Fire Pump sizing 1

[Vusal Quliyev]

Dear Experts,
There is confusing topic about NFPA 14 and NFPA 20 to discuss with you:
If we have Fire Pump serving to header and this header serves to Class I stand pipe system, Class II stand Pipe System and Sprinkler system. (3 pipe coming from pump room). Can we consider this system as combined system or not? (I need to know if we can omit the GPM coming from sprinkler system as stated - 7.10.1.3.1.2 A separate sprinkler demand shall not be required.)

If not, how should we calculate total required Fire Pump GPM? Is it right to calculate like: 500 GPM (from Class I - 14:7.10.1.1.1) + 100 GPM from (Class II - 14:7.10.2.1.1) + Sprinkler Flow Rate (hydraulic calculation)

Your opinion is important.

 

[UFT12]

Are your 3 risers equipped with separate control valves and alarms with no other interconnection? If so, your system is not combined. See NFPA 14, 3.3.17.3. In this case you will need to size your pump based on the maximum of the two systems flow and assuming sprinkler coverage in the building throughout (omissions of areas per NFPA 13 are allowed without affecting the meaning "throughout"). Caution, the total sprinkler demand has to include the hose demand per 13. Last, AHJs or insurers may request otherwise.

 

[Vusal Quliyev]

Dear UFT12,
Thanks for your help.
Based on your comment I am trying to calculate GPM using two method 1. sprinkler system demand (+ hose stream allowance) and 2. stand pipe system demand and then as stated (14:7.10.1.3.1.1) i need to get greater value from this two results.

Nothing confusing with method 1. - Sprinkler system demand is all clear (Based on the NFPA 13 Table 11.2.3.1.2).

What about 2. method - Stand Pipe system demand method???:
We have 3 seperate stand pipe:
- Class I
- Class II
- and last one serving sprinklers
Is it right to calculate like??: 500 GPM + 100 GPM + Sprinkler Demand (Calculated from NFPA 13)? Should I include sprinkler demand which calculated based on the NFPA 13 (Without hose stream allowance)?
What do you think?

 

[UFT12]

Method 2.

A class II system will always give you a lesser demand than Class I. Typically, the system will be either used by Firefighters or trained people, not both so stick with Class I unless there is an ordinance or similar madated by your jurisdiction to inlcude both.

Demand 1: Class I SP demand is 500 gpm,
Demand 2: Sprinkler calculation demand is X gpm, add hose allowance

Size the pump that can serve both demand points with their corresponding pressures, not simultaneously.