Multi Zone System Requirements 1

[jjm1340]

I have a four story building with residential use on 1 thru 4 and incidental storage in the basement. The system is supply by the local utility. Due to local peculiarities of the water distribution system the city requires a 33% margin on pressure for all systems in the area. I have calculated the basement as a OH1 and the upper stories based on NFPA13R.

The water demand for the basement is based on 1500/0.1. I have no problem supplying the low calculated area with city pressure. But I can only muster a 25% margin for the 4th floor. The city is requiring a pump.

I would like to split the system into a low pressure zone and a hi pressure zone serviced by the pump. Any problems with that?

 

[stookeyfpe]

Off the top of my head, I don't see a problem with this.

Is the jurisdiction amenable to Practical Difficult for a reduction in the 33% design factor? Group R-1 and R-2 occupancies are continuing to have far smaller fire losses given the number of buildings be sprinklered. That's a lot of money for pretty large design factor.

 

[TravisMack]

Just to clarify, if you are doing OH1 for the basement, it is 0.15 / 1500 not 0.1. May just be a typo on your end.

Can you get the head spacing down to 16'x16' for pendents? Maybe even smaller spacing and use the low flow K3.0 heads.

At 16' spacing and using a 4.9k residential sprinkler, you are looking at 7 psi end head pressure. That is flowing +/- 52 gpm through the system. If you added extra heads and went to 12'x12' spacing using 3.0K sprinklers, then you only need +/- 32 gpm total demand and 7 psi end head pressure.

You may be adding more heads this way, but it may be cheaper than a fire pump.

Just some food for thought.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[jjm1340]

It is actually LH 1500/0.1 cause the storage is incidental. But the pump is required for the Residential portion 4th floor due to insufficient 25% margin. The AHJ is not flexible.

So you see no code problems with having two zones in this way. The AHJ is telling me that a single pump for the entire system is the only solution. I can not support that opinion based on the code. I know from past experience that a multi pressure zone system is allowable and quite common for High rise building.

I do not see why I could not use a small 50GPM pump for the High zone and street pressure for the basement.

 

[TravisMack]

I have done things like this in the past on several occasions. Just because a pump is on a site, does not mean that it is req'd on all systems.

Under 13R, you have to use a UL listed fire pump. Can you get one that is only 50 gpm? The smallest I recall using is 300 gpm.

I have seen the scenario you described used to even balance rack systems. The in-rack sprinklers we taken off of the city pressure, and the overhead was from a fire pump. It all balanced and worked fine.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[jjm1340]

Thanks. We'll see what happens. It will not be the first time I propose something "innovative" to this AHJ.

 

[chevy4x4trucks]

If you are going to install a pump wouldn't it be beneficial to utilize it for all areas (reduced pipe sizes)?

 

[jjm1340]

Yes, but I am limited by existing electrical service. Trying to keep HP to lowest possible

 

[chevy4x4trucks]

You should be fine sizing the pump for what you need for your top floor, but still utilizing on the remaining floors. Even if it's a small pump it will still give you a little extra kick.

 

[jjm1340]

Thank You All.