Research On Optimal Control Simulation Of Fresh Air System In VAV Air-conditioning System

Along with society’s development and living standard enhancement, people take more and more attention to the indoor environment where they work and life. Their request to air-conditioning system also transformed from comfort to health. Meanwhile, because of the worldwide energy crisis, as a major energy consumer,air-conditioning system’s energy-saving reform is imperative, which sets higher request to the control of the fresh air system.Under traditional optimized strategy of fresh air flow rate, air-conditioning system operates with the minimum fresh air flow rate in hot summer and cold winter, because handing fresh air always consume more energy than handing return air this moment, but in cool spring and autumn, air-conditioning system drags massive fresh air as a natural cold source to cool the room, which is usual achieved by temperature control or enthalpy value control.In fact, the change of fresh air flow rate not only influences the energy consumption of the air-side, but also affects that of the water-side, because fresh air’s cooling load is a part of chiller load. An optimized fresh air flow rate should make the energy consumption it influences lowest in premise that the comfort and health of indoor environment are satisfied. Based on this ideology, this article presents an optimized control strategy on the energy consumption objective function for fresh air flow rate.Another content of optimal control for fresh air system is the optimization of fresh air static pressure, with the purpose of reducing the energy consumption of the fresh air fan. An air-conditioning system that a fresh air system undertakes fresh air requirement of many regions, always adjusts fresh air flow rate of each region through regulating the speed of fan and the opening of damper, while the static pressure of one point in air duct keeps invariable generally. Actually, this method is not the best method to save energy, the optimized control strategy of fresh air static pressure changes static pressure’s setting value real-time, which makes various regions’dampers to arrive at the biggest opening to reduce the loop loss of dampers.In order to examine and compare the energy-saving effect of three kinds of optimized control strategies for fresh air flow rate, this article takes TRNSYS as a platform, takes an office building in Hong Kong as the simulation object, uses the Fortran language to compile temperature controller’s model, enthalpy value controller’s model and optimizing controller of the objective function’s model, then carries on the simulation experiment, and analyzes the results.Finally, combined the optimal control theory and the results of simulation experiment, this article compiles an optimal control software which could apply in a fresh sir system of the actual building, what’s more, it is realized and confirmed off-line.