Accelerate Europe reports from UK retailer Sainsbury's new online fulfilment centre in east London.
Inside Sainsbury's online fulfilment centre in Bromley-by-Bow, east London.
Photo credit: Anna Salhofer
Founded in 1869, Sainsbury’s is proud of its long history of retail innovation. Accelerate Europe visits the UK retailer’s new online fulfilment centre (OFC) in east London to see how natural refrigerants are serving the shopping landscape of the future.
The OFC is entirely dedicated to serving the UK’s burgeoning online retail trade. It is a unique environment. Without a single customer on the premises, Sainsbury’s refer to it as their ‘dark store’. The site serves online shoppers across north and east London, from Camden to West Ham.
The facility is open around the clock. From roughly 02:00am until 09:00am, teams of ‘pickers’ are busy assembling customer orders. Loading of the delivery trucks begins around 04:00am, with the first deliveries going out at 07:00am.
Automation is the name of the game. An extensive lift and shuttle system is capable of taking up to 7,500 delivery boxes – known as ‘totes’ – from the shelves to the delivery trucks and back per hour.
According to sales forecasts, the site is currently operating at just 28-30% of capacity. “We’re currently handling around 7,000 customer orders per week,” says James Hunt, the OFC’s commercial manager. “We’re capable of fulfilling 20,000-25,000 a week.”
The team of pickers fill totes and place the completed orders on a conveyer belt. Lifts drive the totes up above the picking floor, and shuttles take them on to their final destination in storage, from where they are loaded on to delivery trucks.
“What we’ve installed here gave us the best balance between cost, energy and GWP – all the main measures you look at in an installation.”
– Paul Arrowsmith, Sainsbury’s Supermarkets Ltd.
Unique challenge for refrigeration
This poses unique challenges for refrigeration. “During the picking period, the cabinets need to perform with the doors open,” says Paul Arrowsmith, refrigeration design manager in the property department of Sainsbury’s Supermarkets Ltd.
“It was a case of reverse engineering and testing the cabinets to be used as not originally built for.”
At the facility’s heart is an ammonia-CO2 cascade refrigeration system from German manufacturer GEA. “It’s pumped CO2 for the chilled, cascaded from an ammonia system which keeps the pumped CO 2 at -6°C,” Arrowsmith says.
No ammonia circulates on site. Instead, it is restricted to the plant room, the evaporator and the evaporative condensers.
“The liquid CO2 is the heart of the system,” Arrowsmith explains. “The pumped CO2 provides the condensing medium for the subcritical DX frozen food system. We’ve got CO2 for frozen, pumped CO2 for the chilled, and ammonia to keep the CO2 at the required temperature.”
“GEA was our existing installation and service provider,” he says. “They worked in conjunction with one of our commercial refrigeration contractors, who commissioned the frozen and produce cabinets, while GEA did all the commissioning of the refrigeration system.”
The ammonia that keeps the liquid CO2 at -6°C is cooled by three compressors. “With one running, the system is at about 40% capacity,” Arrowsmith explains. “The second would bring it up to 100%, and the third is a spare.”
The CO2 subcritical package serves all the frozen food areas. “Because pumped CO2 is the condensing medium, it’s so efficient. You only need two compressors.”
On the medium temperature side, the system packs 825 kW of duty, with up to 104 kW on the low temperature side.
The consultant also looked into using an ammonia-only or a CO2 transcritical system. It was the ammonia-CO2 configuration that came out on top, based upon a ‘balanced scorecard’ approach of total equivalent warming impact (TEWI), energy efficiency, capital cost, and colleague safety perspectives.
“With a traditional distribution centre, whether for frozen or chilled, your starting point is ammonia,” Arrowsmith says. “Here in Bromley-by-Bow, because this didn’t slot into the category of a distribution centre or a supermarket, we looked at it as a blank canvas.”
“We looked at ammonia only, we took HFCs as a benchmark, and we looked at pure commercial CO2 refrigeration,” he explains. “What we’ve installed here gave us the best balance between cost, energy and GWP – all the main measures you look at in an installation.”
The site remains Sainsbury’s most recent and this is the model that future such sites will follow.