Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland. Impact on indoor climate depending on the moisture buffering of building materials

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1 Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland Paper ID 0101 ISBN: Impact on indoor climate depending on the moisture buffering of building materials Kristin Lengsfeld 1,*, Martin Krus 1 1 Fraunhofer Institute for Building Physics IBP, Holzkirchen, Germany * Corresponding kristin.lengsfeld@ibp.fraunhofer.de SUMMARY It is well-established that the thermal mass of a building s envelope buffers large variations in temperature. The fact that there is also a moisture buffering effect is much less known and appreciated by the construction industry. Hygric mass is defined as the vapour absorption capacity of a material capable of buffering moisture variations inside a room. This is especially relevant for rooms in which the generation of moisture (due to human activity) shows big time dependant moisture loads but no corresponding increase of ventilation. A hygroscopic material has the ability to absorb and store moisture from the surrounding air. When the relative humidity (RH) changes, the changing vapour partial pressure results in absorption or desorption of moisture within the material in order to reach equilibrium. RH levels between 30-65% (DIN EN 15251, 2012) are beneficial to the health of building occupants, reducing risks from common pollutants such as bacteria, viruses, chemicals, allergies and respiratory infections. Most materials have a hygroscopic potential which is too low to have any impact on indoor humidity, however this ability can vary to a great extent for different building materials and is related to the available surface area/porosity and the diffusion properties. To characterize the moisture buffering effect of a material, the so-called moisture buffer value of the NORDTEST (Rode et al., 2005) has been widely used by researchers. However, in recognition of concerns about the test-conditions of the Nordtest a new test setup is developed using more representative boundary conditions, because they are based on a typical diurnal course of a moisture load in dwellings. KEYWORDS Moisture uptake, Hygrothermal laboratory test, Realistic daily moisture profile 1 INTRODUCTION Appropriate indoor climatic conditions are important for human beings for comfort and health. The relative humidity of indoor air plays an important role for both aspects. With regard to thermal comfort temperature conditions in rooms are frequently discussed, but to achieve thermal comfort indoors it is also important to take relative humidity into account. Due to increasingly higher requirements for energy efficiency, air tightness of buildings and a change of habits of the residents, there is an increased risk of mould growth indoors. An essential reason is the reduced air change rate due to the integration of air-tight windows or a change in ventilation habits, caused by a higher absence rate of residents. In this context the

2 influence of high humidity, which may cause mould growth and which can have a negative influence on health is discussed. However, low humidity may also impair health, for example causing dry mucosa or dry eyes. The aim of this study is to investigate and evaluate the behaviour of moisture buffering of different chosen state-of-the art and newly developed building materials within the European funded project ECO-SEE (ECO-innovative, Safe and Energy Efficient wall panels and materials for a healthier indoor environment). A few studies have demonstrated that interior moisture buffering by the building fabric can beneficially affect energy consumption, component durability, thermal comfort and air quality (Janssen and Roels, 2009). However, there is still need for deeper knowledge of these effects, scientific characterisation of materials and development of a suitable design model or tool to support implementation by industry. The buffering effect of a material is strongly dependent on two different material properties which are usually diametrically opposed: vapour absorption capacity and diffusion resistance factor. The duration of the moisture load thus has a significant effect on the amount of absorbed humidity. This is the reason for the ability of some materials to perform well with very rapid changes in relative humidity (low diffusion resistance and medium moisture absorptivity) while others are more suitable for slower humidity changes (medium diffusion resistance and high moisture absorptivity). To characterize the moisture buffering effect of a material, the so-called moisture buffer value of the NORDTEST (Rode et al., 2005) has been widely used by researchers. For a more profound description of the moisture buffering behaviour the Fraunhofer Institute for Building Physics developed a new test procedure with the aim of measuring the sorption behaviour of different materials for a realistic daily moisture load profile in buildings. Different state-of-the-art and newly developed coating materials were tested and evaluated regarding their moisture buffering effect. 2 MATERIALS/METHODS The knowledge of specific hygrothermal material data and realistic typical boundary conditions are important for the assessment of the moisture buffering capability. The moisture profile developed for the following test is based on a constant moisture production by plants and persons and a high moisture load in the morning by taking a shower. Additionally in the afternoon/evening an increase of the moisture load is caused by the presence of additional persons as well as by cooking and drying of clothing. According to this daily moisture production a defined profile of relative humidity is implemented in a climate chamber. Figure 1 shows the diurnal profile of the planned (black line) and the generated (red line) relative humidity and temperature (constant 23 C). Most of the time the relative humidity lies at 50 %, but in the morning it increases for two hours up to 90 % and in the afternoon/evening for six hours up to 75 %. For the measurement of the moisture buffering behaviour samples with a size of 10 x 10 cm² or 20 x 10 cm² are used. Before the test start all material samples are conditioned at 50 % relative humidity and they are sealed on five sides to get one-dimensional processes. This ensures the measurement of the moisture ab- and desorption only for one defined surface. The 24 h test circle for the measurement of the sorption behaviour is running for several days, while the weight of a sample is logged continuously every minute. The temperature and relative humidity in the test chamber is recorded every 10 minutes. The measurement of the short-term sorption behaviour was performed with different state-ofthe-art coatings and newly developed coatings. The materials which are used for the determination of their moisture buffering behaviour are listed in Table 1. The development of novel mixtures was based on the specific selection of aggregates and additives which influence only the short-term ab- and desorption properties of the materials.

