Though all of the chillers on the MSU campus operate on a vapor-compression refrigeration cycle with centrifugal compressors, the two Trane chillers operate quite differently from the McQuay chiller. The largest differences between the two brands are the refrigerants used and the refrigerant compression process employed.
The refrigerant circulating within the McQuay chiller is R-134a; while the refrigerant within the Trane chillers is HCFC-123. R-134a is considered a high pressure refrigerant and has evaporator and condenser pressures usually around 35 psig and 124 psig, respectively. HCFC-123 on the other hand is considered a low pressure refrigerant and has an evaporator and condenser pressures usually around -5.55 psig and 6.1 psig, respectively. Recall that a negative gage pressure indicates that the absolute pressure is below atmospheric pressure, which can also be indicated as a vacuum pressure (5.55 psiv).
refrigerant. Some of the advantages and disadvantages of operating with each refrigerant are: higher/lower compressor work input, fast or slow leaks if they occur, and different effects the refrigerant may have on the environment.
HCFC-123 results in a lower compressor power input and a slower leak rate (if a leak occurs). Comparisons of work input to achieve a ton of refrigeration have been done and this refrigerant, with no economizer, received a rating of 0.473 kW/ton. This refrigerant has a slower leak rate because it can be used at lower pressures (refer to the saturation properties given in the Document Archive section to verify this). Part of the cycle with HCFC-123 drops below atmospheric pressure, meaning if the tank developed a leak, air would be brought in instead of refrigerant flowing out. While the plant workers would not risk breathing refrigerant they would be required to perform additional maintenance to remove the air from the system. This refrigerant has been shown to affect the atmosphere in the form of ozone depletion and global warming; although, the effect is not as great as some other refrigerants.
R-134a takes a higher compressor input and has a potentially higher leak rate. The value of work input to ton of refrigeration on this refrigerant was found to be 0.507kW/ton. R-134a is a high pressure refrigerant, meaning if a leak develops the expulsion rate is higher and is generally out into the chiller room. One interesting tradeoff, this particular refrigerant has is that it possesses no ozone depletion potential because it does not contain any chlorine but it has a larger global warming potential compared to HFCF-123!
