Evaporation from Porous Building Materials and Its Cooling Potential

Abstract

Evaporative 3 cooling is a traditional strategy to improve summer comfort, which has gained renewed relevance in the context of the 6 transition to a greener economy. Here, the potential for evaporative cooling of two common porous building materials, natural stone and 7 ceramic brick, was evaluated. The work has relevance also to the protection of built heritage becauseevaporation underlies the problems of 8 dampness and salt crystallization, which are so harmful and frequent in this heritage. It was observed that the drying rate of the materials is, in 9 some cases, higher than the evaporation rate of a free water surface. Surface area measurements by a three-dimensional optical technique 10 suggested, as probable cause of this behavior, that surface irregularity gives rise to a large effective surface of evaporation in the material. 11 Surface temperature measurements by infrared were performed afterward during evaporation experiments outside during a hot summer day in 12 Lisbon. Their results indicate that ordinary building materials can be very efficient evaporative media and, thus, may help in achieving higher 13 energy efficiency while maintaining a simultaneous constructive or architectural function.

To Coat or Not To Coat: A question on porosity and coating in building material

“…This ability is the basis for both the favourable and unfavourable porosity in building material. As indicated by some researches [2,[4][5][6][7][9][10][11], the transporting ability of moisture and heat is favourable for the passive thermal control in the building. Porosity allows exchange between the inside and outside environment.…”

“…Researches about building material significantly highlight the high and growing building energy consumption, particularly within the cooling process [1][2][3][4]. In accordance with this issue, the use of porous material [2,[4][5][6][7] and the use of coating [1,8] has become the "passive" alternatives to reduce the energy consumption for thermal control. Nevertheless, the majority of researches on building material and coating tend to solely focus on the technical and physical properties of the building material and coating [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

“…Some researches address how porous materials provide transporting ability that support passive cooling through evaporation, moisture and heat transfer [2,[4][5][6][7][9][10][11] while coating supports the thermal control due to its reflectance toward heat source radiation (sunlight) [1,8]. However, in many context, porosity is also considered as the beginning of degradation and deterioration of building material that become the parameter of its durability [12][13][14][15][16][17].…”

Differential thermal expansion as a cause of salt decay: literature review, experiments, and modelling of micro and macro effects on Ançã limestone

“…Allan et al (1993) From the above calculations, we estimate that the compressive strength of the Ançã will be reached, in at least some pores, if the system is subjected to the following temperature ranges: ΔT min NaCl 30ºC, ΔT min Na2SO4 15ºC and ΔT min NaNO3 20ºC. Temperature variations of these or higher magnitudes can be reached on facades exposed to sunlight, namely in southern Europe countries like Portugal, both seasonally and daily during summer (de la Rosa et al 2013, RCCTE 2006, Diaz Gonçalves et al 2015.…”

“…Therefore, considering the three studied salts, 30ºC is the highest temperature range that salt contaminated Ançã can tolerate without microscopic damage occurring. Note that in countries such as Portugal, this temperature range can be achieved both daily and seasonally, on facades exposed to sunlight (de la Rosa et al 2013, RCCTE 2006, Diaz Gonçalves et al 2015.…”