MeyerFire
  • Blog
  • Forum
  • THE TOOLKIT
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR*
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND*
    • FIRE FLOW CALCULATOR*
    • FIRE PUMP ANALYZER*
    • FIRE PUMP DATABASE*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER*
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR*
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'22)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • QUICK RESPONSE AREA REDUCTION
    • REMOTE AREA ANALYZER*
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • SYSTEM ESTIMATOR*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER STORAGE*
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
  • UNIVERSITY
    • ABOUT
    • CATALOG
    • CONTENT LIBRARY
  • PE Exam
    • PE Forum & Errata
    • PE Store
    • PE Tools
    • PE Prep Series
    • PE 100-Day Marathon
  • LOGIN
  • PRICING
    • SOFTWARE & TRAINING
    • STORE
  • THE CAUSE
    • ABOUT US
    • BECOME AN INSTRUCTOR
    • HELP/SUPPORT
Picture

Use Fire Pump at 145% to Avoid 8" Underground?

2/21/2023

15 Comments

 
I have question regarding fire pump capacity.

In my situation the water department is requiring a city tap size to be 2 pipe sizes larger than the fire protection backflow preventer.

In my project, I was using a 4" backflow and 400 gpm fire pump so my underground/city tap would be required to be at least 6 inches.

The AHJ is requiring me to increase the area size in one of my remote areas. So, my sprinkler demand now becomes 582 gpm. To avoid having to use a 500gpm fire pump (with a minimum suction size of 6-inch) and increase the underground to 8-inch, could I still use the 400 gpm fire pump to supply the 582 gpm demand?

This comes out to about 145% of the pumps rated capacity.

I have never come close to the 150% mark before and just want to see what others think. If the underground size wasn't required to be 2 inches larger I wouldn't even think about it and go with the 500 gpm pump.

Thanks in advance.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
15 Comments
Paul Pinigis
2/21/2023 08:12:09 am

There are a few things that need to be addressed.
1. you state that the AHJ is requiring you to increase your remote area. What is his/her basis for this requirement? Did your original design not comply with NFAP 13? If it did, then the AHJ has no authority to require more unless there is a local ordinance that requires more than NFPA 13 compliance.
2. Two pipe sized larger than 4" would generally be 8" since 5" pipe is not a standard size.
3. What is the water company's rationale for the "two sizes larger"? Can you achieve their desired performance without this?

But, yes, 145% is acceptable.

Reply
Jesse
2/21/2023 08:27:42 am

All good questions by Paul.

Most curious is why the increase in remote area size. Is there a slope issue or unprotected vcombustible concealed space??

Reply
Jesse
2/21/2023 08:28:54 am

Meant *combustible. Loose nut behind the keyboard apparently.

Reply
Chad
2/21/2023 08:51:39 am

Or is it in front of the keyboard?

James Evans
2/21/2023 08:43:59 am

Riding a pump curve that far is never a good idea. There is no room for error and if the flow test ever changes then the owner is out of luck for future problems.

It is always recommended to stay around the rating up to about 120% once you pass that you are asking for trouble.

The real question the velocity of the water on the section side of the pump and being sure you will not drop below 20psi during the testing.

Pump suction sizing is based at 15 feet /second at 150% of the pump rating. That is something you need to look at.

Reply
Casey Milhorn
2/21/2023 09:00:39 am

I was thinking 140% was the max for designing out past the pump's rating. Not in front of NFPA 20 to verify, but I was pretty sure of this.

Reply
Wes
2/21/2023 09:18:10 am

I've always held onto the concept that many insurers don't recommend exceeding 120%, but that in worst-case situations not to exceed 140%.

That said, here's some input from NFPA 20-2022 Edition:

Chapter 4 General Requirements
Section 4.10 Centrifugal Fire Pump Capacities
Section 4.10.1
A centrifugal fire pump for fire protection shall be selected so that the greatest single demand for any fire protection system connected to the pump is less than or equal to 150 percent of the rated capacity (flow) of the pump.

A.4.10
The performance of the pump when applied at capacities over 140 percent of rated capacity can be adversely affected by the suction conditions. Application of the pump at capacities less than 90 percent of the rated capacity is not recommended.

The selection and application of the fire pump should not be confused with pump operating conditions. With proper suction conditions, the pump can operate at any point on its characteristic curve from shutoff to 150 percent of its rated capacity.

