Low Emissivity Materials Research Articles

Thermal analysis of hollow clay bricks submitted to a sinusoidal heating

The aim of the present work is to study numerically, in a transient state, the thermal behavior of three types of hollow bricks mostly used in the construction of building walls in Morocco. The coupled heat transfer by conduction through the surrounding walls, natural convection and surface radiation is taken into account. The outside vertical surface is submitted to a sinusoidal thermal excitation, while the inside vertical surface is maintained at a constant temperature. The top and bottom horizontal sides are assumed to be adiabatic. The governing equations for conservation of mass, momentum and energy are discretized by the finite volume approach and solved by the SIMPLE algorithm. The main parameters governing the problem are the amplitude, the period of the exciting temperature and the emissivity of the walls. The effect of these parameters on the global heat transfer through each structure is presented and examined. The results report that the hollow brick of type 3 allows a good reduction of heat transfer from exterior to interior surfaces of the building walls and hence providing an adequate thermal comfort. The emissivity of the internal surfaces affect considerably the heat transfer through the hollow bricks. The use of low emissivity materials on internal surfaces of the hollow bricks would greatly help in improving the energy consumption in buildings.

Integrated operational and life-cycle modelling of energy, carbon and cost for building façades

The buildings sector contributes 20% of global greenhouse gas emissions, and building energy use is anticipated to double by 2050. Building performance research has typically focused on the operational phase, with life-cycle impacts increasingly studied, but often in isolation. This paper presents a novel framework integrating building energy modelling with life-cycle analysis and life-cycle costing. This is applied to four façade glazing materials in a 15-story case study office building in Queensland, Australia – a sub-tropical and commercial example rare in literature but important for future building development. Results demonstrate that double-glazed low-emissivity material (Type 4) was the most energy and financially efficient despite higher embodied energy and carbon than alternatives. It yielded operational energy and greenhouse gas emission savings of 13% against the baseline, and 2% lifetime financial savings. Clear double-glazing (Type 3) had the poorest overall performance, attributed to its low U-value trapping heat within the building and increasing net energy and emissions. This was new evidence that clear double-glazing should be carefully considered in sub-tropical climates. The integrated approach identified a material with improved overall performance. If only embodied impacts (production, transport, disposal) were assessed, GT1 would appear the best option as it takes less energy and carbon to manufacture and transport yet has very poor operational performance. This paper extends existing knowledge on façade materials and will aid future work on sustainable, low-emission building design in other climates, economies, designs and industries.

Footprints of failure: Quantifying carbon impacts of roof leakages in a single-family residential building

To meet the UN Sustainable Development Goals of climate change mitigation and sustainable cities, low-carbon or carbon-negative buildings are becoming increasingly common. The buildings are planned to compensate for the embodied energy in their materials by using low-emission materials and generating emission-free energy. Embodied energy is minimized while energy generation is maximized. However, embodied energy calculations seldom consider the risk of building defects that require repairs or early replacement of building elements. As such, a building’s sustainability is often calculated under the assumption that significant defects do not happen, which is known to rarely be the case. In this article, the material and monetary costs of repairing building defects are analysed. Findings suggest that certain building defects, like major roof leaks, have a significant carbon footprint. A large portion of this footprint can be attributed to the drying of the building after a leak is discovered. Building defects are common enough that the risk should not be neglected in life cycle analyses. Likewise, measures taken to reduce the risk of building defects, such as avoiding design solutions known to pose difficulties, may be considered as means to improve the sustainability of a building as well as reducing economic costs.

High-performance infrared thermal radiation suppression metamaterials enabling inhibited infrared emittance and decreased temperature simultaneously

Infrared thermal radiation suppression techniques are vital to the survival of various vehicles/targets, and low-emissivity materials are conventionally employed to reduce infrared radiant power of targets. However, infrared radiant power depends not only on infrared emittance but also heavily on the temperature according to Steven-Boltzmann law (P=εσT4). In this work, it is for the first time, a novel type of infrared stealth material based on tailoring radiative properties in an ultra-broadband ranging from 0.4 µm to 14 µm is proposed. A low emittance in atmosphere window (3–5 µm, 8–14 µm) is achieved to suppress infrared radiation, and a high emittance from 5 to 8 µm is obtained to reduce temperature via radiative cooling from metamaterial surface to the atmosphere. Meanwhile, low absorptance in the solar spectra (0.4–2.5 µm) can help to resist the solar heat. As a result, the infrared radiant power in the atmospheric window is prominently reduced benefiting from low emittance and decreased temperature. This work helps guide the design of more effective infrared stealth materials and paves the way for the applications of metamaterials in infrared stealth applications.

