Heat, air and moisture transfer through hollow porous blocks Gerson Henrique dos Santos * , Nathan Mendes Thermal Systems Laboratory, Department of Mechanical Engineering, Pontifical Catholic University of Paraná – PUCPR, R. Imaculada Conceição, 1155, Curitiba-PR, 80.2+15-901, Brazil article info Article history: Received 10 June 2008 Received in revised form 5 November 2008 Available online 26 December 2008 Keywords: Coupled heat and moisture transfer Hollow elements Porous material Building simulation abstract The combined heat, air and moisture transfer in building hollow elements is of paramount importance in the construction area for accurate energy consumption prediction, thermal comfort evaluation, moisture growth risk assessment and material deterioration analysis. In this way, a mathematical model consider- ing the combined two-dimensional heat, air and moisture transport through unsaturated building hollow bricks is presented. In the brick porous domain, the differential governing equations are based on driving potentials of temperature, moist air pressure and water vapor pressure gradients, while, in the air domain, a lumped approach is considered for modeling the heat and mass transfer through the brick cav- ity. The discretized algebraic equations are solved using the MTDMA (MultiTriDiagonal-Matrix Algo- rithm) for the three driving potentials. Comparisons in terms of heat and vapor fluxes at the internal boundary are presented for hollow, massive and insulating brick blocks. Despite most of building energy simulation codes disregard the moisture effect and the transport multidimensional nature, results show those hypotheses may cause great discrepancy on the prediction of hygrothermal building performance. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Heat, air and moisture (HAM) transfer through porous media is explored in many engineering areas such as oil extraction, trans- port in textile materials [1], wood drying [2], pollutants infiltration, granular materials drying [3], heat exchangers [4], transport in composite membrane [5] and thermal insulation [6] among others. Therefore, in the construction area, detailed heat, air and moisture models are needed to increase the accuracy of heat and moisture transfer calculation between outdoor and indoor environments for better predicting thermal loads, indoor thermal comfort and air quality indices and mold growth risk. For the thermal performance evaluation of building envelopes, the presence of moisture implies an additional latent heat trans- port that may cause great discrepancies on the indoor air temper- ature and humidity values [7]. Despite the importance, building envelope mathematical models are limited, mainly when air- and vapor-permeable hollow blocks are considered within the building walls. Heat transfer through hollow blocks takes places simulta- neously due to combined processes (radiation–convection–con- duction) within its core. Although the coupled problem has received great attention currently, the available literature on the heat and moisture transfer of hollow porous elements is still lim- ited. In hygrothermal whole-building performance analysis, a com- plete model including all phenomena becomes very complex and simulations very time consuming. Concerning moisture transport, the first developed models were focused on the analysis of porous soils. Lewis [8], Richards [9], Phillip and DeVries [10] and Luikov [11] elaborated the first phenomenological models to characterize the transport in unsat- urated porous media. In the building area, the first technique developed in the eighties to evaluate moisture in building mate- rials was the well-known Glaser’s method. Pedersen [12] and Kunzel [13] have developed more complete models that take into account the liquid and vapor diffusive transport. Mendes et al. [14] have developed a model based on the Philip and DeV- ries model to predict heat and moisture transfer through porous building elements. In the citations mentioned above, only massive elements have been considered. Nevertheless, cavities in building hollow ele- ments may play a very important role on the hygrothermal perfor- mance so that convective transport coefficient values for different geometries are of great importance. In this context, Gill [15] and Davis [16] studied the two-dimensional convective motion in a rectangular cavity. Natural convection problems in cavities have also been presented in [17–19]. McBain [20] studied the natural moist air convection within square cavities and obtained a formula for the total, steady state heat and mass transfer rates across cavities. Considering the pure heat transport, Geem [21] analyzed the thermal transmittance of concrete blocks measured in different laboratories and the values were compared to values calculated using the isothermal planes method. Walls with core insulation, 0017-9310/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijheatmasstransfer.2008.11.003 * Corresponding author. Tel.: +55 41 3271 1691. E-mail addresses: gerson.santos@pucpr.br (G.H. dos Santos), nathan.mendes @pucpr.br (N. Mendes). International Journal of Heat and Mass Transfer 52 (2009) 2390–2398 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt