Loose-fill Insulation Research Articles

A computational analysis of effective R-values of buried ducts – the dynamic performance of buried ducts

This paper evaluates the thermal performance of ducts partially or fully buried in loose-fill attic insulation. The overall thermal resistance between the ducts and the attic is referred to as an effective R-value. This paper shows a strong dependency of assumed attic temperature on the effective R-value. Based on the results, the effective R-value can be about twice as much with an attic temperature of 130 °F [54.4 °C], compared to when the attic temperature is 80 °F [26.7 °C]. Thus, this paper provides a polynomial regression equation based on a large set of simulations to determine the effective R-value of buried ducts depending on attic temperature and whether the HVAC system runs in cooling or heating mode. Further, the work presented in this paper investigated the potential impact of convective airflow within the attic insulation, particularly around the ducts. The analysis was based on computational fluid dynamics (CFD) and indicated that convectional forces are presented around the exterior surface of the ducts, but with negligible impact on the overall heat balance between the duct and the attic space.

Practical Use of Materials of Natural Origin as Loose-Fill Insulations in Open-Diffusion Constructions—Observation and Numerical Simulation

The increasing requirements concerning the consideration of the environmental impact of building materials, along with the simultaneous preservation and enhancement of building thermal parameters, have led to a surge in interest in insulations based on organic or recycled materials. Despite the growing interest in these materials, there remains a scarcity of scientific studies regarding their hygrothermal properties. Within the scope of the research described in the text, the insulation properties of loose-fill materials (hemp shives, cellulose fibers, loose wood wool, and mineral wool as a reference) in wooden frame walls were analyzed. The authors simulated walls with the same U value filled with these materials using Delphin 6.1 software. The simulation time was 3 years, considering the appropriate climatic conditions of Olsztyn and different microclimatic conditions inside the rooms. Insulations made of natural organic can absorb and reveal moisture to the internal environment, while mineral wool transports the moisture to the outside, which may cause condensation problems. Insulations made of hemp shives or wood wool do not increase the level of accumulated moisture over time, which results in thermal stability. In contrast, cellulose and mineral wool store more moisture, which in wet conditions increases the heat flux by 6.9% and 5.2%, respectively.

Bio-based building materials: A prediction of insulating properties for a wide range of agricultural by-products

Sustainable construction is a key solution in the light of today's climate and energy challenges. Indeed, the use of plant-based aggregates in the construction sector helps to improve both energy and environmental efficiency. However, the use of bio-based aggregates as loose-fill insulation remains limited despite the wide availability of raw materials (agricultural by-products or wild plants) and their easy implementation. One of the problems is the diversity of resources that complicates both characterization procedures as well as the understanding and prediction processes of bio-material behaviors. One way to overcome these obstacles is to offer a unified method which is applicable to a wide range of plant-based aggregates. This is the purpose of the following study with the prediction of the thermal conductivity of bulk aggregates. This paper initially focuses on the particle scale in order to identify commonalities across a wide range of aggregates. Based on a multi-scale study, then distinguishes two different types of particulate morphologies. Particulate values of thermal conductivity - unavailable in the literature - can thus be provided over the full range of temperature and relative humidity conditions. A linear relationship between thermal conductivity and density is suggested at the particle scale while this type of relationship was previously known at the material scale. This work will also demonstrate the possibility of anticipating and offering equivalent insulation performances depending on the local resource available for loose-fill insulation cases.

Mold Fungal Resistance of Loose-Fill Thermal Insulation Materials Based on Processed Wheat Straw, Corn Stalk and Reed.

The present study evaluates the mold fungal resistance of newly developed loose-fill thermal insulation materials made of wheat straw, corn stalk and water reed. Three distinct techniques for the processing of raw materials were used: mechanical crushing (Raw, ≤20 mm), thermo-mechanical pulping (TMP) with 4% NaOH and steam explosion pulping (SEP). An admixture of boric acid (8%) and tetraborate (7%) was applied to all processed substrates due to their anti-fungal properties. The fourth sample group was prepared from SEP substrates without added fungicide (SEP*) as control. Samples from all treatments were separately inoculated by five different fungal species and incubated in darkness for 28 days at 28 °C and RH > 90%. The highest resistance to the colonization of mold fungi was achieved by TMP and SEP processing, coupled with the addition of boric acid and tetraborate, where molds infested only around 35% to 40% of the inoculated sample area. The lowest mold fungi resistance was detected for the Raw and SEP* samples, each ~75%; they were affected by rich amount of accessible nutrients, suggesting that boric acid and tetraborate additives alone did not prevent mold fungal growth as effectively as in combination with TMP and SEP treatments. Together, the achieved fungal colonization scores after combined fungicide and pulping treatments are very promising for the application of tested renewable materials in the future development of thermal insulation products.

