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An off grid retail store featuring propane refrigeration
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The technologies included in the Refrigeration Road Map have been divided into three sub-groups, namely technologies currently available for retrofit in supermarkets, technologies that can be installed during a store refit and technologies that could be implemented in a new build store. To identify carbon saving potentials, each identified technology has then been compared to a baseline typical store with a 5,000m2 sales area and 400kg of R404A refrigerant charge. Leakage of refrigerant from supermarkets has been assumed to be <1% per year for integral cabinets and 20% for remotely operated cabinets.
Hydrocarbon chilled and frozen integrals: a CO2e saving option that can be retrofitted
The advantage of HC cabinets lies primarily in their reduced energy consumption, with trials demonstrating energy savings of 10%-15% when using R290. However, the report notes that although the energy saving potential of integral hydrocarbon cabinets alone is relatively large, the usage of integral cabinets in the majority of supermarkets is currently low and hence, the overall energy savings potential over the whole supermarket is relatively small.
Secondary systems: a CO2e saving option during store refits
The report mentions secondary systems as an option that could save more than 250tCO2e per annum. Secondary systems use a contained primary refrigeration system (usually in a plant room) that is used to cool a pumped secondary fluid. Flammable refrigerants such as hydrocarbons can be used as the primary refrigerant in this configuration due to the plant being located in a controlled access room away from the customer sales area, while secondary fluids are generally brines or glycol-based fluids, but can be CO2 or ice slurries.
Secondary systems have refrigerant emissions of 2%-4% of charge per year thanks to reduced refrigerant piping lengths and number of connecting joints. The report, however, notes that there are mixed results regarding the energy use of secondary systems, which depends very much on the design of the system and, therefore, careful design is needed to minimise energy consumption.
Hydrocarbon Water loop systems: a CO2e saving option when designing a new store
The report draws upon the example of retailer Waitrose that has employed hydorcarbon integral cabinets where the condenser is cooled by a water system pumped around the store, as an option enabling high Global Warming Potential (GWP) refrigerants to be minimised in supermarkets.
This option is characterized as particularly attractive, as the integral cabinets operate on a low GWP refrigerant while they have also been shown to have low leakage rates. The system has a relatively high coefficient of performance compared to conventional direct expansion-type supermarket refrigeration system and the condensing temperature is also maintained at a low level. It also requires minimal commissioning and set up as the cabinets are constructed and tested by the manufacturer prior to delivery to the supermarket.
As of end of March 2010, the technology had been installed in seven Waitrose stores, while it will be in all of the retailer’s new build and refitted stores going forward. An “off grid” retail store in Norfolk, UK that will feature propane based refrigeration and that will enable it to reach a near-zero carbon standard was announced earlier this year, while more recently the retailer is looking to open a biomass-powered store in Isle of Wight. If the retailer’s planning application goes through, it will turn an electricity substation into a biomass plant to provide all electricity, heating and cooling needs for the 18,000 square foot store currently under construction. The store will be able to operate 'off-grid' and have a 'carbon negative' footprint.