Prospects for microwave plasma synthesized N-graphene in secondary electron emission mitigation applications

The ability to change the secondary electron emission properties of nitrogen-doped graphene (N-graphene) has been demonstrated. To this end, a novel microwave plasma-enabled scalable route for continuous and controllable fabrication of free-standing N-graphene sheets was developed. High-quality N-graphene with prescribed structural qualities was produced at a rate of 0.5 mg/min by tailoring the high energy density plasma environment. Up to 8% of nitrogen doping levels were achieved while keeping the oxygen content at residual amounts (~ 1%). The synthesis is accomplished via a single step, at atmospheric conditions, using ethanol/methane and ammonia/methylamine as carbon and nitrogen precursors. The type and level of doping is affected by the position where the N-precursor is injected in the plasma environment and by the type of precursors used. Importantly, N atoms incorporated predominantly in pyridinic/pyrrolic functional groups alter the performance of the collective electronic oscillations, i.e. plasmons, of graphene. For the first time it has been demonstrated that the synergistic effect between the electronic structure changes and the reduction of graphene π-plasmons caused by N doping, along with the peculiar “crumpled” morphology, leads to sub-unitary (< 1) secondary electron yields. N-graphene can be considered as a prospective low secondary electron emission and plasmonic material.

Copper-Zinc Oxide Synergistic Approach as Low-Emissivity Material for Energy-Saving Windows

In luxurious glass buildings and constructions, heat gain (or heat loss) mostly comes through the windows. Infrared (IR) radiation is an important factor that causes the entry of heat into the buildings. To save energy consumption of air conditioners, low-emissivity (Low-E) glass coating applications are focused. In the energy-saving field, transparent conductive oxide (TCOs) are used as coatings to minimized IR entry. In this work, copper-doped zinc oxide (CZO) is synthesized for thermal reflective material. Cu(II) ions are doped to ZnO by a sol-gel method to obtain CZO nanoparticles and is coated on a glass substrate. The morphology of CZO is investigated with scanning electron microscopy (SEM); phase crystallinity is determined by X-ray diffraction (XRD); and UV-Vis-NIR spectroscopy is used to characterize UV/IR-shielding and also the optical transparency. IR cameras and in-lab thermal insulation setup are used to test the heat insulation properties. The result shows that 15% copper-doped zinc oxide has the best insulation from IR rays with the lowest temperature in the interior (T3) of 50.6°C while the outer temperature (T2) was at 85.5°C the lowering of the temperature by 34.9°C (cooler by 59%). CZO synthesized from the sol-gel method has promising properties for Low-E glass coating applications.

Emissions of VOCs, SVOCs, and mold during the construction process: Contribution to indoor air quality and future occupants’ exposure

Building materials and human activities are important sources of contamination indoors, but little information is available regarding contamination during construction process which could persist during the whole life of buildings. In this study, six construction stages on two construction sites were investigated regarding the emissions of 43 volatile organic compounds (VOCs), 46 semi-volatile organic compounds (SVOCs), and the presence of 4 genera of mold. Results show that the future indoor air quality does not only depend on the emissions of each building product but that it is also closely related to the whole implementation process. Mold spore measurements can reach 1400CFU/m3 , which is particularly high compared with the concentrations usually measured in indoor environments. Relatively low concentrations of VOCs were observed, in relation to the use of low emissive materials. Among SVOCs analyzed, some phthalates, permethrin, and hydrocarbons were found in significant concentrations upon the delivery of building as well as triclosan, suspected to be endocrine disruptor, and yet prohibited in the treatment of materials and construction since 2014. As some regulations exist for VOC emissions, it is necessary to implement them for SVOCs due to their toxicity.

An accurate instrument for emissivity measurements by direct and indirect methods

Emissivity is a quantity essential to consider when assessing the measurement uncertainty in non-contact temperature measurements. This paper presents a new instrument for measuring emissivity of opaque materials from 200 °C to 450 °C in the spectral range of 2.1 to 2.5 µm. These ranges are ideal for measuring the temperature of metals, such as aluminium, during manufacture or heat-treating processes. The instrument consists of a pair of hemispherical cups coated with Vantablack® and gold respectively, a custom designed radiation thermometer, and a hot plate. This instrument enables both the direct and the indirect methods for measuring emissivity of materials. Use of two identical cups allowed for quantitative analysis of the uncertainty of the instrument to determine the most suitable emissivity measurement range. The expanded uncertainty of the instrument was lower than 0.058 (k = 2) over the entire measuring temperature range. Studies were undertaken using different materials with emissivities ranging from 0.06 to 1. These included aluminium alloy 6082, stainless steel 304, and HiE-Coat 840M paint. Relative uncertainty analysis indicated that the indirect method was more accurate for measuring low-emissivity materials, whereas the direct method was more suitable for all other materials. Our instrument, with experimentally determined measurement uncertainty, aims to offer accurate emissivity references for use in radiation thermometry applications.

