Multilayer Building Research Articles

Mathematical Model of VOCs Emission in Three-layer Building Materials

A simple mathematical model is proposed to account for emissions of Volatile Organic Compounds (VOCs) from three-layer building materials. The model considers both the diffusion within three layer building materials and the mass transfer resistance through the air boundary layer. A general solution method based on Laplace transform is presented. Compared to other models capable of accounting for emissions of VOCs from multi layer building materials, the present model is fully analytical instead of being numerical. The present model was validated by the experimental data from the specially designed test. The results indicated that there was a good agreement between the model predictions and the experimental data. It can also be seen from calculation that model ignoring the boundary layer resistance cannot fully reflect the real situation.

Geometric and physio-mechanical characteristics of the contact layer area of multilayer reinforced concrete structures

In the practice of modern construction, multi-layer building envelopes made of concrete of various physio-mechanical characteristics has been wide applied. During successive layer-by-layer laying of various concretes, contact layers are formed between them, and their physical and mechanical characteristics are different from the adjacent layers. Technological and time factors for the manufacture of this structure affect the formation, physical and mechanical characteristics of the contact layer between the inner and outer structural layers, and effecting to the working of the multi-layer structure. In this article, the geometric and physio-mechanical characteristics of the contact layer zone of multi-layer reinforced concrete structures are researched. The main content of study was conducted on samples of three-layer structural blocks with using strong structural concrete B25 in the external layers, and low-strength concrete in the middle layer. The geometric and physio-mechanical characteristics of the contact layers were researched by the experimental method. Based on the results of experiments, the geometric and physio-mechanical characteristics of the contact layer of multilayer reinforced concrete structures are shown, taking into account the influence of technological and time factors for the manufacture of this structure. Moreover, the results of the study allow us to determine rational parameters in design of multilayer envelopes with reinforced concrete layers of various strengths, interconnected by a monolithic contact layer. According to the results, modification and calculation method for multilayer reinforced concrete building envelopes has been evaluated and applied into the production process of these constructions.

Investigation of the humidity regime of multilayer enclosing structures of buildings and structures

The article describes an approximate analytical method for calculating the moisture regime of multilayer building envelope structures. The novelty of the proposed method lies in the use an analytical dependence for determination the position of the flatness possible condensation, obtained as a result of studying the function which is the difference between the partial pressures of water vapor in the considered section the enclosing structure and the partial pressure of saturated water vapor at the extremum. The article presents the results of calculating the moisture regime of the outer wall of a residential building under construction in Samara using monolithic sandless expanded clay blocks with a density equal to 600 kg/m3. The calculation showed that during the heating period the coordinate of flatness of possible condensation in sandless expanded clay concrete, measured from the inner surface of the wall moves from 0.444 m to 0.5 m. The made assessment of moisture accumulation in the considered outer wall, both for the annual period of operation of the building, and for the period of months with negative temperatures, showed compliance with the regulatory requirements for heated rooms.

Proven Recovery Neurosurgery – Multi-Layer Building Block Implementation of an Universal Early Enhanced Recovery Program for Cranial Surgery at a Large Integrated Healthcare System

Proven Recovery Neurosurgery – Multi-Layer Building Block Implementation of an Universal Early Enhanced Recovery Program for Cranial Surgery at a Large Integrated Healthcare System

Evaluating the performance of WRF urban schemes and PBL schemes over Dallas Fort Worth during a dry summer and a wet summer

AbstractThis study evaluated the Weather Research and Forecasting (WRF) model sensitivity to different planetary boundary layer (PBL) schemes (the YSU and MYJ schemes) and urban schemes including the bulk scheme (BULK), single-layer urban canopy model (UCM), multi-layer building environment parameterization (BEP) model, and multi-layer building energy model (BEM). Daily reinitialization simulations were conducted over Dallas-Fort Worth during a dry summer month (July 2011) and a wet summer month (July 2015) with weaker (stronger) daytime (nocturnal) UHI in 2011 than 2015. All urban schemes overestimated the urban daytime 2m temperature in both summers, but BEP and BEM still reproduced the daytime urban cool island in dry summer. All urban schemes reproduced the nocturnal urban heat island, with BEP producing the weakest one due to its unrealistic urban cooling. BULK and UCM overestimated the urban canopy wind speed, while BEP and BEM underestimated it. The urban schemes showed prominent impact on daytime PBL profiles. UCM+MYJ showed a superior performance than other configurations. The relatively large (small) aspect ratio between building height and road width in UCM (BEM) was responsible for the overprediction (underprediction) of urban canopy temperature. The relatively low (high) building height in UCM (BEM) was responsible for the overprediction (underprediction) of urban canopy wind speed. Improving urban schemes and providing realistic urban parameters were critical for improving urban canopy simulation.

