+/-, E, 1st significant figure [was Central Vacuum System]

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>>> 1 what is the sign of the effect (positive or negative)?; 2 what is the decimal order of magnitude?; 3 what is the first significant figure? >>> Wow. Jim, this is good stuff. People does miss the big picture very easily. It's quite funny that how people (not microbiologist) keep telling me (a Ph.D. microbiogist) that counting 100% of sample is definitely better than counting 25%. The question is that was the 100% counted in a "right" way or a "wrong" way. How good is a "100%" data if it's "wrong"? No wonder people think air sample data doesn't make sense. Wei Tang QLAB "Jim H. White" wrote: Matt The trailing vortex problem does exist outside, but usually (with very few exceptions) the indoor-to-outdoor pressure difference puts the outdoors at a depressurized state, so leaks are OUT from the building, not IN. It would not be a good idea to be reading a book outdoors while the dearly beloved was vacuuming (for a whole lot of reasons, actually) but it should be OK indoors. Jim H. White SSC One of my tutors in science (more practical than the university professors) told me to check the following things, in

sequence: 1 what is the sign of the effect (positive or negative)?; 2 what is the decimal order of magnitude?; 3 what is the first significant figure? After that let a junior figure out the details. It seems to be good advice (if you still have juniors available). I still worry most about the sign, having seen many supposedly-brilliant scientists and engineers assume a direction, and not be able to solve a problem, because the sign was wrong (I have done it myself, so I have a considerable amount of humility about this). Date: Tue, 28 Mar 2006 11:58:15 -0500 Subject: Re: RE: Subject: Central Vacuum System>If the exhaust is to the outdoors, and to the downwind side of the >house, you likely get little re-entrainment.Jim, you might want to rethink this recommendation. Remember that an air pocket (or eddy) might be formed on the downstream of the house due to air traveling over the building. The eddy characteristics will be determined by the building characteristics and the wind velocity. If exhausting contaminants into this eddy, they might get trapped without proper dispersal. I can understand the concern about the windward side and the possibility that contaminants could be forced back into the house through

leaks. However, the windward side offers better dispersal of the contaminant stream. I am thinking the best location, and one that is least likely to be used due to logistics and cost, is a couple of feet above the roof on the windward side.******************************************************If what is written looks too stupid to be written by me, I disclaim it. Onthe other hand, if it is brilliant, then I have no one to blame but myself.Otherwise, whether you choose to accept my opinion is up to you.****************************************************** K. Klein, PE ME, MBAIndoor Air Quality Solutions, Inc.2523 SR 133Bethel, OH 45106-0007VOICE: FAX: (with notice)E-mail: mkklein68@...*******************************************************Wouldn't it be nice if common sense were really common? Wei Tang, Ph.D.Lab DirectorQLABCherry Hill, NJ