Passive heating and cooling

Buildings play a fundamental role in the energy budget of European countries. Accordingly, efforts addressed to optimize building’s thermal behaviour are key important. Numerical analysis of passive systems such as green façades, double skin façades and Trombe walls have been developed and tested in the CTTC for many years.

Large and transparent areas in façades are a common architectural practice. One of the main problems of these designs in Mediterranean climatic conditions is the overheating in hot weather periods. Double skin façades are a good solution for avoiding building overheating. They consist of two layers of glass separated by an air channel, which collects or evacuates the solar energy absorbed by the façade in order to warm up in cold season or to cool down in warm season the inside of the building, respectively, reducing the heating and air conditioning demands. In the CTTC the thermal behaviour of advanced façades which include advanced technological elements, like phase change materials, transparent insulation and façade integrated collectors-accumulators have been numerically studied [1,2].

CTTC has worked in the thermal design of singular buildings such as Agbar Tower in Barcelona [3], central headquarters of Caixa de Terrassa [4] in Terrassa city and headquarters of Association of Technical Engineers in La Rioja [5].

Overheating problems can be solved as well by means of green façades, where the façades of urban buildings are shaded by deciduous plants. During cold seasons, the vegetation loses its leaves and its effect is almost null, while during hot seasons its effect tends to suppress or reduce the overheating (solar protection).

In the numerical simulation of such façades various effects of the plants over the façade were taken into account: (i) Interaction with solar radiation; (ii) Evaporating cooling; (iii) Reduction of wind velocity (and thus, heat transfer coefficient) at the façade surface; (iv) Shielding of thermal radiation. A Monte Carlo ray tracing code (VICACO VIrtual CAnopy COde) was developed to evaluate the fraction of incident solar energy that reaches the façade after multiple reflections within the canopy of plants.

Trombe walls are passive solar designs able to reduce heating needs. They are thick sun-facing walls made of heat-absorbing material on the exterior surface and are separated with the outdoor by a glass. Absorbed solar energy during the day is released toward the interior during the night. CTTC has studied with its newest modular building code, NEST [6], the thermal and fluid-dynamic behaviour of this type of walls [7,8].