Fire pump and Tank 1

[sac32079]

I have a campus that I am designing a fire pump and tank for. I have an ESFR system along with various OH GP 1 & 2 systems. The hose requirement for the ESFR is 500 gpm. Do I have to add the hose for the 750 gpm standpipe system thats going to be installed in the OH building? Or would you think that the the ESFR system is the most demanding? Also there is a hydrant attached to the pipe entering the tank and a hydrant on the pump discharge side outside of the building. I have never done a design like this before and it seems to be a little confusing to me. I have no guidance here and i dont want to fail. I just need a little bit help understanding these requirements.

 

[b1ueshift]

You will satisfy NFPA 13 and NFPA 14 if you system can fight one fire at a time (ie either the ESFR system or the OH2 system).

If you are installing private hydrants, the building code won't tell you what the design flow rate from the hydrants should be and what the spacing is. You can get some hydrant system specifications from a fire code (like NPFA 1 or the International Fire Code) but these codes are generally not mandatory. You should talk to the AHJ about hydrant requirements.

 

[sac32079]

I am not designing the hydrants or the layout of them. The ESFR & OH will be in two different buildings, so fighting the fire one at a time shouldn't be an issue. With that being said, a combined standpipe and fire sprinkler system with a .20 shouldn't be as demanding as the ESFR correct? I have been designing for 8 years. I have now just got hired on as a senior designer and when i have questions my boss lacks the ability to help. he was grandfathered in instead of earning his NICET.

 

[b1ueshift]

The ESFR will probably be the most demanding case, but it's possible for the OH building to be higher.

An OH building could be really big and have 4 standpipes and more than 2 floors and require 1250 GPM to satisfy NFPA 14 (as an extreme case).

 

[sac32079]

what determines the fire pump shut off pressure? from doing all of my calculations i have came up with 2198 gpm @ 102.46 psi. I have it figured out that a 1500 gpm pump will supply me with the required rated flow at 150% which is 1465. I am trying to avoid 175 psi for pressure relief valves. I don't see in any literature as how to come up with this shut off pressure or is there something that I am overlooking?

 

[sac32079]

do you still have to take the city pressures in account when using a water tank?

 

[pipesnpumps]

sac32079: City water pressures only matter for calculating the REFILL rate of the tank. Those requirements are in NFPA 20, 5.6.4.1 and state that when sizing the volume of the tank you can take credit for the refill rate of a /reliable/ water supply.
If you don't take credit for the re-fill of the tank, which is the typical approach, then the city water doesn't matter as far as NFPA is concerned. Other codes/criteria may dictate otherwise. For DoD for instance it must refill the entire volume within 24 hours if normal water use is curtailed, or 48 hours if normal water usage is not curtailed. You didn't say wether the tank and pipe are combined potable/firewater or not, but I'm going to assume dedicated firewater.

Basically you need to take the worst case for each building, and then add in any additional hose stream that might be necessary for exposure protection of adjacent structures while the design building is burning if you feel it is necessary. You should also look at typical firewater demands for the types and quantities of buildings (ISO, etc. flowrates) and compare to NFPA 13/14 design flows. If you aren't designing the hydrants then whoever is designing them should tell you what the demand for the hydrants needs to be.

If a building has both a standpipe and a sprinkler system, the design flow for that building is the higher of the two cases; they are mutually exclusive, so design for either one of the other (sprinklers+hose OR standpipe) but not both at the same time.. In almost all cases the standpipe is going to be higher, but if you have criteria above and beyond NFPA 13 or higher hazard areas the sprinklers can be the most demanding.

lunch over, more tonight on the shutoff pressures if I have time

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[b1ueshift]

You won't find pump curves in a text book because they are different for every pump. You can ask a pump supplier to email you some pump curves and see if you can find one that suits your application. The pump supplier may be able to do this for you. In my experience some pump manufacturers are very helpful about giving out information.