# Research on Real-Time Control Strategy for HVAC Systems in University Libraries
## 2 Materials and Methods
### Energy-Saving Strategies
#### 2.1.2 Optimization of Chilled Water Supply Temperature Setpoints Based on Climate Change  
The chilled water supply temperature is optimized according to the indoor and outdoor meteorological parameters and system operation data (it is necessary to set the chilled water supply temperature of the unit remotely and automatically through the communication card) to improve the system operation efficiency and minimize the total energy consumption of the chiller unit and primary chilled water pump.  
When the HVAC cold load is unchanged, as the chilled water outlet water temperature increases, the power consumption of the chiller unit decreases, and the COP (energy efficiency ratio) of the chiller unit rises by 2-3% for every 1 \({}^{\circ}\)C increase in the chilled water outlet temperature. Generally, the optimal chilled water outlet temperature is the chiller-chilled water outlet temperature set value. However, as the HVAC load continues to change, the optimal chilled water outlet water temperature also changes.  
Figure 2: Client HVAC structure diagram.  
In actual operation, the outdoor temperature is used as the basis for setting the chiller-chilled water outlet temperature. When the outdoor temperature rises, the cold load of the system is larger, and dehumidification is also relatively larger; the chilled water outlet temperature is set at a lower value, both to meet the requirements of dehumidification and to meet the system cooling requirements. When the outdoor temperature is low, the cold load of the system is small, the amount of dehumidification is also relatively small, and the chilled water temperature can be set at a higher value. To meet the requirements of the system, dehumidification can also meet the requirements of the cooling system. A higher chilled water temperature can satisfy the system cooling requirements under the condition of consuming less power by the compressor to achieve energy savings. The relationship between the optimal chilled water discharge temperature and outdoor temperature can be adjusted according to the actual operating conditions of the water system.  
Figure 4: Basic steps of the strategy in Section 2.1.1.  
Figure 3: Refrigeration unit end HVAC structure diagram.  
In actual applications, the optimized chilled water supply temperature is corrected according to the system operation data (mainframe load rate, temperature difference between supply and return water, etc.). In this study, when the load rate of the host was low and the temperature difference between the supply and return water was small, the optimized chilled water supply temperature was increased by the corresponding algorithm; when the load rate of the host was high and the temperature difference between the supply and return water was large, the optimized chilled water supply temperature was reduced by the corresponding algorithm. The energy consumption of the system can be reduced by correcting the optimized chilled water supply temperature to ensure the cooling capacity of the system. Figure 5 shows a basic step diagram of the proposed strategy.