Hygrothermisches Verhalten eingebetteter Holzbalkenköpfe im innnengedämmten Außenmauerwerk: Heizungstechnisch gestützte Innendämmung bei Holzbalkendecken

The hygrothermic performance of wooden beam ends embedded in an inside insulated outside wall considering a heating system. Heating pipe aided inside thermal insulation in case of a timber joist floor. An improvement of the hygrothermal performance of worth preserving facades by means of an inside insulation is proved correct for crucial projects also, using capillary activ thermal insulation materials or a vapor retarder dependent on the relative humididy. On the other hand in case of embedded wooden beam ends there are controversial discussions The experts suggest proposals from an airthight construction and the using of fungicides and the sorptive binding of moisture up to a beam end completely open for air flow rate. This paper is focused to the hygric problems of the wooden beam ends. A lot of measurements are carried out in situ under condition of use in testhouses and by means of a teststand in the Building Physics testing floor of the FHL. In each cases the experiments are supported by a numerical simulation of the coupled heat and mass transfer. Apart from the seasonal process of the wooden moisture content and the hygrothermal state of the air gaps of the beam heads area the results quantify also the effect of local heat transfer by means of heating channels near the floor board area and through so‐called passive and active heat bars within the wooden beam ends.     

Experimental data set for validation of heat,air and moisture transport models of building envelopes

This paper reports experimental studies on heat, air and moisture (HAM) transfer through a full scale light weight building envelope wall under real atmospheric boundary conditions. The main objective of the article is to generate informative data so that it can be used for numerical validation of HAM models. The considered wall is a multilayered structure built up from outside to inside of external board, vented cavity, fibreboard sheathing, mineral wool between wooden studs and interior finishing. The global wall has a surface area of (1.80 × 2.68) m²; and is subdivided into three vertical parts. The parts differ from each other by the applied interior finishing. Between the different layers of each part and on the surfaces of the wall humidity, temperature and heat flux sensors are placed in a 3D matrix. At the outer surface of the wall, the applied sheathing is a bituminous wood board. In the board nine removable specimens are included. By regularly weighing the fibreboard samples, their moisture content could be quantified. Using data collected over a total time span of about two years, insight about the hygrothermal behaviour of the different envelope parts is obtained and at the same time a well-documented data set is generated that can be used for hygrothermal envelope model validation purposes.     

Influence of hysteresis on the transient hygrothermal response of a hemp concrete wall

Building envelopes with bio-materials like hemp concrete are currently undergoing an increasing development due to their low environmental impact and their interesting hygrothermal properties. This kind of hygroscopic material is characterized by a hysteretic behaviour. In this paper, the influence of such behaviour on the hygrothermal response of a building wall is discussed. An experimental facility is designed to measure temperature and relative humidity within a hemp concrete wall submitted to climatic variations. This facility provides a set of experimental data suited for benchmarking. Numerical simulations are performed with a hysteresis model implemented in a heat and moisture transfer model. Comparisons between numerical and experimental results show that hysteresis modelling is relevant to simulate the hygrothermal response of the wall. The discussion is extended to the influence of the initial moisture content.     

Wärme‐ und Feuchtetransport in Holzbauelementen unter freier Bewitterung

Es wurden vergleichende Untersuchungen des Wärme‐ und Feuchtetransportes in unterschiedlichen Holzbaukonstruktionen unter freier Bewitterung durchgeführt. Insgesamt wurden fünf Konstruktionen an Versuchsbauten auf dem Gelände der ETH Zürich getestet. Neben einer verdübelten Massivholzkonstruktion wurden zwei Ständerkonstruktionen und zwei weitere Vollholzkonstruktionen untersucht. Aus den gewonnenen Daten wurden dynamische Parameter der Gebäudehüllen ermittelt. Zusätzlich wurden Messungen an drei realen Bauten (zwei verdübelte Massivholzkonstruktionen, eine Ständerkonstruktion) durchgeführt. Die gemessenen Daten der Versuchsbauten wurden mit den Daten der Messungen an realen Bauten verglichen. Die Ergebnisse zeigen unter anderem, dass die Vollholzkonstruktionen sehr ausgewogene, hygrothermische Eigenschaften aufweisen. Heat and moisture transfer in wood‐based constructions under natural weathering. In this project comparative measurements of heat and moisture transfer in wood‐based constructions were carried out under natural weathering conditions at the campus of ETH Zurich. Altogether, five different constructions designed as small test buildings were investigated. In the first observation, the solid wood construction connected with wooden dowels — without any further binders is compared to two conventional wood frame constructions with one and two insulation layers. In the second observation, the mentioned solid wood construction is compared to one log construction and one solid wood construction with slotted wood elements. From the data, the dynamic parameters of the heat and moisture transfer of these building envelopes were determined. Additionally, the heat and moisture data of three real used buildings (two solid wood constructions with wooden dowels and one conventional wood frame construction) were measured. These data were compared with the data measured on the small test buildings. The results, inter alia, are showing that the solid wood constructions achieve a good balance in hygrothermal properties.     

