Hygrothermal Performance Research Articles

Numerical simulation study on the hygrothermal performance of building exterior walls under dynamic wind-driven rain condition

Numerical simulation study on the hygrothermal performance of building exterior walls under dynamic wind-driven rain condition

Stabilization effect on the hygrothermal performance of rammed earth materials

The increasing interest in earthen materials is primarily driven by their hygroscopic and thermo-buffering capabilities, which contribute to their superior indoor air quality. Stabilization is the commonly used solution to enhance their mechanical and hygrothermal properties. The current study uses an experimental approach to investigate the impact of cementitious stabilizers on the hygroscopic properties and thermal conductivity of rammed earth materials. Measured hygroscopic parameters included sorption isotherms, moisture buffering capacity, and water vapor diffusion resistance factor. The hygrothermal experiments were conducted on the unstabilized specimens with different water masses ranging from 5 to 15% and on the stabilized specimens with different cement content ranging from 5 to 20%. Finally, three mathematical models of Halsey, modified Chung-Pfost and Oswin were applied to the sorption isotherm data. The results showed that stabilization positively impacted decreasing the heat conduction and improving the hygroscopic properties of rammed earth materials. Among the three models, the modified Chung-Pfost model was the best fit for sorption isotherms.

Hygrothermal performance of natural building materials: Simulations and field monitoring of a case study home made of wood fiber insulation and clay

This contribution presents temperature and relative humidity data monitored over nearly two years for a case study building made of natural building materials. The case study building is a single-family house located in Denmark made of wood fiber insulation, wood fiber boards and indoor clay plaster without any membranes. Three different types of cladding systems have been tested: 1) mineral plaster rendering; 2) wood cladding applied directly over wood fiberboards; 3) wood cladding with a ventilated cavity. Monitored data is provided and compared with simulations performed with a commercial hygrothermal software. The moisture content and mold growth index are calculated from monitored data. The data indicates that the hygrothermal performance of the roof is excellent (RH < 70%); the hygrothermal performance of the walls with the three different cladding systems is good; one out of two sensor groups in the floor exhibits a moisture content up to 18% at the cold side of the insulation during summer and fall. Securing sufficient and evenly distributed crawlspace ventilation is recommended for eliminating concerns of eventual mold growth. Measurements show that materials employed in this house respond quickly to moisture changes, more quickly that simulated data. This work highlights the need for validating and adjusting WUFI simulation results with measured data to provide reliable results for building envelopes composed of highly hygroscopic plant-based materials. For these assemblies in these conditions, including a vapor retarder is not needed for achieving a satisfactory hygrothermal behavior.

Experimental and numerical evaluation of the hygrothermal performance of three different building finishing layers including phase change materials

Experimental and numerical evaluation of the hygrothermal performance of three different building finishing layers including phase change materials

Hygrothermal Performance of Bio-Based Exterior Wall Constructions and Their Resilience under Air Leakage and Moisture Load

The use of renewable building materials in construction is crucial to minimising the environmental impact of new buildings. Bio-based building materials have a wide range of positive properties, many of which are due to their hygroscopic behaviour. The purpose of this study is to investigate the hygrothermal performance of chopped straw, sheep’s wool, and cellulose insulated timber frame external wall assemblies in the presence of air leakage and high indoor relative humidity. For this purpose, tests with different moisture contents, overpressures, and defects in the airtight layer were carried out in an outdoor test stand over a period of 18 months. The results were compared with a conventional mineral wool insulated construction. Both sheep’s wool and cellulose are particularly fault-tolerant insulation materials in combination with timber frame constructions. All three bio-based insulations, despite defects in the airtight layer, showed no mould-prone moisture content. An installation level insulated with sheep’s wool can increase the fault tolerance of constructions with insulation made of hygric and more sensitive building materials. For chopped straw and cellulose, the measured U-value was lower than expected. Further in situ measurements of bio-based structures are important to gain confidence in their hygrothermal behaviour and to increase their use in multi-storey construction.

