Hygrothermal Simulation Research Articles

Material characterization models and test methods for historic building materials

Predictions of long term hygrothermal performance can be assessed by dynamic hygrothermal simulations, in which material parameters are crucial input. Material parameters for especially historic materials are often unknown; therefore, there is a need to determine important parameters, and simple ways for estimation of these. A case study of a brick wall was used to create and validate a hygrothermal simulation model; a parameter study with five different parameters was performed on this model to determine decisive parameters. Furthermore, a clustering technique has been proposed to estimate decisive parameters through simple testing of interrelated parameters that are easier to determine.

Calibration of Hygrothermal Simulations by the Help of a Generic Optimization Tool

Hygrothermal simulation represents an established method for the performance evaluation of building constructions. Some validation cases are known where the validity of these models was approved in form of a comparison between measured and simulated quantities under controlled boundary conditions. A further step is commonly not explained but also included, the calibration of uncertainly known model settings, e.g. surface exchange coefficients or measured material properties with a relevant uncertainty range. This paper summarizes a calibration procedure, which was carried out for the data analysis of a hygrothermal test stand with two- and three-dimensional junctions, including brickwork and joist ends. The calibration procedure is based on the definition of quantitative criteria (target values) that describe the accordance between measured and simulated data series. Starting with the thermal two-dimensional simulation model, uncertain parameters are defined with their start values, ranges and steps of variation. This is used as an input for the identification of the best-fitting parameter combination via generic optimization algorithm. The final calibrated simulation model shows a remarkably better accordance to the measurement results. The procedure is systematic and reproducible.

Performance analysis of coupled quasi-steady state air flow calculation and dynamic simulation of hygrothermal transport inside porous materials

The hygrothermal simulation model DELPHIN performs a transient simulation of energy and moisture transport in porous building materials and air gaps. The governing partial differential equations are solved with an advanced error control time integration algorithm. In comparison to the time scales of heat and moisture transport, air flow can be treated sufficiently well as steady-state process. The pressure and flow field needs to be updated whenever ambient air pressures change significantly or free convection is induced due to temperature or humidity variations. Within DELPHIN the air flow pattern is computed with a Darcy-type steady-state flow calculation.The calculation of the flow field is a time-consuming task and should only be done when necessary. A central question that impacts both physical results and performance is the update criteria for the quasi-steady flow field. Indeed, if the flow field is updated in with every change of temperature or moisture, we observe in some cases significant performance losses. For all simulation cases we use an error controlled time integration method.In the article we identify free convection inside an air gap as a performance critical simulation scenario. Dominating convective transport is responsible for divergence of the fully coupled simulation. Reduction of update frequency stabilizes simulation run without loss of calculation efficiency. These results may be generalized for less critical simulation cases.

Towards understanding rain infiltration in historic brickwork

Historic masonry walls are typically afflicted with uncertainties and defects which might induce significant rain water infiltrations. Insight in these moisture transport mechanisms in brickwork is important because the moisture content of brickwork is the predominant parameter for damage functions for frost, mold, and corrosion, and also affects heat flux. Given the increased focus on low-energy retrofits, interior insulation is becoming more popular. However, this typically decreases the drying potential of the wall and might consequently induce even more moisture-related pathologies. The insulation causes the exterior surface of the brickwork to be saturated more often, and this renders it possible for a runoff water film to develop during heavy rainfall. Although it is well known that this water film can penetrate through defects in the brickwork, the amount of water that penetrates remains a big question mark. Consequently, this important transport mechanism is typically omitted in hygrothermal simulations of (historical) brickwork. To obtain quantitative information, a series of laboratory tests is conducted. In a test setup a runoff film is applied in combination with a range of air pressure differences on a surface with different types of deficiencies representing imperfections in the facade. In this first phase, as an abstraction of the real saturated masonry construction a PMMA surface was used. The applied runoff film is imposed precisely and the water infiltration rate through the deficiencies is measured gravimetrically. Finally, the laboratory results are analyzed and preliminary linear relations between pressure and infiltration rate are found.

Comparative study of hygrothermal simulations of a masonry wall

With increasing requirements on reducing heat consumption and improving comfort levels of existing buildings, interior insulation retrofit is a hot topic for many masonry buildings. However, as the drying potential of the wall is lowered as a consequence, interior insulation of massive masonry walls increases the risk of moisture related problems. Therefore, carefulness is needed when approaching such solutions. A useful approach on evaluating moisture risks, when deciding the interior insulation design, is the use of hygrothermal simulations. In the present study a 2D numerical hygrothermal study has been conducted on an internally insulated masonry wall with a smart vapor barrier. The focus has been on comparing and discussing the options available in, and the challenges faced with, COMSOL Multiphysics and WUFI for this purpose.

