Insulation Level Research Articles

MODELAGEM DE PONTES TÉRMICAS NA ZONA BIOCLIMÁTICA 2: CINCO DIFERENTES ABORDAGENS

Thermal bridges are vulnerable points present in the envelope of buildings and influence the thermoenergetic performance and still bring consequences to the opaque surface such as the favoring in the formation of filamentous fungi. The impacts of thermal bridges and their consideration in calculations of thermal transmittance have been discussed in different parts of the world and in regions of cold climates in Brazil. This work aims to evaluate the impact of thermal bridges of reinforced concrete structure in a residential building in the bioclimatic zone 2, considering five approaches for modeling of thermal bridges in the EnergyPlus computational simulation software. The results show that the type of approach used for modeling in computational simulation influences the energy consumption values of the building. The different models tested showed variations in building energy consumption when comparing the strategies that considered the calculations of thermal bridges with the approach that disregarded this calculation, especially in high insulated buildings, where it was possible to identify differences of up to 13%. The conclusions observed show that the level of insulation of the envelope is one of the factors that interferes in the differences in building consumption between the approaches evaluated for thermal bridges. Keywords: Linear Thermal Bridges, Computer Simulation, Energy Performance

Novel in situ measurement methods of the total heat transfer coefficient on building walls

The performance gap between the design and the as-built energy performance of buildings is considered a significant risk that may compromise the efforts on meeting the carbon reduction targets set by governments in Europe. The relative importance of irregularities or defects within building walls is more prominent when the thermal insulation level increases. It is thus necessary to quantify the global thermal insulation level of building walls (i.e., including thermal bridges). Classical contact measurement methods only allow local measurements and would thus require the use of a high number of sensors which would limit their applicability. Besides, the presence of thermal bridges prevents the use of contact heat flux measurements because of the 2D or 3D nature of the associated heat transfers through the building walls. To overcome these limitations, the present study proposes an alternative approach consisting in measuring the heat flux on one location and extrapolating its value on the whole building wall through the measurement of the total heat transfer coefficient. Therefore, we developed and/or further improved five different in situ measurement methods of the total heat transfer coefficient on building walls. The measurement methods were thoroughly tested indoor thanks to lab-scale experiments carried out both in steady-state and transient regimes. The results obtained demonstrated the accuracy and the robustness of the proposed methods, as well as their intrinsic limitations. These in situmethods can be used to assess the heat losses on a whole building wall, including the contribution of thermal bridges.

Closed-Form Expressions for the Estimation of the Minimum Backflashover Current of Overhead Transmission Lines

The minimum backflashover current, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BF</sub> , of typical overhead transmission lines is estimated through ATP-EMTP simulations considering the tower ground resistance and AC voltage phase angle as parameters. Several single- and double-circuit lines are investigated with operating voltage from 66 kV to 765 kV and Basic Insulation Level from 325 kV to 1950 kV. The backflashover rate, BFR, of the investigated lines is obtained using an expression that accurately considers lightning incidence to the line for prospective currents higher than I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BF</sub> ; the relevant CIGRE expression underestimates BFR. BFR can be easily estimated using solely the phase angle values corresponding to zero AC voltage of the phase conductors. Based on the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BF</sub> and BFR results, simple expressions are introduced for the calculation of an equivalent minimum backflashover current as a function of insulator length and tower ground resistance or impulse impedance. These expressions enable straightforward estimation of BFR without the need for time-consuming simulations or laborious analytical methods adopting simplifying assumptions.

Exploring thermal comfort experience and adaptive opportunities of female and male high school students

Students' health and productivity are affected by the thermal conditions inside the educational environments. Considering the lack of thermal comfort research in the Arabian Gulf region, the combination of the extreme climatic conditions, the general restriction on adaptive actions, and the lack of economic responsibility lead to heavy reliance on air conditioning units, which has environmental and economical sequences. A first step in reducing this reliance is understanding the students' thermal experiences. This paper attempts to feed the pool of thermal comfort research in the Arabic region by investigating and comparing the thermal conditions of female and male students considering their neutral temperatures and acceptability limits. Objective and subjective data were collected from five and three female and male schools respectively during the cooler season. Analysing the former data revealed the general similarity of the thermal conditions inside the investigated classrooms except for three classrooms. Around 50% of the female students were (neutral) compared with almost 20% of male students despite the heavier insulation level of the former, which may indicate an addiction to ACs for the male students. Applying Griffiths’ method, the neutral temperature was estimated at 24.3 ± 1.09 °C for the former students and 26.1 ± 0.92 °C for the latter students. Comparatively, the acceptability limits of the male students were shifted to the warm side of the thermal continuum.