Hygrothermal absorption and desorption of deep underground hydropower station envelopes

The heat and moisture environment of hydropower stations underground plants will directly affect the useful life and safe running of electromechanical devices. Engineers need to calculate the transient heat and moisture loads due to the storage and transport of heat and moisture in the porous cavern envelopes. In order to avoid complex dynamic calculations and save design time, this paper gives monthly mean hygrothermal absorption and desorption indexes and regression formulas of limestone envelopes with no-lining. These indexes are obtained by means of numerical calculation method based on the air temperature and moisture fluctuation ranges controlled by air-conditioning systems and hygrothermal parameters of cavern envelop. And then, validity and reliability of hygrothermal absorption and desorption indexes are verified by using monitored data of main plants in Dachaoshan and Jiangkou hydropower stations in China. The results show that the heat and moisture indexes can be applied in real project design and operation management.     

What are the hygrothermal consequences of applying exterior air barriers in timber frame construction in Europe?

Moisture-induced damage is one of the major causes of degradations and reduced thermal performance in wood frame buildings. It is therefore crucial to incorporate the hygrothermal assessment of new timber frame building envelopes systems from the early development phase onwards. The article at hand presents the simulation results studying the hygrothermal performance of various timber frame wall configurations with exterior air barrier systems. A parameter analysis explores the impact of different European climates, insulation materials, exterior air barrier materials and verifies in addition to the impact of bad workmanship in the installation of the insulation layer. This study reveals that the application of mineral wool (MW) insulated timber frame walls in combination with exterior air barriers results in increased moisture loads. Moreover, small air gap channels between the MW and the adjacent exterior air barrier significantly increase natural convection and add up to harmful moisture levels. Yet the simulations indicate that the use of blown-in cellulose insulation can avoid these issues. The study further indicates that the technique of exterior air barrier is more suitable for continental climates rather than for moderate sea climates in Europe.     

Impact of combined moisture buffering capacity of a hemp concrete building envelope and interior objects on the hygrothermal performance in a room

In this article, a hygrothermal building model, taking into account the building envelope, indoor heat and moisture sources, indoor environment and moisture buffering capacity of interior objects, is presented and validated with the test cases found in the literature. The model is used to study the impact of hemp concrete and the moisture buffer capacity of the interior elements on the prediction of the hygrothermal comfort in the building. The numerical results show that the use of hemp concrete in buildings can ensure good hygrothermal comfort. Besides, taking into account the effect of moisture buffering of indoor objects increases the building performance. Our results also suggest that neglecting moisture transfer through the envelope increases significantly the predicted percentage of dissatisfied indices and reduces the acceptability of indoor air quality during the occupied period. This study also confirmed that the combined relative humidity-sensitive ventilation system and moisture buffering capacity of building envelope and of interior objects is a very efficient way to reduce the heating energy consumption.     

Modeling of the hygrothermal absorption and desorption for underground building envelopes

The hygrothermal storage characteristics of an underground building envelope have discernible effects on the heat and humidity of the indoor environment. To predict the hygrothermal storage capacity, it is necessary to accurately calculate the transient heat and moisture flux through the envelope. This paper describes the development of a new hygrothermal model described with relative humidity and temperature based on the results of existing researches. The moisture model fully states actual moisture transfer process involving both vapor diffusion and liquid water migration in porous building envelopes. Verified using the results calculated by the mathematical model of Mendes et al., the new hygrothermal model can accurately predict the heat and moisture transfer of building envelopes. Hygrothermal absorption and desorption of three types of common underground building envelopes in Chengdu region in China are analyzed by using the new model. The results show that the hygrothermal absorption and desorption of underground building envelopes must be considered when the heat and moisture environment is controlled by HVAC. Taking account of these factors can reduce air-conditioning equipment capacity and save running energy.     