PCM Cement-Lime Mortars for Enhanced Energy Efficiency of Multilayered Building Enclosures under Different Climatic Conditions.

Phase change materials (PCMs) are promising materials for the energy efficiency improvement of building enclosures, due to their energy storage capacity. The thermal behaviour of a multi-layered building enclosure with five different compositions of PCM cement-lime mortars was evaluated under heating and cooling cycles. The behaviour of cement-lime mortars with 20% of microencapsulated PCM mixed with other additions, such as cellulose fibres and perlite, a lightweight aggregate (LWA), were studied under climate conditions of 15 °C–82% RH (cooling) and 30 °C–33% RH (heating) that were applied with a climatic chamber. Temperature and heat flux on both sides of the multi-layered enclosure were experimentally measured in laboratory tests. Temperature was also measured on both sides of the PCM cement-lime mortar layer. It was observed that the addition of the PCM cement-lime mortar layer delayed the heat flux through the enclosure. During a heating cycle, the incorporation of PCM delayed the arrival of the heat wave front by 30 min (8.1% compared to the reference mortar without PCM). The delay of the arrival of the heat wave front during the cooling cycle after adding PCM, compared to the reference mixture, reached 40.6% (130 min of delay). Furthermore, the incorporation of LWA in PCM cement-lime mortars also improved thermal insulation, further increasing energy efficiency of the building enclosure, and can be used not only for new buildings but also for energy rehabilitation of existing building enclosures.

On the varieties of build features during multi-layer laser directed energy deposition

Laser directed energy deposition (DED) is an additive manufacturing (AM) process involving progressive deposition of individual layers to form a multi-layer build. A deep understanding of the spatiotemporal variations of the entire build, individual tracks and layers, and the molten pool is critical to the control of undesired deposition profiles and the production of targeted laser DED components. In this work, diverse build features during multi-layer laser DED of Ti-6Al-4 V are systematically explored on multiple scales via advanced 3D numerical modeling and corresponding experiments for various process conditions. The layer wise increments on the build top are demonstrated with distinct additive features of individual layers in transverse and longitudinal sections. The results show that the layer bottom boundaries vary from concave to flat and further convex at higher layers. Moreover, the influences of scanning strategies on the deviations of build profiles are investigated considering the reinforcement or the compensation of the uneven layer geometries along the scanning direction. The underlying mechanisms are revealed through dimensionless numbers and the transport phenomena of energy, mass, and momentum in the freeform molten pool during the multi-layer deposition process. The scientific findings provide useful insight for the deep understanding of the physical processes, and support further researches on microstructure evolution and resultant mechanical properties of the DED components.

Adapting to Extreme Heat: Social, Atmospheric, and Infrastructure Impacts of Air-Conditioning in Megacities—The Case of New York City

Abstract Extreme heat events are becoming more frequent and intense. In cities, the urban heat island (UHI) can often intensify extreme heat exposure, presenting a public health challenge across vulnerable populations without access to adaptive measures. Here, we explore the impacts of increasing residential air-conditioning (AC) adoption as one such adaptive measure to extreme heat, with New York City (NYC) as a case study. This study uses AC adoption data from NYC Housing and Vacancy Surveys to study impacts to indoor heat exposure, energy demand, and UHI. The Weather Research and Forecasting (WRF) model, coupled with a multilayer building environment parameterization and building energy model (BEP–BEM), is used to perform this analysis. The BEP–BEM schemes are modified to account for partial AC use and used to analyze current and full AC adoption scenarios. A city-scale case study is performed over the summer months of June–August 2018, which includes three different extreme heat events. Simulation results show good agreement with surface weather stations. We show that increasing AC systems to 100% usage across NYC results in a peak energy demand increase of 20%, while increasing UHI on average by 0.42 °C. Results highlight potential trade-offs in extreme heat adaptation strategies for cities, which may be necessary in the context of increasing extreme heat events.

