In-cavity evaporation allowance—A drying capacity indicator for wood-frame wall system

Although moisture significantly affects the performance and durability of building envelope systems, effective methods to quantify the relative drying capacity of these systems are yet to be developed. A new testing method and an evaluation approach for comparing the drying capacity of wood-frame wall systems in evacuating water due to rain penetration in the stud cavities are presented in this paper. A controllable and consistent moisture loading is created by placing a water tray on a load cell at the bottom of the stud cavity of the wall assembly which is then subjected to lab generated indoor/outdoor conditions. The data on water evaporation from water trays and the monitored moisture accumulations in the materials surrounding the stud cavities are used to establish load–response relations. Using these relations the relative performance of various building envelope systems in preventing biodeterioration caused by rainwater penetration into the stud cavities can be compared. The concept of in-cavity evaporation allowance (ICEA) has been proposed and it is based on the limit of 20% moisture content (MC) being reached at any location of the building envelope.     

Adapting rain data for hygrothermal models

Design for moisture control has now become an established part of building envelope design. Hygrothermal modeling tools, capable of simulating moisture transfer in materials, are a key element of the design process. There are three principle methods of moisture transfer in envelopes. They are, in order of magnitude, capillary action, vapour convection, and vapour diffusion. Wind-driven rain has the potential to deposit large amounts of liquid water on the exterior surface, as well inside walls through rain penetration, providing a significant source for moisture transport. Most hygrothermal models are capable of handling wind-driven rain impinging on or penetrating the surface of the envelope. Correct results presuppose the availability of reliable rain intensity data. Many data sets, however, do not record hourly rain intensities but qualitative intensities such as light, moderate, or heavy. This paper examines several methods for assigning quantitative values to weather observations available in Canada. Real data, such as data from rain gauges, is preferable although the latter have shortcomings. Differences in catch can be up to 50% depending on gauge type, size, and exposure. When only rain codes are available the values recommended by the local meteorological service can provide adequate estimates. In case where there is observer bias a better estimate can be obtained by adjusting the value for light rainfall. If very little information is available stochastic modeling of rainfall is possible though the accuracy, especially for individual months is low.     

新建节能建筑墙体材料层及排布对干燥过程的影响

建筑围护结构内的热湿耦合传递是一个非常复杂的过程,其研究是降低建筑能耗、评估和预防湿害、提高室内热舒适性、室内卫生及优化围护结构性能的基础。新建节能建筑墙体具有初始含湿量大的特点,若墙体湿积累过大,则容易出现墙体表面剥蚀、渗漏、发霉甚至结构出现损坏的现象。墙体干燥时,传热传质过程同时发生且相互耦合。目前相关热物性仿真软件、理论研究和设计规范主要建立在热传递的基础上,忽略了湿传递的影响,对新建建筑墙体干燥不适用。WUFI~? Pro热湿仿真软件充分考虑了材料本身含湿量、风驱雨、太阳辐射、长波辐射、毛细传输和夏季结露等典型气候的影响,实现了对自然气候条件下建筑构件非稳态热湿性能的真实计算。节能墙体多在外墙添加内外保温层来增加围护结构的传热热阻,且在保温层内外两侧分别添加隔汽层和空气层的措施来防止保温层受潮,最终提高围护结构的保温性能。为墙体美观,多在围护结构的内外两侧分别黏贴墙纸和釉面砖。采用WUFI~? Pro对北京地区2种典型的建筑墙体进行热湿耦合传递模拟,分析新建建筑墙体在不同保温层材料和位置时的干燥过程,以及保温层两侧的隔汽层和空气层、墙体两侧的墙纸和釉面砖对墙体干燥过程的影响。模拟用室外条件为北京典型气象年小时室外气象参数,室内条件设定室内冬季供暖温度T_1=20℃,夏季室内温度设计值T_2=25℃,全年平均相对湿度为50%。模拟外围护结构属于西向,墙体温湿度初始条件为:相对湿度为100%,温度为15℃。模拟结果表明:内保温层的设置非常不利于围护结构的干燥,容易在内保温层和砌块之形成湿积累,降低围护结构的耐久性;EPS、PU和XPS都能降低围护结构含湿量,但EPS更有利于墙体干燥;隔汽层和空气层的添加可一定程度上阻止保温层受潮,避免造成湿积累,进而提高围护结构的保温性能;釉面砖和墙纸的黏贴将严重延缓围护结构的干燥过程,降低围护结构的保温性能,缩减建筑构件的使用寿命。     

