Changing Waterflows 2

[RemoteControlFF]

I'm sure others have run into this situiation before, so I'd be interested in any tips/advice/war stories.

A grocery store was built in 1994 and they are currently constructing an addition (by that I mean its already up, and they just came looking for sprinklers). The static pressure has dropped almost 40 psi between now and then. The same guy did both flow tests (we did the install on the first building), same hydrants, and both tests were overseen by the local water dept. so we would have been informed of any main breaks, etc.

We're going to go re-flow, but what do we do if the numbers don't get any better? The addition is already up, so they are going to want to use it, will we be looking at installing a fire pump?

 

[RWF7437]

"...........so we would have been informed of any main breaks, etc."

Maybe, maybe not. You should have been informed of any KNOWN changes to the public system. If there are unknown changes it is as important to the water supplier as it is to you to find out what they are.

Changes in static pressure are very unusual, especially 40 psi!. They could be caused by changes in pumps, reservoirs or both. They could also, although less likely, be caused by valves set to "open" which should be closed or by closed valves which should be open. Also, check your pressure gages. Are there new large demands on the system ?

Work WITH the water supplier to find out what may have happened between 1994 and 2009. Static pressures should, ordinarily, be between 40 psig and 80 psig in most systems. Reservoirs are usually operated within 10 feet of overflow so normal daily changes in pressure are usually between + or - 5 psig. Pumps will normally operate to keep these pressures fairly constant.

Anything outside these limits should be suspect.

good luck

 

[RWF7437]

Also, of course, are you sure the 1994 test results are correct ?

 

[LCREP]

"The addition is already up, so they are going to want to use it, will we be looking at installing a fire pump? "


How much of a safety cushion did the 1994 sprinkler system have in the calculations? Unlikely 40 psi, heck I am happy when I see 10 psi. So depending on the sprinkler demand of the 1994 sprinkler system, you will most likely need a booster fire pump for both the old and new buildings. BUT make sure you have enough water to support the booster fire pump. If you do not have the required flow at 20 psi, better start thinking of a tank AND fire pump. Can you say $$$$$$$$

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[SprinklerDesigner2]

One of the two flows were/are wrong to begin with.

Exactly what did you get on the 1994 flow and exactly what did you get on the recent flow?

The 40 psi I take it is static pressure?

 

[RemoteControlFF]

Thanks for the input. We will be contacting the water purveyor on Monday to see if there is anything abnormal... but if there is, it looks like it may have happened quite a while ago.

I think this discussion will be more effective with actual numbers...

The 1994 flow test was 73 static / 68 residual @ 839 gpm
the 2009 flow test was 44/28/731

The 1994 flow was done by the same person that did the 2009 and I have no reason to doubt that the original was accurate, he's been in the industry for quite a while and wouldn't fudge numbers or mess up running a pitot tube.

We've been doing the inspections at the location since 1997, and here are the results from flowing the main drain:

1997 - 54/45
1998 - 47/42
1999 - 49/40
2000 - 55/40
2001 - 47/40
2002 - 52/42
2003 - 45/40
2004 - 45/40
2005 - 50/40
2006 - 55/40
2007 - 50/40
2008 - 55/40

This data would lead me to believe that whatever changed, it was pretty soon after the system went into service - or we did mess up the first flow test (though its hard to imagine being 20-30 PSI off)...

Either way, it seems like we're looking at a pump to get the pressures we need... bad news bears.

 

[LCREP]

Does the existing sprinkler system have a hydraulic calculation placard posted? If so, what is the sprinkler demand psi and gpm??

Given the main drain test results looks like it has been inadequate for a long time. I wonder if calibrated gauges were used on the 1st test and where was the test done since this was new construction. Would not be the first time the water flow test was not done near the site.

Looks like you will have enough for a booster pump, guess u got to look at it the positive light. I wonder if all the same players were not involved in the project if this would have been picked up????

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[SprinklerDesigner2]

The 1994 flow test was 73 static / 68 residual @ 839 gpm
the 2009 flow test was 44/28/731

Something smells wrong with the 1994 test.

73/68 indicates a very flat curve but with a flow of only 839 it was taken using a restricted orifice, perhaps a playpipe with a 1 3/4 orifice, or the static/residual gages were misread or inaccurate by 20 psi.

 

[byrnesf]

I would agree with SprinklerDesigner2, concerning the oriface size, however the static pressures would not be a factor. I would verify the accuracy of the test equipment first. If the present readings are correct, I would research any buildings constructed since the 1994 test, for proper design calcs on their systems.
Good Luck.