Applying the Passivhaus standard to a terraced house in a hot and humid tropical climate – Evaluation of comfort and energy performance

In a hot and humid tropical climate, natural ventilation brings high levels of moisture into dwellings that, together with occupant activity, can result in very elevated internal relative humidity levels. Coupling these high relative humidities with high internal air temperatures creates occupant thermal discomfort, which is typically ameliorated in the tropics using energy-intensive air conditioning systems. This paper has investigated the potential benefits for thermal comfort and energy usage of applying the German Passivhaus standard to tropical dwellings. By creating a super insulated and air-tight envelope, the Passivhaus standard reduces fabric heat transfer, controls air infiltration and provides low-energy comfort. Applying this approach to a tropical terraced house might be effective but could, potentially, have an adverse impact on mechanical cooling demand. This study took an actual terraced property in Jakarta, Indonesia and thermally modelled its performance as insulation and airtightness levels were incrementally improved up to the Passivhaus standard. Field measurements in the dwelling of air temperature and relative humidity were used to validate the thermal model of the existing house. The validated model then tested the feasibility of meeting the Passivhaus energy standard for cooling in the modified tropical house. Simulation allowed the effects of air conditioning (AC) and dehumidifiers on thermal comfort and cooling loads to be investigated. The research develop the Passivhaus building model that had the floor insulation removed to let the ground floor act as a thermal sink and potentially provide radiant cooling. Analysis revealed that the building’s predicted air temperatures were affected in a beneficial way by having the Passivhaus without floor insulation. Practical application: Cooling in hot and humid tropical region is an energy-intensive approach. Design approaches that can bring comfort and save energy for the occupant are essential. The success of Passivhaus standard in mild climate might be transferable to bring comfort in tropical housing. Best practice can be developed by analysing the Passivhaus building performance in hot and humid tropical region.

Embodied and Operational CO2 Emissions of the Elementary School Buildings in Different Climate Zones

Life cycle CO2 emissions (LCCEs) including embodied and operational CO2 emissions (ECEs and OCEs) should be comprehensively understood for establishing strategies for reducing CO2 emissions of buildings. Meanwhile, as the climate has a huge impact on building energy consumption, ECEs and OCEs should be investigated considering the climate. This study investigated the relation between ECEs and OCEs of buildings in different climate zones by conducting life cycle assessment and statistical analysis of 39 elementary school buildings in South Korea. As a result, the climate zone was determined to be the significant influence factors. The mean values of ECEs, OCEs, and LCCEs in central region were 611, 2,81 7, and 3,428 kg-CO2/m2, respectively, and those in southern region were 620, 1,652, and 2,273 kg-CO2/m2. The OCEs in central region was significantly higher than that in southern region, but the ECEs was not. In particular, ECEs and OCEs had a significant inverse correlation in central region but not in southern region. The results indicate that different strategies should be established depending on the climate zone. For instance, the thermal insulation levels should be further strengthened to reduce OCEs in central region compared to those of southern region.

Multi-Objective Optimization of Complex Measures on Supplying Energy to Rural Residential Buildings in Uzbekistan Using Renewable Energy Sources

This study presents the first results of multi-objective optimization of typical four-room rural residential buildings in Uzbekistan with different levels of thermal insulation. For that purpose, a simplified static model of buildings based on the heating degree-days has been employed and the optimal designs were found for three scenarios. In the first scenario, the life-cycle cost of the reconstruction measure was analyzed where the optimal thicknesses of the insulation layer were found for the roof, floor, and external walls but no solutions were found for windows, solar collectors, and photovoltaic (PV) panels. In the second scenario, primary energy consumption was minimized to zero for space heating and domestic hot water. In this scenario, the thickness of insulation layers for building envelopes and the size of solar collectors were optimized in various regions. In the final scenario, low carbon communities were considered in technoeconomic conditions of Uzbekistan. However, no optimal solutions were found in the current cost of electricity.

