Theoretical performance analysis of a new hybrid air conditioning system in hot-dry climate

•The proposed hybrid system incorporates a fresh air conditioner with refrigerant system.•In fresh air conditioner, packed bed is linked with three coils to provide evaporative cooling.•The optimum air-to-water heat capacity ratio of packing tower is found to be between 0.4–0.5.•The hybrid system has the optimal energy-saving rate when NTU is between 3–6.•Energy-saving rate of the hybrid system with parallel mode is 42.5–64.0%. A parametric analysis and energy-saving potential evaluation for a new hybrid air conditioning system (HAC) under hot-dry climate are carried out theoretically based on developed models. The HAC incorporates into a conventional air conditioning system with an independent fresh air conditioner which is actually composed of a network of heat exchangers, including a packed bed and three air-to-water cooling coils. The fresh air conditioner can switch its work mode by changing the network connecting relations so as to adapt to different climate conditions. Under hot-dry climate conditions, the network can work like an external dew-point evaporative cooler (DPEC) using the exhaust air as the working gas, which is precooled in one of the three cooling coils. The other two coils are used for fresh air cooling and can be arranged in either parallel mode (HAC-P) or series mode (HAC-S). A sprayer is also designed for appropriate fresh air humidification before DPEC process. For parametric analysis, five independent affecting parameters are included: the air-to-water heat capacity ratio, the ambient temperature and humidity, the characteristic number of heat transfer units of the internal heat exchangers, and the fresh air flowrate. In this article, the energy-saving potential in the HAC-P mode is evaluated for applications in five northwest China cities—Karamay, Urumqi, Hami, Jiuquan and Lanzhou over the summer period (from June to August). The results show that the energy-saving rates are between 42.5% and 64.0% when it is compared with the conventional system.