Two Remote Fire Pumps for One Building?

6/7/2021

We are designing a warehouse which has a system demand of about 150 psi at 2,000 gpm.

There is an existing facility with a 150 psi @ 1,000 gpm rated pump installed approximately 1/4-mile (350 m) from the warehouse. We are planning to add a new 150 psi pump at 1,000 gpm near the warehouse roughly 65-feet (20 m) from it.

Is there any code limitation we might hit to serve one building with two separate pumping stations installed remote from each other?

How would you recommend we set the pump operation sequence for the two pump rooms?

Each pump room will have an electric, diesel, and jockey pump. Thanks in advance.

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4 Comments

Dan Wilder

6/7/2021 08:19:12 am

Couple questions:

-Are these pumps setup in series due to the distance between buildings (thus not allowing a full 2000 GPM supply to the second building) or is there actually 2 separate fire lines to allow a parallel installation?
-Is the water supply sized correctly before the split to accept up to a 3000 GPM demand when the pumps are tested at 150% and not take the pumps into a negative suction pressure scenario?
-Both buildings have the same owner? Different owners would create a huge liability for the 2nd, larger demand building.

Due to the distance of the pumps to each other, I would set the closest pump to its adjoining building, to start first , then have the second pump kick on when the pressure drops (Use the formula in A.14.2.6 _ 20-19 ED.) however the issue will be not setting the 1st pump (original) to start too low because it is still a primary for the first building. There may be some trial and error getting pressures set right to accommodate scenarios in both buildings as the couple of times I have done this in the past the pumps were much closer together.

Casey Milhorn

6/7/2021 09:12:40 am

Same questions as Dan. Will the pumps be in parallel and at what point do the supplies join back together? I would definitely involve a good local pump rep that has done this type of setup before. This is similar to a redundant pump setup for high-rises. It may take the better part of a day playing around with the pressures until you get it right.

CJ Bonczyk

6/7/2021 09:23:00 am

I concur with Dan there is a bit more information that is needed in order to give you a more definitive answer. I would also strongly suggest contacting the local AHJ and advise them of the situation as they may have local requirements that do or do not allow this setup as the location and accesses are required to be preplanned with the fire department per NFPA 20 § 4.14.1.1.4 & 4.14.2.1

Additionally, based on your last sentence in your question are you stating that each remote house will house a main electric and back up diesel pump? In your prior information it sounds as there is is only one single pump in each house? I apologize for any confusion on my end.

If the intent is that they are to operate in series they are required within 20 seconds after a demand to start, pumps in series shall supply and maintain stable discharge pressures +/_ 10% throughout its entire range of operation. Also, if in series they are required to adhere to the requirements of 4.21.2.2.

Franck

6/7/2021 10:45:15 am

It is not uncommon to have fire pumps set up as 2 separate water supplies.
For insurance purposes, when the insured values are high (or if the process is critical, as for nuclear power plants), it is a common recommended practice.
And again, for reliability purposes, it is better to have them in separate places (so that in case of fire, flood...) you may have only one affected at a time.

This being said, as long as they supply the same fire main and you have a Jockey pump to keep the pressure, the starting sequences are exactly the same, if you have separate pumps as if they are in the same area.

In reality, one fire pump house is the back up of the other (these are not 50% duty pumps) and under normal conditions, you should start only one of these pumps, the other ones being used only in case of impairment/no start.

You don't really care if your system is able to receive 3000 gpm or 6000 gpm. If it can't, the pumps will not be operating at 150% anyway at the same time (they cannot deliver more that what the system is able to receive), but probably both operating at 80%. It will only result in a higher pressure in your system for the same flow when both pumps are operating.
It is the same when one sprinkler is operating. Your branch line is not able to accept 1500 gpm, so the pump is operating at 20% of its capacity...
It may be problematic if they all start at the same time (within a fraction of second), but normally you have a delay.

Regarding the setting, as indicated above by other peers, you will find it in NFPA 20 (do not forget the annex section A14.2.6 as mentioned by Dan) for the pressure setting, in order to limit the water hammer).
The only thing you need to consider, when setting the start of the fire pumps, is the possible difference of elevation, as the pressure maitained by the jockey pumps in your system will not be the same at both pumphouse if they are at different height.

Pressures for the automatic start (and stop of the Jockey pump) should be set according to the following (for several pumps):
• Cut-out Jockey Pump : Pressure of the fire pump at churn
• Cut-in Jockey Pump : Cut-out Pressure of Jockey pump – 10 psi
• Cut-in Pump #1 : Cut-in Jockey Pump – 5 psi
• Cut-in Pump #2 : Cut-in Pump #1 – 5 psi
Cut-in Pump #3 : Cut-in Pump #2 – 5 psi
Etc.

You may also go up to a difference of 10 psi instead of 5 psi.

The above mentioned settings are provided to avoid a possible water hammer effect and to limit the delay of activation of the fire pumps in case of fire.

If water requirements call for more than one pumping unit to operate, the units should start at intervals of 5 to 10 seconds.

Example for 3 pumps in parallel arrangement set at 0, 10 and 20 seconds with a sudden large pressure drop:
• Lead pump: no delay (immediate starting); if the pressure remains low, then
• Second pump: 10 seconds; if the pressure remains low, then
• Third pump: 20 seconds

This sequential starting is absolutely necessary, otherwise in case of a sudden sharp drop in pressure, all the switches would trip at the same time.
Where this rule is not adhered to, pump houses have been destroyed when the surge of tons of water breaks the headers or elbows in the underground piping.

Note that this time delay in the starting sequence is only necessary when more than 1 pump is necessary (50% duty pumps, for example).

The only thing that is "strange" in your arrangement, is that apprently you already have one diesel and one electric in the first pump house, and you add one diesel and one electric in the second one. Which means that you will end up with 4 x 100%...
Waow, that's reliability !
Looks like a nuclear power plant!

Two Remote Fire Pumps for One Building?

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