[RE-wrenches] SWH - mixing valves

Doug Wells dwells at thesolarspecialists.com
Wed May 19 06:48:58 PDT 2010


Kelly,

I have also seen mixing valves get leaky over time.  Many mixing  
valves are designed for controlled input from a boiler at steady 140  
degree temps.  It is not uncommon for SHW tanks to reach 180+ degrees  
in certain conditions.  If exposed to these higher temps the valves  
can begin to loose accuracy.  Usually they are designed to "fault"  
into the cold position, so the begin to leak in a little cold and the  
client will complain about low temps at the faucet/shower.

Doug Wells
The Solar Specialists
Morrisville, VT 05661
(p) 802-223-7014
(c) 802-498-5856
www.thesolarspecialists.com

On May 19, 2010, at 2:14 AM, Kelly Keilwitz, Whidbey Sun & Wind wrote:

> 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
>
>
>
>
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