http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Numerical Modeling of a Variable Refrigerant Flow (VRF) System with Refrigerant Injection
This thesis presents the development of a simulation for the variable refrigerant flow (VRF) systems with the refrigerant injection. The VRF system has more complicated configuration compared to the basic refrigeration system owing to modulation of the capacity in the separated zones in a building. Therefore, modularization for numerical models of components in the VRF system is efficient to simulate the performance of the overall system. In this thesis, detailed models for the refrigerant injection scroll compressor, and the fin-and-tube heat exchanger are adopted to simulate the performance of the VRF systems with various system configurations and operating conditions in the cooling mode and heating mode. The refrigerant injection scroll compressor is modeled by the geometry-based model which can calculate compression work, and discharged mass flow rate with consideration of the injection process and suction superheating degree. Therefore, the geometry-based model for the refrigerant injection scroll compressor can analyze the intercooling effects in a compression pocket with application of the refrigerant injection technologies. In addition, the fin-and-tube heat exchanger is modeled by the tube-by-tube method with the dividable sub-element model to guarantee the accuracy of the model in wide range of operating conditions. It is confirmed that evaluation of the heat transfer in the fin-and-tube heat exchanger is acceptably accurate compared to the experimental data. In the VRF system with the refrigerant injection, internal heat exchanger plays an important role which decides the two-phase injection or the vapor injection in a compression pocket under different intermediate pressure. The internal heat exchanger is modeled in order to predict the superheating degree at exit of injection line because the injection temperature influences the input power of the compressor and capacity of the overall systems. Based on the simulation developed in this thesis, the performance characteristics of the VRF system are analyzed in hot and cold seasons. The simulation results show good agreement with experimental data in both seasons under various system configurations and operating conditions. Moreover, the operating characteristics of the VRF system using the refrigerant injection technology are predicted with variation in the sub-cooling method in cooling mode, and intermediate pressure in heating mode.