Integration model of hygrothermal analysis with decay process for durability assessment of building envelopes

In this study a numerical simulation model that integrates hygrothermal analysis with the decaying process of wood structures caused by moisture accumulation is presented. This simulation model can quantitatively predict both hygrothermal conditions within the building envelopes and the progress of decay in wood structures under variable conditions. The following are characteristics of the simulation model used in this study: (1) the development of wood decay represented by a differential equation with a variable of mass loss of wood substance and (2) the addition into moisture balance equations of biochemical reactions within wood decay. Hence, the simulation model enables assessment of the long-term performance of building envelopes with regard to both durability and drying potential. Rate constants of the wood decay and a coefficient of the moisture production for the model were determined by the mass loss data of small wood samples in decay tests using Fomitopsis palustris, a brown rot fungus. Additionally, numerical simulations using the model were implemented to understand both the decaying process and moisture accumulation within building envelopes. The results numerically demonstrated important phenomenon that the moisture production by biochemical reactions of wood decay helps to maintain the decaying process.     

Identification of the hygrothermal properties of a building envelope material by the covariance matrix adaptation evolution strategy

This paper proposes the application of the covariance matrix adaptation (CMA) evolution strategy for the identification of building envelope materials hygrothermal properties. All material properties are estimated on the basis of local temperature and relative humidity measurements, by solving the inverse heat and moisture transfer problem. The applicability of the identification procedure is demonstrated in two stages: first, a numerical benchmark is developed and used as to show the potential identification accuracy, justify the choice for a Tikhonov regularization term in the fitness evaluation, and propose a method for its appropriate tuning. Then, the procedure is applied on the basis of experimental measurements from an instrumented test cell, and compared to the experimental characterization of the observed material. Results show that an accurate estimation of all hygrothermal properties of a building material is feasible, if the objective function of the inverse problem is carefully defined.     

Indoor air microbes and respiratory symptoms of children in moisture damaged and reference schools

Microbial indoor air quality and respiratory symptoms of children were studied in 24 schools with visible moisture and mold problems, and in eight non-damaged schools. School buildings of concrete/brick and wooden construction were included. The indoor environment investigations included technical building inspections for visible moisture signs and microbial sampling using six-stage impactor for viable airborne microbes. Children's health information was collected by questionnaires. The effect of moisture damage on concentrations of fungi was clearly seen in buildings of concrete/brick construction, but not in wooden school buildings. Occurrence of Cladosporium, Aspergillus versicolor, Stachybotrys, and actinobacteria showed some indicator value for moisture damage. Presence of moisture damage in school buildings was a significant risk factor for respiratory symptoms in schoolchildren. Association between moisture damage and respiratory symptoms of children was significant for buildings of concrete/brick construction but not for wooden school buildings. The highest symptom prevalence was found during spring seasons, after a long exposure period in damaged schools. The results emphasize the importance of the building frame as a determinant of exposure and symptoms.     

Entwicklung und Validierung einer hygrothermischen Raumklima‐Simulationssoftware WUFI®‐Plus

Development and validation of the hygrothermal indoor climate simulation software WUFI®‐Plus. Well‐balanced conditions of thermal, moisture and air quality are very important in buildings because an imbalance of these factors could have significant influences on the construction and the inhabitants. The focus of this paper is the influence of different materials on the fluctuation of relative humidity specifically humidity peaks. In lieu of complicated and expensive laboratory testing several different software tools have been developed to estimate the indoor environmental conditions of buildings. The Fraunhofer‐Institute for Building Physics (IBP) developed a hygrothermal simulation tool. With this software the temperature and moisture conditions of the walls, ceiling and floor constructions, of the indoor air and the energy consumption for the building can be calculated. In the context of the IEA‐Annex 41 project “Moist‐Eng“ a common exercise has been carried out for the validation of such software tools. For the common exercise at the free field investigation area in Holzkirchen (Germany) two identical rooms were used to measure the moisture buffering capacity of several interior finish systems. To address the questions of buffering capacity the IBP developed a hygrothermal simulation tool, WUFI®‐Plus [1]. Using the measurement data from the common exercise calculations were carried out with several software tools for the validation of it. In this paper the results of the laboratory tests and simulation results are described.     

