CIBSE Case Study: Innovative Technologies used in Sustainable Supermarket
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Article from the August 2013 edition of the CIBSE Journal written by Andy Pearson.
Sainsbury's has introduced a range of innovative technologies to reduce the impact of its lighting, heating and energy-intensive refrigeration. But will it be enough to meet its self-imposed target of slashing emissions by 30% in the next seven years?
Sainsbury's is a big business. The retailer currently serves 23m people a week from around 600 supermarkets and 600 convenience stores. But it wants to serve more. Its ambitious plans for growth saw 93,000 m2 of floor space added to its estate in 2012, with another 93,000 m2 expected this year.
Along with its commitment to growth, Sainsbury's has also made a significant pledge to sustainability with the recent launch of the 20x20 Sustainability Plan, an initiative based on 20 commitments to be achieved by the year 2020. From an environmental perspective, the plan includes some challenging targets, including reducing the amount of own-brand packaging by half, compared with 2005 levels, and cutting the carbon emissions associated with its own-brand products by a similar amount.
From an engineering perspective, however, by far the biggest 20x20 challenge is the commitment to reduce absolute operational carbon emissions from the estate by 30%, again compared with 2005 levels. That equates to a 65% reduction in emissions for every square metre of existing floor space, including distribution centres, stores and offices. And as Mark Hawker, head of engineering for the estate, points out, the 30% figure stays, "no matter how much Sainsbury's estate grows. So what innovations is it using to hit its target?
The engineering team is currently focusing its energy-saving efforts on lighting, which makes up 20% of the company's energy use. "To minimise this, we try to use natural light wherever we can," says Hawker. As a result, most new stores now feature a form of rooflight that Hawker calls "daylight panels". A lux meter on top of the product gondolas adjusts the artificial light levels by turning the lights up or down, or even off, in response to fluctuating daylight levels.
For day-lit stores, light levels are set to maintain a constant 650 lux. For stores without daylight, light levels are higher at 800 lux during trading hours. When stores are not trading, levels are reduced to 300 lux. According to Hawker, the only time when the lights are turned off completely is Christmas Day.
In addition to daylight, Sainsbury's is starting to achieve major energy savings from the use of LED lamps. It first started using them back in 2005 as a cost-effective replacement for fluorescent lamps in freezer cabinets. "Fluorescent light output dims by 75% at -20C so you need four times as much energy to match the lighting level," says Hawker, whereas LEDs are "agnostic to temperature, meaning their efficiency does not drop off in the same way. Their imperviousness to cold also allows LEDs to be used in the stores" big back-of-house freezers, in conjunction with motion sensors that turn them on and off.
LED technology has moved on considerably since 2005, with improvements in the lamps' colour, cost and life span. Consequently, by 2010 Sainsbury's was using LEDs in spotlights, in fridges, to illuminate counters and freezers and even to light its car parks. This year, the retailer has opened its first store with a shop floor lit entirely using LEDs (see below). And it is investigating a number of new LED products, each with a payback of between two and three years compared to fluorescent technologies.
Hawker says the switch to LED technology will require Sainsbury's to change the way it thinks about warranties because the lamps are expected to last for eight to 10 years: "It means we need to deal with companies that will still be aroundin eight years or so for the warranty to be valid."
He thinks the way Sainsbury's buys light fittings will change too: "If I buy an LED-based luminaire that will last for eight years, will I be able to upgrade the body and reuse the LEDs? And if I do, will the manufacturer reprocess the fittings?"
Hawker's team is contacted on average by three new lighting suppliers each month, all looking to have their products specified by Sainsbury's. If the teams like a product, it will investigate the robustness of its supply chain and quality-control systems to ensure they meet its exacting requirements. Only when a product has met the retailer's technical, commercial and quality demands will the team consider trialling it' and even then only in a non-trading environment.
Most products for use in stores are tested initially in what Hawker calls "mock-shops". Sainsbury's has two of these facilities - one in Coventry and one in north London - where products are put through their paces in a simulated supermarket interior. "For lighting, we'll use these facilities to assess power consumption, light output, cost to install and cost to operate," explains Hawker.
Only about 10% of the products tested make it successfully through the mockshop. Those that do "might" be trialled in an actual store. If that is successful, the product will be incorporated into the retailer's standard specification for roll-out across future stores.
The cold front
In a similar way to the advances in LEDs, the use of carbon dioxide (CO2) as a refrigerant is another carbon-saving technology that required time and effort to bring to a point where Sainsbury's was comfortable to use it in its new stores. Refrigeration is a vital issue for Sainsbury's as it makes up 40% of its total energy use.
On its larger stores, Sainsbury's uses a refrigerant circuit to remove heat from the rows of chilled cabinets and freezers, via individual heat exchangers. The circuit transfers the heat to a large refrigeration plant, usually tucked out of sight on the store's roof, where the heat is removed and, in most cases, used to provide space heating. On top of the carbon associated with the energy consumed by a store, there is always the risk of F-gas leakage from these large refrigeration systems.
To tackle the problem, Sainsbury's set out to replace conventional refrigerant plant with non-ozone depleting CO2-based plant. Initially, Hawker says the technology was up to 40% more expensive than the conventional system. As a result, Sainsbury's worked with three suppliers, who had aligned themselves with European manufacturers producing CO2-based plant. Each supplier's refrigeration equipment was trialled in two stores. "These six stores enabled us to learn about the good and bad of each system to come up with a Sainsbury's standard."
