Under the skin

It’s been two years since Jaguar Land Rover’s £100 million factory on the outskirts of Wolverhampton started production, but it’s only now that it seems to be reaping the benefits of its design. Built to construct over 450,000 engines a year for the firm, the 185,000m² BREEAM Excellent facility, designed in two phases by Arup Associates, recently scooped CIBSE’s Project of the Year Award in its Commercial/ Industrial category – an accolade based on the buildings’ democratic design, sustainability considerations and monitored performance in operation.

JLR took on Arup Associates because it wanted a showcase facility that – as it claims about its new engines – would exemplify a commitment to performance and the environment. JLR felt the ‘one stop shop’ service that Arup offered them would best help to achieve the objective. Key to this was excellent building fabric performance and the adoption of low and zero carbon technologies, along with a comprehensive energy management system. Here, offsetting the highly conditioned nature of the factory floor, are naturally ventilated, daylit office and social spaces, extensive grey water recycling and the largest PV array on a UK building, providing enough energy to power 30% of the facility. The factory is a benchmark for industrial buildings and was the standout winner of the award.

The accolade was partly due to Arup Associates’ strategy to integrate production and administrative functions. ‘Most factories have no connection between blue and white collar workers, so we wanted to change that by connecting the assembly halls and machine rooms with admin and reception areas to allow views through from one to another,’ says Arup Associates project architect Sean Macintosh. ‘They’re broad moves, but they’re done at scale so they’re impressive for that reason,’ he adds. 

Since the cost of the building is dwarfed by the cost of the production line technology, it’s no surprise the design was predicated on its demands. That accounts for the 30m column spans, which allow room for the production line kit and carry the massive steel Vierendeel trusses that form the distinctive saw tooth roof that defines the elevation. Macintosh says Arup initially considered a number of curving roofs but with a risk-averse the client, it settled on the ‘tried and tested’ saw tooth profile, its north-facing roof lights allowing light to pour onto the factory floor. 

In an effort to keep costs down, Arup went for off-the-shelf systems discreetly brought together. For elevations to the assembly and machine halls, the firm went for a standard Euroclad Europanel vertical joint insulated panel system in Prisma, interspersed with recessed panels on the roof gutter line in Anthracite. ‘We really liked the rhythm the huge monopitches created,’ Macintosh explains. ‘But were interested in the recesses between them as a scaling device to give a sense of elevational  hierarchy and articulation – as well as co-ordinating with the overflows to the symphonic roof drainage’. Proprietary systems, he adds, were vital to stay within budget: ‘Prefabrication was all for both walls and roof; we wanted to ensure the financial argument was strong enough to ensure elements didn’t get value engineered out when it went through the D&B mill.’

But within that demand the objective was also to see how well they could make the fabric perform. Given the high energy demands of the building, the reality was that standard facade systems would yield ‘diminishing returns’ in terms of performance; so where it could, Arup looked to using innovative systems that offered greater energy savings per square metre. It was interested in the pioneering use of the customised building facade Colorcoat Renew SC Transpired Solar Collectors. Developed by Tata Steel and University of Swansea’s ‘Specific’ Institute, the system of ‘solar cladding’ combines a double-skinned envelope to pre-heat air with ventilation fans that draw it into the building and use it to offset the internal heating load. Because of the ventilation demands of the staff areas in the spine building on the west side of Phase 1A of the development, it was decided to employ the Colorcoat Renew SC here, as the pre-heating of make-up air would significantly affect its energy consumption. 

While the most visible element is the external steel skin, the real magic occurs in the cavity behind it, an area fed by special perforated collector panels on the cladding surface. With the skin heated by the solar radiation, and ventilation fans creating negative pressure in the air cavity, solar heated air is drawn in via the surface perforations. The design of this and the framing system behind it not only controls the amount of air flow passing into the cavity, it also maintains a consistent draw across the surface and ensures that cooler air beyond this heated boundary is not introduced into the air stream. 

The warmed air is then drawn off at high level and ducted into the building via a connection to the HVAC intake. Tata Steel claims that, with air entering the building at a temperature of 16-38°C, the system reduces or even eliminates conventional internal heat load during the day. At JLR, the system was installed on the south spine wall of Phase 1A, the pre-heated air fed into the HVAC air handling units for the banks of changing rooms. The south facade produces optimum performance and here could accommodate the collector sizing of around 120m² – a factor of the air volume intake and the expected temperature uplift. This spine building was also operational 24hours/day and offered the best opportunity to make best use of free heating. Overall the Colorcoat Renew SC system aims to generate CO2 savings of 1 tonne per 5m² of solar collector. It must be working: Arup Associates’ Macintosh says its performance here encouraged it to specify it in the subsequent phase of the factory’s expansion.

Aside from the facade, to raise the EPC rating from the design brief up from ‘B’ to ‘A’, Arup Associates looked to the roof; where in all, the firm installed an array of 21,000 photovoltaic panels generating a peak capacity of 5.8MWp and with an eight and a half year payback. Producing savings of over 2,000t CO₂/year, it’s understood, says the firm, to be the largest rooftop installation in the UK.

Rowan Crowley, managing director of CIBSE Services and chair of the judging panel, who awarded the building its ‘Best in Category’, says the completeness of the submission was what swung it for the firm, calling it a ‘a thorough and detailed evaluation that was soundly based in engineering’. Additionally, the whole building had been modelled in BIM to the extent that the model formed part of its operation and maintenance manuals. ‘BIM seems to remain a somewhat fractured process in the industry,’ says Crowley. ‘Here it was used not just to co-ordinate the building to look good and perform well technically, but to connect it all the way through to the facilities management strategy on the client side. It was great to see this achieved.’