Coupling of multizone and CFD programs for building airflow and contaminant transport simulations

Liangzhu Wang, Purdue University

Abstract

Building ventilation designs and Indoor Air Quality (IAQ) analyses are important to provide a safe, healthy, and comfortable indoor environment, and to improve the energy savings and substantiality of buildings. However, current design tools have their own merits and drawbacks. Multizone programs can achieve a fast computing speed, but they are still limited to the predictions of the average characteristics of airflows and contaminant distributions due to the various assumptions that revolve around them. CFD programs can provide more accurate results, yet they demand higher computing costs. An integrated program of multizone-CFD methods can combine the merits of both programs while eliminating their drawbacks. This thesis thus investigates the fundamentals, strategies, implementations, validations, and applications of coupling a multizone program, CONTAM, with a CFD program, CFD0-C, for building airflow and contaminant transport simulations. This research first identifies the situations, where the major assumptions of multizone models become problematic: non-uniform distributions of wind pressures, momentum effects, temperatures, and contaminant concentrations. Two coupling strategies have been developed to improve CONTAM assumptions. For non-uniform wind pressure distributions on a building surface, this study develops an indirect coupling strategy, which exchanges wind pressures indirectly between CONTAM and CFD0-C. For the cases with non-uniform distributions of momentum effects, temperatures, and contaminant concentrations, a direct coupling scheme is employed to exchange iteratively information between CONTAM and CFD0-C. Theoretical analyses then prove that the direct coupling scheme has a solution, which is a unique one. This study also finds that for the direct coupling, the most stable method is to exchange pressure boundary conditions between the multizone and CFD programs. This research conducted experiments in a test chamber to validate the coupled CONTAM-CFD0 program. This study shows that the calculations of the coupled program are reasonably accurate, while preserving acceptable computing costs. The performances of the coupled program are also demonstrated by several case studies, illustrating how the coupled CONTAM-CFD0 program can effectively improve CONTAM simulations. Finally, dimensional analyses are conducted to provide suggestions on when multizone assumptions become problematic and thus CFD methods are needed.

Degree

Ph.D.

Advisors

Chen, Purdue University.

Subject Area

Mechanical engineering|Architecture|Environmental engineering

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