Recently, air-conditioning systems that combine natural ventilation with cooling have received increased attention. These systems are expected to reduce energy consumption and maintain thermal comfort. However, concerns have been raised about the effects of natural ventilation on HVAC control and indoor environmental quality. In this study, such an air-conditioning system in an existing office building was evaluated through measurements and steady state CFD analysis with HVAC control for each zone. The following results were obtained: (1) According to the measurements, the indoor thermal environment produced by natural ventilation was more nonuniform than that produced by mechanical ventilation. (2) Calculation results of the temperature distribution and air-conditioning cooling load were mostly in agreement with measured results, and hence, it is concluded that the proposed calculation model has sufficient prediction accuracy. (3) In the case study, natural ventilation produced a good indoor environment, although it caused discomfort to those who were near the inlets for natural ventilation because of the draft.
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