Water heaters; instantaneous water heaters; thermal energy storage units and installations comprising phase change materials; thermal energy storage units and installations utilizing heat exchangers not being part of machines and phase change materials for thermal energy storage in residential, commercial, and industrial use; thermal energy storage units and installations utilizing heat exchangers not being part of machines and phase change materials for cooling of fluid in commercial and industrial use; thermal energy storage units and installations utilizing heat exchangers not being part of machines and phase change materials for heating of fluid in commercial and industrial use