Insulation System Research Articles

Improving energy efficiency in Portuguese buildings: Retrofitting façades with high reflectance finishing coat

The European Union must enhance energy efficiency in its building stock, given that buildings account for up to 40% of the EU's energy consumption. Currently, more than 85% of buildings have been in use for over two decades, with at least 75% lacking energy efficiency. Only 10% of the building stock achieves ‘A’ or ‘B’ ratings in energy performance certificates. To meet energy efficiency standards, retrofitting exterior walls with passive techniques, such as enhancing optical properties, proves highly effective. Employing high reflectance surfaces reduces solar heat absorption, thereby lowering cooling energy use. This study examines the impact of reducing surface temperature through an external thermal insulation system with a high reflectance finishing coat during building envelope renovation in various climatic zones in Portugal. Preliminary findings indicate that high reflectance has a more substantial effect on annual heat gain for moderately insulated walls than well-insulated ones. The effect varies with maximum air temperature, especially in hot summers. A change in reflectance can improve heat gain reduction, especially considering the cost of retrofitting with insulation materials. An optimal balance between reflectance and thermal resistance is key to achieving lower surface temperatures and reducing cooling energy demands for Portuguese climates.

A Novel Space Charge Optical Measurement Method in Electronic Device Insulation System

A Novel Space Charge Optical Measurement Method in Electronic Device Insulation System

Obtaining the parameters of an RC model to know the insulation condition of a distribution transformer

Because it is a topic of great interest in the study of the insulation system of oil immersed Transformers, methods have been sought to determine the moisture content and aging of the pressboard, paper and dielectric oil from Transformers, measuring the response of the dielectric materials, which are characterized by known polarization phenomena. One of these techniques is dielectric spectroscopy in the time domain, measuring the polarization-depolarization currents, with this the parameters of an equivalent RC circuit (Debye model) are determined. Using the Debye model (T. K. Saha, P. Purkait y F. Muller, 2005) and obtaining the polarization current through the insulation resistance test, the parameters to establish the condition of the transformer oil-paper insulation system will be determined, using exponential curve fitting of the data obtained from the insulation resistance test with the high vs. Low connection plus tank, the parameters of the time constant τ, the resistance R and the capacitance C of the equivalent circuit are obtained and with this information, the condition of the transformer insulation system is evaluated and decisions are made regarding maintenance actions.

A novel cost-based optimization model for electric power distribution systems resilience improvement under dust storms

In the recent years, dust storms (DSs) pose a serious threat to critical infrastructure such as power distribution networks (PDNs). During DSs, the contamination of insulators, increases the possibility of damage to the PDNs insulation system and flashover induced power outage may occur. Power outages disrupt the performance of other urban infrastructures and, in addition to heavy financial losses, cause public dissatisfaction. Although this issue is of particular importance in areas with humid climate, a few studies have been reported on PDNs resilience improvement against DSs. This paper proposes a novel cost-based optimization model to make PDNs more resilient to DSs considering uncertainties. The proposed model is based on the two-stage stochastic mixed-integer programming (SMIP). In the first stage, decisions are made to equip repair crews (RCs) with insulator washing machines, hardening distribution lines with silicone-rubber insulators (SIs), and deploy backup distributed generators (DGs). Decisions in the second stage include network reconfiguration, RCs routing, DGs power dispatch, and load shedding as the critical options for PDN outage management during/after DSs. Case studies are evaluated in the IEEE 69-bus test system and a real 209-bus PDN in Khuzestan province, a coastal province in southwestern Iran. The simulation results at different budget levels have confirmed the efficiency of the proposed model for cost-optimal resilience enhancement planning of PDNs against DSs.

