[28517] in Hotline Meeting
11-135 AC alarm
daemon@ATHENA.MIT.EDU (Operator)
Thu May 25 00:59:01 1995
From: root@MIT.EDU (Operator)
Date: Thu, 25 May 95 00:58:58 -0400
To: hotline@MIT.EDU
Cc: op@MIT.EDU, network@MIT.EDU, mccarron@MIT.EDU, mtobin@MIT.EDU
The #1 air conditioning unit (the north one) in 11-135 tripped a high
humidity alarm tonight at about 11:20pm. Then the other AC unit
(against the Consultants' office wall) kicked in. Lou was paged and
relayed the info to me in my office, at which point I went to 11-135
to work with the mechanic (the same one I always deal with during 3rd
shift, Ron McCarron (mccarron@mit.edu)).
I turned off the security alarm. (It had driven some people (wchuang,
at least) out of the consultants' office with the noise in the time
between Ron's entry (to check on the AC unit) and my arrival.)
The AC alarm tripped again (for high humidity, as before) before I
left the area, so I reset it, but it will keep tripping all night.
The humidity is now at 72% to 80% (depending on which unit you read,
and when) with a set point of 45%. I told the Operations Center to
please disregard the AC alarm when it comes back tonight (it's not
like we have the room filled with huge vaxes anymore). Ron called in
a work order (sorry, I forgot to ask for the number), so someone
during the day or evening can give a mechanic access to investigate
the situation further.
NOTE: This looks just like what happened last year. (I was around for
E40, but I also heard about building 11.) I suspect the steam heat
was shut off tonight (for the duration of the summer). What happeneds
is that the AC units cool the air, driving up the humidity level.
(The humidity level rises because cold air can hold less moisture.)
Some water is forced out of the air, but much remains. In the winter,
the air is then reheated by the AC units to drive the humidity
percentage back down. (The warmer air can hold more moisture.) When
Phys Plant shuts off steam, we lose the reheat function of the AC
units. THIS IS SPECULATION based on our discussions with Ron last
year -- I can't be sure that it is what happened either last summer or
now.
If that is correct, the possible solutions are: put electric reheat
units in the AC systems, keep MIT's steam running for just a few
machine rooms, change the humidity set points so the AC alarms don't
trip (can this be done?) and hope our equipment doesn't care, or just
ignore the whole situation. The last option sounds like a bad one.
We'll have to check the docs for the computers to find out what their
environmental humidity requirements are, to find out if the hardware
cares. Turning the steam on just for us seems pretty unreasonable.
Ron (McCarron, not Hoffmann :) did you want to add anything?
(I realize you might not get this email until after we're done
discussing it, but I wanted to include you, anyway.)
Ron and Mary: It has been my understanding that Physical Plant isn't
supposed to enter IS machine rooms without prior clearance. This is a
concern, especially late in the semester, because with these very loud
security alarm horns, students can't work with the noise, and they
have *very* little time left to finish their work. Am I
misunderstanding how our groups work together? (We work indirectly
enough that I'm never quite clear on this sort of thing.)
Thanks again Ron, for your help. I hope we get this thing (high
humidity alarms) settled finally this summer!
