scholarly journals Hygrothermal Behaviour of Ventilation Cavities in Highly Insulated Envelopes

2020 ◽  
Vol 172 ◽  
pp. 07003
Author(s):  
Klaus Viljanen ◽  
Xiaoshu Lü ◽  
Jari Puttonen
Keyword(s):  
Heat Flux ◽  
Relative Humidity ◽  
Experimental Studies ◽  
Thermal Transmittance ◽  
The Future ◽  
U Value ◽  
Hygrothermal Behaviour

This article presents long-term experimental studies on the moisture safety in the ventilation cavities of highly insulated (HI) structures. The tested HI-walls had thermal transmittances of 0.11-0.13 W/m2K. A wall with a thermal transmittance of 0.23 W/m2K represented the baseline wall in the test. In addition to walls, an HI-roof of a newly built house with a U-value of 0.08 W/m2K was measured. The results indicate that, in the ventilation cavity, the relative humidity of an HI-wall exceeds 1-7% of the humidity measured from the baseline wall during winter, which coincides with the 0.4-1.5ºC lower temperatures observed in the HI-walls. The mold risk in the ventilation cavities of the walls is low, as the value of the mold index (MI) remains below one, which indicates small amounts of microscopic mold only on surfaces. However, at the bottom of the cavity, the MI value reaches 1.4 due to lower temperatures. In the HI-roof, the MI values are between 1.0 and 2.0 in the middle of the cavity in winter. The reasons for the higher mold risk of the roof are the humid weather, the built-in moisture of the roof and the low heat flux from inside. The study confirms that, in the future, warmer weather and increased humidity can increase moisture risks in the ventilation cavities. The results support the use of materials that are more resistant to mold in the outer parts of structures.

scholarly journals Comparison of Infrared Thermography and Heat Flux Method for Dynamic Thermal Transmittance Determination

Buildings ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 132 ◽  
Author(s):  
Mergim Gaši ◽  
Bojan Milovanović ◽  
Sanjin Gumbarević
Keyword(s):  
Heat Flux ◽  
Infrared Thermography ◽  
Dynamic Method ◽  
Flux Method ◽  
Microsoft Excel ◽  
Experimental Procedure ◽  
Thermal Transmittance ◽  
U Value ◽  
Stationary Heat Transfer

This paper proposes an alternative experimental procedure that uses infrared thermography (IRT) for measuring the surface temperature of building elements, through which it is possible to approximate the thermal transmittance or the U-value. The literature review showed that all authors used similar procedures that require semi-stationary heat transfer conditions, which, in most cases, could not be achieved. The dynamic and the average methods that are given in ISO 9869 were also used with the IRT and the heat flux method (HFM). The dynamic method (DYNM) shows a higher level of accuracy compared to the average method (AVGM). Since the algorithm of the DYNM is more complicated than that of the AVGM, Microsoft Excel VBA was used to implement the algorithm of the DYNM. Using the procedure given in this paper, the U-value could be approximated within 0–30% of the design U-value. The use of IRT, in combination with the DYNM, could be used in-situ since the DYNM does not require stable boundary conditions. Furthermore, the procedure given in this paper could be used for relatively fast and inexpensive U-value approximation without the use of expensive equipment (e.g., heat flux sensors).

scholarly journals Thermal transmittance prediction based on the application of artificial neural networks on heat flux method results

2021 ◽  
Vol 2069 (1) ◽  
pp. 012152
Author(s):  
S. Gumbarević ◽  
B. Milovanović ◽  
M. Gaai ◽  
M. Bagarić
Keyword(s):  
Heat Flux ◽  
Short Term Memory ◽  
Heat Flux Sensor ◽  
Flux Method ◽  
Short Term ◽  
Term Memory ◽  
Thermal Transmittance ◽  
U Value ◽  
Long Short Term Memory ◽  
Artificial Neural

Abstract Deep energy renovation of building stock came more into focus in the European Union due to energy efficiency related directives. Many buildings that must undergo deep energy renovation are old and may lack design/renovation documentation, or possible degradation of materials might have occurred in building elements over time. Thermal transmittance (i.e. U-value) is one of the most important parameters for determining the transmission heat losses through building envelope elements. It depends on the thickness and thermal properties of all the materials that form a building element. In-situ U-value can be determined by ISO 9869-1 standard (Heat Flux Method - HFM). Still, measurement duration is one of the reasons why HFM is not widely used in field testing before the renovation design process commences. This paper analyzes the possibility of reducing the measurement time by conducting parallel measurements with one heat-flux sensor. This parallelization could be achieved by applying a specific class of the Artificial Neural Network (ANN) on HFM results to predict unknown heat flux based on collected interior and exterior air temperatures. After the satisfying prediction is achieved, HFM sensor can be relocated to another measuring location. Paper shows a comparison of four ANN cases applied to HFM results for a measurement held on one multi-layer wall – multilayer perceptron with three neurons in one hidden layer, long short-term memory with 100 units, gated recurrent unit with 100 units and combination of 50 long short-term memory units and 50 gated recurrent units. The analysis gave promising results in term of predicting the heat flux rate based on the two input temperatures. Additional analysis on another wall showed possible limitations of the method that serves as a direction for further research on this topic.