TINY HOUSE IN THE DESERT: A study in indoor comfort using moveable insulation and thermal storage

A tiny house for seasonal rangers was designed for the extreme climate and diurnal temperature fluctuations of Joshua Tree National Park. The challenging climate conditions resulted in an extensive investigation of the building envelope to act as a passive thermal storage system to naturally cool and heat the house. The north wall was designed as a “cold battery,” which uses a dynamic internal and external insulation system with a high-mass concrete wall to achieve coolth absorption at night as part of a thermal management system and to achieve indoor thermal comfort under extreme desert climates. A combination of opening an exterior insulation system at night to absorb coolth, closing the exterior insulation system when the temperature rises, and opening the interior insulation system to release coolth was attempted. The goal was to achieve a comfortable indoor temperature without the use of HVAC systems. Several software programs were tested for their capabilities to simulate time lag in concrete and thermal storage including Opaque and IES VE. The design of the north wall was carried out for different conditions such as different modulating profiles, locations and thicknesses of insulation, and the data were collected and analyzed again. IES VE was able to successfully simulate the effects of moving interior and exterior insulation twice a day on different sides of a concrete wall. In consideration of the special occupancy type, the expansion of the comfort zone for seasonal rangers is achieved by the specification of a comfortable temperature range from 65°F to 85°F. In a standard year, consisting of 8,760 hours, simulations were conducted on the entire residence, primarily during the months when seasonal rangers were present, to investigate thermal comfort conditions. These assessments encompassed various aspects, including ventilation (2,941 comfort hours), the north wall (4,653 comfort hours), the base model (2,883 comfort hours), and enhancements to the south wall (5,543 comfort hours) and the east and west glazed facade (6,137 comfort hours). The culmination of these findings significantly contributed to an enhanced overall comfort experience within the tiny house design, specifically tailored to accommodate the needs of seasonal rangers at Joshua Tree National Park. Natural ventilation proved to be a good strategy.

ENCLOSING WALL STRUCTURES OF OPERATED RESIDENTIAL BUILDINGS USING THERMAL INSULATION PLATES FROM LINEN NOILS

The article discusses thermal insulation materials of a fibrous structure based on plant agricultural waste. The results of full-scale tests of flax noils insulation used for thermal insulation of an external wall fence with a ventilated insulation system of a one-story residential building are presented. Data from studies of the thermophysical characteristics of a wall enclosing structure with experimental materials are presented. Temperature distribution graphs along the thick-ness of the wall enclosure structure were constructed, after which the values of thermal resistance to heat transfer were calculated. The dependences of the distribution of humidity along the thickness of thermal insulation were revealed. Based on the results of full-scale tests, it was revealed that at an outside air temperature of -23 °C, the value of thermal resistance to heat transfer of a wall with experimental insulation of flax noils is equal to 3,24 (m2·°C)/W. The research results prove the effective operation of thermal insulation materials based on flax noils for wall enclosing structures.

Numerical modeling and optimization of thermal insulation for liquid hydrogen storage tanks

Liquid hydrogen storage is one of the effective hydrogen storage methods due to its high density of 70.8 kg/m3 compared to gaseous hydrogen of 0.0838 kg/m3 at atmospheric pressure. Liquid hydrogen requires cryogenic storage technology, which minimizes heat flux by stacking multiple insulation layers in a high vacuum (10−1–10−5 Pa). However, large-scale tanks use a medium vacuum (100–10−1 Pa) to reduce maintenance expenses. Solid insulation is applied to prevent liquefaction of residual gas up to 150 K, followed by the stacking of multilayer insulation (MLI) with a vapor−cooling shield (VCS) to minimize the insulation thickness. In this study, a numerical model was developed to calculate the heat flux of a storage tank based on the physical tank shape. The insulation thickness was also optimized for two insulation systems (solid insulation + MLI and solid insulation + MLI + VCS). Optimal VCS placement on solid insulation, determined through sensitivity analysis, reduces 64.2 % of MLI layers under 5 Pa vacuum pressure. Total insulation thickness reduction of 51.4 % at 1 Pa vacuum pressure was obtained based on a hydrogen storage tank volume of 4200 m3. The effects of insulation thickness reduction are remained even when the vacuum pressure is increased to 5 Pa.

