Analyze thermal & moisture performance of sustainable insulation materials

Published: 2021-07-07 19:45:04
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Research aim and objectivesBoth heating and cooling of buildings, in order to achieve thermal comfort levels, result in high demands of energy and expenses. Thus, depending on the climate prerequisites, people tend to use insulation building materials so as to reduce the energy loss through the fabric. At the same time, insulation materials play a vital role in harming the environment through lack of sustainability during their production, use and end of life. However, nowadays, there is a small number of sustainable building materials which can perform as well as the conventional ones. The aim of this dissertation is to analyze the thermal and moisture performance of sustainable insulation materials and compare them with some of the conventional materials, in order to assess whether these materials should be taken into consideration for applications in building envelopes.The main objectives of this dissertation are:• Measurement of heat capacity and thermal conductivity of conventional and non-conventional building materials using novel techniques, followed by simulation testing in DesignBuilder. The non-conventional insulation building materials that will be tested are hemp fiber, sheep wool and wood fiber.• Moisture performance testing of the three afore mentioned sustainable materials and comparison of the vapor permeability and the absorption isotherm for different climates through simulation (DesignBuilder).• Comparison of these non-conventional insulation materials to three commonly used ones, including mineral roll, EPS (Expanded Polystyrene) and Celotex insulation.Research context and relevanceThe research is crucial in two levels. Firstly, it attempts to develop novel techniques for quick measurement of heat capacity and thermal conductivity with acceptable accuracy without using very expensive laboratory equipment. This will contribute to more comparative research work on the thermal performance of building materials which is otherwise a costly process. Therefore, not only is it a way to prove the importance of sustainable materials in terms of insulation, but it is also a tool for even more testing of several other materials.Secondly, the assessment of hygric and thermal performance of insulation materials in steady-state and dynamic conditions will inform on the applicability of non-conventional building materials in different weather conditions. It is true that building companies, globally, still elect conventional insulation building neglecting, their negative impact on the environment. Therefore, through this work, the major aim is to provide the technical benchmarks and comparisons to promote sustainability.Literature reviewDuring the past years, thermal insulation materials and systems have become quite popular through numerous attempts to minimize the heat losses in the building sector. It must be stated that insulation materials are generally inhomogeneous, as heat transfer occurs by several mechanisms. Through the years, different measurements of heat transmission contribute to the understanding the thermal performance of these materials, which results in analyzing the heat transmission behaviour so as to develop better and less expensive materials (Bankwall C.,1974).The thermal performance of a material is determined through the calculation of the thermal conductivity for steady state or dynamic models. The steady-state method can be in principle simulated in a simple manner at moderate temperatures. In many countries, this principle has been standardized and measurements in a guarded hot plate can be regarded as the basic method of measuring the thermal conductivity of low thermal conductivity insulations. The main thermal performance testing method that was used for many years before was the guarded hot plate. For instance, Bankvall C. (1974) used a special guarded hot plate to analyze and predict the heat transfer mechanisms in a permeable insulation material. More specifically, he showed the way that heat transfers through a fibrous material, using simple physical models in the guarded hot plate. He concluded to the fact that appropriate laboratory measurements along with theoretical methods provide a reliable way to predict full-scale insulations’ behaviour.The principle of the guarded hot plate, which is also called Poensgen apparatus, is simple and is based on the steady-state heat transfer between a warm and cold plate. The thermal conductivity of an insulation can be investigated by placing the material between the plates. In the same year, Engelke W. (1974) determined suitable steady-state methods of measuring thermal conductivity in rigid insulation. These methods were the guarded hot plate, the comparative rod apparatus, which was used to measure the thermal conductivity of materials from 89K to 13600K and the radial inflow apparatus which was suitable for materials from 1100K to 3000K. This work was done to provide better tools of measuring thermal conductance and conductivity on insulation materials.Nowadays, the majority of new articles are analyzing the thermal performance of non-conventional materials and some of them calculate the moisture performance as well. Also, there are several standards regarding thermal insulation. The most frequently used are the ISO 8302 (which is about the guarded hot plate) and the ISO 9869, which analyzes the heat flow method. More specifically, Jiri Z. et al. (2012) evaluated the thermal performance of the sheep wool insulation, using the heat flow method according to the ISO 8301 (the old version of ISO 9869). Thermal conductivity was measured with the help of a special equipment (Lambda 2300 device) by altering the test sample thickness and material bulk density. They found that sheep wool is capable of high hygroscopicity, up to 35% under normal conditions. They stated that wool can absorb a lot of water and water vapour without major changes in thermal and physical properties, meaning that condensation can be prevented.As far as the hemp insulation is considered, there is a number of papers about its performance, like the analysis of the comparative in situ hygrothermal performance of hemp and stone wool of Latif E. et al. (2014), which used two different protocols of hygrothermal boundary conditions: quasi-steady state and dynamic. The tests were made both in a real-life building and in the laboratory, and the results were measured by temperature and relative humidity sensors, as well as heat flux sensors. Their conclusion was that there was no significant difference to the U-value between these two types of