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This paper reports a review on ammonia heat transfer in plate heat exchangers, from both theoretical and experimental points of view. It also addresses the current ecological aspect implied by refrigerants, by choosing ammonia, which is a natural refrigerant, known for its zero ozone depleting potential and for its low global warming effect. The theoretical study presents the modeling of the convective ammonia heat transfer coefficient in narrow spaces by several correlations, currently available in the open literature and valid for the case under consideration. The experimental study was carried out on specially designed set-ups that allowed both measuring and acquisition of data. The experimental values were further used in order to validate the correlations, under specific geometrical configuration of the plate heat exchanger used and specific operating conditions. The paper concluded all correlations under study describe, more or less accurately, the process of convective evaporation of ammonia in plate heat exchangers and determined a hierarchy among them, based on deviation shown with respect to the experimental values. [ABSTRACT FROM AUTHOR]

This paper reports on optimized ways of chilled water preparation for indoor air conditioning. The first improvement taken into consideration by the authors, with respect to the classical way of preparing it (using compression refrigeration systems), is represented by absorption refrigeration systems. This is a better option from both energetic and ecological points of view. The centralized cooling capacity of the air conditioning system is 17 kW. The chilled water distributed from a central unit to the individual consumers (of fan coil type) is prepared by either electrical or thermal energy input, namely:- One stage vapor compression ammonia system; - One stage R404A vapor compression system; - One stage lithium bromide-water solution absorption system. It is driven by hot water provided by renewable solar energy. The paper concludes with a comparative analysis of the above mentioned systems, in terms of coefficient of performance (COP), coefficient TEWI (Total Equivalent Warming Impact) and life cycle cost (LCC). [ABSTRACT FROM AUTHOR]