Water Heater P&T RV Pressure Setting versus System Design Pressure

[invent11]

Having ordered a 60g Elec. Water Heater for an industrial facility to be installed on a domestic water system, now noticed that WH P&T pressure setting is 150 psig whereas my system design pressure per flow diagram is 100 psig. WH vendor is not ready to change the RV to one w/ 100 psig set pressure. To resolve the issue i am thinking to install one RV on piping right downstream the WH w/ 100 psig set pressure. I am wondering do i need another RV w/ the same 100 psig setting upstream the WH and on cold water supply or the one on hot water line is adequate?
Thank you for your input. Next time i am adding an equipment to any system i check its Flow Diagram/sheet carefully!

 

[PEDARRIN2]

The P/T valve is a fail safe for the water heater if the pressure in the system exceeds 150 psi - so that there will not be a catastrophic event. Your design pressure might be 100 psi, but the actual pressure the system could see in an extreme case could be higher.

Unless there is some component in the system that cannot be exposed to ~150 psig, the 100 psig RV is not required.

 

[BigInch]

It appears that invent11 is saying that the design pressure of the system is 100 psig, but the only RV installed now is set at 150 psig and it is located on the heater. That situation would require at least one RV, set to 100 psig +/-, to be installed somewhere between the high pressure source and the 100 psig design pressure piping. Assuming that the high pressure source is due to overheating of water in the heater and that the pressure reached could exceed the 100 psig piping design pressure (as would be already evident by the 150 psig RV included there now), a 100 psig RV should be installed there. Either reset the 150 to 100 or install another separate RV set to 100.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[PEDARRIN2]

Another thing to be considered.

Depending on what plumbing code you are working with - typically the maximum pressure allowed at a plumbing fixture is ~80 psig.

These are typically placed upstream of any brach to a water heater

With the PRV placed upstream of the water heater, you would have less than 80 psig and would not need another relief valve.