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. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
14 Comments
Dan Wilder
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.
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Alex
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.
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Dan Wilder
1/20/2023 09:14:25 pm
This is what happens when I start a paragraph and get distracted.
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COLIN LUSHER
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.
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Casey Milhorn
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.
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Pete D.
1/20/2023 10:32:34 am
^ This.
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Glenn Berger
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.
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Sean
1/20/2023 10:49:42 am
tank size is based off the dystem demand times the duration.
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Franck
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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Michael Christensen
4/16/2024 12:09:47 am
I think that it is important to remember why the tank is being used. There are three types of tanks that I typically deal with:
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Miguel Moledo
5/14/2024 03:30:15 pm
This makes sense. But then does the Fire Water Storage Tank have to take account for Fire Flow shown on Table 18.4.4.2.1 of 2024 NFPA 1?
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COLIN LUSHER
5/14/2024 03:52:11 pm
That depends. The water supplies in Chapter 18 are for Fire Department use, so that water would need to be accessible to the Fire Department through a fire hydrant. Is your tank supplying fire department hydrants? If so, then yes, the tank would need to accommodate that. But in most cases, the answer would be no; if your tank isn't supplying fire department hydrants, then you don't need to include fire department demand from Chapter 18 in your tank size calculations.
Michael Christensen
5/14/2024 08:49:39 pm
I think of that table as the amount of water for exterior hoses for the fire department to fight a fire; rather than for a sprinkler system. This is the minimum(s) to build the building. Collin is correct that the table in 18.4.4.2.1 is for fire department and they, at least in the US, will draw the water from and use it in combination with their fire truck to apply the water to the fire. This tank and water volume does not automatically need to have a pump. For example if the municipality (city/town) has a tank on a hill/mountain/elevated it does not need to be pumped from the tank since the elevation (head) could be sufficient. Leave a Reply. |
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