Simulation Study On Heat Transfer Properties Of Air-conditioning Chilled Water Systems With Variable Water Volume

Today, there is a crisis of energy shortage in the world. Because air-conditioning systems with variable water volume have significant potential of energy saving, people pay more and more attention on its research and application. However, most of air-conditioning systems with variable water volume fail to reach design requirements. This results in failure of the control system and user's demand to temperature and humidity cannot be met. The main reason is that the thermal properties of the customer side water systems have not been known very well. Based on the air-conditioning system dynamic simulator set in this paper, this study is performed in thermal properties of air-conditioning chilled water systems with variable water volume. It is hoped that this work may give a help to recognize the above problem. Thus corresponding design and control methods will be more scientific and reflect the reality more accurately.Firstly, based on the mathematical model for components of the air-conditioning system, all components are connected as the dynamic simulator of the air-conditioning system in the lab as a simulation platform through TRNSYS. Through input to essential data files and debugging of control loop PID parameters, this dynamic simulator is set up finally.Secondly, the parameters of the dynamic simulator are obtained through experimental tests on the air-conditioning system in the lab. And experimental validation of the dynamic simulator is undergone through experimental tests at the same time. The results show that this dynamic simulator has high precision and good accuracy. It is suitable to simulate heat transfer properties of the air-conditioning system with variable water volume.Finally, using the system dynamic simulator, the simulation study on the air-conditioning system with large temperature difference in winter conditions and on-off control fan coil water systems are conducted under constant temperature difference control, constant delivery head control and constant terminal pressure difference control. The results show that the properties of air-heating coils and fan coils are degraded by increasing the temperature difference of supply and return water when supply water temperature is unchangeable for air-conditioning systems with large temperature difference. If supply water temperature is increased largely enough, the properties of air-heating coils and fan coils are improved when the temperature difference is increased with a certain range. For on-off control fan coil water systems, heat transfer properties of terminal fan coils are associated with the scale of air-conditioning systems, the pipe net layout mode and terminal load distribution characteristics.