Building Envelope Applications Research Articles

Fabrication of smart vapor barrier membranes from polyhydroxyalkanoate and cellulose filaments for building envelope applications

Fabrication of smart vapor barrier membranes from polyhydroxyalkanoate and cellulose filaments for building envelope applications

Numerical model for determining the effective heat capacity of macroencapsulated PCM for building applications

This paper presents a finite difference model of macroencapsulated PCM panels coupled with the genetic algorithm for the determination of effective heat capacity of whole panels via inverse method. This provides an accurate characterization of the thermal properties of macroencapsulated PCMs for building envelope applications. A novel definition of the effective heat capacity is proposed based on the superimposition of two Gaussian curves, applicable to any PCM whose phase transition is characterized by a single peak. Three PCMs were tested, subjected to temperature variation rates typically experienced in building envelopes: 0.5 °C/h and 1 °C/h. Surface temperature and heat flux were measured and used in the inverse method procedure. The developed model is accurate, as numerical results greatly agree with the experiments: the root mean square difference between the experimental and numerical heat fluxes ranged between 0.543 and 1.246 W/m2. Significant differences in the effective heat capacity were found between the whole macrocapsule and small quantities of PCM (specified in the datasheets). The effective heat capacity specified in the datasheets is sensibly greater than that of the whole macrocapsules determined through the inverse method: the specific heat in the solid phase was up to 107.39 % higher in the datasheet values, the specific heat in the liquid phase up to 184.04 %, and the peak effective heat capacity, between 18.28 % and 164.11 %. The same happened to the enthalpy: datasheet values were 61.24 % – 175.55 % greater than inverse method results. This proves that latent heat is overestimated if small quantities of PCM are analyzed, and not the whole panels. The scale effect was assessed by comparing two capsules with the same material, but with different quantities of PCM: 0.5 kg and 1 kg. A greater mass of PCM over the total mass of the capsule implies a different relationship between the effective heat capacity and temperature, with higher peak heat capacity. The capsule with 1 kg of PCM showed a peak effective heat capacity up to 30.65 % greater than that of the panel with 0.5 kg of PCM. Thus, adequate modeling in building applications requires characterization of whole macroencapsulated PCMs. The determination of the relationship between temperature and effective heat capacity of macroencapsulated PCMs presented in this work could easily be incorporated into other simulation software, facilitating the assessment of adaptive envelopes with PCM macrocapsules.

A Review on Recent Research on Bio?Based Building Materials and their Applications

Abstract: Bio-based materials represent a promising alternative in building envelope applications, with the aim of improving inuse energy efficiency. They have the advantage of being renewable, low embodied energy and CO2 neutral or negative. In addition, they are excellent thermal regulators. This paper presents an overview of the state-of-the-art of bio-based materials used in building construction and their applications. The materials outlined include hemp, wood, date palm wood, cork, alfa and straw. Through this literature study we want to get a broad overview of the current state of theoretical and experimental studies of their hygrothermal characteristics and their thermal and energy performances. The aim is not to be exhaustive but to summarise the most important research results on these materials. This is the first part of a research work that deals wit h the contribution to the development of a new bio-based construction material to be used in building.

Development of a novel sandwich-structured composite from biopolymers and cellulose microfibers for building envelope applications

A novel sandwich-structured composite was developed from the surface layers of polyhydroxyalkanoate (PHA) and the interlayer of polylactic acid (PLA)/cellulose microfibers (CMF) composite. Moreover, CMF was chemically modified via a sol–gel process to improve the compatibility between the natural reinforcement and the polymer matrix. According to the obtained results, the modified CMF exhibited a highly hydrophobic characteristic (contact angel value of approximately 118°), and they were homogeneously dispersed in the PLA matrix. The results of the thermogravimetric analysis indicated that the sandwich composites reinforced with the modified CMF showed improvement in thermal stability. Regarding the mechanical properties, the incorporation of the natural reinforcement into sandwich composites increased the values of tensile modulus and strength of materials. The water vapor permeability of sandwich composites increased with the addition of untreated fibers; however, the composites reinforced with the modified CMF showed superior barrier performance than that of untreated CMF. In addition, a durability test was performed to determine the effect of accelerated aging on the properties of sandwich composites. The results demonstrated that the mechanical and barrier properties of composites incorporated with untreated CMF decreased after the accelerated aging, whereas the composites reinforced with the modified CMF experienced the least change.

