One of the most pressing issues facing the American healthcare system is an inability to meet the ever-increasing demand for emergency department (ED) care. EDs across the country are experiencing overcrowding that exhausts resources, creates unacceptable waiting times, diminishes the quality of patient care, and increases financial costs for both the patients and medical departments. The ED at the University of Virginia (UVA) Medical Center is no exception. From 2014 to 2015, the number of patients seen at the UVA ED grew by 4%, which is expected to continue to increase annually. In response, the UVA Medical Center will construct a new "ED Tower" that will double the department's bed capacity, improving departmental efficiency and providing better patient care. This paper reports on a simulation study of patient flows in the UVA ED under alternative demand scenarios, staffing levels, and operating practices. Key performance measures include overall patient length of stay and arrival to provider time. A trace simulation of the current ED was conducted using data from 2014 to validate the model and this model was updated with new logic for the future ED. Our results suggest that the additional space, coupled with staffing schedule changes, will help alleviate the overcrowding problem at the UVA ED for the foreseeable future. For example, the future ED with the current staffing schedule would reduce the average arrival to provider time by 29.5% and overall average length of stay by 3.7%. By incorporating the results of our analysis with our research into best practices of process flow within EDs, we expect our recommendations to improve patient flow efficiency of the future ED and help maximize the quality of care that is delivered to patients.