Guest Editorial: Special issue on the 5th International Conference on Polygeneration 2019

International Conference on Polygeneration (ICP) was started in 2007 and was organized by Universidad Rovira I Virgili, Spain. The 5th meeting (ICP 2019) was held at the International Institute for Carbon-Neutral Energy Research (WPI-I2CNER) in Ito Campus of Kyushu University, during May 15-17, 2019. The technical program of ICP 2019 consisted of three keynote lectures, two-panel discussions, and 113 contributed papers. Papers were selected after peer review of 150 submitted papers from 21 countries. Also, there was a special keynote talk by Prof. Dr. Akio Miyara in the memory of Prof. Dr. Shigeru Koyama (Yamaguchi, 23 July 1952 Fukuoka, 4 August 2018), who was a world-renowned Japanese scientist. He distinguished himself among the world's leading experts in heat transfer and adsorption thermodynamics. From all keynote and contributed papers of ICP 2019, we had selected twelve technical papers for possible publication in a special issue of Applied Thermal Engineering. After review according to journal norms, nine of them are published in this Special Issue.