Comprehensive Review of Innovative Materials for Sustainable Buildings’ Energy Performance

The building sector, one of the most energy-consuming, is among the most current topics due to the maturing concerns about the anthropogenic factor’s impact on CO2 quantities in the atmosphere and its association with global temperature rise. Using sustainable building materials is a promising alternative in building envelope applications to improve in-use energy efficiency. These materials, having a low environmental impact, the advantage of being renewable, and low embodied energy, contribute to global sustainability. This comprehensive literature review presents a broad overview of these materials’ hygrothermal characteristics, thermal performance, and energy use. The main goal is to compile the most important research findings on these materials’ capabilities for building construction and their contributions and effects on energy performance and thermal insulation.

Modelling analysis and performance evaluation of a novel hybrid CdTe-PCM PV glass module for building envelope application

In this work, a novel hybrid CdTe-PCM PV glass module (CdTe-PCMG) was proposed, fabricated and tested. A mathematical optical-electrical-thermal coupled model was established and validated against the experiment data under different ambient conditions. Based on the validated model, a building energy simulation (BES) model integrated with the novel modules as building windows was established. Comparison case study was respectively conducted between the building model with single PV glass module under a continuous hot/cool week. Impacts of several parameters including the PV coverage, ambient conditions, PCM thickness and phase change range on the comprehensive electrical and thermal performance was analyzed. Annual performance in five different climatic cities was predicted to discuss the PCMG's regional application potential. Main conclusions are: (1) The utilization of PCM has improved the electrical output of the PV glass and enhanced the indoor thermal comfort when applied on the building envelope; (2) According to the parameter analysis under the cool week, the optimal PCM layer thickness and phase change range were 3.5 cm and 22 °C ∼ 24 °C; (3) Based on the annual performance predictions, the PCMG was more suitable to be applied in the regions with abundant solar radiation resource or mild climate condition.

Performance Assessment of Two Different Phase Change Materials for Thermal Energy Storage in Building Envelopes

To meet the 2050 EU decarbonization goals, there is a need for new and innovative ideas to increase energy efficiency, which includes reducing the energy consumption of buildings and increasing the use of on-site renewable energy sources. One possible solution for achieving efficient thermal energy transition in the building sector is to assign new functionalities to the building envelope. The building envelope can function as a thermal energy storage system, which can help compensate for irregularities in solar energy availability. This can be accomplished by utilizing phase change materials as the energy storage medium in the building envelope. In this paper, two phase change materials with different melting temperatures of 21 °C and 28 °C are compared for their application in a dynamic solar building envelope. Both experimental and numerical studies were conducted within the scope of this study. The laboratory testing involved simulating the conditions of the four seasons through steady-state and dynamic experiments. The performance of the phase change materials was evaluated using a small-scale PASLINK test stand that imitates indoor and outdoor conditions. A numerical model of a small-scale building envelope was created using data from laboratory tests. The purpose of this model was to investigate how the tested phase change materials perform under different climate conditions. The experimental findings show that RT21HC is better at storing thermal energy in the PCM and releasing it into the indoor area than RT28HC. On the other hand, the numerical simulation results demonstrate that RT28HC has an advantage in terms of thermal storage capacity in climates found in Southern Europe, as it prevents overheating of the room.

