Sprinkler System Pressure Requirements

You'll need to know how many sprinklers you will have. 50 m head is roughly 60PSI. I don't do metric. I don't think you'll have enough pressure. You may need a booster pump.

By my calcs 50m head ~70psi?

The system we are installing is a cheap domestic sprinkler with a design that expects only sprinklers in one space to be required at a time, therefore the maximum number of sprinklers in one space is the design load or flow, rather than the toal number of sprinklers. This is the reason for the "two sprinkler heads at once", but for an extra margin of error because an area may end up very large, we could allow for say 4 at once.

There's more information here than you will ever use:

1. Pipe flow rate calculation | calculate pipe pressure drop with ...

I assume the spec calls out a required pressure, too.

Good Luck.

Well it is actually more, and 50 M of head is on the high side for domestic supply, possibly a little to high. Domestic supply can drop as low as 20 psi during fire demands. The sprinkler system should be sized to meet minimum flows at a lowest available design pressure for fire flows per code, typically 20 psi nationally though local agencies can vary to higher requirements. Reference the national fire codes, AWWA standards, and uniform plumbing code as needed.

Yes, I finally went back and did the math. There are people here who are more current than I in this field. I'm taking myself out of the discussion.

Thanks.

The only sure way to find out what you need is to contact the local Fire Marshall (or whatever the local fire official is called in your country/region) and find out what the system capability requirements are. Such questions as: how many open heads are the system supposed to maintain supply to and for how long; what are the volume capacity requirements for the storage tank; etc?

I am familiar with the USA NFPA codes and my states requirements but they wouldn't be of much help to you if you are expected to meet some other location's requirements. What you don't want to do, especially in a residential installation, is to install what you you think is sufficient and correct and then have Mr. Code Guy come in and tell it is wrong and to redo it. Also in many locations an inspection prior to installing indoor wall/ceilings/floors is mandatory so they can see for themselves what is contained within the system.

Good Luck, Old Salt

when in doubt a design factor of 3 will cover your butt. I would build the system so if you had all the heads on a 1 time the system could handle it. you can always install a pressure reducing valve.. In the beautiful state of New Jersey as per AWWA you can not have a sprinkler system coming off of a domestic water service,they have to be completely separate. i think its a cross contamination thing.

It is people like you who impede the safety and growth of building construction. He is building a residence that is being supplied with water from an onsite tank, for God's sake. He does not have to put any sprinklers in, does he. Why not build for a design factor that will supply all heads at one time? well, for one, it will cost three times as much, directly reducing the odds that it will actually be built, on the order of choosing between poured cast in place walls versus laid up block, ie one is superior, but not cost effective. Just ease up people, and consider reality when you are suggesting solutions. If money were no issue, I'm guessing he would not be posting on CR4.

60 l min = 15.7 gpm

28 mm is more than adequate, sufficient at 60 psi, as long as you don't have more than average friction loss. As you increase flow rates, your supply duration will reduce. If you increase pipe diameter, your psi will remain constant, your flow rate can increase (sprinkler head quantity) but duration will be reduced. If your heads are heat activated, you really have very little downside, because success of the heads results in fire containment. 90 % of all fires are contained with one sprinkler head activation.

By the way, NJ has no requirement to have a separate sprinkler water supply system. A simple backflow preventer is usually all that is required. Of course, in this case, he won't need that.

Actually, the PSI will not necessarily remain constant as you increase pipe diameters for transmission pipes.

Actually, psi at head point does remain constant until flow is initiated. After flow is initiated (ie consumption) the larger diameter pipe will have less psi degradation.

Well that makes very little sense, as static pressure would be constant at any point along the system that was static and the sizing of the pipe doesn't have any relationship to static pressure except wall thickness. For that matter under static conditions the sizing of the pipe doesn't actually effect the flow rate either, because the flow would be 0 for any pipe size in that condition. Change the pipe size and you change the head losses during flow.

A separate water supply IN NOT REQUIRED IN NEW JERSEY. As I stated in post #3, The only sure way to find out what you need is to contact the local Fire Marshall (or whatever the local fire official is called in your country/region) and find out what the system capability requirements are. The requirements of a sprinkler system are mandated by the NJ Fire Code (which is usually based on the NFPA standards) and the local building code (which is usually based on the NJ Building Code). To build a system based on a factor of 3 and with all heads working at the same time would be astronomical in cost and overkill. As others have stated, the operation of a residential fire sprinkler is based on one or two heads opening and containing the fire.