The Simulation Analysis of Factors Affecting Lightning Withstand Level of the Distribution Lines in Oilfield

Simulation analysis is an important method to study the lightning withstand level of distribution lines and conduct the design of line lightning protection. In the process of simulation, the components of the overhead line and the selection of the specific model of lightning current should be taken into account. All the work can be used to get the simulation results which are more consistent with the actual results. Based on the investigating the parameters of oil field lines, insulators and earth resistances, a lightning protection simulation model for typical distribution lines in oil field is built by using ATP-EMTP electromagnetic transient analysis program. By simulation analysis, the influence of line insulation level, earth resistance, layout parameters of arrests and lightning conductor on the lightning withstand level are studied. The results provide a scientific basis for the proposing of the comprehensive lightning protection measures of the distribution lines in oil field.

Case Study: Measuring the Thermal Insulation of Heated Protective Gloves on a Thermal Hand Model

This paper presents a study on the thermal insulation of commercial protective gloves with passive and active heating systems considering different simulated temperatures (-15 °C, -10 °C, 0 °C and +5 °C). The insulation parameter was determined on a thermal hand model for two heated gloves supplied with different heat sources (active and passive) according to an originally developed procedure. The results confirmed that the use of an additional heat source (active or passive) makes it possible to obtain higher values of thermal insulation, expressed by a change in the performance level. In addition, the results indicate that active systems are more effective than the passive heat sources tested. The procedure shows how to evaluate the performance of heated products. It was found that active and passive systems differentially follow temperature changes, and thus differ in the levels of thermal insulation provided in the workplace. Depending on the degree of exposure of the worker to a cold environment, it is advisable to wear gloves additionally equipped with passive or active heat sources.

Influence of outdoor thermal environment on clothing and activity of tourists and local people in a severely cold climate city

Outdoor thermal environment has become a critical factor in both architecture design and urban planning field, and some researchers argued that the reactions of different people to outdoor environments should be considered, for instance, age, gender and so on. While tourists are exposed to an outdoor environment of unfamiliar climate in a short period, and their clothing and activity level which are supposed to be different from local people are surely to influence their outdoor thermal environment experiences, which need to be clearly revealed. This study investigated 1740 samples in Harbin, China, and 844 samples in summer and 896 samples in winter were gathered. The samples were divided into local people and tourists, and their reactions of clothing insulation and activity level to the outdoor environment were studied. The results show that the local people and tourists reacted to the outdoor environment by clothing insulation in both summer and winter, and the tourists dressed more clothing in winter than the local people. The tourists’ activity level was not influenced by the outdoor thermal environment, which should be due to a pre-made plan when they traveled to a new place, as for the local people, their activity level was influenced by the outdoor environment in summer, higher air temperature led to higher activity level, and in winter, it seems that they did not react to the outdoor environment clearly, and they preferred to do more activities in late morning and afternoon, to avoid the very cold early morning maybe.

Control strategy optimization of a Stirling based residential hybrid system through multi-objective optimization

Hybrid systems for space heating and Domestic Hot Water (DHW) production are an attractive option for buildings to decrease their CO2 emissions. In this research, the operation variables of an installation, composed of a Stirling engine, a condensing boiler and a thermal storage tank, were optimized to supply heating and DHW demands of a virtual detached house. For this purpose, in an experimental installation operated with common control set points, the hybrid system was tested during the week of highest demand. Then the installation was modelled in TRNSYS, calibrated and validated against the experimental data and, finally, different multi-objective optimizations were carried out on the model to optimize the operation set points.The results obtained show that solely by optimizing the control variables of the calibrated model of the actual installation gives a reduction of 7% in cost and an improvement of 3.9% in exergy efficiency. Thus, it can be concluded that simply optimizing control variables in this type of hybrid systems can lead to low cost reductions. By reducing the thermal losses of the calibrated model from the experimental 17% of energy consumed to 5% and then optimizing it, a reduction of 17% in cost and an improvement of 23% in exergy efficiency were obtained. Different model insulation levels were tested, and two interesting conclusions were found from this analysis: until the level of transmission losses is below 5% of the energy consumed, the optimized operation conditions lead to a negligible use of the thermal storage, after which it increases drastically. On the other hand, it can be concluded that the cost optimization that optimizes the adiabatic model of the analysed hybrid system is insensitive to the selected control variables.

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.

