Vapor Diffusion Resistance Research Articles

Wood waste as an alternative thermal insulation for buildings

Current insulation materials in the construction market, which are predominantly inorganic materials, have a high performance in relation to heat transfer, i.e. high R-values, but the environmental impacts in their production processes are significant. The use of bio-based natural fibre materials such as cork, cotton, wood fibre, hemp, etc. with their lower embodied energy, moisture buffering capacity and, consequently, improved Indoor Environmental Quality have received increasing focus in both research and application, particularly amongst environmentally-conscious clients and designers.In this study a natural fibre material in the form of wood waste is examined experimentally to assess its suitability for use as a thermal insulation material, without the addition of any binder, within a timber frame wall construction. The wood waste is from primary production sources using untreated material. According to our experimental results, the thermal conductivity values of wood waste with different densities, ranged from 0.048 to 0.055 W/mK. These values are slightly higher than commonly used inorganic based insulation materials, although comparable to other natural insulation materials in the market, but have the economic advantage of being a low-cost by-product. The values relating to the material hygric performance including the water vapour diffusion resistance factor, water vapour permeability, and water absorption coefficient were also determined and presented, which will help facilitate future hygrothermal modelling.

Heat and moisture transfer behaviour in Phyllostachys edulis (Moso bamboo) based panels

This study focuses on the heat and moisture transfer behaviours in the Phyllostachys edulis (Moso bamboo) panels at various temperature and relative humidity (RH) conditions. Moso bamboo panels with different lamination methods were prepared by assembling bamboo strips from different layers of the bamboo culm wall. Dynamic coupled heat and moisture transfer experiments were conducted. Unsteady state numerical modelling was conducted by COMSOL Multiphysics™. A rigorous approach was adopted in this paper. A series of parametric studies of numerical simulation are firstly presented in this paper and then validated by the experiments. Both experimental and simulation results appear to be consistent with the results of measurements of the basic hygrothermal parameters, which demonstrates the robustness of the results. The temperature and RH results indicated that although the panel made from layers of the internal part of bamboo culm wall can provide good insulation performance, its ability to resist high RH variation is inferior to the layer from the external part of bamboo culm wall. The parametric study found that density is the most critical parameters to influence the temperature distributions in the transient state. The thermal conductivity dominates the temperature variation in the steady state. The water vapour diffusion resistance factor is the key parameter which influences the RH simulation results. Numerical simulation with moisture transfer shows better consistency than the simulation without moisture in both equilibrium and transient states. The results of this study demonstrated that the external part of the bamboo culm wall can be utilised to minimise the RH variation of the panel while the internal part is suitable for increasing the thermal insulation performance of the panel.

Water vapour diffusion resistance of larch (Larix decidua) bark insulation panels and application considerations based on numeric modelling

This paper focuses on the vapour diffusion resistance of light particleboard produced from larch (Larix decidua) bark for thermal insulation applications. The influence of panel density and particle orientation, as well as particle size was evaluated in this respect. The former proved to have the most important effect. The panels' structure was illuminated by means of computed tomography and used as an input for a structure-based numeric model for vapour diffusion. The model was found to be suitable to describe the mass flow in the panels and was used to propose some optimisation of panel structure to serve for special needs in building engineering.

Hygrothermal properties of clayey plasters with olive fibers

This research deals with how to use agricultural waste materials in constructions considering that the development of innovative materials has to respond to both environmental and energy issues. The leaves and the small branches derived from the pruning of olive trees were incorporated, after drying, into a clay-sand mixture to obtain a bio-based plaster. Earthen samples, containing different percentages of olive fibers, were prepared and tested to investigate their hygrothermal behaviour. Thermal conductivity and the effects of several parameters on thermal performance were analyzed. The evaluation of the hygric behaviour was based on the measurement of the water vapour diffusion resistance factor and of the isothermal sorption curves. Results showed that the addition of olive fibers in the earth matrix enhances the insulating and hygric performances. The ability of the material to exchange moisture was studied by calculating the ideal Moisture Buffering Value (MBVideal). Results showed that the effects of moisture adsorption/desorption improved with the increase of the fibers content.

