Lateral Technologies & Solutions Closes The Prediction Gap
CIBSE Journal tells how using dynamic simulation modelling to accurately predict performance has enabled Lateral Technologies & Solutions to cut energy use significantly at a new John Lewis store in York.
Detailed modelling of the store – which is situated in the Vangarde Shopping Park – has helped to cut carbon emissions by 30%. Key to these CO2 savings was the chiller, which requires 25% less energy than those used in equivalent stores. It was specified by Lateral Technologies, which used IES modelling tools to predict the building’s performance.
Paul Paterson, sustainability design manager, says the IES Apache HVAC tool gives Lateral a good prediction of a building’s energy requirements, because it integrates building controls into the design model. ‘Most designers can’t model with actual building controls, so end up having bigger chillers than they need, which cost more to run at lower loads,’ he says. ‘The sizing of large central chillers tended to be based on ‘steady state calculations’, where the impact of controls had not been taken into account.’
Using the software, Lateral calculated that the store would require a 550kW chiller, but only for nine hours – or 0.1% – of the year. The designers modelled the store’s thermal conditions with a 450kW chiller, and discovered it was possible to downsize without affecting the comfort of customers and staff.
‘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 to comfort levels, allowing us to justify putting in a 450kW chiller, requiring 25% less energy than those used in other stores.’ Paterson’s team took into account that customers are likely to wear lightweight clothes on warmer days, making it possible to allow internal temperatures to edge towards 26OC at their summer peak.
While the Apache software allowed Lateral to improve energy forecasting and close the prediction gap, the use of another IES tool is helping to close gaps in performance. IES-Scan allows Paterson to import actual building data into the model, enabling the team to identify any issues with the systems, and to adjust the equipment accordingly.
‘Instead of waiting months for a higher-than-expected energy bill to flag up a problem, we wanted a way of continually analysing the building to identify any problem areas from day one’ says Paterson.
This is the first time John Lewis has used IES-Scan to enable a soft-landing, adds Paterson. ‘Everything is metered – from the HVAC and escalators to the catering equipment – and it’s fed back into the model.’
By constantly refining the design model, Lateral can better predict the design needs for future John Lewis stores, so they can ensure equipment is not oversized – which means lower capital costs and minimal material use. ‘We can make savings because we know what the demands are – we will be able to reduce central plant and pipe sizes,’ says Paterson.
IES-Scan also includes data profiles for occupancy, which could be plugged into future stores. ‘Measuring occupancy is useful for hot water,’ says Paterson, ‘as it means you can predict how much storage you need.’
Mark Gifford, consultancy development manager at IES, believes the use of tools such as IES-Scan will become commonplace as more contracts demand performance guarantees. ‘It’s all about visibility. A contractor might guarantee it will make you savings, so you need to find out whether their energy saving device is delivering.’
For a property owner such as John Lewis, being able to model its buildings accurately offers significant benefits, which are already being seen by the amount of CO2 saved at the York store. After setting out to achieve a carbon reduction of 30% – compared to the 2010/11 baseline – the shop is expected to deliver an impressive 35-40% reduction.