## 4 Results and Discussion
### Comparison of District Sharing Strategies on Carbon Emissions  
In addition to meeting more energy demand, environmental benefits can also be obtained by district sharing systems. Therefore, CO\({}_{2}\) emissions were also calculated for comparison. We considered that, for the three districts, part of the energy demand not satisfied by the GSHP system was provided by electricity for heating and air conditioners for cooling. The equivalent emission factors for various heating and cooling systems can be seen in Table 2. Both scenarios (boreholes under buildings and borehole around buildings) were analyzed. CO\({}_{2}\) emissions were calculated for \"no GSHP\", \"individual GSHP system\", \"individual system with borehole sharing\" and \"central district system\" for all three districts, respectively. Figure 7 shows the CO\({}_{2}\) emissions of the three target districts with different heating and cooling systems under Scenario 1 (boreholes under buildings). For District 1, introducing GSHP systems for individual buildings could greatly reduce carbon emissions from around 460,000 kg to 229,000 kg. With district GSHP systems, the emissions can be further reduced to approximately 150,000 kg. Although the central district system (Strategy 2, Figure 1c) showed a better C/D ratio than borehole sharing (Strategy 1, Figure 1b), CO\({}_{2}\) emissions are the same because both of these ratios are higher than 100%, which means that both district systems can fully satisfy the energy demand. Similar to District 1, individual GSHP systems can reduce CO\({}_{2}\) emissions from around 224,000 kg (no GSHP system) to 135,000 kg in for District 2. Sharing can fully satisfy the energy demands of the whole district, and district systems can further cut the emissions to 91,000 kg. As for District 3, mainly office buildings are present, and this type generally has a high cooling demand; thus, the district sharing system benefits carbon emissions saving, but the influence is quite slight. Strategy 1 and Strategy 2 reduced emissions from 431,000 kg to 399,000 kg and 403,000 kg, respectively. Figure 8 shows the CO\({}_{2}\) emissions of the three target districts with different heating and cooling systems under Scenario 2 (boreholes around buildings). For District 1, individual GSHP systems can significantly reduce carbon emissions from around 460,000 kg (electricity heating and air conditioner cooling) to 239,000 kg. The district sharing systems can further cut the emissions to approximately 150,000 kg. Similar to Scenario 1, although Strategy 2 showed a better C/D ratio Sharing Strategy 1, the influences on reducing CO\({}_{2}\) emissions are the same, because both of these ratios are higher than  
Figure 7: CO\({}_{2}\) emissions of district sharing systems (Scenario 1). 100%, and the maximum energy supply can only be 100%. For District 2, individual GSHP systems can reduce CO\({}_{2}\) emissions from around 224,000 kg with no GSHP system to 120,000 kg. Both sharing strategies can fully satisfy energy demand and can further reduce the emissions to approximately 91,000 kg. As for District 3, the impacts of district sharing on carbon emissions saving are not as significant as the other two districts. Strategy 1 and Strategy 2 reduced emissions from 508,000 kg to 389,000 kg and 394,000 kg, respectively. According to the results in Figures 7 and 8, for District 1 and District 2, both sharing strategies can cut the carbon emissions by around 30-35% compared to individual GSHP systems, and the two strategies lead to the same emissions values for each district. The reason for this is that for both of the scenarios, the C/D ratios are higher than 100%, which shows the difference in supply capacity level, but in practice, the maximum energy demand can only be 100%. This means that Strategy 1 and Strategy 2 can both fully satisfy the energy demands for District 1 and District 2.