CO2 refrigeration technology has now evolved to a point where capital cost and efficiency are the same as those of conventional refrigeration plant. To date, CO2 refrigeration has been installed in 160 larger stores. "It has made a big dent in our carbon footprint," says Hawker.
Heating is another area where the engineering team is starting to make signifi cant carbon savings. Biomass is now the default heating system for shops up to 5,570m2 and Sainsbury's has 78 local stores that run on it. The fuel comes from a Scottish firm that makes timber construction products. It uses timber thinnings to power a CHP plant, energy from which is used to process the remainder of the thinnings into pellets. Delivery to stores in the north of the UK is by road; for the south, the pellets are sent by boat to Purfl eet in the Thames Estuary, before distribution by road to stores.
Where it is cost-effective, some of the retailer's larger stores use a closed-loop ground-source heat pump to provide both heating and cooling. In winter, the main source of heating is the captured heat rejected by the rooftop refrigeration plant. Supplementary heating is provided by the heat pumps, which are connected to a series of boreholes that extend up to 200m below ground.The ground acts like a giant thermal storage battery. In winter, the heat pump draws heat from the ground to top up the space heating. A secondary circuit delivers the heated water from the heat pumps to the various air-handling units and domestic hot-water appliances. In summer, heat from the store's rooftop refrigeration plant is collected and used to reheat the ground.
The ground's temperature, at about 14 degreesC, has the advantage of creating a significantly lower condensing temperature for the store's refrigerant circuit than ambient air. "We get about a 30% energy saving on the condenser because of the low ground temperature," says Hawker. The solution also means the store does not require a gas supply for heating.
The technology is being used in new stores, but Hawker says retrofitting on existing stores has been trialled and is on the agenda. "If we grow, to meet our targets, we've actually got to reduce the carbon emissions of our existing stores."
He compares the scale of the task to an iceberg: "The new energy-efficient stores are the bit above the surface of the water, but the bulk of the existing estate is below," he says.
Hawker says Sainsbury's is considering generating its own energy using a low-carbon source, such as combined heat and power. Currently it generates a proportion of its electrical energy using PV panels: Hawker says it is the biggest multi-site user of PV arrays in Europe, with about 100,000 panels installed on the roofs of supermarkets and distribution centres.
There is still much more to be done, but the engineering team's strategy appears to be working: since 2005 the estate has grown by 23%, but total energy use has come down by 6%. Which means there's just 24% to go before it hits its 30% reduction target in seven years.
Globally, water is becoming a resource issue, and it is also a cost issue for Sainsbury's. The retailer has reduced its operational water consumption across its entire estate by 50% relative to the size of the store - an annual saving equivalent to 393 Olympic-sized swimming pools. All new stores incorporate automatic meter reading linked to a central monitoring station. This ensures any major water leaks can be detected and allows Sainsbury's to compare consumption of one store against another. Stores use waterless urinals and percussion taps, toilets are flushed using harvested rainwater and the carwash recycles water. Sainsbury's has also become one of the first organisations - and the first retailer - to achieve the Carbon Trust Water Standard, showing that it's measuring, managing and reducing water use year on year.
The Waste Circle
None of Sainsbury's waste goes to landfill. Comprising a mixture of cardboard, plastic, food, oil and paper, it is all put to positive use. Food fit for human consumption is donated to charities to help tackle food poverty in the UK. Bread waste goes to animal feed with the remaining food waste going to anaerobic digestion to produce gas that is burnt to generate electricity and fertiliser; cardboard is baled and recycled, as is plastic; wood waste is recycled, as is paper. "You do not throw stuff away, instead you reuse it in a circular economy," says Hawker.
Sainsbury's first 100% LED store
When it opened in January, the 3,700 m2 low-energy store in Leek, Staffordshire, was the first Sainsbury's to be fitted with a full LED lighting scheme on the main sales floor. Not only was it a first for Sainsbury's but it was the world's first commercial application of GE's Lumination EL Series "blade" LED luminaires. "The technology is straight out of GE's research and development programme," says Hawker.
The light fittings incorporate a linear LED unit. The most unusual aspect of the unit's appearance, however, is its microlens light diffuser. This is attached beneath the lamps like a glowing, rectangular blade of light (see image above).
The big advantage of the lamps is that the illuminated blades throw most of their light sideways. "The lamps illuminate the products on the shelving and not the shop," says Hawker. At a light level of 650 lux, the units delivered a 65% kWh saving when compared to a conventional high frequency T5 fluorescent lamp system.
In addition to the shop floor, LEDs are also used in feature lighting, staff areas, refrigeration cabinets, sales counters and the bulk-store area, which is fitted with passive infra-red detectors to sense when the room is occupied. The store is even fitted with LED car park lighting, which incorporates very white LEDs. "Because the LED light is so white, it means that you can illuminate that space using lower lux levels, which saves us further energy," says Hawker.
Other carbon-saving measures in the store include daylight panels, CO2-based refrigeration plant and a 520kW Uniconfort biomass boiler. The impact of all of these innovations is a 55% reduction in operational carbon performance and a 59% reduction in kWh for the store.