Development of HAM tool for building envelope analysis

Moisture-related building envelope failures have resulted in costly rehabilitation in various regions of North America. To advance building envelope design towards an engineering approach and reduce the occurrence of future failures, an advanced numerical tool was developed, in conjunction with an extensive full-scale experiment, to investigate hygrothermal performance of various wood-frame wall assemblies. Major features of the tool are multi-dimensional and transient coupling of heat and moisture transport; natural air convection integrated in hygrothermal simulation through Darcy–Boussinesq approximation; heat transfer by conduction and convection of sensible and latent heat; moisture transport by vapor diffusion, capillary suction and convection; material database of common building materials in North America; experimental settings or weather data as boundary conditions; and moisture added in the building envelope to simulate the wetting process. The numerical tool achieves good compliances to the benchmarking cases of the HAMSTAD project, and its predictions have shown good agreement with data from the full-scale wall experiment. The numerical tool employs the commercial finite-element software to solve the governing equations. This approach provides building science researchers the flexibility to modify, maintain and share their modeling work efficiently.     

Proposal of an empirical relationship for moisture storage function of concrete

In this paper an empirical mathematical relationship for concrete’s moisture storage function is proposed. Most of the simple relationships that are used in hygrothermal models for the approximation of building materials’ moisture storage functions cannot provide a very satisfactory estimation for concrete. In this paper, an empirical function, having three branches, is formulated to express concrete’s moisture storage function and to be used in hygrothermal calculations. The formulation of this relationship is analytically presented. The proposed expression can be adjusted to a type of concrete when only the values of free saturation moisture content (relative humidity 100 %) and of moisture content corresponding to 80% air relative humidity are known for this concrete. Vorschlag einer empirischen Beziehung für die Feuchtespeicherfunktion von Beton. Im vorliegenden Beitrag wird eine empirische mathematische Beziehung für die Feuchtespeicherfunktion von Beton vorgeschlagen. Die meisten der einfachen Beziehungen, die in hygrothermischen Modellen zur Approximation der Feuchtespeicherfunktionen von Baustoffen zur Anwendung kommen, können für Beton keine völlig zufriedenstellende Bewertung liefern. Im vorliegenden Beitrag wird zur Darstellung der Feuchtespeicherfunktion von Beton und zur Verwendung in hygrothermischen Berechnungen eine empirische Funktion mit drei Zweigen formuliert. Die Formulierung dieser Beziehung wird analytisch präsentiert. Der vorgeschlagene Ausdruck kann an einen Betonbaustoff angepasst werden, wenn für diesen Betonbaustoff lediglich die Werte für den Sättigungsfeuchtegehalt (freie Sättigung, relative Feuchte 100 %) und den Feuchtegehalt bekannt sind, der 80 % relativer Luftfeuchte entspricht.     

Überlegungen zum hygrothermischen Verhalten von Außenwänden im Holztafel‐/Holzrahmenbau mit direkt beschichteten Beplankungen

