A complete HFC-free supermarket

Designed as the world’s first zero-carbon store, the Tesco Store at Ramsey, Cambridgeshire, UK, is completely HFC-free. The supermarket is hence using natural refrigerants CO₂ and hydrocarbons throughout its fridges, freezers, heating, ventilation and air conditioning systems in the store and petrol kiosk.

Ramsey is one of the first stores of UK retailer Tesco using a transcritical carbon dioxide system supplied by Star Refrigeration in 2009.

The CO₂ system is the result of two years of intensive work by Tesco and Star, seeking to develop a standard CO₂ transcritical plant that could be easily rolled out across the Tesco estate, reports the RAC magazine. The development of these standard modules will enable CO₂ to become the mainstream refrigeration solution. Indeed, the UK retailer plans to install 20-30 systems new CO₂ transcritical systems in the period 2010/2011, and 150 by 2012. Tesco and Star estimate that standardization of the system will save 22% on the rollout costs.

System design

A cascade solution was selected, for it provides the best balance of energy efficiency, availability and flexibility. Each LT package cascades against two or three HT packages so that if one HT package is out of operation, the full LT cooling capacity will remain available.

The LT plant consists of three equal-sized compressors, a common oil separator, a high pressure receiver, a liquid subcooling/sunction line superheater and three CO₂ to CO₂ condensers. The HT plant consists of three equal-sized compressors, a common oil separator, a gas cooler with EC fans, a high pressure regulator, an intermediate separation vessel and a low pressure receiver. The change over between transcritical and subcritical operating modes of the HT system is managed by the modular Danfoss control system.

At a side event during the 1st IIR International Conference on Sustainability and the Cold Chain in March, interested delegates will have the opportunity to examine the CO₂ system at a zero carbon supermarket.

System benefits

The system offers many benefits, including:

• Servicing can be carried out without decanting any refrigerant, as the receiver is large enough to contain the total refrigerant charge of the system

• Compressors fully protected against expansion valve failure, as the receiver is positioned in such a way that it prevents any liquid getting back to the compressors

• System will run on reduced charge in the event of exceeding design pressure: the system will provide partial cooling on reduced charge, while full cooling will be re-established automatically as soon as power recuperates.

• 10% energy savings from compressors running at higher sunction: the system achieves cost savings of up to 10% compared to a R404A system, as the overfeed design reduces superheat in the cases.

Natural refrigerants throughout the store

The Ramsey store is using natural refrigerants throughout its fridges and freezers in the store as well as its petrol kiosk. It also uses hydrocarbon chillers as part of its heating, ventilation and air conditioning systems, reducing its environmental impact even further.

Star and Tesco receive awards

As a recognition of its innovative work, Star Refrigeration was honoured with the “RAC Contractor of the Year” award at the Cooling Industry Awards at the end of last year. At the same event, Tesco was honoured with the “Green End-User of the Year: Large Projects” award for developing with Star the standard transcritical CO₂ plant for retail applications.