Fire Pump High Rise 4

[interlogicapanama]

Our company is in design process of a combined sprinkler standpipe system for a 23 story high rise hotel new construction. 3 meters between floors with the pumps located at the 5th floor above grade.

I would prefer a two zone system NFPA 14 Fig A 7.1 (b) with two pumps. The Law here in Republic of Panama specifies we use NFPA 13-2002 Edition. Is it possible to use a one pump single zone system. We intend to use CPVC (Light Hazard) for teh branch lines so keeping the pressures well below 175 psi is important.

Any input would be appreciated

Thanks,

Alan

 

[TravisMack]

You should look at a variable speed controller pump. If I understand correctly, it will have an essentially flat curve from churn to rating.

Just install PRV hose valve and control valves for your floors and you may be able to use a single standpipe zone. Remember, with the PRVs, you will need a 3" drain riser for testing.

Just be sure that you keep your pressures under 350 psi at any point in the system, and under 175 for the system side of the fire sprinkler system if you are using CPVC.

Travis Mack
MFP Design, LLC

 

[interlogicapanama]

Hi Travis,

Thank you for your reply. Hydraulically Calculated Demand Flow at inflow node is 147 psi/648 gpm. (1350 sq.ft Light Hazard coverage plus 500gpm hose stream allowance) We intend to use an Armstrong 5 x 4 x 11.5FM 500 gpm, which actually has 50% above rated capability giving 750 gpm capacity. We are using Victaulic 747 Riser Manifold Assemblies which can tie in with the 3 inch drain similar to NFPA 14-2007 A.6.5.(a) or (b). I´m attracted to the two zone system as the max static pressure in most can be kept less than 175 psi. Naturally being a high rise this is a Class 111 so that´s a consideration also

The pump performance curve (relatively flat)shows 161 psi max @ 104 HP/3560 RPM would we still need PRV´s or am I missing something. I´m a pretty well rounded Systems Designer but don´t pretend to know everything (or even close) by the way. Any input is very much appreciated

Many thanks and best regards

 

[firepe]

Just a couple of thoughts related to your previous posts.

This is a high rise hotel. Have you considered utilizing residential heads? I am assuming your current design does not since you stated an area/density design.

Your stated design demand is "1350 sq.ft Light Hazard coverage plus 500gpm hose". Just curious how you came up with 1350-gpm for a light hazard system? And 100-gpm hose is the NFPA 13 requirement for Light hazard, not 500-gpm. Even if you had some lundry or storage areas, these would be at most Ordinary Hazard Group 2, which only requires 250-gpm hose.

Using residential heads would limit your design demands to just the 4 most demanding residential sprinklers, with NO hose allowance.

Also, you are planning on a 500-gpm pump and designing to 130% pump capacity, based on your stated demands. Why not go with a 750-gpm pump instead (assuming your stated demand is correct). This would put you demand under the flatter portion of the 750-gpm pump curve.

Now is the time to get the pump size correct. The price difference from 500 to 750 is minimal as is the installation cost, so choose wisely.

And finally, since this is a high rise, a manual wet standpipe system is not possible, so you will need to support the full standpipe demand from the fire pump as well. How many stairwells are there? if there are 2, then your standpipe demand is 750-gpm (which would be 150% pump capacity for a 500-gpm pump) If you have more than 2 stairwells, then your demand will be 1000-gpm for a fully sprinklered building, and the 500-gpm pump you are suggesting is too small.

Just my two cents.

 

[TravisMack]

I think the design area is 1350 sq ft, not the demand of 1350 gpm.

You also design these as separate calculations because they are separate systems. You would design the sprinkler system with 100 gpm hose allowance and calculate it through the pump. The 100 gpm hose allowance it typically added at the standpipe valve for that floor. You are likely looking at a maximum of 250 gpm, including hose, for the residential sprinkler system. This could also be reduced using residential sprinklers as stated above.

You will also calculate and size the standpipe system. This is actually done before the sprinkler system calcs. Calc the standpipes to provide 100 psi at the top outlet at flows per NFPA 14.

As far as your pump churn of 161psi, you need to add that to your city static pressure if you are connecting to a city main. If your city supply has a static pressure of greater than 14 psi, you are going to be looking at PRVs.

I would definitely look at going with a 750 gpm pump if you have 2 stairwells. You should also check the insurance requirements. Many insurers want you to use a pump that is 90-120% of system demand. Therefore, your 500 gpm pump would not meet this.

Good luck.

Travis Mack
MFP Design, LLC

 

[interlogicapanama]

Hi FPE,

Many thanks,

We intend using Victaulic Residential or Quick Response Heads.

The 1350 sq.ft.(not gpm) we derived from 6 flowing sprinklers at 225 sq.ft coverage for typical fire control Light Hazard. This mainly comes from our Elite Software program. We elected a Class 111 Hose system which is common in high rise applications rather than the Light Hazard Demand of 100 gpm.

Interesting and thanks for putting me on the right track for the 500 gpm, this would have been derived from 2 x 250 gpm for two staircases. Now having said that Panama only recently adopted NFPA 13-2002 and NFPA 101-2003. So not many here are even slightly familiar with these publications. In this instance the architects had designed the building with only one staircase as a means of egress. Naturally I advised that doesn´t comply with 101 on two counts Chapter 7 and Chapter 28. I doubt if the Architects intend to make any changes as it had already been signed off by the AHJ at that time. They could have some problems down the road.

I spoke with the tech folks at Armstrong and the pump specified would be adequate, naturally I´m a bit like you and see no practical reason engineering wise not to go with a 750 gpm. And you are right, I never thought of it but demand under the flatter curve so much the better.

The standpipe system will be Class 111 Semi Automatic. Not having much to work with in other areas I prefer the two zone combined sprinkler standpipe system and two pumps as opposed to single zone one pump.

Many thanks for your kind response

Alan