Influence of contact layers on cracking resistance of bending three-layer structures

Introduction. In the present-day construction practice, multilayer building envelopes are applied; their layers are made of concretes having different physical and mechanical characteristics. When different concretes are poured in successive layers, contact layers are formed; their physical and mechanical properties are unlike those of the adjacent layers. The strength and stress-strain characteristics of the contact layers can affect the behaviour of a multilayer structure.
 Materials and methods. Numerical and experimental methods are applied to study the stress-train state of such structures exposed to loading. Bending three-layer structural models, having external layers made of strong structural concrete and the middle layer made of low-strength concrete, were applied in the research project. A contact layer is formed in the process of their manufacturing; its geometrical, strength and stress-strain characteristics are simulated in the process of numerical studies.
 Results. The co-authors have identified the effects produced by geometrical, strength and stress-strain characteristics of contact layers on the analysis of bending multilayer structures. Design models and a novel method of analysis have been developed for bending multilayer reinforced concrete structures with account taken of the influence of geometrical, strength and stress-strain characteristics of the contact layer. According to the results of numerical calculations, differences between cracking moments can reach 4.3 % or more for three-layer reinforced concrete beams. As for the practical calculations, if the thickness of the contact layer is below 0.4 cm, one can ignore the influence produced by the contact layer on the calculation result.
 Conclusions. The results of the research help to identify the rational parameters for the design of multilayer enclosing structures having varying strength reinforced concrete layers interconnected by the monolithic contact layer.

Analysis of the thermal response of a dual phase change material embedded in a multi-layered building envelope

Mastering the thermal inertia of building envelopes is a key issue for properly handling the energy efficiency of buildings. The present study addresses the integration of a dual microencapsulated phase change material mixed with plaster as a coating layer on the inner wall of the building envelope. The purpose for using a hybrid PCM is to control the time shift of the heat load and its a posteriori impact on energy efficiency. The thermal response of the wall subject to different climatic conditions is investigated numerically using a finite volume method. A new mathematical model based on the enthalpy method is proposed, implemented and tested to analyze the effect of the dual PCM in depth. The predicted results demonstrate that the heat storage period is augmented by a factor of 57% when a dual PCM is used with plaster instead of a single PCM. The dual PCM also attenuates the decrement factor and lessens the heat infiltration into the building during the day by more than a 75% margin for the different climates investigated. In addition, the dual PCM contributes to reduce the temperature inside the building by lowering the indoor surface temperature by about 2 °C and also delays the peak in the heat infiltration beyond 3 hours. Consequently, usage of the dual PCM impacts positively on the energy consumption.

DYNAMIC CHARACTERISTICS OF THE WALL STRUCTURE DURING THE HEAT TRANSFER PROCESS

This paper deals with the impact of high-density thermal mass materials of the wall structure on the dynamic characteristics of a multi-layered building envelope during the heat transfer process. Since the final objective is to design the most energy-efficient building, i.e. a building with the lowest heating and cooling energy consumption, it is necessary to achieve good thermal performances of a multi-layered wall. In order to find the optimal wall structure solution with the highest energy-saving potential, different wall structures with different layer thicknesses were analyzed, along with walls of the same structure with different positions of individual thermo insulating layers within the wall. Based on the results presented in this paper, it can be concluded that at walls with similar structures and the same total thickness, but different layer thicknesses that make up the complete structure of the wall, there are differences in delaying external temperature changes on the wall. However, the position of the thermal insulation layer does not significantly affect temperature oscillation amplitude caused by external temperature change.

In-situ Synchrotron imaging of keyhole mode multi-layer laser powder bed fusion additive manufacturing

The keyhole mode in laser powder bed fusion (LPBF) additive manufacturing can be associated with excessive porosity and spatter, however, the underlying physics in multilayer build conditions remain unclear. Here, we used ultra-fast synchrotron X-ray imaging to reveal this phenomena. We in investigated melt pool dynamics, keyhole porosity and spatter formation mechanisms and their impact in all layers of the build. We observed that the transient melt pool dynamics associated with the keyhole include: (I) keyhole initiation, (II) keyhole development, and (III) melt pool recovery. Porosity and spatter were associated with stages (II) and (III). We also discovered that droplet spatter can form due to the collapse of the keyhole recoil zone, causing molten particle agglomeration and ejection during stage (III). Our results clarify the transient dynamics behind the keyhole mode in a multi-layer LBPF process and can be used to guide the reduction in porosity and spatter in additive manufacturing.

