Sprinkler Pressure for "ESFR-Ready" Design?

4/1/2021

We are currently working on a project with a building height of 36-feet that currently has K16.8 ESFR sprinklers installed to protect open rack storage of Class I-IV commodities at 12-feet in height.

The hydraulic calculations are based on Ordinary Hazard Group 2, with a 0.20 gpm/sqft density over 1,500 sqft with a starting pressure of 7 psi. The design area is based on 18 ESFR sprinklers flowing at 100 sqft per sprinkler. The total sprinkler demand is 834 gpm.

They are calling this an "ESFR-Ready" sprinkler system.

It seems to me that the building height would drive the starting pressure for this scenario and the calculation should actually be 12 sprinklers with a minimum starting pressure of 52 psi when using K16.8 ESFR sprinklers. This comes after examining Chapters 12-20.

What would the lowest starting pressure be for K16.8 ESFR sprinklers protecting open rack storage of Class I-IV commodities to 12-feet in height with a building height of 36-feet?

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8 Comments

Jesse

4/1/2021 09:14:03 am

Interesting. Flowing 18 K=16.8 - I hope we have a great water supply.

12-25-ft rack storage of Class I-IV Commodity in a 36-ft building would require end head pressure of 52-psi for K=16.8. Figure a loss of psi due to elevation at 15.59-psi = 67.59 psi without factoring in any friction loss.

I wondered about the original OH2 design and figure that the storage was previously less than 12-ft for Class I-III and / or less than 10-ft for Class IV.

"ESFR-Ready" is a new one for me......

Josh

4/1/2021 09:40:18 am

12.6.7.1 of NFPA 13 2016 says ESFR sprinklers designed to meet any criteria from chapter 12 or chapters 14 through 20 may protect light, ordinary or any storage arrangement referencing OH1, OH2, EH1 or EH2 in chapter 13 (misc/low-piled storage)

So to protect miscellaneous storage with ESFR, you think you'd be able to just pick the least demanding criteria from any of these chapters (while still taking into consideration building height) and that would be good to protect an ordinary hazard group 2 occupancy, but nowhere in any of these chapters would allow you to do a 7 psi starting pressure in a 36' high building with 16.8k ESFR sprinklers that we could find.

Eric

4/1/2021 09:32:43 am

Your research is correct. Based on NFPA 13 (2016), chapter 16 addresses rack storage of class I-IV commodities. Based on building height and storage height, K16.8 ESFR sprinklers will protect up to 20' of storage in a 40'-0 building, with a starting pressure of 52 PSI. The calculations will be based on 4 sprinklers flowing on 3 branchlines with a hose demand of 250 GPM.

When designing per NFPA, storage height and building height determine starting pressure of the sprinklers. When designing to another standard like FM Global for instance, the building height is the determining factor for starting pressure. In both design scenarios, obviously the commodities being stored is the starting point to the design. In this situation you described, there is no relief for starting pressure at 20' of storage until your ceiling height is 35'-0.

James Evans

4/1/2021 10:09:23 am

Just a comment on an ESFR-Ready building. These buildings are constructed to provide ESFR systems in the future. Normally they will base the pipe size on future tenants, even if the actual tenant only needs ordinary group 2. THe key is to have the outlets big enough for ESFR sprinklers and the pipe sizing to support it. Normally that means adding a fire pump and changing out the sprinklers.

Normally that would require a 8" riser 6" front main 4" back main and 2 or 2.5" lines.

You might want to make sure that the pipe you are installing will meet those requirements in the future.

Brian Gerdwagen FPE

4/1/2021 10:10:20 am

We used to design "ESFR Ready" systems. We didn't install ESFR sprinklers as you can not use an ESFR sprinkler and calculate a density/area design with it. The sprinkler isn't designed that way.

The "ESFR Ready" was intended to, at a future date, replace all the K17 CMDA sprinklers with K17 ESFR and drop in a fire pump. Start pressure of 7psi versus 52psi is a big deal.

I wonder if the sprinklers were changed from K8 or K11.2, which would be more appropriate for that arrangement. 800gpm is the minimum discharge for K17 at 7psi, but you are still wasting water if you use a K8 head with a 0.20 density at 100sqft.

If the sprinklers were changed from a CDMA to an ESFR, is the deflector distance correct for ESFR?

4/1/2021 10:39:11 am

They are actual 16.8k ESFR sprinklers installed currently. Our thoughts were switching to a CMDA sprinkler such as a K8 or 11.2 and the calculations would probably work for the current storage arrangement and then swap to ESFR later with a fire pump when the storage arrangements exceed it.

This is an existing building that has been passed and approved and we were doing a small tenant revision on it. It just seemed so wrong for the base building contractor to install 16.8k ESFR heads and calc them with a density/area method with a 7 PSI starting pressure.

matt

4/1/2021 10:12:15 am

one thing to watch out for - depending on your AHJ, the area/density calculation method may not apply to ESFR sprinklers. just because they are discharging .2/1500 does not mean that they are functioning properly. ESFR heads have specific listing requirements and they have probably not been tested or listed for a 7psi starting pressure.

Who has provided the design for this system? Unless they are qualified to produce a new performance based design, you may just have a mash-up of design approaches that don't necessarily work together.

Franck

4/1/2021 11:24:10 am

ESFR operating at 7 psi would not work correctly.
Because of the large orifice, there is a need for a minimum pressure/flow, otherwise the distribution pattern will be completely eratic, not covering adequately the ground floor area and with droplet sizes not adequately distributed.
Remember ESFR are working on the suppression mode (not control mode) and thus require specific limitation, such as minimum operating pressure, distance from ceiling, no obstruction, specific number of operating sprinklers (usually 12)...
The design with 18 ESFR at 7 psi makes no technical sense and does not seem to appear in any design approach with ESFR (to my knowledge).

Sprinkler Pressure for "ESFR-Ready" Design?

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