How to Hydraulically Calculate a Trash Chute?

10/13/2021

How should I properly be sizing a vertical branch line that feeds only a five-story trash chute?

Would a hydraulic calculation be a line calculation, so I would calculate as many as five sprinklers?

I typically feed sprinklers from the adjacent floor level, so I've never ran a separate calculation just for a trash chute. My gut says a 1-inch threaded line isn't enough for a trash chute, but I'm not 100% positive how a hydraulic calculation should be done here.

Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

14 Comments

Alex

10/13/2021 07:26:10 am

Hi Anonymous,

There isn't a clear path outlined in NFPA for calculations of trash chutes. In the past, depending on the number of stories, I would either bring up 1 1/2" or 2" dry main.

In regards to calculating the system, I have never had someone ask for me to provide calculations. I suppose if I were to run a calculation, I would assume all heads within the trash chute were flowing and just calculate the dry riser.

For your situation, depending on the available water supply and distribution to the base of the trash chute, you could get away with a 1 1/2" dry riser feeding (3) heads.

Thanks!
Alex

RayJ

10/13/2021 08:17:55 am

Are you not able to run a 1" line to the trash chute off the lines on each floor? I think that would be more cost effective then running a new line up the entire chute.

Jessica Lutz

10/13/2021 11:59:52 am

I depends on the AHJ-preferred configuration.

Todd Wyatt

10/13/2021 08:20:15 am

2021 IBC 903.2.11.2 Rubbish and linen chutes requires sprinkler heads at the top of the chute, in the termination room, and at alternate floors (begining w/the second level below the last intake and ending with the floor above the discharge) and at the lowest intake.

Craig Hanson

10/13/2021 08:22:24 am

Trash and linen chutes are covered in NFPA 13 22.15. Usually a sprinkler every other floor is needed. There is no specific requirement to calc the chute as the sprinkler head is usually fed of each floors system. I don't think I have ever seen an independent system just for a trash chute.

Glenn Berger

10/13/2021 08:22:35 am

I have never been required to submit a separate calculation for the trash chute.

Typically it is one sprinkler per every other floor fed from a branch on that floor.

The shaft is typically fire rated, such that It will not be anywhere close to the most demanding area of a building.

Steven

10/13/2021 08:34:13 am

I have sized a trash chute riser in a 42-story high rise to be 2" pipe (although this building had fire pumps & PRVs). We used a hydraulic calculation as outlined in NFPA 13 (2016): 11.2.3.4.1, which requires only three sprinklers to be calculated (at a minimum of 15 GPM).

I think in your 5-story building, you would only have three sprinklers in your chute anyways, as Alex & Todd described. I don't know if 1" pipe will work in your situation, but I certainly think 1¼" should be sufficient. We have been having success using a grooved riser with welded 1" POLs, and incorporating flexible hose connections to tie-in to the sprinkler heads in the chute. I would propose trying something similar if your local AHJ does not have any issues with flex hoses.

Jesse

10/13/2021 08:57:16 am

I don't think I have ever calc'd a chute. Chapter 22 in NFPA deals with trash / linen chutes along the auspices of sprinkler placement and such, but typically those sprinklers are fed from floor level systems. I think I'd want to avoid a separate system if I could.

Jack G link

10/13/2021 09:42:05 am

Yes, calc 3 heads.
One head at top.
One in bottom, trash room.
Alternate floors.
Usually the sprinklers come installed in the chute, below the door, within a pocket,with a 45 degree shield over them. You may not be able to see them,
From the floor , inside the door.
I ve designed/ installed them both ways-- separate riser with flow switch/ test and drain, and from the floor.
I like the riser better, for zoning, and protecting just a chute fire.
I ve also installed from the floor, with a flow switch for the chute heads. You get a " double hit" , say if 5 chute head goes, if wired this way you get an alarm for chute, and floor. Although if chute head triggers, all the heads above usually triggers. Thats why i think riser is more appropriate. For the cost of the individual chute heads, it pays for tge 1.5 ir 1.25 inch riser.
I used " picker trunk, gem/ grinnell heads , which are still available but expensive. " Smooth frame, glass bulb, for wiping clean ". .
I like the flex head idea. I would use the " duct version " if providing.
Usually the chute is installed in a fire rated enclosure
Usuall, block, sometimes rated shaft wall, both types enclosures, make it hard to get to, and pipe, the below door, chute cute sprinklers.
Install at least arm or flex, with sleeve, to sprinklers, before the chute is walled in, is appropriate.
Test and drain. Flow switch in trash room below. Sometimes need a dry head in top of shaft.

David anderson link

10/13/2021 01:28:22 pm

I have been placing heads in trash chutes sincince I can nopt remember when. Although NFPA 13 only requires every other floor , Trash chutes are generally manufactured now with a factory installed sprinkler head at the door to the chute. Genrally I have placed an 1 1/4" control assembly and risert to feed this type of assembly at every floor. I have never been asked to calculate it. Lets face it most heads are high rises with 100 plus psi avalable at the highest floor. A single head would discharge 56 gpm. So reasoning rules. Whatever you do don't let this out as it will start a reaction and then the "what if" reviewers will take over. I can remeber years a go (early 1990's) when a Fire Marshall was inspecting a job I was doing and a duct passes through the corener of a closet that was 6 ' by 2'. The bulkheads lowered the cieling in the oine end of the closets by 12" and was about 18" wide. Rather than argue with him I said I'll tell you what, I'll give you a torch and stand you in the corner under the bulkhead and I'll set the head off. Let me know if you get wet.." That was it he pulled off the idea of requitring a second head. Why because common sense prevailed. There are those however where therre is no common sense. So leave dead dogs lie. Technicall y as pointed out it is 3 heads, but then you cna go everyother floor. Pick your poision.

Craig Hanson

10/13/2021 01:32:12 pm

I agree David, I will also add that you are costing your customer to do things that are not necessary or needed. running a separate line just for the heads in the chute on a 5 story building is a waste of money and time for your fitters that are probably going to cuss you out for running it.

David J Anderson link

10/14/2021 12:27:18 pm

Yes but here AHJ's generally require a control valve and flow swtich at every floor. So cost are not necessarialy appples to aples and added cost of addtional Fire Alarm Monitor Modules general out weigh the single feed riser system.

Patrick Drumm

10/23/2021 10:00:19 am

I 100% agree that doing things above and beyond code is not a path to go down often. In this case, there is a potential "what if" situation that may be more probable than some that are often proposed. More often than not this points me to a separate line design. With a separate line and one control valve at the base of the chute water flow can be shut down in a case of accidental discharge of a sprinkler due to physical damage. I know there is protection designed into these chutes and they do there job for the most part. With feeds off each floor, if someone at the bottom of the chute encounters water, they need to close feeds at ever floor until they find the correct floor. By then there could be significant water damage.

I have encountered a few specifications that require a control valve even if the sprinkler is fed from the individual floors. Is anyone aware of a code section in NFPA #13 that requires this?

sean

10/14/2021 11:34:23 am

11.2.3.4 Special Design Areas.
11.2.3.4.1 for dedicated runs.
If it is feed off the floor I would say the hydraulics can be dictated by a similar hazard calculation on the floor and keep the same hydraulic pipe schedule.

How to Hydraulically Calculate a Trash Chute?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES