Experimental study of an innovative element for passive cooling of buildings

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The use of passive cooling techniques has been seen as one of the solutions that can help to reduce energy consumption in the building sector. An innovative element that allows the combined use of two of the passive cooling techniques most mentioned in recent literature, evaporative cooling and night ventilation, is proposed in the present work. The combined application of passive cooling techniques can help to overcome the limitations resulting from their isolated application, which, in general, results from local climatic conditions. In order to optimize the use of those techniques it was decided to include in the element configuration a core component with latent heat storage capabilities. The presence of this core component makes it possible to suit the cooling processes occurrence with its demand and also enables cooling rates not necessarily equal to production ones. Thus the innovative nature of the proposed element results from the combination of evaporative cooling with latent heat storage, and with night ventilation. The present work includes the conception, development, construction and experimental studies of a prototype of this element. Briefly it can be said that the element is composed by the accumulating core, consisting of a mortar vertical panel impregnated with paraffin, with two adjacent channels for air circulation. The element, whose configuration should allow its integration into the buildings envelope, has a parallelepiped shape with one air inlet and one air outlet in each of its opposite faces, the exterior and the interior ones. The airflow in each channel is provided by tangential fans mounted on top of the element. The paraffin wax used corresponds to a commercial wax with phase transition range near 20 ºC, slightly below typical comfort temperatures. After its construction, the prototype of the element was subjected to a series of experimental studies that aim to know its response in operating conditions similar to real ones. These studies took place in a climate chamber for a wide range of conditions. The results suggest that the proposed element exhibits the potential for passive cooling of buildings. It was concluded that the paraffin wax incorporation in the mortar core has substantially improved the capacity of thermal energy accumulation of the element, that the evaporation process on the outside surface of the core provides a substantial temperature reducing of the core, and that its use also during night periods allows to cool the core well below the outside temperatures, thus maximizing the possibility of application of night ventilation.

Doctoral Thesis in Mechanical Engineering of Luís Carvalho Pires, 2011.

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