Prediction of Comfort Parameters for Naturally Ventilated Underground Car Parks
Abstract
With the increased population and rapid motorization in urban areas of Pakistan, the concept of underground car parking areas in multistory buildings is increasing day by day and is a viable solution for modern high rise shopping malls. However, maintaining a thermal comfort level and dilution of vehicle emission for naturally ventilated basements is very challenging since the toxic pollutants cause serious health issues. Computational Fluid dynamics FLUENT is a valuable tool for study of mean air speed, pressure and velocity streams and is supportive in identification of red zones inside the building and is becoming a legal requirement. The research is an effort to implement two of the available FLUENT turbulent models using finite volume technique on an existing two level basement under a multistory building, predicting the best suitable model. The evaluation for each model is performed by developing the 3D model for each level of basement, meshed with equal number of cells and analyzed under same boundary conditions. In addition, an effort is made to investigate the gaseous emission from vehicle exhaust. Indoor air quality is assessed by defining the CO generation rate and respective ACH (Air Changes per Hour) are determined using ANSI/ASHRAE 62-1989 for a maximum concentration of 25ppm and 35ppm. The acceptable indoor air quality specifies a fixed ventilation rate of 7.62 L/s.m2 i.e. 1.5 cfm/ft2 of gross floor area, which means that a ventilation flow of about 11.25 air changes per hour is required for garage with 2.5m (8 ft) ceiling height. Results showed that for level-I the number of air changes required are 17 with a concentration limit of 25ppm of CO in an hour while with limit of 35ppm 12 ACH are enough for dilution of indoor air. For Level-II, which is used to its maximum capacity, the number of air changes required are 11 with limit of 25ppm but drop down to 7 with concentration limit of 35ppm. A parametric analysis for garage height and CO generation shows that with an increase in garage height the ventilation rate required to keep CO level minimum or within acceptable level also increases as the volume of car park increases.References
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