On August 31 and September 1, 2019, the IBPSA Project 1 held its 4th Expert Meeting. The meeting took place in Rome, Italy and was attended by 50 people.The meeting coordinated the ongoing work in the various tasks. Task 1 held hands-on training for the BOPTEST Building Optimization Performance Tests. Joint sessions between Task 1 and 3 discussed methods for how to improve the computing performance of large district energy models. A joint session between Task 2 and 3 clarified how to link district-level data models with Modelica models for district heating systems that are being developed for the DESTEST validation suite.For the slides of the meeting and its various breakout sessions, please refer to the github repository.Further information can be found on the IBPSA Project 1 webpage.