Natural ventilation keeps out aircraft noise at Stockport

Natural ventilation with acoustic attenuation to minimise noise from aircraft passing overhead is provided for stockport academy by Monodraught Windcatchers

The provision of natural ventilation in the main hall and sports hall of a school beneath the flight path to Manchester Airport has been solved using Monodraught Windcatchers with additional attenuation. Both halls have windows of limited size and number, so it would have been virtually impossible to achieve the necessary levels of cross ventilation using opening windows alone.

To find a solution for the £24 million Stockport Academy, Aedas Architects worked closely with environmental engineer Buro Happold and Monodraught to develop a detailed natural-ventilation proposal using the British Standard Code of Practice for ventilation principles and DfES Building Bulletin 101 (‘Ventilation of school buildings’). As a result, Windcatchers were installed as one of a number of active and passive energy-saving technologies to provide natural ventilation in the 2095 m3 main hall and 6435 m3 sports hall, which can accommodate 740 and 150 people, respectively. They can also provide secure night-time cooling in summer.

Independent tests by BRE have shown that, on average, a standard Windcatcher reduces noise transmission by 15 dB compared to an open window. An additional 17 dB of sound attenuation was achieved with internal acoustic lining and fully integrated silencer pods.

Monodraught proposed a ventilation rate of 12 l/s per person in accordance with CIBSE recommendations. Monodraught’s analysis indicated that over 60 kW of heat gain would need to be ventilated form the main hall and over 20 kW from the sports hall.

Six Windcatchers were installed in the main hall to provide 10.5 air changes an hour and two in the sports hall to provide 1.5 air changes an hour. All are 1200 mm square and are designed to achieve the desired ventilation rate at a wind speed of about 2 to 3 m/s, well below the mean wind speed across the UK of 4 to 4.5 m/s. When there is little or no wind, air movement will still be created by the stack effect.

The Windcatchers are controlled automatically by the academy’s building-management system. During Summer, the dampers begin to open at 20°C and are fully open at 24°C

The dampers can be opened overnight but are closed if the internal temperature falls below 16°C.

In Winter, dampers are either closed or set to 5% open to provide trickle ventilation.

Manual over-rides allow staff to fine tune comfort levels and respond to unseasonable weather. The over-ride allows dampers to remain open for an hour before they revert to their pre-set positions.

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