Ignore Fire Pump Boost if City Supply Sufficient?

4/29/2021

I'm designing a fire suppression system for a new boiler room at an existing hospital. It will connect to the existing fire suppression piping. The hospital is served by a fire pump, but the existing pressure at the street is satisfactory to supply this particular space with enough water for Ordinary Hazard Group 2 occupancy without the pump.

Do I still need to include the fire pump in the hydraulic calculation, or can I ignore it?

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9 Comments

Matt

4/29/2021 08:09:44 am

Can you exclude the pump - I suppose. The design will likely work. It is probably not a good idea, especially if the drawing will become part of the building record. The lack of accuracy in the drawings will likely create confusion when the plans are referenced in the future. I would put it in there.

Cameron

4/29/2021 08:15:52 am

Depending on the street static pressure and the pump churn pressure, you may just want to verify and/or document (more importantly document to cover yourself) that your not exceeding the maximum allowable pressure in you system components. I myself would include the pump in order to provide the most accurate picture of the system.

Mr Glenn Scott Berger

4/29/2021 08:16:28 am

It all depends on the piping arrangement.

If the fire pump is on the supply to the sprinklers in that space, no you cannot ignore the pump. If there is a normally opened bypass of the pump, then potentially you can ignore the pump.

Franck

4/29/2021 08:28:46 am

If your connection to your sprinkler is downstream your booster pump, I would suggest you to do both.
That way you can prove that with the booster pump you are not overpressurizing your system (but it shouldn't as the booster pump is already in place for the other systems) and shows a lot of reliability as the demand point of your system will be well below your water supply curve.
And you can also prove that in case of an impairment of your booster pump, you can still adequately supply your sprinkler system by using a by pass (if a bypass is provided around your pump).
This would give credit to the reliability of your installation.

Dan Wilder

4/29/2021 08:47:44 am

Unless there are some pretty specific circumstances to ignore the pump (or any other fire protection feature affecting the design and layout of a system), it should be drawn to match what is installed.

The design may not require the pump, but is there not optimization of the higher available supply curve to reduce pipe sizing?

In other systems (I assume the system is closed sprinkler wet), but with deluge, foam, or preaction systems with delivery times, omitting the pump will have some negative and misleading results that can be crucial for both our design and others (containment, duration of application, over pressurization of equipment being some factors).

Brian Hoole

4/29/2021 08:50:13 am

The pump will allow you to minimize your pipe sizes. Be sure to keep in mind that for lower floors you will either need a pressure limiting device at the floor control when boosted by the pump or to feed a riser manifold prior to the pump that will supply the lower areas.

Our city water has a fairly flat curve with a static pressure above 110 psi. Utilizing a separate manifold on the supply side of the pump we had two small dry/preaction risers for the server room and parking garage. The supply main then tied into a the primary fire pump and filled a tank for the secondary pump. The discharge of the pumps supplied the various standpipes. This allowed us the mitigate three pressure zones within the high rise.

Aaron

4/29/2021 08:54:38 am

You didn't mention whether the total water demand for the ordinary hazard II exceeds the max flow (at 150%) of the pump or not.
We had a similar situation and the EOR directed us to connect the control valve to the system requiring more water than the pumps output to the incoming water supply before the pump. Otherwise the pump will reduce the water supply.
(I'm not sure why we couldn't rely on the normally opened bypass as mentioned by Mr. Berger.)

4/29/2021 09:04:32 am

Most of the AHJ's in our area require a fire pump test report from within one year for hydraulic calculations of buildings with fire pumps. One of the big reasons is to check to see if the fire pump is performing in compliance with NFPA 25. If a pump is performing very poorly the AHJ might ask the building owner to investigate the situation even if the calculations work. Your calculations might work for this project but the the fire pump is most likely needed for a different area of the building and should be maintained per NFPA 25.

CJ Bonczyk

4/29/2021 09:19:35 am

I would suggest that you include the booster pump. The purpose of this is that in your calculation if this area now becomes the most demanding portion of the system on that floor hydraulically then you will want to ensure your new hydraulic calc plate accurately reflects the information based on what is actually boosting the system water supply. You can easily obtain a most recent copy of a fire pump test report that provides the 3 point curve indicating the suction supply along with the booster pump operating and providing the discharge pressures and flows. I would then calculate back to the discharge side of the pump using that information as your supply. It does not hurt to additionally calculate the system without the use of the booster pump to confirm the water supply works alone. Thus at a later date if the booster pump is out of service you will know what minimum water supply is needed to allow the system to work if there is any degradation in the city supply.

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