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Heating and cooling: Thermal store dhw coil setup

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    Hi everyone,
    Been following with great interest and have learnt a great deal so Thanks for that.
    The setup: Galu 300l solar TS as yet not plumbed in . Store has a preheat coil and a top coil. In the room below a morso db15 boiler stove.What I have in mind is a coil around the stove pipe to act as a preheat to the preheat. It'll get pretty hot if no hot water is used for even a short time . My first question being ,would this coil need it's own expansion vessel ?
    And if I fit a pressure reducing valve in the cold supply where would be a good place to put it . I'm wondering if the first preheat could restrict the flow a little ?
    One last thing ,where would a pressure relief valve be best situated in same circuit.
    Any help would be greatly appreciated.
    Alex.
    • CommentAuthorowlman
    • CommentTimeJul 17th 2016
     
    I'm intrigued by your proposed setup. Are the solar and the boiler stove both heating the store water direct, i.e. is there an interchange of the same circulating water in both systems.
    Or, a: is the boiler stove doing an altogether different job, somewhere else?
    Or, b: are the two heat sources solar and boiler exchanging heat to the store water via the two "separate" coils.

    Or, have I completely misunderstood?
  3.  
    The morso goes direct, the solar via a coil in the bottom half of ts.
    • CommentAuthorJonG
    • CommentTimeJul 17th 2016
     
    Taking heat from the flue can be problematic because if the flue gasses lose their buoyancy in the flue by being cooled too much the flue draught may be compromised, or alternatively they may condense higher in the flue and the resultant fluid will drain back into the stove and corrode it, proceed with caution and only after conversations with the manufacturer of the stove and flue.
    • CommentAuthorGreenfish
    • CommentTimeJul 18th 2016
     
    Do you also have a loading pump for the boiler stove?

    Like JonG said about cooling the flue, you need to consider the cold water effects as well as the water getting too hot. That said I understand the desire to take the heat from the flue when the fire is going well, just may need some control circuits to be successful.
    • CommentAuthorowlman
    • CommentTimeJul 18th 2016
     
    I wouldn't use the flue for preheat as you suggest for the reasons given better to have any residual flue heat as space heating. If you feel you need some pre heat on the rising main you could have a look at trace heating.
  7.  
    The idea was to use the coil externally around the stove pipe not internally, and maybe leaving say a two inch space along its length,that way the pipe retains its heat.

    Stove has a laddomat 20/60.
    My main concern is the expansion in the coil, hence the question about an expansion vessel. I have thought about connecting to the solar coil and connect feed and expansion pipes, but some time later on I'll be connecting solar thermal, so I'd be back to square one !
    What's trace heating ?
    • CommentAuthorJonG
    • CommentTimeJul 19th 2016
     
    Up to 15 litres needs no expansion vessel, provided there is no check valve in the incoming mains. I thought you meant the pipework would be external, but in any event the heat transfer would still cool the flue gases.

    Trace heating is electrical resistive cable which is run along a pipe to heat it to protect against frost, pre-heat it etc.
  9.  
    I'd be happy enough if the cold mains water were brought up to ambient room temperature instead of entering the thermal store cold. I've had to alter the chimney breast directly above the stove due to the stove flue outlet not being far enough back and plan to reline flue with pumice liners so that was to do anyway . So the register plate for the stove pipe is over two metres off the floor ,so there's plenty of space to put a coil without needing to use the stove pipe.
    Given that the mains water passes through two coils in the thermal store ,and a pressure reducing valve sounds advisable ,would an additional coil restrict flow markedly ?
    • CommentAuthorJonG
    • CommentTimeJul 19th 2016
     
    It depends on your incoming main pressure and flow tbh and then you have to consider how much heat it will accumulate and what volume of water will be heated, to assess the sense of doing it.
  11.  
    I suppose to make it worth doing the coil would have to hold enough water for an average shower to make sense of it . so probably impractical.

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