High Rise/High Pressures?? 2

[FireSprinkler]

In a high rise building, I am including one standpipe zone and one fire pump. two of the three class I standpipes would be combined with the floor control stations.
On many floors, I should be able to get away with 2 1/2" floor control stations. Therefore, I would be able to use a 2 1/2" inline pressure regulating valve as my system control valve on each floor (with tamper of course).
But, on the lower floors, where there will be many 'amenities', kitchens, storage etc... I am concerned about having floor controls greater than 2 1/2". Would I need to use a high pressure gate valve (floor control valve with tamper) on the inlet side of a monstrous presure regulating valve at each floor control station?? Or would it be more economical to have two zones and step the pressure down on the lower floors with one pressure regulating valve but then add much more bulk mains to feed the other higher zone??

In short, what is everyones experience in dealing with the high pressures in sprinkler/standpipe systems in high rises (ie pressures exceeding 175psi but not higher than 300psi)??

 

[TravisMack]

Do you have enough pressure to feed the lower floors from the supply side of the fire pump (not boosted)? Will the system take the friction loss through the 2½" valve. You could have a 2½" valve coming off the riser in the stair and then increasing up to a 3 or 4" feed main to the grid.

One other alternative is to have the monstrous pressure reducing valve in the lower level. Then just run a second riser to feed the floors that you need. The only extra bulk piping is the riser for the floors where you can use a 2½" reducing valve.

Hopefully this will make sense for you.

 

[FireSprinkler]

I like the idea to use the 2 1/2" valve then increase up to the main size required. Except that the installation would look horrendous. A smaller valve serving a larger main. It would probably raise questions during the approval phase too. But, hey, at this point I'm willing to look at anything. With the pressure's I'll have I'm not concerned about what loss I'll have through the valve. Besides, I'll regulate the valve to give me whatever psi I want system side.

I have considered feeding the lower floors from a pre-pump supply. I'm looking into that option. Although, the siamese connections would need to be very well indicated. This arrangement could cause confusion.

I have also thought of the P.R. valve being on the lower floor and running the bulks up to the other floors where I could use the 2 1/2" valves. But, as usual, space is at a premium. And, although I could cross connect the upper standpipes, the floor that the cross connect would occour on is a mechanical/truss floor. Very tight, very congested.

With either of these (pre-pump supply or lower level P.R. valve) I would, essentially, have 2 standpipe zones. I was hoping to get away with one to reduce bulk mains and also to eliminate the 2 extra siamese connections for the extra zone.

Interesting ideas though. I surely have a few senarios to play with.

 

[TravisMack]

FYI - I have seen several installations with the smaller valve feeding larger pipe. Some for the very reasons you are dealing with. Yes...it does look different, but calcs prove it to work. When you are in a bind....things get creative.

The pre-pump supply will get very creative with the FDC. It will cost you an extra check valve at the least. I have done this several times with rack systems.

Good luck with the outcome.

 

[LCREP]

Another option maybe for a variable speed pressure controller now permitted by NFPA 20, 2003 edition.

 

[FireSprinkler]

LCREP: I've never heard of that. Could you tell me a little bit about what that is?

 

[LCREP]

This is a new addition to NFPA 20, 2003 edition, it permits the controller to be variable speed providing more pressure at greater flow and less at low GPM by increasing and decreasing the pump speed. If you know any firefighters who operate a fire pumper they are doing the same thing manually. The faster the pump operates the higher the pressure. By adjusting the speed of the pump you can eliminate many PRV since under normal pump churn conditions, the pressure is lower. However, if you have a sprinkler operation or hose station used by the FD, the speed of the pump increases to compensate for the additional flow. Suggest you contact the major fire pump and controller manufactures for more information.

A very good article was in the Sprinkler Age magazine, February 2004, put out by The American Fire Sprinkler Association. Go to the web site

http://www.sprinklernet.org

and sign up for a free copy of the magazine. The author of the article, Bill Harvey of Harvey & Associates, Fountain Inn, S.C. is on NFPA 20 and very knowledgeable regarding fire pumps, you may want to give him a call.

I have not scene this new technology in the field, but looks like it will solve a lot of problems with PRV flow testing and maintenance.