# Decarbonizing European Industry: A Novel Technology to Heat Supply Using Waste and Renewable Energy
## 2 The SUSHEAT Concept  
SUSheAT incorporates several novel technologies such as an HTHP, a PCM bio-inspired TES system, and a CIT system for advanced heat upgrading in leading laboratories [25]. Moreover, SUSHEAT effectively assesses the best integration of heat upgrading systems, incorporating key enabling components and leveraging off-the-shelf renewable energy systems, such as solar Fresnel collectors, to enhance feasibility even at low temperatures. On the other hand, the integration depends on harvesting energy from waste heat, utilizing a linear Fresnel collector (LFC), and using ambient heat as a reservoir. Figure 3 shows the four main components that integrate the SUSHEAT system. These main components are detailed as follows:  
(1) High-temperature heat pump: It should be noted that low-temperature heat sources, such as waste heat, cooling water, or ambient heat are upgraded via the HTHP, which employs helium and innovative Stirling technology. This process generates high-temperature heat, ranging from 150-250 \({}^{\circ}\)C, needed for industrial applications like drying, distillation, or rapid heating in the SUSHEAT case studies. Utilizing both waste heat and electrical energy, a heat pump produces steam at temperatures up to 250 \({}^{\circ}\)C and pressures up to 45 bar. This setup can realistically achieve a coefficient of performance for heating (COP) ranging from 1.9 to 2.8. The peak efficiency of Stirling cycle heat pumps [25], is 32% of the Carnot cooling coefficient of performance (COP). However, ENER's calculations suggest that achieving up to 50% of the Carnot cooling COP is possible. The 2022 model of ENER's heat pump is projected to reach the peak Carnot fraction at a temperature ratio of 1.7 K/K--specifically, a 250 \({}^{\circ}\)C sink and a 35 \({}^{\circ}\)C source. Notably, the actual COP tends to be higher with smaller temperature differences, making it essential for R&D to focus on extending the Carnot fraction to lower temperature ratios to enhance the COP further. The highest reported COP at a 1.26 K/K ratio (with a 105 \({}^{\circ}\)C sink and a 26 \({}^{\circ}\)C source) is 2.2, representing 32% of the Carnot cooling COP. ENER's heat pump used in this project is anticipated to achieve 42%, equating to a COP of 2.8 at 1.26 K/K, which could also be reached with a 250 \({}^{\circ}\)C sink and a 142 \({}^{\circ}\)C source once the seals are finalized. However, we observe different COP values  
Figure 3: The SUSHEAT system in this study. (ranging from 1.9 to 2.8) depending on the temperature ratios for the case studies, operating within different temperature ranges. With future enhancements, this efficiency could rise to 50%, resulting in a COP of 2.9 at those temperatures. (2) Thermal Energy Storage: The advanced TES system provides reliable, flexible, and adaptable heat supply, completely independent of waste heat recovery and renewable availability. Technological improvements are being made for novel latent heat TES. In the SUSHEAT system, there are two TES systems: one for storing waste energy at a low temperature for later upgrading, and another for storing heat at a high temperature for use as needed by the industrial process. The optimal PCM is being researched and selected for the SUSHEAT hybrid renewable heat upgrade system. This system is designed to capture and store surplus thermal energy in peak solar periods and then provide it to processes as needed. Low-temperature TES is typically in the range of 70-85 \({}^{\circ}\)C, whereas high-temperature TES operates between 180-200 \({}^{\circ}\)C. The proposed bio-inspired TES maximizes power density by overcoming the heat transfer limitations of traditional PCM-based TES designs, which are typically hindered by the low thermal conductivity of PCM. (3) Linear Fresnel Collectors: SUSHEAT employs commercially available linear Fresnel collectors (LFC), which use linear Fresnel mirrors for solar concentration.