1. Assistant Professor, Dept. of Architectural Engineering, Hanbat National Univ., Daejeon 34158, Korea.
2. Professor, Dept. of Mechanical Engineering, Kyung Hee Univ., Yongin 446-701, Korea.
3. Professor, Dept. of Architectural Engineering, Kyung Hee Univ., Yongin 446-701, Korea (corresponding author).