A systematic method (ECAEL) is proposed for defining additional allocation equations and calculating the exergy cost of flows in thermal system. This method is based on the concept of the energy level, in which the continuous cost change within each component is considered. Thermoeconomic analysis using this method is carried out on a combined cooling, heating and power (CCHP) system, which consists of a gas turbine (TUR), an absorption chiller (ABC) and a heating water heat exchanger (HWHE). The thermoeconomic model for this system is defined to evaluate the productive relationships among the different components. The costs of all flows are calculated by solving the exergy consumption and allocation equations with design conditions. Moreover, a comparative analysis between proposed exergy cost allocation method and the conventional method is presented. As a result, the proposed method not only provides an accurate cost allocation output but also presents the dynamic cost of the flows within each component. Finally, the unit exergy cost is converted into the unit energy cost to evaluate the final products. According to this method, the unit energy costs of electricity ranks highest, followed by those of chilled water and heating water. The proposed method provides an option to complete the thermoeconomic analysis of multi-product systems.
This work proposes a new cost allocation method (ECAEL) based on the concept of energy level to define the allocation equations for components of multi-product systems. The auxiliary allocation equations are obtained by the thermoeconomic modeling, along with energy quality variation of flows. Moreover, this method divides the energy utilization process of each component into multiple differential sections, and the exergy cost of each flow is determined by the continuous calculation.
It is applied to determine the costs of flows, using an example of a combined cooling, heating and power (CCHP) system. The focus has been put on analyzing the costs of products for this system. Furthermore, a comprehensive comparison with conventional cost allocation methods is presented to show the advantages of the ECAEL method.
Considering the energy quality change of the flue gas in the CCHP system, the input exergy costs are reduced from 1.92 to 0.76 as the flue gas flows in sequence through the TUR, the ABC and the HWHE based on the ECAEL method. This result agrees with the economic principle, i.e., high price for high quality. In addition, to satisfy the evaluation criteria of the market (the amount of energy) and avoid the issue of excessive cooling energy costs, the unit exergy cost is converted into the unit energy cost to evaluate the value of products. The unit energy cost of electric power, chilled water and heating water are 2.05, 0.60 and 0.22 when using the ECAEL method, respectively.
This study provides a new cost allocation method to evaluate the thermoeconomic performance of CCHP systems.
