Use of Automated Anti-Icing Systems Heats Up
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 From Transportation Alert Issue 9 |
New technology may have transportation departments in ice-prone areas sending those “Bridge Freezes Before Roadway� signs back to the ice age. Now, a bridge outfitted with Fixed Automated Spray Technology (FAST) and a Road Weather Information Station (RWIS) automatically dispenses a de-icing solution across the bridge deck before ice can form.
Tests of anti-icing systems in the United States and Canada have shown promising results. Ice-related accidents on overpasses can be virtually eliminated, greatly improving safety and reducing liability.
Fully automated anti-icing systems reduce the amount of materials applied and efficiently distribute the anti-icing agents on roadways. This is better for the environment.
Conventional De-icing. For decades, chemical anti-icing has consisted of spreading rock salt at rates based on local experience and weather forecasts. But rock salt begins to lose effectiveness at around 10° F. It is also highly corrosive to structural and concrete reinforcing steel, as well as vehicles.
Anti-icing. Anti-icing systems are utilized prior to freezing to prevent the formation of frost or ice on a bridge surface, unlike de-icing which melts ice after it has formed. The newest anti-icing agents consist of non-chloride based potassium acetate liquids. These are effective to -26° F. Potassium acetate is less corrosive to structural and concrete reinforcing steel than rock salt.
The first chemical based systems were sprayed from trucks dispatched to a site on demand. Now, point-of-need application systems are being installed at some bridges. These consist of deck or railing-mounted spray nozzles fed by tubes from an adjacent pump house. They are controlled either remotely or automatically by an RWIS, which monitors air temperature, road and deck slab temperatures, wind speed, and humidity and initiates the application of anti-icing agents when weather conditions are conducive to ice formation.
Deck Heating. Other anti-icing systems being tested are active and passive geothermal deck heating systems. With active systems, heat is extracted from the earth using a ground loop circulation system to keep deck slabs from freezing. A system of pumps and condenser pipes circulate fluid throughout the deck to an underground heat exchanger installed below the frost level. The pumps are activated based on the temperature of the deck and air.
Passive systems utilize evaporator pipes installed in the ground near the bridge deck and condenser pipes installed in the deck. A liquid (usually ammonia) evaporated by ground heat, rises and circulates through the deck pipes, keeping the deck from freezing. As the air cools, it condenses. The condensed liquid then flows by gravity back to buried evaporator pipes, where it warms, evaporates, and continues the cycle. When the deck is hotter than the ground, circulation ceases. Since no pumps or associated controls are required, operating costs are low. However, the complexity of the system and cost of materials can make it too expensive for most applications.
Typical installations where deck heating can be cost-effective include long, elevated expressway ramp bridges, multiple-bridge interchanges (where weather monitoring stations and supply tanks can be used for multiple bridges, saving costs), bridges affected by mist from water falls, and structures high above the moderating effects of waterways.
Anti-icing in Use. Anti-icing systems are in use in Pennsylvania, Michigan, Minnesota, Utah, Virginia, Wisconsin, and Canada. While interest in RWIS technology has been increasing in New York State, the use of anti-icing technology in combination with an automated RWIS is still rare. The technology, however, is currently being studied for a US Route 15/I-86 Interchange project in upstate New York.
To learn more about current testing and performance of recent installations, explore the following web sites:
Tests of anti-icing systems in the United States and Canada have shown promising results. Ice-related accidents on overpasses can be virtually eliminated, greatly improving safety and reducing liability.
Fully automated anti-icing systems reduce the amount of materials applied and efficiently distribute the anti-icing agents on roadways. This is better for the environment.
Conventional De-icing. For decades, chemical anti-icing has consisted of spreading rock salt at rates based on local experience and weather forecasts. But rock salt begins to lose effectiveness at around 10° F. It is also highly corrosive to structural and concrete reinforcing steel, as well as vehicles.
Anti-icing. Anti-icing systems are utilized prior to freezing to prevent the formation of frost or ice on a bridge surface, unlike de-icing which melts ice after it has formed. The newest anti-icing agents consist of non-chloride based potassium acetate liquids. These are effective to -26° F. Potassium acetate is less corrosive to structural and concrete reinforcing steel than rock salt.
The first chemical based systems were sprayed from trucks dispatched to a site on demand. Now, point-of-need application systems are being installed at some bridges. These consist of deck or railing-mounted spray nozzles fed by tubes from an adjacent pump house. They are controlled either remotely or automatically by an RWIS, which monitors air temperature, road and deck slab temperatures, wind speed, and humidity and initiates the application of anti-icing agents when weather conditions are conducive to ice formation.
Deck Heating. Other anti-icing systems being tested are active and passive geothermal deck heating systems. With active systems, heat is extracted from the earth using a ground loop circulation system to keep deck slabs from freezing. A system of pumps and condenser pipes circulate fluid throughout the deck to an underground heat exchanger installed below the frost level. The pumps are activated based on the temperature of the deck and air.
Passive systems utilize evaporator pipes installed in the ground near the bridge deck and condenser pipes installed in the deck. A liquid (usually ammonia) evaporated by ground heat, rises and circulates through the deck pipes, keeping the deck from freezing. As the air cools, it condenses. The condensed liquid then flows by gravity back to buried evaporator pipes, where it warms, evaporates, and continues the cycle. When the deck is hotter than the ground, circulation ceases. Since no pumps or associated controls are required, operating costs are low. However, the complexity of the system and cost of materials can make it too expensive for most applications.
Typical installations where deck heating can be cost-effective include long, elevated expressway ramp bridges, multiple-bridge interchanges (where weather monitoring stations and supply tanks can be used for multiple bridges, saving costs), bridges affected by mist from water falls, and structures high above the moderating effects of waterways.
Anti-icing in Use. Anti-icing systems are in use in Pennsylvania, Michigan, Minnesota, Utah, Virginia, Wisconsin, and Canada. While interest in RWIS technology has been increasing in New York State, the use of anti-icing technology in combination with an automated RWIS is still rare. The technology, however, is currently being studied for a US Route 15/I-86 Interchange project in upstate New York.
To learn more about current testing and performance of recent installations, explore the following web sites:
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