Strong effect of relative humidity on dryland lichens under climate change

2021 ◽  
Author(s):  
Philipp Porada ◽  
Selina Baldauf ◽  
Jose Raggio ◽  
Fernando Maestre ◽  
Britta Tietjen
Keyword(s):  
Climate Change ◽  
Relative Humidity ◽  
Experimental Studies ◽  
Early Morning ◽  
Ecosystem Functions ◽  
Lichen Cover ◽  
Key Factor ◽  
Underlying Mechanisms ◽  
Experimental Findings

<p>Manipulative experiments typically show a decrease in dryland biocrust cover and altered species composition under climate change. Biocrust-forming lichens, such as the globally distributed <em>Diploschistes diacapsis</em>, are particularly affected and show a decrease in cover with simulated climate change. However, the underlying mechanisms are not fully understood, and long-term interacting effects of different drivers are largely unknown due to the short-term nature of the experimental studies conducted so far. We addressed this gap and successfully parameterised a process-based model for <em>D. diacapsis</em> to quantify how changing atmospheric CO<sub>2</sub> , temperature, rainfall amount and relative humidity affect its photosynthetic activity and cover. We also mimicked a long-term manipulative climate change experiment to understand the mechanisms underlying observed patterns in the field. The model reproduced observed experimental findings: warming reduced lichen cover, whereas less rainfall had no effect on lichen performance. This warming effect was caused by the associated decrease in relative humidity and non-rainfall water inputs, which are major water sources for biocrust-forming lichens. Warming alone, however, increased cover because higher temperatures promoted photosynthesis during early morning hours with high lichen activity. When combined, climate variables showed non-additive effects on lichen cover, and effects of increased CO<sub>2</sub> levelled off with decreasing levels of relative humidity. Our results show that a decrease in relative humidity, rather than an increase in temperature, may be the key factor for the survival of the lichen <em>D. diacapsis</em> under climate change and that effects of increased CO<sub>2</sub> levels might be offset by a reduction in non-rainfall water inputs in the future. Because of a global trend towards warmer and drier air and the widespread global distribution of <em>D. diacapsis</em>, this will affect lichen-dominated dryland biocrust communities and their role in regulating ecosystem functions worldwide.</p>

scholarly journals Effect of Cavity Vacuum Pressure Diminution on Thermal Performance of Triple Vacuum Glazing

2018 ◽  
Author(s):  
Saim Memon ◽  
Farukh Farukh ◽  
Karthikeyan Kandan
Keyword(s):  
Element Model ◽  
Vacuum Pressure ◽  
Cavity Pressure ◽  
Existing Buildings ◽  
Zero Energy ◽  
Mathematical Methods ◽  
Thermal Transmittance ◽  
U Value ◽  
Vacuum Glazing

Long-term durability of the vacuum edge-seal plays a significant part in retrofitting triple vacuum glazing (TVG) to existing buildings in achieving towards zero-energy buildings (ZEB) target. Vacuum pressure decrement with respect to time between panes affect the thermal efficiency of TVG. This study reports a 3D finite element model, with validated mathematical methods and comparison, for the assessment of the influence of vacuum pressure diminution on the thermal transmittance (U value) of TVG. The centre-of-pane and total U values of TVG calculated to be 0.28 Wm−2K−1 and 0.94 Wm−2K−1 at the cavity vacuum pressure of 0.001 Pa. The results suggests that a rise in cavity pressure from 0.001 Pa to 100 kPa increases the centre-of-pane and total U values from 0.28 Wm−2K−1 and 0.94 Wm−2K−1 to 2.4 Wm−2K−1 and 2.58 Wm−2K−1, respectively. The temperature descent on the surfaces of TVG between hot and cold sides’ increases by decreasing the cavity vacuum pressure from 50 kPa to 0.001 Pa. To maintain the cavity vacuum pressure of 0.001 Pa for over 20 years of life span in the cavity of 10 mm wide edge sealed triple vacuum glazing, non-evaporable getters will maintain the cavity vacuum pressure that will enable the long-term durability to TVG.

Masonry: the brittle or plastic material?

2019 ◽  
pp. 22-28
Keyword(s):  
Plastic Material ◽  
Experimental Studies ◽  
Point Of View ◽  
Plastic Properties ◽  
Plastic Deformations ◽  
Base Materials ◽  
Stress States ◽  
Creep Deformations ◽  
Structural Point

