We have a few different spots where we define a maximum temperature for a water heater, but we don't always consistently specify the same maximum value. Here's where I've seen it in waterheater.rb:
Solar water heater: maximum temperature is 99 C
Heat pump water heater: maximum temperature is 90 C
Gas/Electric storage water heater: Stratified tank maximum temperature is 90 C, Mixed tank maximum temperature is 99 C)
The maximum temperature is there to allow the modeling of a temperature and pressure relief valve (T&P valve). There's no reason to think different valves with different settings are installed on different tanks, so we should be using just one temperature in every spot. AO Smith lists that T&P valves are normally rated for 210 F. Rhem says the same, so 99 C is probably more correct. There's also a max pressure rating, but that's not something we track so we don't have to worry about that.
This is super low priority, but one of those technically correct things we someday should make consistent. I think we've received a test file with a high enough setpoint this might have come into play, but I've never seen it practically be something worth worrying about: if you're tripping the T&P valve you're hitting an unsafe condition. The only time I can think of this maybe happening is if you had a pilot light and a tank sitting idle in a space that's > 150 F (say an unvented attic in southern Texas?). A manufacturer told me they heard of this happening in practice once in that scenario, so it is possible.
We have a few different spots where we define a maximum temperature for a water heater, but we don't always consistently specify the same maximum value. Here's where I've seen it in waterheater.rb:
Solar water heater: maximum temperature is 99 C
Heat pump water heater: maximum temperature is 90 C
Gas/Electric storage water heater: Stratified tank maximum temperature is 90 C, Mixed tank maximum temperature is 99 C)
The maximum temperature is there to allow the modeling of a temperature and pressure relief valve (T&P valve). There's no reason to think different valves with different settings are installed on different tanks, so we should be using just one temperature in every spot. AO Smith lists that T&P valves are normally rated for 210 F. Rhem says the same, so 99 C is probably more correct. There's also a max pressure rating, but that's not something we track so we don't have to worry about that.
This is super low priority, but one of those technically correct things we someday should make consistent. I think we've received a test file with a high enough setpoint this might have come into play, but I've never seen it practically be something worth worrying about: if you're tripping the T&P valve you're hitting an unsafe condition. The only time I can think of this maybe happening is if you had a pilot light and a tank sitting idle in a space that's > 150 F (say an unvented attic in southern Texas?). A manufacturer told me they heard of this happening in practice once in that scenario, so it is possible.