I have a job where there are two existing diesel fire pumps that serve an existing warehouse (2 million sq. ft +).
The building is surrounded by an existing 12" underground fire supply loop. The two diesel pumps serve the space.
According to the property manager the system operate as follows:
(1) Pressure is maintained at 160-175 psi.
(2) Below 160 psi the jockey pump turns on to maintain 160-175 psi.
(3) Fire Pump #1 turns on when pressure drops below 150 psi to maintain 175 PSI. (Fire Pump - Static: 165 PSI ; Residual: 134 PSI @ 2000 gpm).
(4) Fire Pump #2 turns on when pressure drops below 140 psi to maintain 175 PSI (Fire Pump - Static: 190 PSI; Residual: 174 PSI @ 2000 gpm).
The pumps are provided by a municipal supply and a back-up private lake dedicated for the fire service.
The pumps are in parallel, so you would add the flows. And to my knowledge the higher pressure would overtake the smaller pressure.
My question is, how do you determine how to calculate the system hydraulically?
If I only use fire pump #1 for water supply, it will not be an accurate representation on how the system operates. In this case it also is very difficult to get the system to work hydraulically off of one fire pump.
I appreciate any input!
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