Water Absorption Curves versus Gamma-Ray Attenuation Profiles: A Comparative Analysis of Hygric Permeance Results

The knowledge of moisture transfer in multi-layered building materials and components using numerical simulations is fundamental to predict the behaviour of that building materials and components when in contact with moisture and to avoid some possible future pathology guarantying a correct performance.This paper describes a comparative analysis of experimental values of Hygric Permeance (HP) obtained by water absorption curves and gamma-ray attenuation profiles, for perfect contact interface. ARTICLE REVISED ON 25.03.2022

Optical and Chromaticity Properties of Metal-Dielectric Composite-Based Multilayer Thin-Film Structures Prepared by RF Magnetron Sputtering

Coated glass products, and especially the low-emissivity coatings, have become a common building material used in modern architectural projects. More recently, these material systems became common in specialized glazing systems featuring solar energy harvesting. Apart from achieving the stability of optical parameters in multilayer coatings, it is also important to have improved control over the design of visual color properties of the coated glass. We prepare metal-dielectric composite (MDC)-based multilayer thin-film structures using the radio frequency (RF)-magnetron sputtering deposition and report on their optical and chromaticity properties in comparison with these obtained using pure metal-based Dielectric/Metal/Dielectric (DMD) trilayer structures of similar compositions. Experimentally achieved Hunter L, a, b values of MDC-based multilayer building blocks of coatings provide a new outlook on the engineering of future-generation optical coatings with better color consistency and developing approaches to broaden the range of achievable color coordinates and better environmental stability.

Development of the engineering procedure for the thermotechnical calculation of a building envelope with air chambers and a heat­reflecting coating

The study has addressed the development of the engineering procedure for the thermotechnical calculation of a building envelope with thermal insulation in which air chambers with a heat-reflecting coating are formed.The engineering procedure implied determining the average RSI-value of the building envelope based on the calculation of a temperature field in it. To find the temperature field, a one-dimensional heat conduction problem in a multilayer building envelope was considered. The thermotechnical heterogeneities caused by the presence of alternating air chambers and dividers of insulation material were taken into account in the mathematical model using the effective thermal conductivity of a corresponding layer. This coefficient takes into consideration the convective and radiant components of heat transfer through air chambers. An expression was obtained for determining its value depending on the temperature at the junction of corresponding layers with adjacent building envelope layers. The iterative procedure was proposed that makes it possible to use this expression for determining the temperature fields in the building envelope under consideration. The geometric and thermophysical characteristics of building envelope elements, as well as the values of indoor and outdoor temperature and heat transfer coefficients of the corresponding surfaces, were used as initial data.The engineering procedure was verified by comparison with the results of three-dimensional CFD simulation, which takes into detailed account the free-convective motion in air chambers and the radiation heat exchange between thermally inhomogeneous walls of the air chamber. It was shown that the use of a one-dimensional mathematical model instead of a detailed three-dimensional one leads to errors not exceeding 2.5 %.As a result of our comparative analysis, the effectiveness of the proposed thermal insulation material having air chambers with a heat-reflecting coating was shown in comparison with the conventional approaches to building envelope thermal insulation. Calculations were performed for the case of the coldest five-day period in the climatic zone of Shymkent (Republic of Kazakhstan)

Experimental and numerical thermal performance assessment of a multi-layer building envelope component made of biocomposite materials

Building envelope systems are rapidly evolving, driven by increasingly stringent requirements for limiting energy consumption. Current trends favour lightweight, prefabricated wall assemblies with high levels of insulation, which have been shown to be particularly sensitive to thermal bridging through anchoring and framing elements. This paper presents a self-supporting multi-layer wall component made from bio-based materials, where novel biocomposite profiles are used instead of conventional metallic frames. The thermal performance of the proposed solution is calculated from numerical modelling and characterised through in-situ measurement of a full-scale prototype. For the plane areas of the wall with continuous insulation, theoretical calculations are broadly in line with results from experimental monitoring (7–15% deviation). Additionally, an area along a framing profile was specifically monitored, and it was found that the numerical model overestimated thermal resistance with a deviation of 121%. The presence of air gaps between the rigid insulation and framing elements, linked to the fabrication process of the prototype, was identified as a plausible cause. A subsequent explanatory numerical assessment, considering the effect of such cavities in the numerical model, provided results that are consistent with measurements from the experiment and previous literature. The study aims at demonstrating the insulation levels achievable with the use of novel bio-based materials of low thermal conductivity, and more generally, contributing to a better understanding of the thermal performance of framed lightweight insulated assemblies in service conditions, by monitoring and modelling the impact of thermal bridges and workmanship at framing elements.

