ASHRAE 15 Chiller PRV Capacity
ASHRAE 15 Chiller PRV Capacity
(OP)
I'm working on a chiller installation project. Our client has detailed pressure relief valve records, so we've asked the chiller vendor for their relief valve calculations. They gave some very basic info and deferred to the ASHRAE 15, Section 9.7.5 Equation:
C = f*D*L
Where:
C = Capacity (#/min, air)
f = Refrigerant Factor
D = Vessel Diameter
L = Vessel Length
I'm confused because ASHRAE also says pressure relief has to be in accordance with ASME, since they're pressure vessels, but I can't find any sort of derivation/explanation of where that equation came from. Also, this capacity doesn't have any sort of orifice area or set pressure component...so how exactly is it in accordance with ASME?
Thanks a lot
C = f*D*L
Where:
C = Capacity (#/min, air)
f = Refrigerant Factor
D = Vessel Diameter
L = Vessel Length
I'm confused because ASHRAE also says pressure relief has to be in accordance with ASME, since they're pressure vessels, but I can't find any sort of derivation/explanation of where that equation came from. Also, this capacity doesn't have any sort of orifice area or set pressure component...so how exactly is it in accordance with ASME?
Thanks a lot





RE: ASHRAE 15 Chiller PRV Capacity
Since ASHRAE refrigeration vessels are pressure vessels, built according to ASME Sec VIII, ASHRAE says to apply the ASME Sec VIII overpressure protection rules (relief design constraints). Then, ASHRAE provides guidance for sizing the relief valves on refrigeration machines - this is guidance which is not found in ASME Sec VIII.
Once the required relief capacity is calculated, using the ASHRAE equation, you select a PSV that provides the necessary flow. The PSV manufacturers provide the necessary information regarding the capacity of their valves.
When you understand what I explained above, you'll recognize that the ASHRAE text is not contradictory.
RE: ASHRAE 15 Chiller PRV Capacity
With regards to relief valves, I understand what you've said. At the same, the API 520/521 methodology for sizing a relief valve for a fire scenario, the basis of the ASHRAE equation, is much more detailed. I'm assuming the ASHRAE equation is a simplified version for refrigerants...but no one I can find is aware of where it came from, so I'm curious.
RE: ASHRAE 15 Chiller PRV Capacity
Since ASME doesn't endorse any particular fire heat input methodology, organizations such as API, NFPA and ASHRAE are free to publish their own. There's no necessity for any of these methods to be derived from the others, or in any way related to the others.