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  1.  
    We have a large open-vented heat store in our loft with 3 spare ports (top, middle, bottom) heated by solar thermal and stove. It seems to work fine. We'd like to combine it with ground floor UFH and first and second floor radiators (see diagram). I'm wondering about the best way to connect and control these different temperature outputs. Would anybody be able to give me any pointers? I'd be very grateful.

    (I also buried some temperature probes in each UFH zone in the screed. I haven't wired these up to see if they work, but I thought it might give us an option.)
      20180327 Central Heating.jpg
    • CommentAuthorTimSmall
    • CommentTimeMar 27th 2018
     
    Just a quick thought - how long can the heat store heat the house for, and does this make it worth implementing?

    I'm guessing you're using this for DHW already? If-so, where does that connect in (and is it using a plate exchanger, or internal finned coil?).
  2.  
    Thanks Tim. The heat store is quite big, around 1,500 litres, so I'd hope it would be okay to heat the house between fires. The SAP calculation suggests that we'd need 2kw to keep the house at 21º when the temperature is -3º, but I suspect this is a bit ambitious. If nothing else, the store would be needed to distribute the heat to the radiators and UFH around the house.

    We're also using the store for the DWH. It has 2 internal finned coils (not shown for simplicity).
    • CommentAuthorTimSmall
    • CommentTimeMar 28th 2018
     
    OK, as a sanity check - if you put this into the Google search bar:

    ( 4,184 joules per (kelvin kg) * 30 kelvin * 1500 kg ) / 2 kW

    it says 1.1 days. i.e. pulling a steady 2 kW out of the store for 1.1 days will drop its temperature by 30 Celsius.

    I assume you'll want to keep a bit of heat in the top for DHW.

    What are the design temperatures for the rads and the UFH?
  3.  
    Posted By: ComeOnPilgrimWe have a large open-vented heat store in our loft with 3 spare ports (top, middle, bottom) heated by solar thermal and stove. It seems to work fine. We'd like to combine it with ground floor UFH and first and second floor radiators

    I would have 3 zones, UFH, first and second floor radiators all taken off the middle port and returned to the bottom port of the heat store. the zones would be each driven by its own pump with a non-return valve to prevent back circuits and each would have a recirculating temperature control valve so that the temp. of the CH water to each zone can be individually controlled and the heat drawn from the store is minimised. After that each zone can (should) have room stats or TRVs to control the temp. of the zone.

    If you take the CH from the top of the store you will compromise the amount of DHW available.

    Don't forger that whilst the calculation by Tim above is valid, by the time you have reduced the store temp by say 25 deg and if it starts at 80 (top to bottom) then you will be down to 55 deg which would be OK for the UFH but a bit low for the rads unless they were designed for this supply temp. and since you are taking the CH from the middle port you will get somewhat less that half a days heating. Or realistically in winter you will get a warm house in the mornings but will probably have to light the stove mid morning or so and make sure you have a full store late evening to carry over to the next morning.

    My heat store is remote from the house (attached boiler house) and I put a couple of adjustable thermostats on the side of the store operating warning lights in the house so that I can monitor the temp. of the store to see when the boiler needs firing without the need to go to the store to check the temps - very useful). If your store is in the loft how will you check the temp. of the store?
    • CommentAuthorArtiglio
    • CommentTimeMar 28th 2018
     
    How far out do you think the heat calcs are? Just to me it looks to be a huge amount of time effort money forva heating system to input such little heat, especially given the n7mber of days it’ll be -3 , i am assuming this is in uk.
    Not criticism , more interested in how the decisions were made.
  4.  
    Posted By: TimSmallWhat are the design temperatures for the rads and the UFH?

    The UFH calculations (specified by the pipe supplier) are: Design Flow Temperature: 45º, 3.5kw.
    I've only bought a few radiators so far, and the specifications are not all consistent, but here is what I've got:
    Bathroom radiator: 666w @ 60º
    Bedroom radiator: 600w @ 70º
    Bathroom radiator: 300w @ 60º
  5.  
    Posted By: Peter_in_HungaryIf you take the CH from the top of the store you will compromise the amount of DHW available.