Hygrothermal Simulation of Wood Exposed To the Effect of External Climate

The article is focused on simulation of moisture transfer in wood of norway spruce (Picea abies L.). Experimental specimen was exposed to the northern climatic conditions in Lund University, Sweden. The moisture content of wood was measured 10 mm from the surface for nearly three years. The ABAQUS program was used for numerical modelling of moisture transfer simulation in 3D. The surface sorption of wood was simulated using user defined subroutine DFLUX developed by VTT Research Centre of Finland Ltd. for the needs of European Project Durable Timber Bridges. Climate data for the analysis was used from insitu measurement nearby realized by weather station. The temperature, relative humidity of the air and precipitation data was record each hour. Numerical analysis took into account influence of rain effect on different parts of specimen surface.

Advanced modelling of vapor resistance of moisture dependent vapor retarder

Moisture dependent vapor retarders (smart vapor retarders) are widely used in building construction especially roofs in order to prevent moisture accumulation or to support drying out processes. The current modelling approaches mainly use only a relative humidity dependent vapor resistance. Recent studies have shown more complex behavior like direction depending flow or vapor pressure gradient depending flow. This paper shows a new procedure for including all these effects into physical model. Furthermore description of necessary measurements with evaluation of results and selection of a proper model with parameter adjustment will be shown based on three different example membranes. Finally the implementation of this model into a hygrothermal simulation code is described

An Investigation into the Hygrothermal Performance of a Mineral Wool Based Externally Insulated Enclosure in a Cold Climate

A high RSI enclosure has been developed for use in low energy buildings in cold climates and utilizes high density mineral wool outboard of typical wood frame construction. This study investigated both the in-situ thermal resistance and hygrothermal performance of the proposed enclosure approach. The in-situ data has been used to calibrate 3d thermal models and 1d transient hygrothermal models. The in-situ testing indicated a clear-wall RSI value of 8.96 m2K/W for the north wall and 10.97 m2K/W for the south wall, a change of -3.4% and +17.5% from expected nominal. Thermal modelling indicated the metal fasteners reduced the thermal resistance by 7% to 24% depending on the fastener and stud configuration. The calibrated hygrothermal simulations assessed the performance of the proposed enclosure, and a split-insulation variant, in several cold climates. The results indicate acceptable performance in all locations except for the split-insulation case located in an extremely cold climate.

Can crawl space temperature and moisture conditions be calculated with a whole-building hygrothermal simulation tool?

The hygrothermal behaviour of an outdoor ventilated crawl space with two different designs of the floor structure was investigated. The first design had 250 mm insulation and visible wooden beams towards the crawl space. The second design had 300 mm insulation and no visible wooden beams. One year of measurements was compared with simulations of temperature and moisture condition in the floor structure and crawl space. The measurements showed that the extra 50 mm insulation placed below the beams reduced moisture content in the beams below 20 weight% all year. A reasonable agreement between the measurements and simulations was found; however, the evaporation from the soil was a dominant parameter affecting the hygrothermal response in the crawl space and floor structure.

Inter-laboratory variability results of porous building materials hygrothermal properties

The knowledge of material properties to predict heat and moisture transport in buildings is essential to well characterize their behavior and predict pathologies. Nowadays it is quite common the use of hygrothermal simulation programs to predict building materials and components hygrothermal performance and those programs need, as inputs, the material properties.Bearing this in mind this study is focused on the analysis and discussion of properties used in different models, its availability and reliability. Laboratory test results to determine some hygrothermal properties of two common materials in walls of historical buildings: a lime natural stone and a lime mortar were developed. Some of these tests were performed by two laboratories involved in a project and the main idea is to present and compare the obtained results also comparing with database values.

Hygrothermal analysis of technical solutions for insulating the opaque building envelope

The application of insulating materials for energy refurbishment of buildings improves the thermal transmittance of the envelope. However, if not properly planned and realized, it could reduce the wall's drying potential, modifying its original features and leaving it generally more humid. This can lead to moisture damages, humid insulation material and risk of mould growth. To avoid any problem related to the increased presence of water in the building envelope, it becomes therefore essential to perform the so-called hygrothermal assessments. In this regard, the international standards offer, beside the traditional Glaser method based on the mere vapour transport, the use of dynamic hygrothermal simulations. These allow to simultaneously consider the transport and storage of heat and moisture in building materials, the influence of climate (including rain and solar radiation in different locations), user behaviour and initial conditions. The aim of this paper is to compare Glaser and dynamic methods and to highlight their advantages and disadvantages, considering the different approaches to the evaluation not only of superficial and interstitial condensation, but also of durability, considering biological attack, freeze/thaw cycles, corrosion, etc.