Summertime comparative evaluation of indoor temperature and comfort in Auckland New Zealand: a survey of green certified, code and older homes

ABSTRACT A frequently stated hallmark of certified green homes is that they are ‘healthier’ and provide superior thermal comfort. This usually requires increasing insulation levels from code requirements on the understanding that this will provide a warmer, drier internal environment. However this solution to ‘cold and damp’ housing may have unintended consequences; while highly insulated dwellings may be warm over the winter, are they still comfortable during warmest months? This study analyses 29 dwellings in Auckland, New Zealand to determine if there is any difference in the temperature and thermal comfort between three types of dwellings: newly built green certified (6-Homestar), newly built non-certified and old dwellings (pre-1978). The results show large differences between dwelling categories with the certified 6-Homestar dwellings exceeding the World Health Organisation (WHO) healthy temperature threshold 75% of the time during the warmest months of the year, resulting in predicted occupant discomfort 16% of the time. These results have significant policy implications with it apparent that not only under-heating but also overheating require specific attention in government legislation, green building rating tools and building codes.

Research on On-line Monitoring and Regulation Technology of Pressure of High Voltage Transformer

In order to analyze the operating status of voltage and current transformers at high voltage levels, the methods of detecting transformer insulation level and infrared temperature are usually used, but such methods usually use manual measurement by portable instruments, and the internal defects of the transformer are difficult to find in time. This article proposes a suitable on-line monitoring method and regulation technology for the insulation oil pressure of high voltage transformers. The defects of the transformer can be judged by the change of the internal oil pressure, which can effectively find faults such as internal short-circuit, degradation, and partial discharge of the transformer. A mechanism is designed to adjust and release the pressure of expanders. The high voltage transformer pressure line monitoring device has developed based on the Internet of Things communication and solar power supply mode, which can monitor the internal operating status of the transformer in real time. When the internal pressure of the transformer suddenly increases, the designed pressure release structure of the expander will automatically rupture, release the internal pressure of the transformer, ensure the safety of the transformer body, and reduce the impact of the accident.

Study on clothing insulation distribution between half-bodies and its effects on thermal comfort in cold environments

Clothing is important for keeping the human body warm in cold environments. In Fanger's predicted mean vote (PMV) model, clothing insulation is a single input parameter that describes the dressing status of the whole body. The objective of this study was to examine the effects of the clothing insulation distribution between half-bodies. The distribution index (DI) was defined to describe the uneven level of the clothing insulation distribution. An experiment with 20 subjects and 9 different clothing conditions was conducted in a climate chamber. Subjects were asked to be sedentary and wear specified sets of garments in a 20 °C environment. The thermal insulation values of the garment sets were measured by using a thermal manikin. The nine clothing conditions were divided into four groups. Although their thermal insulations were very close, the DI values were quite different in each group. Subjective evaluations of thermal comfort were collected, and seven-point skin temperatures were measured. To investigate this topic with a wider temperature range and greater clothing diversity, a one-year continuous field study was conducted with 18 subjects. The results indicated that the subjective thermal evaluations were different when the clothing insulation levels were close and the DI values were different. Sets of garments with a lower DI were more likely to lead to lower thermal sensation vote (TSV) and more subjects preferring a warmer environment. Clothes with an uneven DI (<0.75 or >1.25) and less clothes on the lower body (DI < 1) made people more sensitive to cold environments.

The impacts of nanotechnology on the improvement of liquid insulation of transformers: Emerging trends and challenges

The rise in transmission voltages levels, the demand for insulating reliability of the transformer is getting more and more critical. The mineral oil (MO) together with paper is the main insulation constituents in oil-immersed transformers. To enhance the insulation level of ultra-high voltage (UHV) transformers and to decrease its weight and size, it is highly required to increase the insulating conduct of transformer oil (TO) and oil-impregnated cellulose. Lately, a distinctive novel venture of application of nanotechnology with liquid insulation of transformer has been conducted and the results have displayed marvelous enhancement in the insulation properties of transformer oil. The transformer oil-based nanofluids research domain (i.e., NFs) has been attracting huge attention during recent years both in theoretical and practical fields. NFs may be applied as a potential substitute for MO in the near future. To recognize various brunts of NFs and show evolving developments and challenges, the study demonstrates a scientometric review established on 210 published features from 2004 to 2019 through co-author, co-occurring and co-citation investigations. The significance of the editorial lies in compiling former inquiries, categorizing research nature, motivations and forecasting impending research orientations. Lastly, some recommendations for future NFs research and application are suggested.

