Laser-Scanning-Based Method for Estimating the Distribution of the Convective-Heat-Transfer Coefficient on Full-Scale Bu
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Laser-Scanning-Based Method for Estimating the Distribution of the Convective-Heat-Transfer Coefficient on Full-Scale Building Walls Tomoki Kiyono1 · Takashi Asawa2 · Haruki Oshio1 Received: 29 January 2020 / Accepted: 7 October 2020 © Springer Nature B.V. 2020
Abstract We propose a method for estimating the convective-heat-transfer coefficient (CHTC) distribution on building walls by using the water-evaporation method involving filter paper and three-dimensional laser scanning, and demonstrates consistency with the gravimetric evaporation method. The theory and method are established based on the convective heat- and mass-transfer analogy and a near-infrared laser-scanning system. The equations to remotely estimate the CHTC distribution are obtained empirically, and the proposed method is applied to the walls of a penthouse during winter. The spatial distribution of the surface reflection intensity that determines the evaporation rate is successfully retrieved with 0.2–0.3% accuracy from a measurement distance of 5 m. The comparison of evaporation rates with a gravimetric measurement does not show a statistically significant bias. The results show that the crucial factors for the precision of the CHTC estimation are errors in the laser-scanning system and their amplification when dividing the evaporation rate by the vapour pressure deficit to obtain the convective-mass-transfer coefficient. The estimated CHTC distributions on the target walls have approximately ≤ 2–3 W m−2 K−1 errors in the 95% confidence interval after applying spatial and/or temporal averaging. Although the error in the convective-heattransfer coefficient is larger in winter during minimal vapour pressure deficits, it is generally well explained in the range of the random error in laser scanning. The correlation between the spatially-averaged convective-heat-transfer coefficient and near-wall wind speed is comparable to existing methods (R 0.71–0.79), and the regression relation agrees with that obtained in previous studies performed in similar conditions. Keywords Building wall · Convective-heat-transfer coefficient · Heat- and mass-transfer analogy · Laser scanning
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Takashi Asawa [email protected]
1
Centre for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba-shi, Ibaraki 305-8506, Japan
2
Department of Architecture and Building Engineering, School of Environment and Society, Tokyo Institute of Technology, 4259 Nagatsuda-cho, Midori-ku, Yokohama 226-8502, Japan
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T. Kiyono et al.
1 Introduction The convective-heat-transfer coefficient (CHTC) is a primary parameter in building-energy simulations and urban-canopy models for atmospheric study. It is also a necessary parameter for street-level computational fluid dynamics (CFD) for the evaluation of human thermal comfort. Although it is important to determine the general characteristics of the CHTC distribution on urban surfaces, they have not been clarified sufficiently. The Nusselt–Jürges type model (Nusselt and Jürges 1922
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