Snow Melting - Manual Controls

An on/off control is the simplest and lowest capital cost strategy but it is also the most likely to induce internal thermal stresses and can accelerate the degradation of the slab surface over time. Within transient storm characteristics it can be the most expensive to operate as the heat flux can be as high as five times the steady state load calculation. This is  because a manually operated on/off system leaves room for operator error in as much as turning off the system too early can leave moisture in the micro-cracks and crevices in the concrete surface. These then freeze, expand and induce surface wear.  Leaving the system running longer than necessary increases operating cost. In addition, raising the temperature of frozen concrete rapidly to above freezing with heated pipes as hot as 180F (fluid temperatures can range from 100F to 180F based on design criteria) can create internal stresses that lead to stress cracking. Finally,  let’s investigate operating costs by looking at the results of a sudden heavy and severe snowstorm followed by a very significant drop in outdoor temperature. At the first sign of snowfall the occupant manually turns on the system, which must overcome the pick up load and bring the slab mass and surface to a melting temperature. By the time this happens there could be several inches of snow accumulated on the top. Snow in contact with the slab does begin to melt but the outer layer of the blanket would be approaching outdoor temperatures. In our climate this might be -30F. The moisture between the exterior snow layer and the surface then begins to freeze creating ice dams or bridging. The system must then run long after the storm has departed. The occupant may also have to manually break up or collapse the caves of ice to promote melting. Bridging or stripping can also occur when pipes are widely spaced and the fluid temperature is inadequate for the load. If this occurs frequently during the season,  the operating cost for pick up loads and melting ice can be greater than operating a system to melt snow on contact with idle/on strategies.

Click here for part I, Introduction
Click here for part III, Idle/On Controls & System Performance      
Click here for part IV, Area Free Ratio and Frequency Percentile  
Click here for part V, Conclusion 

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