Comparison of experimental and numerical results of wood-frame wall assemblies wetted by simulated wind-driven rain infiltration

A large-scale building envelope experiment was conducted to study the effect of three sheathing materials and two vapor retarders on the drying performance of walls exposed to simulated rain infiltration in springtime in Montreal. The moisture source was a pre-wetted component within the wall called the bottom plate insert. Its moisture content was monitored on a daily basis through the course of the 35-day experiment. The experimental set-up was simulated using a two-dimensional hygrothermal model, WUFI-2D, and the moisture content within the bottom plate inserts was used to study the ability of the model to predict the wall response to the initial liquid water load. The differences between the experimental results are mainly attributed to: air convection loops within the insulated space, which are not accounted for in the simulation; estimation of the initial moisture content distribution within the bottom plate inserts in the simulation; isotropic material properties for an orthotropic material like wood material properties that were taken from a variety of sources and did not cover the entire moisture content range and use of a two-dimensional domain to simulate three-dimensional wall systems.     

Water entry function of a hardboard siding-clad wood stud wall

This paper presents derivation of a water entry function of a hardboard siding-clad wood stud wall assembly. Water entry function provides input data to heat, air and moisture simulation models to facilitate the prediction of the long-term water entry performance of the specific assembly. Initially, an experimental work was conducted in which the hardboard siding-clad wood stud wall specimen was subjected to simulated driving rain loads, i.e. spray rates and static pressure differential. The specimen included a drainage cavity and specific deficiencies such as a missing length of sealant at the interface between the cladding and penetrating components, i.e. window, ventilation duct and electrical outlet. Water entering the deficiencies was collected at the drainage and stud cavities just below the penetrating components. Water entry results provided information on water entry rates as functions of simulated driving rain loads, which in turn permitted the development of a water entry function of the assembly. Entry function is a basic relationship that relates the quantity of water entry in a certain location within the assembly to the simulated driving rain loads. Measured climatic data of a specific climate, i.e. rainfall intensity and wind speed, was related to the simulated driving rain loads, and the entry function provided a means of estimating the water entry loads of the hardboard siding-clad wood stud wall assembly located in the specific climate.     

Effects of combined heat and mass transfer on heating load in building drying period

In initial used building with EPS walls, the wall still contains a considerable amount of water that evaporates over time. In order to analyze the effect of moisture levels on a drying building energy performance, the heat and moisture coupling transfer of building wall with multilayer composition in the cold serious area Harbin, China, was simulated. The freezing of liquid moisture in exterior envelope was considered and the moisture content gradient was used as mass transfer driving forces. The effect of some impact factors, as initial moisture content, vapor retarder, interior wallpaper and exterior glazed brick on the wall energy consumption were also analyzed. It is concluded that the effect of drying are most significant during the first year of building initial use. The drying rate of the new building was significantly high in the first year, especially in the first few months. These changes during initial drying often account for a significant fraction of the overall load and have notable effect on the building energy performance.     

Monitoring of the building envelope of a heritage house: a case study

The paper describes the long-term monitoring of the hygrothermal performance of the building envelope of a heritage house located in Ottawa. The house, once the residence of two of Canada's Prime Ministers, now serves as a museum. To preserve the historical artifacts within the building, the specified temperature and relative humidity (RH) for the indoor air are 21°C and 35% to 50%, respectively. As the house must also be preserved, there was concern about the effect of the high indoor RH (moisture) on the durability of the building structure. The main objective of the monitoring was to assess the effect of the conditioned air on the building envelope. Selected wall sections and a window were continuously monitored from March 1995 to August 1996. The monitoring included indoor and outdoor conditions and the attic environment. Temperature, RH, surface wetting–drying cycles (from precipitation or condensation), and air-pressure differential were monitored. This paper describes the monitoring approach and results. The results indicated that the brick walls are unlikely to experience internal condensation problems as long as they are subjected to a negative air pressure difference. However, because the building is quite leaky, the negative pressure introduced too much cold dry air from the exterior. It caused localized cold spots with condensation and ice formation on interior of walls and ceiling. Negative air pressure differences are not a solution unless the leakage paths are reduced.     

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.     

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.     

