Influence of prime mover size and operational strategy on the performance of combined cooling, heating, and power systems under different cost structures

Abstract

Combined cooling, heating, and power (CCHP) systems use waste heat from on-site electricity generation to meet the thermal demand of the facility, which includes cooling, heating, and hot water. When compared with traditional set-ups of grid-generated electricity and an on-site boiler for heat, CCHP systems are capable of improving fuel utilization and lowering emissions. One of the critical components affecting the performance of CCHP systems is the prime mover. The objective of this investigation is to study the effect of the prime mover size and operational strategy on the energy, economical, and environmental performance of CCHP systems under different pricing structures. Three different sizes for the prime mover, a natural gas engine, are simulated under different operational strategies such as: following the electric demand of the facility, following the thermal demand of the facility, and following a constant load. The results obtained for the CCHP system will be compared with a reference building operating under conventional technologies to determine the advantages or disadvantages of the CCHP system's operation. In addition, a simple optimization of the system's operation determines the best engine load for each hour during the simulation that minimizes cost, primary energy consumption (PEC), or carbon dioxide emissions (CDEs). For this study, three locations in different climate zones that have different electricity rate structures were chosen: one with a constant flat rate; one that uses seasonal rates; and one that incorporates block charges. Historical monthly natural gas rates were also used. Since most authors perform cost analyses using a fixed constant rate for both electricity and natural gas, a comparison is made between the cost results from using the actual cost data to those that use an average fixed rate. In general, among the three engine sizes that were simulated, the smallest engine yielded the lowest costs and lowest PEC; but, no such trend was found with regard to the CDE. The results also showed that the performance of the evaluated CCHP system can be improved by optimizing the system based on cost or primary energy.