Experimental Assessment and Validation of the Hygrothermal Behaviour of an Innovative Light Steel Frame (LSF) Wall Incorporating a Monitoring System

Currently, the construction sector is witnessing a growing demand for lightweight solutions, which can be justified by the need to adopt high-performance solutions and the fact that the industry is struggling with a shortage of skilled labour. In this sense, this study focuses on a novel and flexible building wall system, constructed using an innovative extensible LSF profile. To enhance its functionality, a monitoring system comprising printed sensors was integrated into the wall. These sensors underwent a thorough verification process. To evaluate the hygrothermal performance of the complete LSF wall solution and validate the novel monitoring system, an extensive ageing test focused on heat/rain, freeze/thaw cycles was conducted on a large-scale wall prototype. Additionally, this research introduces a novel approach by simulating exceptional solar radiation conditions, surpassing the standard cycles outlined in EAD 040083-00-0404, for the first time in this kind of solution. The results cover the measurements taken inside the building system using the incorporated monitoring system. Additionally, supplementary external temperature and heat flow sensors were used to determine the thermal transmittance. Visual and thermography inspections were also carried out. The findings reveal no instances of failures or defects that could potentially impact the hygrothermal behaviour of the system. The hybrid LSF constructive solution leads to more stable temperatures on the inner surface. The presence of direct solar radiation can raise surface temperatures by up to 5 °C compared to surfaces not exposed to such radiation, even when a light-coloured surface is used. The monitoring system worked correctly. In conclusion, the innovative profile proved to be resistant to hygrothermal cycles and the monitoring system developed is efficient.

Hygrothermal Assessment of Insulation Systems for Internal Insulation of Solid Masonry Walls under Various Conditions

Energy efficiency renovation of building stock is an essential aspect of the climate change mitigation strategies in many countries. A large proportion of building stock is historical buildings. For this building stock, developing technology for safe internal insulation of external walls is crucial, preventing possible moisture damage to the building structures. Internal insulation is a risky technique as it has a high impact on the hygrothermal behavior of the wall. This study assesses the hygrothermal performance of massive masonry walls with 17 interior insulation systems exposed to different external boundary conditions, including a steady-state cycle, dynamic dry cycle, wind-driven cycle, and drying cycle. During the steady state cycle, the highest increase of moisture was observed under capillary active materials ranging from 39 to 119% increase in absolute moisture, with the exception of cellulose with an increase of only 7%. All the vapor-tight insulation systems showed no increase in absolute moisture during the steady-state cycle, with the exception being mineral wool in combination with a vapor barrier that showed a 30% increase in ablute humidity. In addition, relative moisture changes in masonry were measured. Results show that tested insulation systems exhibit similar thermal performance while having different moisture performance. Vapor-tight and vapor-open insulation systems exhibit different hygrothermal behavior under various test cycles depending on material vapor diffusion resistance. Numerical simulations are sensitive to the hygrothermal properties of materials.

Energy efficiency and hygrothermal performance of hemp clay walls for Moroccan residential buildings: An integrated lab-scale, in-situ and simulation-based assessment

Hemp-based building envelopes have gained significant popularity in developed countries, and now the trend of constructing houses with hemp-clay blocks is spreading to developing countries like Morocco. Investigating the hygrothermal behavior of such structures under actual climate conditions is essential for advancing and promoting this sustainable practice. This paper presents an in-depth experimental characterization of a commercial hemp-clay brick that has been exposed to the outdoor environment for four years, in addition to field measurements on a building scale demonstration prototype. Additionally, the study simulates 17 representative cities to assess the hygrothermal performance and energy-saving potential in each of Morocco's six existing climate zones, using the EnergyPlus engine. The experimental campaign's findings demonstrate excellent indoor air temperature and relative humidity regulation within the hemp-clay wall building, leading to satisfactory levels of thermal comfort within hemp-clay wall buildings. This is attributed to the material's good thermal conductivity and excellent moisture buffering capacity (found to be 0.31 W/mK and 2.25 g/m2%RH), respectively). The energy simulation findings also point to significant energy savings, with cooling and heating energy reductions ranging from 27.7% to 47.5% and 33.7% to 79.8%, respectively, as compared to traditional Moroccan buildings.

Development and hygrothermal performance analysis of a novel eco-friendly insulating wall under various climatic conditions

This work proposes the development, characterization and modelling of new eco-friendly building walls integrating stabilized forms of phase change materials. The aim is to enhance the hygrothermal and energy performances of buildings by improving their management of thermal energy throughout the year and meeting users’ thermal comfort requirements. These are essential axes to help decarbonize heating and cooling, to rehabilitate buildings and to contribute to the energy transition. The experimental and numerical hygrothermal performances of two different building walls are assessed and compared under realistic weather conditions. The maximum temperature inside the wall is reduced by 2 °C for the phase change material hemp concrete compared to the reference hemp concrete in a context of typical summer heatwaves day. Both phase change material hemp concrete and reference hemp concrete showed good moisture regulation capability by dampening cyclic variations in outdoor humidity. The developed numerical model exhibited a good agreement with the experimental results with a maximum root mean square error between experimental and numerical results of about 0.6 °C and 6% for temperature and relative humidity, respectively.

