It is a cascade configuration cycle with a prototype butane compressor on the HTC and propane as the Operating fluid around the LTC. The cycles are connected to water heat sink This paper stories on the twenty kW ability cascade heat pump with propane while in the lower temperature cycle https://enerblue-heat-pumps16057.blogdanica.com/18444698/the-5-second-trick-for-hydrocarbon-heat-pumps