Nonlinear thermal analysis of multi-holed lightweight concrete blocks used in external and non-habitable ﬂoors by FEM J.J. del Coz Díaz a,⇑ , P.J. García Nieto b , L.M. Díaz Pérez a , P. Riesgo Fernández c a Department of Construction, University of Oviedo, 33204 Gijon, Spain b Department of Mathematics, University of Oviedo, 33007 Oviedo, Spain c Department of Management, University of Oviedo, 33004 Oviedo, Spain article info Article history: Available online 8 October 2010 Keywords: External ﬂoors Lightweight concrete Finite element modelling Nonlinear complex heat transfer Energy savings Thermal analysis Multi-holed block abstract The aim of this current and innovative work is the numerical thermal analysis of multi-holed lightweight concrete blocks for external and non-habitable ﬂoors by the ﬁnite element method (FEM). Twelve differ- ent block designs with the same external dimensions 0.57  0.45  0.20 m were built varying the num- ber of the horizontal intermediate bulkheads, from 3 to 12. Besides, ﬁve different compositions of the lightweight aggregate concrete (LWAC) and ﬁve different bulk temperatures have been taken into account, giving place to a total of 600 different ﬂoor conﬁgurations, 300 cases per each heat ﬂow direc- tion: upward and downward heat ﬂows. A nonlinear thermal problem is solved for all cases analysed and then, it is possible to choose the best candidate block from the standard rule requirements. Mathemati- cally, the nonlinearity due to the radiation boundary condition inside the inner recesses of the blocks is tackled by the matrix radiation method. Once the nonlinear thermal problem is solved, the temperature distribution is obtained and the thermal characteristic values of the ﬂoors, both for downward and upward heat ﬂows, are calculated. From the numerical results, we can conclude that the main variables in the thermal performance are the total number of recesses and the material conductivities. Therefore, increasing the number of horizontal intermediate bulkheads and decreasing the material conductivities, the best thermal efﬁciency is obtained. The selection of the best candidate block of external ﬂoors and ﬂoors in contact with non-habitable spaces is carried out through the following parameters: the average mass overall thermal efﬁciency and the equivalent thermal conductivity. Finally, detailed instructions are provided in order to select the appropriate ﬂoor satisfying the standard rule requirements and conclu- sions of this work are exposed. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction In year 2050 new buildings will consume zero net energy from external power supplies and produce zero net carbon dioxide emissions while being economically viable to construct. Nowadays buildings consume about 40% of energy in developed countries. Consequently, an important effort for transforming the way in which buildings are designed, constructed and operated must be performed [1]. The new buildings require a combination of onsite power gen- eration and ultra-efﬁcient building materials and equipment. These ‘green’ buildings already are erected in various parts of the world but current cost structure prevents widespread adoption by builders. In this way, new standard rules for energy efﬁciency in buildings [2] and the use of new materials (such as lightweight aggregate concrete [3]) will be the starting point for the energy savings objective. Lightweight aggregate concrete (LWAC) was used even before the Christian era. With time, because of the advantages of the LWAC, speciﬁcally its low density and thermal insulating proper- ties, its demand has increased [3]. In recent years, it has become an important structural material in building construction [4]. This has led to the development of synthetic lightweight aggregates which are made from natural raw materials like clay, slate, shale, etc., and from industrial by-products like ﬂy ash, slag ashes, etc. There are many types of lightweight aggregates of mineral origin, ranging from weights below 50 kg/m 3 up to heavy types of 1000 kg/m 3 or even more. They enable the production of concrete and mortars in very wide ranges with properties that will suit the requirements of different building industries [3,4]. Thermal behavior of the LWAC is related to its thermal conduc- tivity and density which, in turn, is inﬂuenced by its pore struc- ture: the air-void system, aggregates, and the matrix. Thus, the thermal conductivity will depend upon the pore structure of the 0017-9310/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijheatmasstransfer.2010.09.016 ⇑ Corresponding author. Tel.: +34 985 182042; fax: +34 985 182433. E-mail address: juanjo@constru.uniovi.es (J.J. del Coz Díaz). International Journal of Heat and Mass Transfer 54 (2011) 533–548 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt