Two-step optimal design method using genetic algorithms and CFD-coupled simulation for indoor thermal environments Taeyeon Kim a , Doosam Song b, * , Shinsuke Kato c , Shuzo Murakami d a Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, Republic of Korea b Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon 440-746, Republic of Korea c Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba Meguro-ku, Tokyo 153-8505, Japan d Keio University, 4-1-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8521, Yokohama, Japan Received 28 February 2006; accepted 18 May 2006 Available online 1 August 2006 Abstract The optimal design method of the indoor thermal environment using CFD coupled simulation and genetic algorithms (GA) is developed in this study. CFD could analyze the thermal environment considering the distribution of temperature and air flow in a room. Therefore, it would be appropriate to use CFD for the optimal design method considering their distribution. In this study, the optimal design means the most appropriate boundary conditions of the room among the conditions where the design target of the indoor thermal environment is achieved. The authors have been examined many types of the optimal design methods using CFD, and find that the high calculating load and the different results according to the initial conditions, among other factors, are the difficulties of the optimal method. Considering these dif- ficulties, a two step optimal design method for the indoor thermal environment is proposed. It includes the GA for determining the optimal design for the indoor thermal environment. To examine the performance of this method, the optimal design of a hybrid ventilation system, which uses the natural cross ventilation and the radiant cooling panel, is completed. The optimal design which satisfies the design target (thermal comfort, minimum cooling load, and minimum vertical temperature difference) is found using a two step optimal design method. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Optimal design; Genetic algorithms (GA); CFD; Coupled simulation 1. Introduction This paper is a basic study for developing an optimal design method using CFD (computational fluid dynamics) coupled simulation method for the indoor thermal environ- ment. Because it allows a detailed analysis considering the distribution of the indoor physical environment, the CFD coupled simulation method is widely used to predict indoor thermal environments and to analyze the performance of air conditioning systems [1]. The design of the optimal thermal indoor environment comprises the process of finding the most appropriate boundary conditions considering the air conditioning system, location of the supply inlet or exhaust outlet, wind velocity and outlet temperature, with the ulti- mate goal of efficiently controlling the indoor environment and saving energy. In the process of designing the optimal method for the indoor thermal environment, therefore, it is beneficial to use CFD coupled simulation method. In general, the process of the optimal design method for the indoor thermal environment can be (1) an expert sys- tem which incorporates the designer’s decision making pro- cess. In this case the applicable design conditions are examined one by one according to the expert system [2], and (2) an optimizing method which could find the most rational design among the combinations of all the design conditions (for example, generic algorithms) [3]. The optimal design method using designer’s decision making process divides the design process into each step, 1359-4311/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2006.05.022 * Corresponding author. Tel.: +81 31 290 7551; fax: +82 31 290 7570. E-mail addresses: tkim@yonsei.ac.kr (T. Kim), dssong@skku.edu (D. Song). www.elsevier.com/locate/apthermeng Applied Thermal Engineering 27 (2007) 3–11