How did M&S’s team get their sustainable store in Cheshire Oaks to perform even better than intended?
Decades of work, from Bill Bordass’s groundbreaking ‘PROBE’ assessments of completed buildings, to the Usable Building Trust, the Carbon Trust, and now the Technology Strategy Board, show that buildings don’t perform as the designers intended.
There are a myriad of reasons for this, including energy prediction tools which are inaccurate because they don’t take into account local climate conditions, don’t calculate the benefits of thermal mass and aren’t ‘dynamic’. In addition many clients are reluctant to pay extra design fees for dynamic simulation models so buildings are often not modelled in a thorough way. And value engineering (removing important kit that makes the building perform well), poor commissioning and modifying the building’s uses can also have an impact.
But having just completed 12 months of monitoring Marks & Spencer’s sustainable store in Cheshire Oaks near Chester, one of the lessons learned is that energy design targets can be met and - in this case - exceeded if the team work together, use proven technologies, keep things simple, and keep an eye on the detail.
In this case all this was done for no additional whole life costs.
The M&S store performed 21% better than the energy predictions and 40% better than comparable stores, without compromising the quality of the environment. So why was the energy consumption so good? I picked out four key lessons.
There was a collaborative spirit within the team which included the designers, contractor, some suppliers, the store manager and the M&S technical team. This mixed skill set resulted in richer, more diverse outcomes. The team also had clear targets from M&S Plan A.
The building set out to have a very efficient fabric, with good use of passive design and U-values which on average exceeded building regulations by 45%. It makes use of natural daylight, reducing the need for artificial lighting, improving the wellbeing of the staff and customers that use the store (22% increase in staff satisfaction compared with benchmark and 18% in customer satisfaction). The air pressure test and thermographic survey showed just how well the building performed, exceeding the building regulation requirements by 70% with a result of 2.93 m3 / h m2 at 50 Pa (the metric, for those interested, is m3 of air, per square-metre of the building’s envelope, per hour when there is 50 Pascals differential pressure between inside and outside the building).
Both these tests make it very obvious when a building is not performing and design teams and contractors should take note about the repercussions which can be expensive and disruptive to fix. On the project particular attention was paid to detailing to minimise cold bridging, meaning that during winter the building lost just 1 degree C during the 10 hours the heating was switched off over night.
Efficient services – heating, cooling, lighting
The team used proven technologies to heat and cool the store with the use of displacement ventilation to provide an even distribution of temperature across the whole building. The integration of heating and cooling into the one system prevents heating fighting cooling and the system is able to utilise free cooling for on average 60% of the occupied time. Refrigeration cabinets utilise heat recovery as well.
The 15 minute data feeds, broken down by an extensive amount of submetering (52 submeteres in total) mean that monitoring the consumption by end use is good so problems are quickly identified and resolved.
Sean Lockie is director of sustainability at Faithful + Gould