تجزیه و تحلیل عملکرد از سیستم پمپ حرارتی دو مرحله ای ترکیبی بر اساس معیار بهینه سازی حرارتی اقتصادی

A thermoeconomic performance analysis based on a new kind of optimization criterion has been performed for a two stage endoreversible combined heat pump cycle model. The optimal performances and design parameters that maximize the objective function (heating load per unit total cost) are investigated. The optimal temperatures of the working fluids, the optimum performance coefficient, the optimum specific heating load and the optimal distribution of the heat exchanger areas are determined in terms of technical and economical parameters. The effects of the economical parameter on the global and optimal performances have been discussed.

High temperature heat pumps play important roles in improving the efficiencies of industrial processes [1]. The temperature range they involve may be too large for a single stage for the vapor compression heat pump to be practical. One way of dealing with such situations is to perform the heating process in stages, that is, to have two stage or multi-stage combined heat pump systems that operate in series. The performance of a single stage, vapor compression and absorption heat pump systems using the technique of finite time thermodynamic analysis has been investigated quite extensively in recent years [2], [3], [4], [5], [6], [7], [8], [9] and [10]. Relatively few efforts on the performance optimization of two stage combined heat pump systems have been made [11] and [12]. In the above referenced works, the objective functions chosen for optimization are usually coefficient of performance, heating load, total heat transfer area and specific heating load (heating load per unit total heat transfer area). In these studies, one of the performance characteristics is chosen as an objective function, while taking the rest as constraints. Some of these optimization criteria are related to investment costs, and some of them are related to energy consumption costs. For a more realistic optimization, the objective function must include both the investment and energy consumption costs. In this context, Sahin and Kodal [13] have very recently introduced a new performance analysis based on an objective function defined as the heating load per unit total cost (total of investment and energy consumption costs). Using this new criterion, they performed finite time thermoeconomic performance analyses for endoreversible [13] and irreversible [14] single stage heat pumps to find the optimal design parameters. The main purpose of this paper is to extend the work performed by Sahin and Kodal [13] for a single stage heat pump to a two stage endoreversible combined heat pump. The design parameters that maximize the thermoeconomic objective function and the optimal performance conditions are investigated.

A thermoeconomic performance analysis has been performed out to determine the optimal operation and design parameters based on a new kind of thermoeconomic criterion for the two stage endoreversible combined heat pump. We have derived analytically the optimal temperatures of the working fluids, the optimum performance coefficient, the optimum specific heating load and the optimal distribution of the heat exchanger areas based on the considered thermoeconomic objective function. It is demonstrated that the effects of the investment and energy consumption costs on the general and the optimal performances can be characterized by an economical parameter, k. The obtained results showed that the economical parameter has a great influence on the optimal operating and design parameters. Since the value of k depends on the economic conditions of a country, the optimal design of the heat pumps may differ for different countries. In this study, the reported optimization results represent the economic design conditions and may provide a general theoretical tool for optimal design of two stage combined heat pump systems.