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When John Lewis asked Lateral Technologies to help create its most sustainable store ever, the mechanical and electrical design consultancy not only had to come up with a BREEAM outstanding design, but also find a way of ensuring the design lives up to expectation.

Paul Paterson, sustainability design manager at Lateral Technologies, explains, "Although the government has ambitious carbon reduction targets in place, John Lewis wants to go beyond this to reduce absolute carbon emissions by 15% across all its stores by 2020."

He adds, "Because the retailer is growing and adding new shops, achieving this target means the carbon emissions for new shops must be 30% less than similar existing shops. So when we were asked to help develop John Lewis York, a new £15m department store in Vangarde Shopping Park, we knew incorporating outstanding sustainability features from the outset would be a key priority."

At the same time, following on from work Lateral Technologies did to significantly reduce energy consumption across all the other existing John Lewis shops, both John Lewis and Lateral Technologies were keen to monitor the performance of the shop after it opened.

"All too often a good design fails to deliver the energy savings anticipated because of changes made during the construction phase or because occupiers don't know how to best control the building," explains Paterson. "Instead of waiting months for a higher than expected energy bill to flag up a problem, as is all too common practice, we wanted to find a way of continually analysing the building to identify any problem areas from day one."

THE APPROACH
Having gone through the arduous process of manually calculating energy use in the past, Lateral Technologies turned to IES, the world leaders in energy modelling. "The way IES is pushing the boundaries of modelling, from using higher levels of detail to optimise design at all levels, to automatically sending operational data back into the model, to deliver impressive levels of post occupancy evaluation, made them the perfect fit for us," says Paterson.

THE SOLUTION
A key part of the sustainability strategy was the use of displacement ventilation to condition clean fresh air at the occupied level. "Although the shop floor was five meters high, the modelling software from IES enabled us to split it into three zones: an occupied 0-1.8m zone, a stratified zone and a ceiling zone," explains Paterson. "By allowing us to focus on creating optimum conditions for the occupied zone, we needed less energy than for the entire area."

Critical to reducing the carbon emissions by 30% compared to similar shops was ensuring the chiller wasn't oversized. "Most designers can't model with actual building controls so end up having bigger chillers than they need, that cost more to run for lower loads," explains Paterson. "The Apache HVAC tool from IES enabled us to consider both the building and its controls to observe that a peak load of 550kw was needed, but only for 0.1% of the year. The model also revealed that the impact of allowing the internal temperature to drift very slightly upwards at those times, in the peak of summer, made next to no difference on comfort levels, allowing us to justify putting in a 450kw chiller, requiring 25% less energy than those in other stores."

Other energy saving measures include Photovoltaic (PV) roof panels to generate 4% of the store's electrical energy from a renewable source, building air permeability of less than 3 m3/(h.m2) and full LED lighting, requiring 40% less energy.

THE RESULTS
"The store achieved BREEAM outstanding in 2014 to become the most sustainable John Lewis shop ever built," says Paterson. "After setting out to achieve a carbon reduction of 30%, compared to the 2010/11 baseline created for similar stores, this store is currently expected to deliver a 35-40% betterment."

He adds, "Far from considering our job done, we're now using IES-SCAN, a new powerful IES tool, to import the actual building data back into the model, so we can continuously analyse the occupied building to quickly identify any performance gaps to deliver a soft landing. The level of detail provided by the model is incredible, enabling us to analyse how everything from the HVAC to the escalators to the catering equipment is performing."

He concludes, "The best thing about IES-SCAN is that instead of having to wait for a utility bill or spend days manually extracting data from the BMS, it lets us easily see which sustainability features are proving the most effective, helping us to decide which future improvements will have the biggest impact on the other stores."
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