NRDC Santa Monica Headquarters (left); Crystal Cathedral Visitor Center (right)
Hybrid ventilation, or mixed mode conditioning, is the integration of natural ventilation with mechanical ventilation. Operable windows and hybrid ventilation designs provide distinct improvements to the quality of the space, as well as minimize the use of mechanical cooling. It is understood that fully, naturally ventilated spaces generally require specific concessions by the occupants and are appropriate in some circumstances. However, hybrid ventilation schemes can realize most of the physiological and environmental benefits of natural ventilation, but do not require the same level of flexibility for the occupants.
The design for the AIA Headquarters in Washington, DC includes central shafts and both manual and automated operable windows at the building façade. Controls on the core spaces allow the air handling units to provide economized air to the core areas, while the remaining areas are naturally ventilated. This strategy broadens the range where natural ventilation can be utilized. Due to the humid nature of the climate, exterior moisture levels, as well as temperature levels, govern the hybrid ventilation scheme. The Natural Resource Defense Council office also used a mixed mode conditioning system. The mechanically conditioned displacement ventilation system was integrated with the manually operable windows.