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?? a combi gas boiler that will take preheated water from a solar thermal buffer tank

  • 05-03-2009 8:33pm
    #1
    Carlow52
    Closed Accounts Posts: 2,389 ✭✭✭


    I gather these are widely used in mainland Europe.
    Some manufactures provide a specific boiler, others provide a solar kit to cater for the preheated water.

    Viessmann dont do one.
    from an email they sent me
    << We do not approve of supplying pre-heated water to our combi boilers.>>


    Thanks


Comments

  • #2
    quentingargan
    Registered Users, Registered Users 2 Posts: 1,627 ✭✭✭quentingargan


    Carlow52 wrote: »
    I gather these are widely used in mainland Europe.
    Some manufactures provide a specific boiler, others provide a solar kit to cater for the preheated water.

    Viessmann dont do one.
    from an email they sent me
    << We do not approve of supplying pre-heated water to our combi boilers.>>


    Thanks

    There are two solutions, depending on whether your combi boiler can take in hot water. Many boilers can take in water up to 55 degrees or so. If that is the case, a three port motorised valve is used on the outlet from your solar cylinder. This is controlled by a stat in the cylinder (which needs to be very close to the top). If the cylinder is above 55 degrees, the motorised valve routes the water directly to the taps. If it is below 55 degrees, it routes the water into the combi boiler.

    If the combi boiler must be fed cold water only (as appears to be the case with your Veissman model), you can use a thermostatic mixing valve on the top of the cylinder, but this is used upside down. You literally screw the cold feed into the top of the cylinder, and the hot feed goes to your combi boiler. If the thermostatic valve is hotter than the set temperature, it won't call for hot water from the combi boiler. I haven't actually done this, but I am assured it works. :)


  • #3
    Carlow52
    Closed Accounts Posts: 2,389 ✭✭✭Carlow52


    I raised the issue with Viessmann overnight and this is the reply, in part.

    <<We do not forbid what you want to do, but if you do it, we would expect the incoming water not to exceed 50oC>>

    which offers the option to use a TMV as described by quentingargan.


  • #4
    quentingargan
    Registered Users, Registered Users 2 Posts: 1,627 ✭✭✭quentingargan


    Carlow52 wrote: »
    I raised the issue with Viessmann overnight and this is the reply, in part.

    <<We do not forbid what you want to do, but if you do it, we would expect the incoming water not to exceed 50oC>>

    which offers the option to use a TMV as described by quentingargan.
    The only concern about this option might be legionnaires. You would need some strategy that sterilised the entire solar cylinder once a week with this system. Q


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