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Green grocers

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Can a supermarket be green? Tesco's new store in Tramore, County Waterford suggests that, at least in terms of the building it’s housed in, the sky’s the limit. Jason Walsh visited a building which meets passive house standards and demonstrates impressive attention to sustainability throughout its design

Among the eco-conscious, supermarkets don't have the greatest reputation in the world. Somehow issues of energy efficiency have been conflated with other concerns such as organic food, fair trade, food miles and the rest. Of course, all of the above can be seen as political issues, or they can be seen as technical issues.

Just as today's supermarkets have made great strides into so-called 'ethical shopping', so has Tesco invested in energy efficiency.

Michael McNerney, Tesco Ireland's energy manager, says that the supermarket chain is serious about energy efficiency: "There's a certain amount of healthy suspicion about this being a publicity stunt – actually it's the culmination of a policy we've had since 2006 here in Ireland and in the UK since 2005."

On one level this is unsurprising: Tesco already has a reputation for efficiency in other areas of its business so why would things be different? It is in Tesco's interest as a business to be energy efficient – waste costs money. On the other hand, the Tesco store in Tramore has gone further than normal: the building was designed and built to the passive house standard.

McNerney is keen to stress that Tesco does take energy use seriously: "Everything, other than the passive house, we've already been doing in our stores. In our new store in Celbridge, County Kildare, we already had a lot of these technologies and developments."

For McNerney, using the passive house design specifications was straightforward: "Passive house is essentially about designing a structure and having it highly insulated so it requires minimal heating, [while] minimising the amount of openings so that air infiltration is minimised."

Air infiltration is always going to be difficult to minimise in a commercial building such as a supermarket – after all, customers coming and going means doors that are frequently open. Tesco has come up with a way of dealing with this without expending massive amounts of energy: an air-curtain.

"We designed a special porch with automatic doors [leading into the porch] and an internal air-curtain [leading into the store] which operates as a barrier," said McNerney.

In order to avoid wasting energy, the warm air used by the air curtain is generated by the store's combined heat and power unit (CHP).

Interestingly, the decision to build the store to passive house standard came quite late: "The business decided they wanted an eco-store – a statement store," said McNerney. "This happened after planning."

This resulted in cost and planning challenges that Tesco overcame by putting together a design group: "We were lucky that someone had the wit to get everyone together," laughed McNerney. "We had clear ideas about low energy [design] but our architect suggested the passive house concept. After some scepticism we came to decide we could do it."

McNerney accepts that a passive house supermarket is a curious idea, but he is adamant that it is a good one: "Passive house might seem rather strange for a supermarket but we've been air-sealing our buildings for years for a number of reasons including the fact that somebody found out that keeping humid air outside results in the refrigerators working more efficiently.

"When our architect suggested passive house we realised we were [already] part-way there. Building regulations ask for an air-leakage rate of ten cubic metres of air [per square metre of floor area] at 50 pascals. We score three cubic metres regularly on our normal projects.