http://mail.airah.org.au/downloads/2004-05-01.pdf
3 - Conclusions
The refrigerating capacity of a R22 compressor that was switched to propane was
reduced between 13% to 20%. These values, though more or less as expected
from refrigerant properties, are somewhat affected by differences in volumetric
efficiency that, at intermediate pressure ratios are lower for propane. On the other
hand, unlike expected by the analysis of isentropic cycles, there is an increase
in COP of the compressor of 1% to 3%. In the case of the scroll compressor
differences in capacity are shorter (up to 15%) and even reversed and COP values
are around 1% to 2% higher with propane. A noticeable result is in the volumetric
efficiency of both refrigerants, showing considerable differences.
In the origin of the observed behaviour, three main factors can be thought to
have an influence: the reduced irreversible heat flow due to the lower discharge
temperatures of propane, the increased electric efficiency of the system working
against a reduced load and the reduced pump losses in the inlet and discharge
valves