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Cool concrete for clever brains

Manchester Metropolitan University’s newest building will be using a cutting edge concrete technology, which its manufacturers hope will bring down energy costs while adding to the city’s impressive skyline. Declan Lynch finds out more.

The new business school and “student hub” at Manchester Metropolitan University (MMU) is set to be the city’s flagship green building. It is split into three interlinking structures of four, six and eight storeys containing lecture theatres, seminar rooms and working spaces. Most striking will be the atriums in between them, housing multi-use workspaces.

Design of the £65M building has been driven by the university’s ambition to create a low energy building utilising thermal mass, natural daylight and controlled ventilation. Architect Feilden Clegg Bradley Studios developed it as a building of three elements: a base; a solid exposed concrete frame; and a glass veil.

Colour and finish

Visually the colour and finish of the concrete was of particular importance to the building, but the major technical challenge was to control the temperature of the exposed concrete at 20˚C. Controlling this has the knock on effect of self-regulating the room temperature between 21˚C and 26˚C, which makes huge savings on energy costs.

During the feasibility stage, consultant Aecom determined that it was possible to use an “open-loop” temperature regulation system using groundwater boreholes near to the site.

“Early contractor involvement enabled us to work with the supply chain to embed the water pipes”

David Firth, Sir Robert McAlpine

“We had to deliver a concrete structure which needed to perform to strict standards on cooling, structure and colour,” says contractor Sir Robert McAlpine project manager David Firth.

Sir Robert McAlpine won the contract in January 2009. It is working to a JCT 2005 contract with contractor design provisions.

“It’s a traditional contract with early contractor involvement with some design duties,” says Firth. “Early contractor involvement enabled us to work with the supply chain to embed the water pipes within the concrete structure.”

The contractor hoped to install a fully precast system with water pipes embedded and developed a number of options for the market.

Best option

After going through the tender process it decided that Hanson’s Coolslab system was the best option.
Coolslab is a development of Hanson’s Omnicore product, a precast floor panel which acts as a permanent formwork, using a polystyrene void former and insitu concrete topping. The precast panel contains the all important pipework.

Hanson worked with cooling and heating systems developer Velta, which has seen is products used widely across Europe. Velta is an expert in Thermo-Active Building Systems (TABS), which are effectively plastic pipes embedded in a building’s structure.

Installing water pipes in concrete is not new; engineers have been trying to do it since the 1930s using steel pipes, but without success.

The technology has been much more successful in the past 10 years, using plastic pipes.

Water running through the pipes cools the concrete, which then absorbs heat energy during the daytime, before releasing it at night. This cycle helps to moderate temperature fluctuations in a building.

Convincing clients

Hanson is pleased with the product, but is conscious of the need to convince building clients.

“Knowing it’s a good product doesn’t mean it’s going to sell - the MMU project focused our minds,” says Hanson floors and precast division managing director Gerry Feenan.
Management of expectations is required though. “It’s not air conditioning, it’s a conditioning system,” adds Gerry.

For MMU Sir Robert McAlpine and Hanson developed a bespoke 1.5m wide slab with an overall depth of 475mm spanning 12m.

“I’m sure Hanson would prefer a 1.2m slab width [standard slab width] but it fits perfectly with the grid set by the architect,” says Firth.

The TABS pipes were embedded in the slabs at the Hanson factory, offering the benefits of controlled conditions and time saving during the construction phase. However, it did present challenges in the factory.

“We brought the Velta team into the factory to help with the installation,” says Feenan.

Once on site the slabs are checked and craned into position. Tolerances are tight with
a 6mm margin of error over a 1.5m length.

The joints are propped underneath to achieve a 10mm positive camber, as engineers had calculated a maximum 20mm sag due to self weight.

The biggest operational issue is connecting the pipes to the centralised chilled waterflow and return pipework.

So as not to compromise floor space a termination box housing pipe connections between the precast slabs was installed within the floor slab. Velta designed a box to be flush with the floor and to withstand the floor loading, which was sealed and pressure tested.

Steel fixers

Once the termination box was installed, steel fixers installed reinforcement and 7,500m2 of concrete was poured and cured.

As with all exposed concrete surfaces the colour is very important. After much deliberation the contractor settled on using 35% white concrete, which gives the required soffit colour.

Although the superstructure is virtually finished it’s not a case of job done for Firth and his team. “My biggest worry is one of the contractors drilling too far into the slab and bursting one of the pipes,” he says.

“I’ve free-issued a Hilti drill bit of the correct length to each of the contractors on site which should prevent it, and if they are not using it they will be moved off site.”

MMU will be unveiling its newest building next year.

Climaspan option

Creagh Concrete has unveiled its version of a Thermal Active Building System (TABS). Creagh’s Climaspan incorporates embedded Pex-A pipework from Velta - a specialist in the TABS system.

Creagh’s Climaspan product is a factory produced precast slab with pipes connecting to an aquifer below the building site.
Creagh has teamed up with Vinci to install the renewable energy system for heating and cooling at Vanguard House at the Daresbury Science and Innovation Centre in Cheshire. It uses a ground water pump to extract cool water from a 120m deep borehole.
The new 3,300m2 office space uses the technology to help drive down energy costs and is due to open next year. It is hoped that the building will get an “excellent” BREEAM rating.

Project facts

Cost: £65M

Client: Manchester
Metropolitan University

Architects: Feilden Clegg
Bradley Studios

Contractor: Sir Robert McAlpine

Subcontractor: PC Harrington

Structural engineer: WYG

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