Summary
This paper presents methods newly developed in Japan for snow melting and de-icing, using a long flexible corrugated heat pipe. Use of these methods is rapidly expanding.
Poles for telephone or power lines in snowy areas in Japan have frequently been damaged by winter snow. Heavy snowfall imposes a settlement force on poles and a tension force on support wires. To prevent snow damage to the poles, a flexible corrugated heat pipe, 4 m in length and 26.5 mm in diameter is buried about 2 m into the
Fig. 1. Hybrid heat-pipe snow-melting system.
earth, with a length of 2 m remaining above the ground along the support wire. The heat pipe extracts about 10W of heat from the earth at temperatures above about 6°C throughout the winter season, and melts the snow surrounding the support wire. A hollow space with a diameter of about five times that of the heat pipe is formed around the support wire, releasing the tension force. By this method, support wires of telephone poles can be completely protected from snow damage without further equipment or costs.
This system, using only the heat of the earth, requires no running cost. However, in cases of heavy snowfall, it is insufficient, and the cost of construction is higher than for other systems. These shortcomings are solved by a new method of hybrid heat pipe snow-melting system. The key element of the system is an auxiliary electric heater, added to the lower part of the heat pipe (see Fig. 1), which is buried vertically about 7 m into the earth. When snowfall is below 10 cm a day, this system melts snow by using only the earth’s heat. On days of heavier snowfall, or extreme cold, the auxiliary heater is activated. The operating cost is several tens of times lower than that of other snow melting systems. Much of the heat source is that of the earth, so this system is very effective at melting snow in relatively small areas such as a door area, passage, small parking lot, etc.
There are many hot springs in snowy areas of Japan. In these districts as well as others, snow removal is a significant task. Waste hot spring water from hotels is used as a heat source for large-scale snow-melting systems. Exhausted waste hot spring water, at above 20°C even in winter, led into a ditch along a road, flows downward. The lower end of a flexible heat pipe about 1 m long is concreted into the bottom of the ditch to extract heat from the water flow. The remaining part of the heat pipe is installed under the road with an inclination angle of several degrees.
A very large-scale snow-melting system with low operating costs has been developed by combining a flexible long heat pipe and a boiler with burners. A U-shaped heat-exchanger jacket is attached to the lower part of the heat pipe. A heating liquid (e.g. solution of ethylene glycol or propylene glycol in water) warmed to about 40°C by a boiler is circulated in the jacket, transferring heat to the heat pipe. The system recently constructed in Japan has a snow melting area of 6200 m2. The operating cost of the sytem is about one third that of a system on the same scale using electric heating.
These methods will be widely used in the future, not only in Japan, but also in other countries.
