Benefits/Reasons for Flow Tests vs. Modeling?

9/14/2022

Most cities require fire flow tests before design and calculation of a sprinkler system, but I have dealt with a few cities that instead use a water modeling system to calculate the pressure and flow at certain locations.

What is the reason for this?

Are there benefits or downsides to one or the other?

Is one more accurate?

Thanks in advance - appreciate the input.

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16 Comments

Ray Jackson

9/14/2022 08:07:17 am

I have not heard of this, but... I am old school, give me a flow test everytime. It's worked very well years. If it ain't broke, don't fix it.

Connor

9/14/2022 08:19:31 am

I would say the models are useful, and they can give importand data such as seasonal fluctuations. A flow test is necessary during the shop drawings phase to see the current condition of the piping and if there are any issues. The model doesn't know if a valve was closed since its last regular inspection, for instance.

Dan Wilder

9/14/2022 08:21:58 am

To prevent the loss of water from the system along with any potential secondary effects like water hammer and/or property damage is my guess.

The water models I have been provided by AHJ's have been pretty spot on because they have their entire system (mains, pumps, elevations, valves, pressure reducing/restricting valves) generally near 100% accurate. Water models provided by engineers have been less reliable as they typically encompass a much smaller section of the water supply.

As to overall accuracy, I haven't seen anything pro or con however identifying issues early with the water supply like closed valves or debris in the system early on.

Dwight H Havens

9/14/2022 08:32:25 am

Either method works. Both depend on the accuracy of the assumptions used to develop the data and results. My personal bias is to flow tests, but you must recognize that a flow test only represents a single point in time, and without broad knowledge of the operating characteristics of a water supply source may only be of limited value. A good model will allow one to evaluate water supply availability 24/7/365 and allow you project potential changes to the available water supply over time. Given the expected life of a fire suppression system, there are many factors that need to be watched to ensure viability of the fire suppression throughout its useful life. Water supply is only one of them.

Casey Milhorn

9/14/2022 09:05:05 am

Everyone pretty much covered it, but I will say it's probably going to be the way things are going so get used to it. I personally like the liability being on the water purveyor and I also like the fact that they are modeling (hopefully) daily, weekly, monthly, seasonal fluctuations that may be occurring. As someone else said, I just hope that the water purveyor is doing annual flows on their hydrants to verify what the models show.

Franck

9/14/2022 11:00:14 am

As indicated by Casey, if you go to modeling, check anyway if an actual flow test confirm the expectations.
Models might not discover potential issues such as pipe ageing, settlement, MIC corrosion...

I personnaly prefer actual testing (I trust what I see) as I don't know what is behind the models.
But as indicated by other peers, a true test is only a check at a point of time and characteristics may vary during the day, with possible huge difference depending on the hour (especially close to industrial facilities operating during the daytime), and during the season (especially at touristical resorts).

Aviv

9/14/2022 11:02:59 am

Sometimes it's required due to draught conditions. For example, it is highly encouraged in California:

https://www.dgs.ca.gov/-/media/Divisions/DSA/Publications/bulletins/BU_15-02.pdf?la=en&hash=7907B865C5C99EE7DCB24AC27304F0F74F83A652

As for pros and cons, I agree with the above.

Chris

9/14/2022 11:16:24 am

How new are the models they give you? The only locality I deal with that does water modeling will sometimes provide a model that is 3-4 years old so I am not a fan of that, so we will go do an actual flow test when possible.

Kelsey

9/14/2022 11:16:49 am

In my area, we almost exclusively use municipal models. Very rarely do we have to go out and do a flow test ourselves.
We are in a very environmentally conscious area, which is a big part of it.
I love it - it is quick, and reliable for a year-round idea of what the water will be. We don't have to wait for warm weather to have a single point in time flow test.

Glenn Berger

9/14/2022 11:52:38 am

Modelling is not accurate. Modelling may or may not be validated by a flow tests. Hydraulic models are only as good as the input assumptions that cannot be verified.

Always, always use a fire hydrant flow test.

Jesse

9/14/2022 12:21:15 pm

Flow characteristics are the foundational basis of AS design. I don't like using exclusively modeled data as the basis of design. I will always opt to physically flow water.

In one AHJ in my metro area, they combine the 2. The physical flow test is done with all city pumps off, using only gravity tanks. We then submit the flow data to the FD and they use that to model the worst-case scenario. I.E. low water level in gravity tanks, etc. in order to prove system efficacy in a worst case scenario. Its a pain, but it really provides a clear and accurate design picture.

Besides, modeled data isn't going to find a closed water valve in the system somewhere.

Bill

9/14/2022 12:46:33 pm

I’d plan on getting used to models, if for no other reason than water conservation alone. Consider all the water discharge from a fire sprinkler system in one year, then multiply that by how many systems, and you have a lot of discharge! Then throw on flow tests… it’s a lot of water that we can use for fire fighting, etc.

Jim Buchanan

9/14/2022 02:23:57 pm

All are solid points. However, Bill’s thoughts regarding water conservation address our future, which is reality, or soon will be…

Travis Mack

9/14/2022 01:00:35 pm

Model is the way to go. If you are only accepting physical flow tests, why are you accepting fire sprinkler systems without flowing the design area fully?

The models are good if there are good data to support it. Flow tests are a single spot point in time. Are you adjusting flow test values for season and peak demand times. That 10% or 10 psi may not cover it.

You do need accurate data to input in the models. Many water companies today have that data and can model it properly.

As far as finding closed water valves via flow testing, that is the responsibility of the water purveyor. Sprinkler contractors don't need to take on more liability than they already have.

Jay

9/16/2022 10:39:16 am

Chicago flow tests their water supply system. If your requesting flow info in an area they haven't tested in a while, they run the test and send you the results.
However, last June I requested flow data near a hotel on the Magnificent Mile. I was told they don't conduct flow tests there because they're worried about business interruption and possible property damage. They gave me a computer model instead.

schulman

9/20/2022 01:38:19 pm

i've never seen water leave the atmosphere ... and Flow Tests are real

Benefits/Reasons for Flow Tests vs. Modeling?

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