Masashi Imano

Cross Comparisons of CFD Results of Wind and Dispersion Fields for MUST Experiment: Evaluation Exercises by AIJ

In order to apply Computational Fluid Dynamics (CFD) techniques to estimate pollutant dispersion in urban areas, it is important to assess the performance of numerical models used to estimate these phenomena. Recently, the MUST (Mock Urban Setting Test) has often been adopted as a test case for evaluating numerical models for micro-scale urban meteorology. This paper presents the results of model evaluation exercises carried out using MUST based on the Architectural Institute of Japan (AIJ) experience. The results of model evaluation exercises conducted by AIJ are broadly consistent with the results obtained by the COST group. However, the variety of results by each computation can be minimized by setting standard computational conditions. All computations including both RANS and LES show good agreement with wind experiment data. In general, LES cases show comparable accuracy to RANS in predicting U and W. However, LES shows better agreement than RANS in TKE and concentration.

Utilization of Cross-ventilation in High-density Urban Areas

Abstract The increased density of buildings in urban areas in Japan over the past several years has meant that less outdoor wind blows into buildings. Additionally, houses with many or large-size of openings are difficult to build due to concerns about security and privacy. In the present study, we have investigated the cross-ventilation characteristics of void, monitor roof and wind tower for the purpose of improving the cross-ventilation in detached houses built in high-density urban areas based on wind tunnel experiment and flow-network model calculation. At first, wind-pressure characteristics of a detached house in high-density urban areas were obtained by the wind tunnel experiment. From this result, we found that it is difficult to ensure adequate cross-ventilation in houses located in high-density urban areas by only openings in the wall surface. So, void, monitor roof and wind tower have been investigated as techniques of improving the cross-ventilation. Wind-pressure characteristics of each technique were examined by wind tunnel experiment. And rates of cross-ventilation flow from cases (i.e., void, monitor roof and normal roof) were calculated by flow-network model using wind-pressure coefficients from previous experiments. It can be concluded that void is a very effective technique for improving cross-ventilation in detached houses.

Cross-ventilation Utilization in Housing in Congested Urban Areas in Taiwan

abstract This research aims to investigate the current condition regarding ventilation use in congested urban areas of Taiwan. There is a remarkably high level of humidity and dense populations in many housing areas. The study targeted terraced houses, which are the most common style of housing in urban Taiwan. The current study attempted to understand the thermal environments of residential buildings as well as utilization of the cross-ventilation system. This was achieved by combining data of the current weather conditions and a questionnaire survey of those tested. Also included in the testing was a series of wind tunnel experiments conducted to examine the issues related to the ventilation flow rates of these congested areas. Following that testing, ventilation improvement techniques were proposed and studied for ways to decrease the negative environmental impact from over-use of air conditioners. The results calculated by simulation software demonstrated that through the use of our roof top designed component for air circulation, the heat removal decreased by 16% annually, compared to current condition.

Study on Utility Cross-Ventilation in Guangzhou and Shenzhen, China

abstract As rapid increase in energy consumption has raised concerns among researchers regarding the use of conventional air-conditioning systems, substantial effort has been devoted to the exploration of alternative solutions. One possible solution is a natural ventilation approach. In the present study, the authors have focused on the feasibility of cross-ventilation due to natural ventilation potential. The study centered on cases located in the Guangzhou and Shenzhen areas on the Pacific coast of China, well known for their dense population and high-energy consumption. In the current research, the analysis of weather data to investigate the feasibility of cross-ventilation in Guangzhou and Shenzhen was initially performed. A questionnaire survey was then carried out in order to grasp the residences’ actual configurations and conditions. Sequentially, based on the results obtained from the prior investigations, the existing problems were raised and solutions for cross-ventilation enhancement were tested by means of a wind tunnel experiment. It can be concluded that the presence of VOID (vertical opening common space) without an opening on the lower part of the buildings significantly improves the cross-ventilation flow rate by 1.3-2 times over the cases without VOID.