Abstract
With the change of the distributed Combined cooling, heat, and power (CCHP) system operation environment, such as the operation under the power market, CCHP needs to adopt the operation strategy based on cost minimization instead of the traditional following thermal load strategy (FTL). However, the current CCHP system simulation adopts FTL or FEL or a combination of the two; whether these strategies have the least cost has not been confirmed. In this paper, all kinds of operation strategies of the CCHP with two cooling methods are investigated according to the KKT conditions (Karush–Kuhn–Tucker conditions) of the optimal operation model. Among all the feasible operation strategies, most of them do not meet the KKT condition, and only 43 strategies may be the optimal ones that constitute candidate set. The conditions of the optimal operation strategy in the candidate set are obtained, and it is easy to calculate, so the optimal operation strategy can be easily selected from the candidate set. Some previously unnoticed strategies, for example, TEWM, PE-FPG, FTL-R, and FEL-L, may become optimal. A rule-based CCHP simulation method is established that selects the strategy with minimal cost as the optimal strategy from the candidate strategy set. The presented method has small time consumption and can simulate the optimal operation. The case study verified the characteristics of the proposed simulation method.
Highlights
With the change of the distributed Combined cooling, heat, and power (CCHP) system operation environment, such as the operation under the power market, CCHP needs to adopt the operation strategy based on cost minimization instead of the traditional following thermal load strategy (FTL)
Comparison of exhaust-gas-and-hot-water-driven absorption chiller (AC) and another three cooling modes, including AC combined with electric chiller (EC), AC combined with gas-fired absorption chiller (GFC), and AC combined with ground source heat pump (GSHP) based on the simulation model, is made in reference [10]. e results show that the CCHP system with GSHP under following electric load (FEL) strategy has the best comprehensive performance
When the cold demand is met by electric chiller or absorption chiller alone, traditional FTL-L and FEL-R may be the optimal strategies in some cases, but there are other strategies that may be the optimal strategies, such as FTL-R and FEL-L
Summary
A schematic of the CCHP system is shown in Figure 1. ere are three energy buses in the system, namely, heat bus, cold bus, and power bus. Since in some operation strategies, heat is abandoned, the heat for equation (3) is not balanced. Equation (5) is the relationship between PGU’s generation and fuel consumption; equation (6) is the relationship between waste heat recovery and PGU’s generation; equation (7) defines the PGU’s output ratio; equation (8) is the PGU’s efficiency function which is the quadratic function of PGU’s output ratio. By substituting equation (5) into equation (6), the relationship between the waste heat recovered and power generation can be expressed as equation (17) according to equations (5)–(8), and the Q-E curve in Figure 2 is its geometric representation. Equation (9) is the relationship between boiler heat production and its fuel consumption. Because purchasing and selling electricity are not implemented simultaneously, it can be decomposed into two nonlinear programming problems that are called purchasing electricity operation model when x 1 and selling electricity operation model when x 0, respectively
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