Paying attention to the shallow ground heat inside a tunnel, a Horizontal U-Tube (HUT) road heating system was introduced for the first time in Japan in order to prevent winter traffic accidents associated with road freezing at the west side mouth of Nanaori-Toge tunnel, Aizu-bange, Fukushima Prefecture. Horizontal U-tubes were buried at a depth of 1.2 m in the ground of the central part of the tunnel. The ground heat extracted by the HUT is injected into the anti-freezing pavement at the tunnel mouth.
In this study, attempts were made to propose a simplified heat transfer model of HUT system. The proposed model consists of the energy balance equations of the fluid circulating in the HUT and the surrounding ground. Solving these two equations simultaneously, the extracted ground heat could be calculated as well as the fluid and ground temperatures. The model could also lead the overall heat transfer coefficient between the fluid and the surrounding ground. The validity of the model was accepted from the comparison with indoor experimental results using a miniature HUT.

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