Reply
Wes
2/21/2023 09:19:04 am

Then, additionally, ASK THE AHJ for Enhanced Content out of the NFPA 20 Handbook (highly recommend getting this):

ASK THE AHJ:
The required flow for a fire protection system is higher than the rated flow for the fire pump selected by the designer. Is this allowed?

ANSWER:
Yes, a fire pump can satisfy any point along its performance curve. This includes points up to its overload point (150 percent of rated flow).

Selecting a pump so that the system demand falls between 90 percent and 140 percent of rated capacity ensures that the pump is not oversized and conversely is not operating at its maximum output. Note that while NFPA 20 recommends selecting a pump of a size such that the system demand falls between 90 percent and 140 percent, some insurance companies limit pump sizing to 120 percent of rated capacity, and some municipalities limit the maximum system demand to 100 percent of rated capacity. The intent of these limitations is to avoid operating the pump at or near the overload point, which, over time, can compromise pump performance. After years of service, a fire pump might begin to show signs of wear and might not be capable of reaching 150 percent of rated capacity. If such a pump were selected based on performance at 150 percent capacity, a deficiency would eventually result. Selecting a fire pump of such a size that the system demand falls below 90 percent results in a fire pump that is too large for the system. The results of such a design include higher power supply demand, excessive cost, and more water usage during testing.

Reply
Wes
2/21/2023 09:33:25 am

Without naming names, I think I know where this jurisdiction is, and this requirement has caused so many issues on installation.

The cost difference that the city charges for a 4-inch tap versus an 8-inch tap is already extreme, and then when pressed about this "two-pipe-sizes-larger" requirement, no one has been able to explain why that longstanding requirement is important.

The only explanation that's ever come across my desk was to limit the velocity of the water service so that the pipe wall doesn't wear. With how infrequent fire pumps operate and are tested, I don't fundamentally understand the difference in wearing out a pipe wall at 2.3 fps versus 4.0 fps, but that's the only reasoning I could get out of why this specific locally-adopted requirement exists.

It's very frustrating for both the subs, the general, and the owner, who are surprised to learn that their small private garage, which only houses 6-8 cars, needs a pump because of locally-adopted requirement for garages to be 0.25 / 2,500 sqft at that time, and then also is going to need a very expensive 8-inch underground tap. Very costly and surprise-galore.

Not to be a total grump, but tough place to design. And I love my AHJ friends, so please don't take this the wrong way. Just hope it's gotten better since I did work there.

Reply
Michael
2/21/2023 09:37:10 am

120% is about the highest I would go on the pump curve. Higher then 120% is opening yourself up for many other issues that have been discussed in the above responses.

Reply
Glenn Berger
2/21/2023 10:27:34 am

1) You comment says that you have a 400 gpm fire pump. This is not a standard size fire pump.

2) As others have said, review your remote area and verify that it complies with NFPA 13.

I try not exceed 120% of fire pump rating with projects that I work on.

Reply
Franck
2/21/2023 12:32:15 pm

I will express my practical point of view, which is definitely not the one the AHJ may have.
For a new system, I would never go further than 120% for all the reasons above.

In your case, I would defend it as it is not a new installation but a new requirement on an existing installation
If you can prove that this new requirement is met (and 145% can be OK), why should you not approve it ?
As long as your demand point remains below the water supply curve, I don’t see any issue.

To come back to the first assessment: the reason why I won’t go further than 120% for a new installation is to give me the flexibility to go beyond (up to 150%) if you have a greater demand in the future.

Reply
Anthony
2/21/2023 01:07:14 pm

Have you thought about using 2 backflow preventers in parallel? You could get two (2) 3'' to flow (600 gpm 300 through each), with no added pressure loss and keep your tap at 6''. I'm not sure how the money works out on that but it's an option worth considering I'd think.

Reply
Wes
2/21/2023 01:20:28 pm

Not the OP, but never thought of that. If this is the area I'm guessing it is, then this is an RPZ-required area, so that'd have to help. Nice!

Reply
sean link
2/21/2023 01:29:38 pm

Can you do this. Technically yes (see the appendix) but I would strongly recommend not. There is a greater chance of real life performance issues.

Reply



Leave a Reply.

    Picture
    Why Sponsor?

    ALL-ACCESS

    Picture
    GET ALL OUR TOOLS

    SUBSCRIBE

    Subscribe and learn something new each day:
    I'm Interested In:

    COMMUNITY

    Top ​Feb 2023 Contributors
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    SEE LEADERBOARD

    YOUR POST

    SUBMIT A QUESTION

    PE EXAM

    Get 100 Days of Free Sample Questions right to you!
    SIGN ME UP!