Im vorliegenden Artikel wird gezeigt, dass es möglich ist, im Versuch erhaltene hygrothermische Messwerte aus Bewitterungsversuchen an Außenwänden im Holztafel‐/Holzrahmenbau mit direkt beschichteten Beplankungen mit dem Programm WUFI 4.0 nachzurechnen. Anschließend erfolgte die hygrothermische Berechnung der Wandkonstruktionen mit dem in WUFI 4.0 enthaltenen Klimadatensatz von Holzkirchen. Die erhaltenen Zeitkurven der relativen Luftfeuchte und Lufttemperatur dienten als Eingabewerte in WUFI‐BIO 2.0 zur Berechnung des Risikos eines Schimmelpilzwachstums in der Konstruktion. Das Risiko eines Schimmelpilzwachstums in der Konstruktion konnte mit den Berechnungen nicht generell ausgeschlossen werden. Es wird empfohlen, innere Dampfbremsfolien mit s_d ⩾ 25 m zu verwenden. Weiterführende Untersuchungen sollten an realen Bauobjekten erfolgen. To observe the hygrothermal behavior of exterior walls in timber frame construction with direct rendered sheathings. The presented paper shows that it is possible to calculate with the program WUFI 4.0 the hygrothermal measurement data of weathering tests in the climate chamber on exterior walls in timber frame construction with direct rendered sheathings. Afterwards, hygrothermal calculations of walls under the use of climate data from Holzkirchen/Germany were conducted. The obtained relative humidity time diagrams and temperature time diagrams were used as input values in WUFI‐BIO 2.0 to calculate the risk of mould growth in the construction. In general, the risk of mould growth in the construction could not be excluded with the calculations. Therefore, the use of interior vapor barrier sheets with s_d ⩾ 25 m is recommended. Further research should take place on real buildings.     

Hygrothermal behavior modeling of the hygroscopic envelopes of buildings: A dynamic co-simulation approach

High levels of humidity in buildings lead to building pathologies. Moisture also has an impact on the indoor air quality and the hygrothermal comfort of the building’s occupants. To better assess these pathologies, it is necessary to take into account the heat and moisture transfer between the building envelope and its indoor ambience. In this work, a new methodology was developed to predict the overall behavior of buildings, which combines two simulation tools: COMSOL Multiphysics© and TRNSYS. The first software is used for the modeling of heat, air and moisture transfer in multilayer porous walls (HAM model: Heat, Air and Moisture transfer), and the second is used to simulate the hygrothermal behavior of the building (BES model: Building Energy Simulation). The combined software applications dynamically solve the mass and energy conservation equations of the two physical models. The HAM-BES coupling efficiency was verified. In this paper, the use of a coupled (HAM-BES) co-simulation for the prediction of the hygrothermal behavior of building envelopes is discussed. Furthermore, the effect of the 2D HAM modeling on relative humidity variations within the building ambience is shown. The results confirm the importance of the HAM modeling in the envelope on the hygrothermal behavior and energy demand of buildings.     

基于正交试验制备生土基复合墙体材料及其热湿综合性能分析

基于正交试验设计,以石灰和粉煤灰为改性剂制备了生土基复合墙体材料.通过多元非线性回归,分析研究了改性剂掺量和含水率对生土基复合墙体材料热湿综合性能的影响,并得到生土基复合墙体材料的优化配方.结果表明:改性剂掺量和含水率对生土基复合墙体材料热湿综合性能的影响显著,敏感程度依次为含水率>粉煤灰掺量>石灰掺量>空白因素;生土基复合墙体材料的优化配方为石灰掺量6.24%+粉煤灰掺量8.93%+含水率13.57%,此时其导热系数为0.721W/(m·K),平衡含湿量为7.645%,且抗压强度和耐水性均满足相应要求.通过墙体材料组成结构分析和微观形貌分析可知,粉煤灰在碱性环境中的水化作用使得优化生土基复合墙体材料内部呈现出更加致密的结构体系.     

Non-isothermal moisture transport through insulation materials

An experimental investigation was conducted in order to draw some conclusions on the magnitude of moisture transport due to temperature gradient on a range of porous light-weight building materials. A special constructed non-isothermal set-up allowed the creation of a temperature gradient of 10 K and given humidity gradient over the sample. The resulting moisture flux as well as the hygrothermal states around and within the material were monitored.     

被动式太阳能集热蓄热墙对室内湿度调节作用的研究

在两间分别采用被动式太阳能集热蓄热墙体和普通保温节能墙体的同实体大的实验房屋中,利用多点温湿度及风速的计算机巡回检测系统,在2004年供暖期对室内外温湿度、风速、太阳辐射照度及墙体内温度等参数进行了实测。结果表明,未采用被动式太阳能集热蓄热墙体的对比房内相对湿度比太阳房高20%左右,并因湿度较高在窗户上出现结露现象。分析了两间实验房屋的热湿传递特性以及对一些物性参数如室内相对湿度、墙体的含湿量、人的舒适性等的影响。