Thermal environment in indoor spaces with under-floor air distribution systems: Part 2. Determination of design parameters (1522-RP)

This article reports on the continued study of the thermal environment in indoor spaces with under-floor air distribution systems, with a focus on the determination of supply airflow rate. Supply airflow rate of under-floor air distribution needs to be carefully determined to achieve thermally comfortable conditions in an occupied space. The design parameters, such as airflow rate, temperature of supply air, and types and number of diffusers, need to be properly calculated to ensure an acceptable vertical temperature difference between the head and ankle of occupants. This study introduced an empirical model to predict the vertical temperature difference between the head and ankle of occupants and calculated the supply airflow rate for under-floor air distribution design. This investigation developed the model based on a database summarizing vertical temperature distributions that correspond to various airflow and thermal conditions. The model used dimensionless numbers to group design parameters in order to represent the two driving factors of thermal stratification, namely, inertial and buoyance forces. Linear regression analysis was conducted to correlate the empirical equations of stratification for swirl, square, and linear diffusers. With the model, this study developed an airflow calculation method for under-floor air distribution as well as a graphical interface for designers.