The results of experimental studies of masonry on the action of dynamic and static (short-term and long-term) loads are presented. The possibility of plastic deformations in the masonry is analyzed for different types of force effects. The falsity of the proposed approach to the estimation of the coefficient of plasticity of masonry, taking into account the ratio of elastic and total deformations of the masonry is noted. The study of the works of Soviet scientists revealed that the masonry under the action of seismic loads refers to brittle materials in the complete absence of plastic properties in it in the process of instantaneous application of forces. For the cases of uniaxial and plane stress states of the masonry, data on the coefficient of plasticity obtained from the experiment are presented. On the basis of experimental studies the influence of the strength of the so-called base materials (brick, mortar) on the bearing capacity of the masonry, regardless of the nature of the application of forces and the type of its stress state, is noted. The analysis of works of prof. S. V. Polyakov makes it possible to draw a conclusion that at the long application of the load, characteristic for the masonry are not plastic deformations, but creep deformations. It is shown that the proposals of some authors on the need to reduce the level of adhesion of the mortar to the brick for the masonry erected in earthquake-prone regions in order to improve its plastic properties are erroneous both from the structural point of view and from the point of view of ensuring the seismic resistance of structures. It is noted that the proposal to assess the plasticity of the masonry of ceramic brick walls and large-format ceramic stone with a voidness of more than 20% is incorrect, and does not meet the work of the masonry of hollow material. On the basis of the analysis of a large number of research works it is concluded about the fragile work of masonry.

Improvement Of Curvilinear Diagrams Of Concrete Deformation

2019 ◽  
pp. 99-104
Keyword(s):  
Reinforced Concrete ◽  
Peak Load ◽  
Experimental Studies ◽  
Concrete Structures ◽  
Deformation Model ◽  
Reinforced Concrete Structures ◽  
Significant Difference ◽  
Deformation Diagrams

Problems when calculating reinforced concrete structures based on the concrete deformation under compression diagram, which is presented both in Russian and foreign regulatory documents on the design of concrete and reinforced concrete structures are considered. The correctness of their compliance for all classes of concrete remains very approximate, especially a significant difference occurs when using Euronorm due to the different shape and sizes of the samples. At present, there are no methodical recommendations for determining the ultimate relative deformations of concrete under axial compression and the construction of curvilinear deformation diagrams, which leads to limited experimental data and, as a result, does not make it possible to enter more detailed ultimate strain values into domestic standards. The results of experimental studies to determine the ultimate relative deformations of concrete under compression for different classes of concrete, which allowed to make analytical dependences for the evaluation of the ultimate relative deformations and description of curvilinear deformation diagrams, are presented. The article discusses various options for using the deformation model to assess the stress-strain state of the structure, it is concluded that it is necessary to use not only the finite values of the ultimate deformations, but also their intermediate values. This requires reliable diagrams "s–e” for all classes of concrete. The difficulties of measuring deformations in concrete subjected to peak load, corresponding to the prismatic strength, as well as main cracks that appeared under conditions of long-term step loading are highlighted. Variants of more accurate measurements are proposed. Development and implementation of the new standard GOST "Concretes. Methods for determination of complete diagrams" on the basis of the developed method for obtaining complete diagrams of concrete deformation under compression for the evaluation of ultimate deformability of concrete under compression are necessary.

DIGITALIZATION OF LABOR MIGRATION PROCESSES IN UZBEKISTAN. WORLD EXPERIENCE

2020 ◽  
Vol 4 (3) ◽  
pp. 29-39
Author(s):  
Sulkhiya Gazieva ◽  
Keyword(s):  
Labor Market ◽  
Technological Change ◽  
Labor Migration ◽  
Smart Phone ◽  
Logic Circuits ◽  
Digital Logic ◽  
The Internet ◽  
The Future

The future of labor market depends upon several factors, long-term innovation and the demographic developments. However, one of the main drivers of technological change in the future is digitalization and central to this development is the production and use of digital logic circuits and its derived technologies, including the computer,the smart phone and the Internet. Especially, smart automation will perhaps not cause e.g.regarding industries, occupations, skills, tasks and duties

Der Wald-Wild-Konflikt – was kann die Forstökonomie zur Lösung beitragen? (Essay)

2017 ◽  
Vol 168 (4) ◽  
pp. 181-185
Author(s):  
Marc Hanewinkel
Keyword(s):  
Forest Economics ◽  
Production Risk ◽  
Damage Compensation ◽  
Land Expectation Value ◽  
Compensation Methods ◽  
The Future ◽  
Single Tree Selection ◽  
Simplifying Assumptions ◽  
Forest Enterprises

The forest-game conflict – how can forest economics contribute to solve it? (Essay) Core parameters of forest economics such as land expectation value or highest revenue show that damage caused by wild ungulates can critically influence the economic success of forest enterprises. When assessing and evaluating the damage in order to calculate damage compensation, methods are applied in Germany that look either into the past (“cost value methods”) or into the future (“expected value methods”). The manifold uncertainties related to this evaluation over long-term production periods are taken into account within a framework of conventions through strongly simplifying assumptions. Only lately, the increased production risk due to game-induced loss of species diversity is also considered. Additional aspects that should be taken into account in the future are the loss of climate-adapted species, the change of the insurance values of forest ecosystems and the impossibility of specific management systems such as single-tree selection forestry due to the influence of game. Because of high transaction costs when assessing the damage, financial compensation should only be the “ultimate measure” and a meditation between stakeholder groups with the goal to find a cooperative solution before the damage occurs should be preferred.

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