ACR Journal

April 2022 | May 2022 REFRIGERANTS 16 Neil Roberts, senior technical sales manager at Climalife, highlights how the transition to low GWP refrigerants may not be as energy efficient as you might think. Is energy e ciency more important than low GWP? Volume 8 No.3 We are all aware of the F-Gas legislation and the drive to low GWP refrigerants but this is only a small part of the overall solution to reduce climate changing emissions. Choosing a low GWP refrigerant does not guarantee a better energy e ciency and in some cases, it may even lead to an increase in the lifetime total emissions from the system if a lower e ciency option is selected. As well as refrigerant choice, there are other actions that can be taken to maintain or improve energy e ciency, reduce total emissions and in most cases they will even pay for themselves over the lifetime of the equipment. Good maintenance and correct control settings This is probably the easiest strategy to employ but often end users do not see the benefits of spending money on a system that appears to have nothing wrong with it. Simply cleaning the heat exchangers, using reliable leak detection methods, ensuring fans are operating correctly and checking the system operating parameters can have a significant impact on system emissions. Even moderate fouling of a condenser will lead to an increase in condensing temperature of the system. Equally if the system has a high/condenser pressure controller, checking the setting is not causing the system to operate at excessively high conditions or is set correctly for the refrigerant used (for example after a retrofit) can have a big impact. Figure 1 shows the impact of increasing condensing temperatures with R-449A at low and medium temperature conditions. Even a very small increase in the condensing temperature can lead to significant decreases in energy e ciency, for example, an increase from 25°C to 27°C condensing temperature can lead to a 5-8% loss of compressor energy e ciency. It doesn’t take much fouling of the condenser coil to cause a small pressure increase and it is easily prevented by regular use of cleaning products such as Frionett condenser coil cleaner from Climalife, which will prevent build-up of debris that can block the air flow through the coils, maintaining the optimum energy e ciency. Figure 1- Degradation of C.O.P. with increasing condensing temperature for R-449A In situations where condenser fans have either failed or are malfunctioning, energy e ciencies could easily drop by 25% or more. Refrigerant Pressure difference to R-404A @ 25°C 35°C 40°C R-407A -0.710 -0.753 -0.767 R-407F -0.141 -0.023 0.056 R-448A -0.392 -0.395 -0.276 R-449A -0.401 -0.464 -0.491 Table 1 - Pressure differences of R-404A alternatives Systems which have been retrofitted and have high pressure controllers can often lose some of the energy e ciency benefits available if the controllers are not correctly adjusted. For example, if a R404A system is retrofitted to a lower GWP alternative, it is very likely the alternative product has a lower pressure temperature relationship (Table 1). If the pressure controller is not lowered to match the new refrigerant, then the energy e ciency of the system could be 5-10% lower than for the optimum setting. Refrigerant choice Di erent refrigerants do have di erent energy e ciencies when used in the same equipment. In practice there are many potential variables that can a ect this, but if it’s thermodynamically proven then it should be possible to achieve improved energy e ciency if the system is set up correctly. Refrigerant GWP(AR4) CombinedMT& LT C.O.P.* compared to: R-404A R-744 R-448A 1387 +4% +29% R-449A 1397 +4% +29% R-452A 2140 +1% +25% R-454A 239 +4% +29% R-454C 148 +4% +29% R-455A 148 +3% +28% Table 2 - Theoretical cycle calculation comparisons