Sidewalk road heating system using sewer heat
The heat required for the system was set at 123 W/m2 by comparing heat required for snow melting to that required for freezing. The system is able to melt the snow up to a maximum snowfall intensity of 1.49 cm/h.
Sewer heat is collected by a heat-extraction pipe installed at the bottom of a reconstructed sewer pipe. The heat-extraction pipe is filled with a medium of heat transport exchange. This medium is heated directly by the sewer water before being circulated through a heat radiation panel by a pump to heat the pavement for snow melting. This system for transferring heat from sewage to a medium operates without need a heat pump to raise the temperature of the medium. The simple system uses a pump only for circulation. For scenic beauty, some sidewalks are paved with natural stones. But the temperature of the circulating medium is prone to decrease when such stones are used. To address this, stainless steel pipes are used for the heat radiation panel, because steel conducts heat more efficiently than other materials. This is because stainless steel allows for a thinner layer of cover soil and a shorter length of heat-extraction pipes.
By making each heat radiation panel smaller than usual, the system is able to melt snow well enough even when the medium is at a low temperature.
Polyethylene, which has better long-term durability than other materials, is selected for heat-extraction pipes that are fixed to the bottom of a reconstructed sewer pipe in a box culvert. The pipes are fixed to a frame made of rigid polyvinyl chloride.
●Location:
In front of the annex to the city hall in Niigata, Niigata Pref.
● Design conditions:
Daily snowfall: 6.0cm/day, Ambient air temp.: -0.04℃, Wind speed: 3.61ｍ/s, Hourly snowfall: 1.49 cm, Snowfall density: 80 kg/m3, Sewer temp.: 8.5℃
● Facility outline:
Snow-melting area: 108 m2, Design heat radiation: 123 W/m2，Design temp. of circulating medium at the header pipe: 6.46℃; at the return pipe: 5.22℃, Heat radiation pipe: SUS15A, Pavement materials: Natural stone and concrete, Length of heat-extraction pipe: 50.4 m (total length: 100.8 m), Heat-extraction pipe: polyethylene pipe (φ17 mm), Circulation pump: 3.7 kW, Control system: Two-element control (ambient air temp.＋ road surface temp.）
Snow melting sprinkler
Snow is melted by sprinkling pumped up groundwater that is conveyed through the transmission pipe and nozzle buried in the pavement. It is used in snowy regions whose ambient temperature tends to be above the freezing point.