Jon, Cao
In effort to try to reduce the noise level inside the cleanroom, we have dialed all four HEPA fan-filter units (FFUs) down from HIGH to MEDIUM speed. These dials can only be accessed from inside the cleanroom, by bringing in the large ladder and opening adjacent ceiling tiles.
We tested three configurations, in each case with all the FFUs on either HIGH (initial state), MEDIUM, or LOW. We measured the ambient noise in each configuration.
| Fan speed |
Noise inside cleanroom (dB) |
Noise outside cleanroom (dB) |
| HIGH |
80 |
70 |
| MEDIUM |
74 |
66 |
| LOW |
71 |
66 |
Going from HIGH to MEDIUM yields the largest improvement, reducing the ambient sound intensity by 6 dB (i.e., by a factor of 4, corresponding to a ~35% reduction in perceived volume).
An additional 3 dB of noise reduction can be achieved by further reducing the fan speeds to LOW. However, even after allowing some extended settling time (few hours), we found the particle counts to be fluctuating right at the threshold zone for ISO Class 5. Thus we dialed the fan speeds back up to MEDIUM with the expectation that this will be sufficient for Class 5 performance.
The cleanroom now needs to be recertified with a fresh round of five-zone particle count measurements. |