I have a quiet fan application that doesn't directly involve computers. Mostly around here, we want very quiet fans that we manually adjust their RPM to be a balance between noise and empirically-determined heat (CPU/MB temps). However, my constraint is a minimum total air exchange, with a maximum of a one fan (really opening) for exhaust and one for intake. So, here are my thoughts and questions.
1. My understanding is that total air throughput is limited by the highest CFM fan in a push-pull system. The added intake fan mostly improves the efficiency of air exchange and/or provides additional internal pressure to minimize dust intake. Is this correct?
2. How can one actually calculate the air exchange rate? Simply taking the box's volume and dividing by the CFM seems straightforward, but somehow simplistic and possibly wrong.
3. RPM and CFM vary linearly (0.5 X RPM ==> 0.5 CFM), and are proportional to voltage from 12V base. Or have I got this mixed up?
4. The commercial box I'm looking at has a single 80mm AC fan for exhaust rated somewhere around 25-35 CFM and 36-46 dBA (!!!), but is spec'ed for a somewhat smaller box. I'm chatting with the vendor about modifications and would like to offer them some specific alternatives. SPCR standard 12V fans should be fine with a low-cost transformer (and possibly a Fanmate
). We can porbably build some baffles for larger fans. The box is approximately 3'x3'x4' (36 cu. ft). I think we want at least 2X complete air exchanges per minute--more if possible. Thus, a total minimum 72 CFM. Any recommendations for quiet high air-flow fans?
Thanks in advance. For the record, I use Enermax and Panaflo 120mm at ~800 rpm in most of my computer systems.