3 Figure 1. Implemented and generated 24h-course of the temperature and relative humidity in a climate chamber. Table 1. Materials for the test of moisture buffering effect State-of-the-art Classification Use Application Gypsum plaster Mortargroup P IV Ready-to-use with water; thickness t per layer = min. 10mm internal Clay M1 DIN ) Ready-to-use with water; Base coat; t per layer = 5-20mm internal Clay M3 DIN ) Ready-to-use with water; Top coat; t per layer = max. 3mm internal Lime Tradical décor NF EN 998 Ready-to-use with water; Top coat; t per layer= 2-3 mm / two layers internal Lime Tradical DTU 20.1 and Additional sand on site; Base coat; t per layer= 2-5mm all PF Hemplime Professional rules for the construction with hemp Manual application or mechanical application by spraying from 3cm to 8cm all Newly developed ClayH2/+1D experimental Ready-to-use with water; Base coat; t per layer = 7-10mm internal Clay H2/+5 experimental Ready-to-use with water; Base coat; t per layer = 7-10mm internal Clay E14/+2 experimental Ready-to-use with water; Base coat; t per layer = 7-10mm internal Lime_VER experimental Additional sand on site; Base coat; t per layer= 10-40mm all Lime_PCM experimental Additional sand on site; Base coat; t per layer= 10-40mm all Lime+5% experimental Additional sand on site; Base coat; t per layer= 10-40mm all Cellulose 1) DIN 18947:2013- Water Vapour Adsorption Class II 2) DIN 18947:2013- Water Vapour Adsorption Class III The test cycle of the materials runs over several days and the evaluation of the results is carried out for the fourth day according to ISO 24353: RESULTS Material properties The buffering effect of the material is strongly dependent on the two material properties vapour absorption capacity and diffusion resistance factor (µ-value). The duration of the moisture load thus has a significant effect on the amount of absorbed moisture. Therefore the µ-values and the moisture storage function of all state-of-the-art and newly developed materials are measured and compared (see Table 2). The µ-values (dry- and wet-cup) of the newly developed clay plasters are a little bit lower compared to the state-of-the-art clay

4 materials. The effect of the different ingredients means, regarding the moisture storage function, that the clay plasters Clay H2/+1D and Clay H2/+5 have a higher sorption at high relative humidity and the clay plaster Clay E14/+2 shows a lower absorption at low relative humidities compared to the two state-of-the-art clay plasters. The effect of the new mixtures on the µ-value is more significant for the lime plasters. The reduction of the water vapour diffusion resistance factor is more than %. The comparison of the moisture storage functions shows similar results for Tradical décor and the lime plaster with vermiculite, but the moisture storage functions for lime with PCM and 5 % Cellulose are distinctly higher. Table 2. Comparison of the measured material properties Material Density Water vapour diffusion resistance factor (dry) Water vapour diffusion resistance factor (wet) Hygroscopic absorption / Moisture Storage Function [kg/m³] Relative humidity in % [kg/m³] [-] [-] State-of-the-art Gypsum Clay M Clay M Lime Tradical décor Lime Tradical PF Hemplime Newly developed Clay - H2/+1D Clay - H2/ Clay - E14/ Lime Vermiculite Lime - PCM Lime 5% Cellulose For the demonstration of the moisture buffering effect of the different materials the difference of the change of weight [g/m²] at the fourth day is shown in Figure 2 and Figure 3. The curves display the differing moisture uptake behaviours in the period of high relative humidities in the morning and the afternoon/evening. The Clay H2/+1D coating (green line) in Figure 2 shows the best moisture absorption in the morning. In contrast to that during the moisture load in the afternoon /evening the weight increase of Clay H2/+5 is a little bit higher than that of Clay E14/+2. Figure 3 depicts that both newly developed lime plaster show better moisture absorption in the morning than the standard lime plaster. During the moisture load in the afternoon/evening the results are different. In this period the lime with cellulose shows a much higher weight increase than the Tradical décor lime and the amplitude of lime with vermiculite is slightly lower than that of the Tradical décor lime. For the different materials the increase of weight is listed in Table 3. By the comparison of the weight changes the differences of the moisture buffering behaviour are getting obvious. The clay materials absorb about twice as much as the gypsum coating and the hemplime. This is caused by their steeper sorption isotherm in the range from 50 % to 90 % relative humidity in conjunction with an only slight increase in diffusion resistance factor. The absorption ability of the lime coatings is mostly slightly higher than that of the gypsum coating. Compared to the state-of-the-art materials regarding the short-term absorption of moisture (in the morning) the composition of lime plaster with cellulose (5% Cellulose) and Clay H2/+1D show the best results.

