Multi-objective evaluation and operation strategy analysis for combined cooling, heating and power (CCHP) systems

Following hybrid electric-thermal load operation strategy was proposed recently based on following thermal load operation strategy and following electric load operation strategy, and widely used in combined cooling, heating, and power (CCHP) system. However, whether following hybrid electric-thermal load operation strategy always performs the best is still debatable. This study investigates the application range of following hybrid electric -thermal load operation strategy and the essential difference among these three operation strategies. Both theoretical analysis and case study show that when large amount of heat is required, following electric load operation strategy is always better than following thermal load operation strategy from energy saving, economic and environmental aspects. When electricity demand is high, following thermal load operation strategy can definitely minimize the energy loss of CCHP system, which yields a better energy saving performance. In such case, however, we find that following thermal load operation strategy does not always have a better economic and environmental performance compared to following electric load operation strategy. To address this issue, we define the gas-to-electricity price ratio and the gas-to-electricity environmental impact ratio, which dominate the performance of CCHP system under following hybrid electric-thermal load operation strategy. Our analysis shows that following hybrid electric-thermal load operation strategy can give the highest evaluation index (least energy consumption, least cost and least carbon dioxide emission) among these three strategies, only when both these two ratios are greater than the efficiency of the power generation unit. These are validated through the comparison of the performance for a typical CCHP system serving one hotel building under these three operation strategies. The integrated performance (IP) evaluation index for following thermal load, following electric load and following hybrid electric-thermal load operation strategies are 0.1877, 0.2369 and 0.2232, respectively. This work provides the important insight into the energy saving, economic and environmental performance under different operation strategies in CCHP system.

Automated summary

This study investigates the application range and essential difference of the hybrid electric-thermal load operation strategy in CCHP systems. The results show that the electric load operation strategy is better than the thermal load operation strategy in terms of energy saving, economy, and environment when a large amount of heat is required. However, when electricity demand is high, the thermal load operation strategy can minimize energy loss. To achieve the best performance, the gas-to-electricity price ratio and the gas-to-electricity environmental impact ratio must exceed the efficiency of the power generation unit.