Vernacular housing practices in Burkina Faso: representative models of construction in Ouagadougou and walls hygrothermal efficiency

In Burkina Faso, particularly in Ouagadougou, the walls of the houses are made of several local materials. The choice of a material implies a suitable constructive technique and an appropriate architecture. The walls are either earth-based, i.e. Compressed Earth Blocks (CEBs) or Adobe, or based on cement-based materials such as hollow concrete blocks. This paper proposes a description of the vernacular construction practices according to the material used for the walls and tries to explore the hygrothermal behaviour of various wall compositions. A hygrothermal simulation of a hollow concrete blocks wall and a CEBs wall using the WUFI®Pro software is carried out in order to compare the humidity flux passing through interior surface of each wall and to analyze the influence of integrated moisture in the calculation of heat flow. It is shown that, for CEBs wall, both thermal and hygrothermal simulation of heat flow give similar results.

Application of typical and extreme weather data sets in the hygrothermal simulation of building components for future climate – A case study for a wooden frame wall

A method for synthesizing representative weather data for future climate out of regional climate models (RCMs) was introduced previously for the energy simulation of buildings (Nik, 2016). The method suggests creating one typical and two extreme data sets based on the distribution of the outdoor dry bulb temperature (Tdrybulb). This article extends the application of such weather data in the hygrothermal simulation of buildings by simulating a pre-fabricated wooden frame wall. To investigate the importance of considering moisture and rain conditions in creating the representative weather files, two more groups of weather data are synthesized based on the distribution of the equivalent temperature (Tequivalent) and rain. Moisture content, relative humidity, temperature and mould growth rate are calculated in the façade and insulation layers of the wall for several weather data sets. Results show that the synthesized weather data based on Tdry bulb predict the hygrothermal conditions inside the wall very similar to the original RCM weather data and there is no considerable advantage in using the other two weather data groups. This study confirms the applicability of the synthesized weather data based on Tdry bulb and emphasizes the importance of considering extreme scenarios in the calculations. This enables having distributions more similar to the original RCM data while the simulation load is decreased enormously.

Experimental assessment of rainwater management of a ventilated façade

Façades are not watertight systems in which the exterior surface of the cladding plays the role of the water shedding surface; the air space is the drainage plane; the exterior surface of the thermal insulation layer acts as water-resistive barrier, and the interior layer of the inner leaf is supposed to be the air barrier. The degree of watertightness of ventilated façades relies on the characteristics of the materials used, the geometry of the external cladding element, and edge profile of the joints. Hence, in this article, we extrapolate the laboratory testing to develop a holistic approach on the water management of ventilated façades. The laboratory test showed that 50% of the water deposited to the surface of the wall splashes back, 22% creates a runoff film along the exterior surface of the cladding, 27% infiltrates into the cavity behind the cladding, and <1% reaches the inner layer of the wall. Given these results, the moisture load has been determined for a range of wind-driven rain loads and vertical joint configurations. Such information can be used as input to hygrothermal simulations.

Hygrothermal assessment of internally added thermal insulation on external brick walls in Swedish multifamily buildings

Proper and efficient renovation requires understanding the behavior of existing buildings and of different building materials. Analyzing hygrothermal measurements in two case studies, one with and the other without an internally added thermal insulation system, enabled us to identify factors of critical importance for further assessment through simulations, and to validate a hygrothermal simulation model of a solid brick masonry wall, a model used then to assess internally added thermal insulation systems of different types. A mold resistance design (MRD) model shows that, in connection with all internally added thermal insulation systems, the risk of mold growth is appreciable when brought on by solar driven vapor from the exterior. This, if biological material is present in either of two critical areas, those of the boundary between the thermal insulation and either 1) the existing masonry wall, or 2) the exterior surface of an internally added vapor barrier. Furthermore, assessments of corrosion risks are conducted for two critical placements of the bed-joint reinforcement. At a depth of 30 mm from the exterior surface, the corrosion risk was found to be less with use of capillary-active vapor-open systems than when no thermal insulation was employed, other systems increase the corrosion risk. At a depth of 90 mm, all thermal insulation systems increase the corrosion risk. Excluding precipitation uptake eliminates all risks, showing that this is the most crucial factor. Solutions that limit this uptake or increase the drying-out rate should thus be considered beneficial.