Vapor Barrier Membranes Based on Polylactic acid and Cellulose Microfibers for the Building Envelope Application

Vapor Barrier Membranes Based on Polylactic acid and Cellulose Microfibers for the Building Envelope Application

Thermal and structural behavior of thermal inertia-reinforced mortars for building envelope applications

Phase-change materials (PCM) are applicable to various building components and systems. In this study, a thermal storage mortar is manufactured by mixing thermal storage aggregate (TSAs) synthesized using a vacuum-impregnating PCM with blast furnace slag. In the scanning electron microscopy analysis, the TSAs were mixed and dispersed relatively uniformly in the thermal storage mortar and maintained their physical shape. From the differential scanning calorimetry result, the theoretical latent heat amounts of the thermal storage mortar mixed with 10, 20, and 30 wt% TSA were 3.27, 6.21, and 8.86 J/g for both heating and cooling, respectively. The cumulative specific heat of the thermal storage mortar was 160.95 J/g when the temperature increased from 0 °C to 80 °C. Results of the thermal conductivity analysis showed that when the TSA content for the thermal storage mortar increased to 20 wt%, the thermal conductivity increased because of the effect of blast furnace slag. In the structural analysis, the reference mortar and the thermal storage mortar containing 10 wt% TSAs exhibited brittle fracture, whereas the thermal storage mortar containing 20 or 30 wt% TSA showed ductile fracture. Results of the dynamic heat transfer analysis showed that the upper and lower surfaces of the thermal storage mortar indicated a peak temperature reduction and time lag in the phase-change temperature range during heating and free cooling.

Comparative analysis of form-stable phase change material integrated concrete panels for building envelopes

Phase change materials (PCM) can reduce energy consumption and improve thermal comfort in buildings. However, they have some limitations in integrating into construction materials. The significant difficulty is the selection of suitable porous materials, which should be compatible with construction materials with high PCM absorption capacity and strength and no seepage, leakage, or acidification. Therefore, this study aimed to select suitable porous material for developing Form Stable PCM (FSPCM) cement composite that can be integrated into concrete panels for building envelopes. It considered five different porous materials based on their porosity, geometry, and surface morphology to encapsulate the capric acid (CA). The synthesized FSPCM composite was tested for seepage, leakage, and chemical stability before its integration into a cementitious composite to develop concrete panels. Thermophysical properties and thermal performance of those FSPCM and concrete panels were measured following ASTM standards and compared using six indicators: absorption, thermal conductivity, strength, thermal inertia, latent heat storage and thermal storage. The comparative analysis revealed that silica aerogel granules (SAG) have stably encapsulated CA up to 80 wt% due to its high porosity, whilst recycled expanded glass (REG) absorbed only 25 wt%. The Capric acid-Silica Aerogel Granule (CASAG) integrated concrete panel had the least compressive strength (3.66 MPa), but it had the lowest thermal conductivity (0.39 W/m-K), higher storage (690 kJ/m3) and higher thermal inertia (1.32 °C). In contrast, the Capric Acid/Recycled Expanded Glass (CAREG) panel had the highest compressive strength (13 MPa), but its thermal conductivity was also very high (1.0 W/m-K), and had lower storage (542 kJ/m3) and thermal inertia (0.62 °C). However, the Capric Acid/Hydrophobic expanded Perlite (CAHEP) panel had moderate compressive strength and thermal conductivity, and its thermal inertia and heat storage were comparable to CASAG-integrated concrete. Overall, the CAHEP showed the best performance in terms of the six indicators and therefore was recommended to be the best porous material to absorb polar PCM like CA to develop FSPCM integrated concrete panels for building envelope applications.

