1. R. Aarlien, On the design, efficiency and market potential of residential air conditioning and heat pump units with CO2 as working fluid, Doctoral Thesis at the Norwegian University of Science and Technology, 2004 [ISBN 82-471-5309-2].
2. Hochtemperatur Hauswärmepumpen mit CO2 als Kältemittel;Brandes;KI Luft- und Kältetechnik,2000
3. Energy efficiency comparisons for heat pumps working with CO2 and R-407C;Kerherve,2002
4. Regeneration of expansion energy by ejector in CO2 cycle;Ozaki;Sixth IIR/IIF Gustav Lorentzen conference on natural working fluids, Glasgow, Scotland,2004
5. CO2 heat pumps in controlled ventilation systems;Rieberer,1998