Cascade utilization of low-grade thermal energy by coupled elastocaloric power and cooling cycle.

• A new elastocaloric cooling system is proposed to harvest low-grade heat. • Transition temperature gradient facilitates cascade utilization of low-grade heat. • Transition temperature gradient improves system COP by a factor of more than 5. • Optimizing transition temperature profile can further boost performance for 20%. • Solar thermal air-conditioner and refrigerator are two potential applications. Unlike the conventional elastocaloric cooling system that depends on electricity, the coupled elastocaloric power and cooling cycle proposed in this study exploits low-grade thermal energy in a cascade manner, which opens a new paradigm for the caloric cooling community. Cascade utilization of heat relies on a gradient of transition temperature inside the shape memory alloy actuator that best matches the temperature profile of the material during operation. A transient numerical model is developed to simulate the performance of this new system, and the model is experimentally validated. The transition temperature gradient should exceed 60 K for optimum utilization of input heat. At the same gradient, the distribution of transition temperature can be optimized, where at least 10% improvement over linear profile can be expected in terms of efficiency and cooling power density. Based on the superior performance, this technology could be powered by solar thermal collectors working at 110 °C and could be applied to residential air-conditioners and off-grid refrigerators. The novel system proposed in this study not only complements the existing library of heat-activated cooling technologies, but also provides a new pathway for the expansion of caloric cooling at large. [ABSTRACT FROM AUTHOR]