Performance increase of carbon dioxide refrigeration cycle with the addition of parallel compression economization

In the future, it would be preferable to replace the halocarbon refrigerants with natural
refrigerants like carbon dioxide, but there have been concerns over the use of carbon dioxide as
a refrigerant due to its perceived inefficiency. It is possible to partially overcome this problem
by the manipulation of the cylinders of the compressors used in the vapor compression
refrigeration cycle. If some of the cylinders are used to compress vapor in a parallel
compression system from an intermediary pressure, a refrigerating effect and COP greater than
that of the system with all of the cylinders on suction can be achieved. An analytic model was
created that allowed environmental and physical parameters to be altered. The investigations
also included experimentation with the addition of superheat for the primary compression path,
for which performance increases were noted for some operating conditions. The primary focus
of the research was for the use of carbon dioxide in a standard air conditioning application.
Accordingly, evaporation and condensation pressures were selected to correspond closely with
evaporation and condensation temperatures for other refrigerants. Under the conditions used for
the following research, superheating did not improve efficiency, and was not included. Physical
limitations placed on the ratio of the suction cylinder swept volume to the economized cylinder
swept volume suggest that building this economized compressor would be feasible. In fact, a
standard reciprocating compressor could be altered such that 2 to 4 cylinders, depending on the
volumetric ratio, are used for the economized path. The research demonstrates that under some
conditions an economized carbon dioxide system outperforms a similar halocarbon system in
terms of efficiency and capacity. In the end, this is the litmus test that proves that carbon
dioxide can compete on the level with popular halocarbon refrigerants in this economized mode.