Booster Pump on a Dry Pipe System? 2

[sl3656]

I am currently designing a dry pipe system for a facility (OH Group 2 occupancy) located in NYC.

I am attempting the design this system to the 750 gallon limit (with a QOD) but am finding through hydraulic calculations that there is sufficient available flow (after including the inside and outside hosestream allowance) but not enough pressure. Conversely, if I increase the main / cross main / branch diameter sizes, I get sufficient pressure, as well as flow, but surpass the 750 gallon limit. I have spent the best part of the day trying to find a system 'sweet spot' where I can satisfy both volume and pressure/flow constraints to no avail.

I am now thinking of sticking to smaller pipe sizes to keep within the 750 gallon limit, and adding a booster pump connected downstream from the city main. This booster pump would supply 30-40 psi more only.

Any thoughts and considerations on this approach? Thanks in advance.

 

[TravisMack]

Why not split your system into 2 smaller systems. That way you eliminate the need for a pump and eliminate the issue of having to meet a 60 second water delivery time.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

"Follow" us at

https://www.facebook.com/pages/MFP-Design-LLC/92218417692

 

[sl3656]

Thanks Travis.

The issue is this is a rather large infrastructure facility (125,000SF on a single level). Splitting the system into smaller systems will inevitably result in a myriad of pipework having to negotiate many clearances (e.g. vehicle dynamic envelopes etc.) within the facility.

I am finding that having a 6 inch main, 4 inch cross main and 2 inch branch sizing works best in eliminating the need for pumps. To get the system below 750 gallons, I estimate a zone size of around 10,000 SF. This would result in as many as 13 zones in the facility.

Furthermore, there's about a 10 psi safety factor between the required and available pressures, assuming no pump. I am afraid that even if 13 dry zones with no pump was feasible, there would be little in the way of expandibility, in case a few extra sprinklers are required for whatever reason later.

Right now, I am thinking about having 5 zones of around 20,000 to 25,000 SF each, fed from a pump room equipped with a booster pump.

Thoughts appreciated. If 13 zones / no pump is feasible, what other considerations do I need to think about? I am concerned that there's little margin for error if I omit the pump, in case the client / contractor encounters unknown conditions requiring additional pressure and flow. As a designer, that's the worst place to me in.

 

[TravisMack]

If I'm going to spend money on a pump, I'm going to maximize it to help mitigate some of the costs. So, you say you only need 40 psi boost. I would try to size the pump to get churn around 160 psi. This would typically help to reduce the size of the system piping. Just be aware of the hanging requirements when pressures exceed 100 psi.

Also, be cognizant of your bulk piping. 6" bulk pipe adds volume very quickly.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

"Follow" us at

https://www.facebook.com/pages/MFP-Design-LLC/92218417692

 

[sl3656]

Thanks again for the reply Travis.

Your reply about splitting the system got me thinking again on whether I should really try to get away from the pump requirement. For the sake of simplicity and at the risk of repeating myself again, I have listed my two possible options below, as well as my constraints / design parameters:

Building SF: 125,000 single floor facility
Water Supply Static / Residual / GPM: 52 PSI / 51 PSI / 920 GPM
Occupancy: OH Group 2
Density: 0.2 gpm/ft2
Fire Area: 1500 x 1.3 (for dry systems) = 1950 SF

I have 2 options available to me:

OPTION 1

5 dry sprinkler zones, each 20,000 to 25,000 SF.
System volumes below 750 gallons
4 inch main, 3 inch cross main and 2 inch branch
Per HASS calculations, 70 PSI and 500 GPM required.
Need a booster pump connect direct to city main to boost around 20-30 PSI more.

OPTION 2

Max. 18 dry sprinkler zones, each 7,000 to 10,000 SF.
System volumes below 750 gallons
6 inch main, 4 inch cross main and 2 inch branch
Per HASS calculations, 40 PSI and 500 GPM required.
NO NEED FOR PUMP - 10 PSI safety factor between required and available.