The installation of modern residential system is very simple in NJ and is accomplished with CPVC pipe and residential heads with an additional cost of $3-5,000 for new construction in a 3,000ft² house. Retrofit is about 50% higher.

If you would like to benefit all NJ homeowners get on your state legislators/senators to pass the residential sprinkler law.

I am a fire chief in the "beautiful state of New Jersey" and I am seeing more and more minor fires which did not become "room and contents" or structure fires because the home owners were smart enough to install a sprinkler system. That one head can contain many fires and same both lives and property.

To learn more about residential sprinkler requirements call the fire marshal/fire inspector. Why spend money when it isn't needed or when it won't do the job you want it to do?

Good Luck, Old Salt

50m appear to be good head for sprinklers. Even after the pressure drop due pipe and fittings friction you should get around 50 psi at sprinkler inlet, sound good enough.

50 mm sounds lot bigger for this requirement alone. 50 mm could be a good chaise.

50 mm pipe has 3 times the cross section of 28 mm pipe (not just double), which means 3 times the flow.

Yes,

You have a head of 50 meters. approx. 65 psi at the house; city pressures are usually closer to 100 psi.

Should a fire occur; the sprinkler heads in that area will be the only ones to erupt.

Therefore you could have enough volume / pressure to extinguish a ""One Room Fire"".

However, you can have a system designed, with pipe sizes, pumps, stymies connection for fire dept hook-up etc. that will eliminate gray areas and worry.

The majority of this system can be installed by yourself; the piping material and fittings are a form of plastic with primer and glue application.

This will also reflect favorably for you in House Ins. Premiums.

Not enough people are thinking as you are, if this were the case; the cost would be considerably less.

I hope this sheds a little light on your project.

Jim

You don't say what the water supply is but only that the pressure tanks have 50 meters of head to overcome. If you are using a submersible pump you may want to consider the new constant pressure pumps now on the market. These pumps ramp up rpms to match the output. You will need to know your total demand and total head to match the pump. Generally, you will use this system but you need very little in terms of pressure tank capacity. Any decent pump installer should be able to match a system for you and this looks like an ideal case for constant pressure. I would strongly recommend them and is the system of choice for my own house. I have used Grundfos constant pressure pumps but find these a little more reliable and I don't have have a special motor. Good Luck.

Great discussion fire Marshals, factors of 3 an so on. People really shouldn't give advice if you don't know.

1) fire marshals are not qualified engineers and if you're system didn't work they would be sues if they gave engineering advice.

2)state laws do not determine pressures at sprinkler heads, if fact there are no state laws for sprinklers other than for buildings legally required to have them and that does not include domestic residence under law.

3)where a building falls under legal requirements of sprinkler systems the fire marshals can provide you with minimum requirements of area coverage. If they offer advice on a design or product that does not work they are liable, again as they are not engineers.Fire safety is called that because it relates to the safety of lives not the saving of property. Safe exit routes etc

4)in respect to increase the pressure by a factor of 3 or any factor greater than the sprinkler head flow rate, you will create mist and lose the design and ability of the head to put out fires.

if you want to design a system, you need flow rate of litres/gallons per minute, a simple bucket test will tell you this. Secondly the size of your current pipe is moot, the flow rate and pressure will change when you downsize the pipe to fit the sprinkler, even if you ran 2 inch pipe to the head, the inlet of the head will only be about half an inch to an inch max, the purchased head will have a desired flow rate. Take 80 percent of you flow rate as you rate, after you attach the correct size to your tank line do the bucket test for litres per minute, or go an but a cheap 20 dollar engine pressure tester, the one with the rubber half sphere on it that goes on the spark plug outlet and place it on the end, it will give exact pressure, dive this by the sprinkler head pressure and it will tell you how many you need to use to have the right pressure on the head. Except in cases where there is mains line pressure this is exactly how it is done on the job.

Pressure/flow rate divided by the sprinkler head requirement to operate equals number of heads available. If you are wondering how buildings in the same area have different amounts of sprinklers, then they choose higher lower flow sprinkler heads, or put a line restrictor on the system.

