To obtain a system level, integrated perspective on vehicle energy management, the traditional methods for conducting preliminary design, gauging independent requirements, must be abandoned. This method does not capture critical interactions between the various aircraft subsystems. Instead, a more global appreciation for interactions across boundaries needs to be realized with a mosaic scheme, where models are integrated and co-simulated. The advantage of this approach is to enhance the preliminary design stage by predicting integration issues early in the development process. Legacy design practice involved gathering data from multiple vendors in order to produce design iterations. The ability to link models directly is extremely beneficial, as requirements no longer have to be executed independently. This approach reduces cumbersome iterations between model owners and accelerates trade studies. GE Aviation is developing a PREliminary Optimized Vehicle Integration Design Enabler Tool (or PREOVIDE) to facilitate this approach. PREOVIDE is an integrated toolset with a strong emphasis on performance of thermal management systems at the vehicle level. This initiative has led to new and/or improved models for environmental controls systems, air-cycle systems & engine deck integration, vapor cycle systems, fuel tank modeling, cabin thermal modeling, Simulink/NPSS API integration and much more. The paper will outline this modeling philosophy, which demonstrates modeling flexibility, expands the design space, accelerates trade studies, and encourages collaboration in the design of vehicle energy systems.