Room Air Distribution and Indoor Air Quality of Hybrid Air Conditioning System based on Natural and Mechanical Ventilation in an Office

The characteristics of a hybrid air-conditioning system, utilising natural and mechanical “task” ventilation, are investigated in an office setting. The characteristics of the indoor environment are examined by means of CFD (Computational Fluid Dynamics) simulations under various conditions of incoming outdoor air. The control of the task air conditioning system (VAV system) is included in the calculation through changing the supply air volume to keep the task zone‘s temperature at a target temperature. Results show that the thermal environment at the task zone is maintained comfortably with the aid of mechanical air conditioning and indoor air quality is achieved by providing natural ventilation through window opening. When the temperature of the in-flowing outdoor air rises and the vertical width of the window opening that lets in the air decreases, the inflow jet flows deeper into the room and therefore mixes easily with the indoor air. When the in-flowing outdoor air volume increases, the inflow jet exhibits a 3-dimensional aspect in a room. A vertical temperature gradient appears at the task zone with the increase of the temperature and volume of the in-flowing outdoor air. The distribution of the age of air is strongly influenced by the flow fields. The average age of air at the task zone depends mainly on the natural ventilation rate.