# A little bit about spacing, placement and coverage



## sprinklertech (Oct 24, 2010)

A little bit about spacing, placement and coverage

First we will touch upon spacing and placement rules for pendent sprinklers. Pendent sprinklers are installed through ceilings with pipe concealed either in the space between floors or attic.

A photo of a pendent sprinkler.










Sidewall sprinklers are installed on walls below ceilings like this.










While we will begin talking about pendent sprinklers it's my opinion that sidewall sprinklers are about the most abused and improperly installed sprinkler available. Unless listed otherwise these sprinklers must be installed between 0'-4" and 0'-6" below the ceiling. That's a pretty narrow band but lucky for us most residential sidewalls are listed to be used up to 1'-0" below the ceiling (I have yet to find one listed to be installed less than 0'-4") but in most cases there is a price to be paid when installing more than 0'-6" down. For example a certain sidewall sprinkler may have a listing requirement of 12.0 gpm if installed between 0'-4" and 0'-6" down but if installed more than 0'-6" to 1'-0" from the ceiling this same sprinkler in the same room might call for 14.0 gpm. 

*The following is only my opinion. I can be an opinionated kind of guy.*

Properly designed sidewall sprinklers are the way to go laid out and designed these sidewall sprinklers should be used anywhere freezing temperatures can be encountered.

In my opinion water pipe should never be installed in exterior walls or attics anywhere there is a possibility of freezing temperatures. It's nuts to do something like this it opens one to monstrous liabilities.

I don't care if you cover it with insulation. These systems are going to go into a house and (hopefully) sit there unused for 30, 40 and maybe even 100 years. You mean to tell me over those sorts of time frames the possibility doesn't exist where maybe a workman in the attic won't accidentally kick off a piece of insulation? All he has to do is lay back one foot insulation over the second floor bathroom and you got the makings of a huge disaster come cold weather.

You mean to tell me over 50 years there isn't a possibility of birds, maybe a raccoon or some other varmint taking attic residence moving insulation to make a nest?

Gentlemen, all it takes is one freeze to do $100,000 worth of damage. Think of 30 gallons per minute into an attic for 10 minutes. What if the homeowners are gone for the weekend? How would 100,000 gallons of water do over a weekend if nobody noticed the river running under the front door after the basement completely filled up?

It is going to be from freezes where residential sprinklers get a bad reputation. If a sprinkler head or line freezes 95% of the time it will be due to poor installation practices.

Would you run a cold water line in the attic content to laying batt insulation over it in a home in Minnesota? Of course you wouldn't.

Why should sprinkler be treated any differently? Answer is it shouldn't.

I always run sidewall sprinklers in interior walls. Never had one freeze up on me yet (35 years).

But because of spacing limitations it is a safe bet sidewall sprinklers will always cost more because 1)there will be more of them 2)they are harder to install drilling the studs out and all and 3)calculations will require larger pipe and 4)there is going to be more pipe in order to keep a circulating system intact. 

How much in an average home? My off the cuff estimate would be identical homes, one in Florida the other in Minnesota, the home in Minnesota will have $500 more in material and require one man one additional day labor which will mostly be drilling stud walls.

Between just us knowing what I know if someone wanted to install a residential fire sprinkler in my house I would insist they use sidewall sprinklers. I'd tell you to keep your stinking water pipe out of my attic and I wouldn't care if I did live in Florida.

Ok, I'll get off my soapbox but I did want you to know there are alternatives. I will be covering both but first let's spend a little more time on pendent sprinklers.

Consider this









Above we have two identical 14'x16' rooms. Whenever possible I'll nearly always try to claim the space in the center of the room (this is usually where lights and I fight) because it can mean considerable savings in pipe size and might even make the project possible.

For example unless you have extremely high public water pressures it's hard for me to envision a system with a 1" public tap, main and meter that feeds two sprinklers in a compartment each requiring 20.0 gpm that is a theoretical minimum of 40.0 gpm 

Plugging the numbers into our *Engineering Toolbox *with 40 gpm flowing through 1" Blazemaster (ID=1.101 C=150) we suffer a head loss of 24.7 psi over 100'. That is pretty significant.

But in the same room say you have two spaced so they aren't more than 16' apart or 8' off a wall our head loss is only 11.1 psi. Less than half the 24.7 psi developed flowing 40.0 gpm..

