## 2 Model and Method
### Operational Strategy
#### 2.5.3. HOS Operational Strategy  
To solve the problem of insufficient utilization of energy in the above operational strategies and to reduce the carbon dioxide emissions of the DES, HOS is proposed to comprehensively consider the structure of the load and the operating efficiency of the equipment. The cooling/electricity and heating/electricity ratio of the gas turbine and load at time \(i\) are as follows:  
\[CER_{gt}=H_{gt,i}\cdot\eta_{ar}/E_{gt,i} \tag{28}\]  
\[CER_{i}=C_{i}/E_{i} \tag{29}\]  
\[HER_{gt}=H_{gt,i}/E_{gt,i} \tag{30}\]  
\[HER_{i}=H_{i}/E_{i} \tag{31}\]  
As shown in Figure 6a, the operational mode of HOS in the summer is as follows:  
Figure 5: Flowchart of FTL operational strategy. (1) \(CER_{gt}>CER_{i}\) and \(C_{i}>V_{gt.H^{*}}\eta_{ar}\)  
Under these circumstances, the cooling and power load demands are greater than the refrigerating output generated by the gas turbine and absorption refrigeration unit. The gas turbine operates at full load (\(x_{i}=1\)) due to the load of the building being greater than the rated capacity of the gas turbine. The deficit cooling and power load are provided by the electric refrigerating unit and the municipal power grid. (2) \(CER_{gt}<CER_{i}\) and \(C_{i}<V_{gt.H^{*}}\eta_{ar}\)  
The cooling load of the building is lower than the rated refrigerating output of the absorption refrigeration unit. At this time, the cooling/electricity ratio of the building is higher than the equipment. The cooling load determines the load rate of the gas turbine, which does not waste energy. Therefore, performing FTL in this hour is the most reasonable solution under these circumstances. (3) \(CER_{gt}>CER_{i}\) and \(E_{i}\cdot\eta_{er}+C_{i}>V_{gt.E}\cdot\eta_{er}+V_{gt.H^{*}}\eta_{ar}\)  
The cooling/electricity ratio of the building is higher than the equipment and the total power of the gas turbine is lower than the building's load demand. The rated capacity of the gas turbine may be greater than the power load demand of the building and the excess power generation can be provided to the electric refrigeration unit. Otherwise, the deficit power and cooling load is provided by the municipal power grid. (4) \(CER_{gt}<CER_{i}\) and \(E_{i}\cdot\eta_{er}+C_{i}<V_{gt.E}\cdot\eta_{er}+V_{gt.H^{*}}\eta_{ar}\)  
The rated capacity of the gas turbine is greater than the cooling load demand of the building. The power load of the building and the power consumption of the electric refrigeration unit can be met by the gas turbine. It was found that when the load rate of the gas turbine is equal to \((E_{i}\cdot\eta_{er}+C_{i})\ E_{gt. }/H_{gt.i}\cdot\eta_{ar}\), the gas turbine can exactly meet the cooling and power load of users. Under this operational mode, the efficiency of natural gas is maximum. Figure 6: Flowchart of HOS operational strategy in the summer (**a**) and winter (**b**). As shown in Figure 6b, the operational mode of HOS in the winter is as follows:  
1. \(HER_{gt}>HER_{i}\) and \(H_{i}>V_{gt.H}\) The operational model is similar to that in summer under these circumstances. The gas turbine operates at full load (\(x_{i}=1\)). The difference is that the deficit heating and power load are provided by the gas-fired boiler and the municipal power grid. 2. \(HER_{gt}>HER_{i}\) and \(H_{i}<V_{gt.H}\) The heating/electricity ratio of the building at time \(i\) is less than the gas turbine, and the heating load of the building is lower than the rated heating capacity of the gas turbine. The heating load determines the load rate of the gas turbine, which does not waste energy. Therefore, performing FTL in this hour is the most reasonable solution under these circumstances. 3. \(HER_{gt}<HER_{i}\) The heating/electricity ratio of the building at time \(i\) is larger than the gas turbine. The electric load determines the load rate of the gas turbine, which does not waste energy. When the heat load demand of the building is less than the rated heating capacity of the gas turbine, performing FEL in this hour is the most reasonable solution.