Waitrose moves on in its quest for low-GWP refrigerants
Having addressed the issue of ozone depletion in the atmosphere, the air-conditioning and refrigeration industry then found itself faced with the global-warming potential of refrigerants. Step forward Klima-Therm with a very low GWP refrigerant that has been trialled by Waitrose.
With concerns about the environmental impact of HFC (hydrofluorocarbon) refrigerants because of their high global-warming potential, there is increasing pressure to use alternative refrigerants with lower GWPs — and some organisations have a policy to do just that.
One such organisation is the food retailer Waitrose, which has already committed itself not to be using HFCs after 2020. Given the life of chillers for applications such as chilled and frozen cabinets, that commitment means that alternative refrigerants such as propane are already being used for new projects and replacement equipment.
The first Waitrose store to use a propane-based water-cooled refrigeration system was Altrincham, opened in October 2009. For comparison, propane has a GWP of three, compared with 3760 for the HFC refrigerant previously used — a significant improvement indeed.
However, there are real concerns about the flammability of propane, even in chillers installed outdoors. Those concerns resulted in Waitrose responding to an opportunity presented by Klima-Therm to try out chillers using an HFO refrigerant R1234ze from Honeywell.
This refrigerant has a GWP of six, double that of propane but still very low compared with HFCs in general. R134a, for example, has a GWP of 1300.
And according to Tim Mitchell, sales director with Klima-Therm, HFO R1234ze is not flammable at 20°C and only slightly so at 30°C. A naked flame will ignite it at 60°C, but the same applies to HCFC22.
So off to the Bromley store of Waitrose, where two air-cooled chillers each rated at 180 kW and using this HFO were installed. They extract heat from a glycol/water circuit into which heat is rejected from cabinets using propene [yes, propene] as the refrigerant. The flow/return temperatures are 16/10°C.
To obtain an indication of performance, this installation was compared with that at the Canterbury store, which is the same size, but using propane (R290) as the refrigerant. Initial comparisons show a 20% reduction in energy consumption for the HFO air-cooled chillers compared with similar chillers using propane — so there is the double bonus of using less energy and the refrigerant having a much lower GWP than the one being replaced.
|The performance of a semi-hermetic compressor using HFO refrigerant R1234ze is tested by compressor manufacturer Frascold.
If the trial is successful, Waitrose plans to adopt the HFO solution as part of its refrigerant plant for future stores, along with the continued use of hydrocarbons and tri-generation energy centres where appropriate.
Jim Burnett of Waitrose, said, ‘We believe the HFO solution shows great promise as it combines good efficiency with very low global-warming potential. This is obviously a highly desirable profile in a refrigerant. If the ongoing monitoring of energy continues to prove successful, we plan to include HFO-based chillers in our choice of refrigeration platforms for stores in the future.’
Klima-Therm’s Tim Mitchell says, ‘The focus at the moment is on HFO R1234ze as it is already available at commercial levels. In the longer term, we are also interested in the potential of HFO R1234yf, which has an even lower GWP [four] and other potential benefits. This is one for the future, but it is in our sights.’
The Waitrose chillers used Frascold semi-hermetic compressors. The chillers were made by Geoclima and supplied and commissioned by Klima-Therm, which will also maintain them.
Giuseppe Galli, managing director of Frascold, explains, ‘From a compressor engineering point of view, the properties and operating characteristics of HFOs are a very good match for traditional refrigerants, but obviously without the environmental penalty of high-GWP HFCs. Our policy is to provide solutions for all of the mainstream refrigerant alternative — which include hydrocarbons, CO2 and now HFOs.’
Frascold also has information about the performance of R1234ze compared with R134a. Tests with its 8-cylinder reciprocating compressors W40168Y indicate a loss of capacity of about 24% compared with R134a across various application conditions — because HFOs are less dense than R134a. However, mean power absorbed is about 27% less, so its COP is actually better than R134a across a range of applications and conditions.
Frascold’s research-and-development team believe that performance with HFOs could be significantly improved with further optimisation. Possibilities include refinements to the valve plate design, motor sizing and reducing pressure losses through the compressor.
This application used HFO 1234ze for refrigeration, but there is great interest in the car industry in the use of HFOs for air conditioning. It cannot be too long before HFOs get a look in at static air conditioning.