Will a thermostatic shower mixer work with two hot supplies?

[justcarter]

I won't go into the specifics here because it'd be far too long, but in a system I'm building I have two hot supplies - one between 25C and 35C, and one between 45C and 70C. (In short, I have two heat sources that perform differently under different conditions).

I want an output temperature of 40C, and to mix no additional cold into the system. Will a thermostatic shower mixer do this? The engineer in me says 'yes, the wax will still expand and contract according to the overall temperature', and the plumber in me says 'bUt ThAt'S NoT WhAt It'S DEsiGnEd FoR!!?'

If it won't, has anyone got any smart ideas on how to do this?

 

[steadyon]

1. As an example, the Pegler TMV won't do it. It requires a maximum cold temperature of (from memory) around 20 degrees.
2. You could look at a thermostatic shower mixer valve, but I suspect they will have similar issues, as they have to have a set temperature differential. I suspect 35 / 45 is too close.
3. Depending on your application you might try two motorised valves with a pipe thermostat on each of the input pipes. Probably only do for relatively high flows and probably not very sensitive.

 

[Brambles]

For blending hot water from ground source with gas we do it by pre blending the hot to 48 degrees. You need an electronic valve (wax operated valves don’t work on cooler flows above 25degrees) They are not cheap - £250 for a Chinese version or £1k for a bespoke European valve - Legiomix and the like