Hygrothermal Performance Research Articles

Hygrothermal performance of micro inhomogeneous insulation materials - EPS-based wall panel

Presence of water in liquid or vapor form leads to mould growth in building materials, weakening the building's structural integrity. Excess moisture in non-breathable materials also impacts thermal properties and performance over time. Hygrothermal analysis and understanding moisture movement within walls are crucial for comprehending wall assemblies in the enclosed spaces of buildings. Numerous commercial software packages are available for estimating moisture risk in wall assemblies. However, it's essential to recognize that these software tools are primarily designed for conventional insulation walls and may not be suitable for materials like EPS-based concrete, which incorporate expanded polystyrene particles. Since micro-level analysis of moisture flow is largely unexplored, this study used mass diffusion theory with ABAQUS-CAE. The study found that EPS beads increased moisture levels in walls by 2–6%. Additionally, due to the porous nature of concrete, moisture penetration and fluctuations were lower compared to other materials. Accumulated moisture made the wall impermeable and weakened the load-bearing material over time. To mitigate moisture effects of 20–28 %, it's recommended to use cement-fiberboard (CFB), which can be replaced if damaged without affecting structural integrity. SEM and EDX/EDAX analyses were used to show moisture accumulation at the micro level. It was observed that more oxygen elements were present at the border of the EPS-bead-mortar mix. The fuzzy-based MCDM method helped mitigate uncertainty in parameter selection, while ABAQUS model analysis considered different scenarios with variations in parameters. This research helps developers and practitioners choose materials with low concrete solubility and high concrete vapor diffusion factors for EPS-based panels, reducing moisture damage.

Effect of connection methods on hygrothermal performance of prefabricated concrete building walls

With the ongoing surge in global energy demand and the escalating environmental concerns, attention has turned to building energy consumption in numerous countries. According to a 2019 report by the International Energy Agency (IEA), the global building industry is responsible for 36 % of energy consumption, ranking first among all industries. The 2022 China Building Energy Consumption and Carbon Emissions Research Report highlighted that in 2020, China's building energy consumption and carbon emissions represented 45.5 % and 50.9 % of the national total, respectively. Achieving carbon neutrality now hinges on decarbonizing buildings. Prefabricated buildings, as a prime example of industrialized construction, aid in reducing carbon emissions through standardized, factory-based production. However, unlike conventional construction, prefabricated concrete buildings (the dominant form of prefabricated buildings) employ metal connectors to join the prefabricated components. These metal connectors generate thermal bridges that can influence heat and moisture transfer through the walls. In this study, a coupled heat and moisture transfer model will be established to analyze the influence of different connection methods on the hygrothermal performance in prefabricated concrete building envelopes. Two typical connection methods for prefabricated buildings are mainly investigated: the grouted sleeve connection and the bolted connection. The findings indicate that different connection methods for prefabricated building connectors increase both the heat and moisture transfer rates in prefabricated concrete structures. Compared to the grouted sleeve connection method, the bolt connection method has a more significant impact on the thermal and moisture performance of the wall. In the tests on the T-shaped structure, the grouted sleeve connections increase heat transfer by 9%–10 %, while the bolt connections increase it by 52%–55 %. During summer, the bolt connections show a 7.42 % higher moisture transfer than the grouted sleeve connections, whereas, in winter, the bolt connections reduce moisture transfer by 12.4 % more than the grouted sleeve connections.

The Thermal Comfort and Hygrothermal Performance of the First Certified Passive House in Estonia

The Thermal Comfort and Hygrothermal Performance of the First Certified Passive House in Estonia

