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In Taiwan, light gauge steel buildings are employed for a multitude of purposes; for instance, large light gauge steel buildings are used to house factories and workshops and small light gauge steel buildings are used as pre-fabricated housing units or restructured cargo containers. Thermal insulation is provided through reflection, isolation, and heat dispersion. However, after a long period of use and lack of repair & maintenance, the heat insulation layer gradually loses its initial heat insulation efficiency and the crude roofing insulation of these structures results in overheated interiors. This paper aims to find the best method for ensuring the outer roof heat insulation efficiency for the light gauge steel buildings, thereby maintaining comfortable indoor thermal environment. The paper conducted an indoor thermal environment experiment on a small light gauge steel building. In the experiment, a comparison between outer roof heat insulation and inner roof heat insulation was implemented to see the heat insulation improvement. Four types of materials were used in the procedure. For the outer roof heat insulation, black shade nets and white insulation paint were applied; for the inner roof heat insulation, fine air bubble heat insulation sheets and coarse air bubble heat insulation sheets were used.
An analysis of the experiment revealed that the respective heat insulating methods had similar average semi-outdoor temperatures. The outer roof heat insulation has been more efficient in reducing direct penetration of heat into the interior; furthermore, it’s noted that the white insulation paint had a significant time lag effect of two hours at a smaller level of heat flux. Each heat insulation material had an average radiation temperature difference of merely 1.9℃ during day. As for the slope of the indoor vertical temperature fluctuation trend line from roof to floor in the daytime, the greatest slope, 0.0094, was noted under the fine air bubble heat insulation sheet. A comparison between the temperature at a 170-cm height and the temperature beneath the ceiling showed a temperature difference of 0.4℃ for each material. It is apparent that the average radiation temperatures and vertical temperature fluctuations of the respective insulation materials have similar effect on the indoor thermal environment. Furthermore, according to the psychrometric chart, the indoor environments under the foregoing insulation materials are outside the range of summer season thermal comfort of the ASHRAE Standard 55.
Experiment findings revealed that the efficiency of the outer roof heat insulation applied on the small light gauge steel buildings is better and more capable of reducing direct penetration of heat into the interior. Moreover, the white insulation paint has a significant time lag effect at a smaller level of heat flux, thus effectively reducing penetration of heat into the interior. Thus in the future, it is imperative to make indoor floor-to-ceiling distance and proper ventilation the priority consideration when designing the light gauge steel buildings, and to coat white insulation paint or apply other insulation materials on the exterior roof before constructing and installing the roof in order to make sure a comfort indoor thermal environment.
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