    Thanks very much Peter! I saw some valve (Esbe?) that can take the water from 3 ports on the store, so might this achieve the same aim? See attached diagram from Akaterm.
      Akvaterm_Geo_Example1.jpg
  6.  
    Posted By: Peter_in_HungaryI would have 3 zones, UFH, first and second floor radiators all taken off the middle port and returned to the bottom port of the heat store. the zones would be each driven by its own pump with a non-return valve to prevent back circuits and each would have a recirculating temperature control valve so that the temp. of the CH water to each zone can be individually controlled and the heat drawn from the store is minimised. After that each zone can (should) have room stats or TRVs to control the temp. of the zone.

    Hi Peter, would you have the pumps at the heat store, or at the manifold on the relevant floor for each zone or both? The UFH has a pump at the manifold, but presumably this is to push the water round the UFH coils, not to draw it from the heat store in the first place?
  7.  
    For convenience I have them at the heat store. It also means that there is minimum hot pipe from the store before mixing down to circuit temperature. The pump(s) push the water around the circuit but also pulls the water through the mixer valve which takes water from the return and the store to maintain the set temperature
    • CommentAuthorTimSmall
    • CommentTimeMar 29th 2018
     
    For the rads, you'll need a heat loss calc for the room, and then ideally size them for the same temp as the UFH.
  8.  
    Posted By: TimSmallFor the rads, you'll need a heat loss calc for the room, and then ideally size them for the same temp as the UFH.

    Hi Tim, I was assuming that we'd normally run the UFH at a very low temperature. If the house needs 2kw at -3° and the floor alone will produce 3.5kw at 45°, then presumably the UFH can run much lower. Wouldn't that be too low for a radiator, unless the radiators were huge?

    Why do the rads need to run at the same low temperature as the UFH? Won't the UFH mix down to a low temperature, even if the supply temp is much higher?
  9.  
    Posted By: Peter_in_HungaryFor convenience I have them at the heat store. It also means that there is minimum hot pipe from the store before mixing down to circuit temperature. The pump(s) push the water around the circuit but also pulls the water through the mixer valve which takes water from the return and the store to maintain the set temperature

    Thanks Peter. So the three ports could be combined through a mixer valve, which then splits into three, each with a pump and valves, which respectively supply the the floors? Do you think it would be possible to achieve the same with a single pump?
  10.  
    I would split the store output into 3 and then have the non-return valve, mixer valve and pump for each circuit. This makes control easier. A single pump could do it but you will still need the non-return valves and mixer valves and in addition you will need 3 motorised valves to control the individual circuits and a set of relays on the electrical side to prevent back circuits between the controls of the 3 electrical circuits operating the one pump.

    By having 3 mixer valves, one on each circuit, you are able to individually adjust the water temp. of each circuit. So the UFH can have a lower temp, the 1st floor rads a higher temp and perhaps the top floor rads a slightly lower temp because as heat rises you might find that on the top floor you can get away with a lower temp which will be more efficient for the heat store.

    All in all IMO it will be simpler and more controllable to have 3 separate circuits rather than having one pump, motorised valves, electrical relays etc. (and probably a bit cheaper to have 3 pumps rather than motorised valves relays etc.),

    As an after thought if the UFH is already at the input of the manifold then it could stay there, just I would put the mixer valve at the store. (if you don't want to disturb that bit).
  11.  
    Thanks Peter! Very insightful. In the meantime I've found a link to a site showing a system that uses a single pump and motorised valves: https://www.underfloorheatingsystems.co.uk/2013/08/14/is-it-possible-to-combine-traditional-radiators-with-underfloor-heating/
  12.  
    A single pump and motorised valves will work - Just personal preference, if it were mine, I would be using 3 pumps to keep the electrical side simpler. (simpler usually means less faults an easier to fix)

    It might be interesting to do the costings of each, although in the scheme of things a few extra quid at installation time doesn't make much difference over the life of the system - providing you have the few extra at the time.
  13.  
    Thanks very much Peter! I've drawn up a revised schematic, with motorised valves for the time being, though it would look very similar with pumps and one-way valves instead. See attached. I forgot that I had put the radiator circuits in a manifold arrangement like the UFH.

    Is there an off-the-shelf system that could manage this, or is it something that I need to make myself?
      20180401 Central Heating.jpg
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