Experimental analysis of building components with paper and textile waste

The fast growth of building constructions industry and of the universal population is the main cause of increase in global energy consumption. Therefore, the improvement of the building envelope encourages the scientific community to investigate the use of alternative materials that assure indoor comfort conditions and at the same time promote the reduction of energy consumption by adopting energy saving strategies in the manufacturing process. The present research contribution aims to focus on the potential use of innovative building materials developed with waste paper, classified as urban non-hazardous discard component. The use of paper pulp originated from recycled paper and cardboard with the addition of textile fibers from industrial by-products was explored. Here, an effort has been made to realize sustainable insulating panel for internal use, considering different mix design and recycled components in various percentages. The research focuses on hygric, thermal, and physical performances of recycled waste based panels, measuring physical aspects as bulk porosity and bulk density and testing hygrothermal performances as the dry-state thermal conductivity, thermal diffusivity, volumetric heat capacity, and water vapour permeability. Furthermore, in order to assess the hygrothermal behaviour of the building envelope, a numerical simulation, carried out by WUFI® Plus in a Mediterranean context, was developed using as inputs the results collected from the measurement campaign in laboratory.

Enhancing the hygrothermal performance of corn cob residue-based eco-friendly building materials through biochar and microencapsulated phase change material incorporation

Amid mounting environmental concerns and the relentless advance of climate change, this study delves into the potential of biochar derived from corn cob waste to enhance the hygrothermal performance of bio-based building materials. Focused on eco-conscious construction, the research explores the integration of biochar and phase change materials (PCMs) to reduce carbon emissions and improve energy efficiency. Results show that adding biochar at 5 % and 10 % ratios increases surface area and porosity, enhancing PCM loading and energy storage. Biochar also improves thermal stability by approximately 13.3 %, delaying PCM oxidation and boosting resilience. The addition of 10 % corncob biochar yields optimal heat capacity and energy storage. Furthermore, biochar increases the water vapor resistance coefficient by 84.57 % compared to materials without biochar. Although there is a slight decline in thermal conductivity across different humidity levels, attributed to the enhanced water vapor resistance coefficient, the overall insulation performance remains robust. In summary, this study demonstrates the enhanced hygrothermal potential of biochar derived from bio-waste and exhibits high compatibility with phase change materials, contributing to sustainable building.

Hygrothermal response of a wood-frame thick-wall assembly to rainwater wetting under future climate scenarios in Canada

Current exterior wall assembly designs for new low-rise residential buildings targeting low-energy demand in heating dominated countries include split-insulation wall and thick-wall assembly designs. Both have been shown to result in thermal efficiency gains compared to building-code minimum assemblies, however long-term hygrothermal performance can vary depending on boundary conditions and the presence of construction deficiencies. Future climate scenarios estimate many heating-dominated climates will experience a reduction in heating-degree day hours and an increase in annual rainfall. Using validated assembly performance data from a Passive House certified facility, a sensitivity analysis is performed to determine the impact of rainwater wetting, air exfiltration and insulation material properties on the hygrothermal response of a thick-wall assembly. Results show that rainwater leakage values of 0.50% and greater of the adhering rainfall on the exterior surface of the assembly results in the greatest risk for failure. The hygrothermal response of the assembly is then examined under a global temperature rise scenario of 3.5°C for five geographic locations across Canada. Results show that an increase in average annual total rainfall does not directly result in an increase in the failure rate of the assembly when a rainwater leak is present. Additional climatic factors, including outdoor air temperature, driving rain and solar radiation received will influence the hygrothermal response of the assembly and need to be considered when modelling the performance under future climate change scenarios.

Hygrothermal Performance of the Hemp Concrete Building Envelope

The search for environmentally friendly and low-carbon-footprint construction materials continues progressively. Researchers are now interested in innovative materials that connect with the principles of sustainable construction, and materials such as hemp concrete prove to be promising. This article presents the results of a study that aimed to evaluate the hygrothermal performance of hemp concrete integrated into the building envelope using the hygrothermal tool WUFI Pro 6.2. The simulation model was compared and verified with existing models before its utilization for this study. The results of this verification were in good agreement, which gave us more confidence in its application for further parametric studies of building envelopes in hot climate zones. Three wall systems were simulated: (i) a wall system with hemp concrete, (ii) a compressed earth block wall, and (iii) a cement block wall. The most important variables used in the simulations were the hygrothermal properties of the materials or wall components and the incident solar radiation. The simulation results showed that hemp concrete has good thermal performance and temperature and humidity regulation capabilities of the building envelope. The interior surface temperatures of the hemp concrete walls were between 22.1 °C and 24.6 °C compared to the compressed earth block and cement block walls, where the surface temperatures were between 22.0 °C and 27 °C and between 21.2 °C and 28.7 °C, respectively, and between 23 °C and 45 °C for the exterior temperatures. These values remain the same with the increase in exterior temperatures for hemp concrete walls. In conclusion, hemp concrete could be a great alternative material for use in construction for hot climate zones.

