Determining overall heat transfer coefficient (U-Value) of wood-framed wall assemblies in Canada using external infrared thermography

Mahmoodzadeh, Milad; Gretka, Voytek; Eng., Hay, Katie, P.; Steele, Casey; Mukhopadhyaya, Phalguni

doi:10.1016/j.buildenv.2021.107897

Cited by 30 publications

(8 citation statements)

References 32 publications

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“…This leads to increased uncertainty in the determination in the surface-to-air temperature gradient, which is potentially transferred into increased uncertainty in the determination of the surface heat transfer coefficients. This is in line with the requirements and accuracies for IRT assessments identified in Lucchi (2018): Stable temperature gradients in the range of 3/U-value (European Committee for Standardization (CEN), 1998) (i) and deviations in the range of 10%-20% against heat-flux measured U-values (Albatici and Tonelli, 2010;Mahmoodzadeh et al, 2021).…”

Section: Introductionsupporting

confidence: 84%

Surface heat transfer coefficients in building envelopes: Uncertainty levels in experimental methods

Garay-Martinez

Arregi

Lumbreras

2023

Journal of Building Physics

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There are several research methods for the on-site assessment of U-values that aim to avoid the use of surface heat flux measurements and rely on tabulated or empirically developed correlations to define this parameter. This works performs a detailed process to estimate indoor surface heat transfer coefficients based on several experimental campaigns over building walls. Data is filtered out to remove periods with large temperature variations and/or unstable convective conditions due to HVAC. A statistical analysis is conducted, and the outcomes used to test the validity of U-value estimation approaches. The outcomes show that the actual surface heat transfer coefficients are in the range of reference works, but variations in the range of up to 2 W/m2 K are found. Uncertainty levels associated to the estimation of surface heat transfer coefficient are in the range 60% for instantaneous values while this is reduced down to 12%–20% for 8-h averages. Variations and uncertainty levels are higher for low temperature gradient situations, which are considered to be very likely for modern insulation levels. It is concluded that methods seeking to avoid the use of surface heat flux measurements need to develop much deeper knowledge in this field to gain accuracy and reliability.

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Section: Introductionsupporting

confidence: 84%

Surface heat transfer coefficients in building envelopes: Uncertainty levels in experimental methods

Garay-Martinez

Arregi

Lumbreras

2023

Journal of Building Physics

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“…where U-value is in W/ m 2 •K , thermal conductivity in W/(m•K), and thickness of samples is taken in meters. When considering U-values, a lower number is better; a lower U-value implies that a material transfers less heat and thus is a good insulator [43]. Table 4 shows the U-values of four insulation samples.…”

Section: Thermal Conductivity (K) and Diffusivity (α)mentioning

confidence: 99%

Date Palm Surface Fibers for Green Thermal Insulation

et al. 2022

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Some of the major challenges of the twenty-first century include the continued increase in energy consumption and environmental pollution. One approach to overcoming these challenges is to increase the use of waste materials and environmentally friendly manufacturing methods. The high energy consumption in the building sector contributes significantly to global climatic changes. Here, by using date palm surface fibers, a high-performance green insulation material was developed via a simple technique that did not rely on any toxic ingredients. Polyvinyl alcohol (PVA) was used as a binding agent. Four insulation samples were made, each with a different density within the range of 203 to 254 kg/m3. Thermal conductivity and thermal diffusivity values for these four green insulators were 0.038–0.051 and 0.137–0.147 mm2/s, respectively. Thermal transmittance (U−value) of the four insulation composites was between 3.8–5.1 , which was in good comparison to other insulators of similar thickness. Thermogravimetric analysis (TGA) showed that insulating sample have excellent thermal stability, with an initial degradation temperature of 282 °C, at which just 6% of its original weight is lost. Activation energy () analysis revealed the fire-retardancy and weakened combustion characteristics for the prepared insulation composite. According to differential scanning calorimetry (DSC) measurements, the insulating sample has a melting point of 225 °C, which is extremely close to the melting point of the binder. The fiber-based insulating material’s composition was confirmed by using Fourier transform infrared spectroscopy (FTIR). The ultimate tensile range of the insulation material is 6.9–10 MPa, being a reasonable range. Our study’s findings suggest that developing insulation materials from date palm waste is a promising technique for developing green and low-cost alternatives to petroleum-based high-cost and toxic insulating materials. These insulation composites can be installed in building envelopes during construction.

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“…Concerning our drone image data, it should be noted that all images include vignetting. The vignetting effect is a shadowing toward the edge of an image which falsely signals a higher intensity in the image's central region [25]. This is caused primarily by the camera itself.…”

Section: Discussionmentioning

confidence: 99%

Comparison of building thermography approaches using terrestrial and aerial thermographic images

Mayer

Epperlein

Volk

et al. 2022

IOP Conf. Ser.: Earth Environ. Sci.

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Thermography is commonly used for auditing buildings. Classical manual terrestrial thermography records images of individual buildings at a short distance. When auditing a large number of buildings (e.g. whole city districts) this approach reaches its limits. Using drones with thermographic cameras allows images to be recorded automatically from different angles, with faster speed and without violating property rights. However, an airborne camera has a significantly greater distance and more varied angles to a building compared to terrestrial thermography. To investigate the influence of these factors for building auditing, we perform a study evaluating seven different drone settings of varying flight speed, angle, and altitude. A comparison is drawn to manually recorded terrestrial thermographic images. While we find that a flight speed between 1m/s and 3m/s does not influence the thermographic quality, high flight altitudes and steep viewing angles lead to a significant reduction of visible details, contrast, and to falsified temperatures. A flight altitude of 12m over buildings is found to be the most suitable for the qualitative and quantitative analysis of rooftops and a qualitative analysis of façades. A flight altitude of 42m over buildings can only be used for qualitative audits with little detail.

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Determining overall heat transfer coefficient (U-Value) of wood-framed wall assemblies in Canada using external infrared thermography

Cited by 30 publications

References 32 publications

Surface heat transfer coefficients in building envelopes: Uncertainty levels in experimental methods

Surface heat transfer coefficients in building envelopes: Uncertainty levels in experimental methods

Date Palm Surface Fibers for Green Thermal Insulation

Comparison of building thermography approaches using terrestrial and aerial thermographic images

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