Effect of nozzle temperature on the emission rate of ultrafine particles during 3D printing.

Ultrafine particles and other hazardous materials are emitted during 3D printing, but the effect of temperature on such particles has not been studied systematically. The aim of this study was to evaluate the effect of temperature on the emission rate of particulate matter during fused deposition modeling (FDM) three-dimensional (3D) printing using different filament types. The number concentration of particles was measured with direct-reading instruments in an exposure chamber at various temperatures while using four filament materials during 3D printing. The temperature was increased from 185 to 290°C in 15°C increments, while incorporating the manufacturer-recommended operating conditions. The emission rate increased gradually as the temperature increased for all filament types, and temperature was the key factor affecting the emission rate after filament type. For all filaments, at the lowest operating temperature, the emission rate was 107 -109 particles/min, whereas the emission rate at the highest temperature was about 1011 particles/min, that is, 100-10000 times higher than the emission rate at the lowest temperature. To reduce particle emissions from 3D printing, we recommend printing at the lowest temperature possible or using low-emission materials.

INCREASING SUSTAINABILITY WITH SLIM FLOOR STRUCTURES

AbstractSlim floor structures greatly increase the sustainability. Height of the buildings will be lower, while commercially available connections can help to design structures that can be dismantled later for re‐use. Choosing products that utilise recycled raw materials and building methods that accommodate low emission materials such as wood will result in even lower CO2 emissions.

Evaluation of the bandwidths and spatial resolutions achievable with near-infrared observations of Venus below the cloud deck

We identified potential atmospheric windows with which to study the Venusian surface on the nightside and calculated the approximate scattering footprint as would be seen by a prospective aerial mission. The emission from the surface, its scattering through the atmosphere, and the emission from the atmosphere were calculated from the surface to various heights beneath the cloud deck. We explored the effects of different sensor altitudes, varying surface emissivity, variation in elevation causing changes in surface temperature, and variations in the temperature profile, on the possible surface viewing atmospheric windows. The effects of surface emissivity and surface elevation dominated, and those of sensor altitude and variation in temperature profile are relatively small. The prospective windows are largely expanded versions of previously identified windows that have been exploited by satellites and ground-based observation with an additional window centered at 1.27 μm. Any mission that exploits the improved visibility beneath the cloud decks should make use of 0.7–1.0, 1.1, and 1.27 μm windows, as these provide a comprehensive ability to extract information about the surface. We explored the effect of sensor altitude and surface elevation on the scattering footprint. The scattering footprint beneath the cloud deck varies from ~15 to 5 km depending on wavelength at our nominal altitude of 40 km, a significant improvement over the 50–100 km footprint for orbiting satellites. Lowering the sensor altitude only mildly reduces the scattering footprint, as most scattering is caused by the dense lowermost atmosphere. Increased surface elevation reduces the scattering footprint. We concluded that regions elevated above the mean planetary radius represent the best targets as these have the greatest amount of the electromagnetic spectrum identified as surface viewing atmospheric windows and the smallest scattering footprint. These windows have the potential to elucidate questions about the composition and redox state of the surface of Venus, even for low emissivity materials (e.g., fine-grained hematite at ε~0.5), which have important implications for the evolution of the planet.

Building Energy Performance Analysis: An Experimental Validation of an In-House Dynamic Simulation Tool through a Real Test Room

This paper focuses on the experimental validation of a building energy performance simulation tool by means of a comparative analysis between numerical results and measurements obtained on a real test room. The empirical tests were carried out for several months under variable weather conditions and in free-floating indoor temperature regime (switched off HVAC system). Measurements were exploited for validating an in-house simulation tool, implemented in MatLab and called DETECt, developed for dynamically assessing the energy performance of buildings. Results show that simulated indoor air and surface room temperatures resulted in very good agreement with the corresponding experimental data; the detected differences were often lower than 0.5 °C and almost always lower than 1 °C. Very low mean absolute and percentage errors were always achieved. In order to show the capabilities of the developed simulation tool, a suitable case study focused on innovative solar radiation high-reflective coatings, and infrared low-emissivity materials is also presented. The performance of these coatings and materials was investigated through a comparative analysis conducted to evaluate their heating and cooling energy saving potentials. Simulation results, obtained for the real test cell considered as equipped with such innovative coatings and material, show that for the weather zone of Naples a 5% saving is obtained both in summer and in winter by simultaneously adopting a high-reflectance coating and a low- emissivity plaster for roof/external walls and interior walls, respectively.

