What is the purpose of a fire pump, and how is it sized to meet the demands of a sprinkler system?

The purpose of a fire pump is to provide an adequate and reliable water supply to a fire sprinkler system, ensuring that the system can effectively suppress a fire. Fire pumps are used when the municipal water supply cannot provide sufficient pressure or flow to meet the demands of the sprinkler system. This can occur in tall buildings, large industrial facilities, or areas with low water pressure. A fire pump increases the water pressure and flow to the sprinkler system, ensuring that the sprinklers can discharge the required amount of water to control or extinguish the fire. Fire pumps are sized to meet the specific demands of the sprinkler system. The sizing process involves calculating the required flow rate and pressure based on the size of the building, the occupancy type, and the hazard classification. The flow rate is determined by the number of sprinklers that are expected to operate simultaneously, as well as the required discharge rate per sprinkler. The pressure is determined by the height of the building, the friction losses in the piping system, and the required residual pressure at the sprinklers. The fire pump must be capable of delivering the required flow rate and pressure at the highest sprinkler head in the system. The pump's performance is typically specified at three points: rated flow, 150% of rated flow, and shutoff. The pump must be able to deliver its rated flow at the required pressure, 150% of its rated flow at a reduced pressure, and shut off completely without exceeding a certain pressure limit. Fire pump sizing also considers the water supply characteristics, ensuring that the pump has an adequate source of water to draw from. NFPA 20 provides detailed guidelines for fire pump sizing and installation.