Calculation to Determine if Pipe in Wall Freezes?

12/10/2020

We have a lot line sprinkler installation with sprinkler piping being recessed in a furred out wall. We are concerned about pipe freeze ups.

Since we are connected to the existing system that serves the entire floor it would not be feasible to do a dry pipe system or add anti freeze.

Does anyone have a good calculation to determine if the piping will freeze in the wall cavity?

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5 Comments

Jonathan Sullivan

12/10/2020 09:28:41 am

You could try this to get started: https://www.wbdg.org/guides-specifications/mechanical-insulation-design-guide/design-objectives/time-freezing-fluid-insulated-pipe-calculator

This is for insulated pipe, and it would give you an idea of the range of the solution.

Can you post more details, maybe a sketch? It may help someone recommend a better solution for this application

12/10/2020 10:31:17 am

By code the cavity must be maintained at 40 degrees for wet system piping. Can you monitor ambient and account for all fluctuations accurately? If there are too many variables or lack of a controlled environment, then dry or antifreeze may be the option to meet code as an auxiliary system valve within the existing wet system per NFPA 13, 7.1.3

Glenn Berger

12/10/2020 10:41:36 am

If there is a chance of freezing, recommend a heat tape system be installed on the concealed pipe sections.

Most of the calculation methods that I have seen are for systems with flowing water, not static water as seen in sprinkler systems.

Brian Gerdwagen FPE

12/10/2020 11:24:36 am

We have done this calculation before as a means to show why a dry system or listed heat-trace was required. The simple answer was stated before: NFPA 13 requires wet systems to be installed in areas that are maintained at 40F. Listed heat-trace would be the only acceptable option from what I understand of the situation.

Jonathan Joseph

12/10/2020 12:52:23 pm

What type of material is the exterior wall made of? Are they putting up foam panels before the finish on the exterior? That will help tremendously. How cold does it get in the area?

Heat tracing is expensive but depending on your circumstances it might be your only option because you would have to prove that is will not get below 40 and that it will take geographic conditions and thermal ratings of materials used and pipe sizes to figure to determine if insulation will work.

Jonathan Sullivan provided a great calculator link

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