Learning from success: A machine learning approach to guiding solar building envelope applications in non-domestic market

Solar building envelopes, also known as Building Integrated PV (BIPV) show significant growth in Asia and Europe, although other regions such as Australia are still lagging. The decision to uptake BIPV is complex due to the heterogeneous interest of adopters and multi-dimensional features. Instead of redesigning BIPV in hypothetical buildings, we built a machine learning model using a database of real BIPV and building-attached PV (BAPV) applications, for the purpose of learning and predicting a BIPV adoption decision-making in non-domestic buildings in western countries. We used Australia as a case study to execute the support vector machine (SVM) prediction model. It was revealed that the combination of project determinants such as geographical conditions, equivalent building materials, interest rates and capital cost influenced the decision of BIPV. The prediction model provides pieces of information for stakeholders across the BIPV ecosystem to take their decision on investment, policymaking, and research directions. The current global industry transformation and innovations in technology are favourable to politically promoting and investing in BIPV. Such promotion and investment would help both expand the current market and reach the greenhouse targets.

Development of bio-based membranes for building envelope applications from poly(lactic acid) and cellulose microfibers

A bio-based membrane was developed for building envelope applications. Biocomposites with enhanced water vapor permeability were fabricated based on poly(lactic acid) (PLA) and cellulose microfibers (CMF). To improve the interfacial adhesion between PLA and fibers, polyethylene glycol (PEG) was used as a compatibilizer for the modification of CMF. The properties of prepared PLA-based biocomposites were investigated in terms of their morphology, thermal stability, thermomechanical properties, and water vapor permeability. The morphological investigation showed the improved dispersion of cellulose fibers in the PLA matrix after modification of the bio-filler with PEG. The thermogravimetric analysis illustrated that the addition of modified CMFs increased the thermal stability of materials. Moreover, the water vapor permeability of PLA-based biocomposites was enhanced by adding modified CMFs to the PLA matrix. The results suggest that the utilization of PEG as a biopolymer compatibilizer represents a cost-effective and environmentally friendly method to improve the properties of PLA/CMF biocomposites. The developed membranes are potential materials for the fabrication of bio-based membranes with permeable properties that facilitate the transmission of entrapped water vapor through the building, eventually prolonging the service life of building envelope materials.

Laboratory Assessment and In-Field Monitoring of Macro-Encapsulated Phase Change Materials for Building Envelope Applications

Phase Change Material (PCM) based products represent an emerging technology for the building sector. For their application in the building envelope, they are usually macro-encapsulated in plastic/metal containers or placed in bags/pouches that allow an easier and safer installation. Unfortunately, most of the product data on PCMs are obtained by means of the differential scanning calorimetry method (DSC) applied to bulk PCMs. This method, even though accurate, can lead to results that are not fully representative of the complex behavior of PCM-based products. The results of an experimental laboratory campaign, aimed at characterizing the thermal properties of a full-scale PCM product, are presented in this paper. Tests were carried out on a commercial macro-encapsulated PCM considering three different melting temperatures. The obtained results show that the overall equivalent thermal properties of the macro-encapsulated PCM products maybe somewhat different from those of bulk PCMs. In a second step, two PCM products were selected and applied to a parallel roof testing room system, directly exposed to the outdoor environment. The results of the monitoring of this system have demonstrated the effectiveness of PCMs in reducing the peak heat gains through the roof components by up to 48%. Nevertheless, by comparing the laboratory results with the monitored data, it was also possible to observe that the latent heat capacity of the PCM was never fully exploited. Thus, greater benefits could be achieved in different monitoring periods, or if a PCM with a lower melting temperature were adopted.

Characteristics of new cement-based thermoelectric composites for low-temperature applications

