"Low Pressure FDC" Allowed Upstream of Pump?

5/6/2024

I have seen this method of arranging fire suppression components (see attached schematic) several times where I live. The attached is a partial re-creation of the fire water entry schematic for a high-rise building with a fire pump. The system has low and high pressure zones.

The underground parking dry systems are served by the municipal water directly, and the standpipes and aboveground sprinklers are fed by the pump.

Questions: 1. Can you have a FDC serving the low pressure zones as shown on the suction side of the pump per NFPA-14 6.4.3.1?

2. If not, how should the schematic be arranged instead?

3. What could happen if the Low Pressure FDC were pressurized as shown?

This project was built under the 2013 editions of NFPA-13, 14, and 20. I am asking because I am beginning design of a sprinkler system for a 22 story high-rise. Thanks for your help.

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9 Comments

Anthony

5/6/2024 07:36:11 am

1. No
2, have all systems fed from the pump.
3. probably nothing but I think the worry would be cavitation.

Why don't you have the pump service all the systems? There are plenty of 300 psi sprinklers available for high pressure zones that you'll have on your first several floors. Or after the pump do a PRV station and split the building into 2 systems a high pressure and low pressure system. Thats what I do on most high rises. see FIGURE A.7.2.4 Dual Pressure-Regulating Device Arrangement.( 2016 ed)

Also not sure your pump is rated high enough. that seems like a low boost for a building that's 22 stories.

5/6/2024 09:59:09 am

Thanks, Anthony. To clarify - the schematic shown is for a previous project that's only 13 storeys, and I wasn't the designer. The 22 storey building is a new project that I will be designing.

5/6/2024 08:04:23 am

So the part 3 was bugging me and looked it up in the 2019 handbook:

TL;DR: So the system is over pressurized, and reliability concerns .

According to 6.4.3, the fire department connection (FDC) is made on the system side of the check valve. For installation on systems with fire pumps, the FDC needs to be made on the sprinkler system side of the discharge check valve for the fire pump. Full efficiency and reliability cannot be obtained for a suction-side connection because of losses through the pump and valves and because of the inability to supplement the system if the discharge-side control valves are closed. Pumping into the suction side of a fire pump or booster pump increases the discharge pressure of the pump, frequently beyond the pressure limits of the system. The FDC should be made on the system side of a pump and on the system side — that is, the discharge side — of the pump’s discharge check valve and control valves."

5/6/2024 08:24:08 am

In order to have a low pressure zone like that, the entire subheader for P2 & P1 should be subdivided with a check valve to ensure it cannot feed the suction side of the fire pump.

Sure there are Pressure Reducing Valves and high pressure sprinklers, but these can be more costly than sub dividing the the zone for various reasons:

-Potential for extra devices for the owner to maintain and test.
-Certain window sprinklers are also listed to 175 psi.
-Need special screwed fittings
-Fire pump may only be rated for small flow and high pressure to save on building generator costs (or to shave a bit of money off of the overall fire pump install too.)

5/6/2024 09:59:58 am

That's generally what I'm thinking for my 22 storey project. Thanks!

chad

5/6/2024 08:42:23 am

It is common to have the garage with a separate FDC in many larger metros in colder climates with mid and high rises. How does the FD regularly operate?

From a design perspective I can see the advantages. From the AHJ perspective I can see confusion without detailed preplans and signage unless its common.

Dan Wilder

5/6/2024 08:59:37 am

Missing some info here but my thoughts:

The rule Anthony cited is a little dated and does not make allowances for both this situation and the ability of fire pumps to regulate their discharge pressures with the increasing use and availability of variable speed/frequency fire pumps (more recently addressed in the 14'-2019 Edition).

This arrangement, while not unique, should not generally be utilized*. The reasoning of not allowing the FDC on the suction side of the pump is to avoid over pressurization of the components on the discharge side of the fire pump (above 175PSI).

*However, in this case, the static pressure shown plus the rated pressure of the fire pump already exceeds 175 PSI, i.e. is already in excess of the lower, more standard rated components. The use of a High Pressure FDC also (likely) indicates that the signage will (likely) show a required pressure above 175 PSI.

It does show the use of Pressure Reducing Valves for both the sprinkler and hose valves on the discharge side of the pump so the issue of over pressurization is addressed (would need to verify final design pressure with all components affected).

To fix this, either provide a dedicate second water supply into the building to be used for the lower zones or flip the fire pump & P1/P2 systems to the discharge side of the pump (addressing the >175PSI issue). Hopefully, there can be additional guidance available within NFPA 14 in the future (I have not read through the PC's and minutes from the committee if it's already in the works).

Casey Milhorn

5/6/2024 09:15:57 am

Anthony has the code reference and no it is not allowed. JI has the proper solution if you want to keep low pressure zone, or Anthony if you want to have just one pressure zone. You can also use a master PRV to reduce pressure for wet and dry risers, if you are using it for standpipes you will need to provide (2) master PRVs in series w/ bypass. Depending on the applicable code and standard, (2) FDC's for each zone may be required as well. That would make the two pressure zones even more expensive vs the one. Also make sure to check the pumping ability of the responding FD. Sometimes redundant pumps are required if above the ability of the FDC to get 100 psi @ 500 gpm.

Jack G

5/6/2024 11:06:19 am

1. No, not legal.
3. Running the fdc thru the pump , the added pressure is added. This could exceed component rated pressure. Pump churn is 211, if fdp low zone pumper — pumps in 100 psi or more, component will see over 300 psi.
A solution would be to relocate it to pump discharge, add a prv , pipe to the 4 low zone dry systems, and or low zone standpipe.
Or could just change the heads and components to 300 psi, feed low zone from pump discharge.
***My favorite would be to add a check valve above each dry system control valve to match the window sprinkler configuration. Then I would pipe the fdc ( low zone ) supply to each system—- with a check valve for each system, so the systems are not co mingled. So adding 6 checks and reviling the low fdc supply pipe.
Now if you wanted to go a bit further, and have a 175 psi low zone, you could add 1 prv to the low zone standpipe, eliminate some prv s, and connect that riser to the low zone fdc, and or feed the garages and window sprinklers after that prv.
*** I personally prefer my favorite above.
I add signage ( like described in nfpa 14 ) which describe — what it supplies- system pressure, flow, maximum psi for the standpipe/ attached sprinklers. Metal signs for fdc s, metal for each system riser/ stand pipe. Then I ve made peel and stick standpipe hydraulic stickers, and stick them on each low zone risers/ standpipe—- as I’ve found , the signs will eventually disappear.

"Low Pressure FDC" Allowed Upstream of Pump?

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