Hygrothermal properties of bio-insulation building materials based on bamboo fibers and bio-glues

This study focuses on manufacturing by thermo-pressing new low-environmental-impact bio-insulation fiberboards from bamboo fibers and bone glue, modified with sodium lignosulfonate. The aims are to measure moisture buffer value, water vapor permeability, bending properties, thermal conductivity and vapor sorption isotherms of these materials. The moisture buffer values of these materials belong to the “excellent” category, ranging from 2.5 to 3.9g/(m2.%RH), higher than the value for bamboo fiberboard without glue (1.7g/(m2.%RH). The water vapor diffusion resistance factor ranges from 8 to 17, which is similar with other fiber insulation materials. The bending properties show a significant improvement when 30% (w/w) glue is used, the glue being a mixture between bone and sodium lignosulfonate glues. Moreover, the variation in thermal conductivity of the fiberboards with relative humidity and moisture content is investigated to evaluate the hygrothermal performance of the fiberboards. The results are promising for both thermal insulation and moisture buffering, thus these fiberboards could be used for passive control of indoor environment.

Hygric properties and thermal conductivity of a new insulation material for building based on date palm concrete

Experimental investigations of hygric and thermal conductivity properties of a new biocomposite material dedicated for construction which contains cement, sand and water and reinforced with 15wt% of date palm fibers were carried out. The investigations were based on the measurement of water vapor permeability, of sorption isotherm, of moisture diffusivity and thermal conductivity. The results reveal that the presence of date palm fibers improves the performance and the efficiency of the composite material: lowering of water vapor diffusion resistance, enhancement of moisture transfer. The results were compared to other kind of biocomposite materials used for construction. Finally, we have shown the effect of temperature on thermal conductivity for both moist and dry states.

SELECTION OF THE INSULATION MATERIALS FOR REFURBISHMENT PURPOSES

Refurbishment of the building facades of residential buildings, including insulation, is often considered as the most energy efficient renovation measure with the largest potential. One of the solutions to increase energy efficiency is the selection of the appropriate insulation materials of the external walls. The article proposes the approach for selection of the insulation material based on SAW multiple criteria assessment method. The proposed methodology is applied for the case of insulation material selection in refurbishment of 12-storey building in Vilnius, Lithuania. Research reveals that rock wool outperforms other materials by thermal conductivity, light weigh, water vapour diffusion resistance, highest flammability class, durability and lowest emission of CO2 and is an efficient insulation to be used for sustainable refurbishment solutions.

Physiological response of cidró to different water replacement levels in two seasons of the year

ABSTRACT We aimed to determine the response of cidró (Aloysia triphylla) submitted to different water replacement levels in summer and winter, in order to understand and relate the plant physiological performance under adverse weather conditions. The research was developed in a protected environment, in the city of Frederico Westphalen, Rio Grande do Sul State, Brazil. The experimental design was completely randomized, arranged in a 2x4x2 factorial scheme, two seasons of the year (summer and winter), four water availability (50, 75, 100, 125% of ETo) and two faces of leaf (abaxial and adaxial), with four replications. There were evaluated stomatal vapor diffusion resistance (s/cm), transpiration (µg/cm2/s) and leaf temperature (°C), on both faces of the leaf from 10 a.m. to 11 a.m., 1 p.m. to 2 p.m. and 4 p.m. to 5 p.m., 45 days after the beginning of the season. We concluded that the physiological response of cidró plants was influenced by water replacement levels, in a different way according to the seasons of the year. The summer season was responsible for the highest values of incident photosynthetically active radiation, leaf temperature, transpiration and stomatal vapor diffusion resistance. The reduction in water availability promoted the increase in values for stomatal resistance to vapor flow, reducing leaf transpiration rate. The incident photosynthetically active radiation, leaf temperature and transpiration showed highest values on the abaxial face of the studied species.

