Thermostatic Mixing Valve

[RickH]

I have an underfloor heating system fed by a Thermal store.
Temperature is limited by the thermostat on the Thermal Store to 60C
Water is pumped on Return circuit from distribution manifolds for the UFH

To aid in boiler efficiency and solving some other issues, I intend to add a 28mm Thermostatic Mixing valve .... The first picture represents position a 'as is'




The 2nd picture is Option 1 ... preferred as much easier to add to the existing layout, pump position as is, i.e. pumping the return.




The 3rd picture is Option 2 ... moving pumping out the flow of 'mixed water' rather than on return.



Any reason that Opt 1 or 2 should be used .... or perhaps easier Q (for me) any reason I can't use Option 1

 

[Hendog]

Just saw your question as Iv just posted my own and am also struggling for answers.
You have put it very well and your diagrams are lovely and clear, so while I know little to nothing about UFH I have observed that the pumps are always fitted after the mixing valve leading me to assume they work better under negative pressure….I may be wrong or maybe the mixing valves are certain types but I felt your clear and concise post at least deserved an attempt.

Good luck and if it’s already sorted it would be interesting to know the outcome

 

[RickH]

I had confirmation by valve manufacture and UFH company that Opt 2 must be used - you pump out of the valve blended output. Otherwise you can end up impacting the blended flow with water passing across instead of out through the mixing valve blended output.
Opt 1 was what my heating engineer advised, glad I did not follow his advice,