Subject: Dripping Ceiling Problem Solved

From: [email-masked] (Lynnette)
Date: 1 Aug 1995 22:09:43 GMT

Okay, folks, I know you've all been waiting for this one:
;^)

Let me recap the problem, then the solution.

1. Outside air fan was injecting fresh air into a VAV
unit (inlet vanes) which was supplying VAV boxes in turn.
2. SA side of unit in mech room and ceiling tiles outside the 
mech room were dripping with condensation. Return air plenum 
fed into mech room, and return air dampers into each unit
in turn. Ceiling tiles were just below the common return 
air plenum.

Turns out that the OA fans were sized for double the actual
fresh air (IAQ) requirements of current "people-loading". So the 
OA was feeding into the side of the mixing box, out the RA dampers, 
and into the mech room, finding it's way even into the RA plenum
somehow (ceiling tiles dripping into the space).

Solution: Provide VFDs for the OA fans to track the loading of the 
inlet vanes or reduce the volume of the OA fans so that the SA fans
at part loads will not be overwhelmed...essentially a 100% OA system !

The other problem was that the OA fans (ducted into the mixing box
of each unit) was seeing no resistance...so some (not verified yet)
will be putting out twice the design volumes. A balancing damper in 
addition to changing the sheaves is required at the discharge of the 
OA fan. 

Lynnette 
Disclaimer: My statements are my own, and do not represent those of my 
employer. Any opinions or advice are not guaranteed to work or even make 
sense !!!