For determining the capacity of a water storage tank, is the tank capacity calculated by the max flow extension of a pump curve or by 140% rated capacity? Or could it even be 120% of the pump rated capacity?
Looking for guidance on how the pump size and water storage tank size would be directly related.
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1/20/2023 07:17:39 am
My approach has been to provide 150% of the pump capacity (140% refers to rated head I believe) multiplied by the duration needed as the "Useable" volume. Find the tank size that provides at least that minimum amount.
1/20/2023 08:03:23 am
To add off of Dan, make sure you account for unusable water within the tank and ensure you have enough head to get to the suction side of the pump.
1/20/2023 09:14:25 pm
This is what happens when I start a paragraph and get distracted.
1/20/2023 08:38:02 am
The only ACTUAL requirement from NFPA 22 that relates tank size to fire pump capacity is for a "break tank". In this case, the minimum size for a break tank is 150% of pump capacity for 15-minutes. For anything OTHER than a break tank, the demand is based solely on the demand and duration of the fire suppression system (standpipe or fire sprinkler, whichever is most demanding), independent of the fire pump capacity. While many, like Dan mentioned above, may consider the fire pump size when determining tank size, it is NOT a requirement of NFPA 22 to the best of my knowledge.
1/20/2023 08:51:51 am
It's also a good idea to make sure the tank isn't expected to provide fire flow demand as well, which could be more GPM and duration than the fire sprinkler demand. I have had an AHJ take a tank from something like 15k gallons to 80k gallons on a small light hazard building all because of fire flow. That's assuming the tank is feeding hydrants or will have a draft hydrant connected to it.
1/20/2023 10:32:34 am
1/20/2023 09:57:13 am
You need to consider the location of the pump and water tank with respect to hydrants. Sometimes hydrants are not located downstream of the pump/tank assembly. Also you need to consider the max flow of the sprinkler system and the max flow when testing the fire pumps.
1/20/2023 10:49:42 am
tank size is based off the dystem demand times the duration.
1/20/2023 11:18:30 am
For an existing system, take the flow demand of the most demanding area from hydraulic calculations, add the water supply requirement for hoses and multiply by the required duration.
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