Tire storage area fire sprinkler system 2

[dysung]

This is my first posting on this forum.
I've tried this forum for any postings about how to calculate the water demand for fire sprinkler system but no luck so far.
Here is the situation: I am trying to calculate the water demand for a fire sprinkler system in new transit facility building. The building will be used mainly for tire replacement shop for busses and also there is small machine shop and welding room. I looked up NFPA13 Section7 and there is 3-4 ways to provide fire sprinkler system for tire storage area(since tire storage area has the most water demand, this will yield the required water flow rate).
The first option is using ordinary sprinkler system and it requires 3000gpm!.
The second option is to provide in-rack sprinkler system along normal sprinkler system and it requires 1950gpm.
The third option is using large drop sprinklers and in NFPA13 Table7-6.2.1(b), there is only number of head required with min and max areas of 1200 and 1500SF.
Here is my question. How do i determine the water demand only from number of heads? Does the min and max area means i only have to design the sprinkler system based on those min and max area even though the storage area is larger than 1500SF (actual area is 2200SF).

Thanks for reading..
Dan

 

[apostolka]

First you have to find out piling method and piling height. Based on these information, you define whether you will be using Standard Spray, Large Drop or ESFR sprinklers. Then just follow appropriate table to define density and area of application.
Multiply coverage area per sprinkler, density and number of sprinklers in the area of application. Add cca 10-20% for overdischarge. Finally add inside/outside hose allowance - for this occupancy it is 500gpm. And that is you water demand.
You calculate only sprinklers within your area of application.

 

[dysung]

apostolka,
I really appreciate your response.
I have followed your guide to come up with water demand for the fire sprinkler system described in my previous posting. However i am still not clear on a few things.

Once i decided to go with "large drop sprinkler", i looked up table7-6.2.1(b) in NFPA13.
It says 15 sprinklers @ 75psi with note saying "The design area shall consist of the most hydraulically demanding area of 15 sprinklers, consisting of five sprinklers on each of three branch lines. The design shall include a minimum operating area of 1200SF and a maximum operating area of 1500SF and shall utilize a high temperature-rated sperinklers" There is no mentioning of what area denstity curve i have to look up or what K value i have to use.

I interpreted above note as &quot;i only need to consider between 1200 to 1500SF of operating area and i can choose K value of about 12 <- lower end of K value that constitute as a large drop sprinkler.
By choosing K value of 12 and water pressure of 75psi, i obtained 104gpm by using (P=Q^2/K^2).
104gpm X 15 sprinker = 1560gpm + 20% of over discharge 312gpm + hose demand of 500gpm =>2372gpm
Is this legitimate calculation? Or is there any density curve reading requirement implied in the Table7-6.2.1(b).

This is the first time i ever calculated sprinkler water demand and i swear NFPA is one of the most confusing code to understand or interprete..

If anyone sees any error or misinterpretation of code in my calculation, please be kind to lead me to right direction.

Dan

 

[sia101]

It is best to assume 1500sf to be calculated for ESFR system for estimating purpose. At the same time..., you want to make sure type of storage configuration. If high-piled storage racks are to be used, you must consider the design density based on minimum 2000sf design area,plus 100GPM fire hose allowance for inside and 400GPM for outside hose allowance.

 

[apostolka]

Dysung,
Your calculation is right. Allow me a small correction: k-factor for large drop sprinklers is 11.2.

Deciding on what type of sprinkler you would use depend on, beside the piling method and pile height, some other factors as type of structure, obstructions, arrangement of different occupancies in the same space...
But if you decided to use large drop sprinklers your calcs are correct.

 

[dysung]

Thanks Guys
As long as the method i used to calculate the water demand on above posting is right, I'm good to go.
I chose large drop sprinkler system following the selection criteria on NFPA13 closely, actually been somewhat conservative side.
The actual design of the system will be done by certified sprinkler designer hired by a contractor. Only thing i need is the estimated water demand so that i can determine whether available water main is enough to handle the water demand of sprinkler system and if so sizing it correctly.