Regional flow motion and heat energy balance analysis of a 10,000 class pharmaceutical cleanroom with secondary return air conditioning system

Abstract

• Cleanroom with the secondary return system was modeled with airflow and energy network. • The air change rate has a notable influence on the mean age of air globally and locally. • The air change rate has a small effect on contaminant removal effectiveness and air change efficiency. • Promotion of return air volume in the occupied area could reduce local pollutant concentration levels; • Computational fluid dynamics procedure was validated by the on-site measurements. Improving air quality in occupied area has always been the core focus of ventilation design in cleanrooms. A 10,000 class pharmaceutical cleanroom, with secondary return system, was firstly introduced. Full computational fluid dynamics procedure validated by on-site measurements was then applied to model such cleanroom airflow and particle transport. Energy balance of this ventilation system was also analyzed. Details of room airflow and contaminant fields for the specific zone (above the device and around the human body) were subsequently analyzed concerning the effect of delivering ventilation flow rate and return air volume. Representative parameters, mean age of air, contaminant removal effectiveness, and air change efficiency at the occupied zone and the whole space were evaluated. Results demonstrate that promotion of the return air volume in the occupied area could appropriately reduce pollutant concentration level. Moreover, an increase in ACH (air change rate per hour) did not always shorten the local age of air near the equipment. For a large ACH, it not only will raise the dust around the machine again, it will also cause uncomfortable flow draft. Additionally, when ACH = 20 h − 1 and 25 h − 1 were achieved respectively, the age of air was reduced by 32% and 21.4% in the whole room and further done by 31.1% and 23.5% in the occupied zone; with identical changes, room air change efficiency (RACE) was achieved at 49.3 % and 50.4 %, respectively. It shows that the increase of ACH seems to have little effect on the air change efficiency. When ACH increases from 15 h −1 to 20 h −1 , the efficiency of pollutant removal at the occupied zone will not be significantly improved ( ε = 1.78).