Eco-efficient boards with agro-industrial wastes – Assessment of different adhesives

Laboratory tests were carried out to evaluate the feasibility of producing boards or coating panels with good hygrothermal performance by using different agro-industrial wastes (grape and olive press wastes, hazelnut shells, spent coffee and pine) and adhesives (gypsum-based binder, sodium silicate solution and starch-based glue). Hygrothermal properties and resistance to mould growth, including the effect of citric acid, were evaluated. The results highlighted the benefits and drawbacks of each adhesive: the binder seems more adequate to produce bio-based plastering mortars than boards; the other adhesives seem efficient solutions to produce boards with good hygrothermal properties; for the natural glue the bio-susceptibility needs improvement.

Influence of Spanish Energy-Saving Standard on Thermal Comfort and Energy Efficiency Owing to the War in Ukraine: Case Study of an Office Building in a Dry Mediterranean Climate

The energy-supply crisis, aggravated by the war in Ukraine, has prompted EU governments to approve urgent energy-saving measures. The new Spanish energy-saving standard aims to reduce energy consumption by changing the regulatory limits for indoor hygrothermal conditions in buildings. This regulation has provoked a great social debate about its real effectiveness and its impact on user comfort. This work explores the hygrothermal performance of an office building in southeastern Spain. The objective of this research is to determine qualitatively and quantitatively how the new energy-saving standard in Spain influences energy efficiency and indoor thermal comfort, by considering the characteristics of the dry Mediterranean climate (BShs) within a warm semi-arid climate (BSh). The scientific novelty of the study is to demonstrate that the new Spanish standard not only reduces energy costs but also makes the indoor comfort of buildings much worse; for this reason, an improvement in the standard is also proposed. The study methodology consists of a comparative study between the thermal performance, thermal comfort, and energy demand of the building, considering both the new and previous standards’ requirements. It also includes the evaluation of a proposal to improve the current standard. The results showed that the new energy-saving standard reduced energy consumption by 21.78% in comparison to former standards, but the new comfort ranges were not acceptable for 60% of the users. The proposed improvement does achieve acceptable comfort for most users (75%) and an additional reduction in energy demand of 48.76% compared to current standard. We conclude that the thermal comfort requirements of the current energy standard should be modified to better adapt the design criteria to the dry Mediterranean climate.

Investigating the impact of construction workmanship defects on the hygrothermal performance and airtightness of lightweight-structure wooden envelope systems

Global energy demand continues to increase, and the construction sector has a fundamental role in this subject by achieving high hygrothermal performance. This study evaluates the impact of construction quality defects on the hygrothermal performance and airtightness of a lightweight-structure wooden envelope system. Four typical defects were evaluated, orifices in the weather barrier, staples in the vapor barrier, nails diverted to external insulation, and separated structural elements. The results showed that all the defects decreased the hygrothermal performance of the wood-frame envelope assessed. Structural separation and staples over the vapor barrier caused the most significant negative variations, increasing heat loss, the probability of interstitial condensation and air infiltration considerably.

Experimental and numerical simulation study on hygrothermal migration of damaged envelope walls during wind-driven rain

The optimal design of building envelopes, indoor environmental control, and energy efficiency are significantly impacted by damaged envelope walls. Cracks are crucial for accurately assessing the hygrothermal behavior of damaged walls, especially under the dynamic boundary of wind-driven rain (WDR). To evaluate the hygrothermal performance of envelope walls with cracks, we conducted experimental and simulated comparative studies on walls under the action of WDR. A capillary pressure model for high humidity environment was established. By analyzing field measurement results of damaged walls subjected to the WDR of Shenyang in 2022, we performed heat and humidity coupling numerical simulations of damaged envelope walls. The crack penetration depth, distance from cracks, and wall height were analyzed comparatively. Compared with the undamaged wall, the moisture content of crack depth under 36 mm (penetrating crack), 20 mm, 12 mm and 6 mm increased by 17.2%, 6.9%, 3.9% and 1.5%, respectively. Compared to the humidity distribution at 0.50 m, the relative humidity at 0.1 m, 0.2 m, 0.3 m and 0.4 m increased by 29.9%,27.6%,23.1% and 15.2%, the temperature changed by 1.20K,1.11K,0.72K,0.41K. The effects of various factors such as crack penetration depth, distance crack length, and wall height on the hygrothermal behavior of porous material building enclosures subjected to the WDR are derived. A theoretical basis is provided for the analysis and research of coupled hygrothermal transfer in porous buildings under the dynamic boundary of WDR.

