I am not implying that we should ignore AF because there is a
significant pressure loss difference but HOW we want to address it so
more than a few PE's can understand what we are doing and the AHJ can
judge it is correct. Otherwise, we can make a similar charge against
the entire hydraulic process.
Do you really want to debate the basis of the 40 gal trigger (besides
who doesn't consider maintenance as PART of the economic comparison)?
Roland
On Sep 19, 2008, at 2:04 PM, Chris Cahill wrote:
Well slow down there partner. Isn't the code as it stands today
about right
on for what we know? Travis points out a big surprise, to me
anyway. What,
he had a 100 psi difference in the demands pressure. That ain't
fly... in
these part. Even if DW is academically more pure what does it
matter if HW
is 90 or 110 psi differences. That is still significant. And we
know HW is
based on a certain density of liquid and temperature. -30 and anti-
freeze
ain't it. DW is a fairly easy tool today. Sure in 1950 perhaps it
was a
bit more cumbersome thus the development of HW and the '60 where it
entered
the code.
The 40 gallons was the annex section on a should keep them below for
maintenance reasons. Who cares where it comes from really it's a
made up
code number at this point. Like 52,000 sq.ft. or 12" down. Nothing
magical
just a made up limit based on judgment. And we know judgment is
loosely
defined in our field.
Seems to me until there is testing that actually shows what is
happening at
-30 and how fast the anti-freeze clears given testing volumes in the
path of
travel we should leave it as is. If you want to go big (over the
arbitrary
40 gallons) here's the penalty. It's just like the 500 and 750 gallon
limits to dry system. None of us are old enough to recall if these
are
tested number but I bet they are nice round places to cut some
things off
based on judgment.
Chris Cahill, P.E.
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