# A Review of Worldwide Strategies for Promoting High-Temperature Heat Pumps
## 3 Heat Pumps: Technological Principles, Challenges, and Potential
### Strengths and Barriers
Also, the limitations of the power network are a significant, often overlooked barrier to the broader application of HTHPs that should not be underestimated. Intensive electrification of the heating industry will significantly impact electrical distribution systems, historically designed for lower demands. For instance, in the UK, HPs' adoption could increase peak power consumption by up to 14%, potentially requiring network strengthening and impacting the economic sustainability of HP integration. Overloading and voltage stability issues could arise with higher HP penetration, highlighting the need for further research into the relationship between RES and peak electricity demand and new strategies to manage peak-to-average demand ratios [30]. Furthermore, the technology readiness level (TRL) of some HTHPs is relatively low compared to more mature fossil-based technologies like boilers. Low-temperature electric HPs (<90 \({}^{\circ}\)C), electric boilers (both resistance and electrode types), and electric resistance heaters are well-established technologies and are fully ready for deployment (TRL 9). However, for HPs with output temperatures over 90 \({}^{\circ}\)C, the TRL decreases as the temperature increases, ranging from 9 at <90 \({}^{\circ}\)C to as low as 3 at <160 \({}^{\circ}\)C [27]. The adoption of HTHPs is also significantly hampered by public acceptance and understanding issues. These issues often stem from unfounded concerns, misconceptions, factual inaccuracies, and negative experiences with HTHP reliability. Even in highly developed societies, there is sometimes a lack of public awareness regarding the financial and environmental benefits of integrating HTHPs. For instance, noise pollution from HTHPs can raise public concerns and hinder adoption. To address this, noise levels are often managed using noise barriers. Despite their net positive environmental impact, HTHPs face environmental challenges such as land subsidence and water pollution, which affect their integration into industrial processes [30]. A major barrier to consider is also the policy uncertainty to clear heat decarbonization pathways and the adoption of new technologies, including HTHPs. Many countries lack specific policies tailored to HTHPs, opting instead for broad, one-size-fits-all heating policies. This generalized approach is often ineffective in reducing carbon emissions. A cross-country analysis within the EU demonstrates that the absence of clear legal and regulatory frameworks impedes technological progress. The economic and fiscal design for low-carbon heating systems significantly varies depending on the end-use and heating technology employed. Furthermore, inadequate financing for HP research and development (R&D) negatively impacts the economic viability and acceptance of these technologies [30]. This aspect gains even more importance considering that energy-intensive industries face international competition, making it challenging to impose regulations without risking job losses and industry relocation [68]. Eventually, due to the higher sink temperature and the bigger T\({}_{\text{lift}}\) between the cold reservoir and the hot reservoir, IHPs present technical barriers that do not exist for household HPs. In fact, HPs operating between 150 \({}^{\circ}\)C and 200 \({}^{\circ}\)C need special refrigerants and compressors, technologies that are still in the early prototype stages [63]. In fact, the lack of suitable refrigerants that can effectively operate within the desired temperature range is a major challenge, and, additionally, there is a shortage of experimental and demonstration plants, limiting opportunities for testing and refining HTHP technology. Managing compressor discharge temperatures presents a formidable challenge. Achieving higher sink temperatures without compromising lubrication oil integrity or encountering material issues is a complex task. Incorporating additional components to manage oil in the compressor adds to system complexity and costs.