This paper describes a combined system of air conditioning and natural ventilation for large enclosures. A multi-zonal model to simulate the vertical temperature distribution is established. This model describes airflow and heat transfer on a ‘macro’ scale compared to CFD model, but it appears very efficient for engineering application. In this model, air density is considered to change with air temperature. Multiple air jets, buoyancy driven natural ventilation and coupled heat transfer are taken into consideration. It is governed by non-linear equations and is resolved by an iterative solution. A program is compiled to calculate the mass flow and temperature distributions. It shows that the combined system of air conditioning and natural ventilation cut considerably down heat gain in occupied zone. By comparison, the combined system can be expected to give lower temperature both in the enclosure and on interior surfaces. Some cases are calculated, and the results suggest that it depends on many factors such as the height of ventilating opening, the effective opening area, and outdoor air temperature to effectively make use of natural ventilation in the combined system. To sum up, this paper presents an energy efficient system for large spaces and also a theoretical model to design the system and predict the vertical temperature distribution.

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