Inward vapor diffusion due to high temperature gradients in experimentally tested large-scale wall assemblies

Inward vapor flow due to high temperature gradients as a moisture source in building envelope has been documented, specifically when the exterior cladding is wetted by rain and then exposed to solar radiation. This phenomenon can bring large amount of undue moisture across the envelope assembly with a risk of damage of the wall elements. In this paper, inward vapor flow is applied to five large-scale monitored wall assemblies using a large-scale experimental facility consisting of a spraying array, a radiation array, and a test hut to provide controlled interior conditions. The variables studied include type of cladding (brick and cement stucco), presence and ventilation of air space, type of exterior sheathing (oriented strand board and extruded polystyrene) and type of interior finish (vinyl wall covering and paint). The results show that the presence of vapor tight interior finishes leads to the accumulation of moisture in the interior gypsum board, even in the presence of a vapor tight exterior sheathing. The presence of an air space reduces, but does not prevent moisture accumulation, while connecting the air space to the outdoor seems sufficient to short-circuit the inward vapor flow and prevent moisture accumulation.     

Selecting moisture reference years using a Moisture Index approach

Recent history has documented the premature failures of building envelopes in various regions—in North America most notably on the West Coast and the East Coast. The MEWS Consortium, a project undertaken by IRC and its partners, has addressed this issue in detail. The strategy for answering these questions was based on predicting the moisture management performance of wall systems as a function of climate, wall construction, and material properties through mathematical modeling. A key task was to determine what years to use as input for the simulations. Moisture Reference Years were selected using a Moisture Index approach developed for MEWS. This paper will develop the approach and compare it with other methods of selecting moisture reference years for hygrothermal simulations.     

Proposed method for calculating water penetration test parameters of wall assemblies as applied to Istanbul, Turkey

Water penetration of a building envelope assembly is typically assessed on the basis of the degree of watertightness (i.e. lack of water ingress) of the components of the assembly when subjected to simulated driving rain conditions. Test standards provide the magnitude and extent of these test conditions as suggested by the test parameters, i.e. the water spray rates and pressure differences and the dwell time over which these are to be applied. Such conditions would presume to simulate driving rain and wind conditions of locations spread over a broad geographical area. For example, the water spray rate suggested for use in watertightness performance tests in EN 12155—Curtain walling–watertightness–laboratory test under static pressure—is considered appropriate for simulating driving rain and wind conditions for locations across Europe. However, test parameters should be based on the expected driving rain intensities and wind pressures that are likely to occur for a specific climate and a given return period. It might also be based on the building type (e.g. high or low-rise building), or even on the location on the building facade. Hence, a method is required for calculating water penetration test parameters for specific buildings located in a specific climate. The purpose of this paper is to propose a method for calculating water penetration test parameters. A survey of existing methods is first provided that focuses on the quantification of driving rain on buildings and thereafter, calculation of water penetration test parameters. The merits and drawbacks of these methods are then discussed. Based on this review, a method for calculating test parameters is proposed and is applied to developing water penetration test parameters for Istanbul, Turkey. A comparison of test parameters calculated from the proposed method with those given in existing Turkish standards TS EN 12155–Curtain walling–watertightness–laboratory test under static pressure—and TS ENV 13050—Curtain walling–watertightness–laboratory test under dynamic condition of air pressure and water spray—related to Istanbul, indicated that the water spray rate given in the TS standards is higher than spray rates calculated from the proposed method for return periods of 5, 10 and 30 years.     

Experimental study of the performance of porous materials to moderate the roof surface temperature by its evaporative cooling effect

The change of urban surfaces from permeable to impermeable materials, i.e. asphalt or concrete, has caused the rising of surface temperatures, particularly in densely developed cities. The consequences of this problem lead to higher energy consumption, especially for cooling purposes and other environment related issues. This paper aims to investigate the performance of several non-porous and porous potential roofing materials, to determine which ones might best be used to create a more effective system by utilizing their moisture absorption and evaporation capabilities. Here, four kinds of materials—pebbles, silica sand, volcanic ash, and siliceous shale—were tested to evaluate their moisture and thermal performance, including the effects from different particle sizes. First, the necessary physical properties and pore characteristics were obtained. Thus, each material, under simple boundary conditions, was evaluated in an evaporation experiment, to determine comparative moisture and thermal behavior. Next, cyclic experimentation was conducted, in which variations of temperature, relative humidity and simulated solar radiation were included. The measurement results showed that porous materials can satisfactorily lower surface temperature. Among the tested samples, siliceous shale of both small and large particle diameter was found to lower the daily average surface temperature by up to 6.8 and 8.6 °C, respectively. The better performance of large size particles could possibly be caused by the ventilation occurring within the material layers and high solar penetration through the large gaps between particles, which would release more latent heat when compared to materials of smaller particle size. Finally, analysis of surface energy balance suggested that water contents, solar absorptivity, and wind effects all have significant influences on cooling the surface temperature.     