Material VOC Emissions and Indoor Air Quality Simulation

The contribution reports on a simulation study of indoor air quality in relation to different ventilation rates specified for 3 categories of the indoor environment according to EN 15 251. Indoor air quality and energy management are often at the opposite ends of the building management spectrum. The buildings are polluted by occupants of the building themselves. The indoor air quality can be expressed at the required level of ventilation or Carbon Dioxide (CO2) concentration. Actually, the indoor air quality is influenced by emission from building surface materials and furnishing, occupants and their activities. VOCs play an important role in the indoor air quality evaluation process. VOC emissions adversely affect both occupant comfort and health. Most of the health hazards associated with VOC emissions occur during the first few weeks of building use. The Indoor Air Quality Emission Simulation Tool developed by National Research Council is used for simulating the VOCs emission impact of selected materials based on the amount of materials used and the ventilation rates in a model room, in this case study. IA-Quest predicts the emission of VOCs from building surface materials and furnishings, helping to select low-emission materials and effective ventilation strategies. The results showed the benefit of removing the increased amount of TVOC generated in time of the unoccupied period. The differences in TVOC concentrations were not obvious between two higher ventilation conditions (2.00 and 1.40 l/s.m2). More significant difference was estimated between categories A, B and category C (0.80 l/s.m2).

Implementation of green building materials in construction industry in Johor Bahru, Malaysia

The research paper is to investigate the implementation of green building materials by construction industry stakeholders in Johor Bahru. Several features and the main types of green building material used in construction industry in Johor Bahru is determined. Barriers and solutions is identified in adopting the green building materials and questionaire is used to gauge response from targetted respondends. The design structure of the questionnaire is to achieve the three objectives of the research. The first objective of the study intends to investigate the importance level for features of green building and the types of green building materials. The second objective of the research is to investigate importance level of the core barriers for the usage of green building materials and the third objective is to investigate importance level of the solutions for the barriers in adopting green building materials.The data collected is analysed using SPSS software, descrptive statistics eg. mean score and standard deviation interpretations. In conclusion, the GBM features preferred are energy efficiency, low carbon emission and raw material and waste is recyclable. Preferred GBM types are “sustainable brick”, “lightweight reinforced concrete” and “wood flooring” are the top three ranked GBM in Johor Bahru. The research also found that, “Higher cost”, “Lack of awareness” and “Lack of rules and regulations” are the top three ranked core barriers. Finally, the research concluded that, “Reduce green building material cost”, “Education” and “Training campaign” are the top three ranked solutions importance level in adopting GBM in Johor Bahru.

Analysis of fluid flow and heat transfer characteristics in multiple glazing roofs with a special emphasis on the thermal performance

This study aims to investigate the effect of air layer thickness, glass coating emissivity and number of panes on the flow and heat transfer characteristics in glazing roof and evaluate thermal performance of glazing roof in terms of overall heat transfer coefficient and inner surface temperature. A conjugate heat transfer analysis including radiative heat transfer is conducted considering different emissivity values and air gap values available in the market for double, triple and quadruple pane windows. Computational results show that a progressive improvement is achieved by adding more panes or decreasing surface emissivity. However, increasing air layer thickness may promote heat transfer considerably which defeats the purpose. The-best thermal insulation performance is achieved with-the air gap width of 9 mm for all the cases considered while the poorest performance is obtained with the gap width of 6 mm or 15 mm depending on the number of panes. By using quadruple pane windows, coating the glass surfaces with low emissivity materials and optimizing air gap, the U-value can be reduced down to 0.77 W/(m2 K) providing a great amount of energy saving potential (up to 71%). Besides, the inner surface temperature of window approaches to the indoor temperature which enhances thermal comfort.

Temperature and emissivity retrieval from low-emissivity materials using hyperspectral thermal infrared data

ABSTRACTLand surface temperature and emissivity separation (TES) is a key problem in thermal infrared remote sensing. Many TES algorithms have been proposed and validated on natural surface materials such as water or vegetation. However, when those algorithms are applied to low-emissivity materials such as some metals, the retrieval accuracy needs significant improvement. Here, we propose a new temperature and emissivity retrieval algorithm for hyperspectral thermal infrared data based on bias characteristic of atmospheric downward radiance. This approach is aimed at weakening the large influence of errors in atmospheric downward radiance on the TES of low-emissivity materials due to stronger coupling between the surface and atmosphere. Compared with traditional approaches such as the iterative spectrally smooth temperature and emissivity separation (ISSTES) method, the proposed method improves retrieval accuracy for low-emissivity materials by about 0.3, 0.4, and 1 K for three low-emissivity test materials (galvanized steel metal, metallic silver paint, and gold paint sandpaper). Thus, the proposed algorithm can weaken the influence of atmospheric downward radiance error. In addition, the computation efficiency is higher than ISSTES because fewer groups of channels are involved in the calculation.

