scholarly journals Development of Psi Factors for Thermal Bypass Due to Insulation Gaps in Low-Slope Roofing Assemblies

Buildings ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 68
Author(s):  
Sudhakar Molleti ◽  
David van Reenen
Keyword(s):  
Research Study ◽  
Measured Data ◽  
Dimensional Changes ◽  
Thermal Transmittance ◽  
Average Decrease ◽  
R Value ◽  
Thermal Bridging ◽  
Gap Height ◽  
Roof Design ◽  
Gap Width

In commercial roofs, the presence or formation of gaps could be due to improper installation, thermal expansion, and dimensional changes in the insulation boards. The heat loss from these gaps could lead to higher thermal transmittance in the roof assembly. The current research study conducted around 70 experiments to investigate the effect of gap height, gap width and gap offset on the thermal transmittance of the roofing assembly. The measured data showed that in a staggered insulation layout with a joint offset of 610 mm (24 in), formation of 6.4 mm (1/4 in) to 12.7 mm (1/2 in) gaps at the insulation joints could contribute to an average decrease of 2% to 9% in the effective R-value of the roof assembly. As the insulation thermal resistance increases or becomes thicker, the thermal losses in the roof assembly increase. Generalized gap impact curves were developed to provide the relation between gap parameters (i.e., gap widths and height) and the thermal performance of the roof assembly. The experimental data were further analyzed using the psi factor approach of linear thermal bridging generating thermal transmittance data to support the calculation of thermal bypass from gaps in the thermal roof design.

scholarly journals Thermal bridge effect of vertical diagonal tie connectors in precast concrete sandwich panels: an experimental and computational study

2020 ◽  
Vol 172 ◽  
pp. 08001
Author(s):  
Paul Klõšeiko ◽  
Reimo Piir ◽  
Marti Jeltsov ◽  
Targo Kalamees
Keyword(s):  
Computational Study ◽  
Precast Concrete ◽  
Sandwich Panels ◽  
Building Envelope ◽  
Heat Fluxes ◽  
Air Cavity ◽  
Thermal Transmittance ◽  
Thermal Bridge ◽  
Thermal Bridging ◽  
Air Cavities

The purpose of this work was to quantify the thermal bridge effect of vertical diagonal tie connectors in precast concrete sandwich panels (PCSPs). Special interest was in cases where the use of rigid insulation (e.g. PIR) would leave air gaps between insulation boards and diagonal ties, thus intensifying the thermal bridge. A climate chamber experiment using 5 different joint types was performed to gather reference data for CFD model validation. In the experiment, natural convection was observed in joints where no additional insulation was used, i.e. in air cavities. Significantly larger heat fluxes were measured in these cavities compared to insulated joints. The thermal bridging effect was evaluated for a typical PCSP (thermal transmittance without thermal bridges U = 0.11 W/(m²·K)) using CFD software taking into account 3D heat conduction and convection. Simulation results indicate that diagonal ties without adjacent air cavities increased the average thermal transmittance (U-value) of the envelope by 8%, diagonal ties with a 6 mm air cavity – 19...33% and diagonal ties with a 10 mm air cavity – 45...56%. In conclusion, it was found that the joints in insulation caused by diagonal ties affect the overall thermal performance of the building envelope significantly when efforts are not made to fill the air cavities around the connectors.

scholarly journals Analysis of Convergence Characteristics of Average Method Regulated by ISO 9869-1 for Evaluating In Situ Thermal Resistance and Thermal Transmittance of Opaque Exterior Walls

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1989 ◽  
Author(s):  
Doo Sung Choi ◽  
Myeong Jin Ko
Keyword(s):  
Thermal Resistance ◽  
Average Method ◽  
Test Duration ◽  
Test Environment ◽  
Building Envelopes ◽  
Thermal Transmittance ◽  
The Third ◽  
U Value ◽  
R Value

In the last few decades, an average method which is regulated by ISO 9869-1 has been used to evaluate the in situ thermal transmittance (U-value) and thermal resistance (R-value) of building envelopes obtained from onsite measurements and to verify the validity of newly proposed methods. Nevertheless, only a few studies have investigated the test duration required to obtain reliable results using this method and the convergence characteristics of the results. This study aims to evaluate the convergence characteristics of the in situ values analyzed using the average method. The criteria for determining convergence (i.e., end of the test) using the average method are very strict, mainly because of the third condition, which compares the deviation of two values derived from the first and last periods of the same duration. To shorten the test duration, environmental variables should be kept constant throughout the test or an appropriate period should be selected. The convergence of the in situ U-value and R-value is affected more by the length of the test duration than by the temperature difference if the test environment meets literature-recommended conditions. Furthermore, there is no difference between the use of the U-value and R-value in determining the end of the test.

