Study On The Optimal Control Of VAV Air-Conditioning System In Large-scale Rooms

The rapid growth of building energy consumption is the result of the high pursuit of building quality, not only the appearance of beautiful and fashion, with the strengthening of healthy concept, indoor environment comfort has been widely noted by people. With the widely application of air conditioning system, the energy intensive feature of building becomes more and more highlighted. In the buildings which use central air-conditioning system, the energy consumption for the operation of central air-conditioning system accounted for more than60%of the total energy consumption. Reducing the energy consumption of HVAC system is an effective measure to reduce building energy consumption and of great significance for building energy conservation.In the VAV air-conditioning system of large-scale rooms, the supply air volume is regulated to suit for the variable of indoor load by the change of damper position which the terminal device is used to adjust through the deviation of detected and set value of indoor air temperature. However, the return air temperature is higher than the actual demand temperature of human activity high for the large vertical temperature gradient in buildings. It can’t effectively reflect the actual demand air temperature of human, so that the supply air volume will become larger and the operation consumption of terminal device is increased. Therefore, the control accuracy of the system is not high and the energy saving potential of the VAV system can’t be entirely played out. At the same time, VAV air-conditioning system is of variable, strong coupling and nonlinear features. In the process of actual operation, the VAV system will be instability because the control loops of the system is in different coupling effect degree. The traditional air volume control methods, constant static pressure, variable static pressure and total air volume, can’t effective to solve the instability problem of the VAV system. A new kind of effective air volume control method needs to be studied. Based on the above analysis, this study chooses a large-scale market in Guangzhou as the study object. First, use PHOENICS simulation software to build the market model, and then use the collected data through on-site investigation to set the boundary conditions of the simulation model in order to obtain the range rule of indoor temperature and air distribution in VAV system. On this basis, optimize the position of the indoor temperature testing point by importing the wireless sensor technology. To those places which can’t install temperature detection for wireless sensor networks, propose a temperature correction method based on the computer simulation results. When the VAV terminal control basis of parameter can reflect the human body needs, it can effectively reduce the supply air volume and the fan can be energy-saving25.4%. Aiming at the shortcomings of the air volume control method, propose a total air volume control method which is based on the speed of the terminal fan by using the frequency conversion fan to replace the air valve as the air volume adjusting mechanism. The fan frequency control of the air handling unit is based on the sum of the actual supply air volume of the terminal variable air volume branch. Using Matlab/Simulink software to establish air volume adjusting model of the VAV air-conditioning system. The simulation results show that:Under the total air volume control method which is based on the speed of the terminal fan, the total supply air volume is regulated according to the sum of terminal supply air volume without the effect of the static pressure in the pipeline, it can guarantee the stable operation of the VAV system. The terminal air supply pressure is provide by the respective fan, so that the pressure head of the total fan is small. The system can have good energy-saving performance and provide good comfort to the indoor air-conditioning room.