max temp of water produced from the heatpump is 45 degrees.

    We have one array of solar tube panel for hot water feeding into 250L tank which is topped up by electric heating element at night.

    In sunny weather like today (and since early march) our solar panels are heating water to 50 degrees all day, but this hot water is just been fed into our 250L tank which is probably already at 65 degrees from being heated from the night before by electricity.

    We have a night meter so generally heat the water for 2 hours a night. Coupled with the solar tubes we always have 250L of 65 degree hot water.

    I think though that there is a lot of hot water being produced from the solar panel that could be kept in reserve for use at night for the UFH, instead of using the heatpump.

    Is it possible to use my setup including a thermal store to store water for the UFH. What i mean is that the solar tubes feed hot water into our 250L tank and a thermal store for later use in the UFH system.

    Anybody have experience of this or could recommend a company (by PM) that could advise on this type of setup.

    Thanks in advance

    Could you post a picture of the 250L HW cylinder showing the positions of the solar heating coil flow&return pipes and also the location of the electric heating element or elements if more than one installed.
    Normally, the solar coil is in the bottom of the cylinder and the heating element is in the top 1/2 so that you all ways have a "dedicated" solar volume, in this case ~ 125 litres.


  • #4
    Turner
    Moderators, Society & Culture Moderators Posts: 3,931 Mod ✭✭✭✭Turner


    John.G wrote: »
    Could you post a picture of the 250L HW cylinder showing the positions of the solar heating coil flow&return pipes and also the location of the electric heating element or elements if more than one installed.
    Normally, the solar coil is in the bottom of the cylinder and the heating element is in the top 1/2 so that you all ways have a "dedicated" solar volume, in this case ~ 125 litres.

    Sorry for late reply and thanks for your post.

    Pic is attached but sideways for some reason.

    The black insulated pipe between the heating element and the thermostat dial is the "hot water in" coming from the solar panel on the roof.


  • #5
    John.G
    Registered Users Posts: 3,464 ✭✭✭John.G


    Turner wrote: »
    Sorry for late reply and thanks for your post.

    Pic is attached but sideways for some reason.

    The black insulated pipe between the heating element and the thermostat dial is the "hot water in" coming from the solar panel on the roof.

    That looks to me as if it was set up to have hot water circulating from the HP through the coil, the (auxiliary) electric heating element would then be switched in as required, ie "regularly" (once/week?) for legionella protection or to boost the hot water if it falls below say 35/40C etc.
    I just cannot see how this will work properly with a conventional solar array, there would/should be another probe located just above the top "hot water in" coil, there should also be a probe mounted in the solar collector flow pipe, when the solar collector temp is 7/10C higher than the cylinder probe then the solar collector circ pump will start up and continue to run until this differential temp falls to ~ 3C, this continues until a max cylinder temperature is reached, normally ~ 65C, the solar circ pump is then inhibited from running until this temp falls by ~ 10C. Normally a solar E.Tube panel would have no problem in getting the cylinder temp above 50C which you say is its max. The positioning of the electric heating element also seems wrong.
    Are there any other temp sensors in the cylinder?

    The only other explanation I have is that you have a small solar panel complete with a compressor, they are called thermodynamic solar panels.


  • #6
    Turner
    Moderators, Society & Culture Moderators Posts: 3,931 Mod ✭✭✭✭Turner


    No the solar we have are the fluid filled tubes.

    There is a wire going from the thermostat housing on the tank to the solar controls/pump.

    Presume this is for what you talked about above to let the solar kick in.

    Just seems a waste. In this type of weather the solar is heating water all day to 55 degrees plus.

    Then at night when heat is required for rads upstairs we use the heatpump to heat water from cold to supply the rads and underfloor.

    If anybody knows of a company that specialises in thermals stores for the above set up could they let me know


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  • #7
    esox28
    Registered Users Posts: 800 ✭✭✭esox28


    are you sure that tank is not a thermal store? how many actual pipes are connected to the tank?


  • #8
    Turner
    Moderators, Society & Culture Moderators Posts: 3,931 Mod ✭✭✭✭Turner


    The heatpump is seperate it does not feed into that tank.

    All that feeds into the tank are the solar tubes, with one hot out pipe that feeds the bath/taps.


  • #9
    esox28
    Registered Users Posts: 800 ✭✭✭esox28


    okay, so you have roughly 70% of hotwater from solar, would you have a rough annual cost for heatpump ?


  • #10
    Turner
    Moderators, Society & Culture Moderators Posts: 3,931 Mod ✭✭✭✭Turner


    Annual no. But on the reduced rate night meter about 2-3 euro per night id say in cold weather. Its ten years old.

    Might be time for an upgrade, the modern heat pumps will obviously be way more economical than our one.


  • #11
    esox28
    Registered Users Posts: 800 ✭✭✭esox28


    reality of it is new heatpump would be the only move forward and return on any investment in your heating and hotwater., without a complex refit of existing setup


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