Annual usage characteristics of air conditioners in residential buildings in the Yangtze River Basin

To report the heating and cooling characteristics in residential buildings of the Yangtze River Basin, this study investigates the annual usage characteristics of room air conditioners (AC) in 19 households from four cities. These cases are all new buildings, with similar family structure and the same types of energy effective ACs. The indoor air temperature, relative humidity and AC electricity consumption are continuously monitored for one year. The results show that occupants use AC for heating mainly in December, while in summer the ACs are used at night and mainly from middle July to early August, and the proportion of ACs operation at the same time is higher than 50%, mainly occurring after 20:00. The duration hours for AC operation show a left-skewness distribution. The proportion of continuous operation time of less than 2 h is the highest (61.8%) in winter, while the proportions are close for 1 to 4 h in summer (10.2% to 15.5%). The driving temperature profile for occupants to turn on ACs is in U-shape in winter (min: 12.6 ℃ in January) and inverted U-shape in summer (max: 29.4 ℃ in July), indicating the dynamic thermal adaptability and comfort demands for occupants in residential buildings. The monitored power for AC increases with increasing/decreasing outdoor temperatures, and the daily electricity consumption for cooling in summer (2 to 4 kWh) is significantly higher than that for heating in winter. The annual mean electricity consumption for AC varies from 9.96 kWh/(m2·a) to 12.65 kWh/(m2·a) in different cities, while great differences exist among different homes. The results can provide references for understanding the energy usage characteristics of ACs for cooling and heating, formulating appropriate indoor thermal environment standards for residential buildings, and guiding the reasonable AC usage behaviors for occupants in the Yangtze River Basin.