A comprehensive review on hybrid heat recovery systems: Classifications, applications, pros and cons, and new systems

With the growing rate of energy, depletion of natural resources, and the impact issues of conventional energy sources on the global climate changes, there is a growing demand for heat recovery that saves over 90% of the lost energy in terms of saving wasted energy. Throughout the research, it is noticed that hybrid heat recovery systems, which means employing more than one heat recovery system into one single system, are showing great potential in many applications, where the recovery systems exceed 28% and the coefficient of performance reaches 2.2 times the conventional system. At this point, the current study presents a comprehensive review of hybrid heat recovery systems and gives a rich and useful summary of previous works. The main aim here is to (1) classify energy recovery systems into specific methods, (2) provide an overview of hybrid energy recovery systems, (3) demonstrate a detailed description of each method, (4) point out their applications, (5) present innovative systems, and (6) show the pros and cons of each system alone and each system combined into a hybrid heat recovery system. Finally, this review shows that hybrid heat recovery is a promising solution, especially when combined with thermoelectric generators (TEG), where 60% of the studies involve TEG in a hybrid heat recovery system. Moreover, this review answers the main question which is: does the rise in the percent of heat recovery in a hybrid heat recovery system is worthy of employing a complement or new heat recovery system, or may it cost more than it recovers? •Hybrid heat recovery systems are showing great potential in many applications.•The current study presents a comprehensive review of hybrid heat recovery systems.•The pros and cons of each system alone and each system combined into a hybrid heat recovery system are shown.•Hybrid heat recovery is a promising solution especially when combined with thermoelectric generators.