Case Study: R22 “Drop-in” Replacement
LocationHereford
ValueFree of Charge Trial
Point of interestR22 Replacement
The Background
The phase out of R22 refrigerant, as part of the Ozone Regulations affecting all HCFCs, has left users facing the choice of either (a) replacing the refrigerant with a non-ozone depleting equivalent, or (b) the replacing the equipment as a whole.
Special Metals Wiggin Ltd, a leading global manufacturer of nickel alloys, has a significant quantity of R22 equipment throughout its factory. To help them decide on their strategy, they wanted to know what the effect would be on their equipment if an alternative refrigerant was “dropped in.”
EMS agreed to conduct a trial on a system, whereby the performance and energy consumption of the existing R22 system was measured. The system was then converted to operate on an alternative to R22, and the performance and energy consumption re-measured for comparison.
The Method
The method chosen to measure system performance and efficiency was to take temperature and pressure measurements at points throughout the refrigeration cycle, plot these results on an R22 Pressure Enthalpy (ph) Diagram, and measure the input power to the compressor.
This typical ph Diagram shows the refrigeration cycle comprising Evaporation (Points 1 to 2), Compression (2 to 3), Condensation (3 to 4) and Expansion (4 to 1). The Evaporation process is the Refrigerating Effect – effectively the system cooling capacity.
The difference in Enthalpy between points 2 and 1, when divided by the difference between points 3 and 2, represents the system efficiency – referred to as the COP (Coefficient of Performance). This ratio can be determined by plotting the measured figures on the ph Diagram.
Therefore, by multiplying the measured compressor input power by the plotted COP, the resultant cooling capacity can be determined.
The refrigerant chosen for the drop-in replacement was R417A, because of its similar properties to R22, and because no compressor oil or component changes were required.
The Results
| Measurement | R22 | R417a | |
|---|---|---|---|
| Evaporating pressure | psi | 50 | 40 |
| Condensing pressure | psi | 220 | 190 |
| Evaporating temperature (ET) | oC | -3 | -10 |
| Condensing temperature (CT) | oC | 45 | 40 |
| Suction line temperature (SLT) | oC | 4 | 2 |
| Liquid line temperature (LLT) | oC | 44 | 38 |
| Superheat (SLT – ET) | k | 7 | 12 |
| Subcooling (CT – LLT) | k | 1 | 2 |
| Compressor current | A/ph | 11.0 | 10.2 |
| Compressor input power | kW | 8.3 | 7.0 |
| COP (from ph Chart) | 2.6 | 3.4 | |
| Cooling Capacity (COP X Compressor Power) | kW | 21.6 | 23.8 |
The Evaluation
The results suggest that the system with the drop-in refrigerant has a greater cooling capacity (by 10%) and is also more efficient. This, however, should be treated with a degree of caution due to:
- The margin for error in taking readings and plotting ph Chart points, which we estimate could be +/- 10%
- The other factors affecting overall system efficiency – i.e. condenser and evaporator fan power – are the same for both refrigerants, and including these figures would reduce the percentage difference.
The Conclusion
Based on this single trial, we would conclude that there is no risk in converting R22 equipment to R417a, and that this retrofit option is worth considering as an alternative to replacement of the plant.
Such an option is more likely to be appropriate for larger systems such as close control AC or chillers, where the capital cost for replacement is higher and where there is still a reasonable life expectancy. In such cases the evaporating and condensing pressures may be different to the comfort cooling system tested, and the results therefore different, but we would still conclude that there would be no risk in modifying these system types.