Thermoelectric cement, the mixture of cement and thermoelectric additives, can convert energy between thermal and electrical forms due to the thermoelectric additives. Potentially, they could be the material for building envelopes to harvest waste heat and/or provide space cooling or heating. When there is a significant difference between indoor and outdoor temperatures, the thermoelectric cement can generate electricity using the temperature gradient. And the same material can cool or heat building space via building envelopes with an electrical input. The research aimed to identify and characterize thermoelectric cement candidates for building envelope applications. The additives used in the studied thermoelectric cement candidates include graphite and MnO2. Except for the additives, the study also explored the impact of the two different fabrication methods: wet-mixing and dry-mixing on thermoelectric performance. The images of TE cement candidates taken by scanning electron microscopy and energy dispersive X-ray microscopy visualized the morphology and distribution of additives in the thermoelectric cement composites. The DynaCool Physical Properties Measurement System used in the study simultaneously measured the candidates' thermoelectric properties, including thermal conductivity, electrical conductivity, Seebeck coefficient, and Figure of merit (ZT). The test results showed that the thermoelectric cement with the additives of 10% (weight ratio) graphite and 5% MnO2 has the highest ZT of 6.2 × 10−6 at 350 K. ZT of the thermoelectric cement is even higher to 10−5 orders of magnitude when applying a four-probe electrical resistivity method to account for the contact resistance.

Influential aspects on melting and solidification of PCM energy storage containers in building envelope applications

ABSTRACT Phase change materials (PCMs) incorporated building envelope for thermal energy storage (TES) considerably enhances building thermal energy and improves indoor comfort. Amongst other methods, macroencapsulation provides a flexible and efficient PCM utilization among practical incorporation methods during a long time of service. Nevertheless, there is still arguement regarding PCM thermal performance during melting and solidification phases due to macroencapsulation containers, not to mention PCM’s poor thermal conductivity. A brief overview of possible practical integration methods of PCMs with building elements is presented along with the main advantages and drawbacks in this work. This is followed by the popular incorporation techniques in building applications giving special attention to the macroencapsulation method and its role in improving building performance. The main influential aspects of macroencapsulated PCM performance during the melting and solidification, namely the shape, material type, compatibility with PCM type, and enhancement methods of encapsulation containers, are highlighted and discussed. We believe that this work analysis and conclusions provide a clear understanding of the main trends and gaps in this research area for further investigation and optimization studies by researchers, engineers, and developers.

Empirical validation and comparison of methodologies to simulate micro and macro-encapsulated PCMs in the building envelope

Thermal Energy Storage (TES) has the potential to shift peak electricity demand. Passive TES is usually implemented in building envelope as micro and macro encapsulated phase change materials (PCM) to shift electric energy demand and therefore requires careful heat transfer analysis. Whole building energy modelling with simplified heat transfer analysis has become extremely important for designers, architects, engineers, and researchers to predict energy performance of buildings. It is important to validate PCM modelling algorithms used in building energy programs to quantify their error and prove their capacity to model different PCM encapsulation types. This study uses data from a microencapsulated PCM and two macroencapsulated PCMs (Bio based PCM and hydrate salts) tested in full-scale using the Advanced Multiscale Building Energy Research (AMBER) Lab located at the Colorado School of Mines and is used to validate a numerical algorithm written in MATLAB language. To approximate the heat transfer through a wall assembly with macroencapsulated PCM pouches, several modelling techniques that can reduce 3D heat transfer characteristics to 1D are explored in this research. A parallel path heat transfer modelling approach is found to give the closest agreement with the experimental data for the pouched PCMs in building envelope applications.

Paraffin As a Phase Change Material to Improve Building Performance: An Overview of Applications and Thermal Conductivity Enhancement Techniques

In recent years, phase change materials (PCMs) have increasingly received attention in different thermal energy storage and management fields. In the building sector, paraffin as a phase change material (PPCM) has been introduced as an efficient PCM incorporated in a building envelope, which showed remarkable results. However, the poor thermal conductivity of PPCM is still the topmost drawback in experimental and numerical investigations. In this paper, a general assessment of paraffins, their common uses and applications, have been presented with a particular focus on their potential in building envelope applications. Moreover, the general and desired properties of PPCM are highlighted and evaluated. The primary practical limitation of PPCM of poor thermal conductivity and their effect on PPCM performance is presented and discussed. Correspondingly, the popular techniques applied to improve the poor thermal conductivity are presented and discussed in four categories: the dispersion of nanoparticles, expanded graphite, metallic foam, and extended surfaces technique (fins). All in all, the analysed research works indicated that PPCM based building envelope applications could remarkably improve the thermal performance of buildings in terms of thermal load reduction, energy-saving and thermal comfort. Furthermore, the adoption of enhancement techniques is essential to improve the thermal performance of PPCM in building applications for better utilisation. This review provides a clear vision for the newcomers and interested parties about the main application aspects of PPCM in the building sector for further investigations towards technology commercialisation.