Modular approach to multi-objective environmental optimization of buildings

The application of heuristic algorithms with life cycle assessment (LCA) is a promising approach to efficiently optimize the building and minimize the environmental impact even in a very large design space. In this paper, a modular parametric optimization framework combining advanced building modelling, LCA, energy calculation and single- and multi-objective environmental optimization was developed and applied to a multi-apartment house in Hungary. The variables comprise geometry, envelope, fixtures, as well as the heating energy source. The objective is the life cycle environmental impact expressed in terms of the six most common LCA indicators. The results show that a relatively compact shape, large windows to south equipped with shading and very high levels of insulation are optimal from an environmental perspective. It was also proven that focusing only on the embodied or operational impact leads to a suboptimal solution, and the choice of the energy source for the operation of the building has a significant influence on the achievable optimum. Through the optimization, significant environmental savings of 60–80% were achieved compared to the initial design options showing the potential for the application of such methods in architectural design.

Environmental impacts of housing conditions and manure management in European pig production systems through a life cycle perspective: A case study in Denmark

The potential of modifications in the housing conditions and manure management to reduce the environmental impact of a European pig production system were evaluated. The study was carried out using a cradle-to-farm gate life cycle assessment (LCA), with a functional unit of 1 kg of live weight pig at farm gate. The study used Danish pig systems as a case in point, with data provided by the Danish Pig Research Centre (SEGES).Potential environmental impact hotspots at pig housing and manure management were identified through a local sensitivity analysis. A set of pig housing and manure management alternative scenarios were analysed using parallel Monte Carlo simulations, to quantify interactions between these two components of the system. The manure management scenarios were slurry acidification, screw-press slurry separation and centralised anaerobic digestion of slurry. The pig housing scenarios were constructed around variations of the following factors: i) level of barn insulation, ii) in-barn temperature, iii) ventilation efficiency, iv) level of slurry dilution and v) frequency of slurry removal from barn pits.Anaerobic digestion significantly reduced the environmental impact for Non-Renewable Resource Use (−34.1% compared to baseline), Non-Renewable Energy Use (−40.1%) and Global Warming Potential (−9.20%). Slurry acidification led to significant reductions in Acidification (−28.1%) and Eutrophication Potential (−14.2%). Slurry separation significantly reduced only Non-Renewable Energy Use (−2.26%).The scenario analysis showed that the environmental performance of all manure management alternatives was affected by variations in all housing related factors, except for in-barn temperature. The largest improvement in environmental performance of the manure management component was achieved for Acidification Potential (−5.51%) by increasing the level of slurry dilution under baseline manure management conditions. Slurry acidification was the least sensitive manure management alternative to modifications in pig housing. Both manure management and housing conditions have the potential to reduce the environmental impact of pig systems in Europe.

Gas sensing mechanism of dissolved gases in transformer oil on Ag–MoS2 monolayer: A DFT study

Abstract Based on the density functional theory (DFT), the adsorption capabilities and electronic properties of Ag–MoS2 monolayer were discussed to fully discover the gas sensing performance to transformer oil decomposed gases (H2, CO, CH4, C2H6, C2H4 and C2H2). Specifically, the adsorption structure, adsorption energy, Mulliken charge analysis, deformation charge density, density of state (DOS), frontier molecular orbital analysis and band structure were explored. The analysis results illustrate that the adsorption to CO, C2H4 and C2H2 is strong, which is superior to the adsorption of H2, CH4 and C2H6. The narrower band gaps and increased electrical conductivity in all adsorption structures indicate that Ag–MoS2 monolayer is promising for the detection of studied gases. Therefore, the present study proposes an effective gas-sensing material to estimate the working state and insulation level of power transformers.

Residential buildings with heat pumps peak power reduction with high performance insulation

Revised EPBD directive has set ambitious targets for nearly zero energy buildings. In residential buildings, energy performance can be improved mainly by applying better insulation of building fabric and by efficient energy sources, i.e. heat pumps. Electricity use and peak powers will increase when heat pumps, both air to water and ground source heat pumps, are used for heat source in new residential buildings compared to heating solutions that do not use electricity. The purpose of this study was to determine how much the high performance thermal insulation can compensate the increase of electricity use and peak power caused by extensive application of heat pumps in Finland residential buildings. The present study used five residential buildings that describe residential newbuild market. Finnish regulation defines minimum insulation level and high performance insulation level which were applied to single family houses, terraced house and apartment buildings to simulate electric power values all year round. Hourly electrical power values were simulated with dynamic simulation software IDA ICE. Results show that electricity use and peak powers are rising significantly when heat pumps are used, but better insulation level significantly decreases or even fully compensates the amount of additional electric power. The results can be used for the assesment of implications of extensive use of heat pumps to power grid.