Valorisation of Waste Heat in Existing and Future District Heating Systems

Abstract

To recover thermal energy from different sources, its quality and possibilities for utilisation are essential. The wide range of engineering solutions includes a direct connection to the district heating (DH) system and the integration of low-quality heat using heat pumps to increase the temperature level of recoverable heat. Therefore, this article compares waste heat valorisation strategies for integration into existing DH networks, low-temperature DH, and ultra-low heat supply systems using the multi-criteria assessment method. In addition, a local scale assessment was performed to identify the waste heat role in existing RES-based DH systems. The results show that the highest waste heat valorisation rate could be reached when integrated into low-temperature DH systems due to high waste heat potential and suitable temperature conditions. However, a local scale assessment shows a significant impact on the already implemented solar technologies, as waste heat could cover around 70% of the summer heat load.

Industrial Waste Heat Utilization in the European Union—An Engineering-Centric Review

“…• Group 1: retrofits of existing processes can be problematic (e.g., due to insufficient space) [20], while some technologies require specific conditions to work properly [21]; • Group 2: the selection of the best technology may not be straightforward [22], and corrosion, erosion, and fouling of the heat transfer surfaces can severely limit the prospective operator's options [23]; • Group 3: the environmental impact of the working fluids [24] and their degradation at higher temperatures [25] may prove to be problematic, higher exergy losses [26] and low conversion efficiencies of conventional thermoelectric materials [27] have often been reported, and some technologies are still under development and are largely unproven (thus risky and unattractive to, e.g., shareholders); • Group 4: the seasonal nature of the demand [28] as well as the greater distances between the heat source and sink [29] are often major challenges, and some technologies have also been shown to suffer from low efficiency [30]; • All groups: long(er) payback periods may discourage the investors [31].…”