How to Approach Heat Loss for Sprinkler Pipe?

10/14/2020

NFPA 13 states the following:

8.16.4.1.5 Water-filled piping shall be permitted to be installed in areas where the temperature is less than 40 deg F when heat loss calculations performed by a professional engineer verify that the system will not freeze.

For some reason I had always thought that Tyco or some other heat trace provider had a program available to perform these calculations. I feel there is a better way than breaking out my old heat transfer book. Our general consensus is that the risk is relatively high with these types of calculations.

I’m sure you been tasked with this before; what is the best approach to going about these calculations?

Some owners require these calculations to be performed to avoid dry-pipe systems in Florida, even though the location of the iso-thermal line would require dry-pipe systems - I feel this essentially puts all the liability on the engineer.

I'd be curious to see how others would normally approach this. In this case we would look to run calculations to justify that a wet-pipe system would be sufficient without any insulation or heat trace. Thanks in advance.

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5 Comments

FIREPE25

10/14/2020 10:15:56 am

Do not put in a space that would be subject to freezing. If there are concerns install a dry system. Working in New England anything that is outside the heated envelope is assumed to have freeze issues.

Nolan Baker

10/14/2020 10:21:34 am

1. Determine R-Values of wall, door, ceiling, etc.
2. Assumed temperature of occupied spaces.
3. Perform heat gain calculation: Q=U x A x TD (wall)
4. Perform #3 calculation for wall.
5. Perform #3 calculation for door.
6. Perform #3 calculation for ceiling/roof
7. Determine Qtotal. If Qtotal is a positive number (gain) in BTUH, then the area will maintain a minimum of 40F.

Brian Gerdwagen FPE

10/14/2020 10:24:18 am

Get with your Mechanical Engineer, if you have one on the project. Look for the 99.6% Low temperature and use that as a guide. If the piping is installed in an unheated attic and the 99.6% is 39.9F, you are probably fine.

If you are putting things outside, you probably need to look at the age of other items on the exterior of other buildings. In Los Angeles, we never balked at putting risers on the outside of a building as long as they were tamper resistant. In Florida, you need to be aware of the area. If the only devices you see are new, they either haven't frozen yet, or were replaced after a freeze. If you see aboveground exterior piping with old FDC's and OS&Y's, you are also probably fine.

Felipe Pedraza

10/14/2020 11:51:44 am

This is a very fine line that we are looking into here in deep South Texas with little to no freezing periods that may occur in the year. After dealing with the different code requirement's for 10 years in he prevention office and understand the important and heard jobs that the engineers have in determining the correct numbers for everything that gets done. We also understand the price difference from a wet and dry system and depending on size and number of system it can make a big difference on the price. Perhaps the biggest issue that I see right now is:
1. Where is this system to be installed?
2. How long will the temperature be below 40 degrees which eventually lowers the water temperature in a pipe and will lead to freezing sooner, such as having the system in open loading dock?
4. If it is in cold storage facility, does the facility have the capabilities to bring the temperature below or close to freezing?
5. Will a system be install in an attic if so, what type of heat trace will be used and also the type of insulation?
6. Will the system be up-rights or pendant's?

These area some of the question I would ask the designers and especially the owner. I know what NFPA 13 says on the matter and this are only minimum requirements. Do talk to the local AHJ as well since they may require a dry system to be install.

David Castillo

10/14/2020 04:14:36 pm

I would suggest getting with a Mechanical (HVAC) Engineer to have the analysis done. A good HVAC engineer will use ASHRAE data files and a good heat loss/gain program that will do an hourly analysis to determine if freeze protection is required.

How to Approach Heat Loss for Sprinkler Pipe?

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