Investigation on microstructural evolution and property variation along building direction in friction stir additive manufactured Al–Zn–Mg alloy

A multilayer build was fabricated by friction stir additive manufacturing (FSAM), using 4-mm thick 7N01-T4 aluminum alloy sheets in this study. The microstructural evolution along the building direction during the FSAM process and its effect on the microhardness and tensile properties were investigated using combined optical microscopy (OM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and Vickers hardness and tensile tests. The stir zone with fine equiaxed grains was considered to be the effective area of the build, and inhomogeneous microstructures were observed along the building direction. It was found that the sizes of grains and the precipitates in the non-overlapping interface regions increased from the top to the bottom influenced by the multi-pass thermal cycles. Furthermore, the degree of precipitate dissolution decreased from the top to the bottom region. These phenomena were considered to be the key factors that contributed to the decrease of the hardness and the strength recovery from the top to the bottom region. The strength of the tensile samples that were extracted from the effective area of the cross-sectional build increased with the increase of the natural aging time. After natural aging for 180 days, the average strength of the build increased to 352.7 MPa which corresponded to about 73% of the strength of the base material (BM) (483.1 MPa). Moreover, the tensile strength and the elongation of the samples that fractured along the overlapping interface were lower than those of the samples that fractured away from the overlapping interface. The kissing-bond defects formed in the overlapping interface regions affected the tensile properties of the build.

How the morphology of urban street canyons affects suspended particulate matter concentration at the pedestrian level: An in-situ investigation

Exposure to near-ground air pollution in urban street canyons poses a serious threat to pedestrian health. To develop design guidelines for air quality improvement, correlations among PM1, PM2.5, PM4, PM10, TSP, street canyons morphology and climatic conditions were investigated by field experimental studies. The results showed that street canyons morphology and air humidity were two of the most important factors affecting suspended particulate matter concentration in urban street canyons. The concentrations of PM1 (9.18 ± 0.17 μg/m3), PM2.5 (18.12 ± 0.43 μg/m3), PM4 (31.66 ± 0.82 μg/m3), PM10 (77.57 ± 2.04 μg/m3) and TSP (104.06 ± 2.85 μg/m3) in deep canyons were significantly lower than those in medium and wide canyons. The pollutants distributed in E-W or N-S street directions were at a lower concentration compared with those in NE-SW or NW-SE street directions. Moreover, the pollutants showed significantly lower concentration in high-rise building areas than in multilayer building areas. This study provides a reference for future urban planning to reduce suspended particulate matter concentration in street environments.

How effective is kaolin clay for the creation of a perfect hydraulic interface contact between materials?

Due to interface phenomena such as compaction pores, a mismatch of the pore structure, etc., moisture transfer in multi-layered building elements can deviate from the moisture transfer observed for the combination of the separate materials. Several studies on interface phenomena make use of kaolin clay to provide – as a reference – a perfect hydraulic contact between materials. This paper investigates, based on a series of imbibition experiments, whether kaolin clay truly creates this perfect contact, and thus, whether the hydraulic interface resistance between materials can be nullified by use of kaolin clay. For a low absorptive material or a large distance between the contact interface and the water surface, composite samples put together with kaolin clay show an identical water uptake curve as observed for homogeneous samples. For a material with a high absorptivity and a contact interface closer to the water plain, however, even with kaolin clay a hydraulic interface resistance is observed and estimated to be in the order of 6 000 m/s till 12 000 m/s. If present, such an interface resistance is furthermore shown to have no impact on the water uptake curve for samples composed of low absorptive bricks or with a contact interface further away from the water plain.

Monitoring and thermal performance evaluation of two building envelope solutions in an apartment building

A bio-based multi-layer building envelope assembly has been developed for its integration in newly built and retrofitted buildings. Forest-based materials and biocomposite profiles are used as an alternative to fossil-based insulants and metallic framing, providing a well-insulated and low-thermal-bridge technical solution. The wall assembly has been installed as the external envelope of one apartment of a housing block in Donostia-San Sebastián (Basque Country, Spain). A comparative study has been performed for the bio-based wall and the reference wall of the building. Their in-situ thermal resistance has been obtained by means of three different methods: (1) the steady-state average method, (2) a semi-dynamic method from heat balance at the internal surface, and (3) a dynamic multiple regression method. Reasonably consistent results have been obtained with the three methods: a discussion is provided on the influence of measuring periods and boundary conditions. Outputs from this experimental campaign are valuable as a counterpoint to desktop studies and tests under controlled laboratory conditions. Learnings and outputs from the present study should contribute to a better understanding of the in-situ performance of building envelope assemblies and their assessment methods.