Exergoeconomic analysis as a tool for supporting the design and operation of multiple chiller systems in air conditioning applications.

Abstract

Multiple-Chillers systems represent viable solutions for medium/large-scale air conditioning applications. In these systems, however, design and energy savings are highly affected by the configuration and operation strategies adopted. For instance, when considering multiple chillers of same size, “symmetric” or “sequential” load sharing strategies are two viable options. Conversely, when considering chillers of different sizes, a wide combination of chillers cooling capacities may be adopted. It is apparent that an integrated analysis of the design and operation of these systems should be carried out in order to achieve profitable energy saving. With this respect, Exergoeconomics, which rests on exergy as a rational basis for cost allocation, could provide a support for energy analysts. In fact, by means of the exergoeconomic cost both design and operative aspects are accounted for during the analysis of any energy conversion system. In this paper, a multiple-chillers system serving a large office located in the Palermo was considered as a case study. In particular, the following options were investigated: (i) multiple air-cooled chillers of same size operated according to a “sequential” and “symmetric” load sharing strategies (ii) multiple air-cooled chillers of different sizes. To this aim, an ad-hoc model was developed in Engineering Equation Solver which accounted for the effect of outdoor conditions and the off-design performances of the chillers. In the first part of this analysis, two load sharing strategies were compared for equally-sized multiple-chillers system. In this case, results allowed to recognize the relative incidence of capital and operating costs on the unit cost of chilled water produced. Also, in order to account for environmental impacts, exergoenvironmental cost profile were drawn for both the investigated strategies. In the last part, different design alternatives were compared for unevenly-sized parallel multiple-chillers systems. Daily and yearly results are duly presented. Exergoeconomic and exergoenvironmental unit costs results allowed to select the best performing alternative among the proposed ones.