Partial Discharge Inception Modelling of Insulating Materials and Systems: Contribution of Electrodes to Electric Field Profile Calculation

Partial discharge inception modeling is a powerful tool for material investigation and insulation system design in order to achieve the objective of PD-free operation of insulation systems. Model validation, however, requires accurate and repeatable testing conditions, and the aim of this paper is to look at the influence of electrodes and electric field simulation on partial discharge inception model prediction accuracy. Awareness of the geometric electrode configuration is important to forecast both the typology of discharge and the corresponding partial discharge inception voltage value. It is shown, in fact, that inaccurate evaluation of electrode shape (e.g., its flat part and contour) might impact significantly on electric field estimation, the typology of incepted discharges, and, thus, on model accuracy, i.e., on partial discharge inception voltage prediction, which is the basis for the partial discharge-free design of insulating materials and systems. In particular, small electrode curvature radius variations do not significantly affect the PDIV value or PD typology identification. However, worsening electrode/insulation specimen contact can significantly impact PD inception and typology evaluation.

Natural esters as sustainable alternating dielectric liquids for transformer insulation system: analyzing the state of the art

Natural esters as sustainable alternating dielectric liquids for transformer insulation system: analyzing the state of the art

Optimizing insulation and heating systems for social housing in Chile: Insights for sustainable energy policies

Due to the climatic conditions in central-southern Chile, there are high heating energy consumption and PM2.5 emissions. Among the alternatives to mitigate it, the Chilean government has implemented subsidies to improve the housings envelope and to replace firewood stoves by pellet stoves and air-to-air heat pumps. Accordingly, for evaluating the effectivity of above-mentioned initiatives, this study proposes to identify the optimal solutions that minimize the energy demand, the environmental impacts, and the global costs, for social housing using different insulation materials and heating systems in four Chilean cities located in central-southern Chile. Results reveal pellet stoves with lower environmental impacts but higher global costs, while heat pumps offer an intermediate solution that can be enhanced with a greener electricity grid, but the global costs are still too high. Firewood stoves could be optimal solution depending on optimization weighting factors. The study emphasizes prioritizing housing envelope improvements in energy policies, followed by heating system enhancements. Although replacing firewood poses challenges due to costs, it is crucial for Chile's 2050 decarbonization goal. This research provides valuable insights into the complexities and potential solutions for transitioning away from firewood in Chilean social housing.

Determination of the kinetic parameters of a supersonic plasma flow of a gas-discharge source from the current measured by an insulated probe system

The aim of this work is to develop a procedure for determining the kinetic parameters of charged particles in a supersonic jet of a gas-discharge source of collisionless plasma by measuring the current collected by an insulated probe system of cylindrical electrodes placed transversely to the jet. Based on the authors’ mathematical model of current collection by the above-mentioned probe system and asymptotic solution for the probe current in the electron saturation region, the ion temperature and directed velocity and the electron temperature are related to the measured probe current. The effect of the probe system parameters and the current and voltage measurment error on the reliability of diagnostics of a diatomic gas-discharge plasma is studied. Within the framework of the probe current collection model for the electron saturation region, numerical and analytical estimates of the errors in determining the kinetic plasma parameters are obtained as a function of the geometric parameters of the probe system, the accuracy of probe current measurement, and the bias potential of the probe relative to the potential of the reference electrode. The measuring-to-reference electrode area ratio and the probe current measurement conditions optimal for adequate estimation of the average kinetic energy and the directed velocity of ions in a supersonic gas-discharge plasma jet are determined. A priori quantitative characteristics of the effect of the probe measurement errors on the reliability of the determination of the charged particle kinetic parameters are given. The reported procedure and estimates of the error in kinetic plasma parameter determination allow one to choose the probe system parameters and estimate the required measurement accuracy when planning and conducting experiments on laboratory plasma diagnostics.