I know a general conversation about hot rods or solar panels or any other engineering subject is great for throwing around ideas, but this involves the safety of human lives, and perhaps lack of actual knowledge should make you think twice before answering.(though we do appreciate the thought)

Archie

_{(I have held qualifications in sprinkler system design since 1996- Grovelly Tafe Brisbane)}

Hi folk, Firstly, thank you to all for your comments. I really appreciate all of them and the thought and effort made. When I posted the Q, I knew that I did not have sufficient detail for an absolute "yes or no" answer, just an, "It looks possible/I don't think it will work" recommendation, and I know a margin of error needs to be allowed. I think I need to clarify a few things too, and apologise for not making them clear earlier. I didn't think a very wordy question would invite many answers so had tried to just put down essential facts! I am in New Zealand, so the legislative environment is a little different from that for many of you. The domestic sprinkler industry is a relatively fledgling one here, as the Standard for domestic sprinklers that can be fed off the house water supply and be installed by suitably certified plumbers was only introduced in 2002. Prior to this, all sprinkler systems had to comply with the more expensive and higher standard of commercial sprinklers. These systems are not yet compulsory here, but I know they are worthwhile, especially because the location and access to my house site means the Fire Service, (a volunteer organisation in rural areas like my site), would really only be turning up to damp down the embers. My water supply will be any rainwater collected off my roof, draining to a smaller tank then pumped uphill to the two 25,000L tanks (with room for one more) 50m vertically up the hill from the house site, (which is as high as I can practically go on my site). The actual stored volume will therefore vary from season to season, and I accept that at times there may not be a lot left for fire suppression! I do not wish to use a pump for primary water supply pressure, as my power supply will be off-grid solar and wind, with diesel generator backup. One that switches on to boost pressure when needed might be possible, but is an additional expense and complication I would prefer to avoid. Because of the timing for my project, I really need to install the main water supply pipes to and from the tank prior to completing the house design, (as I will initially be living on site in temporary building), but do not want to install 250m of a pipe size that will make sprinklers useless. So any water flowing to the sprinklers will flow from these uphill tanks, through estimated 50mm pipe for 250m to the house, where it will enter the probably 28mm house loop of (guessing only) up to 70m full loop length, so 35m worst case, and then through any necessary extension to individual sprinklers probably ~2m max. The standard requires the flow for 2 sprinkler heads at once to be 60L/min 1L/s, and assumes that a maximum of 2 sprinklers are likely to be set off at once. I could contact certified installers for more detailed information about the system design, but they are still establishing themselves in a new field and of course charge for advice, so I came here. I will have to get someone involved at the time the design is finalised, but cannot afford it now. Thank you for your help with this. Sorry for the formatting: my paragraphing with line breaks seems to be removed on submission

Good Luck.

Install the largest affordable pipe to the house, therein lies the gravitational maxim, after you reach the lowest point of fall then you change down to your house line size - otherwise you only have gravitational; weight pressure not increased pressure by reduced line size, as for all these loops you mention, the fire system loop needs to be a separate line from the entry point to the house directly to the sprinklers. Reasons are.

1)the water will loose pressure by friction loss the more turns it has to make through your system

2)the system will be non operational or less operation if any other system is left running - or if plumbing repairs are needed in the house - in fact during construction if the fire line goes in first, any fire that ensues before the building is finished will be covered. Put on the heads as soon as the ceiling is up

3) in the event of a fire in the house they usually start low at floor or wall level, any system linked to general plumbing through the walls risks being destroyed in the first stages of the fire - not because the copper melts, usually a wall section collapses and breaks or kinks the softer heated pipe. So single line in from outside as short a route to the ceiling space as is possible.

Hope this helps

In my opinion, very sound recommendations. Speculation may lead to overdesign or under performance. And when dealing with something as critical as fire protection, under performance is not desired. Considering Sprinkle may become a design reference for NZ authorities, it would be best to design to the best available technology. As noted previously, NFPA 13 on sprinkler systems, provides design guide for pipe sizing, water flow, and pressure requirements and should provide the basis for a sound design. The references posted, upon quick scan only, seem to provide clear direction for installing a well thought out system.

I don't know if you get ahold of a copy of NFPA 13D, but that would help you out. I belive you have a good idea and should have enough water and pressure for a resident system. Look inot listed plastic pipeing if you can get ahold of it. In the US, you would need sevral inspections and maybe a design by a registered engineer. or maybe not. In TN, a P.E. in needed for any facility above 5,000 sq. ft. I am a register P.E. in fire protection and I hope this helps out.