# Integrated Energy System Optimization Based on Standardized Matrix Modeling Method
## 3 Integrated Energy System Optimization
### Structural Optimization of Integrated Energy System  
The purpose of structural optimization of the integrated energy system is to decide on the system components and their interconnections (i.e., energy flow structure and equipment type). As a complex energy utilization system, not only should the connection between the physical boundary of the integrated energy system and the environment, policies, and economic boundaries be considered, but also the interaction and coupling of energy flows, such as cooling, heat, and electricity, should be considered in the integrated energy system. At the same time, the interdependence among various links of production capacity, energy conversion, energy storage, and energy utilization, should be considered in the integrated energy system. (1) Optimization target  
Three categories of indicators (i.e., economics, energy saving, and environmental protection) can be selected as optimization target. 1) Economics  
The total amount of annual heat, cooling, and electricity supply is selected as an economic evaluation index. \[E_{\text{IES}}^{\text{h}}+E_{\text{IES}}^{\text{c}}+E_{\text{IES}}^{\text{e}} \tag{11}\]  
2) Energy saving  
The total amount of annual nonrenewable energy consumption is selected as an energy-saving evaluation index. \[Q_{\text{IES}}=(F_{\text{AB}}+F_{\text{CHP}}-B_{\text{f}})\theta_{\text{f}}+(E _{\text{c}}+E_{\text{h}}+E_{\text{IES}}^{\text{e}}-\eta_{\text{W}}F_{\text{CHP }}-S_{\text{e}}-W_{\text{e}})\theta_{\text{e}} \tag{12}\]  
where \(\theta_{\text{f}}\) is the converted standard coal coefficient of fossil fuel, which is 1 for natural gas. \(\theta_{\text{e}}\) is the converted standard coal coefficient of power supply by State Grid, which is 1.95 when thermal power accounts for 75% of the total power production. 3) Environmental protection  
Annual CO2 emissions of the integrated energy system include CO2 emissions from natural gas and CO2 emissions from system outsourcing electricity. The total amount of annual CO2 emissions is selected as an environmental protection evaluation index. \[E_{\text{IES}}^{\text{CO2}}=[(F_{\text{AB}}+F_{\text{CHP}}-B_{\text{f}})\theta _{\text{f}}+(E_{\text{c}}+E_{\text{h}}+E_{\text{IES}}^{\text{e}}-\eta_{\text{ W}}F_{\text{CHP}}-S_{\text{e}}-W_{\text{e}})\theta_{\text{e}}]\varphi \tag{13}\]  
where \(\varphi\) is the carbon emission factor of natural gas. Therefore, considering the economic, energy-saving, and environmental indicators, the system's annual comprehensive energy efficiency is used as the optimization target:  
\[\eta=\frac{E_{\text{IES}}^{\text{h}}+E_{\text{IES}}^{\text{c}}+E_{\text{IES}}^ {\text{e}}}{Q_{\text{IES}}} \tag{14}\]  
\(E_{\text{IES}}^{\text{c}}\) is the total amount of cooling delivered to the end user through cooling network and \(E_{\text{IES}}^{\text{c}}\) can be calculated by the integrated energy system standardized matrix model, as follows. \[E_{\text{IES}}^{\text{c}}=[\eta_{\text{C}}][E_{\text{c}}]+[\eta_{\text{R}}][ H_{h}] \tag{15}\]\(E_{\text{IES}}^{\text{h}}\) is the total amount of heat delivered to end user through heat network and \(E_{\text{IES}}^{\text{h}}\) can be calculated by the integrated energy system standardized matrix model as follows. \[E_{\text{IES}}^{\text{h}}=-[H_{\text{h}}]+[\eta_{\text{AB}}][F_{\text{AB}}]+[ \eta_{\text{Q}}][F_{\text{CHP}}]+[\eta_{\text{H}}][E_{\text{h}}]+[S_{\text{h}}] \tag{16}\]  
\(E_{\text{IES}}^{\text{e}}\) is the total amount of electricity delivered to end user through power network and \(E_{\text{IES}}^{\text{e}}\) can be calculated by the integrated energy system standardized matrix model as follows. \[E_{\text{IES}}^{\text{e}}=[E_{\text{i}}]+[S_{\text{e}}]+[W_{\text{e}}]+[\eta _{\text{W}}][F_{\text{CHP}}]-[E_{\text{h}}]-[E_{\text{c}}] \tag{17}\]  
The ratio of the total amount of cooling provided by the electrical refrigeration equipment to the total cooling demand by end users is as follows.