Environmentally Friendly Wood Adhesives Based on Dextrin/Arabic Gum Blends

Wood adhesives are widely used consisting of urea-formaldehyde resins. Most of the studies aim to find alternative natural materials to replace the carcinogenic chemical adhesives. A mixture of natural materials that are available in abundance, cheap in price and are resistant to water and heat, the failure of the interface between two solid dielectrics is a major source of insulation system failure, hence it is crucial to understand the principles regulating this breakdown occurrence. It is generally agreed that the tangential AC breakdown strength of solid-solid surfaces is primarily determined by the elastic modulus (elasticity), radial/tangential pressure, surface smoothness/roughness, and dielectric strength of the ambient environment. For this purpose, we made use of dextrin and Arabic gum. Physical parameters (Lap shear strength, pull off strength, hardness, roughness, electrical and thermal insulations) of the combination formed with varying amounts of each ingredient were investigated. The adhesive characteristics of D were enhanced by the incorporation of AG, with improved pull off adhesion and lap shear strength at increasing AG levels at 80%. D /AG 20/80 compositions had pull off adhesion values 189 times greater than pure D, and lap shear strength values 820 times higher. It is evident because of the dispersion of AG molecules in decreasing the surface roughness of D/AG films and increasing their hardness on the shore scale. There is a positive correlation between the amount of AG added and the blending matrix of D, therefore boosting A with AG increases A. The dielectric strength, and thermal insulation increases with the increase in the weight ratio of Arabic gum. The blend prepared as an adhesive for wood is a good electrical and thermal insulator at 8% AG/20% D.

Investigation of Novel Solid Dielectric Material for Transformer Windings.

Improvement techniques aimed at enhancing the dielectric strength and minimizing the dielectric loss of insulation materials have piqued the interest of many researchers. It is worth noting that the electrical breakdown traits of insulation material are determined by their electrochemical and mechanical performance. Possible good mechanical, electrical, and chemical properties of new materials are considered during the generation process. Thermoplastic polyurethane (TPU) is often used as a high-voltage insulator due to its favorable mechanical properties, high insulation resistance, lightweight qualities, recovery, large actuation strain, and cost-effectiveness. The elastomer structure of thermoplastic polyurethane (TPU) enables its application in a broad range of high-voltage (HV) insulation systems. This study aims to evaluate the feasibility of using TPU on transformer windings as a solid insulator instead of pressboards. The investigation conducted through experiments sheds light on the potential of TPU in expanding the range of insulating materials for HV transformers. Transformers play a crucial role in HV systems, hence the selection of suitable materials like cellulose and polyurethane is of utmost importance. This study involved the preparation of an experimental setup in the laboratory. Breakdown tests were conducted by generating a non-uniform electric field using a needle-plane electrode configuration in a test chamber filled with mineral oil. Various voltages ranging from 14.4 kV to 25.2 kV were applied to induce electric field stress with a step rise of 3.6 kV. The partial discharges and peak numbers were measured based on the predetermined threshold values. The study investigated and compared the behaviors of two solid insulating materials under differing non-electric field stress conditions. Harmonic component analysis was utilized to observe the differences between the two materials. Notably, at 21.6 kV and 25.2 kV, polyurethane demonstrated superior performance compared to pressboard with regards to the threshold value of leakage current.

РЕЗУЛЬТАТЫ СРАВНИТЕЛЬНЫХ РЕСУРСНЫХ ИСПЫТАНИЙ СИСТЕМ ИЗОЛЯЦИИ КЛАССА НАГРЕВОСТОЙКОСТИ Н (180°С) ТЯГОВЫХ ДВИГАТЕЛЕЙ ЭЛЕКТРОВОЗОВ С ИСПОЛЬЗОВАНИЕМ ПОЛИЭФИРКЕТОНОВОЙ И ПОЛИИМИДНОЙ ПЛЕНОК

The operation of electric locomotive traction motors in conditions of constantly increasing temperature and humidity naturally leads to a decrease in the resistance of the body insulation of the coils of the main and auxiliary poles, which then leads to insulation breakdown and engine failure. In the general statistics on TED breakdowns, the percentage of failure due to low insulation resistance is up to 30%.
 Manufacturers of electrical insulation are constantly working to increase its reliability, using modern systems of polymer materials for this purpose. This article provides a brief description of the insulation systems of traction electric motors of heat resistance class H (180 °C) based on polyethyrketone and polyimide films. The main normative documents on the basis of which the assessment of insulation characteristics was carried out are indicated. Insulating tapes based on fiberglass and mica, mass-produced by ZEIM Elinar LLC, were used as objects of research. The methods are given, the equipment and the main results of resource tests of various insulation systems are indicated. According to the test results, it is shown that the system based on a polyester ketone film is in no way inferior in terms of heat resistance to a system based on a polyimide film.

