Personalized environmental control systems (PECS) have the potential to save energy by enabling setpoint relaxation of the heating, cooling, and ventilation systems without compromising comfort. The authors have previously reported on the heating, cooling, and air distribution performance of a stand-alone PECS prototype. The developed prototype, together with additional mockup devices developed and tested to improve the future prototype design, were modelled and assessed in terms of energy use and CO2 emissions. Annual building energy simulations were conducted with the medium office building model developed by the U.S. Department of Energy. Based on experimental data, characteristic curves for heating and cooling of the PECS and mockup components were derived as a function of the corresponding power use. When PECS was installed, the heating/cooling setpoints and outdoor air intake of the background variable air volume system were relaxed by the maximum performance of PECS in terms of equivalent temperature and ventilation effectiveness, respectively. It was assumed that PECS was always modulated to provide optimal conditions within its available performance. The electrical power use of the corresponding settings was calculated with the characteristic curves and treated as internal heat gain. The current PECS prototype resulted in a 3% energy penalty due to its high standby power, indicating the importance of minimizing unnecessary power use. The combined use of mockups providing more efficient heating through contact and cooling through isothermal air flow resulted in a 13% reduction of energy use and CO2 emissions, even with the same standby power as the PECS prototype.