Considering that integrated testing of the TCS and ECLSS of the Attached Pressurised Module (APM) of the Columbus Orbital Facility (COF) is limited in scope and planned late in the programme in line with the Proto-Flight Model (PFM) approach, it is pivotal to make the system-level analysis of the interaction between the two subsystems as comprehensive as possible. The paper presents analysis with the Integrated Overall Thermal Mathematical Model (IOTMM) that is used by Alenia Aerospazio to determine the operational envelope of the combined TCS and ECLSS. It describes the model architecture and a number of the analysis cases that were selected to represent the wide range of COF APM operational modes. The analysis cases include both steady-state cases and transient cases simulating transitions between different heat load configurations. Based on the results of the IOTMM analysis, the paper discusses improvements to the COF APM TCS and ECLSS design.