Present study is devoted to IEQ, Indoor Environmental Quality, which plays a vital role in recent decay, while energy efficiency in public buildings is a target when designing, or evaluating of any building to meet the requirements of the Egyptian Energy Efficiency In Buildings Cod “EEEBC”. This study is concerned to the influence of IEQ needs and criteria’s on global energy needs for HVAC centralized systems that used in public buildings, In addition, it focuses on the effects of occupation, operation profiles and fresh air requirements, on the global building energy efficiency limits that complying with EEEBC . Filed and numerical simulation investigations were applied on a real centrally air-conditioned project as a case study “25,000 m² shopping centre”. Different concepts for optimizing IEQ were considered in accordance with the EEEBC limitations. It was concluded that numerical energy simulations can achieve realistic and accurate results “Nearly Similar” to the energy bills when detailed operation profiles and occupancy schedules were similar to reality and applied for each source of heat. These profiles may contribute in the energy code as a guideline for designers. Although in this case study results from simulation task reach the real bills, but sometimes, with large open zones for ski and café shops there is another schedule for the Pre-Action days. Those days before holidays and feasts on which the air conditioning system shall operate in a certain procedure for scavenging and cleaning. Another important issue is the influence of Effective Temperatures [ET*] that should be considered to reduce the total cooling capacities by increasing the room temperature against indoor relative humidity.