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Strength in numbers

Eleanor Young

Closing the gap between designed and actual energy use is one of construction’s biggest challenges. The CarbonBuzz databank could be the honeypot that makes it possible

If your building used more than one and a half times the energy it was predicted to would you be surprised? Perhaps not. Recent figures suggest that buildings are regularly missing their energy targets by this much. One of the biggest failures of the construction industry over the last decades has been to deliver buildings that perform as they were designed to. Despite collaborative working, an increasing understanding of building physics and, more recently, the advent of BIM, there is still a yawning performance gap. In recent years Bennetts Associates has been very honest about the way the performance of its sustainable flagship Wessex Water Headquarters has been affected by an unfortunately unpredicted IT loading in use (RIBAJ May 2009, p66). But few dare to be so candid, fearing litigation and reputational damage. 


Educational buildings are using nearly double their predicted amount of electricity a year and nearly one and a half times the heat

Data sharing

Evidence of the enormous performance gap comes from an analysis of figures from hundreds of projects uploaded to the Carbon Buzz. This is an online tool for live benchmarking which attempts to take the stigma out of sharing information on performance monitoring. A collaboration between the RIBA and the Chartered Institution of Building Services Engineers, it was relaunched in its all-singing, all-dancing form last year. It puts designed and actual energy use side by side, the first garnered from existing documentation, the second from the real energy costs (using the same methodology as Display Energy Certificates). Uploading a project is anonymous, although helpfully there is a bundle of fairly recent case studies on the website. This data on CarbonBuzz gives practices a clear and standard way of evaluating their building’s designed versus actual performance, an idea of where they sit in performance for that building typology and in relation to the CIBSE benchmark for it. 

More widely, it offers a chance for a body of knowledge to be built up and analysed by researchers. The Bartlett’s Energy Institute is on the case and so far has produced around 10 papers based on its data. The latest summary of data details the disparity between design and performance in offices and education buildings in particular. Educational buildings are using nearly double their predicted amount of electricity a year (106kWh/m2/yr against design predictions of 56) and nearly one and a half times the heat (see table opposite).  Interestingly, Aedas’ Judit Kimpian, a prime mover behind CarbonBuzz, notes that it doesn’t seem to matter whether the design predictions have been based on Building Regulations method based calculations or on a full energy model – the gap was still the same. ‘People seem to be reverting to compliance with Building Regulations,’ she speculates. She is now working on an extra layer for the platform to make it easier to calculate accurate predictions in the first place. Look out for this in September. 

Prioritising performance

CarbonBuzz is supported by the Technology Strategy Board, the government’s innovation agency. Throughout 2014, dealing with construction’s performance will occupy much of the time it spends on the built environment. It has formulated a series of challenges: design and decision tools that show performance when built and usage patterns of occupiers; the management and operation of buildings; and materials and components and how to ensure they perform better. It is no surprise that many TSB-funded projects have their data on the CarbonBuzz platform. 

Nor is it any surprise that some of them have entered the CIBSE Building Performance Awards, due to be announced on 11 February. With categories covering training, products, contractors and clients it aims to look at many of the ingredients in a well performing building. Its new build and refurbishment shortlists showcase some of the trailblazers in post occupancy assessments, sustainable design and, ultimately, building performance. Some clients, typically those with most to lose on energy bills – and those used to evidence-based process improvement – are forging ahead to measure performance, such as Sainsbury’s and M&S. Schools and, of course, the Olympic Development Authority – which commissioned the London 2012 Velodrome – have cost savings and, perhaps, common good driving them. 

Below we profile two CIBSE-shortlisted retail projects with a look their operational energy use and at how they are trying to bind users more closely with the operation of the building. We also examine how one shortlisted primary school is attempting to make a difference. These are the projects that get near to closing the performance gap. We just need a few thousand more of them.

