New Zealand’s 2^nd transcritical CO₂ supermarket opens its doors

Foodstuffs Wellington had signed a Design Build Contract with Cowley Services (CS) to build a transcritical CO₂ refrigeration system for their New World supermarket at Newlands, Wellington in the first quarter of 2011. The now completed supermarket opened its doors to the public on 21^st August 2012.

CS has been designing and building hybrid CO₂/R134a systems for New Zealand’s major food retailers for the past four years and saw the move towards transcritical technology as a natural progression.

‘With the increasing demand for more environmentally friendly solutions and the relatively benign nature of carbon dioxide in comparison to other refrigerants in terms of Global Warming Potential led us to believe that transcritical CO₂ refrigeration systems were the way forward,” said Peter Oliver the National Engineering Manager and primary design engineer for this project, adding “the reduced size of copper pipe, the ability to recycle high grade heat for water and space heating and the relative ease of installation has confirmed that belief.”

About the transcritical CO₂ system

The 2,400 m² New World Newlands store features a transcritical CO₂ system with: 

• Bespoke rack system by Bitzer Australia to fit the specific needs of the supermarket.
• Seven CO₂ compressors by Bitzer are installed in a booster configuration. Four 4FTC- 30K and one 4FTC-15K compressor make up the Medium Temperature (MT) Rack. One 2HSL and two 2HHC compressors make up the Low Temperature (LT) Rack.
• The LT system has a capacity of about 21kW at -36°C, and the MT system has a capacity of about 150kW at -10°C
• The lead compressors on both the LT and MT Racks are fitted with a VSD for smooth operation.
• The system features waste heat recovery from the high pressure side of the system to heat Domestic Hot Water to 70°C and by using a variable speed pump to regulate the water flow the temperature of the water can be manipulated. The remaining system waste heat is recovered and used to heat the main retail space area, this equates to approximately 150kW.
• The total CO₂ refrigerant charge is less than 150kg.
• Floating suction pressure control from the coldest cabinets
• Floating gas cooler pressure from ambient outside air temperature and retail space heating requirements. Pulse EEV for all cabinets and rooms.
• Full refrigeration system control by Emerson, including E2 for the rack system and Dixell for cabinet controllers.
• Full HVAC system control by Emerson E2, including car park and retail space CO and CO₂ sensors. Full remote monitoring via Emerson ProAct Web based interface.
• State of the art Alfa Laval Gas cooler with EC fans. Room evaporators with EC fans are by Alfa Laval.

Cascade vs transcritical CO₂: Comparing performance to inform future decisions

At the same time as being engaged as consultants for the design of the refrigeration system for the New World Newlands store, Cowley Services was also involved in the refrigeration system design of the nearby New World Churton Park supermarket. This store employs a CO₂/R134a hybrid system which has been the refrigeration system of choice for supermarket refrigeration systems over the past three to four years. The hybrid system features:

• Bitzer Australia LT rack system and MT rack system.
• Three 2GHC CO₂ compressors and four 6GE R134a compressors by Bitzer are installed in a cascade configuration.
• The LT system has a capacity of about 21kW at -36°C, and a MT capacity of about 152kW at -12°C
• The lead LT compressor is fitted with a VSD for smooth operation.
• Domestic Hot Water is preheated to 45°C. The remaining system heat is recovered and used to heat the main retail space area, which is approximately 150kW.
• Full Emerson E2e controller for the rack system, cabinet controllers.

With the two supermarkets having the same store format and located in close proximity, thus exposed to very similar climatic conditions, the consultant pointed out a unique opportunity to the retailer: build a transcritical system, and compare the efficiency and performance of a transcritical system against that of the hybrid system facilitating the collection of valuable data which will enable the industry to make better informed decisions about future technology choices in the quest for more sustainable refrigeration solutions.

Preliminary simulations of the two systems have shown that the performance of the transcritical plant to be 8% more efficient than the Hybrid plant. Cowley will use the results of the actual system performance tests for internal use only and to make informed choices when advising clients.

About Foodstuffs

Foodstuffs is New Zealand's largest grocery distributor, touching every town and community on either a retail and/or wholesale level.

With more than 700 owner-operated full service supermarkets, retail food warehouses, grocery and small convenience stores, large and small format liquor stores and fuel sites nationwide, Foodstuffs’ retail operations cover all the major retail segments in the grocery market.
Some of Foodstuffs’ brands include ‘New World’ full service supermarkets (138), ‘Pak’n’Save’ retail food warehouses (52) and ‘Four Square’, neighbourhood grocery stores (272) in New Zealand, but also smaller size supermarkets such as Shoprite and more.