Recently in Hong Kong, an increasing number of commercial buildings have been equipped with split air-conditioning systems, rather than central systems. Two main reasons for this include reducing the initial capital investment by installing relatively inexpensive split-type air conditioners and saving energy. Individual systems can be easily measured by submeters, which enables all occupants to be billed for their own energy use. Using split air-conditioners can motivate occupants to use less energy and save money. However, individual systems normally are less efficient than large central systems. The maintenance and operation cost for split systems usually is higher than that of central systems. Therefore, it is necessary to compare both systems.