It is, therefore, no surprise that the architects also took the opportunity to specify bespoke Monodraught Windcatcher natural ventilation systems. The importance of well ventilated, healthy environments for learning is supported by empirical evidence that the provision of fresh air through natural ventilation (and for that matter the provision of daylight using natural lighting) does promote learning and improves academic results. St Joseph's College is an independent, co-educational Catholic day and boarding school for up to 200 pupils aged from two to 18. Set in the grounds of Birkfield House near Ipswich, the 1550 square metre Primary Centre, which occupies the western corner of the college campus, was completed in September 2007 following a design competition that required the building to fire the imagination of pupils and instil in them a sense of fun.
The building also provides a clear statement of environmental intent by naturally ventilating the 125 square metre hall, a circular library and a series of interlinked shared spaces. The simple yet effective Monodraught Windcatchers specified are not only reliable and sustainable, but also highly cost effective when compared with air conditioning and mechanical ventilation systems.
Commenting on the system Greg Allen, facilities manager at St Joseph's College, says the Windcatchers have worked well since commissioning last year and are proving highly efficient. "While some minor adjustments have been made to the control settings to take account of ‘un-seasonal' weather conditions, the systems have regulated the internal temperatures without any outside assistance." He adds that the college is currently considering retro-fitting Monodraught Windcatchers to a hall on the main campus.
The current single-storey building was planned around a gentle curve with corner windows in the east-facing classrooms providing a strong visual link across the school. There are four class bases each comprising two classrooms whose rendered walls are painted in vibrant colours to establish a sense of identity between year groups. Located at the heart of the plan adjacent to the reception area is the ‘hub' a drum-like, double-height space housing the school library.
Naturally ventilating the building proved relatively straightforward in the classrooms using automatically controlled opening lights. However, the main inboard spaces comprising the hub, shared areas and hall posed a number of problems. The glazing used in the turrets and the hub precluded the use of opening lights and the area of glazing in the turrets was thought to be insufficient to provide adequate summer ventilation. Similarly in the hall, safety and security issues severely limited the use of windows, a problem that was solved by using the Monodraught Windcatcher systems.
The decision to use Windcatchers was taken for a number of reasons. First, the Windcatchers can be designed and sized to meet the exact needs of the individual spaces, without relying on elements such as opening windows and vents. Second, the system can provide night time cooling during the summer without compromising security by having to leave windows open. Third, the Windcatchers operate at comparatively low wind speeds, contain few moving parts, require little or no maintenance and are therefore inherently reliable. In addition, the Windcatcher system is a tried-and-tested solution, and Monodraught could be relied upon in terms of technical back-up and resourcing.
The roof-mounted "topdown' ventilation systems comprise a series of external louvres linked to internal turning vanes that are designed to catch the wind from any direction. The flow of fresh air into the building is controlled using a damper system fitted to the base of the unit. Warm internal air is expelled in the same way. The Windcatchers also incorporate anti-bird mesh and rain-trap louvers and were installed by Monodraught following completion of preparatory work by the main contractor.
The units installed in the two central shared areas are mounted on timber-framed ‘turrets' projecting four metres from the top of the flat roof. The original intention was to install a Windcatcher on each of the six turrets, but the high efficiency of the units required only one for each cluster of three towers. The Windcatchers serving the two remaining shared areas, the hub and the hall, are bolted to steel and timber aprons formed on the respective roof structures.
The control philosophy was very important, especially as the use of underfloor heating meant that too much warm air could be extracted during colder periods. The Windcatchers are controlled automatically using a combination of temperature and carbon dioxide sensors mounted on the walls (away from direct heat sources) at heights of approximately 1.5 metres from the floor. The readings from the sensors determine the amount by which the dampers are opened or closed.
In summer the dampers begin opening at 16°C and continue to open by increments of 20 per cent with each additional degree rise in temperature. At midnight the dampers open fully for night time cooling, which purges the building of stale air while cooling the structure and fabric to well below daytime temperatures. The dampers are programmed to automatically close if the internal temperature drops to below 16°C. In winter, the dampers are either closed or set to five per cent open to provide trickle ventilation.
Regarding CO2, if levels rise above 1500ppm the dampers open to 40 per cent for 15 minutes and then close for 30 minutes with the cycle repeated until CO2 falls below 1400ppm. Manual overrides allow staff to fine-tune comfort levels and the facility is linked to a timer, which re-sets the system to its original position after a specified period.