Performance of Bio-based Products for Interior Insulation of Solid Masonry Walls

A recent Danish project has studied the possibilities of using bio-based materials for interior insulation of solid brick walls, without the use of a vapour barrier. The purpose was to give indications of the possibility to use hygroscopic insulation material in positions as interior insulation, where it is known to be potentially vulnerable to moisture accumulation. Three bio-based thermal insulation materials were investigated: loose-fill cellulose insulation (two variants) and hemp fibre insulation commercially available in Denmark. The hygrothermal performance of the three insulation materials for internal retrofitting purposes was investigated in a large-scale experiment comprising several solid masonry walls. The test walls were built in an outdoor test field north of Copenhagen, and exposed to a controlled indoor climate. The experiments were conducted over 1 year and 9 months where moisture measurements were done in several locations within the walls, including the interface between insulation and masonry, as well as in embedded wooden components such as a beam end and a wall plate. The paper illustrates the results from experiments with or without a hydrophobizing treatment on the exterior surface as causes of moisture content in potentially critical places in the walls. Finally, some results from mould growth determinations are reported. Generally, high levels of moisture content were found in the interior insulation, particularly for non-hydrophobized walls, but critical mould growth conditions were found only in the case of one of the tested materials.

Measured Impact of Material Settlement in a Timber-Frame Wall with Loose Fill Insulation

Loose-fill thermal insulations in timber-frame structures are designed to provide efficient thermal protection with the ability to fill intricate details. In a previous study, we detected several air cavities formed in timber-framed wall samples filled with loose-fill mineral fiber insulation. This discovery led us to retrofit the walls by adding appropriate insulation, thus enabling us to evaluate the importance of proper amendment. This paper focuses on a wall fragment with an 80 mm high air gap at the top and a 30 mm high cavity in the middle of the wall height. The following paper compares data collected before the discovery and after the replenishment (refill of air gaps with additional insulation), evaluating potential thermal performance improvement. We were able to quantify the impact of these defects on the external wall exposed to realistic conditions. Based on temperature and relative humidity measurements, the results show significant advancement in the middle of wall thickness with an 8 °C and 45% difference. The results show that although this defect did not directly affect the energy balance of the building, it significantly increases the risk of mold growth due to thermal bridging.

Optimization of Thermal Conductivity vs. Bulk Density of Steam-Exploded Loose-Fill Annual Lignocellulosics.

Lignocellulosic biomass (LCB)-based thermal insulation materials available in the market are more expensive than conventional ones and consist mainly of wood or agricultural bast fibers which are primarily used in construction and textile industries. Therefore, it is crucial to develop LCB-based thermal insulation materials from cheap and available raw materials. The study investigates new thermal insulation materials from locally available residues of annual plants like wheat straw, reeds and corn stalks. The treatment of raw materials was performed by mechanical crushing and defibration by steam explosion process. Optimization of thermal conductivity of the obtained loose-fill thermal insulation materials was investigated at different bulk density levels (30-45-60-75-90 kg m-3). The obtained thermal conductivity varies in range of 0.0401-0.0538 W m-1 K-1 depending on raw material, treatment mode and a target density. The changes of thermal conductivity depending on density were described by the second order polynomial models. In most cases, the optimal thermal conductivity was revealed for the materials with the density of 60 kg m-3. The obtained results suggest the adjustment of density to achieve an optimal thermal conductivity of LCB-based thermal insulation materials. The study also approves the suitability of used annual plants for further investigation towards sustainable LCB-based thermal insulation materials.

Cellulose-based Material for Sound Absorption And Its Application – A Short Review

Cellulose is a natural fiber potentially used as a sound absorber material due to its excellent properties, biodegradability, and lower environmental impact than synthetic materials and can be sourced from various plant-based materials, such as wood, Cotton, and Hemp. Which effectively traps and absorbs sound waves. The fibers dissipate the energy of sound waves as they pass through the material and absorb sound energy across a wide range of frequencies. Cellulose can be installed as loose-fill insulation, rigid panel form, composite with other matrix material, or foam. It's important to note that the specific characteristics and performance of cellulose-based sound absorbers can vary depending on the manufacturing process, fiber treatment, and the overall design of the sound-absorbing material. The size of cellulose fibers used in sound absorption can impact their effectiveness. Microfiber and nanofiber cellulose show different sound absorption characteristics. Microfiber has a good absorption coefficient at lower frequencies, and nanofiber cellulose performs better at higher frequency ranges. This paper involves a shortreview study of experimental methods and parameters used to regulate cellulose's sound absorption performance, which seems to be a potential alternative as an acoustic absorber, thereby reducing sustainability concerns related to synthetic materials in acoustics applications.