Characterization of hygrothermal properties of two wood species- the impact of anisotropy on their thermal and moisture behaviors

Wood is an anisotropic material that has non-identical properties in different structural directions. Due to its particularly biological characteristics, wood is susceptible to moisture degradation. To better understand the hygrothermal performance of wooden products in buildings and reduce moisture-induced deteriorations, a complete hygrothermal measurement of oak and spruce in three structural directions is carried out. The oriented-dependent moisture transport characteristics are acquired from water vapor transmission, drying, and water absorption tests. The anisotropic properties of both wood species are characterized, and their impacts are further investigated by studying the thermal and moisture behaviors of spruce and oak beams embedded in the wall assemblies interiorly insulated by the calcium silicate and mineral wool insulation systems. Hygrothermal simulations performed by the 2D and 3D models with the isotropic property are compared with those of the 3D models with the anisotropic property. The results show that the 3D hygrothermal models with the anisotropic property can properly represent the heat and moisture conditions of wooden beams. The longitudinal property yields a similar hygrothermal performance of the wooden beam to the anisotropic property. For simplification, the longitudinal property can replace the anisotropic property of wood in the 3D model of the wall assemblies to assess the moisture deterioration risk with sufficient accuracy.

Evaluation of a modular construction system in accordance with the Passivhaus standard for components

Passivhaus is an energy performance standard for buildings that has been deeply analyzed in the current scientific literature. However, the study of the Passivhaus standard for components and the use of certified components in the construction of new nearly-zero energy buildings have not been thoroughly discussed. Additionally, hygrothermal performance evaluations of components in accordance with this standard have not been fully presented to the scientific community. This paper addresses this topic and aims to evaluate the hygrothermal performance of a Spanish modular construction system of extruded aluminum, in accordance with the criteria for Passivhaus components, suitable for warm temperate climate. A three-part methodology was implemented, including hygrothermal performance simulations on fourteen connection details comprising wall, roof, window, and floor solutions. The initial outcomes reveal that only four connection details fully meet the Passivhaus criteria for components. Therefore, an optimization of the connection details is proposed to validate the Passivhaus suitability of the construction system. The connection details are redesigned to reduce thermal energy losses in the junctions and to eliminate the risk of interstitial condensation. Several simulation processes are then conducted and the new results are compared against the criteria for components, validating the Passivhaus suitability. The evaluation presented in this paper provided valuable data that enabled to later optimize and submit the construction system to the Passivhaus Institut to become the first lightweight metallic construction system for walls and roofs manufactured in Spain with a Passivhaus certification for warm temperate climate.

Hygrothermal Performance of Thick PCM Mortar behind PV Panels in Energy-Activated ETICS Facades

The concept of integrating PV panels into traditional ETICS facades has been developing for several years. Problems concerning the options for passively controlling the temperatures of PV panels with PCM and directing excess moisture out of the wall via diffusion channels have been previously studied theoretically. During this study, real wall-scale experiments were conducted to test the thermal and hygrothermal performance of the wall system in an extreme climatic environment, as well as in a real outdoor environment in Tallinn, Estonia. Finally, a simulation model was calibrated according to the measured data. It was found that in case of test walls with diffusion channels, it was possible to keep the moisture content of PCM mortar under 0.11 m3/m3. Excess water drained out via channels leading to the external environment. Without diffusion channels, the moisture content rose as high as 0.18 m3/m3. Both the experiments and hygrothermal modelling showed that the high moisture content of PCM mortar, caused by water leakage, dropped to 0.08 m3/m3 over 10 solar cycles as moisture escaped via the diffusion channels. PCM mortar with a moisture content of 0.08 m3/m3 endured extreme rain and freeze-thaw cycles without visual damage, and PV panels retained their electrical production capabilities.