Sainsbury's, Hardwick Place, King's Lynn

‘Nothing we do in this team is green wash, we believe it is going to add value,’ says Sainsbury’s head of sustainability, energy and engineering, Paul Crewe. ‘We want to trial technologies and processes and if they are proven right we adopt them and make them part of our DNA.’ 

The new 72,000ft2 store at King’s Lynn was designed, with CHQ Architects, to use 50% less carbon than a store of a similar scale built in 2005/6. As measured in operation it actually used 60% less. Heavily insulated cladding panels meant 30% less heat was needed in store, on the roof 1000 photovoltaic panels supply 5% of the store’s electricity (when the sun is out) while solar reflectors bring in daylight, and LED lights were used where possible. Mains water use was cut by 50% thanks to rainwater harvesting, time control taps and water efficient equipment.

Crewe is most proud of the ground source heat pump: unusual in retail, he says, but working brilliantly now it is integrated in the refrigeration system, harvesting rejected heat and ensuring the system operates far more efficiently. ‘This has become an intrinsic part of store design,’ he says. The pumps are now running at 12 Sainsbury’s stores, including three which have been retrofitted with what he describes as pioneering drilling methods. This is where the focus will be in the next year, the retailer’s ‘graphite programme’ investing tens of millions in cutting existing stores’ carbon use. 

‘King’s Lynn is historical now,’ says Crewe. The target is to reduce absolute carbon use by 30% by 2020 against a 2005/6 benchmark. It’s not easy – made harder by a 30% increase in square footage since then. In Leicester, last November, 81,700m2 of store opened tagged with a ‘Triple Zero’ label, designed for zero carbon in operation (including use of a farmer’s biogas in its combined heat and power system), zero water (including the use of local offsetting in the same catchment) and zero waste. We will have to wait for the operational figures. 

M&S Cheshire Oaks, Cheshire

Plan A has proved a great statement of sustainable intent by M&S. In line with that, the Cheshire Oaks sustainable learning store was designed by Aukett Fitzroy Robinson to be the most carbon efficient, biggest green M&S store to date. It incorporates strategies that address several areas of sustainability at once including energy, water, waste, biodiversity, community and materials. The store was opened on 29 August 2012, and for the first year of its operation Faithful+Gould carried out an independent evaluation of the performance of its environmental features, while University College London assessed their social impact. Highlights of the findings are below.


Montgomery Primary School, Exeter

Helped out by a Zero-Carbon Task Force grant and match funding, Montgomery Primary School, designed by NPS, is based on Passivhaus principles – and certified as such. The most important aspect of the building, over its lifetime, was considered to be a reduction in carbon emissions during operation so whole life costing was essential. Orientation, high thermal mass, sustainable materials, reduction of construction waste and climate readiness (for 2080) were all critical to the design.

Extensive thermal modelling in IES:Virtual Environment was used to test the concept and when it came to details Warm Consultants also provided cold bridging modelling. The extensive building modelling undertaken has fairly accurately predicted the energy and comfort requirements of the building in use. The prediction was for 32kg CO2/m2/yr and the CarbonBuzz figures for meter readings show it performing at 33 (well below the CIBSE benchmark for schools of 50). 

An energy saving lighting strategy was a key element from the early stages. To reduce lighting energy consumption, room reflectance was considered early and materials with light colours and high reflectance were specified. This allowed lower lumen light fittings. Absence detection and daylight dimming were used in class areas – requiring manual switching to turn the lights on (allowing teaching staff to leave the lights switched off until needed).  Manual dimming has also been provided to all classrooms.

Joining up construction and use through commissioning and handover was smoothed by BSRIA’s ‘Soft Landings’, along with an extended commissioning period as specified in the contract. Through Soft Landings and follow up visits with school staff, the design team, client and contractor have worked together to identify and resolve many items to reduce energy consumption and improve the overall operation and client satisfaction. The whole of its first five years are also under scrutiny from Exeter University.

Credit: Girts Gailans
Internal Management
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