Water vapour diffusion resistance factor of Phyllostachys edulis (Moso bamboo)

This study measured the water vapour diffusion resistance factor of the Moso bamboo specimens in all directions of the cylindrical coordinate system at both internode parts and node parts. The measurement was conducted by the dry cup method. Major findings included three aspects. The water vapour diffusion resistance factor results of Moso bamboo specimens present a decreasing trend from the external surface to the internal surface in the radial directions. This fact may be attributed to the more densified fibre cells and low quantity of pits at the external surface. The water vapour diffusion resistance factor of bamboo specimens is remarkably lower in the longitudinal direction than in the radial and tangential directions. The large diameter, high interconnectivity and straight structure of the vascular bundle vessel influence the lower water vapour diffusion resistance factor in the longitudinal direction. The majority of the node specimens demonstrated lower water vapour diffusion resistance factor values than the internode specimens in the radial and tangential directions. The irregular orientation of vascular bundle vessels in different directions can be considered as the reason.

Comparison of ET partitioning and crop coefficients between partial plastic mulched and non-mulched maize fields

The ratio of evaporation to evapotranspiration (E/ET) and crop coefficients (Kc) are important parameters for evaluating the water-saving potentials of agronomic technologies and they may vary with different practices of dryland cultivation. This study synchronously investigated changes of E/ET and Kc for three years using two eddy covariance systems and multi-microlysimeters under two cultivation methods—conventional flat planting without mulching (CK) and a furrow-ridge system with plastic film partially mulching (MFR)—on the semiarid Loess Plateau of China. Due to an increase of vapor diffusion resistance at the soil-air interface partially mulched by plastic film, the average E and ET of MFR were lower than those of CK by 38.1% and 9.3%, respectively, for the three growing seasons. Thus, the average E/ET in MFR decreased by 11.2 percentage points compared with CK. E/ET showed a significant logistic function with the green leaf area index (GLAI) under both treatments during the three growing seasons. The seasonal Kc varied with GLAI following a step function curve for both treatments, and was linearly correlated to GLAI with significance levels when GLAI was below the thresholds of 3.0 and 3.2–3.4 for CK and MFR, respectively. Maximum Kc values were 1.01±0.05 and 0.91±0.09 for CK and MFR, respectively, at the middle crop growth stage. These results suggest that MFR can significantly reduce E/ET and maximum Kc, which help to improve yield and water use efficiency in rainfed spring maize fields. Consequently, MFR enhanced the average grain yield and crop water use efficiency by 12.5% and 24.6%, which amounted to 11527kg/ha and 3.36kg/m3, respectively. Therefore, MFR promoted crop water productivity and is an effective approach to solve water crises in dryland regions.

Improvements to Water Vapor Transmission and Capillary Absorption Measurements in Porous Materials

Abstract The vapor permeability (or equivalently the vapor diffusion resistance factor) and the capillary absorption coefficient are frequently used as inputs in hygrothermal or heat, air, and moisture (HAM) models. However, it has been well documented that the methods used to determine these properties are sensitive to the operator, and wide variations in the properties have been reported in round-robin testing. This paper presented an investigation into how these errors can be minimized for porous materials by different edge sealing techniques and also looked at whether automating these techniques can reduce operator artifacts. To automate the measurements, specimens were attached to a balance or load cell and then required no further interaction, which allows massive amounts of data to be collected. The extra data is advantageous for the beginning of the capillary absorption test where the moisture uptake is rapid. Most of the potential for errors in the vapor diffusion tests resulted from uncertainties in how the sample was sealed between the chambers and determining when the steady state region was reached, neither of which can be improved by automation.

