Computational Fluid Dynamics-Driven Evaluation of Air-Change Effectiveness in Laboratory HVAC Design Optimization
Alexy Kolesnikov, Ph.D., CPP
Computational Fluid Dynamics (CFD) has become an accepted design tool in indoor airflow applications. With detailed airflow data provided by CFD simulations, which is unavailable otherwise, applications involving thermal comfort, ventilation effectiveness, and occupant safety all benefit from prudent application of CFD-driven design. Verification of numerically calculated airflow parameters via appropriate benchmarking and interpretation of CFD-generated dataset, consistent with a specified design objective, are important for successful application. The initial section of this presentation considers a room airflow benchmark to establish the ability of a CFD simulation to accurately reproduce experimental room airflow patterns. Subsequent sections focus on addressing the evaluation of air-change effectiveness in mechanically ventilated spaces using a CFD driven approach, which was used to optimize the HVAC system design in a training space within the National Bio and Agro-Defense Facility (NBAF).
The design ventilation rate for a specific mechanically ventilated space is based on the space type, occupancy, and the analysis of expected contaminant sources and is determined by the perfect airflow mixing assumption. HVAC system setup and modes of operation, as well as local heat loads, result in recirculation patterns within the space that compromise airflow mixing. This leads to the concept of air change effectiveness. Thus, ASHRAE Standard 129 outlines an experimental procedure based on the age-of-air approach and aimed at adjusting initially calculated design ventilation rates to account for the actual operating airflow patterns within the space. This approach is only applicable after the space (or a mock-up of the space) is built, and resulting design changes are often prohibitively costly. In addition, varying HVAC operational modes require multiple physical testing, which is often not feasible, thus necessitating broad design assumptions based on an insufficient dataset. The CFD approach following the specified ASHRAE 129 procedure allows for mitigating these drawbacks by evaluating multiple expected combinations of supply airflow set points, supply temperatures, and occupant and equipment heat loads to provide a dataset applicable for establishing conservative supply air change requirements supplementing those provided by the initial design flow rate.
The application example in the presentation considers a training space within the NBAF facility. CFD-driven air-change effectiveness analysis is performed for the initial design ventilation rate and several expected operational heat load conditions. HVAC optimization recommendations are clearly identified on the basis of the performed analysis.
Alexy Kolesnikov was the research and development manager at Flow Sciences, Inc. from 2000 to 2004. Mr. Kolesnikov was responsible for providing technical direction in new and custom product design, performing computer modeling, and the optimization of airflows in laboratories and ventilated enclosures. Mr. Kolesnikov holds a patent covering the CFD-optimized laminar low airflow hood design. Mr. Kolesnikov was a supervisor within CFD Consulting Services group at CD-adapco from 2004 to 2007, where he managed multiple projects for established clients, focusing on a variety of automotive applications. Mr. Kolesnikov joined CPP in 2007 as a senior associate, responsible for CFD business segment development, project management, and execution. Mr. Kolesnikov has participated in multiple high-visibility laboratory design projects, authored peer reviewed papers in the Journal of Computational Physics and American Biological Safety Association Journal, among others, and has presented at numerous Labs21 Annual, American Biological Safety Association, and American Institute of Chemical Engineers conferences.