Hygrothermal characterization of lightweight biosourced composites based on date palm fiber and lime

ABSTRACT Biosourced materials derived from agricultural by-products hold significant promise in both enhancing the hygrothermal performance of buildings and reducing their environmental footprint. We investigate the hygrothermal properties of green composites based on date palm fibers and lime. The eco-friendly building composites explored are manufactured using either trunk fiber (surface fiber) or rachi and petiole fiber (wood fiber). Through an experimental approach, for different fiber percentages, the hygrothermal characteristics of the explored composites were experimentally determined in terms of thermal conductivity, diffusivity, porosity, water vapor permeability, and sorption scanning isotherms. The results show that date palm fiber has a positive effect on the thermal properties of the composite material. Indeed, it significantly enhances the insulating capacity of the composites. Water vapor permeability exhibits significant variation depending on the fiber content, with samples containing higher fiber content exhibiting greater permeability. Furthermore, the effective moisture penetration depth (EMPD) model proved effective describing the experimental adsorption scanning isotherm curves. It was observed that the sorption process is significantly influenced by both the type and percentage of fibers. Finally, the observed results demonstrate that date palm fiber and lime composites could offer notable advantages for construction applications and serve as an effective, cost-effective insulation.

Assessment of hygrothermal performance of raw earth envelope at overall building scale

Environmental challenges in the building sector have made raw earth a significant ecological alternative. The development of sustainable materials and a clear understanding of their behaviour are essential for sustainable construction. This work aims to respond to this societal issue.This investigation uses a HAM-BES cosimulation methodology that integrates dynamic thermal simulation code (TRNSYS) with a hygrothermal transfer model developed by Luikov and solved by Comsol Multiphysics. The study aims to investigate the energy needs of different building envelopes in several climates where there is raw-earth architecture. A comparison between a cob monolayer envelope and a polystyrene insulated polystyrene insulated brick multilayer envelope has been carried out. This study shows that the raw earth monolayer wall has a higher energy need for oceanic and tropical climate with, respectively, 14 and 19%. A decrease in demand has been found for the desert climate. Moreover, it was shown that the coupling of heat and mass transfers results in a notable reduction in energy demand that can reach 11.5% annually and up to 23% quarterly for tropical climate. These findings highlight the efficiency of raw earth materials and stress the importance of thoroughly understanding and incorporating heat and mass transfer dynamics in the evaluation of sustainability for biobased and earth-based construction materials.

Timber-framed exterior walls insulated with wood shavings: A field study in a nordic climate

Wood processing residues provide a possibility to produce thermal insulation material with low environmental impact. This paper deals with the hygrothermal performance of timber-framed exterior walls with wood shavings as insulation material. The presented study consisted of field measurements of five exterior wall structures with two different types of wood shavings insulation and three reference walls. The study was performed in cold Nordic climate, where hygrothermal conditions at outer parts of a wall structure are critical. Untreated wood shavings and wood shavings coated with pulverized clay were compared as insulation materials. Different wind barriers as well as a water vapour barrier and sheathing acting as vapour retarder were also used. Results indicated no suitable conditions for mould growth inside any wall. The thermal resistance of wind barriers as well as the clay-coating of wood shavings had positive effect on the hygrothermal performance of the test walls. Wood shavings proved to be suitable insulation materials for well-insulated structures from the hygrothermal point of view, when the overall design, construction and maintenance are carried out in a proper way.