Application of Ceramic Powder as Supplementary Cementitious Material in Lime Plasters

In this paper, the properties of plasters based on lime – brick powder binder of varying composition (ceramics content from 0 to 80 %) are studied. The plasters are prepared with a constant water amount. The pore size distribution is thus influenced in a positive way; the total porosity increases with the ceramics content but the volume of capillary pores is reduced. It results in lower water vapor diffusion resistance factor while the apparent moisture diffusivity coefficient increases just moderately. The influence of ceramic on strength of plasters is not found very important. The thermal conductivity of plasters containing ceramics is lower than those with the pure lime what is again in agreement with the pore size distribution. It can be concluded that fine brick powder can be used as pozzolanic admixture in lime based plasters with a positive influence on its functional parameters.DOI: http://dx.doi.org/10.5755/j01.ms.22.3.7433

Intrinsic Evaporative Cooling by Hygroscopic Earth Materials

The phase change of water from liquid to vapor is one of the most energy-intensive physical processes in nature, giving it immense potential for cooling. Diverse evaporative cooling strategies have resulted worldwide, including roof ponds and sprinklers, courtyard fountains, wind catchers with qanats, irrigated green roofs, and fan-assisted evaporative coolers. These methods all require water in bulk liquid form. The evaporation of moisture that has been sorbed from the atmosphere by hygroscopic materials is equally energy-intensive, however, yet has not been examined for its cooling potential. In arid and semi-arid climates, hygroscopic earth buildings occur widely and are known to maintain comfortable indoor temperatures, but evaporation of moisture from their walls and roofs has been regarded as unimportant since water scarcity limits irrigation and rainfall; instead, their cool interiors are attributed to well-established mass effects in delaying the transmission of sensible gains. Here, we investigate the cooling accomplished by daily cycles of moisture sorption and evaporation which, requiring only ambient humidity, we designate as “intrinsic” evaporative cooling. Connecting recent soil science to heat and moisture transport studies in building materials, we use soils, adobe, cob, unfired earth bricks, rammed earth, and limestone to reveal the effects of numerous parameters (temperature and relative humidity, material orientation, thickness, moisture retention properties, vapor diffusion resistance, and liquid transport properties) on the magnitude of intrinsic evaporative cooling and the stabilization of indoor relative humidity. We further synthesize these effects into concrete design guidance. Together, these results show that earth buildings in diverse climates have significant potential to cool themselves evaporatively through sorption of moisture from humid night air and evaporation during the following day’s heat. This finding challenges the perception of limited evaporative cooling resources in arid climates and greatly expands the applicability of evaporative cooling in contemporary buildings to water-stressed regions.

Ecological, thermal and acoustical insulating composite from hemp shives and sapropel binder

The technological parameters for the production of hemp shives (HS) composite with organic sapropel binder and reinforcement additive – paper production waste (PPW) is developed and properties of this composite are investigated in this paper. The amount of sapropel in composite was 5% of HS mass by the amount of dry materials. Thermal processing with highest temperature of 190°C was used for hardening of the composite. The thermal conductivity and sound absorption coefficients, compressive stress, short-term water absorption, water vapor diffusion resistance factor of composite were investigated. The impact of various factors on the properties of composite was evaluated. The greatest impact has the compaction level of composite, also PPW additive. The impact of HS particles size ranging from 2.5mm to 20mm is much smaller. The regression equations enable prediction of thermal conductivity and compressive stress of composite depending on density and HS particles size were derived. The impact of surface hydrophobization on short-term water absorption was evaluated. Compared to HS-lime composite, better thermal and acoustic properties of HS-sapropel composite were obtained.

Heat flux measurements for determination of the liquid water diffusivity in capillary active materials

A method is described to determine the liquid water diffusivity in capillary active materials and a model for the mathematical description of this material property is proposed.Heat flux measurements by means of a guarded hot plate apparatus are employed for the assessment of the total energy transfer through dry and water-saturated calcium silicate samples. The radiative and conductive contributions to the heat transfer are estimated using an empirical model and separated from the enthalpy fluxes, connected to the water (liquid and vapor) transfer. After mathematical transformation the liquid water diffusivity can be calculated.The proposed method differs significantly from other procedures generally employed to the same aim, and is advantageous since no further equipment but a guarded hot plate and a balance is needed.Considerations on the effect of the water content on the vapor diffusion resistance factor are made, taking into account the experimental results.The obtained results are compared with data by other authors and an error estimation is included.

