Optimum Operation of a Heat Source System considering Bidirectional Heat Interchange among Multiple Buildings

This study aims to develop an operational planning system based on mixed-integer linear programming (MILP) to optimize the energy consumption of heating and cooling plants by considering bidirectional heat interchange among multiple buildings. The system was implemented in a facility comprising four buildings. The heating and cooling plants are distributed across all buildings and each building is connected by bidirectional heat interchange pipes. The operation planning system formulates a 24-hour operation plan that regulates the number of operating units, including chillers, heat pumps, and water pumps, and their outputs every 30 minutes. In a demonstration experiment, the MILP-based operation was compared with the rule-based operation to evaluate its energy efficiency under actual operating conditions in buildings during the cooling period. In the rule-based operation, each building managed its chiller based on its respective cooling demands. Similarly, in the MILP-based operation, the chillers were operated in each building when the cooling load was high. Regarding the system coefficient of performance (COP), a slight difference was observed during the corresponding period. However, when the cooling demand was low to medium, the operation of the chiller was consolidated, and chilled water was supplied to other buildings to maintain the high-efficiency operating points of the chiller. The system COP of the MILP-based operation was higher than that of the rule-based operation when the outdoor temperature was below 28.8 °C. In the intermediate cooling season, the MILP-based operation improved the system COP by 21.6% compared with the rule-based operation. The MILP-based operation that considers bidirectional heat interchange was particularly effective in the intermediate cooling season.