Ammonia was the first gas to be used in refrigerators. Later, R12 and R22 refrigerants were used for cooling purpose. These gases were all Freon based. Due to their ozone layer depletion property, these refrigerants were banned. Now, some new energy efficient and environmentally friendly refrigerants are used for cooling purpose such as 410A and TDX 20.
As it was used to be R12 (CFC) and R22 (HCFC), then with the passage of time, R134a (HFC) came into the picture. And now many of them are either R134a or (increasingly) hydrocarbon based refrigerants R600a (isobutane) or R290 (propane). The reason for the recent switch is simple: R134a is not as ideal as the hydrocarbon based refrigerants and is decidedly much more expensive. Also hydrocarbon based refrigerants tend to be more hydrophobic, leading to less contamination, and require much less pressures causing less wear and tear on compressors and less power usage.
Comparison Between R134a & R600a Gases
R600a is Isobutane, when compared with the change of temperature with pressure, the change is drastic in the case of isobutane than in R134a. Secondly isobutane is a bigger compound. From the ASHRE hand book itself it is seen that for normal refrigeration purpose R600a better than R134a. it is because of the following reasons:
1) Latent heat of vaporization of R600a is much higher than R134a.
2) With small change in pressure the temperature of R600a can be easily brought to required cold condition condition.
3) Cp of R600a much higher than R134a. but the density is a bit low for R600a.
From the above mentioned reasons R600a is better than R134a in the performance division.