testing. Also, the frequency of occurrence of condensation seemed to be lower in Hemp than in stone wool.Walker R. and Pavía S. (2015) tested and compared the performance of seven insulation materials on a historic brick. Firstly, they used a laboratory technique with an oven to find the different heat capacities and the bulk densities and then they performed an in-situ technique (with the aid of heat flux sensors, thermal imaging survey and internal wall temperature) in order to calculate the U-Value of the materials.Additionally, Latif E. et al. (2015) tested the hygrothermal performance of wood-hemp insulation, according to ISO 9869 about the heat flow method. They performed a full-scale test building and they compared the heat transfer properties and the possible frequency of mould growth and condensation of two insulations panels (with and without a vapour barrier). They found that the U-values were almost identical to the manufacturers’ declared.Moving on, Cai S. et al. (2017) reviewed the moisture behaviour and thermal performance of the conventional insulation material, polystyrene. In this work, different protocols of moisture and thermal performance are stated and an interesting comparison between field and laboratory testing is analyzed. They analyzed guarded hot plates, heat flow meters, thin heater apparatus and hot box methods for thermal conductivity testing, along with field testing with the use of appropriate sensors. In terms of moisture, they mentioned water immersion tests, soil immersion tests and field testing.After taking into consideration all the work that has been done for both thermal and moisture performance, this dissertation will review the main protocols that are currently used and develop a method to test three sustainable insulation materials in dynamic and steady-state conditions. According to the literature review, heat conductivity and moisture performance are missing analysis in different weather data. Therefore, it is interesting to explore the way that insulation materials respond to different locations around the world. Additionally, the comparison between conventional and non-conventional materials will provide benchmarks and results to fully understand the importance of the sustainable materials.Research design and methodologyThe first step is to develop a quick and cheap testing protocol to calculate the performance for both the heat capacity and the thermal conductivity with acceptable accuracy. The determination of the thermal properties will be done according to the BS EN ISO 6946:2007 (British Standards Institution, 2007). Therefore, the thermal resistance will be calculated through the equation:(British Standards Institution, 2007)where,d is the thickness of the material layerλ is the design thermal conductivity of the materialThe design thermal conductivity can be obtained from the tabulated design values of another British standard (British Standards Institution, 2000). Hemp fibre, sheep wool and wood fibre are the sustainable insulation materials that will be tested using the above formula, and also there will be a simulation analysis through the simulation software, DesignBuilder.Then, the testing of moisture performance of these materials will be done by calculating their vapour permeability and absorption isotherm. The determination of the water vapour transmission properties will be based on the procedure included in the BS EN ISO 12572:2001 (British Standards Institution, 2001). More specifically, each insulation material will be sealed to the open part of a test cup which will contain an aqueous saturated (wet cup) or a desiccant solution (dry cup). This cup will then be inside a chamber that will control both the humidity and the temperature. It is expected that due to the difference of the partial vapour pressure between the cup and the chamber, a vapour flow will occur. The cup will be weighed for multiple times during a period of time in order to calculate the rate of water vapour transmission in a steady state environment. Additionally, according to same standard, all facings and skins have to be removed and the insulation material should be at least 20 mm thick. After that, a series of different equations will be calculated so as to determine the material’s hygro-properties (British Standards Institution, 2001). Further assessment will be performed through WUFI and/or DesignBuilder in order to search for possible performance differences for weather variations. Therefore, I will run multiple simulations for different climates.The aforementioned steps will be carried out to compare the non-conventional materials with the conventional ones, and more particularly, to mineral roll, EPS and Celotex insulation. The results will be analyzed resulting in turning data into knowledge of thermal and moisture performance of insulation materials.TimetableFigure 1 shows the tasks of the dissertation and their dates of completion. More specifically, in crucial tasks that involve development or analysis, such as the development of an easy and cheap testing protocol, more time is required. The target is to start the dissertation in 4th of June and finish by 16th of September. It is also very important to mention that during all these sections, the aim is to procced writing gradually, avoiding the possibility of being anxious to write everything in the end. Additionally, arranging as many meetings with my tutor as possible is crucial, in order to confirm the ongoing processes. To conclude, the part that will take the most time is the final one, the connection of all the information together and the correction of any possible mistakes.Figure 1. Timetable using a Gantt chart.Resources and obstaclesDuring my dissertation, the main obstacle is the fact that laboratory tests cost quite a lot, thus using a laboratory is not feasible. At the same time, fire testing would be interesting as well, but again, the limitations of the budget do not allow to do that. Therefore, the dissertation results will be highly connected to the current scientific papers in this particular topic. However, laboratory testing requires a lot of time as well which is, unfortunately, lacking.Also, the University does not provide students with software licenses except for Design Builder. Therefore, using WUFI software for the moisture performance will require spending time to one of the four in total computers that the master has. Thus, working from home is not possible and the MSc’s computers, which are quite few, are in a noisy environment. Finally, the version of WUFI on those computers is not the new one, meaning that access to the latest and most improved software is not feasible.

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