Hygrothermal Properties of Steel Fiber Reinforced Concretes

This paper defines the hygrothermal material properties (thermal conductivity, density, specific heat capacity, vapor diffusion coefficient and resistance, moisture storage function, water absorption coefficient and liquid transport coefficient) of steel fiber reinforced concretes that are widely used for industrial floors, based on laboratory measurements. The measured and calculated material properties are necessary to carry out a dynamic heat and moisture simulation of a component or a building containing steel fiber reinforced concrete layers.

Hygric Properties of HPC with Natural Pozzolana

The water vapour transport and the liquid water transport of high performance concrete (HPC) with the content of natural pozzolana are the described in this paper. Studied properties are presented by means of water vapour diffusion coefficient, water vapour diffusion resistance factor and absorption coefficient respectively. The natural pozzolana (NP), namely natural zeolite, is used as supplementary cementitious material which affects the durability properties of the end product. The obtained results revealed the effectiveness of NP in the terms of both studied properties when used in small amounts, i.e. at about 20% of cement weight. On the other hand substitutions higher than 40% result in worsening of the resistance of the concrete to water and water vapour ingress and its movement trough the material.

Hygric Properties of Lime-cement Plasters with the Addition of a Pozzolana

There are more than seven billion people currently living on the Earth and the demands of population are rising. Lime and cement are parts of most building materials, so their global consumption grows. Therefore, it is necessary to think both economically and ecologically, and search for a suitable alternatives and replacements. This study is aimed at an investigation of the influence of pozzolana as the third binder component on basic physical characteristics and hygric properties of lime-cement plasters. Results show that with the increasing amount of pozzolana in the mixture the open porosity goes down. This is accompanied by a liquid water absorption decrease. Also diffusion parameters are somehow worsened, as the water vapour diffusion resistance factor increases.

Hygrothermal Behaviour of Three Internal Retrofit Prototype Solutions

Although the application of internal insulation to existing perimeter walls poses significant challenges in terms of building physics and loss of habitable space, it is sometimes an inevitable choice because of practical or legislative constraints. Innovative solutions are then required to deliver satisfying performances and reduce nuisance to inhabitants of residential buildings in case they are going to remain in their flats during the retrofit works.Three systems for inner thermal retrofitting purposes have been designed and produced as prototypes. Two of them are composed by silica aerogel containing fibrous material: the first one is a rigid flat laminated panel, the second one is a rollable solution with a fabric finishing layer. The third insulating system is a perlite based board with a hydrophobic layer. All the materials composing the retrofit solutions have been characterized by means of laboratory tests in order to measure their main hygrothermal properties. In fact, some parameters are fundamental for determining the hygrothermal performance of the composite systems: thermal conductivity, at dry and wet state (moisture dependant), water vapour diffusion resistance factor, hygroscopic sorption at isotherm condition and water absorption coefficient. All those measured data were necessary for optimizing the solutions, guaranteeing energy efficiency and vapour open layers to systems that are intended for installation on existing walls.

Effect of External Environment on the Properties of Selected Plasters

The effect of external environment on the aging process of commercially used lime-cement plasters is studied. Three different kinds of plasters are tested at three different ages, namely in the reference state after 28 days of standard curing and after one and two years of exposure to the environmental conditions of Central Europe. The basic physical properties (bulk density, matrix density, open porosity), mechanical strengths (compressive strength, bending strength) and water vapour diffusion resistance factor belong to the studied properties. Experimental results show that not only the compressive strength but also all other studied characteristics are affected by the external environment in a significant way.