 

[SprinklerDesigner2]

Most standard hydrants with a 2 1/2" outlet have a K-Factor of around 150 to 155.

P=(Q/K)^2

With 839 gpm I would expect a residual pressure of somewhere around 32 psi.

With a residual of 68 psi I would expect a flow of 1,236 gpm and certainly no lower than 1,000 gpm unless the flowing hydrant was at the dead end of an old 6" sand cast main having a c-value of 100 or less.

Depending on the store height one might be able to get it done using large pipe, optimally spaced sprinklers (probably k=8) and the area reduction allowed for using quick response sprinklers and you would still not have much of a safety factor.

Just hope nothing in the building is > 20 feet.

That all said someone should have noticed something amiss on the first flow test. Doesn't pass the smell test.

 

[SprinklerDesigner2]

I was just playing around on HASS and I don't see a problem.

Laid out a grid system 150'x150' with 2" sch. 40 branch lines and 4" sch. 10 mains having sprinkler heads 18' high.

I used 17/32 sprinklers spaced 10' on lines with lines 12' apart for 120 sq. ft. spacing. Minimum end head pressure is 9.0 psi.

I did not apply a reduction for quick response sprinklers calculating a total of 13 heads.

I needed 569 gpm @ 22.1 psi and given the water flow given I have 33.9 psi available.

For these numbers I figured 200' of 6" feed main and 300' of 6" underground and we still have a safety factor of about 10 psi.

Backflow. If a double check use an Ames SS series and you will lose another 2.5 lbs leaving a safety factor of slightly over 7 psi

Apply the reduction for quick response and you might even end up with a 10 psi safety factor.

Maybe a little higher price in material but not all that much. I find it sometimes amazing we layout techs will tweak and tweak, sometimes spending hours, only to end up saving $500 on a $50K sprinkler project on a $2 million dollar building.

I bet if you figured the price difference between a 1 1/2 grid with 3" mains vs the 2" grid and 4" mains we wouldn't be talking but a lousy thousand bucks.

Sprinkler contractors with layout techs have to be among the most competitive people in the construction trades.

To you and I a thousand bucks is a lot of money but when measured against a $2 million dollar project it's nothing.

What about the old system, do you have to "re-prove" the hydraulics on it too?

 

[RemoteControlFF]

The addition is not a seperate compartment from the existing sales floor, they are extending the existing building 50' to the right, and removing the existing wall, thus growing the existing sales floor. This means that we'll have to calc the entire building, and the existing head spacing and orifice size would have to change throughout if we did anything different.

While I was out of the office yesterday a co-worker called in to the water purveyor, and was told that a PRV was put on that line in late '94 - the water purveyor is going to adjust the settings on it and we will re-flow.

Needless to say, they were given an earful about the possible consequences of that PRV had there been a fire in any building with an automatic sprinkler system constructed before its installation.

 

[RWF7437]

"While I was out of the office yesterday a co-worker called in to the water purveyor, and was told that a PRV was put on that line in late '94 - the water purveyor is going to adjust the settings on it and we will re-flow."


With 73 psig static pressure the is NO need for a PRV. Who thinks there is ? Get rid of it.

good luck

 

[SprinklerDesigner2]

The PRV is good news (it can go) but I still have problems accepting the first flow test.

 

[RemoteControlFF]

The water dept. said that they were worried about pressure surges when they are pumping to fill their water tower, so they installed a 10" PRV a while back, and just recently hooked up a 4" PRV (both somewhere upstream of our test hydrants). The way it was described to me (second hand) was that the 10" opens when the downstream demand is for more volume than the 4" can supply... which seems really weird to me. I'm just a sprinkler guy, but the whole situation seems to be failing the smell test.

The chain of events, as I understand it, is that they installed the 10" and the 4" and never turned the 4" on, just left it wide open. Then a few years ago a new supervisor took over the dept, and saw the 4" not hooked up, so he put it into service and "told the businesses fed by the line to let him know if they had any problems."

Well, we're re-flowing tomorrow and the water dept. will be on site to "tweek" the PRVs until we can hit our flow requirements, so I'll be sure to bring more details of the mystery to the forum as they become available.

 

[SprinklerDesigner2]

RemoteControlFF,

The scariest "dodged the bullet" sprinkler near disaster I ever had happened in the small town of West Union, Ohio some 30 years ago.

Large three story 100 plus dwelling unit apartment building before NFPA 13R came along so it was a full sprinkler including dry system in the attic.

