# Research on Real-Time Control Strategy for HVAC Systems in University Libraries
### Literature Review  
Many meaningful studies have been conducted on the optimized control of HVAC systems, with researchers mainly concentrating on the following aspects: the optimized control of HVAC cold and heat sources, the variable-flow control of HVAC water systems, and the automatic control technology used in HVAC systems. This study will introduce the research results of the algorithm model and other techniques in this field, before introducing the research of the Levenberg-Marquardt algorithm used in this study. As an important part of an HVAC system, air conditioning accounts for more than 50% of the total energy consumption of the entire HVAC system. With the gradual recognition of the importance of energy saving in HVAC systems, researchers have conducted extensive research on the optimization of HVAC cooling and heating source control. [PERSON] [11] analyzed the COP of a single-chiller operation control and a multiple-chiller group control and proposed a control system with the whole chiller system's overall efficiency taken as the optimization control objective. With this approach, the system can adapt to the environment and its own transformation design scheme at any time. [PERSON] et al. [12] established a deterministic solution model for an optimal dynamic load distribution strategy based on the dynamic planning principle for a fixed-unit combination under the changing dynamic load of the system, and proposed an energy consumption coupling optimization strategy for a heat pump district heating (cooling) system to save energy. In recent years, increasing attention has been paid to the energy-saving potential of variable-flow operations in HVAC water systems, which has become a focal point for research. On the basis of the feasibility of variable flow in a central HVAC water system, [PERSON] et al. [13] described the principle of energy saving using HVAC pumps with frequency conversion and frequency conversion control, and combined them in a specific renovation project. The authors found water pump frequency conversion to be a feasible approach with significant energy-saving effects. [PERSON] et al. [14] combined a centralized HVAC cooling water system renovation project based on the characteristics of HVAC load distribution, analyzed the impact of variable flow on the chiller and variable-frequency cooling water pump energy consumption, and calculated the energy-saving rate of different variable-flow control methods. They found that the variable-flow control system has a greater energy-saving effect with a larger impact. With the progress of science and technology, automatic control technology has developed significantly and has begun to be integrated into the study of HVAC systems, with the aim of achieving precise control and automation of the air treatment process and saving energy. HVAC technology that incorporates automatic control has achieved good results so far. [PERSON] et al. [15] followed the principles of energy saving, comfort, economy, and other principles in the design and analysis of the operation of an HVAC system in a large-scale library. The researchers used PID technology to monitor and control HVAC units, fresh air units, and cooling source systems to achieve energy savings. [PERSON] et al. [16] discussed the automatic control involved in the energy-saving operation of variable air volume HVAC systems, and clarified these automatic controls by discussing the control of the fan speed, supply temperature, fresh air volume, and room temperature. In recent years, algorithmic modeling, neural networks, and other techniques have been introduced into HVAC systems. [PERSON] [17] worked on an intelligent HVAC control strategy to provide a comfortable and energy-efficient environment for schools, achieving significant results. [PERSON] [18] provided new theoretical support for the design and application of thermal-storage HVAC systems by intensively investigating the load feedback control of the systems, which improves energy efficiency and comfort.