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Heating and cooling: Thermal store, adding ufh

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    • CommentAuthorrwski
    • CommentTimeFeb 14th 2024
     
    We have 2000l Akvaterm thermal store fed by wood gasification boiler and solar thermal.
    Current output is domestic hot water and 3 radiators.
    We are going to add ufh.
    Does anyone have a plumbing and wiring setup for this that they could share. The important difference to lots of schemes that I see is that adding heat is manual so we don’t want to turn on the ufh when the tank is not hot enough. Everything I look at just sends a call for heat and carries on turning the ufh on…

    Ideally we will use heatmiser neo, but at the moment I’m interested in detailed information about what others have done.

    Current radiators are just turned on by a thermostat on the tank, if the tank is above the set temperature the pump is turned on.

    Thank you!
  2.  
    The UFH will be no different to the rads. in respect of limiting the turn on to only when there is heat in the TS. If you are happy to restrict the UFH to the same TS temp. as the rads then the same thermostat can be used.If you want to allow the UFH to run with a lower TS temp then a separate thermostat will be needed.

    When you say the radiators are just turned on by a thermostat on the tank this sounds like the only control for the rads. is a hot TS. It is usual to have the rads. turned on by a room stat or similar which calls for heat and this request is only allowed if the TS stat is above the set temp. so you are not heating when it is not needed, if you had this then the UFH would be no different.

    If you wanted to stay with the current system of the heating controlled by the TS temp. then you could just plumb in the UFH on to the rad. flow/return but with it own mixer valve to regulate a lower UFH temp. Balancing between the rads and UFH may be problematic and it may be easier to have a separate pump for the UFH.

    Most systems with a TS use a mixer valve on the rad. flow to limit the rad. temp. and conserve TS temp. the UHF will need its own mixer valve as UHF runs at a lower temp to rads. This means that you could run the TS down to a lower temp before restricting the UFH turn on but this will lengthen the time before you can get heat into the rads. or DHW because of the longer time to recharge the TS.

    My system doesn't have UFH but is 2 houses from 1 TS each with its own circuit and separate mixer valve. each house has its own CH controller and pump. In this respect it would be the same as your rads.and UFH.

    The DHW is an indirect tank also from the TS with its own pump, there is no mixer valve on the DHW flow/return but there is a differential thermostat on the TS and DHW tank such that the DHW circuit only runs when the TS is at least 3 deg above the DHW tank. I have a mixer valve restricting the DHW output temp.

    There is no thermostat limiting the CH when the TS temp drops.
    • CommentAuthorrevor
    • CommentTimeFeb 15th 2024
     
    We have a 350l TS solar thermal and propane gas. Have two manifolds one for upstairs and one for downstairs with 12 stats each some controlling 2 or3 loops and are Heatmiser with a hub. The manifolds were prepared by the supplier with the manifolds mounted on boards complete with mixing valves and mounted above, a control unit into which the manifold vales are connected to. The system tested before delivery.
    The length of the loops were determined by the supplying company along with flow rates for all the loops and pipe layout was also supplied.
    When a room calls for heat then the manifold pump draws hot from the TS and if not hot enough will turn boiler on as it is controlled by a stat low down on the TS. From experiment we have this set at 35 C as the flow to the UFH is above this and due to stratification the water is hot enough for the UFH and we maintain a TS temp of 55 C by means of the boiler stat. The boiler has it own pump as normal setup. In summer the solar will take the TS temp up to 79 C. The DHW comes of a heat exchanger the water (at 55 c at the top) is drawn off the top of the tank to the HE when the hot tap is turned on. Whilst our system was expensive I do not think I would have manged to have cobbled together anything of the quality I got for the price. Ideally I could do with a thermostat on the top of the tank but the space is occupied by a thermocouple for the solar control system. What the system does not do is if the boiler timer is not synched to the UFH times then the boiler will not come on but most of the time the boiler comes on slightly before the UFH and if not we put boiler on advance.
    Hopefully something her may be of use to you in your project.
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 23rd 2024
     
    Maybe missed the boat on this one, but as PiH suggests...

    1. add a temp stat on the TS, in the lower part of the the TS, where the UFH water usage should be located. This is wares in series with the room stats switched live feed to the circ pump. This stat would open on fall (close on rise).
    2. the UFH installer should have something similar in the design as an over temp protection. It is a failsafe stat, attached to the hot UFH manifold, which is in series with the UFH circ pump, and will open, stopping the circ pump, if the inlet temp to the UFH manifold rises about the sest point. This is to protect against the TMV on the manifold failing, and letting thru very hot water. It's part of the building reg's guidance, which installers often miss.
    3. you just need to add the TS stat to limit the UFH permission, as in point 1 above, in series along with point 2.

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