Energy consumption analysis of building air-conditioning systems using centrifugal compressor with gas bearing under annual operating conditions

The water chiller using centrifugal compressor with gas bearing is an important development direction for building energy saving, but the additional refrigerant cycle for bearing and motor colling leads to more complex performance especially under the various operating condition. Based on the heating and cooling loads of a building in Nanjing and the local climate conditions, this paper innovatively establishes an air conditioning system model using centrifugal compressor with gas bearings (CCGB), and analyzes the performance of air-cooling and water-cooling methods. Considering the heating and cooling loads, the annual energy consumption of two systems was compared consider the climate condition. The results show that the COP of water-cooling system is larger than that of air-cooling system due to the better heat transfer condition. The larger power consumption of compressor for air-cooling system leads to the larger motor cooling load. The cooling methods have obvious influence on the vapor-injected mass flow rate, but have small impact on the mass flow rate of motor cooling and bearing gas supply. The energy efficiency of air-cooling and water-cooling system in summer are 3.77 and 5.12 respectively, and the total energy consumption in the whole year are 32.4 tons and 33.5 tons of standard coal. The mathematical model of air-conditioning system using centrifugal compressor with gas bearing (CCGB) is built, and the performance using air and water-cooling system is analyzed based on the annual climate conditions in Nanjing. For the whole refrigeration season, the water-cooling system have higher energy efficiency, but the air-cooling system is more efficient for the heating season due to the added heat from the heat pump. Although the air-cooling system consumes more energy in summer, the annual energy consumption is only slightly lower than that of the water-cooling system. The energy consumption in winter is higher than that in summer for both of the air and water-cooling systems, and they consume 32.4 and 33.5 tons of standard coal throughout the year, respectively.