Sustainable and energy-efficient domestic hot water systems: A review

For a very long time activities related to efficient domestic hot water (DHW) production and distribution have been neglected and left behind due to an insignificant share in total energy use for buildings. It is in recent years that DHW has emerged as one of the key energy factors in the total energy use in buildings and its share is continuously increasing as energy use in other segments is continuously decreasing, for example space heating, ventilation, and energy for lighting. It becomes suddenly undeniable that efforts in the field of energy-efficient DHW must be strengthened, and as such, there is increased activity in the field. However, the work reported is very dispersed and fragmented. The objective of this review article is to collect and present recent works related to improve performance of a DHW system in terms of energy. The scope and content of the paper aims to address the topics of high relevance to the field, these are shift towards the new situation in which DHW becomes a significant energy use responsible factor in buildings, distribution and weighting of losses related to DHW systems and purpose of DHW use. The article focuses on novel actions to obtain energy-efficient DHW in the following domains: DHW production, DHW distribution and circulation, wastewater heat recovery, and control strategies. The article finishes with conclusions.