Hygrothermal assessment and design models for mass timber building envelopes in northern conditions

Log construction has a long and rich tradition in Northern Europe, yet the rising demand for energy-efficient log housing poses challenges for designers seeking optimal hygrothermal performance. One proposed solution involves utilizing a double-log structure, integrating thermal insulators between two log layers to maintain heritage while enhancing thermal resistance. This study addresses the complexities of designing energy-efficient log buildings in cold and arctic conditions and investigates steady-state and dynamic approaches to hygrothermal assessments. Emphasizing various cold climate scenarios, hygrothermal design intricacies, moisture safety considerations, and critical parameters impacting building performance, the research fills knowledge gaps in design strategies and highlights the risks associated with the double-log structure.

A Numerical Study of Methods to Improve Moisture Safety of Ventilated Wooden Roofs

The hygrothermal performance of highly insulated, prefabricated wooden roof structures is likely to deteriorate due to the low heat flux to the ventilation cavity. This article evaluates the possibility to improve the moisture safety of such roofs in a Nordic climate by using different control methods for the ventilation rate of the roof and by using thermal insulation above the roof sheathing. The results support the use of adaptive roof ventilation as it decreases the probability of mould growth in the roof. The use of thermal insulation above roof sheathing decreases the probability of mould growth only slightly in a roof with elevated amount of built-in moisture.

Exploring the integration of bio-based thermal insulations in compressed earth blocks walls

The growing concern about the environmental impact of contemporary construction has posed emphasis on the possibilities offered by bio-based and raw earth construction. The front challenge for the establishment of earth-based technologies in contemporary building markets is the guarantee of high structural and energy performances, while maintaining a low environmental impact. This work focuses on the performance analysis of compressed earth blocks (from now on CEBs) which are currently commercialized for the construction of massive vertical envelopes, with high thermal inertia. However, to obtain an acceptable comfort and an optimized thermal behavior, CEBs walls must also reach a high thermal resistance. This issue can be overcame by the design of insulated CEB stratigraphies using bio-based thermal insulations presenting hygrothermal properties compatible with raw earth-based materials. In this way, the thermal performance of CEBs walls can be increased, while preserving their hygroscopic behavior. In this spirit, this work reports the results of the experimental characterization of three materials: CEB, lime hemp and sugarcane bagasse bio-based insulation panels. It includes their composition, their main physical (dry density, porosity, capillary water absorption), thermal (specific heat capacity, thermal conductivity) and hygrometric (sorption isotherm, water vapor permeability) properties. Finally, these experimental data are used for the implementation of several numerical simulations at a wall scale in a reference climate to estimate the hygrothermal performances of both uninsulated and bio-insulated CEB walls. The simulations allow for a better comprehension of CEBs’ behavior in view of their combination with the chosen bio-based thermal insulations, and give insights into possible moisture-related issues as mold growth or increase of U-value.

Hygrothermal performance of straw bales split-insulation wall assembly in cold and humid climates

The abundance of straw in Quebec makes this material an interesting insulation option to reduce the energy consumption of buildings. At the same time, studies indicate that straw bales’ outstanding hygrothermal performance can provide a comfortable living experience for the occupants. However, due to the slightly higher thermal conductivity of straw bales insulation compared to common insulation materials, the walls are found to be 30–90% thicker, which can lead to moisture-related problems especially under a humid and cold outdoor climate. Therefore, a split-insulation wall structure was used in this study to reduce the wall thickness by combining straw bales with expanded polystyrene (EPS) exterior insulation. Results show that straw bale walls generally have higher thermal inertia and better moisture buffer capacity compared to the reference wall using glass fiber insulation. The hygrothermal profiles show that the sheathing-insulation interface is the position having the highest relative humidity in the walls. The biohygrothermal model also suggests that under Quebec’s climate, the mould grow risk in a straw bales wall with two inches EPS exterior insulation is within acceptable limits.

