Brambletye, a leading day and boarding preparatory school for children aged three to thirteen, occupies a large country house set in its own 140 acre wooded estate in the rolling countryside of West Sussex. In order to increase its teaching capacity the school has recently completed a new two-storey classroom block housing three ground floor and four first floor classrooms, each fitted with a single Windcatcher natural ventilation system as part of an overall Monodraught natural ventilation strategy.

The school’s board of governors, which worked with architects Hazle McCormack Young and building services consultants G K Salter & Associates, was conscious of the need to provide well ventilated classrooms that would create a natural working environment for its pupils, whilst also considering the long term implications of energy consumption, the school’s carbon footprint, and the on-going need to minimise potentially costly maintenance.

Following a thorough review of options ranging from the simple opening of windows to mechanical systems and heat exchangers, natural ventilation was chosen because it best met the requirements of the building bulletin and part L2 of the building regulations.

Roof mounted and designed to operate with virtually no moving parts, Monodraught Windcatchers use established atmospheric principles and the natural effects of the wind to bring fresh air into the building and extract stale warm air, using only natural forces. Warm air rising to roof level decreases the air pressure within classrooms, allowing cooler air to enter via the Windcatcher units.

The resultant change in pressure produces sufficient airflow to make the space comfortably fresh. Wind blowing onto the windward side of the ventilation stack increases the through-put of air and with the assistance of negative pressure on the leeward side of the Windcatcher, encourages stale air to be extracted through the stack’s leeward side. Opposed blade dampers, whose ventilation rates are controlled by temperature and CO2 sensors, precisely control airflow through the system. At night they can be programmed to open fully, providing a downwash of cool air to purge the classrooms, leaving the interior feeling fresh and clean for pupils and staff the following morning. A lower-limit sensor ensures that classrooms are not overcooled.

Architect Bryn Warlow and consultant Geoff Bradley, who both have previous experience of Monodraught natural ventilation systems, accept that unlike the older school buildings, the new classrooms are sealed against the elements, which is why automatically controlled natural ventilation systems, regulated by rises in either temperature or CO2 levels, now play an essential role in modern education buildings, such as building schools for the future.

Based on the air movement calculations, Monodraught recommended the size and type of Windcatcher. In all, seven roof-mounted 600mm square Windcatchers were installed together with separate Monodraught iNVent control systems for the ground and first floors. Monodraught also supplied special ducts that enable the Windcatchers natural ventilation to be channelled through the first floor to the ground floor below.

Commenting on the completed building, headmaster Hugh Cocke said, “The Monodraught natural ventilation system creates a healthy working environment for pupils and staff; and the Windcatchers themselves stand as a modern interpretation of the many older chimneys that are a feature of the original country house.”