| A cleanroom designer must consider many factors | | | | of 1.07 lbs/sf. By using a compressed air source and |
| when specifying a new cleanroom. Air changes, | | | | a Dwyer mass flow meter and our eight point |
| temperature and humidity control, size of clean room, | | | | pressure transducer, we were able to plot flow into |
| amount of human and machine activity and climate | | | | the box verses pressure. So far as we know, this is |
| conditions to name a few. One of the critical | | | | the only study of leakage rates in cleanroom ceilings |
| characteristics of a clean room is positive air pressure. | | | | ever conducted. |
| Adequate positive air pressure keeps "unwanted" air | | | | Our results are given below. However, readers should |
| from leaking in, thereby compromising the cleanroom | | | | note that these numbers are for tile installed in a grid |
| integrity. A cleanroom must be designed to maintain | | | | under ideal conditions. Our technicians were able to |
| positive air pressure through out the typical traffic | | | | razor cut the gasket edges so that no corner leaks |
| and external conditions that may occur through out | | | | occurred. In actual practice razor cut edges to within |
| the day. The biggest source of air leakage may be | | | | 0.003 rarely occur. We suggest designers use two |
| the cleanroom ceiling. | | | | times the values in the graph for leakage values of |
| Most cleanrooms have hung ceiling grids with clean | | | | tee grid ceilings. |
| room compatible tile. These tiles have gaskets to | | | | The measurements were as follows |
| reduce leakage, but even under ideal conditions, that | | | | Air pressure Air Flow (Standard |
| leakage will never be zero. Therefore airflow design | | | | (Inches on Water Column) Cubic Feet Per Minute |
| must include ceiling leakage so that incoming air will | | | | .09 1.15 |
| adequately compensate for this leakage. On a similar | | | | .14 1.55 |
| note, a designer must consider the quality of the | | | | .20 2.3 |
| ceiling tile as well as the installers. | | | | .26 3.10 |
| How much air leaks through a cleanroom ceiling tile | | | | The values can be approximated by the equation |
| with a factory gasketed grid? | | | | P=.083 times Flow. This equation should be subject to |
| To find the answer to leakage rates for cleanroom | | | | the same design compensation suggested above |
| ceiling tile, Gerbig Engineering built a 4 foot by 6 foot | | | | (assume twice the leakage value) |
| by 1 foot sealed box with three ceiling tiles resting on | | | | Conclusion: By using the equation above, a designer |
| a typical 1/2 gasketed aluminum ceiling grid. The tiles | | | | has a better tool for compensation for ceiling tile |
| are the typical vinyl covered gypsum with a weight | | | | leakage when designing the clean room. |