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

[Bill Loesch]

Hi Fellow Thermal Wrenches (seated in the back of this Solar PV Bus),

It doesn't even have to be "Energy Smart". Once the limit switch (on every
electric water heater that I have ever seen or serviced) trips, the
corresponding element is deenergized until _manually_ reset. Not a big deal.
You tell the customer about the situation when you install. Unfortunately,
they forget. There is no hot water one day in the early fall. They call. You
explain again. They remember this time, especially when you tell them they
can save the cost of a service call if they are willing to turn off the 240
volt power to the elements, remove the cover plate, push the red button
until it clicks, reassemble, and remember to do the same thing again next
fall when there is no hot water.

This user intervention eliminates the second mixing valve (and any
associated maintenance issues).

The ultimate in control simplicity is Bob-O's technique of a caution label
at the faucet of "Solar Heated Water". This technique alone; however, does
cross more than one Code line.

Bill Loesch
Solar 1 - Saint Louis Solar



----- Original Message ----- 
From: "Travis Creswell" <tcreswell at ozarkenergyservices.com>
To: <RE-wrenches at topica.com>
Sent: Saturday, May 10, 2008 5:09 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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