Long-term hygrothermal performance assessment of wood-frame walls considering climate uncertainties using partial least squares (PLS) regression

As one of the most important input parameters for hygrothermal simulation, the climate data have a significant impact on the simulation results that are used for assessing moisture-related degradation risks of the wall. Climate change brought more uncertainties in the climate data, such uncertainties are related to different global warming (GW) scenarios in the future, and different initial conditions when projecting climate data using a meteorological model; the uncertainties of initial conditions result in different climatic realizations (runs) in each GW scenario. The objective of this work is to develop a climate ranking system concerning the mould growth risk of the wood-frame wall assemblies by considering uncertainties associated with different GW scenarios and different runs. A meta-model based on Partial Least Square (PLS) regression was developed and used as an alternative to the hygrothermal simulations for ranking the moisture severity of climatic data. The PLS model was developed for a brick cladding wall for one Canadian city, Ottawa under different levels of GW from historical (1991–2021) to future periods with an average of 3.5 °C rise in global temperature (2064–2094). The PLS model was developed using the representative climate data sets and it was further applied to the climate dataset generated over 15 runs across all GW levels to cover all the uncertainties in the projected future climates. The results showed the model can predict the mould index and can assist in ranking the runs and GW scenarios based on their moisture severity to mould growth. The ranking system will allow the researchers to assess the mould growth risk of wood-frame building envelopes during their service life without running physics-based hygrothermal simulations.

Experimental Analysis of Moisture-Dependent Thermal Conductivity, and Hygric Properties of Novel Hemp-shive Insulations with Numerical Assessment of Their In-Built Hygrothermal and Energy Performance.

The use of lime as a binder in hemp-lime considerably increases the drying time of hemp-lime after casting. Furthermore, lime is a non-renewable mineral resource. As such, this paper explores the effectiveness of using an alternative non-mineral binder instead of lime to formulate a novel hemp-shive insulation. The moisture-dependent thermal conductivity, adsorption isotherm, vapour diffusion resistance factor, and in-built hygrothermal performance of four variants of a novel bio-based insulation were investigated. The hygrothermal performance of the novel hemp-shive insulation was compared with that of a previously developed novel hemp-lime insulation. No significant variation in thermal conductivity of hemp-shive insulations between the equilibrium moisture contents (EMC) at 0% and 50% relative humidity (RH) was observed, but there was a substantial increase in thermal conductivity hemp-shive insulations when the material reached the EMC at 98% RH. The average dry thermal conductivity values of hemp-shive and hemp-lime insulations were also similar. The adsorption isotherms of hemp-shive insulations were determined at 0%, 20%, 50%, 70%, 90%, and 98% relative humidity steps. At 98% RH, the moisture adsorption capacity of hemp-shive insulations was 4-to-5-times higher than that of hemp-lime insulation. Hemp-shive insulations' vapour diffusion resistance factor (µ value) was about double the µ value of hemp-lime insulation. Hemp-shive insulations exhibited 4-to-5-times higher water absorption resistance than that of hemp-lime insulation. Numerically determined porosity values of hemp-shive agree with the values of wood-based insulation materials of similar density. Finally, using all experimentally acquired data as inputs, dynamic whole-building hygrothermal simulations were carried out and the results show that novel hemp-shive insulation materials perform at a similar level to the hemp-lime insulation in terms of heating and cooling energy demand but require 45% less energy for humidification. However, the relative humidity inside the hemp-shive wall remains higher than 70%, which can potentially induce mould growth.

Drying of an aerogel-based coating system in Swedish climates: Field tests and simulations

Aerogel-based coating mortars (ACM-systems) introduce new solutions for energy-retrofit of uninsulated building envelopes, preserving their characteristics while minimizing the material thickness. However, when introducing new solutions, the long-term durability needs to be investigated. The hygrothermal (heat and moisture) performance is one aspect that needs to be secured. The aim of this study is to investigate the hygrothermal performance, with specific focus on moisture drying, of an ACM-system for external applications in Swedish climates. A field test was conducted where an ACM-system with 40 mm of ACM was applied on the exterior of a brick masonry wall partition. The temperature and relative humidity in the wall were monitored for 15 months. Furthermore, numerical hygrothermal simulations were used to predict the early stage drying and long-term performance of the ACM-system in four Swedish climates. The field measurements showed that the built-in moisture dried out after approximately 6 months, after which the ACM-system followed the variations in the surrounding climate for the remaining period. The simulations predicted that the early stage drying time ranged from 134 to 336 days, depending on climate and time of application. Furthermore, the elevated relative humidity in the ACM due to rainwater absorption resulted in an average thermal conductivity of up to 9 % above the rated value. Consequently, mitigating water absorption at the exterior is crucial for enhancing the long-term thermal performance in high rain load scenarios.

