The envelope is one of the most important driving factors in the energy efficiency of buildings. Typical for office and commercial buildings, curtain wall facades allow solar heat gains to be used during the winter but can lead to difficulties in reducing the cooling load during summer. The cooling load is dominant in most building types in the temperate maritime climate, while in the temperate continental climate, it is dominant mainly in office and commercial buildings. The goal of this research was to determine the potential of night passive cooling in an office building model in the most populated urban areas in Croatia-Zagreb and Split, which are located in two different climate zones. Suitable to the climate on-site, an appropriate building envelope and various types of passive and mechanical ventilation systems were selected for each location and case. Additional factors included and analysed were climate conditions, heat gains, the heat accumulation of the building, night ventilation through openings, unwanted air infiltration, and cooling loads. Through a detailed description of the model, passive cooling potential calculations, and Computer Fluid Dynamics (CFD) simulations, the results showed a potential of up to 43.5% savings in the cooling energy need for the temperate continental climate and 32.2% in the temperate marine climate. It was found from the analysis that night ventilation is expected to cool down the building enough to delay a need for cooling by several hours and improve fresh air requirements, thus saving power for cooling, and effectively reducing the need for air conditioning.

Although glass façades have been on the market for over a century, new improvements, following sustainable standards, are still being invented. An improvement of the actively maintained CCF has occurred in passive maintenance with natural ventilation of the cavity and insulation glass unit placed on the external side, which has served as a true motivation for further research. To develop the idea, a new type of CCF was invented, followed by the creation of the software, whose purpose is to determine optimal CCF façade components. During this research, an experimental and mathematical model was made regarding the thermal behavior, later validated by the measurements on-site in Rugvica, Croatia. Using simplified but unconventional methods, numerous formulae and variables, a simulation of climatic loads onto the CCF was conducted. Validations of the thermal model were made during winter and summer periods for southern and western façade orientation, explaining how heat transfers from the environment to close cavity façade elements. It was found from the analysis that air temperatures of the façade elements follow the outer air temperature, by constant air exchange with the outer space. The results showed great potential with up to 3 °C (5–10%) of difference in experimental and calculated results, thus creating a basis for further improvement of the software with the addition of structural and hygric behavior of the façade element, regarding climate conditions.