I was recently asked in a PM, "How are you calculating the cfm that is required of your exhaust system? Or the number of air changes needed per hour? Are you approximating it on a per gpu basis? I can do the math from cfm of a fan to air changes per hour based the cubic feet of my mining room, but I'm not sure what goes into calculating the cfm or air changes per hour that my set up will require."
My response:
As for calculating the CFM required for exhaust, I have not done any such calculation(s). I have no idea of number of air changes per hour. If one wanted to know the number of air changes needed per hour, I believe they would ALSO have to decide WHAT TEMPERATURE would be the "mean temperature" they want to achieve in order to come up with an answer.
As for what "mean temperature" would be ACCEPTABLE for rigs to mine efficiently and/or effectively, that would also have to be determined by the operator. It can be 100 degrees Fahrenheit in the room and the mining cards still mine fine. However, I do not want the temps that high in the mining room. Mainly for humans to be more comfortable [Temperature wise] in the house.
I'm shooting for mid to upper 80's [Fahrenheit] in the mining room with outside temps at 100 degrees Fahrenheit this summer. That's with bringing in outside air with the intake fan. Keep in mind, the outside air will be cooled as it is accelerated through the intake fan into the mining room. Hence, the lower temperature in the room. I would "accept" the ambient temp in the mining room in the 80's [Fahrenheit] this summer. I would be "ecstatic" with those temps this summer. That would put my GPU's in the low 50's to low 80's Celsius range [Depending on the GPU]. For example, my REFERENCE RX 480's already run at fairly high temps Celsius compared to GPU's with multiple fans.
I may be forced to get higher CFM intake and exhaust fans this summer. I'm not sure yet. Hence, the reason for your question(s) on calculating the CFM air changes per hour equation. I've always been one to learn the hard way [Via experience] rather than by math in regards to temps in the mining room. I'm "winging it" so to speak.
With the mining room currently at 99 degrees Fahrenheit, my EVGA NVIDIA 1080 Ti rigs are at mid 60's to upper 70's [Depending on location of GPU]. Why am I saying, "...depending on location?" My 1080 Ti rigs sitting on a rack with my newly designed fan frame for 12 x box fans are currently mid 60's. While the other 1080 Ti's [With fans but NOT with newly designed fan frame] are mid to upper 70's Celsius. It's only logical to conclude if I had the entire rack system of four (4) racks properly sealed with my new design of fan frames TO KEEP HEAT GENERATED BY THE RIGS FROM BEING SUCKED BACK INTO THE BOX FANS AND BLOWN BACK ONTO THE RIGS; the rigs would run much cooler. The main reason the mining room is 99 degrees Fahrenheit currently is because racks are sitting out in the open with no new fan frames on them to SEAL in a HOT ISLE (area/room) to separate from a COOL ISLE (area/room).
By the way, when I said, "One would need to determine what mean temperature would be acceptable to them," I was referring to the COLD ISLE (area/room).
I currently have NO COLD ISLE (area/room). All the air brought in from outside is currently being mixed with heat from the rigs and sucked into the box fans to blow on the rigs. Hence, the reason for my design to seal off the outside air brought in via the intake fan FROM the heat generated by the rigs BY CONSTRUCTING the fan frames for each rack with properly sealed frames around each fan to keep heat from the HOT ISLE (area/room) from getting out into the COLD ISLE (area/room) and heating up the COLD ISLE (area/room) to make the air no longer COLD but warm or hot. Which would get sucked back into the fans and onto the rigs.