Most of the time the requirements are easy enough to reach where you have just one head in the compartment... where you start running into difficulty is when you have two or more.











In figure #2 and #3 we're demonstrating sprinklers do not have to be in a perfect symmetrical pattern around the room. They can be offset, to miss lights, HVAC or whatever, about the room but more often than not these sorts of offsets will require more water discharge and more water discharge is equal to the real possibility of larger pipe being required.

You can have irregular rooms as shown by Figure #4.










For the next post in this thread we'll dive into using sidewall sprinklers.


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## sprinklertech (Oct 24, 2010)

Now a little bit about residential sidewall sprinklers.

There's lots and lots of these available on the market but a brand new one out is the Viking FREEDOM® RESIDENTIAL HORIZONTAL SIDEWALL SPRINKLER VK453 (K4.0) and you can *view the complete data sheet here*.

Let's take a quick look at the data sheet.









First thing you will notice is two tables.. one is for positioning the deflector between 4" and 6" down from the ceiling and another table below it giving water rate requirements for the deflectors located more than 6" up to 12" below the ceiling.

In nearly all cases where the deflector is located farther than 6" more water is required.

Also, in comparing pendent sprinklers with sidewall sprinklers, in nearly all cases sidewall sprinklers require more water. 

In nearly all cases I can design a residential system that requires no more than 3/4" pipe, which a standard 3/4" house tap, feed and meter as long as the length between the house and street doesn't become overly long, reasonably good city water pressure (55 to 65 psi which can be found in most locations) and a judicious process of sprinkler selection and spacing. But when using sidewall sprinklers this becomes much more difficult to do. Not impossible in some cases but harder.

Using a pendent sprinkler all I need is 13.0 gpm with a 7.0 psi to cover a 16'x16' area but with a sidewall I need 16.0 gpm @ 16.0 psi. This is pretty substantial especially if dealing with a compartment requiring more than one sprinkler head.

But I really like them. You can run the pipe in the walls insuring they remain in heated environments and away from possible damage from workmen in the attic, rodents etc. Another reason I particularly like using them is I don't have to worry about blockage from lights and they are particularly nice in rooms with decorative beams. Like a family room having 6"x6" decorative beams 3' on center. These are a pain with normal pendent sprinklers.

But they do take more water and in the practical world our goal should be to limit the size of required domestic waterlines if possible. Many cities charge a surcharge for over-sized domestic lines that sometimes get ridiculous.

From practical experience it isn't that hard to run 3/4" in stud walls. A good quality wood drill bit makes short work of it and *Blazemaster CPVC* will bend enough so you can slip it in without using couplings. Other reasons I like it is that it's specifically listed for fire protection, it is rated at a 175 psi working pressure and I have yet to hear where a rodent has chewed into it and we've installled it in some pretty bad rodent infested areas. The only times I've heard of failures is 1)where the installer forgot to glue the joints and 2)it froze up which in my opinion is negligence and not product failure.


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## sprinklertech (Oct 24, 2010)

For those interested Viking has a very good pdf on design and installation using Blazemaster that can be found *here*.










Our pipe and fittings will be BlazeMaster. What is the total equivalent pipe and fitting length from Point “A” to Point “B” in the diagram above?

Our pipe and fittings will be BlazeMaster. What is the total equivalent pipe and fitting length from Point “A” to Point “B” in the diagram above?

Where the information is published use the manufacturers data and where not I have always used the equivalent fitting lengths found in NFPA #13D for Type L copper. Maybe this isn’t absolutely accurate but we are not building Swiss watches and the answer will be close enough to determine if the system will work or not.

The Answer:

Total Length of Pipe =24’-8” (only add pipe that has water flowing through it). From Point “A” to “B” we added 5’-0”+6’-0”+2’-6”+6’-0”+3’-0”+5’-0”+2’-8”+3’-6”+4’-6” for a total of 24’-8”.

