Bridge in Japan Uses Stored Summer Heat to Melt Snow
by Lloyd Alter, Toronto on 09.25.07
Bridges are dangerous in cold climates; because they cool more quickly than regular roads, ice can form when the rest of the road seems safe. More de-icing chemicals are used, which can cause the bridge to deteriorate.
In Fukui, Japan, the Snow Management and Construction Technology Research Center has developed a system where they store summer heat for snow-melting in winter by driving a large number of dedicated heat-exchanger piles into the riverbank.
According to Japan for Sustainability:
This is a closed-conduit system, in which heat-radiating pipes built in the bridge surface and 378 piles (42 rows and 9 columns) embedded 1.5 meters apart into the riverbank are connected through a circulation pump. During daytime in summer, the circulation pump operates automatically as the bridge surface becomes hot, carrying the heat to the underground storage piles. This system warms to 35 degrees Celsius a section of the riverbank measuring 15 meters wide, 64.5 meters long and 23 meters, and maintains the temperature until December for snow melting.
Counting emissions from construction and 50 years of operation, this new technology will result in one-twenty-fifth the carbon dioxide emissions compared to conventional electric snow-melting equipment. ::Japan for Sustainability and ::Snow Management and Construction Technology Research Center
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What happens to the riverbank when the rods warm it? I hope it has no adverse effects on the soil or water temperature.
With a closed loop geothermal system the heat of the summer has little to do with the winter melting. The ground is around 10°C (50°F) year round. Pumping the summer heat into the ground keeps the bridge cool and does transfer that heat into the earth, but even if you didn't run the pumps in the summer time, it would still work exactly the same to melt ice in the winter.
The earth has plenty of heat to do the job without them dumping summer heat in there to get at later.
If they're using solar powered water pumps, then it's not a big deal, but if the pumps are grid-powered, then I'd argue that they're wasting power 90% of the days of the year. They should just kick on during cold periods.
There might be some benefit from a structural stand point to preventing the bridge from thermally expanding and contracting, keeping the concrete at a constant temperature, but other than that there's not really any reason to run the pumps if it's not near freezing.
Actually you're wrong. It's a myth that the soil is at a constant temperature. It is only at a constant temperature if you don't remove any heat from it.
There isn't enough heat in the soil to defrost unless you store heat first.
Extensive research by ICAX and TRL has shown that if you continually remove heat from the earth it will cool down - it is possible to store hot or cold within the first 15m or so of the soil. In a long term trial we showed that you need to store the heat from the road in the summer for the de-icing to work. If you don't all that happens is after the first year the soil goes cold and never recovers.
Actually you're wrong. It's a myth that the soil is at a constant temperature. It is only at a constant temperature if you don't remove any heat from it.
There isn't enough heat in the soil to defrost unless you store heat first.
Extensive research by ICAX and TRL has shown that if you continually remove heat from the earth it will cool down - it is possible to store hot or cold within the first 15m or so of the soil. In a long term trial we showed that you need to store the heat from the road in the summer for the de-icing to work. If you don't all that happens is after the first year the soil goes cold and never recovers.