A review of waste heat sources for district heating

As the world’s energy needs rise, carbon emissions and climate change become a bigger concern. Therefore, there is a growing need for cleaner energy sources as well as higher levels of energy efficiency. Building energy is of great interest to researchers and policymakers, as it accounts for about a third of global energy consumption, and this is projected to rise as more people gain access to higher incomes and improved amenities. For over a century, district energy systems have proved to be an efficient means of providing thermal energy to buildings, and developments in district heating have enabled the use of various heat sources, including low-temperature sources, such as waste heat. Waste heat is a viable and technically mature source of building energy, as proven by many operational cases, but there seem to be only a few sources of waste heat utilized in practice or explored in literature. Additionally, many research studies focus on only one source of waste heat for district heating and, to the knowledge of the authors, there is currently no existing review paper on the various sources of waste heat utilized in district heating. Therefore, the goal of this paper is to examine various sources of waste heat that are utilized in real operational district heating cases or discussed in research studies. Additionally, the paper discusses the various performance metrics utilized for quantifying waste heat potential in existing literature, and rounds off with recommended future study.