Preservation of comfort conditions for buildings' occupants and minimization of energy consumption and cost are the main targets of the energy and indoor environment management systems. This paper aims to achieve those targets by presenting the optimal operation of chilling systems within the building supervisory control systems using fuzzy control instead of a conventional Programmable Logic Controller (PLC) - solutions. An optimal operation means reducing operation time and operation costs of the system; and reducing cooling energy generation and consumption costs. The optimal operation of a chilling system can be achieved using the fuzzy control system. The system addresses the shortcomings of conventional PLC-solutions that occur due to limited abilities of PLC functions with their binary logic. The optimization technique is realized by the use of fuzzy control via the FuzzyTECH®-Fuzzy Design Wizard (FDW) windows. The optimal operation of the system is analyzed using two controllers. The first controller consists of three inputs and one output, whilst the second controller consists of four inputs and one output. The chilling system described here supplies chill water to the air-conditioning systems installed in Universiti Teknologi Petronas (UTP). The data are obtained from the Gas District Cooling (GDC) that handles the operation of the chilling system and generates the chill water. The simulation results of the fuzzy system demonstrate significant improvement in the performance of the chilling system. Future work suggests the implementation of the fuzzy logic system on the target hardware platform, such as programmable logic controllers (PLC) using some special fuzzy logic function blocks.