• Energy Research

Abstract Taipei City, located in the subtropical zone, has a basin landform. The summer is always hot and humid and the air temperature right after sunset is typically higher than 30 °C. Heat rejection from residential buildings in urban area, equipped with lots of the window type air conditioners, not only increases the air temperature outside, but also burdens the cooling load. Based on the time schedule of air conditioner use of Taipei citizens, the heat rejection/building energy use and the air temperature distribution were evaluated, and finally the additional electric consumption of air conditioners was predicted. Two software, EnergyPlus (building energy program) and Windperfect (CFD, computational fluid dynamics software) were employed in this study. In the CFD simulation, the geometry of buildings that covers 700 m in diameter was created with GIS (geographical information system) and the total mesh number was more than 3 millions. Three specified temperatures (Tam, Tbu and Tac) were used to describe the temperature distribution within the urban canopy by hourly time variation and spatial distribution with height and horizontal profile. The results revealed that the temperature gradually increased with height and the temperature next to the buildings was always higher than the ambient air. The feedback (penalty) of heat rejection to cooling load was found 10.7% during 19:01 to 02:00 h on the following day.

The exhaust performance of a cooling tower placed in the interior space of a building is crucial due to limited space and stochastic ambient wind conditions. Improper design of the cooling tower could lead to a reduction in thermal efficiency and could also deteriorate the operational performance of the chillers. In this paper, the exhaust performance of cooling towers in a super high-rise building considering both side exhaust and interlayer exhaust methods is investigated using CFD simulations. The results show that the exhaust performance of cooling towers under interlayer exhaust is better than that under side exhaust. However, the exhaust recirculation phenomenon of the cooling towers on the windward side caused by outdoor wind is still obvious because the outdoor wind speed is low. The total pressure differences between the inlet and outlet of the tower units under interlay exhaust become larger with increases in wind speed in each district. The fan total head should be carefully determined to overcome the surplus pressure drop caused by the wind. This study helps to guide other similar cases utilizing the interior space of buildings for the cooling towers.

Abstract This study analyzes the PV potential on rooftops and vertical facades in the research area of West Central District of Tainan City, a rich insolation area in Taiwan. By using the energy calculating software EnergyPlus and the grid-based computational fluid dynamics (CFD) software Windperfect, the electrical energy generated by PV modules on vertical walls from eight directions in both shading-covered areas and non-shading-covered areas was simulated and calculated. Three databases – the database of the electrical energy generated by building facades, of spatial information, and of shadow coverage – are established to estimate the potential electrical energy. The covered-shading condition was simulated by sunshine trajectory method, and the insolation potential of building surface was evaluated by analyzing the accumulating insolation hours and the spatial location data. It was observed that shading affects vertical facades more significantly. The average electricity generation of per unit area on rooftops demonstrates that the electrical energy in summer is twice as much as that in winter. Although the electrical energy generated by that of per unit area on vertical facades is higher in winter, it is only 1.1 times greater than that in summer. If the amount of electrical energy generated is taken into consideration, the installation area for the southwest walls should be 1.5 times larger than that of the rooftops so that the same amount of electrical energy can be generated. When considering the installation of PV panels in the research area of this study and other geographically similar locations, the priority should be the rooftops, followed by southeast-, southwest-, and south-facing vertical facades.

Abstract Simulations are conducted to investigate the influence and improvement potential of air conditioning heat rejection management of residential buildings on microclimate and energy use. The microclimate and building energy use are simulated on a typical high-rise building in Taipei, Taiwan, on a summer night. Heat rejection from the air conditioners is estimated with a building energy program, EnergyPlus, and a computational fluid dynamics (CFD) program, Windperfect, is used to analyze how heat rejection affects the outside thermal environment. Results show that heat rejection from air conditioners worsens the thermal environment below the urban canopy, thus increasing building energy use. Three countermeasure cases of heat rejection management, which consider the type of cooling system and its installation position, are proposed in this study. The average air temperature increase around the buildings caused by heat rejection was analyzed by transferring the simulation results of the building energy program to the CFD model on an hourly basis. Results show that the air temperature next to the building envelope and the air temperature around air conditioners decrease and that there is a reduction in electricity consumption by the air conditioners when a split-type air conditioner is installed on each floor or on every third floor. A reduction in the ambient air temperature below the urban canopy can be obtained by placing a cooling tower on the roof of the building.