AN INTEGRATED METHODOLOGY FOR IMPROVING MOISTURE PERFORMANCE OF BUILDINGS

Transcription

1 AN INTEGRATED METHODOLOGY FOR IMPROVING MOISTURE PERFORMANCE OF BUILDINGS Antonia MOROPOULOU Prof. Maria KAROGLOU Ph.D Cand. Magdalyni KROKIDA Lect. Zacharias MAROULIS Prof. National Technical University of Athens, School of Chemical Engineering, Zografou Campus, 15780, Athens, Greece Keywords: decision making, materials properties, isotherms, capillary, drying, simulator Summary The building envelope restoration and retrofitting suffering from moisture problems is one of the critical key issues in sustainability of buildings, considering that moisture effects indoor air quality, energy consumption and durability of building materials and components. New approaches are needed for the ability of building, its parts, components and materials to resist the degrading action of moisture over a period of time. An integrated methodology is proposed for the moisture performance assessment of structures suffering from rising damp. This methodology consists of basic research laboratory experimental study, concerning materials microstructural and hygrometric characteristics; mathematical modeling for the prediction of hygrometric properties; development of a simulator for the scientific support concerning decision making on the moisture performance of materials interrelated to the environmental conditions and materials microstructure. 1. Introduction Rising damp and moisture, in general, cause a number of structural and aesthetical problems to the masonries of the buildings. The effects of moisture can be combined with other deteriorating factors such as air pollution and/or environmental loads (such as frost) and create an even more aggressive situation for the condition of the building. Apart from creating structural, aesthetical problems, moisture can cause degradation of indoor quality, since it enhances the development of mold, and mildew, creating favourable conditions for biological attack of a building, deterioration of comfort of living indices and aggravated problems for humans with mold allergies and respiratory morbidity (Oliver, 1997). It also increases the relative humidity of the indoor environment, and decreases the thermal insulation of the building, increasing the energy requirements to attain acceptable conditions of living, and subsequently deteriorating the behaviour of the building (Künzel, 1995). Thus, building envelopes, suffering from moisture problems restoration and retrofitting, is one of the critical key issues in sustainability of buildings. The incompatible materials and techniques that are used in many cases, especially for historic structures accelerate the degradation process. There is a growing need for the development of new approaches, which will contribute in long-term innovation planning for historic research. Moisture transfer in buildings is a very complex process and is influenced by a lot of physical phenomena. Controlling the accumulation of moisture in building enclosures has been a topic of growing interest especially over the last 15 years (Karagiozis, 2003). In this work a methodology is proposed for the assessment of moisture performance of a building, when main moisture source is rising damp. The advantage of this methodology is that it uses real experimental data, but also includes mathematical modeling as well. Moreover the development of a simulator for the moisture transfer at building components integrates experimental data and mathematical modeling. The validation of simulator results will be performed in real scale of buildings. 2. Moisture performance assessment 2.1 Methodology analysis The proposed methodology consists of three phases:

2 Laboratory Scale. This stage includes basic research laboratory experimental study, concerning chemical/ /mineralogical/ microstructural and hygrometric characteristics of building materials. Mathematical modeling of all the related transport phenomena is also carried out. The development of a general phenomenological model is achieved. With the aid of this model it is possible to predict all the hygrometric properties of materials, based on the effect of the environment and materials microstructure, when experimental data are missing, or is not easy to be obtained (like for materials from historic structures). Simulator. Development of a simulator, for the scientific support concerning decision making on the moisture performance of masonries, interrelated to the environmental conditions and materials microstructure. Building. Validation of the simulator results at buildings situated at different regions, under of different environmental conditions. The proposed methodology is summarized in FIGURE Laboratory A1. Environment A2. Building Materials T RH u Meterelogical data Τ min, Tmax, RHmin, RHmax Different Cities, Regions Characterization (Chemical/Mineralogical ) Microstructure investigation, (ρ ο, r ) Hygrometric properties Sorption, (Χ e, b o ) Drying kinetics, (c o, t cd ) Capillary rise kinetics (H e, t cr ) 2. Simulator B. Masonry Η D w,p Win Wout Databases Process model Problem solution algorithms Interface 3. Building C. Building Figure 1 Moisture performance assessment flow sheet

