Automatic Fill Valves for Sprinkler Tanks

[SprinklerDesigner2]

I have a cold storage warehouse with a double interlocked preaction system where I plan to use a water storage tank and fire pump. Pump will be rated at 1,500 or2,000 gpm.

Flow test results of the city watermain show 68 psi static, 42 psi residual @ 993 gpm. 20 psi @1,400 gpm.

500gpm hose stream demand will be from city hydrants.

Storage is a Class II commodity consisting of nonencapsulated frozen chicken in multiple row racks per Figure 21.4.1.2(b) which requires a density of .55/2,600 after applying Figure 21.4.1.4.1.

Theoretically the minimum discharge is 0.546x2,600=1,419.6 gpm but my preliminary calculations indicate I will need 1,850 gpm.

There will not be any hydrants downstream the fire pump and tank.... hose stream demand of 500 gpm will be obtained from the city water main.

For a 2 hour supply it appears I will need a stored water tank having 120*1,850=222,000 gallons.

What a difference multiple row racks make!

Anyway, I have calculations that show if I install a 6" fill line with an automatic fill valve https://www.watts.com/dfsmedia/0533dbba17714b1ab581ab07a4cbb521/17388-source/es-acv-f100-f1100-pdf I shouldn't have a problem automatically filling the tank at 800 gpm given the city water supply we have. The fill valves are not UL:/FM nor do they have to be since they are not directly supplying the sprinklers.

In two hours we could replace 800*120=96,000 gallons which would lower my tank size to 126,000 gallons saving a bit of money.

Let's face it, installing tanks isn't something we do every day and I seem to remember the last one I did was an FM job and FM would allow the fill valve only if TWO (2) fill valves were used. It was some time ago so it could have changed.

Why the 1,500 gpm pump? I am giving the owner the option, which is his choice, to limit the height of storage to 20'-0" because it is surprising the extra water required that 2'-0" will require with multiple row racks. With 20' high storage the design is .42/2,600 which my preliminary calculations indicate I will been 1,400 gpm which , with the full valve at 800 gpm, would reduce the tank size to 96,000 gallons.

Overhead sprinkler pipe size is crazy. I am going to go with three systems covering 48,000 sq ft just to make sure I can meet the 60 second trip time.

Anyone have any input it would be most appreciated.

 

[UFT12]

If you re planing to use your tank as a break tank (< 100 % capacity), then the way I see it, your fill valves do supply your sprinklers directly.

Also, I wouldn’t use the criterion of 48,000 ft², rather the 750-gallon limit (with accelerator) in this case, since we are talking about dry systems. Unless you have software to calculate trip times or are 100% confident from experience, keeping the volume under 750 gallons will save you the headaches.

 

[SprinklerDesigner2]

To be clear the tank is the sole supply to the fire sprinklers. And yes, the fill valves do supply the sprinklers but I do not believe the fill valves are required to be UL/FM approved. So far I haven't seen one that is UL/FM.

The 48,000 sq ft will have three systems each covering approximately 16,000 sq ft. The capacity of each system ends up around 1,200 gallons and in my 50 years of experience I have never had an issue with a system of 1,200 gallons where we have a water pressure of 140 psi @ 1,500 gpm. No calculations just my personal experience.

 

[TravisMack]

SD2 - How have you been? Been a long time since we've talked. I hope you are doing well.

I just did the prep for a webinar on sizing break tanks. You have to check for multiple points before you are good.

1 - Do the makeup. You have done that. It is total demand - refill rate. That is minimum sizing. You came up with 126k gallons.
2 - You want to make sure that you are storing at least 30 minutes of demand. If not, you are basically using the break tank as a backflow preventer and nothing else. That would be a min of 55.5k gallons. Your value in #1 meets that.
3 - You need to make sure you have at least 15 minutes of 150% of rated capacity. This is 33,750 gal assuming a 1500 gpm pump. Again, you are well beyond that.
4 - Lastly, you have to make sure you meet the refill rate requirement. Rr ≥ 1.1 (Td - Tc)/d. This is where you fail at 126k gallons.

Based on your numbers:
Total demand of 222000 gallons and a refill rate of 800 gpm, you are doing to need to store 134,727 gallons of usable water. I can't remember if you are an autosprink user. But if you are, reach out to me at MEPCAD and I'll get you my breakdown of this. We will be doing a webinar later in the year that goes over all of this.

Essentially, it's because of the metric in NFPA 22 that requires for break tanks, the refill rate must be 1.1 x (Td - Tc)/d
Td = Total Demand (222k gallons)
Tc = 126k gallons based on your numbers above
d = duration

To meet that refill rate, you must have ±880 gpm for a refill rate with the 126k gal tank. You state you can only get 800 gpm. Therefore, you need to rearrange that equation to solve for minimum tank capacity. That is where I got to 134,727 gallons. Again, that is usable water. Remember that with your pump, you must have net positive suction head while delivering your total demand. After that you can go to -3 psi. We also recently did a webinar on determining the water supply values when using a tank as your water source with a fire pump. Again, if you are an autosprink user, you will want to log into our training library and look this up. It will be a great value to you.

I hope this helps you with what you are trying to accomplish.