[RE-wrenches] SWH - mixing valves

[Kelly Keilwitz, Whidbey Sun & Wind]

Thermal wrenches,
I'm having an ongoing issue with mixing valves in my own system not  
keeping a steady mix domestic HW temperature as the tank temperature  
varies with solar heating. If I set it for (say) 122˚F mix when the  
tank is 135˚, it seems to hold that differential at all tank temps -  
i.e. when the tank is hotter the mix is too hot (sometimes dangerously  
so), and when colder the mix is too cold for a comfortable shower.  
Thus, I need to change the setting all the time.

I'm now using a Honeywell valve with a 90˚ - 145˚ range. This is a  
replacement for a valve with a wider range that acted the same way.  
Any ideas,  suggestions for better valves, or....?

This has me wondering how many of our SWH customers are experiencing a  
similar thing, but just aren't bothered enough to say anything. We  
seem to have encountered many plumbing situations where the mixing  
valve allowed weird backflow or siphoning situations to mess with  
system operation, especially with HW recirculation. I thought I had  
all such causes eliminated on my system, but maybe not.

Thanks for sharing your experience with such matters.
-Kelly

Kelly Keilwitz, P.E.
Whidbey Sun & Wind
Renewable Energy Systems
kelly at whidbeysunwind.com
360-678-7131