Manchester College of Art and Technology

Active rainscreen cladding made up of solar photovoltaic cells is a prominent feature on this award-winning development.

For generations of Manchester citizens the imposing Victorian public baths at Harpurhey were a local landmark. The Grade II listed structure finally closed in 2001 after serious structural defects were discovered and judged to be uneconomic to repair. In 2004, however, work began on an imaginative redevelopment of the site, aimed at providing new facilities for the Manchester College of Art and Technology (MANCAT). Part of the original building has been retained, with the potential for an alternative reuse. A new three-storey 5,000 m2 building alongside provides a home for the North Manchester Sixth Form College and North City Public Library; one that uses the latest microgeneration and energy saving techniques to minimise its carbon footprint.

From the outside the most distinctive feature of the £7.1 million building is the blue wall of polycrystalline silicon photovoltaic cells that dominates the southern façade. A total of 482 SHARP 80 W modules are used, backed up by a further 238 SHARP 165W modules mounted unobtrusively on the extension's flat roof. Together these total some 720 m2, which can generate a maximum of 76 kW, and which are capable of producing more than 43,000 kWh annually - a saving of at least 18,000 kg of CO2.

Such a large array might seem hard to justify economically. However, a high quality building façade would have been specified in this particular location anyway. Integrating the cladding and electricity generation functions into one component makes the case for solar PV even more persuasive. Advantage is also taken of the heat-generating properties of the PV array, which has to be cooled to keep it operating at maximum efficiency. A 200 mm void between the cladding and the main wall of the building is intended to create an effective solar chimney, with air drawn in across internal spaces and out through louvres in the wall behind the cladding gaining heat from rear of the cells and rising up to roof level vents. This void also serves to reduce solar gain within the building during the summer months.

Solar gain through the west-facing atrium glazing is managed by an array of three cylindrical windcatchers above the main entrance, which boast mechanical dampers controlled by the building management system. In the warmer months these windcatchers

Technology Behind Solar Chimney

MANCATat night (Reproduced with permission from

Facade Solar Cladding

Solar cladding replaces more conventional alternatives (Reproduced with permission from

draw cool night air into the building through courtyard windows; air that is circulated over the exposed soffits of the concrete floor slabs, cooling them ready for the following day. Thanks to this use of the building's thermal mass, no conventional air conditioning is considered necessary.

Insitu normal density concrete was the preferred option for the building's structural frame. Floor slabs 300 mm thick span between exposed columns at 6,750 m centres. This high thermal mass is boosted by block-and-plaster internal partitions and coupled with unusually high levels of insulation. High-performance structural glazing with a typical U-value of 2.2W/m2K forms much of the Library Block's external skin. External cavity walls feature a 100 mm rendered normal density concrete block outer skin, a 162.5 mm cavity with full fill mineral wool insulation, and an inner skin of 140 mm plastered normal density block. This yields a U-value of only 0.22 W/m2K. Beneath the single ply membrane roof there is cut to falls mineral wool insulation, and U-value is 0.25 W/m2K. Air-tightness is 5.4m3/hr/m2, as against the 10m3/hr/m2 demanded by current regulatory requirements.

An indirect active solar thermal water heating system is used to supplement domestic hot water supplies. Solar heat from a roof-mounted array of evacuated tube collectors feeds a 350 l thermal store. A high-efficiency gas-fired condensing boiler is the main source of hot water, which is also used for space heating.

Rotex supplied the unusual German-developed heating system. Underfloor heating is used on all floors of the Library Block, based around a double skinned cross linked polyethylene (P-EX) pipe, with the inner surface of the outer skin ribbed to maintain a constant insulating air space between the skins. Water flowing through the pipe's core can therefore enter the system at a significantly higher temperature than with conventional underfloor heating systems, eliminating any need to blend in cold water to reduce the initial heating circuit temperature to safe levels. The network is supported on polymer 'system plates' and cast into the floor screed.

Although underfloor heating is very compatible with the water temperatures generally produced by microgeneration technologies such as heat pumps and solar heating, its safe

Roof-mounted modules supplement the PV façade (Reproduced with permission from

operating temperatures are normally well below that of the optimum operating temperature of modern boilers. With this system, however, the same temperature water also feeds conventional wall-mounted radiators in the Teaching Block.

Room has been found on the site for a large underground rainwater storage tank, which is used for cistern flushing. A very popular feature in the atrium is a panel that monitors the performance of the PV arrays. Readouts display the current output, the total output since the building opened in March 2006 - and how many years that total output would light an average three-bedroomed semi-detached house. This figure has now passed the 100-year milestone. The UK Department of Trade and Industry provided some of the funding for the PV installation, as part of its programme of demonstration projects.

Client: Manchester College of Art and Technology

Architect: Walker Simpson Architects

Structural engineer: Arup

Building services engineer: Operon

Solar PV supplier: solarcentury

Main contractor: Eric Wright Construction

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