The purpose of this study is to compare the capabilities and accuracy of two publicly available underfloor air distribution (UFAD) design tools (ASHRAE RP-1522 and CBE). The comparison is based on the air distribution models, diffuser types, ability to predict the design cooling load, supply plenum heat balance, temperature profile and setpoint, plenum configuration, and air distribution effectiveness. A combined database is fed into each tool’s air distribution model to assess their accuracy. The results show the RP-1522 model predicts thermal stratification slightly more accurately than the CBE model in cases using swirl and square diffusers, but both results are comparably accurate for design purposes. The CBE UFAD tool has the key advantage of being able to predict the UFAD cooling load and model four different plenum configurations and both interior and perimeter zones. The RP-1522 tool is able to calculate the air distribution effectiveness.

This paper describes a coupled dynamic simulation of an indoor environment with heating, ventilation, and air conditioning (HVAC) systems, controls and building envelope heat transfer. The coupled simulation can be used for the design and control of ventilation systems with stratified air distributions. Those systems are commonly used to reduce building energy consumption while improving the indoor environment quality. The indoor environment was simulated using the fast fluid dynamics (FFD) simulation programme. The building fabric heat transfer, HVAC and control system were modelled using the Modelica Buildings library. After presenting the concept, the mathematical algorithm and the implementation of the coupled simulation were introduced. The coupled FFD–Modelica simulation was then evaluated using three examples of room ventilation with complex flow distributions with and without feedback control. Further research and development needs were also discussed.