In this work we are exploring the influence of the design of air diffusers on a number of parameters that influence the thermal comfort of building occupants. In particular we are looking at calculating the Air Diffusion Performance Index (ADPI) and vertical temperature difference as well as the throw and drop parameters for various diffuser designs. The results show that while a complex radial vane diffuser that uses the Coanda effect could offer good performance if the HVAC system is used for cooling, the same design might not give any advantage as compared to a regular multi-cone design while the system is used for heating. This is mostly due to the strong air stratification observed for both diffuser designs, while the HVAC system is in the heating mode. Consequently we propose a better alternative, namely, to use a variable geometry (angle) air diffuser. To prove this concept we performed a CFD analysis of several diffusers, each delivering the air at different angles, for both heating and cooling mode, and we show that indeed using a design that allows changing the angle of the air jets between the heating and cooling season is the optimal way of delivering air to a room.

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