the trick is picking the most demanding hydraulically remote area
(with each sprinkler assigned their actual area of coverage). When
the system is not nice and symmetrical, one may need to look at more
than one possible remote area. Bottom line is if the location of the
hydraulically most remote area is not apparent, you need to be able to
show the AHJ why your selection is right.
Roland
On Feb 25, 2011, at 9:45 AM, Johnson, Duane (NIH/OD/ORS) [C] wrote:
I don't want to beat the horse until it is dead, but as an AHJ, I
would have to look at the calc area as possibly not being the most
demanding area. And, would likely ask for another hydraulic
calculation for proof that all areas of the system are hydraulically
proven.
Scenario: Say you have 6 branchlines in the calc area, numbered 1
thru 6 (tree system). One being the farthest from the main and six
being the closest. And say you input the exact area of coverage of
each sprinkler into your hydraulic program. Now suppose branchline
5 had the sprinkler covering the largest floor area.
Argument: I would have to argue that the most demanding area has
not been hydraulically proven. The more demanding calc would start
with branchline 5 at or near the sprinkler covering the largest
floor area. Then, add the six branchlines to your calc, numbers 5
thru 11. Although these branchlines are closer to the riser than
the given scenario, this calc would be more demanding because of the
over discharge that is introduced in all the pipes of the calc area
(extra flow in the pipes, thus extra friction loss in the pipes,
thus higher pressure demand). The given scenario of branchlines 1
thru 5 would only have over discharge in branchlines 5 and 6. So,
the given scenario would not be the most demanding area and
therefore all pipe sizes are not hydraulically proven.
I'm not stating you can't do what Roland stated, just that it may
not be the most demanding scenario...be cautious! You may need
additional calcs to prove the entire system works. So, for the sake
of time (and profit), it may be easier to use the maximum coverage
of all the sprinklers in the calc area. One and done.
Duane Johnson, PE
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