Review of water-heating systems: General selection approach based on energy and environmental aspects Review Article

Water heating contributes an important proportion of residential energy consumption all around the world. Different kinds of domestic hot-water production systems exist. The operational cost, environmental effect and performance of these systems differ according to various energy sources, climates, system types and system designs. Hence, the proper choice of a domestic hot-water system could save energy, protect nature and reduce operational costs, significantly. This paper illustrates, to the best of the authorʹs knowledge, the existing water-heating systems all along with the principle, advantages, disadvantages and state-of-the-art for each. Six different categories were presented, namely wood, oil/gas, electric, heat pump, solar and instantaneous systems. The heat-pump systems were further classified into several groups, namely air source, ground source, solar assisted, ground source-solar assisted, photovoltaic–thermal and gas-engine driven systems. In addition, concerning solar water heating, different types of systems and collectors were presented and reviewed. Principal conclusions from the review are outlined and a general approach to recommend the appropriate water-heating system is proposed.