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Energy efficiency Supermarket case study Greening the aisles


In the second in a series of CIBSE-sponsored building-performance case studies, John Field and Alexandros Balaskas look at whether a ‘green’ supermarket is saving lots of energy – and what can be done to improve its performance


I


n August 2008, the supermarket group Sainsbury’s opened a new ‘flagship’ green store in the UK. The outlet in Dartmouth, Devon, received a BREEAM Excellent rating for its environmental features, and


a grade D score on its display energy certificate (DEC), which is based on metered energy usage. Following the opening, Sainsbury’s said that most of the energy- saving features from Dartmouth would be replicated in other new stores, as part of plans for a 25% cut in CO2 emissions across its stores by 2012. But, two years later, how has Dartmouth performed


as a ‘green’ building? In order to learn lessons from the store’s first full year of monitored operations, an up-to-date assessment of the efficiencies of its building services installations was recently commissioned by CIBSE as part of the institution’s ongoing programme of investigations into real-life building performance. The assessors from energy management consultancy,


Power Efficiency, reviewed energy data monitored at the store, and they found that the store has indeed performed well and that there was more that could be done to reduce energy consumption – and within identifiable payback periods. Power Efficiency was able to provide detailed recommendations for improvements, which Sainsbury’s is now considering taking on board. For CIBSE, the lessons learnt will provide key insights for both energy assessors and the wider engineering community involved with such green-building developments.


Energy consumption Metering arrangements at the store comprise one half- hourly energy meter for imported electricity and several sub-meters dedicated to metering the HVAC, wind turbines and refrigeration consumption respectively. Energy metering data is uploaded to the supplier’s web portal and can be interrogated remotely by Sainsbury’s


44 CIBSE Journal October 2010


engineers at its London headquarters. The sub-meter information is remotely read using the company’s internal IT network. Recorded energy costs for the store in 2009 were £72,800, comprising £66,500 for electricity and £6,300 for wood pellets (for the biomass boiler). Energy supplies were 201,000 kWh from wood pellets and 1,019,000 kWh of electricity including 95,000 kWh of on-site electricity derived from wind turbines. The actual emission figure of 173 kg CO2/sq m illustrates that the Sainsbury’s store performance was 17% better (lower) than the DEC benchmarks (207 kg CO2/sq m), but this would improve further to 24% better than the benchmarks if the bakery and server room could be separated off.


Installations Wind turbine: energy is generated on-site by two 6kW rated output wind turbines reducing the amount of imported electricity. Metered electrical energy generated in 2009 is reported at 95,044 kWh, representing around 10% of the store’s total electricity consumption. Cooling: the main issues affecting energy


consumption at the site are refrigeration and the air conditioning units. The air conditioning systems are


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