Rib-induced eddies increase inactivation efficiency and air handling capacity of in-duct ultraviolet germicidal irradiation systems with low energy cost

Abstract

Attaching ribs on duct walls is an effective way to improve the inactivation efficiency of in-duct UVGI systems (ID-UVs), and this study explored the optimal rib design. The Critical Survival Fraction Probability (CSFP) and Maximal Bearable UV Dose (MBUD) methods were employed as indicators. Results showed that ID-UVs with ribs could be optimized by balancing the positive effect of rib-induced eddies and the negative effect of rib-induced high airflow velocity. The optimal rib spacing was equal to the duct height (namely, 1.0 H), the optimal shape was two rows of trapezoidal ribs aligned the same direction. The best inactivation performance was achieved by attaching 0.15 H ribs on all walls alone downstream of lamps. Compared to the condition without ribs, the optimal ID-UVs increased inactivation efficiencies by 31.4 % (CSFP, 10.5 times greater than that achieved by optimizing lamp array) and 68.6 % (MBUD) for the highly UV-susceptible MS2 Bacteriophage, and, up to 146.4 % (MBUD) for the low UV-susceptible MS2 Bacteriophage. The optimal ID-UVs additionally allowed a 10–20 % increase in air handling capacity and an 85.3 % reduction in annual energy cost, when compared to conventional conditions with the same air-cleaning level. These findings suggest promising prospects for implementing the ID-UVs with ribs.