For fittings I see one (1) Tee (Run) which is equivalent to 1’-0”. For 90 Deg. Elbows I count two (2) which have an equivalent length of1’-0” each for a total of 2’-0”. I see two (2) tees with flow turned 90 Degrees and with each being 3’-0” in equivalent length we have a total of 6’-0” for the two tees. I threw you off here, one of the tees is 1”x3/4”x3/4” and we always count the smallest diameter in the turn so this tee should be counted as a 3/4” tee. We have two (2) 45 Deg Elbows and each of those is counted as 1’-0” for a total of 2’-0” for the 45 Deg. Elbows. Finally we have a globe valve and these are killers. Always avoid globe valves opting to use a ball valve instead. The equivalent length for one (1) globe valve is 18’-0”. Added all together the total equivalent fitting length is 29'-0".

Now we add the total equivalent fitting length of 29'-0" to our actual pipe length of 24'-8" to get our total equivalent length of 53'-8". In other words from point A to point B the total friction loss will be exactly as if we had 53'-8" of straight pipe.

Let's assume we had 13.0 gpm flowing from point "A" to point "B". What would be our total friction loss?

Simply go to the *Engineering Toolbox*, plug in the blanks and your answer should look like this:











Flowing 13.0 gpm we will lose 5.1 psi through this section of pipes and fittings.

That isn't so bad but what happens if we increase that flow from 13.0 gpm to 20.0 gpm?

If you still have the toolbox up all you have to do is change one number and we discover we will lose 11.3 psi. More than double what we lost with 13.0 gpm.

Interesting to note if we do double the 13.0 gpm to 26.0 gpm the total friction loss increases to 18.4 psi our nearly quadruple what we lost at 13.0 gpm.


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## sprinklertech (Oct 24, 2010)

Referring to the above post if we had a VK468 sprinkler at Point A located in the center of a room measuring 12'-0x12'-0" that sprinkler would have to be supplied with 13.0 gpm.

In order to discharge 13.0 gpm the VK468 sprinkler is required to be supplied with 7.0 psi pressure.

Assume we had a sprinkler at Point A. What calculations are is if we needed 13.0 gpm at Point A we would have to have 7.0 psi at that point "A" and to get this accomplished we have to have 7.0+5.1=13.1 psi with 13.0 gpm flowing will be required at point "B" to adequately supply the sprinkler.

How hard is this? If point "B" happened to be the point of city connection and the pressure at that point was equal to or greater than 13.1 psi then we are good to go. We're done with the basics.

But let's say it isn't done here and we want to add an additional sprinkler at Point "B". How do we do that?

First thing we will assume is both sprinklers at point A and point B are in the same compartment. 

It would be easy if all we had to do was add another 13.0 gpm at point B and carry the 26.0 gpm to the street but it doesn't work like that. It isn't hard but it isn't that easy either.

Fire sprinklers work the same way two identical lawn sprinklers would work in your yard. What happens if you feed two yard sprinklers from one two 50' sections of garden hose? From the hose bib you run 50' to the first yard sprinkler, connect a 3-way attachment so you can fix one yard sprinkler then continue with another 50' of hose to the second yard sprinkler at the end. What is going to happen when you turn the water on?

We all know the sprinkler nearest the hose bib will put out more water... you guys see this every day in everything you do. 

Fire sprinklers are no different and knowing the k-factor of the sprinkler at point "B" we can calculate its output.

Remember this?










The K-Factor of the VK468 pendent sprinkler is 4.9 and knowing we must have 13.1 at point B (this is required so we can provide the sprinkler at Point A with 7.0 psi) the actual output of water will be:

q=4.9*13.1^.5 or *18.1 gpm*. 

We add the 18.1 gpm to the 13.0 for a total gpm of 31.1 required at point B to adequately provide enough water for both sprinklers.

I have often mentioned "theoretical minimum" water demand and now you can see why it so very seldom happens. With two sprinklers operating, each sprinkler requires 13.0 gpm but to supply the one farthest away you need more pressure at the B which will cause more water to be discharged.

This making some sense to you?

And about these calculations.

It isn't something you need a degree from MIT to do but if you're thinking you can gloss over and catch enough to do it you're wrong there too. Here is what I think. Given two to three days diligent study anyone here can grasp this. I remember taking my first hydraulics course in the mid 1970's, this was well before computers when we did everything by hand using a calculator and pencil, and I admit it was confusing at first. Just remember it isn't that hard to do but if you feel a little frustrated while learning welcome to the club... we've all been there.


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