We propose an energy efficient demand control method for air-conditioning systems for buildings installed with multi-split packaged air-conditioning systems (PAC). Energy efficiency is improved by controlling the operating point constantly to target power consumption while limiting PAC electricity power demand and recovering a normal condition without relying on PAC internal logic. The constant operating point is determined as the ratio of the number of units requiring 100% heat load among all indoor units when all units are set to either 100% or 0% using only ordinal external interface information such as temperature setting and operating mode. The proposed method is a practical measure that enables quick, precise, energy efficient control of PAC demand. The results of experiments and case studies showed that the proposed method is 10% more energy efficient than the conventional intermittent operation method and has 4-5% accuracy for operating point control.