The site was at the end of a 6" dead end main away from the water tower that sat on a hill. Went to flow the last hydrant on the line and it was broken. Moved to the next hydant 500' up and it was broken too so I had to settle on my flowing hydrant 1,000 feet from the end of the line with my test hydrant 1,500 feet from the end.

Great water, static of 120 psi with a flow of around 1,100 gpm and residual of 65 or 70 psi. On top of this great water my site was still downhill from the test hydrant by a good 20 feet.

City water told me the 6" was cement lined DI put in about 10 years previous so I felt rather comfortable calculating the loss through the dead end city main to the test hydrant.

Got drawings approved, building went up, sprinkler installed and everyone was happy until the day our fitters tripped the dry system, they told me they had 130 psi static, and it took water over 10 minutes to reach the inspector's test on a dry system that might have been 600 gallons.

Scared to death I investigated the problem thinking there must have been a closed valve or something.

Turned out nothing was really closed.

A few years prior the nursing home at the end of the line complained about water hammer and surges damaging toilets and things.

The old guy in the water department, sure he is retired by now, "fixed" the problem by installing his version of "surge arresters" that consisted of half a dozen 2"x12" galvanized pipe nipples with 6 MJ x 2" FIPT ends cut into the 6" every 100' to arrest water hammer.

The building owner, a wealthy high powered Ohio lawyer with political connections, didn't want to hear my tale of woe his way of viewing it was it was my problem to fix at my expense.

Unrelated to the project the county was bring a large 12" line to tie into the 6" because some residents were complaining they couldn't get water at peak times.

I got real lucky on this one, the system ended up being one of the most overdesigned I've ever done but it was pure luck on my part.

Thirty years ago and I never forgot the lesson it taught me. I've run into beams, I've run into duckwork and once I even misscounted bays in a metal building (another lesson learned, now I count them three times up back and up again, but all that I can overcome.

The most important part of any sprinkler project is to make sure and double check then triple check your flow test because lower than aticipated water can present a problem that can not be easily overcome.

 

[RWF7437]

" I'm just a sprinkler guy, but the whole situation seems to be failing the smell test."

I'm just a water system guy but my nose, and experience, tell me this makes little to no sense. A PRV reduces pressure by WASTING energy. In a water system such devices are to be avoided if at all possible. There are some places where PRVs can't be avoided but unless you happen to be in one of those rare areas, a better solution is to change the way the system is operated.

Any pump can be designed, and/or operated, to minimize "surges" at startup. Retrofitting an existing pump/motor may cost something but that cost will almost certainly be recovered in saved energy costs over the life span of the pump. This is even more likely of the cost of energy is rising. Is the cost of energy going down in your area ?

 

[RWF7437]

Correction:

"This is even more likely IF the cost of energy is rising. Is the cost of energy going down in your area ? "

 

[RemoteControlFF]

Energy prices aren't going down here - in fact they are brutal right now considering how much energy it takes to heat a home on a day like today (-15 when I left for work).

The project is in a town of 3,600, they just seem to do things they way they're going to do them, because that is the way they've been done. Neither the city nor the county does building inspections (they issue land use permits, but not building permits) so nothing is inspected before a building is occupied.

The PM for the project can't get up there today for the flow test, so I'm being sent in his place... I'll ask some of the questions you all have brought up and see what I can come up with.

 

[RemoteControlFF]

We did a second flow test yesterday and the results were 72 static, 48 residual, 919 gpm. The static pressure only got to 72 after we flowed the hydrant for a minute or so and then shut if off, the "true" static was 52psi.

The water dept said they increased the reaction time of the PRV and that we could count on having the higher pressures and flows in the event of a fire, but it still smells bad.

The reason they gave for having a PRV on the system is that the whole city is located on a hill, the water tower is at the top and the water treatment plant at the bottom... the plant was showing pressures over 100psi on the water coming in, and they were afraid that damage was going to be caused to homes in the area if such a high static pressure was maintained. The head of the water department said that he lowered the pressures and "we waited for anyone to complain, but nobody did so we left it alone."

I'm totally at a loss for what to do here... we have another job we're about to bid on in the area, fed off the same main, with more demanding areas (Extra Hazard 2). I don't want to tell either of these clients they have to put in booster pumps to make up for the pressure that the city is bleeding off the system, but at the same time I don't want to have a fire in one of these buildings, and have the system fail, only to find out after that the water department had been playing fast and loose with their system again.