Performance assessment of a double-lift absorption prototype for low temperature refrigeration driven by low-grade heat

This work investigates the use of a water-ammonia double-lift absorption cycle for low temperature refrigeration driven by low-grade heat, as waste-heat or solar energy. Among the various double-lift cycles, the investigation focuses on the self-adapting two-pump series cycle, using water-ammonia as working pair. At first, by means of a numerical investigation, it is verified that an air cooled unit can operate with driving temperature of 90 C, air temperature up to 32 degrees C and brine temperature down to 15 degrees C. Then, it is discussed how to modify an existing prototype to achieve the mentioned working conditions. The influence of the two restrictors of the refrigerant on the cycle behaviour is discussed in a qualitative manner, pointing out that the restrictor after the condenser sets the intermediate and low pressures and, consequently, the maximum allowed thermal lift. Finally, the prototype performances are experimentally assessed, confirming that the influence of the restrictor between high and intermediate pressure and pointing out that the use of a fixed restrictor prevents the full exploitation of the potential of the cycle. As a consequence, the use of a variable restrictor could represent an option for optimizing the appliance COP in a wide range of thermal lifts. (C) 2017 Elsevier Ltd. All rights reserved.