Decreasing electricity costs of clean room for cell products during non-operation

Introduction: Cell processing facilities are susceptible to environmental bacteria and must maintain sterile environments to safeguard cell products. This process involves circulating air through high-efficiency particulate air (HEPA) filters, which incurs significant maintenance costs. While cost-reduction strategies have been explored in the semiconductor industry, validations specific to cell processing facilities remain unreported. This study aims to verify whether optimizing air-conditioning management in cell processing facilities can achieve energy savings by using particle counters to measure air quality during both non-operational and hypothetical operational conditions.

Methods: The study assessed particle generation under varying air conditions to evaluate potential savings and the impact of reducing air-change rates. The air conditions were defined as follows: Condition 1 (C1) represented normal air conditions (100 %), followed by C2 (72.87 %), C3 (45.74 %), C4 (18.60 %), and C5 (0 %). The number of particles was evaluated across these conditions. Particle counters measured the quantity of particles during non-operational periods and during a 2-min walking motion. The time taken for particle levels to stabilize and become undetectable was also analyzed. Theoretical electricity cost savings were estimated for hypothetical operating and non-operating hours, with calculations adjusted for facilities ranging in size from small (100 m²) to large (1000 m²).

Results: Results indicated that under air conditions C1, C2, C3, and C4, almost no particles were detected, whereas in C5, where air conditioning was halted, particle counts still remained below guideline values. Total particle counts at the four positions were significantly higher at both 0.5 and 5 μm under conditions C4 and C5 compared to other settings. The study also demonstrated that the rate of particle increase during operation varied by air-conditioning condition and position. Notably, reducing the air-change rate significantly enhanced energy savings, especially in larger facilities. For instance, annual electricity consumption in a large facility could potentially be reduced from approximately 31 million yen to approximately 9.6 million yen, yielding savings of approximately 20 million yen.

Conclusions: Even with a reduced air-change rate during non-operation, it was possible to maintain the cleanliness standards for each grade. The findings suggest that current operational practices are often excessive and that significant reductions in operating costs can be achieved by adjusting ventilation frequencies during non-operational periods. This study provides crucial insights for managing cell processing facilities facing challenges such as low production rates, the necessity of operating at full capacity due to on-demand autotransplantation, and high maintenance costs.