Energy efficiency evaluation for building air-conditioning systems determined by coincident design weather data

Accurate design weather data are important for the energy efficiency of building air conditioning systems. Design cooling load of air conditioning system can be calculated accurately by coincident design day (CDD). It is important to evaluate the effect of coincident design day on the energy consumption and thermal comfort of air conditioning systems for promoting its application in engineering design. In this study, the coincident design days were determined and applied to the building's air-conditioning systems design. Using DesignBuilder simulations, cooling electricity consumption and thermal comfort performance of the proposed system have been investigated in three climate zones. A comparative assessment of the systems using coincident design days has been made against the systems using traditional design days. Results show that for the rooms with single external walls using the packaged terminal air conditioner (PTAC), the energy saved by coincident design days is 3.27%-7.19%, 1.43%-5.46%, and 2.25%-5.18% in Beijing, Changsha, and Hong Kong. For the whole buildings using fan coil with dedicated outdoor air (FCU + DOA), constant air volume (CAV), and variable air volume (VAV) systems, the energy saved by coincident design days is 11.38%-12.67%, 17.89%-17.9%, and 14.99%-16.06%, respectively in Beijing. In Changsha, these systems determined by coincident design days save energy are 11.19%-11.47%, 14.7%-17.82%, and 13.42%-16.05%. In Hong Kong, these systems determined by coincident design days save energy are 11.73%-12.48%, 17.97%-18.8%, and 14.99%-15.35%. The application of coincident design days to the CAV systems has the highest efficiency. These results demonstrate that the air conditioning systems determined by coincident design days can significantly reduce cooling energy consumption without affecting indoor thermal comfort, and fulfill the requirements of indoor thermal risk levels in the three climate zones of China.