My questions are:

1) Which option looks better at this point?
2) For Option 2, is a possible maximum of 18 dry pipe valves 'too much'?
3) Does the pipe sizes for Option 1 and 2 appear 'reasonable'? Travis, thanks for your comment regarding the 6 inch piping.
4) Travis, you mentioned to be aware of "hanging requirements when pressures exceed 100 psi". What do you mean by this?
5) Any other considerations? Am I missing anything?

I am leaning more towards Option 1...

Thanks again.

 

[skdesigner]

With that kind of money on the line, I would recommend getting in touch with a company that has a copy of SprinkFDT and paying them to run a water delivery calc for your system.

Who knows, maybe you can get away with 3 big systems and still meet the trip time requirement. Vizor accelerators are a big help in these situations as well.

 

[Ehendrix]

Sl3656, I did exactly what Travis said when I ran into that issues with a materials supply building. The only option I could come up with was splitting the system in 2 systems with a single tank mounted air compressor & 2 air maint. devices.


Eric Hendrix, SET
NICET Certified
Design Manager

 

[SprinklerDesigner2]

It was back in 2013 that I wrote about a 1,409 gallon system but with a little more water supply.

Here's my post from the past.

But what I would do is read the analysis by James Golinveaux

A Technical Analysis: Variables That Affect The Performance Of Dry Pipe Systems

and try a little loop like I did... it really worked for me!

 

[skdesigner]

Purple star, SprinklerDesigner2. I was going to link that white paper in my post, but for some reason I thought it was by Viking, not Tyco, and couldn't find it.

 

[SprinklerDesigner2]

James left Tyco a year or two ago and is now with Viking.

What impressed me most on his technical analysis is it flew in the face of everything we were naturally assumed. With the low pressure valves and the analysis paper 1,000 gallon systems no longer scare me like they did. With that said I do always leave myself some sort of a path out just in case.

 

[sl3656]

SprinklerDesigner2 and skdesigner - many thanks for your helpful posts. This is certainly food-for-thought.

I have currently gone for Option 1 based on my previous post on September 15. I have kept the zone sizes such that the system volumes are below 750 gallons, as a belts and braces approach. A pump is necessary due to the smaller pipe size diameters adopted (maximum pipe diameter is 4 inches). At the moment, the pump is only required to boost pressure - sufficient flow is present in the source.

Edit: @SprinklerDesigner2 - in your previous referenced post, you mentioned " I did it in such a way we could have easily manifolded the riser making two systems of less than 750 gallons involving a days extra labor and the cost of a dry valve with trim." Could you clarify exactly what you did to achieve this - I am having difficulty seeing how you did this. If you needed to split a system into two smaller zones, surely you would need another riser (with dry pipe riser valve) and a main at least. Appreciate your feedback. Thanks.

Edit 2: @SprinklerDesigner2 - another question regarding you previous post - you mentioned that "I also did a little trick with a 1" "loop" on the last two branch lines to allow air to compress in the closer non flowing main instead of being forced out of the inspectors test. I think it worked.". I had read the Tyco white paper and it stated the benefits of having additional pipe volume beyond the inspector's test valve. How would a loop help in this case?

 

[UFT12]

Funny, this article on page 24 of this issue of Sprinkler Age seems to contradict the benefits of low air pressure as discussed in the other thread. It is difficult to comprehend fully the balance between air and water and their behavior as too many factors are into play.

Dry Pipe Water Delivery Time - Sprinkler Age

 

[stookeyfpe]

Funny, this article on page 24 of this issue of Sprinkler Age seems to contradict the benefits of low air pressure as discussed in the other thread. It is difficult to comprehend fully the balance between air and water and their behavior as too many factors are into play.

I somewhat agree. However, the scope of the analysis was limited to Extra Hazard Group 1 occupancy hazards. I concluded that if one has a hazard that warrants an Extra Hazard classification, maybe NFPA 13 should require that the water delivery time be calculated, which is great if you sell software. The paper did a good job of indicating that a number of variables must be considered. I wished it would have gone into greater detail on conditions where water delivery calculations should strongly be considered.

A study that looked at this issue based on Light and Ordinary Hazard occupancy hazards would have touched a much broader audience.