Design and Validation of a New Test Rig for Brush Seal Testing Under Engine Relevant Conditions

2011 ◽  
Author(s):  
D. Pfefferle ◽  
K. Dullenkopf ◽  
H.-J. Bauer
Keyword(s):  
High Surface ◽  
Test Rig ◽  
Friction Forces ◽  
Brush Seal ◽  
Main Emphasis ◽  
Rotor Surface ◽  
Brush Seals ◽  
Gap Height ◽  
Radial Gap ◽  
Gap Width

Brush seals play an increasing role in turbomachinery due to their improved behavior towards leakage and their capability to compensate for gap variations caused by thermal expansion and rotor excursions. The flexible bristles of brush seals are able to endure short-term reductions in gap width without severe damage. Consequently the necessary gap between the rotor and brush seal can virtually be reduced to zero, leading to a considerable reduction in air leakage of up to 80 percent. However the reduced gap height increases the probability of rubbing between the bristle package and the rotor surface. The friction forces generated can cause an unwanted heat load on the rotor, bristles and leakage air. In addition, the surfaces involved are exposed to abrasion effects. Especially in the thin and lightweight rotor structures of aircraft engines, the additional heat impact can lead to a problematic level of material stress. To study these effects and to give reliable quantitative design rules, a versatile test rig for brush seals was designed and built. The simulation of seal behavior under relevant engine conditions is the main emphasis of this rig, including high pressure drop, leakage flow and high surface speed. The key feature is the possibility to vary the axis symmetric radial gap width during the test rig operation by up to a 0.5 mm overlap. The so caused rubbing induces a transient rotor temperature rise which is measured via a set of 12 thermocouples embedded in the rotor. These temperature readings can be used to calculate the brush seal heat impact on the rotor structure. Preliminary results with moderate differential pressure and rotor speed proved the functionality of the test rig and confirmed the global approach of the project.

scholarly journals Timber Framing Factor in Toronto Residential House Construction

2021 ◽  
Author(s):  
Rana Qusass
Keyword(s):  
Thermal Control ◽  
Building Envelope ◽  
Construction Sites ◽  
House Construction ◽  
Residential Units ◽  
Residential House ◽  
R Value ◽  
Thermal Bridging ◽  
Under Construction ◽  
The Impact

Achieving energy efficiency with thermal control in residential houses is crucial for the reduction in the energy consumption. Timber framing as the main structural component in the building envelope has a big influence on the effective R-value depending on the framing percentage, and this impacts the overall thermal performance of the building. This project, carried out in Canada, measured the typical framing percentages that are achieved in residential construction sites and compares them with code recommendations. It provides framing factors measured for 17 residential units under construction including detached, row-housing, and semi-detach dwelling units in three different locations in the Toronto area. Detailed on site measurements provide data for numerical calculation to evaluate the amount of framing within external walls, ceilings, and exposed floors. The overall framing factor calculated for each dwelling is found to exceed the recommended percentage by Canadian Model National Energy code for dwellings and ASHRAE Handbook- Fundamental. The research considers the impact that additional regular thermal bridging from the increased framing percentage will have on the effective R-value, and consequently, the impact on thermal effectiveness of the envelope leading to an increase in the overall energy above the expectations of the codes and standards.

Research on Amending the Energy Efficiency Provisions in the Building

2014 ◽  
Vol 568-570 ◽  
pp. 1991-1994
Author(s):  
Hai Hong Cui
Keyword(s):  
Energy Performance ◽  
Hot Water ◽  
Building Regulations ◽  
Thermal Transmittance ◽  
Energy Performance Of Buildings ◽  
Air Tightness ◽  
Thermal Bridging ◽  
Technical Basis ◽  
Fuel Costs

The purpose of this paper is to identify the main requirements of the Building Regulations Part L1A for new dwellings. An explanation of the technical basis for energy rating is given including how they are calculated, how fuel costs are used, the role of the standard occupancy pattern, and an appreciation of the Building Research Establishment Domestic Energy Model (BREDEM). The aims and requirements of the European Directive on the Energy performance of Buildings and its implementation for new and existing domestic buildings is also considered. Design/methodology/approach – The requirements of Part L1A of the Building Regulations are developed. These relate to the thermal properties of the building fabric including insulation, thermal bridging, air tightness and glazing, the efficiency and responsiveness of heating and hot water systems, ventilation and lighting. The methodology for calculating thermal transmittance coefficients (U-values) is also demonstrated.

