Study On Energy Saving Control Stratedies Of Central Air Conditioning System

The energy consumption of central air conditioning system accounts for a large proportion in the total energy consumption of the building. Most central air conditioning systems are designed according to the maximum load of the building at present time. However, the time frequency of the system running in full load is very small. Therefore, the study on the optimal operation strategies of the central air conditioning system under partial load is carried out in this paper.To investigate the energy saving potential of the existing central air conditioning system, a real-world shopping mall located in Nanjing together with its central cooling plant is used for data collection. By using a theoretical-empirical modeling approach, the mathematical models of the main equipments of the system are established, which is the basis to analyze the energy saving characteristics of the devices and to optimize the operation parameters of the whole system.The optimal operation mode of the system is discussed by analyzing the energy saving characteristics of the system components. And the optimal load distribution strategy of the joint running chillers, the optimal operation mode of the cooling tower under partial load, and the best operation mode of parallel pumps under different control methods were proposed. By applying the heat exchange efficiency method, several factors which have impact on the thermal performance of the cooling coils are discussed, providing a theoretical basis for quantitive control and quality control of central air conditioning system. A new method to calculate the maximum chilled water temperature under different weather conditions is proposed which synthetically considers the dew-point temperature of the outside air and the dehumidification demand of the terminal air conditioning units. The optimal temperature gap between the outlet water of the cooling tower and the outdoor wet-bulb temperature is figured out under different load and weater conditions.After optimizing the operation mode of the central cooing plant components, the dynamic optimization of the system running parameters is carried out by using the established mathematical models with the optimal objective function of the integrated energy consumption of the system. Appropriate constraints are incorporated to satisfy the heat transfer principle and the range of the variables. The typical nonlinear programming algorithm is adopted to solve the minimization problem of the global energy consumption. The dynamic simulation of the central air conditioning system is implemented on the platform of Simulink and the optimized parameters are validated by comparing with the simuliation results. The effects of each variable on the total energy consumption are observed by the scope module.The system group control strategies are extracted from the optimized system operation mode and parameters, whicn are based on the adaptive fuzzy PID controllers. The calculation of the energy consumption of the target central air conditioning system under the optmal control strategies is implemented. It is shown that the total energy-saving rate could be up to 10% comparing with the conventional method.