NFPA13 Hose Demand with Anti-Freeze System

[ESny]

We have a freezer building with a design operating temperature of 0-degrees F. Because of this, we have a system with 50% Propylene Glycol, which should allow for anti-freeze safety in the building down to a temperature of -26. However, the Propylene Glycol increases the water density (Specific Gravity = 1.041) We also have a 500 gpm hose stream allowance per table 11.2.3.1.2. This hose allowance is approximately 50% of our total required flow rate, including sprinklers. My question is, should sprinkler calculations be done at the higher specific gravity, assuming that everything is happening at once, or can the assumption be made that by the time the fire department responds, and hose demand is needed, that the sprinkler system would be clear from the antifreeze? There is apparently enough pressure from the main to provide for the hose allowance and normal water flow, but the propylene glycol may cause a problem. I'm not the fire sprinkler designer - just trying to wrap my mind around this. Thanks

 

[cdafd]

not a designer or engineer but if the system is over 40 gallons need to do the Darcy-Weisbach calculations. Seems like you have to calc with the anit freeze.

2010 nfpa 13:::


22.4.2.1.3 For antifreeze solutions greater than 40 gal in size, the friction loss shall also be calculated using the Darcy–Weisbach formula:


where:
ΔP = friction loss (psi)
f = friction loss factor from Moody diagram
l = length of pipe or tube (ft)
ρ = density of fluid (lb/ft3)
Q = flow in pipe or tube (gpm)
d = inside diameter of tube (in.)


is this a high piled stock building??? how many sq ft and how high is the storage?? do you know what kind of sprinkler head is to be used?

 

[ESny]

Thanks for the response, cdafd. Yes, it is high-pile storage, up to 20-ft. It's approx. 13,900 (200x69.5) SF in the freezer, and the designer has specified Tyco ELO.231B Pendents, K-11.2. Standard Response. It's a gridded system with 2" branch lines and 6" cross mains.

 

[skdesigner]

NFPA 13-2010 table 11.2.3.1.2 requires a maximum of 500 usgpm total combined inside and outside hose allowance. At the maximum, you only need to calculate 100 gpm inside hose, with 400 usgpm being added at the city connection or a yard hydrant if there is one. 13-10 12.8.4 states "Where inside hose stations are planned or are required, the following shall apply:

(3) The water allowance shall be added in 50 gpm increments beginning at the most remote hose station, with each increment added at the pressure required by the sprinkler system at that design point.

13-10 11.1.4.2 The minimum water demand requirements for a sprinkler system shall be determined by adding the hose stream allowance to the water demand for sprinklers.

Given this, I believe you do need to include the 100 usgpm inside hose allowance in your Darcy-Weisbach calculation.

Have you considered NFPA's sanctions on antifreeze? TIA 10-2 7.6.2.1 limits the concentration of propylene glycol to pre-mixed solutions with a maximum concentration of 38% by volume.

A 50% solution in the sprinkler system you described is A LOT of propylene glycol ($$$). Has the designer considered alternate measures such as a pre-action system, a dry system or - if it's a freezer "box within a box", ESFR dry pendants fed from a wet system in the warm area.

 

[cdafd]

Is this located in the US?

 

[ESny]

Thanks guys,

cdafd, yes, this is located within the US.

Skdesigner, I found a copy of this Tentative Interim Amendment, effective 3-21-11 dealing with Premixed Antifreeze Solution. Am I correct in assuming that this is essentially code for now? This may be the issue, actually, as this would seem to require glycerin for the building's operating temperature, which has a much higher specific gravity than propylene glycol. I don't thin that a dry system will provide adequate response time.. may have to heat-trace.

So I understand that hose allowance has to be calculated in with the demand. My question is though, does everything need to be applied at the same time? Can there be one calculation for the sprinkler system with friction loss due to anti-freeze, and a separate calculation with sprinklers and hose allowance, all with straight city water (no antifreeze)? The rationale being an assumption that the sprinklers will be set off first, and by the time hose demand is required, the antifreeze will be depleted from the sprinkler system? Or, at a minimum, assuming less than 500 gpm total hose demand initially? Is there any case to be made for making that assumption? I deal mostly in structures, and it's rare to have a load case that has 100% of everything applied all at once. Normally when multiple loads are applied, they're factored (reduced from maximum) to account for the unlikelihood that maximum loads of every different type would be applied all at once.

 

[cdafd]

What edition of nfpa 13 do you have to design to?

 

[cdafd]

http://www.nfpa.org/assets/files//NFPA_Safety_Alert_on_Antifreeze_April_2011.pdf

 

[ESny]

It's the 2010 NFPA 13 that we're subject to. Just speaking with the Fire Sprinkler designer, and the issue is the antifreeze concentration (above 38%). Originally a dry system was planned, based on original water main pressure numbers, but the City did some newer testing, and the numbers were significantly lower, and a dry system would require an additional pump, thus they agreed to go with an antifreeze system using Propylene Glycol. I just glanced through the 2013 code, and I don't see any mention of limitation on the concentration of antifreeze in that code. At least not in Chapter 7, where I would think it should be. There is mention of using ESFR heads, but it also doesn't specifically seem to require them either (?). ESFR heads would also be a problem with current available pressure, and require a booster pump.
The only other option is to heat trace the lines and use water, but we're nervous about the heads freezing, as they drop into the freezer box. It seems possible to put antifreeze solution in the 2-ft drops at each head only to help ensure they don't freeze, but then again it's antifreeze which according to the interim amendment is taboo, but according to 2013 code seems ok.

 

[cdafd]

Is this a stand alone freezer/ building
Or freezer in a building
Or freezer as part of the building, like one wall of it??

http://www.nfpa.org/Assets/files/AboutTheCodes/13/TIA13-10-2.pdf

http://www.nfpa.org/Assets/files/AboutTheCodes/13/TIA13-13-1.pdf

Were you going to use food grade anti freeze???

 

[ESny]

Building is a freezer.

 

[stookeyfpe]

Your concept of putting antifreeze into the drop nipples penetrating the freezer box is a violation of NFPA 13. If you were to employ the water-only strategy and rely on heat-tracing and insulation, you would need to use dry pendant sprinklers for such an application.

 

[cdafd]

Sounds like you need a FPE, especially if the designer is not familiar with the latest anti freeze rules and can not give an alternative design.

Normally see double interlock dry system, and may have to add a pump which may be cheaper in the long run, than trying to maintain an anti freeze wet system in a freezer.

 

[cdafd]

Would not even try heat trace and if presented to some ahj's would be turned down

 

[stookeyfpe]

Too bad CDA since Tyco Thermal Products manufacturers a listed heat tracing system for fire protection service and it is allowed by NFPA 13, 2010 edition.

 

[cdafd]

Ok thanks again, did not know someone got some heat trace listed!!!

Guess we do not need to much heat trace in tx most of the time

Still a lot of pipe to heat trace

 

[cdafd]

Interesting

http://www.tycothermalcontrols.com/...s/5373/H58652_Fire_Sprinkler_Reprint_0610.pdf

Seems like in a deep freeze it would be heating 24 hrs a day.

And seems like a big liability if the lines are in the freezer area, if the heat trace fails, or does not keep the pipe from freezing.