Hour-by-Hour Load Management Effects on System Demand

System planners and dispatchers plan and operate the electric system with hourly information. Generation expansion and production costing models require hourly load shapes. When planning for the day´s generation schedule, the dispatcher must determine the hourly load for the day in order to have the most economical generation mix to meet needs. But some air-conditioning load research programs developed by the utilities do not utilize hourly load shapes which are a function of both temperature and time. Some load research programs are used to develop only the expected average air conditioning load reduction achieved via direct load control at the time of system peak. Air-conditioning load is primarily a function of outside ambient temperature. This load will increase as the temperature rises because of two characteristics inherent to air conditioners. First, the constant torque characteristic of the compressor/motor increases the instantaneous demand of each air conditioning unit as temperature increases. Second, an increase in capacity factor (load factor) or average demand over a period occurs as more heat must be removed because of the greater temperature differences between inside and outside. The latter means simply that the air conditioning unit runs longer in each period. Since most air-conditioning load research data do not quantify the hourly load as a function of temperature, neither the system planner nor the dispatcher can do an adequate job in developing the costs and benefits of a control system or in determining the timing of control to maintain the most economical generation mix.