Procedures in the construction of a test reference year for Porto-Portugal and implications for hygrothermal simulation

The exterior weather is a key factor in the behaviour of buildings, which may affect mechanical resistance, durability and appearance of materials and components. Also, it may influence the indoor air quality, limit the comfort of users and increase energy costs. Therefore, exterior weather data is an important input for hygrothermal simulation, as a tool to previously assess the behaviour of buildings.In this work, the methodology to create a reference year according to ISO 15927-4 was assessed. The meteorological data were statistically analysed and the missing data were filled. Two reference years were obtained: one with gaps and the other without omissions, in order to find out what were the implications brought by filling the data. Hygrothermal simulations were conducted considering the two reference years.The results were statistically compared and they showed the reference years presented differences, although only three months are actually different. The outputs of the hygrothermal simulations are similar in some periods and different in the periods of time close to the months that are different in the reference years. Although these dissimilarities are highlighted by statistical differences they are not relevant enough to result in a significant difference in the durability of the materials.

The impact of the temperature dependent thermal conductivity of insulating materials on the effective building envelope performance

Constant thermal conductivity values of insulating materials are typically used in building design and assessment. However, the thermal conductivity depends on many factors, such as on the temperature and moisture content. Linear temperature-dependent laws have been occasionally proposed for inorganic fibrous materials such as fiberglass or rock wool that exhibit a decreased thermal conductivity (better performance) at low temperatures. However, the petrochemical-foamed insulating materials such as the polyisocyanurate, have less regular temperature dependent behaviors with a poorer performance at both extremely cold and warm temperatures. This means that the use of constant thermal conductivity values results in actual building envelope performance different from the design predictions, with increasing building energy consumptions, greater risks of condensation issues, and decreased occupants’ comfort. This paper aims to quantify the impact of the temperature dependency of the thermal conductivity in exterior walls and flat roofs. Experimental results over a large temperature range (from −20°C to +60°C) for different insulating materials were used in hygrothermal simulations in both continental and humid temperate climates. Common insulating materials were taken into accounts, such as fiberglass, rock wool, polyisocyanurate, and extruded polystyrene. The increase in the energy fluxes from common building envelopes once the effective thermal conductivity was considered resulted below 10% for walls and as high as 70% for roofs, especially in the cold weather. Finally, a hybrid insulation system constituted by two layers of different materials, i.e. a polyisocyanurate and a rock wool is investigated.

Hygrothermal Simulation Applied to Energy Efficiency Improvement

The exterior weather data is a key factor in buildings’ behaviour and an important input of hygrothermal simulation, as tool to previously assess the buildings’ behaviour and achieve sustainable buildings with high degree of user satisfaction and lower energy costs. Hygrothermal simulations were conducted using a commercial hygrothermal simulation tool considering two reference years. The results were statistically compared. They showed that the weather data-gap filling to create the TRY did not influence considerably the outputs of the hygrothermal simulation, mostly because they were only used in the month selection of the TRY and not for numerical simulation purposes.

Assessment of Indoor Climate Environment Via Hygrothermal Simulation in Historical Churches

This paper studies how well the interior climate is naturally maintain. The church subjected to simulation is a Romano-Catholic one, Saint Archangel Michael in Sabaoani, Romania. Taking into account the construction, the exploitation during the years and the data from humidity and temperature sensors, some simulations are performed. In the simulations is used Ansys Fluent software. Historical churches, when they are unheated for hundreds of years, often face problems with moisture after a heating system is introduced. Because of the large number of persons attending to the liturgical service humidity in the air exceeds the limits and condenses on the walls and windows. High humidity can also damage the artworks and painting inside the churches. The conservation using heating control was tested in simulation model. Furthermore, are tested two different systems with and without ventilation in order to create in indoor climate for preservation of a monumental building and its monumental interior. Finally, is given a set of rules to create the interior climate proper for artworks conservation.

Impact of Moistened Bio-insulation on Whole Building Energy Use

One of the key properties of hemp insulation is its moisture adsorption capacity. Adsorption of moisture can increase both thermal conductivity and heat capacity of the insulation. The current study focuses on the effect of moisture induced thermal mass of installed hemp insulation on the whole building energy use. Hygrothermal and thermal simulations were performed using the CIBSE TRY weather data of Edinburgh and Birmingham with the aid of following simulation tools: WUFI and IES. Following simplified building types were considered: building-1 with dry hemp wall and loft insulations, building-2 with moistened hemp wall and loft insulation and building-3 with stone wool insulation. It was observed that the overall conditioning load of building-1 was 1.2 to 2.3% higher than building-2 and 3. However, during the summer season, the cooling load of building-2 was 3-7.5% lower than the other buildings. It implies that, moistened insulation can potentially mitigate the effect of increasing cooling degree days induced by global warming.