Holophane's Prismatron saves energy at Woolworths big W, Aberdeen

Innovation and efficiency

The new Woolworths big W store in Aberdeen features energy efficient lighting using Holophane's innovative Prismatron system. The Prismatron system incorporates prismatic glass high bay luminaires and a special remote electronic ballast to provide dimming for 320W metal halide lamps. The luminaires are controlled in relation to natural daylight levels and set to preset dimmed levels for non-trading periods. The project incorporates a Scheider Electric, Canalis twisted pair bus bar system. This allowed faster installation of the lighting system, thus reducing the overall cost of the project. Further savings are expected for Woolworths big W from an ongoing improvement in energy efficiency, compared to other big W stores.

Woolworths big W, Aberdeen

The Aberdeen big W store, which opened in July 2003, is the 19th big W store in the UK and the fourth in Scotland. It covers an area of nearly 9300m2 (100,000 ft2), of which the trading area occupies 6500m2 (70,000ft2).

Woolworths big W's stated aim is to reduce the cost of living by providing consistently low priced goods within a unique, fun and family-friendly shopping environment. Each store sells in excess of 54,000 different product lines sourced specifically for Woolworths big W including: homewares, clothes for all the family, health and beauty, electrical goods, books, videos and CDs, toys, furniture and gardening equipment.

Building on the experience of previous stores, the company was keen to minimise energy consumption and environmental impact whilst maintaining the atmosphere of the stores. The design of the lighting was integral to this policy. "I said that I wanted prismatic glass high bay fittings with metal halide lamps that could be dimmed in relation to the amount of daylight entering the space," recalls Woolworths' David Gray. "Most companies said that it couldn't be done with higher wattage discharge lamps but Holophane took a more positive approach, by applying their new Prismatron system, together with Schneider Electric, and produced a solution," he adds.

Lighting layout

The lighting solution uses 314 Prismatron luminaires in the store area, directly suspended from the multi-pole bus bar system, with 320W metal halide lamps from Venture Lighting. These are spaced on a 4.5m grid at a height of 5.7m to the underside of the fitting.

"The combination of Holophane's Prismatron system and high quality metal halide luminaires gives Woolworths big W the best of both worlds," says Venture's Keith Huxley. "Bright, white lighting with excellent colour rendering and dimmable control will allow the store to ensure a comfortable and effective lit environment for customers and staff, while optimising energy consumption," he adds.

Each pair of luminaires is connected to a remote Prismatron dimmable ballast which is linked to a Canalis bus bar system supplying mains power as well as an integral low voltage control wire. "The ballasts are connected to the control wiring using RJ45 connectors and the fittings use a plug and socket connection to the 230V mains supply," explains electrical contractor Bruce McFarlane of Albion Electrical(*SEE NOTE BELOW). "This arrangement helped to ensure a fast and simple installation, so the extra control element could be introduced at the same installation cost as a conventional Woolworths big W store," he continues.

The 0-10V analogue control system is supplied from the building's PLC control installation, which is a special system developed by Schneider Electric and provides a strong interface to the Prismatron system. The 230-volt supplies to the luminaires are provided via the multi-pole contactors located within the main switch panel. The trading area is divided into four zones of luminaires, each connected to a photocell mounted at the same 5.7m height as the undersides of the light fittings. The system is designed to provide high levels of lighting to ensure that the merchandise is displayed at its best. "During the trading day the 0-10V control signal provides a maintained average horizontal illuminance of 900 lux at 800mm and a vertical illuminance of 450 lux up to a height of about 1.8m," explains George Cunninghan of consulting engineers GW Building Services. "This is achieved without using the full light output of the lamps, so that as they age the output can be increased to maintain the illuminance levels," he continues.

Prismatron luminaires have also been used in the café area, and these are fitted with a blue acrylic decorative canopy to provide a coloured halo effect. They are mounted at a height of 3.9m and are connected to a separate control loop and are preset to approximately 75% of their output for the optimum decorative effect.

Taking control

Previous Woolworths big W stores had used high bay fittings with 250W metal halide lamps and simple on/off switching. As the Aberdeen store has a 10% glazed roof, there was scope to make better use of natural daylight and to significantly reduce energy consumption as a result. It has been estimated that the installation will save around 150,000kWh, amounting to a reduction in CO2 emissions of 64 tonnes per annum.

"During the trading periods of 08:00-22:30 the illumination level within the retail area is monitored by the photocells so that, as the level of natural daylight increases, the output from the luminaires decreases accordingly," says George Cunningham. "The BMS/PLC dimmable lighting system also monitors the illumination level continuously and provides an alarm function when the average illumination level falls below 800 lux for more than 120 minutes, as measured at the working plane".

This arrangement provides a great deal of flexibility in the space, as the luminaires are able to respond quickly to changes in daylight levels. "If it gets dark quickly, due to clouds overhead perhaps, the lamps will increase their output within a few seconds," explains Bruce McFarlane. "You could not do this with conventional on/off switching of metal halide lamps as they would require a warm-up period of up to five minutes," he adds.

Outside trading periods the illumination level is set to fall to 225 lux, providing enough light for cleaning and re-stocking of merchandise and generating a 35-40% energy saving during non-trading hours. Earlier stores had a similar arrangement but this was achieved by turning off half of the luminaires. "In the older stores, we needed two control circuits to switch off half the lighting, but at Aberdeen all of the lighting can be dimmed from one supply, so there was less installation of control cabling," notes Bruce McFarlane.

The building management system also provides an interface with the ADT Security system so that, when the security alarm is activated, the luminaires within the retail area are de-energised. When the security system is de-activated the luminaires are energised.

In the stockroom areas additional energy savings are achieved by linking luminaires to PIR occupancy detectors so the lighting is only activated when there is someone in the area.

Cost savings

The attention to detail within the design, combined with the innovative design of the PrismatronTM system from Holophane, provides cost savings in several areas to defray the extra cost of the lighting control system, so that a payback is anticipated within 18 months.

The use of 320W luminaires instead of the 250W used in other stores has enabled the required lighting levels to be achieved with fewer luminaires, thus reducing capital costs. In addition, by making better use of daylight penetration into the store, Woolworths anticipates a 50% reduction in energy costs for lighting. It is also expected that this will be combined with extended lamp life so that re-lamping cycles can be extended, thus reducing maintenance costs.

About Prismatron

Holophane's Prismatron™ system is a technological breakthrough with a fully controllable remote electronic ballast and prismatic glass high bay luminaire combination. The system is designed specifically for 320W, 350W and 400W metal halide lamps and was developed as a direct request from large end users, especially retailers where energy consumption is becoming a key issue when planning new store designs and refurbishment roll-out programmes.

The Prismatron™ system is kind to the lamp providing a less aggressive start-up to the arc tube prolonging lamp life and reducing ballast energy consumption. The operating characteristics of the Prismatron™ system also enable the lamp to generate up to 15% more mean lumens than a conventional lamp after 8,000 hours duty. This offers a significant saving in luminaire quantities when a maintained illuminance calculation is used as well as the added advantage of extending lamp life.

Client: Woolworths big W
Consulting engineers: GW Building Services
Lighting: Holophane Europe
Lamps: Venture Lighting
Electrical Distribution: Schneider Electric
Building Management System: Schneider Electric
System integration: Sitel