The Behaviour of Wood Fibre Insulation Systems for Solid Wall Buildings: Lessons from a Long-term Monitoring Study

The majority of the traditional building stock in the UK is made of solid brick walls. Internal wall insulation is one of the possible interventions to preserve the external appearance of a building while improving the energy efficiency of its walls. However, it can lead to moisture-related risks, such as excess moisture accumulation and mould growth. This paper presents an overview of the lessons learnt from the long-term monitoring of two case-study solid wall buildings, insulated with wood fibre-based systems and monitored for a year. The aim of this monitoring campaign was to provide evidence on the main moisture transfer and storage mechanisms occurring in solid walls insulated with wood fibre-based systems under actual environmental conditions. Results showed that the dynamic interaction between the insulated wall and moisture sources could be controlled by means of an appropriate specification of the insulation system, considering the influence of orientation, material properties and indoor moisture loads. It was also found that construction moisture influenced the initial conditions of the interface, but mitigation strategies can be considered to reduce mould growth risk during installation and before the drying of construction moisture.

Surface Flashover Over a Microprofiled Cylinder in Air

Increasing the lightning impulse (LI) flashover voltage of insulators can require significant changes to the geometry and material properties of the insulator or electrodes. In some cases, such changes can be difficult to implement as they may require more volume or may compromise e.g. mechanical properties of the insulating parts. In this work, a new micro-scale surface profile which inhibits streamer discharge propagation without introducing major changes to the insulation system geometry or materials is demonstrated. Polyoxymethylene (POM) cylinders with 25 % glass fibre in air were machined with 0.5x0.4 mm rectangular grooves spaced 0.6 mm apart and stressed with LIs. A non-profiled cylinder and a cylinder with a larger, semi-circular grooves were tested for comparison. The cylinders were tested in a 48.5 mm atmospheric air gap with an exposed triple junction as the positive electrode. The rectangular surface profiles increased the LI flashover voltage (U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> %) from 70.0 to 96.5 kV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">peak</sub> . High-speed imaging showed positive surface streamer discharges stopping on the surface profiles. Discharge inception calculations were used to explain the influence of the surface profile on the flashover process. The results are relevant for technological applications with electrically stressed solid insulators in gases.

Openings in ventilated Attics

How big should ventilation openings be in ventilated attics? In Denmark, guidelines describe what is sufficient to remove excess moisture penetrating through the ceiling. These guidelines are based on many years of experience. An important parameter is the tightness of the ceiling. With current regulations for the airtightness of buildings, convection through the ceiling is reduced compared to older buildings. Therefore, it is relevant to review these old rules of thumb and maybe revise them. In this two-year study, tests with different sizes of ventilation openings were conducted in a test house with 18 separate ventilated attics and airtight ceilings. One third of the attics were ventilated according to the guidelines, one third’s ventilation was reduced by one third and the last third had 50 % ventilation of the recommendations. Hourly measurements of temperature and relative humidity in the attics were conducted. Rafters in the attics were tested for mould growth. Six different types of insulation systems were used in the attics (with and without a vapour barrier, different insulation materials, and insulation thickness), therefore, the study also includes these differences. Earlier investigations, with full ventilation in all attics, showed no significant hygrothermal differences between them; consequently, it was assumed that the amount of ventilation would be decisive for the hygrothermal performance. This study follows up on this assumption. Results show little differences between the attics, mainly that having a vapour barrier becomes more important with reduced ventilation, and the insulation thickness and thereby U-value is of less importance. Reducing the requirements for ventilation of attics could be relevant, provided that the ceiling is airtight.