Thermal Properties of Hemp Shives Used as Insulation Material in Construction Industry

The article presents the results of studies concerning raw hemp shives obtained from the Polish crop of industrial hemp as a loose-fill thermal insulation material. The study focuses mainly on the measurements of the pore size distribution, thermal conductivity and air permeability of material. An increase in the value of the thermal conductivity coefficient (0.049–0.052 W/(m·K)) was demonstrated with an increase in the bulk density. The porosity of the individual pieces of shives is 78.7% and the predominant number of pores is in the diameter range of 0.9–3 μm. The paper also presents an example of the use of the tested material as thermal insulation of the wooden frame wall. The heat flow analysis was performed in various wall variants (insulation thickness: 100, 200 and 300 mm and pressure difference 0, 5, 10 and 15 Pa). A clear influence of the variables on the temperature distribution was observed.

Experimental Verification of Thermal Insulation in Timber Framed Walls.

Current environmental crisis calls for sustainable solutions in the building industry. One of the possible solutions is to incorporate timber-framed constructions into designs. Among other benefits, these structures are well established in many countries, originating in traditional building systems. This paper focuses on experimental timber-frame walls. Different wall assemblies vary in thermal insulation materials and their combinations. We investigated ten experimental wall structures that have been exposed to natural external boundary conditions since 2015. The emphasis was on their state in terms of visual deterioration, mass moisture content, and thermal conductivity coefficient. We detected several issues, including defects caused by inappropriate realization, causing local moisture increase. Material settlement in loose-fill thermal insulation was another issue. Concerning was a significant change in the thermal conductivity of wood fiber insulation, where the current value almost doubled in one case compared to the design value determined by the producer.

Heat Losses Caused by the Temporary Influence of Wind in Timber Frame Walls Insulated with Fibrous Materials.

The paper presents the results of research concerning three fiber materials—mineral wool, hemp fiber and wood wool—as loose-fill thermal insulation materials. The analysis used the material parameters determined in previous works conducted by the authors, such as thermal conductivity and air permeability in relation to bulk density. These materials exhibit open porosity; thus, convection is an essential phenomenon in the heat transfer process. The paper aimed at conducting thermal simulations of various frame wall variants which were filled with the above-mentioned insulation materials. The simulations were performed with the Control Volume Method using the Delphin 5.8 software. The studies accounted for the effect of wind pressure and the time of its influence on a wall insulated by means of fiber material with a thickness of 150 as well as 250 mm. The simulation enabled us to obtain such data as maximal R-value reduction and time to return to equilibrium after filtration for the analyzed materials. The study proved that heat transfer in these insulations strongly depends on the bulk density, thickness of the insulation and wind pressure. The decrease in R is reduced as the density increases. This results from the decreased air permeability characterizing the material. Wind washing causes lower R reduction than air filtration in all models. The greater the thickness, the longer it takes for the models to return to the equilibrium state following air filtration (and wind washing). This period is comparable for air filtration and wind washing. Hemp fibers were characterized with the strongest susceptibility to air filtration; in the case of wood wool, it was also high, but lower than for hemp fibers, while mineral wool was characterized with the lowest.

Research of Wood Waste as a Potential Filler for Loose-Fill Building Insulation: Appropriate Selection and Incorporation into Polyurethane Biocomposite Foams.

Currently, the recycling potential of wood waste (WW) is still limited, and in a resource efficiency approach, recycling WW in insulation materials, such as polyurethane (PUR), appears as an appropriate solution. It is known that the quality of WW is the main aspect which influences the stability of the final products. Therefore, the current study analyses different WW-based fillers as possible modifiers for polyurethane biocomposite foams for the application as loose-fill materials in building envelopes. During the study of WW-based fillers, it was determined that the most promising filler is wood scobs (WS) with a thermal conductivity of 0.0496 W/m·K, short-term water absorption by partial immersion—12.5 kg/m2, water vapour resistance—0.34 m2·h·Pa/mg and water vapour diffusion resistance factor—2.4. In order to evaluate the WS performance as a filler in PUR biocomposite foams, different ratios of PUR binder and WS filler (PURb/WS) were selected. It was found that a 0.40 PURb/WS ratio is insufficient for the appropriate wetting of WS filler while a 0.70 PURb/WS ratio produced PUR biocomposite foams with the most suitable performance: thermal conductivity reduced from 0.0523 to 0.0476 W/m·K, water absorption—from 5.6 to 1.3 kg/m2, while the compressive strength increased from 142 to 272 kPa and the tensile strength increased from 44 to 272 kPa.

