The extended use of double skin facade (DSF) in different kinds of buildings imposes HVAC (Heating Ventilation Air Conditioning) designers to use quick and accurate software to help in taking the right decisions related to energy consumption and thermal comfort. The lack of such methods was the motive to present this paper. Validation of a simplified mathematical model for dynamic simulation of the thermal performance of DSF was presented by comparing results with another detailed simulation model DIGITHON, for a complete year. Moreover the mathematical model was developed to calculate thermal energy due to convection losses from outer facade layer, solar gains and internal loads. A more detailed comparison of energy consumption at different climatic conditions of four cities in Europe has been shown. Implementation of the simplified model in thermo-active-building-system-(TABS) also was illustrated, and how such a model could be useful in one of four methods mentioned in standard ISO-11885-4 to predict heat transfer on TABS. This particular method needs the solar gains and losses due to transmission determined with a constant room temperature by another software which the mathematical model could be implemented in (C) 2015 Elsevier B.V. All rights reserved.