Sprinkler heads

[wickedspins]

If I'm looking to convert an existing wet-pipe system to a dry-pipe system, I figured I need to do the following:

1) Recalculate to ensure the system has enough flow and pressure.
2) Replace fire riser with one used for a dry-pipe system.
3) Add riser mount air compressor.

I'm not sure if sprinkler heads need to be replaced. Is there a difference between sprinkler heads used in wet-pipe vs dry-pipe sprinkler system?

I have seen comments about adding a heater in the attic to maintain the attic above 40 deg F so the water in the pipe won't freeze. Would any heater works? Gas or electric? And how would you size one when there are louvers in the attic used for ventilation?

Thanks.

 

[KLH]

Wet pipe systems typically use black steel piping. Dry pipe systems are limited to internally galvanized steel pipe.

Check your pipe material before converting.

See 2010 NFPA-13, Paragraph 8.4.7.2.1.

 

[skdesigner]

1) Correct, don't forget to increase the area and decrease the c-factor (assuming black pipe)

2)Called a dry pipe valve, don't forget to add it into the calcs.

3)..or tank mounted, or shop air

You need an inspector's test connection at the most remote point.

And, my personal favourite...Dry piping needs to be graded, whereas wet systems are permitted to be installed level. I can imagine there will be quite a few trapped sections of pipe. If you can't back off the hangers enough to get grade, you'll need auxilliary drains (NFPA 13 2010 Figure 8.16.2.5.3.5) at all the low points.

As for the sprinkler heads, it depends on what sprinklers are on the system (upright, pendant, CMSA, ESFR etc), though you do say attic, so I presume upright. While you're checking them out though, are they QR? Time to replace them per NFPA 25 anyways? Food for thought.

Presumably the best heater is the one that does the job for the cheapest cost. Can't speak to your local codes though.

KLH: Follow that code reference up one point. Galvanized piping is required in dry systems where CMSA sprinklers are in use.

 

[TravisMack]

Some things to consider:

1 - Dry piping is only to be galvanized internally with K4.2 sprinklers or large drop sprinklers in a dry system, if I recall correctly.

2 - As mentioned above, dry systems must be pitched so that the mains pitch at 1/4" per 10' (unless in refrigerated spaces, then must be 1/2" per 10'). Lines are to be pitched at 1/2" per 10'.

3 - Aux drains need to be converted to drum drip drains.

4 - The system needs to be recalculated with the following parameters (and there may be more depending on the system): Design area increased 30% due to dry system delay | QR sprinkler reduction is not applicable | if black pipe, the C-factor for calcs shall be 100 instead of 120, etc..

5 - If the system capacity is >500 gallons, you need an accelerator on the dry valve trim. If the capacity is >750 gallons, you need to deliver water to the remote insp test connection within 60 seconds.

6 - You need a remote inspector's test connection. Wet systems often have the ITC at the riser for ease of maintenance.

7 - air compressor as noted above

8 - etc...

Have a mech engineer determine the heating system that you would need in the attic to maintain at 40°F.

Depending on the occupancy and your temperatures, you may be able to go with an anti-freeze solution. However, you may need to add a RPZ backflow preventer. Also, if the capacity is >40 gallons, you need to calculate using the Darcy-Weisbach formula instead of Hazen-Williams. This would require a hydraulic analysis to determine if the AF option is viable or not.

From my experience, it is possible to convert a dry to a wet system, but very challenging to convert a wet system to a dry one.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[wickedspins]

Thanks all for the responses. Lots of great information there.

I forgot to mention that we are using 2002 NFPA 13 for this one. 2002 NFPA 13, paragraph 8.4.7.2.1 states "Where steel pipe is used in preaction and dry pipe systems, piping materials shall be limited to internally galvanized steel." I don't have 2010 NFPA 13. I am not seeing anything about CMSA. So it looks like I can't use black steel in the dry-pipe system under 2002.

There are upright, pendant, and sidewall sprinklers throughout the building. Dry-type sprinklers quick-response, standard coverage, 5.6 K-factors are also used in areas subject to freezing.

So there aren't any restrictions on the type of heater in the attic? I guess gas would be cheaper to operate than electric.

 

[skdesigner]

I don't have 2002 readily available, and 2010 has a change bar beside it for 8.4.7, which I belive just incorporates the fact that they are now called "Control Mode Specific Application" instead of "Large Drop" in 2007 and earlier.

What is the title of 8.4.7? I'm guessing Large Drop Sprinklers.

In which case, every requirement from 8.4.7 until 8.4.8 is referring to CMSA (formerly Large Drop) sprinklers.

 

[TravisMack]

Do you have large drop sprinklers, or standard spray? Since you are talking about an attic, I would assume standard spray. As SKD said, you need to read the title of the section you are looking at. It may not be applicable to the sprinklers you are using.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[wickedspins]

You guys are correct....

8.4.7 Large Drop Sprinklers
8.4.7.1 Large drop sprinklers shall be permitted to be used in wet, dry, or preaction systems.
8.4.7.2* Galvanized Pipe.
8.4.7.2.1 Where steel pipe is used in preaction and dry pipe systems, piping materials shall be limited to internally galvanized steel.

I do not have any large drop sprinklers. Seems like a lot of things to consider to switch to a dry-pipe system as you all have pointed out. I'll leave it to the client to decide if they want to change the system or put in the heater.

Thanks you very much!

 

[cdafd]

What is this system protecting????


If you make it a dry no heat is required in the attic just the riser room


Do not have the book do you need return bends if the pipe is not kept heated????

 

[skdesigner]

Not if it's uprights. Return bends only if the pipe, drop and pendant sprinkler are in a heated portion of the building. Otherwise it's dry pendants.

 

[cdafd]

Sk


Huh ???? Do not have the book

 

[TravisMack]

You can only use return bends to avoid dry pendents if both the sprinkler and the piping are in heated areas.



Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[NJ1]

First what is your location. What Jurisdiction.
Then. To what elements you will be considering the installation.
Is it a warehouse, attic, residence, etc.

Then you could determine what type of sprinkler and piping you will need. Most guys answer all basic questions but you need to dig deeper.

 

[wickedspins]

The buildings I have are: dormitory, multi-family dwelling, office building, and fire station where the fire trucks are parked with a small office and restroom.

 

[TravisMack]

The residential buildings will be a challenge if they have residential heads. There are some pretty crazy trip times in residential occupancies.

It will be interesting to see how it turns out.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com