Hot-box measurements to investigate the internal convection of highly insulated loose-fill insulation roof structures

The purpose of this study was to investigate how internal convection in loose-fill insulations affects the insulation properties of highly insulated roof structures. This study consists of laboratory measurements of roof structures insulated by two different blown-in insulations. The measurements are repeated with two temperature differences and air velocities for 300 mm and 600 mm thick insulation layers both with and without trusses, making a total of 24 case studies. The measurements were conducted with equipment using the calibrated hot-box method. The results of the tests show that internal convection can reduce insulation capacity significantly, especially with low-density loose-fill insulations, such as blown-in glass wool. A critical evaluation should be performed as to whether international standards and national building regulations take internal convection into account adequately. According to this study, 5 should be used as a critical modified Rayleigh number for horizontal roof structures with an open upper surface when used insulation material is loose-fill glass wool or wood fibre insulation as in this study.

Thermal Diffusion in Fibrous Aerogel Blankets

Nowadays, the usage of thermal insulation materials is widespread not only in the building sector but also in the vehicle industry. The application of fibrous or loose-fill insulation materials like glass wool or mineral wool as well as aerogel is well known. Aerogel-based materials are among the best solid materials for thermal insulation available today; they are prepared through a sol–gel process. For building walls, the glass-fiber-enhanced types are the frequently used ones. They are prepared by adding the liquid–solid solution to the fibrous batting, which is called a sol–gel process. In the present paper, the changes in the most important building physical properties of aerogel blankets after thermal annealing are presented. The samples were subjected to isochronal heat treatments from 70 to 210 °C for 24 h. The changes in the thermal conductivity were followed by Holometrix Lambda heat flow meter, and differential scanning calorimetry results were also recorded. From the measured values, together with the densities, the most important thermal properties were calculated, such as thermal resistance, diffusivity, effusivity (heat absorption), and thermal inertia. In this paper, we attempt to clarify the role played by thermal annealing in the transient thermal properties of aerogel materials. Besides presenting the measurement results, a theoretical background is given. The investigations of not only the steady-state but also the transient thermal parameters of the materials are momentous at the design stage.

Mass Transport and Thermal Conductivity Properties of Flax Shives for Use in Construction Industry

ABSTRACT The paper presents the results of studies concerning raw flax shives obtained from Polish crop of flax as a loose-fill thermal insulation material. The study focusses mainly on measurements of the thermal conductivity and water vapor permeability of material, but on water absorption and capillary rise as well. The shives showed satisfactory lambda values, comparable to traditional thermal insulation materials. They also showed high mass absorptivity and the ability to uptake large amounts of water by capillary action in a short time. The paper presents also an example of the use of the tested material as thermal insulation of the flat roof. The analysis of the heat flow through the flat roof with different thicknesses of flax shives insulation was carried out.

Smouldering Combustion in Loose-Fill Wood Fibre Thermal Insulation: An Experimental Study

A bench-scale experimental setup has been used to study the conditions necessary for smouldering ignition in four types of loose-fill wood fibre thermal insulation, and to study the development of the smouldering process. The products varied with regard to wood species, grain size and fire retardant chemical additives. The test material was placed in an insulated open top container and heated from below. Temperatures within the sample and mass loss were measured during the tests. Both the fibre size and the level of added fire retardant seem to influence the smouldering ignition. Two different types of smouldering were identified in this study. Materials undergoing smouldering Type 1 obtained maximum temperatures in the range 380°C to 440°C and a total mass loss of 40 wt% to 50 wt%. Materials undergoing smouldering Type 2 obtained maximum temperatures in the range 660°C to 700°C and a total mass loss of 80 wt% to 90 wt%. This implies that Type 2 smouldering involves secondary char oxidation, which represents a risk for transition to flaming combustion and thereby a considerable fire hazard. This has been an exploratory project and the results must therefore be considered as indicative. The findings may, however, have implications for fire safety in the practical use of loose-fill wood fibre insulation in buildings, and further experimental studies should be performed with this in mind to obtain more knowledge about the topic.

