Quote:
Originally Posted by Patrick
The TPV will open and vent the hot water.
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When I checked my PT valve it was seized because I have en expansion tank so it never opens.
But even working TP valve is set @ 210F and 150PSI. Your unit has designed pressure that is printed somewhere. Usually for R22 unit it is in 400psi range. R22 @ 210F will have 600-700psi or even higher (most pt charts are only up to 150F). This is much more than designed pressure.
This unit is meant to be installed on somebody's HWT. They don't know anything about it.
Everything can fail and nobody wants to be responsible for somebody's faults....
Now when you design complete unit from scratch you can add extra safety locks to make sure temperature in HWT NEVER goes above let's say 145F. Is it possible? Yes. This is why complete unit (HWT + refrigeration unit) have "hybrid" mode.
Xringer, if you ever want to add "hybrid" feature to your HWT you can do it but you have to make sure you have extra safety controls. You can add another thermostat or even 2 in series. This thermostat will be set higher than regular but bellow design pressure (just check PT chart). If temperature for whatever reason rises above it's settings it will disconnect or even lock out your elements.
Here is online PT calculator. Very basic but easy.
http://fridgetech.com/calculators/