Dynamic moisture sorption and hygroexpansion of Populus euramericana Cv. under two cyclic hygrothermal conditions

Holzforschung ◽  
2016 ◽  
Vol 70 (12) ◽  
pp. 1191-1199 ◽  
Author(s):  
Tiantian Yang ◽  
Erni Ma ◽  
Jianhui Zhang
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Environmental Conditions ◽  
Moisture Sorption ◽  
Longitudinal Direction ◽  
Measured Data ◽  
Populus Euramericana ◽  
Dimensional Changes ◽  
Unit Change ◽  
Condition B

Abstract Poplar (Populus euramericana Cv.) specimens, 20 mm in radial (r) and tangential (t) directions with thicknesses of 4 mm and 10 mm along the longitudinal direction, were subjected to cyclic environmental conditions, in the course of which the relative humidity (RH) changed sinusoidally between 75% and 45% at 20°C (condition A), or the temperature (T) was changed sinusoidally within 5–35°C at 60% RH (condition B). Moisture content (MC), as well as the t- and r-dimensional changes were measured as a response to the dynamic environmental conditions. The measured data also changed sinusoidally but they lagged behind the triggering original RH or T data. This effect was much higher under condition A than under condition B. The observed equivalent RH and T changes at different ΔMCs or Δts served for comparison of the responses to RH and T, and the former were less pronounced than the latter. MC and t-dimensional changes per unit change of RH were greater than those per unit change of T but still lower than static values. In summary, the effects of dynamic RH change are larger than those of T, especially concerning MC responses compared to dimensional changes.

scholarly journals Thermal resistance of masonry walls: a literature review on influence factors, evaluation, and improvement

2021 ◽  
pp. 174425912110095
Author(s):  
Maysoun Ismaiel ◽  
Yuxiang Chen ◽  
Carlos Cruz-Noguez ◽  
Mark Hagel
Keyword(s):  
Energy Consumption ◽  
Literature Review ◽  
Thermal Resistance ◽  
Influence Factors ◽  
Masonry Wall ◽  
Thermal Design ◽  
Masonry Walls ◽  
R Value ◽  
Thermal Bridging ◽  
Code Compliance

Increasing the thermal resistance of masonry wall systems is one of the effective ways to reduce energy consumption in the operation of masonry buildings. This increase is also demanded by newer, more stringent energy codes. However, the effective thermal resistance ( R-value) of masonry walls is affected by many factors, such as thermal bridging, which occurs in places where highly conductive structural components penetrate insulating materials. Thermal bridging is common when connecting masonry veneers to structural backup walls. Furthermore, quick and precise methods for estimating the R-value are needed for thermal design improvements and code-compliance calculations. This study presents a comprehensive literature review on key factors that influence the overall thermal performance of masonry walls, methods to effectively estimate and measure R-values, and improvements in thermal design. In addition to identifying the main technical and practical challenges and the corresponding progress made on each front, key design considerations, such as code compliance, material properties, insulation types, and location, as well as special ties and shelf angles types, are also discussed. This study summarizes critical information and recommendations that will help improve the thermal design of masonry walls, hence reducing the energy consumption of buildings.

scholarly journals Timber Framing Factor in Toronto Residential House Construction

2021 ◽  
Author(s):  
Rana Qusass
Keyword(s):  
Thermal Control ◽  
Building Envelope ◽  
Construction Sites ◽  
House Construction ◽  
Residential Units ◽  
Residential House ◽  
R Value ◽  
Thermal Bridging ◽  
Under Construction ◽  
The Impact

Achieving energy efficiency with thermal control in residential houses is crucial for the reduction in the energy consumption. Timber framing as the main structural component in the building envelope has a big influence on the effective R-value depending on the framing percentage, and this impacts the overall thermal performance of the building. This project, carried out in Canada, measured the typical framing percentages that are achieved in residential construction sites and compares them with code recommendations. It provides framing factors measured for 17 residential units under construction including detached, row-housing, and semi-detach dwelling units in three different locations in the Toronto area. Detailed on site measurements provide data for numerical calculation to evaluate the amount of framing within external walls, ceilings, and exposed floors. The overall framing factor calculated for each dwelling is found to exceed the recommended percentage by Canadian Model National Energy code for dwellings and ASHRAE Handbook- Fundamental. The research considers the impact that additional regular thermal bridging from the increased framing percentage will have on the effective R-value, and consequently, the impact on thermal effectiveness of the envelope leading to an increase in the overall energy above the expectations of the codes and standards.

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