Underfloor air distribution (UFAD) is an effective strategy to provide both ventilation and air conditioning for buildings. To predict indoor airflows and temperature distribution, zonal model has advantages over other methods such as multi -zonemodel and computational fluid dynamics (CFD) by considering the prediction accuracy and computational cost. In this work, a numerical algorithm for floor-mounted diffuser flows, which calculates the airflow mass conservation and energy conservation separately, was implemented in a newly developed zonal model computer program for UFAD application, based on the established zonal model-pressurized zonal model with air-diffuser (POMA). This computer program was validated by lab experiments under both natural convection condition and mechanical ventilation for a lab -scale mixing UFAD system. Comparisons of zonal model simulation results and experimental measurements for both temperature distributions and air flows in the lab room showed that the newly developed zonal model is a good tool for predicting the indoor thermal environment with UFAD system. (C) 2017 Elsevier B.V. All rights reserved.