Hygrothermal Performance of Adobe Structures

Vernacular architecture incorporates many cooling and heating passive design strategies related to the structural envelope, the different architectural arrangements and the way of living of the inhabitants. Adobe walls are considered to be high thermal mass masonries, as they have the ability to store thermal energy. The high thermal inertia of these materials regulates indoor temperature variations through considerable time lags, thus contributing to the improvement of thermal comfort conditions. This study deals with the environmental behaviour of an adobe historic building in the rural area of Nicosia, Cyprus. The aim of this study is the investigation of the hygrothermal performance of the external adobe masonry walls of the structure under study. For this purpose, in-situ long-term monitoring is currently being carried out, focusing on the indoor and outdoor environmental conditions of a south wall of a room which has two exposed surfaces, the north towards the street and the south towards a courtyard. The south wall is being monitored with temperature/moisture sensors, installed at various locations along its thickness and height. In situ monitoring is complemented with laboratory measurements of the thermophysical (thermal conductivity, porosity, and sorptivity) properties of the main masonry material (adobes). Rising damp height, time of wetness, thermal inertia and decrement factor have all been calculated based on the laboratory and in-situ measurements. The results are analysed in terms of existing standards and analytical equations. The findings of this research may be used to evaluate the overall thermal performance of historic adobe buildings and the effectiveness of adobe walls in the improvement of indoor comfort conditions.

Experimental investigation of parameters influencing mechanical properties of hemp concretes using design of experiment method

Global concerns about climate change have led to the development of building materials that use plant biomass with the added benefit of sequestering carbon from the atmosphere. Lightweight concrete made with hemp, is a material with huge potential in terms of its ability to achieve hygro-thermal performances close to those of polystyrene. This ecological material, referred to in the literature as hemp concrete, is made of some components that, depending on the chosen combination, can generate different results of the physic-mechanical properties. The method is based on a series of experiments that are generated using a program called Design of Experiments (DoE). This program uses statistical analysis of a series of experiments performed by varying one of the input parameters, like the amount of hydrated lime or cement. Following this analysis, it is possible to identify those elements used in the composition, which produced a significant influence on the physical-mechanical properties of hemp concrete. Moreover, this method also allows a quantification of the influences so that the parameters can be ranked, with a minimum number of experiments. The method is, in the same time, a modern and an economical technique used for experimental planning. The aim of the research is to quantify numerically the influence of each component element of the mixture that determines variations of the physical-mechanical properties in hemp concrete. This study will contribute in the future to the optimization of compositions, which will be differentiated on the basis of mechanical performance or thermal insulation criteria.

The Importance of Moisture Transport Properties of Wall Finishings on the Hygrothermal Performance of Masonry Walls for Current and Future Climates

A render is the first protective layer of exterior walls against the outdoor climate, which, due to its constitution, aims to gradually slow down the liquid moisture penetration to prevent it from reaching the wall inner layers. Due to the future expected changes in the outdoor climate, today’s exterior mortar might not be adequately designed to protect these walls. This paper aims to analyse the influence of mortars on the hygrothermal performance of solid brick walls under current and future climates. The study includes four types of assemblies and three types of mortars, and it was carried out for Lisbon and three other climates by using a computational simulation tool. Finally, the moisture gains and respective reach due to the future wind-driven rain (WDR) spells were assessed by means of using future weather files for Lisbon’s climate. It was shown that the solid brick layer is influenced differently depending on the characteristics of the mortar layers and outdoor conditions. In terms of WDR spells, aside from the precipitation and the spell period, the distribution of the WDR events within the spell also conditions the dryness of the assembly. The depth that the outdoor moisture was able to reach varies between 94 and 200 mm.

Hygrothermal Properties Analysis of Bamboo Building Envelope with Different Insulation Systems in Five Climate Zones

Laminated bamboo lumber (BLL) and bamboo scrimber (BS) are potential environmentally friendly building materials, considering that they are hygroscopic materials and that their hygrothermal performance is closely related to the occupants’ comfort, their building durability, and building energy consumption. This study carried out material property tests on bamboo-based materials (BLL and BS) and analyzed hygrothermal performance simulations on bamboo exterior wall constructions in five major climatic zones using WUFI. Results show that BS had a greater heat storage capacity than BLL. However, BLL showed a relatively higher moisture sorption capacity, and BLL was more easily permeated by vapor than BS. The water content (WC) of 12 walls of BLL and BS was below 20%. BLL and BS met the requirements of the envelope, and the WC of BS was lower than that of BLL. Based on the results, the walls designed in this study are suitable for the corresponding climate zones. In the cold and severe climate zones especially, the external insulation system walls performed better than the internal insulation system. The external insulation system was recommended for these two climate zones. The design and simulation results of walls made of two types of bamboo-based materials provide a scientific basis for the application of the material.