The objective of this study, including field investigations and energy modelling, is to evaluate the feasibility of retrofit for energy performance of a hospital in Taiwan. This hospital consumes around 8500000 kWh annually with 37490 m2 floor area including twelve stories and two floors of basements. The current facility systems of this hospital present relevant signs of degradation and obsolescence with high energy consumption. The retrofitting plan of facility systems for this hospital is assessed and conducted to improve energy performance accordingly. Based on ASHRAE procedures for commercial building energy audits (PCBEA), field study and energy audits were conducted to collect information of building geometry, building materials, space types, density and activities of people, capacity of HVAC system, loads and operating schedules of lighting and other facilities. The energy consumption baseline can be derived through PCBEA and BEMS (building energy management system) data. Energy modelling using Energy Plus code has been conducted extensively to evaluate the energy saving approaches. The results reveal that the energy saving strategy of increasing chiller water supply temperature 1℃ could obtain 1% of annual energy saving, while increasing room set point 1℃ may reach 2% saving of annual energy consumption. Besides, applying the insulation film for glass also presents about 0.8% of annual energy saving through energy modelling. The retrofit feasibility has also been evaluated in terms of annual savings and pay-back period of the investment. The procedural investigation of building energy consumption should provide valuable information for facility engineers facing energy saving concerns.