GBlist: Demand Controlled Ventilation

IMSHAPIRO@aol.com
Wed, 26 Mar 1997 20:37:12 -0500 (EST)

A CO2 switch is not a bad way to control ventilation. I've used Telaire's a
few times and my experience is that their drift is not too bad (although I
did once have a catastrophic drift of 300 ppm). But your concern about them
never being recalibrated is probably valid. Caution: Also, never use them
to control ventilation in a smoking room. I made this mistake once. The
amount of CO2 produced by cigarette smoke is not large, I guess, and a single
smoker can produce a lot of smoke but not a lot of CO2 - the switch does not
trip fast enough.

You might check about whether the occupancy merits demand-control. I can't
imagine a classroom occupied more than a few hours a day. A two-speed fan
might be good enough, or a fan with a manually variable speed control.

Lastly, you might consider a humidistat. We're coming out with a software
program for humidity analysis (much more than a psychrometric chart) by late
summer, which would help in crunching the numbers, but it's not ready yet.

Ian Shapiro, PE
Director
Taitem Engineering
963 Comfort Road
Spencer, NY 14883
607 277 1118
607 277 2119 FAX
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