Abstract

Heat transfer through building envelopes constitutes the dominant part of indoor cooling load in summer. Coating building external walls with high reflectivity materials proves to be an effective way to reduce heat gains from solar radiation and save cooling energy consumption accordingly. In this paper, the transient heat transfer model of building external envelopes is established and validated through experiment, to investigate the thermal performance of building walls coated with retro-reflective materials. Moreover, taking an office building in Chengdu as an illustrative example, the cooling energy saving potential of such retro-reflective material coated building is evaluated in summer. The experiment results show that for the building box with retro-reflective coating materials (r = 0.59), the average indoor air temperature is about 2.4℃ lower than the reference box without coating materials, resulted from decreasing heat absorption of solar radiation for external walls. Furthermore, the illustrative example in Chengdu shows the cooling load can be reduced by about 9.1 W/m2, with such retro-reflective coating materials for building external walls, saving 15.2% electricity consumption in a whole summer. The incremental investment for coating can be paid back by 9.1 years for the studied case. Moreover, economic analysis and comparison indicate that such coating material is more applicable to southern cities in China, since the payback period is shorter due to more cooling energy saving for those with hot summer. This work can provide guidance for practical building envelope thermal design.

Highlights

  • With the rapid modernization and urbanization over the recent two decades, global energy usage keeps growing dramatically with an average annual rate of over 10% (Douthwaite, 2002; Zhang et al, 2015)

  • Yes Total electricity consumption by chillers solar radiation heat gain in summer, retro-reflective coating material can be painted on the external surface of building walls

  • Box 1_calculate aforementioned retro-reflective coating material (r 1⁄4 0.59) and the two boxes are set under the same conditions

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Summary

Introduction

With the rapid modernization and urbanization over the recent two decades, global energy usage keeps growing dramatically with an average annual rate of over 10% (Douthwaite, 2002; Zhang et al, 2015). Keywords Solar radiation, heat transfer, building wall, coating material, cooling load Meng et al (2016, 2015) measured the indoor air temperature variations in the building coated with retro-reflective materials and explained the heat transfer mechanism for the walls.

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