5 Figure 2. Differences of the weight change of clay materials on the fourth day. Figure 3. Differences of the weight change of lime materials on the fourth day. Table 3. Weight increases of the different materials by defined moisture loads (Fig. 1) Material morning [g/m²] evening [g/m²] State-of-the-art Gypsum Clay M Clay M Lime Tradical décor Lime Tradical PF Hemplime Newly developed Clay H2/+1D Clay H2/ Clay E14/ Lime Vermiculite Lime PCM Lime 5% Cellulose DISCUSSION With the newly developed test method for the measurement of the moisture buffering behaviour of materials the determination of the moisture buffering effect of interior materials for a realistic typical diurnal moisture load profile in buildings is possible. This enables the assessment of situations when moisture peaks occur in rooms due to their use by occupants. Results indicate whether materials used have a positive influence on the relative humidity in rooms. The moisture buffering behaviour depends in a complex way on the diffusion

6 resistance factor and the moisture storage function but with the demonstrated test procedure the moisture buffering effect at short- or long term periods of humidification can be rated and the influence on indoor climate can be estimated regarding the reduction of the diurnal variation of indoor humidity. 5 CONCLUSIONS Moisture buffer behaviour of materials is determined by the interaction of moisture storage function, described by sorption isotherms, and diffusion openness, described by the diffusion resistance factor. Therefore, it must be expected that materials behave in a different way concerning the moisture buffer effect depending on long- or short-term periods of humidification and drying. For a realistic assessment of the moisture buffer behaviour, materials must be tested under practical conditions. Within this project, a test method was developed to reflect the daily moisture cycle in inhabited rooms. Special consideration is given to a relatively short but strong increase in humidity in the morning caused by taking showers, and a longer increase of humidity in the evening when the whole family is at home, is cooking meals etc. The materials are exposed to this daily cycle in a climate chamber and their weight is continuously measured. Results of the hygrothermal measurements show that all newly developed materials have a positive effect on the moisture buffering behaviour thus softening the amplitude of the relative humidity in rooms. Especially the effect of the lime plaster with 5 % cellulose fibres and the clay plaster H2/+1D are remarkable. By these modifications the amount of moisture uptake of the material samples during the period of high moisture load of 90 % RH and the lower moisture peak of 75 % RH could be approximately doubled in comparison to a state-of-the-art gypsum plaster. In the future this newly developed test procedure and its results could be helpful for the selection of finishing materials for the inner surface of rooms to improve the indoor climate. 6 ACKNOWLEDGEMENT This project has received funding from the European Union s Seventh Framework Programme for research, technological development and demonstration under grant agreement no Note: The views expressed are purely those of the authors and may not in any circumstances be regarded as stating an official position of the European Commission. 7 REFERENCES DIN 15251: Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics. DIN Deutsches Institut für Normung e.v.. Beuth Verlag. DIN 18947: Earth plasters Terms and definitions, requirements, test methods. DIN Deutsches Institut für Normung e.v.. Beuth Verlag. DTU Building works - Small mansonry unit walls - Partitions and walls. Éditée et diffusée par l Association Française de Normalisation (AFNOR). DTU Building works - Rendering and plastering works done with mortars. Éditée et diffusée par l Association Française de Normalisation (AFNOR). ISO 24353: Hygrothermal performance of building materials and products Determination of moisture adsorption/desorption properties in response to humidity variation. Janssen H. and Roels S Qualitative and quantitative assessment of interior moisture buffering by enclosures. Energy and Buildings, 41(4), NF EN 998: Specification for mortar for masonry - Part 1 : rendering and plastering mortar. Par décision du Directeur Général d'afnor. Rode C., Peuhkuri R., Hansen K.K., Time B., Svennberg K., Arfvidsson J., Ojanen T. 2005: NORDTEST project on moisture buffer value of materials, AIVC Conference Energy performance regulation, Brussels, September 21-23