22 Jan 09 7:49
I am reviewing Hydraulic Calculations for a wet type fire sprinkler system to be installed in an existing building. The new sprinkler system will connect to an existing fire pump fed by a 25,000 gallon underground water storage tank (the tank is dedicated to fire protection).
From the hydraulic calculations, it appears that the designer is using a minimum pressure of 14 psig at the sprinkler heads located in the Hydraulic remote zone.
I though that NFPA required a minimum fire sprinkler pressure of 7 psig at the sprinkler head. I do not own a copy of NFPA.
Our agencies fire suppression specifications require a 10% safety margin for pressure. The hydraulic calculations are based on connecting to the existing fire pump. Using the performance characteristics of the existing fire pump and a minimum sprinkler head pressure of 14 psig, a safety margin for pressure of only 5% is achieved (per the submitted calculations). The safety margin is calculated back at the pump discharge point. In other words, if the pressure at the sprinkler head is set at a minimum 14 psig (lets call it the required residual pressure), what pressure must be available at the pump discharge point (+10%) to achieve this, taking into consideration friction losses between the two points.
The calculations show that a new pump or new larger diameter piping from the pump to the new sprinkler system would have to be installed (or both). This is cost prohibitive, considering built out nature of the surrounding building.
Is 7 psig at the sprinkler head the NFPA minimum pressure?
Sorry for the long winded question. This is my first post and I often see responses that start with "you need to provide more information"!