# Optimal Configuration of Integrated Energy System Based on Energy-Conversion Interface
## 4 Case Analysis
### Economic Analysis
The overall change level of the thermal load in one year is opposite to the change trend of the electric load and cold load in the system. In a month when the heat load is high, the cold load and the electric load are relatively low. The residual smoke generated by the gas turbine is fully used by the waste-heat boiler. The residual smoke can be regarded as zero-cost energy. The heat supply is preferentially supplied by the waste-heat boiler. When the waste-heat boiler cannot meet the heat-load demand, the higher-efficiency electric-heat pump is used to improve the thermal efficiency of the system. It can be seen from the heat-conservation figure of a typical season that heat energy is mainly supplied by the waste-heat boiler and the electric-heat pump. Heat energy is reserved when the heat of the waste-heat boiler is abundant, and the electric-heat pump is mainly applied during the lower-price period. Figure 15 shows the output of the device with daily cooling energy conservation, and gives the cooling energy conservation graph for typical days of three seasons. The cold-load supply consists  
Figure 14: Daily running of heat-conserving device: (**a**) days of running heat-conservation device output; (**b**) January; (**c**) July; (**d**) October. of an electric chiller and an absorption chiller. In addition to the cold-load supply, there is also cold-energy storage. As concluded from the figure above, the whole system satisfies the conservation of cold energy. The change law of the cold load is positively correlated with the electric load. Therefore, residual smoke generated by the gas turbine can be fully utilized by the absorption chiller during the high electric-load period to improve the cooling efficiency of the system. When the absorption chiller cannot meet refrigeration demand, the electric chiller is applied. This can be obtained from the cold-conservation graph of the typical season. The system-cooling load of the system is mainly supplied by the absorption chiller. When the working efficiency of the absorption chiller is relatively high, the cold-energy storage device stores cold energy, and the cold energy is released when absorption refrigeration fails to meet cold-load demand. The electric refrigerator has high energy-conversion efficiency, but because of its high energy cost, as well as its restricted outputs, this only occurs during the period of low electricity price so as to meet the energy conservation of the system. Energy-Use Efficiency Analysis  
From Table 1 we can see when the comprehensive energy-utilization efficiency of the system is optimized. Overall energy utilization has efficiency over 1.0 due to the high conversion efficiency of electric refrigeration and the electric-heat pump. As per the results of device configuration, only the electric refrigerator and the electric-heat pump with a high energy-utilization rate could be installed. The maximum output level of each device in different months of the year is shown in Figure 16.  
Figure 15: Daily output of cold-conserved device: (**a**) days of running cold-conservation device output; (**b**) January; (**c**) July; (**d**) October. As can be seen from Figure 16, the output level of the device has a large-scale fluctuation range. The load rate of several months is below 0.2, so the load rate of the device is low. By adjusting the actual working quantity of the unit, the corrected output level of the device is obviously improved. The reasonable option among the devices could also relatively improve the service life of the devices. The energy-flow figure obtained with the goal of energy efficiency is relatively simple. As shown in Figure 17, daily-operation power distribution notes that electricity purchased from the grid flows to the electric load, electric-heat pump, and electric refrigerator. It can be seen from the figure that the purchase of electricity is mainly for electric-load supply.