Experimental investigation and annual performance mathematical-prediction on a novel LT-PV/T system using spiral-descent concentric copper tube heat exchanger as the condenser for large-scale application

Abstract

The condensers of loop thermosyphon PV/T systems (LT-PV/T) are usually integrated inside water tanks, which may bring some challenges during combination use. This research innovatively proposed a concentric copper tube heat exchanger as the condenser, which is combined with a copper tube evaporator beneath the absorber. The gaseous working fluid flows in the inner tube and the cooling water flows in the outer tube. Since ordinary water pipes are used for water circulating between the outer tube and water tank, this LT-PV/T collector can be used individually or combined with other collectors flexibly. To access its' performance, researches have been conducted: (1) Designing and fabricating the system prototypes; (2) Investigating system performance with different volume-filling ratios (26.5%, 34.8%, 43.2%); (3) Investigating the influences of working fluid (water, ethanol and R134A). (4) Evaluating the systems’ performance with energy efficiency, exergy efficiency, and semi-empirical system efficiency models; (5) Conducting two case studies in South China (an individual collector & a 4 parallelly/serially-combined LT-PV/T collectors system). The system is first-of-its-kind and has obvious advantages in reliability, flexibility, space-saving and large-scale applications. The typical primary energy-saving efficiency of the LT-PV/T with R134a of 40% filling ratio can reach 78.0%, higher than the published LT-PV/T systems.