Detailed Analysis of Microclimate and Its Impact on Thermal and Energy Performance of High-rise Buildings: A Case Study
1Concordia University, Montreal, Canada; 2Texas A&M University at Qatar
Urban microclimate refers to the surrounding detailed weather conditions around a building and building blocks in terms of local air temperature, heat transfer conditions, wind speed, and direction. This detailed information could affect building energy modeling significantly, especially in a dense urban context with many high-rise/medium-rise buildings. In this study, we combined an urban microclimate model, CityFFD (City Fast Fluid Dynamics), with a building energy model, EnergyPlus. The integrated model was applied to studying the microclimate impact on the cooling demand of a high-rise office building surrounded by many buildings in the city of Montreal, Canada, on a typical hot summer day. The integrated CityFFD+EnergyPlus model runs in a “Ping-Pong” manner at each time step. The building surface temperatures output from EnergyPlus are used as inputs of CityFFD and then to generate more accurate microclimate factors used as EenrgyPlus weather information instead of typical meteorological year (TMY) data or measured data in rural regions in next time step. A comparison of the building cooling demand and indoor thermal conditions within/without the microclimate is presented to investigate the significance of the urban microclimate on predicting building cooling demand and its impact during the design stage.
Ventilation Improvement and Energy Loss with Window Opening in Air-conditioned Room
Shinshu University, Japan
Under the influence of biological hazards including COVID-19, it is required sufficient ventilation to decrease the infection risk in the indoor area. In particular, the natural ventilation with window opening is recommended in rooms with inadequate ventilation. However, the ventilation rate, energy loss, and indoor thermal environment with window opening in air-conditioned room varies hourly with given environment. The purpose of this study is to evaluate the changes of ventilation rate, energy loss, and indoor thermal environment with window opening. To achieve this purpose, actual measurement in a residential house and numerical analysis were performed. In the actual measurement, fluctuations in ventilation rate, indoor temperature distribution, and electric power usage of air-conditioner with the window opening area were measured. Then, the analysis model was created based on the actual measurement results, and the validation of the model was confirmed. After that, numerical analysis examined the heating and cooling load due to the increase in natural ventilation. As the result, when the temperature difference between indoor and outdoor was approximately 8.0 °C, the ventilation rate of 30 m3/h could be secured by opening 0.02 m in width using 2.0 m height window. On the other hand, the result was that the room temperature and the cooling load increased proportionately with opening width of window.
CFD Modeling for Near Source Exhaust Dispersion
RWDI, 600 Southgate Dr., Guelph, ON N1G 4P6
Interaction of building exhaust with wind flow patterns over and around building structures significantly affects the dispersion and transport of pollutants and contaminants. Exhaust re-entrainment at air intakes and natural ventilation openings is common issue of poorly designed stacks. In addition to potential health and odor risks, re-entrainment of hot or moist exhaust can adversely affect equipment efficiency and operating range. Development and implementation of practical modeling tools to assess the dispersion and transport of stack exhaust is key to reducing the risk of any potential exhaust re-entrainment. The tools currently used include desktop numerical models, wind tunnel testing and Computational Fluid Dynamics (CFD). Desktop numerical models are typically limited to simple building geometries producing conservative design recommendations. Wind tunnel testing is the most accurate tool for simulating the aerodynamic influence of building geometry on exhaust dispersion. CFD advantages include the capability to simulate complex physics without scaling limitations or infrastructure requirements of physical wind tunnels. However, standard CFD turbulence models struggle to accurately predict wind flows around buildings – especially the separation and reattachment zones and thus to associated turbulence scales. Consequently, the use of CFD to predict exhaust dispersion around buildings is often fraught with errors. The current study aims to assess the accuracy levels of CFD modeling approaches for exhaust dispersion through comparison with wind tunnel testing data. The CFD model is set-up using the same-scale, geometry and testing conditions as the wind tunnel to avoid any scaling uncertainties. Comparison between the capabilities of different Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES) models in predicting upstream structure effects on wind flows, and consequently exhaust dispersion is presented with conclusions about future work.