Determining thermal stratification in rooms with high supply momentum

Computational Fluid Dynamics simulations of a typical occupied office were performed to study the effects of ventilation parameters (supply momentum and heat gain intensity) and inlet geometry (height and area of the supply) on the temperature profile of the air in the space. A knowledge of this profile is critical to ensure that the occupants are comfortable according to commonly used standards. Different room configurations were characterized in terms of their Archimedes number, which compares the effects of buoyancy and supply momentum, and dimensionless geometric variables. A high Archimedes space was found to be divided into a warm region of uniform temperature above the occupants and a zone where the temperature increases approximately linearly with height. In a low Archimedes space the air is mixed by the supply jet in the lower part of the room, especially near the outlet, resulting in this area having uniform temperature. However, the supply jet was found to be less efficient at mixing the air near the ceiling, resulting in higher temperatures in this zone than with higher Archimedes numbers. For a given Archimedes number, as the supply area increased, the air temperature was found to decrease in the lower part of the room but to increase near the ceiling. A high inlet increased the vertical mixing in the room. Correlations were proposed to establish the temperature profile within 5% of the temperature rise of the room. The inputs of the correlations are readily available in multi-zone software, facilitating their integration in this kind of software. The proposed correlations will allow the user of the multi-zone software to evaluate comfort conditions more accurately, while maintaining the high speed, simplicity and design flexibility of the multi-zone models.