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Where and how to place the injection structure of a cascade high-temperature heat pump with large-temperature differences: A comprehensive analysis.

Author(s) : WANG Y., LU Y., WU S., QI Y., WU L.

Type of article: IJR article

Summary

In the context of utilizing cascade high-temperature heat pumps (HTHPs) for heating applications with largetemperature differences, the optimal placement and implementation of the injection structure continue to present an unresolved issue. To this end, this paper develops two otherwise-identical cascade HTHP configurations: the HT-VIE-CS with the injection structure placed in the high-temperature stage and the LT-VIE-CS with the structure placed in the low-temperature stage. Subsequently, performance and stability are compared over wide ambient temperature (Tam) and heating temperature (Th) ranges, and several refrigerant pairs are screened. Results show that placing the injection structure in the low-temperature stage generally increases heating COP, with a maximum advantage of 4.0 % over HT-VIE-CS in the investigated conditions, while HT-VIE-CS retains a larger stability margin. Across refrigerant pairs, LT-injection remains favorable, and R152a/R245ca provides the best overall trade-off. Based on the stability-performance balance, a flexible selection strategy is proposed: as Tam rises, the recommended configuration shifts from HT-VIE-CS to LT-VIE-CS and then to a simpler two-stage injection system, with transition Tam of -1/5/10◦C and 48/56/64◦C for Th = 120/130/140◦C, respectively. A techno-economic and carbon assessment indicates that under current conditions, when Tam > 3◦C, its operating costs are lower than those of gas boilers, and when Tam > 24◦C, its emissions are lower than those of coal boilers.

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Pages: 12 p.

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Details

  • Original title: Where and how to place the injection structure of a cascade high-temperature heat pump with large-temperature differences: A comprehensive analysis.
  • Record ID : 30034917
  • Languages: English
  • Subject: Technology
  • Source: International Journal of Refrigeration - Revue Internationale du Froid - vol. 186
  • Publication date: 2026/06
  • DOI: http://dx.doi.org/https://doi.org/10.1016/j.ijrefrig.2026.106902

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