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Abstract: When a wind flow approaches a building, a recirculation zone is created on the leeward side of the building. This turbulent zone behind the building increases the air mixing at the leeward openings between entering and leaving air. As a consequence the effective temperature difference is reduced at the opening, counteracting the stack effect. Therefore, the air change rate is lower than that in absence of wind. Some empirical correlations have been set up to assess the airflow rate due to the combination of stack and wind effects. However these correlations do not take into account the reduction of airflow rate in leeward conditions. This paper aims to improve the existing correlations and in particular to confront the issue related to leeward openings. The study is based on CFD simulations and full scale experiments. A comparison of Warren''s correlation with CFD and experimental results shows that this correlation captures well the stack and wind effects in windward conditions but shows poor results in leeward conditions. Thus, a new correlation has been developed by using CFD simulations in leeward conditions. The new correlation is then compared with the full-scale experiments and concords well. [Copyright &y& Elsevier]

Abstract: Single-sided natural ventilation is a simple and energy-efficient method to passively cool a building, thus reducing or avoiding air-conditioning use. CFD has the potential to give detailed information about the complex flow generated by the interaction of buoyancy and wind in single-sided ventilation. In this paper, three experiments on single-sided ventilation are reproduced by CFD, using two turbulence models (RANS and LES). A detailed description of the experimental set-up, the numerical methods and the comparison method between experiments and simulations are provided. Results from RANS and LES are compared to experiments in terms of average and turbulent flow field, local airspeed, turbulence and temperature at the opening and airflow rates. The comparison shows that LES has the potential to provide more accurate results than RANS in most of the cases, capturing better the turbulent characteristics of the flow. However, the computational cost of LES is at least an order of magnitude higher than that of RANS. [Copyright &y& Elsevier]

Abstract: Natural ventilation can contribute to the reduction of the air conditioning demand and to the improvement of thermal comfort in buildings. In this paper, the flow field and the air change rate generated by a simple configuration of natural ventilation, namely single-sided ventilation, are examined experimentally. The experiments are realized in a full scale building exposed to outdoor conditions, using several measurement techniques. The main features of the flow generated by stack and wind effect are examined for different outdoor conditions (temperature difference, wind speed and direction). Finally, measured air change rates are compared to those calculated by existing correlations in order to analyze their applicability to the experimental configuration. Results show that the wind generates turbulence diffusion at the opening, counteracting the stack effect. Moreover, in the case of windward opening, there is an additional effect, namely the effect of mixing layer, which tends to increase the airflow rate. Existing correlations give reasonably good results in the case of windward opening, while in the case of leeward opening they overestimate the airflow rate. [Copyright &y& Elsevier]