Where to position a non-return valve in C/H system

[GoferBlue1947]

I would be grateful for some advice regarding the installation of a non-return valve (NRV).

I have a thermal store (TS) with three coils and which is essentially being used as a buffer tank (boiler is wood pellet fired) in that one coil is used for the boiler flow, the second is used for the C/H and the third is for input from the solar thermal system i.e. all indirect. This setup is working pretty well except that I have a problem with thermosyphoning. When the C/H is off, C/H pipework (on the flow side) is wicking heat away from the TS. The C/H pump is in the return pipe but I need to put a spring NRV in the flow to stop the thermosyphoning.

Two questions: (a) can I put the NRV in a horizontal part of the C/H flow pipe (the vertical pipework is inaccessible) and (b) do I have to move the C/H pump from the return pipe into the flow pipe?

 

[roasty]

I have a similar (albeit even more complicated) setup.
Be careful of non-return valves, they can be troublesome, and in my experience, only the flapper type (that will only go in the vertical pipework) are of any longterm use in a heating system... (the spring based ones seem to get gunked up)

Google anti thermo-syphon loop, it's much more elegant solution, and the one I ended up using for my fiendishly complex setup at home!

Cheers
Dan

 

[GoferBlue1947]

Dan - thanks for your response. What size loop did you put in your system? I have space for about a 40cm drop from where the C/H flow pipe exits the thermal store - is that sufficient? I guess I could put an NRV in the vertical drop as a belt & braces approach.

 

[GoferBlue1947]

Just wondering what is the "take home" message here - 92 views to the thread but only one reply? Is it a difficult issue or is the answer so obvious that I should not have been so naive to even ask? Not being provocative, just curious. I always appreciate advice given on this forum.

 

[roasty]

the anti thermosyphon loop i have is about 1.5m, but thats the space I had available. Also mine is in the return leg, not the flow.
I suspect it would work with far less, certainly the entire thing doesn't get warm. If you imagine that it looks like a 'n' with the two legs 1.5 (ish) metres long, the entire upwards bit can get warm, but only maybe 15cm or so of the downward bit gets warm. As you say though, you could include a non-return in the loop bit also, which could be one of the more reliable flapper types. I think that's what I'd do, but the loop really does work on it's own, I just can't comment on how high it needs to be, other than in 28mm pipe (if that's applicable) mine works fine at 1.5metres.

Good luck.
Cheers
Dan

 

[GoferBlue1947]

Dan - just to let you know that the loop idea combined with the NRV have worked a treat! The loop is about 300mm as that's all the space I have. However mine looks like an upside-down "n" (i.e. a "u") - I thought the loop would have to be that way because the cooler water, being denser, would form a "plug" at the base of the loop?

 

[roasty]

Glad to hear it! Regarding the u or n shaped loop, my understanding is that it matters not. Essentially, as long as there is a downward section then the hot water can't circulate due to gravity. i.e the hot water (being less dense) rises up, but cannot get down the downward section.