Experimental evaluation of a vertical heat bridge insulation system for the structural performance of multi-residential buildings

This research aims to evaluate the impact of thermal bridge solutions on the structural performance of wall connection components in multi-residential buildings. After incorporating an H-type reinforcing system that utilized stainless steel and a UHPC shear key, four experiments were conducted under static loading conditions, employing an I-shaped specimen with dimensions of 800 mm × 600 mm × 200 mm. Furthermore, to properly evaluate the damage state and crack propagation of a structure under shear load, the specimens with, and without SK and UHPC were developed and tested to determine fracture pattern and shear strength. The experimental results showed that specimens with the UHPC and shear key contributed 2.5 and 3.1 times improvements in maximum loading capabilities, respectively. Additionally, the experimental findings were validated by performing simulations using the LS-DYNA program. This numerical analysis provides an additional understanding of the mechanical response of the building components.

Classification and simplified design rules concerning the moisture performance of capillary active insulation materials

Conventional interior insulation systems protect the wall from condensation in winter by the help of vapor barriers or vapor retarding insulation materials. However, these solutions also reduce the drying potential of the walls towards the inside. This can be a disadvantage if wetting from the outside due to rain or other influences takes place and the drying potential to the outside is not sufficient. In such cases, so called capillary active materials can be an alternative, because they provide additional drying potential to the inside in summer thanks to a rather low vapor diffusion resistance. In winter they work without vapor retarders because they can store and wick water away from the condensation plane back towards the interior by capillary action. In practice, there are currently many different materials under the label "capillary active" with a correspondingly wide range in terms of moisture storage, liquid transport and vapor diffusion resistance and it is difficult to decide, whether material is suitable for an application or not. There is still missing a common definition of the performance of such materials. While for most other materials already simplified design and application rules for the application as interior insulation are available, capillary active interior insulation materials still require an individual design, normally by the help of hygrothermal simulation. In order to simplify also their practice application, a classification of the moisture performance of capillary active interior insulation, considering the influencing parameters of relevance on the moisture level at the critical interface between wall and interior insulation was developed. On this basis, also a simplified verification process as well as design rules for the main practical application fields become possible, which allows designers to choose an appropriate system for the specific situation.

Experimental study of thermal energy storage system for solid particles/ heat transfer oil in shell and tube heat exchangers with H-shaped fins

The solid-state sensible heat storage method is cost-effective, technically simple, and works well across wide temperatures. Using return fines (RFs) as the heat storage medium (HSM) can ease problems like RFs in excess and high energy consumption in the sintering process. This article first characterizes the thermal properties of RFs. Results show a specific heat capacity of 0.67–0.97 kJ/(kg·°C) within 20–380 °C, with stable thermal properties from 100 to 1000 °C. Then, the heat transfer performance of RFs and heat transfer oil (HTO) in a shell and tube heat exchanger is experimentally investigated. H-shaped fins are added to enhance the heat transfer. Stacking solid particles on the shell side can avoid direct contact between the HSM and HTO, the tiny size limitations of HSM particles, and cracking problems caused by thermal expansion. The thermal energy storage (TES) unit operates within 170–270 °C. Effects of different flow rates (30, 20, 10 L/min) and charging/discharging temperatures (300/160, 290/150, 280/140 °C) on system performance are explored. Increasing the HTO flow rate and charging temperature and lowering the discharging temperature can reduce charging/discharging time and enhance average power. Cycle efficiencies for flow rates of 30, 20, and 10 L/min are 86.9%, 85.2%, and 79.5% respectively. The 30 L/min working condition shows the best performance. Remarkably, system performance improvements are relatively limited compared to the 20 L/min setting. Regarding charging/discharging temperatures of 300/160, 290/150, and 280/140 °C, cycle efficiencies stand at 73.3%, 85.2%, and 70.6%, respectively, with the 290/150 °C setting displaying the most favorable characteristics, including the shortest total charge and discharge time of 59.3 min and the highest cycle efficiency. Efforts to enhance the system's insulation and maintain a substantial temperature differential between HTO and HSM are pivotal in accelerating the charge/discharge process and minimizing heat loss.