mixing valves on SHW systems with gas backup [RE-wrenches]

[Ken Schaal]

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As we approach the summer season, and overheating of anti-freeze systems, 
it's a good time to remember that drainback designs require nothing but 
gravity to prevent dangerous temperatures that lead to increased callbacks 
and maintenance problems. Not to mention the liability issues of scalding 
water, and the increased corrosion activity in the tank.

Ken Schaal
CommonWealth Solar


----- Original Message ----- 
From: "Travis Creswell" <tcreswell at ozarkenergyservices.com>
To: <RE-wrenches at topica.com>
Sent: Saturday, May 10, 2008 6:09 AM
Subject: RE: mixing valves on SHW systems with gas backup [RE-wrenches]


>
> The same thing can happen on electric water heaters with "Energy Smart"
> controls.
>
> Yes, thermal questions are allowed and I would like to see more.
>
> Travis Creswell
> Ozark Energy Services
>
>
> -----Original Message-----
> From: Karl Schwingel [mailto:karl at northwindrenewable.com]
> Sent: Friday, May 09, 2008 10:00 PM
> To: RE-wrenches at topica.com
> Subject: RE: mixing valves on SHW systems with gas backup [RE-wrenches]
>
>
> Davis,
>
> What I've heard is that you run the risk of tripping the overthermal
> protection in the gas water heater if you should on a hot summer day run 
> 190
> deg water into the bottom of the tank.  Of course you don't realize it 
> till
> months or weeks later when there's no solar preheated water and you get 
> the
> call that "my water heater doesn't work"
>
> I've never put a mixing valve on the preheat tank, and have only seen it
> done when you want to keep the tank at a high temp (such as when you're
> pulling water off for a space heat loop.  However, I'm working mostly 
> around
> electric water heaters.
>
> Is this forum open to thermal questions too? All I've seen so far has been
> PV related.
>
> Karl Schwingel
> Nabcep Certified Thermal Installer
>
> NorthWind Renewable Energy
> Karl at northwindrenewable.com
> PO box 723,
> Stevens Point Wi.
> 54481
> cell: 715 209 0446
>
>
>
>
>
> -----Original Message-----
> From: Davis Terrell [mailto:davis at brightearthsolar.com]
> Sent: Saturday, May 10, 2008 12:28 AM
> To: RE-wrenches
> Subject: mixing valves on SHW systems with gas backup [RE-wrenches]
>
>
> Wrenches,
>
> I have seen some literature call for a mixing valve in between the solar
> storage tank and the gas hot water tank.  Can anyone give some ideas as
> to why this second mixing valve may be necessary?  Does anyone else use
> one?  Thanks.
>
> -- 
> Davis Terrell
> Bright Earth Solar
> (802) 492-2273 / brightearthsolar.com
>
>
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