3 2.2.1 Laboratory Scale Primary stage (FIGURE 1), for the realization of this methodology is experimental study concerning materials properties. Historic buildings such as stones, bricks and plasters, as well as restoration materials in use are investigated. Initially, the materials morphological/ chemical/ mineralogical characteristics are investigated, using techniques like, fiber optics microscopy, differential thermal and thermogravimetric and X-ray diffraction analysis. Their microstructural characteristics are also investigated. Materials bulk density, ρ o and average pore radius r, can be estimated with the use of mercury intrusion porosimetry. For mortars the grain size distribution, should be also investigated. For the critical properties that describe moisture transport phenomena, it is considered, that the transport in liquid phase is driven by capillary suction, while the moisture moves to environment at vapour phase through drying process, after material saturation with water. In this framework capillary and drying kinetics are investigated. For the description of equilibrium state, water sorption isotherms are used. The effect of environmental conditions is expressed via the effect of air temperature T, relative humidity RH and air velocity u. The transport phenomena mathematical description is based on phenomenological models, including parameters with physical meaning. More specifically, moisture sorption (adsorption and desorption) isotherms, should be defined (Karoglou et al., a2005). This can be made using a water sorption analyser, obtaining materials sorption isotherms gravimetrically at three different temperatures. A modified Oswin equation is used, to predict experimental data, for water activity in the range of The output of this step is the estimation of the moisture equilibrium X e for each material. The parameter b o of the modified Oswin equation, describes the effect of material on the moisture equilibrium. For the study of drying kinetics an experimental air dryer of controlled drying air conditions can be used (Karoglou et al., b2005). Environmental factors, such as air temperature, relative humidity, and velocity affect drying. Drying kinetics must be examined at different values of air temperatures, relative humidity and velocity. A first order kinetic model is used to describe the drying process. The model predicts successfully the experimental data. Drying time constant t cd, is a function of drying conditions and materials characteristics. The parameter c o, describes the effect of material on the moisture equilibrium. For the study of capillary rise kinetics, the changes of height to time should be measured (Karoglou et al., c2005). A first-order kinetics model is proposed, in which the equilibrium moisture height H e, derives from Jurin law, based on materials average pore radius. The concept of capillary height time constant is introduced. The model predicts successfully the capillary rise of water. The capillary height time constant t cr, is strongly affected by the material characteristics. All the suggested models predict successfully the experimental data. A correlation between moisture transport models parameters affected by materials characteristics (b o, co, t cr ), with microstructure parameters is achieved (average pore radius r). Main objective at this stage is the development of a general phenomenological model, which based on microstructural characteristics, can predict all the related hygrometric properties. This approach is very significant, because permits the prediction of materials hygrometric properties, when the only experimental data available concern materials microstructure, or there no ability to perform experimental tests, like in case of historic materials or lack of samples Simulator A Simulator is developed for a two-dimensional masonry, consisting of two layers (substrate and plaster), for one-dimensional flow. Main moisture source is considered the ground. The Simulator uses simplified calculation methods, based on produced knowledge and experience. This means that experimental results concerning hydrometric properties of building materials, as well as numerical simulations are used. The simulator depending on the environmental conditions can predict the seasonal wall equilibrium moisture height H, the capillary rising water flow rate, W in, and the wall drying flow rate, W out, (FIGURE 1). The Simulator consists of four units; databases worksheet, process model, problem solution algorithms and graphic interface (Maroulis & Saravacos, 2003). All the data coming from Laboratory study is organised at databases worksheet. This sheet contains all the data needed for calculations in the form of Data lists. The data could be extended or modified via appropriate dialogue boxes. The following databases are developed: Construction materials properties. Microstructural data, capillary rise kinetic data, drying kinetics data, sorption-desorption isotherms Meteorological data. Daily or monthly variations of air temperature, relative humidity and velocity. Data concerning different cities or areas can also be added. The Graphics interface worksheet is for man-machine communication. The graphic interface consists of three parts:

