# Low-Carbon Operation Strategy of Park-Level Integrated Energy System with Firefly Algorithm
## 5 Case Study  
Taking an industrial park as an example, the actual thermal load of the region is 4.8 MW and the actual cooling load is 4 MW. The power load is 4 MW, with a typical load curve shown in Figure 2. The weighting coefficients \(\alpha\), \(\beta\), and \(\gamma\) in objective function are 0.3, 0.3, 0.4. The integrated energy system in the region operates in a grid-connected mode with self-consumption. The installed capacity of photovoltaics is 1.2 MW, and a ground-source heat pump system with a design cooling load of 350 kW is used. Moreover, the efficiency parameters of electrical efficiency, thermal efficiency, and the natural gas utilization efficiency are described in Table 1. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameters** & \(\eta_{E}\) & \(\eta_{H}\) & \(\eta_{GB}\) \\ \hline Value & 40\% & 90\% & 98\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Efficiency parameters. Figure 3 illustrates the cooling demand during the daytime and how it is satisfied by various equipment. During the night time, ice storager cooling generates more cooling for daytime. It can be observed that during the summer, the main cooling supply relies on the coupling of screw compressors and gas engine-driven bromine chillers. Ice storage tanks are used for overnight cooling storage, which significantly reduces the peak load of the screw chiller units. Figure 4 illustrates the typical daily power output of different equipment during the summer, in which the equipment power consumption is negative. The main power consumption components of the multi-energy coupling system include nighttime cooling storage power consumption, screw chiller power consumption during the day, ground-source heat pump power consumption, and bromine chiller power consumption. The ice cooling storage generates more cooling for daytime during the night time. The power sources mainly consist of grid electricity, internal combustion engine generation, and photovoltaic (PV) generation, with a higher reliance on purchasing electricity from the grid. Figure 3: Cooling output of different equipment. Figure 2: Load demands. Figure 5 shows the typical daily energy costs during the summer, with natural gas prices being relatively high during the project design phase. To balance the project's goals of being both clean and economical, a smaller internal combustion engine with a capacity of only 1250 kW power output and 1350 kW heating output was chosen, along with 1200 kW of photovoltaic power. According to the output of Figure 4, the hourly energy cost is calculated. It can be seen that the highest hourly cost in summer occurs from 19:00 to 20:00, mainly due to the large demand for cooling load and electrical load at this time, and this period is also the peak electricity price. Figure 6 displays the typical daily heating output of different equipment during the winter. The ground-source heat pump operates 24 h a day as a renewable energy supply. Due to the small capacity design of internal combustion engines, the heating output of waste heat boilers coupled with internal combustion engines is not high, and the main heat load is provided by gas boilers. Figure 4: Power output of different equipment. Figure 5: Cost of the integrated energy system. Figure 7 illustrates the typical daily power output of different equipment during the winter. The power consumption of the equipment is negative, and the ground-source heat pump consumes electrical energy 24 h a day. The power source mainly comes from the municipal grid power, internal combustion engine power generation, and photovoltaic power generation. The typical daily energy cost in winter is shown in Figure 8. Due to the high gas consumption of gas-fired boilers for heating in winter, the gas cost is high. When there is a feed-in tariff, the amount of electricity purchased from the municipal grid decreases significantly, while the gas consumption cost increases significantly, with some online revenue.