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Heating and cooling: mixing valve position

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  1.  
    • CommentAuthorjohnnyh
    • CommentTimeMar 17th 2017
     
    Hi everyone, i've got a question for you about where best to have a mixing valve. I have a system with wood boiler, thermal store, mixing valve and radiators and the boiler and store and valve are in an adjacent building about 8 metres away from the house with the pipes passing through a timber box channel which is basically outside although under a roof. The pipes are insulated but with the mixing valve generally at about 30 - 40 % open i suppose 60 or 70% of the return from rads is back outside across the 8 metres of "outside" pipework and then through the mixer to come back again accross the 8m external pipework. The question is should i move the mixer inside the house to reduce losses?

    Thanks in advance,

    John.
  2.  
    A difficult one. If you move the valve to the house then you have the hot TS water going to the house and the cooler water going back to the TS. Next to the TS you have cooler supply water going to the house (stepped down by the valve but hotter return water going to the valve by the TS. So in the external pipes you trade a hotter and cooler pipe with the valve by the house for a cooler and a hotter pipe with the valve by the TS.

    Perhaps the greater temperature difference from ambient the greater the heat loss, then maybe the better solution would be to have the lower temperature pipes outside - which would mean having the valve at the TS.
    • CommentAuthorowlman
    • CommentTimeMar 18th 2017
     
    You may be able to use an infinitely variable mixer valve linking flow and return somewhere near the TS.
    The thermostatic sensor controlling this valve, ( wired link required ), would be in the house. This valve then controls the water temp "flowing" into the CH circuit, to meet demand. The "returning" water is re-mixed accordingly, across the flow return link, before being pushed back into the CH circuit. There will be inevitable losses in the connecting pipework, whatever you do.
    Yes it's a mixer valve but unlike the common set temp ones, which you may have??, it's controlled according to demand.
    • CommentAuthorjohnnyh
    • CommentTimeMar 20th 2017
     
    Mine's controlled by its own controller which can do either valve temp or room temp. Owlman, do you mean it could be more efficient with regard to losses if it was on room temp mode?

    I see what you mean about the trade off Peter. Maybe not worth thinkng about moving it then.

    Thanks as always for your input.
    • CommentAuthorowlman
    • CommentTimeMar 20th 2017
     
    Where is your valve controller located ?
    • CommentAuthorjohnnyh
    • CommentTimeMar 21st 2017
     
    Well, the valve controller itself is in the house but there is a temp sensor on the valve output pipe. There is another sensor for the room temp.
    • CommentAuthorowlman
    • CommentTimeMar 21st 2017
     
    Is your valve variable,- motorised?
    • CommentAuthorjohnnyh
    • CommentTimeMar 21st 2017 edited
     
    Yes variable motorised. The valve output sensor is in the shed next to the valve, the room sensor is of course in the house if that makes it clearer. At the moment i work things by valve temp. 30 when mild, 35 when chilly and 40 when cold. Thkis works pretty well on a comfort level even this yeàr which was pretty cold for a few weeks back there.
    • CommentAuthorowlman
    • CommentTimeMar 22nd 2017
     
    It sounds similar to my setup.
    I too have a variable motorised valve, bridging the CH flow and return with it's own pipe temp sensor , but I let my room-stat do the thinking, regarding water temp in the system. Sometimes its barely tepid others hot depending on demand. My modulating pump runs continuously for the whole heating season, so effectively the system is "on" for 5 or 6 months with just water temp varying.
    The roomstat/controller, motorised valve, and pipe sensor are all part of a single designed system.
    In an ideal/perfect system,- not mine I add,- you'd have such a central control and pump on each of your house zones. with no TRVs on the rads and just let individual zone water temp do the rest. That's the beauty of having a large accumulator full of hot water to draw on.

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