Air-cooled condensers optimization for novel Ultra-Low Charge ammonia chillers to achieve competitive packaged units

Abstract

Novel Ultra-Low Charge (ULC) ammonia chillers are being investigated as a highly efficient and sustainable solution in the field of refrigeration with natural fluids. These chillers were conceived to minimize the refrigerant charge using air-cooled condensers, semi-hermetic compressors, and direct expansion evaporators, becoming reliable solutions for commercial and industrial applications. However, the economic feasibility of ULC packaged units is still questioned, in the long term, compared to traditional ammonia chillers. Accordingly, this paper focuses on the air-cooled condensers optimization due to both, its investment cost relevancy over the packaged unit and its direct influence on the system performance. For this purpose, the experimental performance data of a commercial ULC ammonia chiller of 230 kW have been used to validate a numerical model which predicts the Seasonal Performance Energy Ratio (SEPR) and the Net Present Value (NPV) of the unit. Considering the commercial unit as the baseline case, the number of parallel condensers together with the condensing set point have been optimised to maximise the NPV along the lifetime expectancy of the unit. The results reported an optimal condensing temperature of 12 K above the outdoor temperature for the operating conditions defined in the Eco-Design Directive 2015/1095 and an optimal number of single parallel condensers which ranges from four to six depending on the lifetime considered and the interest rate. Likewise, the NPV varies from 4 000 €, at the fifth year of operation, up to a range between 15 000 € and 35 000 € at the twentieth year of operation.