Thermophysical characterization of Posidonia Oceanica marine fibers intended to be used as an insulation material in Mediterranean buildings

The present work focuses on the study of the thermophysical properties of Posidonia Oceanica natural fibers in order to investigate the potential of their use as loose-fill thermal insulation material in the Mediterranean construction. 24 samples were prepared. Bulk densities were varied from 17 kg m−3 to 155 kg m−3. Chemical alkali treatments with various conditions were applied to these fibers. The influence of treatments and of density on morphological and thermophysical properties of samples was evaluated. The surfaces were examined by using scanning electron microscopic. The thermal measurements were performed with the Hot Disk thermal constants analyzer. Results have shown that thermal conductivity decrease when density decreases until an optimum. After that, it increases as the density is reduced. Furthermore, regarding thermal conductivity, it was found out that the effect of chemical treatment is not significant mainly at the low densities. A very slight improvement was found at high densities with treated fibers, mainly the treatment that consists of immerging fibers twice in 2% sodium hydroxide solution during 2 h at 80 °C. Higher mass heat capacity was observed with this same treatment.Additionally, it was revealed in this study that Posidonia-Oceanica fibers have thermal conductivity and thermal diffusivity close to conventional insulation materials and higher mass heat capacity that reached 2533 J kg−1 K−1.

Moisture and wetting properties of thermal insulation materials based on hemp fiber, cellulose and mineral wool in a loose state

ABSTRACTThe paper presents the results of research concerning three fiber materials – hemp fiber, cellulose fiber and mineral wool as a loose-fill thermal insulation materials. It focused on the study of moisture properties and wettability of these materials. The analysis involved evaluation of moisture sorption in different relative humidity conditions and evaluation of wettability of fibers by contact angle measurement. The study showed that the sorption equilibrium has been achieved at different times, which proves the various nature and properties of the materials. Hemp fibers were less wet than cellulose fiber, but the time needed to stabilize was shorter. The largest contact angles, indicating the strongly hydrophobic properties, were shown by mineral wool. Some samples of hemp and cellulose fibers were characterized by similar contact angles providing high wetting properties.

Thermal Properties of Raw Hemp Fiber as a Loose-Fill Insulation Material

ABSTRACTThe article presents the possibilities of using hemp fiber as a loose-fill insulation material. The article presents the results of research concerning raw hemp fiber obtained from the Polish crop of industrial hemp of Białobrzeskie variety. The analysis involved evaluation of thermal conductivity in function of bulk density and air permeability, the properties important for insulation materials. The results of laboratory investigation were used to create the numerical simulation models of heat transfer in the frame wall partitions filled with hemp fibers. The study showed that with the increase of bulk density, the thermal conductivity and air permeability of material decrease. The obtained lambda values are comparable with the characteristic values for conventional thermal insulation materials. The results of heat transfer and temperature distribution reveal that hemp fibers characterize with strongly air permeance, what affects on the need for additional barriers against air filtration.

Characterization of Barley Straw, Hemp Shiv and Corn Cob as Resources for Bioaggregate Based Building Materials

Expanding the use of low-environmental impact materials in the field of building materials is a major aim in a context of sustainable development. These alternative materials should be non-polluting, eventually recycled, and locally available. Bioresources are already used in some building materials but few studies have investigated their relevance in such applications. The aim of this paper is to evaluate the suitability of three kinds of vegetal aggregates: barley straw, hemp shiv and corn cob. The availability of these bioresources, extracted from a French database, is discussed, as are their physical properties and chemical compositions. Their microstructure is described with SEM images and their particle size distributions are provided through image analysis. Sorption–desorption isotherms are measured by a Dynamic Vapour Sorption system. Bulk density, thermal conductivity and water absorption are also quantified. The results highlight a tubular structure for the three different aggregates, with low bulk density and thermal conductivity (0.044, 0.051 and 0.096 W m−1 K−1 respectively for straw, hemp shiv and corn cob) and high water absorption, especially for barley straw and hemp shiv (414 and 380% vs. 123% for corn cob). Their hygric regulation capacity is also sufficiently good, with a water sorption of between 20 and 26% at 95% of relative humidity. These plant aggregates could therefore be used as additions in an earth matrix, or a hydraulic, pozzolanic, air lime or gypsum binder, or just as loose-fill insulation material. However, future research should focus on their resistance to fire and bacterial growth to validate this approach.