An experimental study on performance of digital variable multiple air conditioning system under part load conditions in hot summer and cold winter zone was conducted in this paper. The effects of outdoor air temperature and on-unit ratio on total power consumption in 1 h, hourly heating performance factor or hourly energy efficiency ratio were analyzed by experiments. The variations of hourly heating performance factor (or hourly energy efficiency ratio) and total power consumption in 1 h with part load value under different outdoor air temperature were obtained. The results indicate that digital variable multiple air conditioning system can keep economical and reliable operation under part load conditions. And it is necessary to study the index which may reflect the seasonal energy consumption of digital variable multiple air conditioning system. (C) 2010 Elsevier B.V. All rights reserved.