Chimney feats

M&E contractor Drake and Scull has just finished work on a new 12 000 m2 library and learning resource centre for Coventry University. A central tenet of the design strategy for the building, which will provide research and study facilities for over 17 000 students, was the need to be energy efficient and low maintenance. Out goes air conditioning and in comes natural ventilation.

With a noisy site, openable windows for the ventilation are a no-no. Extensive modelling was carried out using computer-based fluid dynamics models to look at alternative strategies. The eventual design solution, led by architect Short & Associates and m&e consulting engineer Environmental Design Partnership, employs a 50-m square plan, with stacks supplying natural light and ventilation, which is also boosted by chimneys around the perimeter. The result is said to be the biggest naturally ventilated building of its type in the world.

The new centre has four floors built around its plan. Under the ground floor is an air supply plenum, and three vertical stacks supply and remove air. Four corner lightwells, seven metres in from the perimeter, supply air to all floors and a single well extracts air from these areas. Twenty stacks are used to ventilate the perimeter.

So how does the system work? Air enters from the supply plenum and travels into the corner lightwells. Here, air is tempered by a heater battery before being supplied into the rooms via low-level dampers. Trench convective heaters warm the air further. High-level dampers exhaust air into the central lightwell or the perimeter stacks.

There are vents in the windows controlled by motorised actuators according to the direction of the wind. The corner lightwells have glazed roofs, also with actuated window vents.

The characteristic chimneys, or perimeter ventilation stacks as the designers like them to be called, are 3-m square and rise to a height 6 m above roof level. With their aluminium terminations, they are not unlike air traffic control towers. They take extract air from dampers on each of the four floors around the square plan, as well as from the basement level.

With an innovative approach to ventilation and building services generally, it is vitally important than on-site relations are good. According to Drake and Scull, handover on the project was 99.9% defect-free and the company's performance drew high praise from Jim Palmer, an associate with the consultants Environmental Design Partnership.

As Drake and Scull's project manager at Coventry University, Nyree O'Conner explains: "Customer requirements rather than cost were the driving factor, with constant communication underpinning day-to-day operations. This ensured the customer's requirements were fully understood and taken into account." Weekly on-site meetings adopted a no-blame approach, cutting down on correspondence and fostering a proactive attitude from the earliest days of the project. Out of this came a rolling programme of work schedules, with clear objectives complementing those of the University and with specific tasks allocated to named individuals.

Programmes were monitored and adjusted to benefit the entire project team rather than specific members, for example the co-ordination of the installation of 300 dampers in the ventilation package. By working closely with the main contractor, Drake and Scull was able to make just-in-time deliveries, reducing on-site storage space requirements and costs.

So far, the University is very pleased with the performance of its new building. Obviously, the acid test comes in the hot summer months, if we have any, when the natural ventilation has to cope with outdoor heat and humidity as well as the heat gains from students and computers.