Trends in research of heating, ventilation and air conditioning and hot water systems in building retrofits: Integration of review studies

Heating, ventilation and air conditioning (HVAC) and domestic hot water (DHW) systems are the main end-use energy consumers in buildings. Simultaneously, building retrofitting plays a key role in reducing energy consumption and environmental burdens. Therefore, this study aimed to identify the main research trends and possible developments in the interrelated fields of HVAC&DHW systems and building retrofitting. To this end, we searched scientific databases for related reviews studies. The search yielded 100 eligible articles; however, only 13 of them fully focused on HVAC&DHW in building retrofitting, indicating considerable potential for further reviews. The retrofit measures in the reviews were dominated by space heating, heat/cool generation, and control systems. Heat pumps were the most frequent retrofit measure, quoted in 42 of the reviews, followed by upgrading the control system (41). Energy efficiency was the focus of 61 of the reviews, followed by energy modelling (13), indoor environment quality (11), and life cycle assessment (8). The research suggestions found in the reviews were grouped into four main topics: reducing uncertainty in energy savings, developing calculation tools for building retrofit, more complex retrofit evaluation, and digitisation. For specific technologies, the potential was mainly related to adapting HVAC&DHW technologies to retrofit and integrating renewable energy sources into existing buildings. Research was also lacking for specific regions and building types. The results of this review help professionals better focus their efforts in the research and review activities of heating, ventilation and air conditioning, and hot water systems, especially in the context of building retrofitting.