Simplified model for desired airflow rate in underfloor air distribution (UFAD) systems

As one of the forced air ventilation methods, the underfloor air distribution (UFAD) system has been a subject of active research for its potential advantages of indoor thermal comfort (ITC) and indoor air quality (IAQ). In a UFAD system, the conditioned air is directly delivered to the occupied zone, causing thermal stratification from the lower zone to the upper zone. The performance of thermal stratification is critical to the ITC and IAQ. This paper focuses on the characteristics of thermal stratification in the UFAD system. The characteristic parameters as well as the ratio of temperature gradient are proposed, and thus the models are derived from the regression analysis. Furthermore, the simplified model for calculating the airflows in the UFAD system is deduced on the basis of the characteristic parameters and the ratio of temperature gradient. The limitation for the application of the simplified model is also provided for achieving a satisfied ITC. This study will help to simplify the design and operation for the UFAD systems.