Double Envelope Unitized Curtain Wall for solar preheating of ventilation air

Despite recent efforts on energy performance improvement, curtain walls remain a significant contributor to the energy consumption of commercial buildings. A novel double envelope unitized curtain wall system is presented, aimed at the substantial improvement of the energy performance of glazed systems. Outdoor air is ventilated through an integrated cavity in its paths to the ventilation air intake of the air handling unit. In its path through the glazed envelope, the air is heated from both incident solar radiation and transmission losses recovered from the indoor environment. A substantial energy performance improvement is achieved by means of the preheating of fresh air. Energy consumption is reduced in the heating season, and even net gains above the heating demand are delivered under favorable conditions. By-pass elements are integrated to allow free cooling and natural ventilation when required in cooling mode. In this way, the double envelope also provides advantages in summer mode, where solar heat gain coefficients are substantially lower than for other systems due to the double envelope and the ventilation of the cavity to the ambient. The overall architectural concept, engineering design and outcomes of an experimental campaign over a 2-story full scale test in Spain are presented.