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NIRE Annual Report
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 1999

Development of a Snow-Melting System Which Utilizes Thermal Functions of the Ground

Geo-Energy Division
Geotechnology Department
Objectives
The ground has thermal functions such as heat source, heat sink and heat storage body. The purpose of this study is to develop technologies for utilization of the thermal functions for space heating and/or space cooling, indoor swimming pool, melting snow on roads and so on.
In northern part of Japanese Islands, snow-melting equipment that utilize electric heating cables or boilers burning kerosene or natural gas have been used for melting snow and increasing its number. These systems not only consume large volumes of fossil fuels but also produce carbon dioxide.
At first, we have developed the Gaia Snow-Melting System that utilizes the ground as a heat source and as a heat storage body. This snow-melting system consists of downhole heat exchangers, a heat pump and heating tubes embedded in the pavement. The Downhole Coaxial Heat Exchangers (DCHEs) developed by us are used for efficient heat extraction.
Results
The main heat source of the system is the geothermal heat contained in the ground and the auxiliary source is summer-time solar heat. In winter, heat extracted from the ground with DCHEs is transferred to the heat pump. After increasing its temperature with the heat pump, the thermal energy is transmitted to a heating medium circulating through a network of heating tubes for melting snow. In summer, heat is recovered from the hot pavement heated by the sun, and stored in the ground.
The first Gaia Snow-Melting System was installed in Ninohe, Iwate Prefecture, and has been operating since December 1995. The area covered by the snow-melting system is 266 m2. Three DCHEs, each 8.9 cm in outer diameter and 150 m deep, and a heat pump driven by a 15 kW electric motor are used. The heat supplied to heating tubes is approximately 50 kW.
Operational performance of the snow-melting system in FY1996 was as follows : Coefficients of performance (COP) were 4.2 for the heat pump and 3.6 for the whole system. The Gaia's annual electric power consumption per unit area was only 18 % that of the electric heating cable systems in the city. This means that more than 80% of carbon dioxide can be eliminated by replacing electric heating cable systems with the Gaia systems. Average heat extraction rate per unit length of the DCHEs was about 83W/m.
Fig.1. Concept of the Gaia Snow-Melting System
Fig.1. Concept of the Gaia Snow-Melting System

Fig.2. Snow melting condition
Fig.2. Snow melting condition

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