Experimental apparatus and methodology to test and quantify thermal performance of micro and macro-encapsulated phase change materials in building envelope applications

Abstract Thermal energy storage (TES) is used as a viable technology to shift peak electricity demand caused by the space cooling requirements in buildings. Passive TES is implemented in building envelope via micro and macroencapsulation methods. This study describes the use of a state-of-the-art laboratory to test different PCM inclusions in simplified building walls. A microencapsulated PCM and two macroencapsulated PCMs are tested in a controlled environment to gather data for validation purposes of PCM modelling algorithms in building energy modelling programs. Data indicates that the chamber environment and the heating and cooling system can conduct full-cycle tests of wall panels with PCM inclusions. This study also generates data from parallel tests on 4 wall panels which can be used in building energy modelling programs to validate the PCM modelling algorithms. The cyclic tests also capture the thermal effects of PCMs and complex PCM behaviors like sub-cooling in PCM hydrate-salts.

Performance analysis of an improved PCM-to-air heat exchanger for building envelope applications – An experimental study

The applications of PCM-to-air heat exchangers (PAHXs) face operational challenges regarding the local climatic conditions. One of the main issues is the insufficient cooling potential during the phase change material (PCM) solidification process. In order to increase the cooling charging power of the system, in this study, a unique PAHX type is proposed for building envelope applications. The objective is to magnify the thermal radiation losses from the PCM panels to the nocturnal sky during the solidification process. Two real-scale prototypes were designed and constructed to monitor the effect of radiative cooling on the PAHX thermal behavior during solidification. Accordingly, the cooling performance was investigated for different operational scenarios. In addition, specific key performance indicators were defined to analyze the system charging performance. The experimental results proved that exposure to the clear sky during solidification increases the charging power of the system due to the maximized thermal losses by radiation. The results confirmed that the sky condition and the ambient air temperature profile are key factors in determining the cooling potential of the system. It was shown that making use of the radiation thermal loss to the clear sky increased the charging energy by up to 22% of the proposed PAHX application.

Palm oil-based bio-PCM for energy efficient building applications: Multipurpose thermal investigation and life cycle assessment

This study aims at investigating the potential use of a bio-based phase change material, i.e. expired palm oil from the food industry, as a more sustainable alternative to petrochemical-based organic PCMs. To this purpose, thermogravimetric analysis (TGA) and isoconversional methods (Starink and Miura-Maki methods) are applied and the main thermo-physical properties of the blend are investigated by means of differential scanning calorimetry (DSC) and extensive thermal monitoring in a controlled realistic environment. Finally, a life cycle assessment is used to evaluate the environmental impact of the bio-based material in comparison to the more common petrochemical-based application. Kinetic analysis results indicate the two dimensional phase boundary reaction model as the most reliable scheme for describing the oxidation of palm oil, with an activation energy of about 73 kJ · mol−1. The DSC and the thermal monitoring procedure, showed two separate melting peaks in the ambient temperature range, which globally guarantee a melting enthalpy of about 50 kJ · kg−1, i.e. of the same order of magnitude of the first developed PCMs. Results from the life cycle analysis reveal that the expired palm oil can be considered a promising material for bio-based latent applications.Globally, the palm oil has proved itself as a promising, low cost, and environmentally friendly alternative for passive thermal storage solutions (e.g. building envelope applications) where stability across multiple thermal cycles, low health risks, and low leakage are crucial parameters to be addressed.