To create the world’s most voluminous, naturally ventilated museum space for the California Academy of Sciences, the San Francisco office of project consulting engineer Arup commissioned wind-tunnel tests to confirm its computational fluid dynamics (CFD) models. Then it rebuilt its CFD model. The combined studies took 18 weeks, which is 16 weeks more than it would have taken to study a simple rectilinear space, says Karl Lyndon, Arup’s project mechanical engineer.

Digital model validated with wind tunnel.
Digital model validated with wind tunnel.

Rowan Williams Davies & Irwin Inc., Guelph, Ontario, constructed a 1:100 scale model to simulate air flow through entrances, the piazza and the roof. Instruments measured wind pressures exerted on the building, while sensors measured the speed of air moving through it. RWDI also built a smaller-scale model that included trees outside the building.

Arup was looking for dead-air spots or for areas that might be too breezy. “Early in design development, we were wondering whether the roof hills would create too much air suction,” says Lyndon, who adds that it is unusual for Arup’s mechanical group to commission wind-tunnel tests.

Arup used results of the RWDI tests and created a new CFD model, using exact pressures measured. “Each set in the analysis takes two months,” says Lyndon.

To maintain indoor-air quality, the engineer had to keep boiler flues and other dirty exhaust, including from penguin habitats, away from exhibit-hall vents. “Penguins are really smelly,” says Lyndon.

Roof and vent windows automatically open and close to let hot air out through tops of the domes. Motorized facade windows automatically open and shut to allow cool air into the building. As the wind speed picks up, the roof vents close and cross ventilation kicks in.

The result: Ventilation in the 1.8-million cu ft exhibit space is better than in an air-conditioned building. “That’s great news,” says Lyndon.