土壤含湿量对绿化屋顶隔热性能影响的数值研究

绿化屋顶因其特有的蒸发作用而展示出独特的隔热性能,其能力就如同给建筑增加了被动降温装置一样。本文用数值模拟的方法来分析土壤水分在绿化屋顶隔热系统中的作用,比较分析了间歇灌溉、连续灌溉和不灌溉三种模式下不同含湿量对屋顶传热的影响。研究得出：绿化屋顶隔热能力与土壤湿度呈正相关;采用间歇灌溉,屋顶热流密度对土壤湿度反应更敏感,在土壤含湿量不超过0．2时,随着湿度的增大,热流显著降低,在含湿量超过0．3后,热流反应较为迟钝;采用连续灌溉,屋顶的隔热性能较间歇灌溉提高3—4倍。     

某游泳馆节能改造设计分析

某游泳馆存在围护结构结露腐蚀、温湿度控制不佳等问题,分析问题出现的原因,针对游泳馆项目热舒适度要求高、散湿量大、水质要求高的特点,从提高围护结构保温性能、优化冷热源系统形式及暖通末端措施、改善泳池水处理系统卫生品质等方面提出了具体解决措施,达到节能环保的设计要求。     

Verringerung der Feuchtigkeitsbelastung geschädigter Bauteile durch Temperierung

Thermal treatment of moisture damaged construction elements. High moisture contents in construction materials involve the danger of several damages. The moisture content of a construction element consists in the equilibrium of moistening and drying processes depending on the frequency and quantity of these processes. The moisture supply can be reduced placing waterproofing or vapour‐proofing layers, the evaporation can be increased placing permeable membranes. Also drainage and ventilation are used to optimize the moisture protection. In this paper the investigations on heating systems in external and partition walls suffering rising damp are represented. The temperature of these construction elements is increasing only some degrees compared with the ambient temperature to support the evaporation. The findings of this investigation are the influence of temperature on capillary suction strength, viscosity, evaporation and others. In case of high moisture load and low evaporation the drying effect by thermal treatment is low, in the opposite case this method will be very successful. The aim of this investigation is to find out and show the possibilities of this method, the boundary conditions of the application and the efficiency of this method. Results are that the material properties of the building elements and the moisture load from subsoil and soil water is decisive. The method can be successful applied on sandstone, limestone, lime sandstone, and gas aerated concrete. For brick masonry this method can not be recommended in common.     

The moisture performance of framed structures—A mathematical model

A mathematical model is developed for the moisture performance of a framed structure (e.g., a flat roof or a wall), containing a hygroscopic framing material and a cavity filled with air or insulation. A formula is developed that connects the enclosed and unenclosed drying time constants for the framing material. The enclosed drying time constant alone describes the longer term moisture behaviour of the structure (much greater than one day) under any driving forces given the linearity assumptions used. The model allows for anisotropic framing materials with initial moisture contents above or below fibre saturation.     

Water penetration resistance of residential window installation options for hurricane-prone areas

While recent building code advancements have reduced structural failures in residential buildings during hurricane events, water intrusion through the building envelope is a recurring problem. Water ingress poses a significant threat to the building interior and its contents. The interface between the window and the wall system has been identified as a significant source of this water ingress. The fenestration industry has made extensive efforts to develop installation methods to improve water tightness; however, the body of research needed to guide window installations in high-humidity, hurricane-prone areas is sparse. The goal of this research is to investigate the water penetration resistance of selected window installation options consistent with current construction practice of single-family homes when exposed to wind-driven rain.     

Experimental evaluation of potential transport of mold spores from moldy studs in full-size wall assemblies

A research project was undertaken on full-scale wood-framed wall assemblies to evaluate the transport of mold spores from slightly moldy wood studs within the stud cavity to the indoor environment. A series of tests were performed with variations of such parameters as rates and patterns of air leakage, presence or absence of insulation and vapor barrier. Wood studs with slightly visible surface molds (10% of surface area) were used for some of the wall assemblies, while clear studs were used for the remainder. A pressurization setup was used to create an air infiltration through the wall assemblies. Air samples were taken to measure the spore concentrations in the stud cavities, infiltrating air, and laboratory background. Statistical significance testing methods were used to draw observations and conclusions from these data. The results from this experiment do not support a statistically significant increase of spore movement out of stud cavities into the indoor space due to the use of slightly moldy studs in the wall assemblies.