Wet standpipe and Dry standpipe together?

[orator]

Hello everyone! I have designed a Fire protection system for a 5 storey building which is fully sprinklered and also have wet standpipe system (Combined system). The building has got 5 staircases which are all provided with vertical standpipe risers to serve one hose valve at each floor. Also 3 main fire water risers supply fire hose valves (fire hose cabinets) on each floor as per coverage requirements. Total system demand is found to be 1750gpm with 205 psi following NFPA14-7.10.1.2.2 & 7.8 (2010 edition). My sprinkler demand ( 620gpm @ 150psi) is much less than standpipe demand that's why I am considering Standpipe demand as my design basis. Now my question is Can I have 2 standpipe risers to be DRY type. This is actually the requirement from end-user. I don't know how we can combine wet and dry standpipes in same building. Please help.

 

[3cio]

As per NFPA-14 (2010 ed.) clause 5.1.2, The AHJ shall be consulted regarding the required type of system, class of system, and special requirements.

Further, please check your calculation for the standpipe.

As per NFPA-14 (2010 ed.) - clause 7.10.1.1.5 - the maximum flowrate shall be 1000 gpm (3785 lpm) for buildings that are sprinklered throughout, in accordance with NFPA-13, and 1250 gpm (4731 lpm) for buildings that are not sprinklered throughout, in accordance with NFPA-13.

 

[PEDARRIN2]

If you are 5 storeys, you might be considered a high rise building (>70 feet from fire fighter access) and some building codes will not let you have a dry standpipe in a high rise.

 

[GeorgeMech]

NFPA 101 states that if the habitable height is more than 23m (High Rise Building), automatic wet standpipe shall be used and as per above post, you have to check again your calculation on how did you arrived in 1750 gpm demand, in your case you need only 1000 gpm since you also have sprinkler protection.

 

[orator]

Thanks guys for responding.
3cio & GeorgeMech , I got 1750gpm based on section 7.10.1.2.2 of NFPA 14 (2010). I have 5 staircase risers and 3 separate sprinkler system risers (also providing connection to hose cabinets). Now following 7.10.1.2.2, 750 gpm will be for 2 hose connections on most remote staircase riser and 250 gpm for each of the other 4 staircase risers. Thus getting 750 + (250*4) = 1750gpm. Please let me know if there is any maximum flow restriction on this.

 

[zubinsha]

Hi Orator ,

From NFPA 14

7.10.1.1* Minimum Flow Rate.
7.10.1.1.1 For Class I and Class III systems, the minimum flow rate for the hydraulically most
remote standpipe shall be 500 gpm (1893 L/min), and the calculation procedure shall be in
accordance with 7.10.1.2.
7.10.1.1.2* Where a horizontal standpipe on a Class I and Class III system supplies three or
more hose connections on any floor, the minimum flow rate for the hydraulically most
demanding horizontal standpipe shall be 750 gpm (2840 L/min), and the calculation procedure
shall be in accordance with 7.10.1.2.
7.10.1.1.3 [highlight #CC0000]The minimum flow rate for additional standpipes shall be 250 gpm (946 L/min) per
standpipe, with the total not to exceed 1250 gpm (4731 L/min) or 1000 gpm (3785 L/min) for
buildings sprinklered throughout.[/highlight]
7.10.1.1.4 Flow rates for combined systems shall be in accordance with 7.10.1.3.
7.10.1.1.4.1 When the floor area exceeds 80,000 ft2 (7432 m2), the second most remote
standpipe shall be designed to accommodate 500 gpm (1893 L/min).

So the Maximum pump capacity required is 1250 or 1000GPM as per NFPA .I don't know how you arrived in 1750 GPM..

 

[orator]

Hi Zubinsha, What you are saying is ok but please check NFPA 14 (2010) section 7.10.1.2.2 "Where a horizontal standpipe on a Class I and Class III system supplies three or more hose connections on any floor, hydraulic calculations and pipe sizes for each standpipe shall be based on providing 250 gpm (946 L/min) at the three hydraulically most remote hose connections on the standpipe and at the topmost outlet of each of the other standpipes at the minimum residual pressure required by Section 7.8".
This section contradicts with NFPA 14 (2010)section 7.10.1.1.5 The maximum flow rate shall be 1000 gpm (3785 L/min) for buildings that are sprinklered throughout, in accordance with NFPA13, Standard for the Installation of Sprinkler Systems, and 1250 gpm (4731 L/min) for buildings that are not sprinklered throughout, in accordance with NFPA 13.[/b]
I am following section 7.10.1.2.2 and that is how I am getting 1750gpm.