Friday, 12 August 2016

Pulling together

In July 2014 the John Lewis store in York made history by becoming the first department store in the world to be awarded a BREEAM Outstanding rating – the highest category achievable under the BRE’s environmental and energy assessment method.This achievement was recognised at the 2016 CIBSE Building Performance Awards where the scheme won the Collaborative Working Partnership Award. Andy Pearson writes about the secrets to their achievements.

The path to the team’s success started two years earlier in 2011, when JLP announced its commitment to reduce carbon emissions from a 2010 benchmark by 15% in absolute terms by 2020. This is an exceptionally challenging target when you factor in that the business is growing and adding new shops. To help achieve its objective the business set a carbon reduction target for its new shops of 30% less than existing similar shops.

Inside York's award winning John Lewis store
In 2012, JLP approached consulting engineers Lateral Technologies & Solutions to develop a building services solution for its new mid-sized, flexible-format department store in York. This had a target carbon saving of 30% compared to JLP’s the flexible format Exeter store.

This fabric envelop of the 12000m2 York store was designed to be airtight to help the design team meet the carbon saving target by preventing heat and energy leaking through gaps in the building fabric. In fact, the building’s air permeability was later measured and found to be only 3m3/hr per m2 at 50Pa, three times better than the Building Regulations minimum.

To develop its building services solution Lateral Technologies joined with IES Consulting as its technology partner and building energy management specialist Next Controls.

The model showed that peak cooling was only needed for 0.1% of the year
Lateral Technologies used utilities information from JLP’s Exeter store as a benchmark for the new building and to inform the York store’s low carbon M&E design. The York store’s airtight building envelope enabled Lateral Technologies to develop a ventilation solution using an energy efficient displacement ventilation system serving the retail floors. Displacement ventilation releases fresh, cool air at floor level; as the air is warmed it rises, taking with it heat from people, lights and equipment before it is extracted at ceiling level. To save even more energy, the back of store areas also have the option of being natural ventilated.

A chiller cools the supply air on days when the outside air temperature is high. Lateral Technologies was able to optimise the size of the chiller because it modelled the store using Integrated Environmental Solutions’ Virtual Environment software. “At this stage we were using the HVAC module within the IES package, which allowed us to input the control strategies that we wanted to use to understand their influence on the plant sizes,” says Iain Gibb, managing director of Lateral Technologies & Solutions.

The software showed that the building had a peak cooling load of 550kW. Critically, the model also showed that this load was only needed for 0.1% of the year. It also indicated that if the temperature in the store was allowed to drift upwards very slightly at times of peak cooling, then a smaller 450kW chiller could be used. The exercise resulted in the installation of chiller that used 25% less energy to operate.

An energy efficient displacement system serves retail floors
Lighting was another area exploited by Lateral Technologies to deliver big energy savings. Front and back of store areas are lit using LED lighting, which uses 40% less energy than traditional retail lighting solutions. In addition, sun pipes (effectively mirrored tubes) bounce daylight from the roof deep into the space to reduce the need for artificial lighting. While in the storerooms presence detectors automatically turn the lights on and off.

A sophisticated Trend building energy management system (BEMS), complete with control strategies written by Next Control Systems, was installed in the York store to control the building services.

The team working really came into its own once the new store had opened its doors. A number of processes were put in place to ensure the team could work collaboratively and effectively together to prove that Lateral Technologies’ innovative building services solution was providing JLP with the 30% savings it was looking to achieve.

IES had recently developed IES-SCAN, a software solution created to take data from the building management system and to calibrate it with the design model. IES provided a secure server on which to host the data collected from the York store by Next Control Systems. Working in partnership with the two organisations allowed Lateral Technologies to extract information from IES-SCAN, via IES’ servers for use in its performance reports. The reports enabled energy used to be optimised by flagging up systems that were not performing as expected. “We input the actual performance back into our model to compare the actual with the theoretical so that we could understand how accurate our model was,” Gibb says.  

The actual results confirmed that the scheme was performing to within 3% of what the consultant had predicted. In fact Lateral Technologies design was so successful that the project exceeded JLP’s 30% target and Lateral Technologies expectations. “We’d predicted a 40% saving and the scheme actually achieved a 43% reduction in carbon,” says Gibb.

The plant room at the John Lewis store in York

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