Effect of reducing ventilation rate on indoor air quality and energy cost in laboratories

Numerous Computational Fluid Dynamic (CFD) studies have been performed to support innovative approaches to revising indoor air quality (IAQ) standards in laboratories. In a previous study,(1,17) the author demonstrates that a slot bench exhaust system can be an effective and energy saving strategy to control thermal comfort by removing the heat dissipation on the bench top and that this system has a negligible effect on the containment ability of a fume hood located upstream from the bench. In this subsequent case study concerning the ventilation requirement in a typical lab with a high cooling load, CFD is used to focus on assessing both the IAQ and the cost impact of the bench slot system versus a conventional ventilation system on IAQ when the number of ACH is reduced from the typical 12 ACH to 6 ACH. The ability of the bench slot exhaust system to remove airborne chemicals in the case of a bench top chemical spill is examined at the reduced ACH. This paper provides quantitative justification to support the concept that IAQ is not directly proportional to a reduction in ACH but rather is dependent on a combination of factors including the ventilation system design, the control of local conditions and the use of standard operating procedures specific to the laboratory operations. The results suggest that a lower ventilation flow rate can be used without remarkable impact on the air quality in the occupied zone, whether or not the bench slot exhaust system is employed.