4 Problem specifications: the specifications and the required data for the problem to be solved are entered by the user or estimated from the databases. Data are inserted via dialogue boxes or buttons for changing some important magnitudes. The specifications will consider the wall configuration, which means the type and dimension of the masonry, the ground water characteristics, meteorological data etc. Problem type selection. The type of problem to be solved is selected via buttons. Results presentation. The results will be obtained automatically and are presented in the form of tables or graphs. The presented simulator takes into account (a) the moisture transfer mechanisms to and from the building (capillary rise, drying, etc); (b) the wall configuration (materials and size); (c) the construction materials properties (d) the seasonal region meteorological data (air temperature, humidity and velocity); and calculates: (a) the seasonal wall moisture content along with the corresponded equilibrium moisture height; (b) the capillary rising water flow rate; (c) the wall drying flow rate etc. The proposed simulator is a powerful tool in decision making concerning the building deteriorating evolution and the selection of the appropriate protecting strategy, e.g., the plaster selection (material, size, replacing time). The Simulator has open architecture, this means that is possible new models, new data concerning materials properties, library containing site meteorological and individual buildings library, can be added Building The results of the Simulator can be validated at real scale at building consisting of materials with known microstructure. Moisture detection in building materials is typically done by taking cores at various heights and depths and measuring the weight loss after heating. Non-destructive methods can also be used. Infrared thermography is applied successfully in many cases for mapping of the moisture distribution in masonries in-situ. Infra-red thermography is very useful in monitoring the moisture on the building surface and microclimatic conditions inside the building and it gives detailed information on spatial distribution (Moropoulou et.al, 2001). The results of the campaign investigation of masonries should be compared to the theoretical ones derived from the simulator. 3. Case study Two categories of materials are investigated; materials used as substrate material and restoration plasters. The materials used as substrate materials are a brick of traditional type, symbolized as BRM and sandstone symbolized as SRY. Two restoration plasters are also investigated. PEM, an industrial macroporous plaster suitable for masonries suffering from rising damp and soluble salts decay, and the PTI an industrial plaster, cement-based commonly used at modern structures. 3.1 Laboratory Characterization The microscopical observations of materials give a first idea about their morphology and their microstructural characteristics. In FIGURE 2 are shown fiber optics microscopy results (magnification x50). BRM SRY PEM PTI Figure 2 Fiber optics micrographs x50 for the selected materials

5 It can be observed that BRM presents mainly small and a few large pores, aggregates of various colors. The stone SRY presents small pores homogeneously distributed at the surface. PEM has pores of all sizes distributed homogenously. PTI plaster has white aggregates and small pores scattered all over its surface. With the aid of differential thermal and thermogravimetric analysis, as well as x-ray diffraction, it was found that BRM was fired at temperature greater than 1000 C and contains as main mineral phases quartz, anorthite and illite. SRY contains calcite at a percentage of 92%. PEM consists of hydraylic lime binder and aggregates of quartz, fibers and organic additives. PTI has a white cement binder, with calcite aggregates and organic additives Microstructure study The materials microstructural characteristics investigated with the use of mercury porosimetry. The results for average pore radius r and bulk density ρ o, are shown in Table 1. Table 1 Mercury porosimetry results Materials r(µ) ρ o (g/cm 3 ) BRM PEM PTI SRΥ PEM presents the highest value of average pore radius and the lowest of apparent density, corresponding to the highest porosity values Moisture transport phenomena properties The results for moisture transport kinetics investigation are summarized in Table 2. The FIGURES 3-5 show the fitting of the proposed model to the experimental data. Table 2 Transport phenomena parameters estimated Material b o (kg/kg db%) sorption c o (hrs) drying t d (hrs) drying t cr (d) capillary BRM SRY PEM PTI b 1 =3( o C) b 2 =0.36(-) c 1 =0(-) c 2 =0.75(-) c 3 =-0.8(-) The sorption-desorption isotherms (experimental and predicted values), of the examined materials at three different temperatures are shown in FIGURE 3. The modified Oswin equation is successfully fitted to experimental data. The main results of drying kinetics for all the examined materials are summarized in FIGURE 4. The effect of various process conditions is shown. The effect of air relative humidity on the drying process is significant for all the examined materials. There is an acceleration of drying process due to the decrease of relative humidity values from 70 to 40%, or to the increase of air velocity is considered for all the examined materials. It is interesting to note that the materials exhibit almost the same values for drying time constant.

