Wet Pipe or Dry Pipe Sprinkler System

[Vo_Dich]

I'm struggling to figure out if I can use a wet pipe sprinkler system for projects throughout California. Most of my projects are either single story commercial buildings or low-rise residential buildings with sloped roof, wood framed, and the insulation is at the ceiling. So any piping in the attic above the insulation has the potential to freeze or the attic space cannot be maintained above 40 deg F.

Per NFPA (2016) 8.16.4.1.1 Where any portion of a system is subject to freezing and the temperatures cannot be reliably maintained at or above 40 deg F, the system shall be installed as a dry pipe or preaction system. Which temperature do you gurus use to determine if you are above or below 40 deg F? It seems that most (if not all) cities in California I have looked at either in ASHRAE Handbooks, design winter dry bulb temperature either in EnergyPro or Trane Trace 700, the temperatures are all below 40 deg F. I have looked at weather.com, they list Average Low and Record Low for different cities. So which do you guys use? Does NFPA mention which to use?

NFPA mentions that you can put insulation covering over the sprinkler piping, but there are places where this can't be done, such as sprinkler heads in the attic, or sprinkler heads for the large overhang or patio area. Does NFPA allow pipe insulation? Mention of "insulation covering" and "tenting insulation" in NFPA leads me to thinking that this is not the same as pipe insulation.

Thanks in advance.

 

[stookeyfpe]

In my jurisdiction we use n=50 year Extreme Annual Data Condition from the ASHRAE Fundamental Handbook as a basis for design. I'm located in Austin and we annually have temperatures < 32F. NFPA 13 is silent on how one makes the determination. This a discussion you should have with the owner and the AHJ.

Sprinkler piping is commonly insulated in my jurisdiction. We use the insulation criterion in the International Plumbing Code as a basis for compliance. When CPVC pipe is employed the chemical compatibility of insulation in contact with the pipe and fittings must be verified.

 

[Vo_Dich]

Thanks stookeyfpe. I'll checkout the ASHRAE Fundamentals Handbook.

Curious as to what others are using to make this determination. And I wonder if others have a preference between a dry pipe system vs a wet pipe system with heat trace.

 

[MGXFP]

Are there any freezing problems with fire sprinkler insulation? That would only buy time until freezing occurs as the water is typically non circulating. There is no way to add heat to the system outside of an external heat source.

 

[wickedspinz]

I would like to know this as well. I'm surprised there are not more input. Isn't this one of the things you need to determine when designing the sprinkler system?

 

[LCREP]

Ask the local AHJ and see what they want since they are the ones reviewing the plans and know the area. No use spending a lot of time on a wet system and the plans get bounced back to you because they want a dry system a phone call sometimes helps.

 

[TravisMack]

Use the figures in Chap 10 of the 2016 and older additions of NFPA 13. That gives you the isothermal lines. It is based on when "underground" pipe is used above ground in the protection of piping section. That is where NFSA directed me when I was looking at temps we need to figure to calc anti-freeze systems when that was allowed.

If you are inside of the insulated envelope of the building, you can go wet. If you go outside, check the maps for the temps. Here in the SW USA, many of our outside systems are wet. There are some places in higher elevations that we have to do freeze protection. As far as insulation, we have some AHJs that want the pipe insulated when it is outside. The idea is that we get such rare temps of ≤32°F for more than a couple hours that the insulation will buy enough time for it to prevent freezing.

Per NFPA 13, you do wet unless you need a dry for freeze protection. So the starting point is wet. When you are driven to a dry system you have to be very cognizant of water delivery times based on your occupancy.

Travis Mack, SET, CWBSP
MFP Design, LLC

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