Performance Evaluation of Low-Cost Infrared Thermal Imagers for Quantitative Surface Temperature Measurement in Building Enclosures
ObjectiveAccurate surface temperature measurement of building enclosures is crucial for determining thermal performance parameters and evaluating indoor thermal environments. While traditional contact-based temperature measurement methods are precise, they are invasive, time-consuming, and unsuitabl...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Editorial Department of Journal of Sichuan University (Engineering Science Edition)
2024-01-01
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| Series: | 工程科学与技术 |
| Subjects: | |
| Online Access: | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202400853 |
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| Summary: | ObjectiveAccurate surface temperature measurement of building enclosures is crucial for determining thermal performance parameters and evaluating indoor thermal environments. While traditional contact-based temperature measurement methods are precise, they are invasive, time-consuming, and unsuitable for fragile structures such as historical buildings. Infrared thermal imagers offer a non-contact, rapid alternative, but their accuracy is influenced by various factors, including emissivity, ambient temperature, the thermodynamic temperature of the measured object, relative humidity, wind speed, solar radiation, distance factor, atmospheric transmittance, and instrument parameter settings. Furthermore, infrared thermal imagers with high measurement accuracy are expensive, limiting their application in quantitative measurements. With the development of uncooled infrared thermal imaging technology, low-cost, compact consumer infrared thermal imagers are expected to see wide application. When using low-cost infrared thermal imagers for quantitative surface temperature measurement of walls indoors, how can we simplify the influencing factors of measurement errors to further reduce infrared temperature measurement errors? Does their measurement accuracy meet the minimum accuracy requirements for surface temperature measurement instruments specified in current standards? To address these issues, this study focuses on the effects of the thermodynamic temperature of the measured object, instrument emissivity settings, and ambient temperature compensation, and explores how these factors influence the measurement accuracy of low-cost infrared thermal imagers. The applicability of simplified on-site measurement methods for surface emissivity and ambient temperature was experimentally tested and analyzed. This study provides solutions and recommendations for achieving low-cost, non-contact, quantitative temperature measurements in field surveys.MethodsThis experimental study was conducted in an artificial climate chamber, setting four environmental conditions: two with uniform temperature distributions and two with non-uniform temperature distributions, resulting in a total of 2200 infrared thermal images. The key variables investigated included wall surface thermodynamic temperature, emissivity settings of the instrument, and ambient temperature compensation. A simplified on-site method for measuring surface emissivity and ambient temperature was tested using the reflected temperature compensation method and infrared thermometry principles. The performance of a low-cost smartphone-connected infrared thermal imager (Fluke TC01A) was compared to reference measurements obtained using contact thermocouples. The measurement accuracy was assessed by comparing the infrared temperature values with the reference values, and measurement errors were calculated.Results and Discussion The results showed that the accuracy of the low-cost infrared thermal imager was significantly influenced by the interaction between the wall surface thermodynamic temperature, emissivity settings, and ambient temperature compensation. In uniform environments, the measurement errors were minimized when the emissivity setting was close to the actual surface emissivity (0.95). However, in non-uniform environments, the temperature difference between the wall surface and the surrounding environment increased the measurement error, especially when the emissivity setting was low. The reflected temperature compensation method effectively determined the ambient temperature in both uniform and non-uniform environments, providing a reliable input for infrared imager calibration. When the emissivity setting closely matched the actual surface emissivity and the ambient temperature was accurately compensated, the infrared temperature measurement error was minimized to -0.13±0.33 ℃. This performance met the minimum accuracy requirements specified in China's Evaluation Standard for Indoor Thermal Environment in Civil Buildings (±1 ℃) and aligned with the ideal requirements set by ISO 7726 for surface temperature measurement devices. The study also found that the simplified methods for measuring emissivity and ambient temperature were applicable, particularly in non-uniform environments, and effectively reduced infrared measurement errors. The research demonstrates that low-cost infrared thermal imagers, when properly calibrated, can be used for non-contact quantitative surface temperature measurement in building environments. However, further investigation into the effects of other factors such as measurement distance, angle, and dynamic environmental conditions is needed to improve the reliability and accuracy of these devices in real-world applications.ConclusionsIn conclusion, this study shows that low-cost infrared thermal imagers, when properly calibrated, can effectively be used for non-contact, quantitative surface temperature measurement in building environments. The accuracy of infrared temperature measurements is significantly influenced by the thermodynamic temperature of the surface, the emissivity setting, and ambient temperature compensation. By adjusting the emissivity to match the actual surface emissivity and accurately compensating for ambient temperature, infrared thermal imagers can achieve measurement errors within the ±1 ℃ accuracy requirement specified by China's Evaluation Standard for Indoor Thermal Environment in Civil Buildings. These results also align with the ideal performance requirements set by ISO 7726 for surface temperature measurement devices. The simplified methods for measuring emissivity and ambient temperature, particularly using the reflected temperature compensation technique, were shown to be effective and applicable, especially in non-uniform environments, further reducing measurement errors. This research provides valuable insights into the application of low-cost thermal imagers in building diagnostics, energy assessments, and thermal comfort studies. |
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| ISSN: | 2096-3246 |