6 The main results of capillary kinetics for all the examined materials are summarized in FIGURE 5. The fitting of the proposed model to the experimental data is considered satisfactory, for all the examined building materials. Highest value of capillary height time constant presented PTI, while the lowest PEM plaster probably due to the hydrophobic additives that it contained. Figure 3 Water sorption-desoption isotherms at three different temperatures Figure 4 Drying kinetics investigations

7 Figure 5 Capillary rise kinetics investigation Simulator results The investigation and the knowledge of the materials moisture transport and microstructure parameters individually, are not sufficient for the assessment of moisture performance of a system, when two materials are combined together. The Simulator will solve the problem what plaster will be more suitable/ compatible restoration by predicting the moisture height variations before their real application. The two restoration plasters PEM and PTI will be applied at two different masonries, consisting of BRM and PTI. Variations of ambient conditions are considered; temperature ranging from 1-20 C, relative humidity between 40-75% and air velocity equals to 3m/s. For the selection of the appropriate restoration plaster the various masonry systems are presented at FIGURE 6. It can be seen two masonries made of BRM (i) and SRY(iv), with a width of 50cm, before the application of a plaster. The moisture height at both masonries reaches 4 meters. FIGURES (ii, v) show the variations of height at both masonries after the application of PEM and FIGURES (iii, vii) after the application of PTI. The plaster application width is selected to be equal to 3cm. (i) (ii) (iii) (iv) (v) (vii) Figure 6 Moisture height variations (minimum and maximum value), at two different masonries (BRM, SRY), with the use of PEM and PTI as restoration plasters As it is shown in FIGURE 6, PEM seems to be more suitable, because it reduces in both cases the moisture height under the two meters. This must be attributed to the fact that it presented the lowest capillary time constant. Of course the validation of the results will be made with pilot application of the materials at real masonries constructed with either brick or stone.

8 4 Conclusions The proposed methodology is a useful tool for the assessment of moisture performance at building components. It includes all the necessary material and building system analysis that is necessary for understanding and predicting all the related moisture transport properties in the framework of the interrelation of environmental conditions and materials microstructure. References Oliver, A., 1997, Dampness in buildings, 2nd Ed. Revised by Douglas, J., Stirling, J., S., Blackwell Science Ltd Künzel, H., M., 1995, Simultaneous heat and moisture transport in building components, Fraunhofer IRB Vertag, ISBN Karagiozis, A., N., 2003, Importance of moisture control in building performance, Canadian conference on building energy simulation, September 11th - 13th, Montreal, Canada Karoglou M., Moropoulou A., Krokida M.K., Maroulis, Z.B., 2005, Water sorption isotherms of some building materials, J. Drying Technology (in press). Karoglou M., Moropoulou A., Krokida M.K., Maroulis, Z.B., 2005, Drying kinetics of some building materials, J. Drying Technology (in press). Karoglou M., Moropoulou A., Giakoumaki A., Krokida M.K., 2005, Capillary rise kinetics of some building materials, J. of Colloid and Interface Science, 284, pp Moropoulou, A., Avdelidis, N.P., Theoulakis, P., Koui, M., (2001), Thermography as an evaluation tool for studying the movement of water through various porous materials; capillary rise and evaporation, Thermosense XXIII, ed. R.B. Dinwiddie et al., Publ. SPIE, Vol. 4360, pp Maroulis, Z., B., Saravacos, G., 2003, Food Process Design, Marcel Dekker, New York.