Original Research Article Experimental study of an innovative element for passive cooling of buildings L. Pires a , Pedro D. Silva a,⇑ , J.P. Castro Gomes b a Centre of Materials and Building Technologies, Department of Electromechanical Engineering, University of Beira Interior, 6201-001 Covilhã, Portugal b Centre of Materials and Building Technologies, Department of Civil Engineering and Architecture, University of Beira Interior, 6201-001 Covilhã, Portugal article info Article history: Received 6 March 2013 Revised 31 July 2013 Accepted 27 August 2013 Keywords: Passive cooling of buildings Indirect evaporative cooling Latent heat thermal energy storage Night ventilation abstract 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 passive cooling techniques, evaporative cooling and night ventilation, is proposed in the present work. In order to optimize the use of those techniques it was decided to include in the element configuration a core com- ponent with latent heat storage capabilities. Briefly it can be said that the element is composed by the accumulating core, consisting of a cement 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 oppo- site faces, the exterior and the interior ones. The core surface adjacent to the exterior channel is main- tained continuously wetted by a water sprinkler system integrated in the element. 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 21 °C, slightly below typical comfort temperatures. A prototype of the element was constructed and 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 cement mortar core has substantially improved the capacity of thermal energy accumulation of the ele- ment, 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-time periods allows to cool the core well below the outside temperatures, thus maximizing the possibility of application of night ventilation. Ó 2013 Elsevier Ltd. All rights reserved. Introduction Energy demand increased continuously in last decades and it is expected to continue to increase in the near future. Accordingly to the U.S. Department of Energy projection, world primary energy consumption in 2030 will be 44% higher than it was in 2006 [1]. On the other hand, one-third of the world population still has no access to basic energy services, which means that to ensure an equitable development on the planet, more energy is required. In 2007, 2.4 billion people were using charcoal, agricultural waste or animal waste as energy source for cooking, and 1.6 billion peo- ple worldwide live without electricity [2]. A significant portion of global energy consumption occurs in the building sector. For exam- ple, in the European Union, buildings consume more energy than any other sector of the economy, about 40% of the total energy consumed. Additionally, energy use for climatization purposes accounts with the largest share in the global energy consumption of buildings, about 60% in the European Union [3]. It has been re- cently observed, with particular emphasis on developing countries, a growing demand for cooling in the building sector. Factors as the rising expectations of comfort of buildings occupants, the urban heat island effect felt in densely built cities, the increase of the internal heat gains of buildings, the reduction of the cost of cooling equipments, the increase in household disposable income and an architecture often little concerned with local climate characteris- tics have contributed to such phenomena [4–6]. A future increase of cooling demand is also estimated in the developing countries as personal income is expected to increase in these countries [7]. The present work proposes an element for passive cooling of buildings that allows the combined use of techniques such as, evaporative cooling, night ventilation and latent heat storage. The element configuration has been designed in such a way that permits its integration in the building envelope. The study of passive or low energy solutions for cooling of buildings has received attention in several studies. The use of such 2213-1388/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.seta.2013.08.002 ⇑ Corresponding author. Tel.: +351 275 329 916; fax: +351 275 329 972. E-mail address: dinho@ubi.pt (P.D. Silva). Sustainable Energy Technologies and Assessments 4 (2013) 29–35 Contents lists available at ScienceDirect Sustainable Energy Technologies and Assessments journal homepage: www.elsevier.com/locate/seta