Attic System Design
Attic System Design
(OP)
Please see attached PDF for reference. I am having a heck of a time getting this system to work and I have ran out of ideas so I figured I would come here and see if any of you can see an option that I may be missing.
This is an assisted living center with a NFPA 13 system. It is fed from a riser in the South West corner of the building. Dwelling units and common areas are protected by pendents that are fed from CPVC piping tented in the attic. This forces me to use attic sprinklers that are listed for protection of CPVC piping. Attic system is a dry system to add to my frustrations. At this point, in order to satisfy demand I am having to run a 4" main line throughout most of the building with 2" & 1 1/2" branch lines everywhere else. This pushes my system over 1000 gallons which will force me to have a specific water delivery time.
Does anybody have any design suggestions that I may be missing in my layout that may help reduce pipe sizes to get my system volume down?
This is an assisted living center with a NFPA 13 system. It is fed from a riser in the South West corner of the building. Dwelling units and common areas are protected by pendents that are fed from CPVC piping tented in the attic. This forces me to use attic sprinklers that are listed for protection of CPVC piping. Attic system is a dry system to add to my frustrations. At this point, in order to satisfy demand I am having to run a 4" main line throughout most of the building with 2" & 1 1/2" branch lines everywhere else. This pushes my system over 1000 gallons which will force me to have a specific water delivery time.
Does anybody have any design suggestions that I may be missing in my layout that may help reduce pipe sizes to get my system volume down?





RE: Attic System Design
The only things that have worked in the past is adding Exhausters at the end runs. These are expensive.
Optimally, adding system risers to split the volume is best. Though no one wants to run separate underground feeds etc..
Do you have FDT (INSERT TRADEMARK SYMBOL HERE) from TYCO? It always helps to know what the actual is showing now..
Your pipe sizes look good considering what is being delivered..
Good Luck
R/
Matt
RE: Attic System Design
A low pressure dry valve would be your best option since your system is pretty much one long line so you want to get as little resistance as possible from air pressure.
But I agree with Matt that you should run this through FDT and see what kind of water delivery time you get with the software. It will take a while to input it since it looks like you are working with HydraCAD, but it would save you a lot of headaches later on when it's time to test.
RE: Attic System Design
1 - I assume at the hips, you are using Tyco AP sprinklers. They can only protect up to 3000 sq ft, then must be separated from other areas by 15' of BB sprinklers. You may have exceeded that in some areas.
2 - Don't forget you will need to put those BB sprinklers on sprigs where they are directly on the pipe.
3 - You may have to run a wet main under the insulation tent to locate a second dry valve some where in the building to cut your system size.
As Matt stated, that is the problem with big attics and dry systems. You will of course have an accelerator, and these make a big difference in trip times. You can use a low differential dry pipe valve to reduce system air pressure. Being that you have a tree, it will trip faster than a loop will. I have seen tree systems of 1250 gallons trip in <30 seconds with a Tyco QRS accelerator, but it also had about 150 psi sitting under the dry valve due to the fire pump.
Travis Mack
MFP Design, LLC
www.mfpdesign.com
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RE: Attic System Design
Have seen large systems meet the 60 second with no problem lately, but we have good water, and a quick opening device
RE: Attic System Design
Also, I will be putting all the heads on sprigs. I currently do not have sprig tags because I hadn't raised the drawing up to get elevaitions. Thank you all for the ideas. I will keep these in mind next time I run into this issue and cannot remedy it.
RE: Attic System Design
Recently we installed a large ~750 gallon dry system with about 65 psi static water and met the 60 second test time. We used a victaulic NXT with 13 psi air pressure and QOD IIRC.
RE: Attic System Design
My system volume is now down to about 680 gallons. We have 88 psi residual. So hopefully the 60 sec delivery time isn't an issue.
RE: Attic System Design
Are you just using standard heads?
No tyco attic heads at all?
RE: Attic System Design
RE: Attic System Design
A Technical Analysis: Variables That Affect The Performance Of Dry Pipe Systems
James Golinveaux, Sr. Vice President,
Research & Development
Tyco Fire & Building Products
If you don't have this you will want to grab it.
About two years ago I had a large dry pipe system, I forget the exact size but I think it was approaching 1,400 gallons, and needless to say I was very concerned with trip times seeing as how all we had was 65 psi static from the city but going for us it was a very flat curve.
After reading the paper I figured I would try some experimenting and setting up the system I made it so I could add an additional dry pipe valve if needed and as I already had it figured in my price no great harm would be done. It was a gamble, worth risking $1,000 in labor and re-submittal of plans to save $4,000? I thought it was.
So I ended up fighting the dry valve and I won!
What I had was two large tree systems and what I did on the last line was simply tie the two end branch lines together with 1" pipe making the system a "loop" if you will.
I was taught "loops are bad because you got to fill up all the pipe before water gets to the inspectors test" and did I ever prove myself wrong on that.
I tried it both ways, fitters wanted to drink beer but I wanted to see for myself, to discover ten feet of 1" pipe with a union cut 15 seconds off the time water to the inspectors test connection.
This might be old hat to some of you but I was completely floored because it went against everything I've been taught for 40 years.
But when you think about it, analyze a bit, it makes sense that it would cut the time because it gives the air someplace else to go other than through a small orifice and globe valve.
I learn something new every day.