    FILTERS

    All
    A117.1
    ABA
    ADA
    ASCE 7
    ASME A17.1
    ASTM E1354
    Daily Discussion
    Design Documents
    EN 12845
    Explosion Protection & Prevention
    Fire Detection And Alarm Systems
    Fire Dynamics
    Flammable & Combustible LIquids
    FM Global
    Human Behavior
    IBC
    ICC-500
    IFC
    IMC
    IPC
    IRC
    ISO
    Means Of Egress
    NBC
    NFPA 1
    NFPA 10
    NFPA 101
    NFPA 11
    NFPA 110
    NFPA 1142
    NFPA 1221
    NFPA 13
    NFPA 13D
    NFPA 13R
    NFPA 14
    NFPA 15
    NFPA 16
    NFPA 17A
    NFPA 20
    NFPA 2001
    NFPA 214
    NFPA 22
    NFPA 220
    NFPA 24
    NFPA 241
    NFPA 25
    NFPA 291
    NFPA 30
    NFPA 30B
    NFPA 33
    NFPA 400
    NFPA 409
    NFPA 415
    NFPA 495
    NFPA 497
    NFPA 5000
    NFPA 502
    NFPA 54
    NFPA 55
    NFPA 654
    NFPA 68
    NFPA 70
    NFPA 701
    NFPA 72
    NFPA 75
    NFPA 770
    NFPA 82
    NFPA 855
    NFPA 90A
    NFPA 92
    NFPA 96
    NICET
    OBC
    Passive Building Systems
    PE Prep Guide
    PE Prep Series
    PE Sample Problems
    Poll
    Smoke Management
    Special Hazard Systems
    UFC 3 600 01
    UFC 3-600-01
    UFC 4-021-01
    Updates
    Water Based Fire Suppression
    Weekly Exams


    ARCHIVES

    March 2023
    February 2023
    January 2023
    December 2022
    November 2022
    October 2022
    September 2022
    August 2022
    July 2022
    June 2022
    May 2022
    April 2022
    March 2022
    February 2022
    January 2022
    December 2021
    November 2021
    October 2021
    September 2021
    August 2021
    July 2021
    June 2021
    May 2021
    April 2021
    March 2021
    February 2021
    January 2021
    December 2020
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    October 2019
    September 2019
    August 2019
    July 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    November 2016
    October 2016
    July 2016
    June 2016


    PE PREP SERIES

    Fire Protection PE Exam Prep
    SEE LEADERBOARD

    RSS Feed

Picture
​Home
Our Cause
The Blog
The Forum
PE Exam Prep
The Toolkit

MeyerFire University
​Pricing
Login
​Support
Contact Us
Picture

MeyerFire.com is a startup community built to help fire protection professionals shine.
Our goal is to improve fire protection practices worldwide. We promote the industry by creating helpful tools and resources, and by bringing together industry professionals to share their expertise.

​MeyerFire, LLC is an International Code Council Preferred Education Provider.

All text, images, and media ​Copyright © 2023 MeyerFire, LLC

We respect your privacy and personal data. See our Privacy Policy and Terms of Service. 
The views, opinions, and information found on this site represent solely the author and do not represent the opinions of any other party, nor does the presented material assume responsibility for its use. Fire protection and life safety systems constitute a critical component for public health and safety and you should consult with a licensed professional for proper design and code adherence.

Discussions are solely for the purpose of peer review and the exchange of ideas. All comments are reviewed. Comments which do not contribute, are not relevant, are spam, or are disrespectful in nature may be removed. Information presented and opinions expressed should not be relied upon as a replacement for consulting services. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a small commission for orders placed elsewhere.

  • Blog
  • Forum
  • THE TOOLKIT
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR*
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND*
    • FIRE FLOW CALCULATOR*
    • FIRE PUMP ANALYZER*
    • FIRE PUMP DATABASE*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER*
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR*
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'22)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • QUICK RESPONSE AREA REDUCTION
    • REMOTE AREA ANALYZER*
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • SYSTEM ESTIMATOR*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER STORAGE*
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
  • UNIVERSITY
    • ABOUT
    • CATALOG
    • CONTENT LIBRARY
  • PE Exam
    • PE Forum & Errata
    • PE Store
    • PE Tools
    • PE Prep Series
    • PE 100-Day Marathon
  • LOGIN
  • PRICING
    • SOFTWARE & TRAINING
    • STORE
  • THE CAUSE
    • ABOUT US
    • BECOME AN INSTRUCTOR
    • HELP/SUPPORT