# Interoperability between Building Information Modelling (BIM) and Building Energy Model (BEM)
## 3 Results and Discussion
### Simulation Results  
After analyzing the import of the gbXML and IFC files of the residential building and the warehouse into BEM software, all the models were simulated with the aim of assessing whether the energy results would differ, with respect to the BEM software used. The simulations were executed monthly, from 1 st January to 31 st December, using the weather file of Madrid, Spain, under ideal loads. However, among the three processes carried out, only the first and the third related to the residential case presented results. The gbXML file of the house imported in Open Studio showed some fatal errors in its geometry (e.g., missing walls and floors), which made its energy calculation impossible. Furthermore, the warehouse case was not simulated. Its gbXML and IFC files were imported in BEM tools without any problem; however, the model was not constructed properly. Missing elements and gaps in the thermal envelope, such as in the roof and external walls, were among the fatal errors encountered. Therefore, only the results of the first and the third processes (see Figure 1) of the residential case were analysed:  
1. gbXML file exported from Revit and imported in Design Builder. 2. IFC file exported from Revit and imported in CYPTHER HE. As this research intends to verify the interoperability between the data transfer from BIM to BEM, at the moment of comparing the results, two constructive elements were selected that can be inserted and modified in BIM and are essential to the study of energy modelling: the windows and the opaque envelope. * Windows Heat Gain  
As can be seen in Figure 10, there was a big difference between the model results of the residential case. First of all, the windows heat addition value of the first process was six times smaller than the third case, simulated in CYPTHER HE. Once the huge discrepancy among these values was determined, we intended to discover where the problem originated from and, so, we collected the information about three parameters that could have influenced the window heat addition: Area of multiplied openings (m2), glass U-factor, and glass SHGC (Table 5). Figure 10: Heat gain components of the residential building simulations. Therefore, we found that, in the gbXML file, the glass U-values and SHGC were not equal to those in Revit (see Table 5). For some reason, the U-value was 2925 W/m\({}^{2}\) K and the SHGC was 0.13, while, in Revit, they were 3.68 W/m\({}^{2}\) K and 0.78, respectively. This was a failure in the transfer of the data from BIM to the gbXML file, which explains the lowest value of window heat addition among the two cases. On the other hand, the third process, which had the IFC file imported in the CYPETHERM HE software, presented the exact same glass U-value as in Revit. However, at the moment of analysing the IFC file in Notepad, we detected that the glass SHGC was not transferred to the IFC and, therefore, a SHGC default value equal to 0.70 was set automatically in CYPETHERM HE. Regarding the area of openings, gbXML had a value closer to the BIM. In Revit, the window total was 39.24 m\({}^{2}\), while the gbXML and IFC files presented values 3% and 15% smaller than BIM, respectively. Another interoperability problem was related to the window frames. In the BIM model, the openings had wooden frames, but their thermal properties were not defined. This information was not extracted to the gbXML and IFC files and, therefore, none of this opaque fraction of the opening was transferred to the BEM. * Opaque Surface Conduction As can be seen from Table 6, there were differences between the areas and U-values of the thermal envelope opaque elements (i.e., floors, walls, and roof). The gbXML presented the lowest value for the exterior walls: 132.84 m\({}^{2}\), 57% less than the area in the BIM (309.00 m\({}^{2}\)). In addition, the IFC also showed a small value, but only 21% less.