Hygrothermal performance of hempcrete in a multi-layer wall envelope

Hempcrete is a promising self-bearing thermal insulation material, as it has low thermal conductivity and a minor to negative CO2 footprint. It is also believed to be applicable not only in building construction, but also for renovation or additional insulation, since hempcrete hygrothermal properties are compatible with wooden structural elements. To utilize it efficiently, it must be possible to make predictions regarding hempcrete hygrothermal performance and whether it is up to the modern standards — this requires a verified material model for use in numerical simulations. Previously, we have shown that hempcrete by itself performs well as insulation for building wall envelopes, and we have validated a material mode for hempcrete. This study assesses, both experimentally numerically, if hempcrete is suitable for use in multi-layer envelopes. A multi-layered wall envelope of a wooden multi-story building was insulated from the inside with hempcrete blocks. Relative humidity and temperature within the wall, as well as heat flow, were monitored over ∼2 years. The wall envelope was modeled numerically using WUFI. Temperature and humidity dynamics predicted numerically are in good enough agreement with experimental observations. In addition, the mold risk forecast derived from simulation and experiment results agree rather well with actual observations — no mold risk was predicted, and no mold was observed upon inspection. All of this suggests that hempcrete could indeed be used as a part of multi-layer building insulation envelopes, at least for climate conditions sufficiently similar to Latvian.

Assessment of hygrothermal performance and mould growth risk in roofs of post-retrofitted non-dormer and dormer attic rooms with reduced ventilation

Building insulation upgrades focusing on energy conservation must also consider the hygrothermal performance of materials and the indoor environment. Previous research has shown that deep insulation retrofit may inadvertently reduce ventilation and increase relative humidity, increasing the risk of mould growth. This study used traditional housing in Ireland with pitched roofs as the case study to examine changes in the hygrothermal environment following the energy retrofit of a dormer-style attic room. The study compared the mould growth index (MGI) of roof rafters under different energy retrofit scenarios to understand the effect of adding a habitable dormer-style attic room on the house's mould growth risk. The results show that adding an occupied dormer room can increase the MGI of spruce rafters from below 1 to around 5.2 at 0.2 air changes per hour (ACH) of infiltration. In most scenarios, a ventilation rate lower than 1 ACH cannot prevent the MGI of rafters from reaching the critical threshold of 3, unless a 1 mm vapour barrier is added. A ventilation rate over 5 ACH is adequate to limit the mould growth risk, but mechanical ventilation may be required to achieve this level of attic ventilation. This study enhances understanding of the relationship between attic roof ventilation rate and the risk of mould growth during the energy upgrade of dormer style attic rooms, a common housing type across Northern Europe and further afield.

Questionnaire survey on the use of thermal insulation solutions in building facades of Portugal, Italy and Norway

The use of adequate thermal insulation solutions in the opaque walls is one of the most efficient passive strategies towards the improvement of the buildings’ thermal performance. Nevertheless, beyond the thermal performance, a set of different performance criteria (i.e., hygrothermal performance, fire behavior, environmental footprint, among others) must also be considered when selecting thermal insulation materials. This study aimed to enhance understanding of the use of thermal insulation solutions in new construction and for the thermal retrofitting of building facades in Portugal, Italy and Norway. To that end, a questionnaire survey was prepared considering the relationships among the different Political, Economic, Social, Technological and Environmental criteria involved in the selection of thermal insulation solutions. The questionnaire was available online between November 2022 and February 2023 and respondents, primarily living and/or working in Portugal, Italy and Norway, were asked to answer questions related to the use and performance of different thermal insulation solutions. Results showed that different perceptions and levels of knowledge regarding the performance of several insulation materials could be ascribed to the respondent's country of residence.