Use of Low Smoke and Halogen Free Cables for Marine Fire Safety Design

Safety of shipping is a growing concern. The causes of shipping casualties are various. A fire on a ship is one of the most hazardous incidents which can happen on board and a common cause of damages and accidents in ships. However, this knowledge decreases where electrical installations, whose effects are less well-understood, are involved. Because of these effects and risks, the regulations related to cables for a vessel’s electrical installations anticipate the use of special low fire propagation and fire-resistant cables made with low smoke emission and halogen-free materials. Despite these criteria, the regulations permit the use of materials such as PVC. The main purpose of this research is to identify the risks associated of the use of PVC versus Low Smoke Zero Halogen (LSOH) cables that could be present for equipment safety and people in case of fire. As a result of the implementation of the regulatory framework, test results from PVC and LSOH cables used in ships have beenobtained. Finally, the use of LSOH cables is implemented to assess the effect of fire risk reduction measure for the enhancement of safety of shipping in coastal waters, efficiency and protection of the environment.

Risk Assessment and Preservative Measures for Volatile Organic Compounds in Museum Showcases

ABSTRACT The first step in preservative measures for artworks in airtight showcases is the exclusion of outgassing from construction materials or, at least, limitation of the emissions to a minimum acceptable level if the volatile organic compounds (VOCs) generated may be qualified as harmless. Once it is ascertained that the objects in the showcases are responsible for VOC emissions, a step forward becomes necessary, implying showcase ventilation with air flowing through active sorbent materials. Solid phase micro-extraction (SPME) followed by GC separation and MS identification has been applied for checking the outgassing characteristics of different types of materials used for the construction of airtight showcases, and the method was found particularly attractive in terms of speed and sensitivity, suitable for measurements in presence of low-emitting materials. Sampling could also be done in the case interiors, thus making possible detection and recognition of emissions from art objects within a case. A comprehensive preventive conservation scheme has been further devised by means of active air circulation within the showcase and functional sorbent materials along the flow, for complete suppression of gaseous compounds. Control of the compounds in the air flow and of their filtration efficacy was achieved by direct sampling, also using SPME fibers. Continuous monitoring of the air quality in the showcases has been developed with insertion of a photoionization detector capable of detecting the VOCs in the air by inducing molecular ionization, and measuring the generated photocurrent. The system is not selective, but gives the total concentration, reaching ppb sensitivity with high-quality data. In addition it includes temperature and humidity sensors, making the whole a useful instrument for environment control.

VOC emission rates in newly built and renovated buildings, and the influence of ventilation – a review and meta-analysis

ABSTRACTFew field studies have evaluated ventilation strategies, such as temporarily increasing the ventilation rate, to counter the high pollutant-load from off-gassing of volatile compounds from new materials in these buildings. We reviewed longitudinal studies that measured both ventilation rate (i.e. fresh air change rate) and airborne concentration of total volatile organic compounds (TVOC). Rates of emission of TVOC follow a multi-exponential decay trend over time after completion of a building. A tri-exponential trend-was fitted by quantile regression. Although the ventilation rate is key to controlling airborne concentrations, it does not noticeably influence TVOC emission rates. Specifying low-emitting materials, or bake-out before occupancy, both have a significant impact on emission rates . The results can be used to assess and size energy-efficient practical ventilation strategies (such as demand-controlled ventilation) to keep the concentration of TVOCs within acceptable levels during hours of occupancy after completion of a new or renovated building.

Assessment of VOCs material/air exchanges of building products using the DOSEC®-SPME method

Using low emissive materials in building is an effective way to reduce indoor concentrations of pollutants such as VOCs. Material emissions are assessed by the ISO 16000-9 standard. This procedure is time-consuming and is not suitable for on-site measurements. This work aimed in assessing an alternative method, DOSEC®-SPME, for simple measurements. To validate it, emissions of 30 materials were characterized by both ISO 16000-9 and DOSEC®-SPME. A first correlation was found between the two methods for formaldehyde emissions of raw materials. This encouraging result allows considering the development of new decision making tools for the selection of healthy building materials.