It’s the dog days of summer, so snow isn’t on most people’s minds. But now is the time when HVAC contractors who work on radiant heat install snowmelt systems. The systems appeal to property owners because they eliminate much of the need for snow removal and the associated cost. They also provide a more environmentally friendly solution than using chemicals to clear off ice.
ASHRAE provides standards for contractors to calculate the snowmelt needs of any project. The basic technology of snowmelt systems and the way contractors install them has stayed pretty much the same for the last half century, said Ian Levergood, sales director for Danfoss. But many other aspects of the systems have improved.
“Electric snow melting solutions have been around for over fifty years in North America, and while the technology of the heating element has remained relatively unchanged, the quality and durability of surrounding materials have improved,” Levergood said. “Where technology has advanced is in the speed and accuracy of controls that instantaneously measure temperature, moisture, and precipitation, by quickly activating. This has been key to lowering energy consumption, and now these controls are so accurate that they are only energizing the heating cables when necessary.”
Before taking on any snowmelt project, there are a number of factors a contractor needs to take into consideration, he said. The first is the primary use of the system. This could be a downtown sidewalk, a person’s driveway, or the entrance to a critical building, such as a hospital.
Type of Surface Matters
Then there is the question of what type of surface material covering will be used. Levergood said concrete remains the most popular option because of its ability to conduct heat. When using concrete, he said, the installation crew need to know where the expansion joints will be located so the system can be designed with cables fitting between expansion joints. This ensures maximum system longevity.
The National Electric Code (NEC) and Canadian Standards Association (CSA) prohibits any electric cable system from passing through concrete expansion-contraction joints. So even though these radiant cables will be embedded directly in the concrete, multiple cables and/or mats must be used to cover these larger areas that require expansion joints. Concrete will heave, expand, and move slightly, so it’s important to not cross under any circumstances. Otherwise, if the concrete moves, the cables will break.
When placing the cables before concrete is poured, it’s important to prepare the concrete forms and reinforcement/rebar to ensure the cable is suspended at the correct depth, Levergood said. The NEC requires a minimum depth of 1.5 inches (38 mm), but most manufacturers recommend a depth of 3 inches (76 mm) as being ideal to achieve as much horizontal heat dissipation as vertical dissipation.
“Depth matters,” he said. “Too deep and you’re heating the earth below the concrete first, and heat will slowly migrate to the concrete eventually. Too shallow and the cable doesn’t have enough time to thermally dissipate heat horizontally before it rises.”
Asphalt is another popular covering. Levergood cautions that it does require planning and may lead to additional labor costs due to the required slow and cautious pouring processes. Contractors working with asphalt need to use a high-quality, durable heating cable, since only some cables can withstand the heat and compression from freshly poured asphalt.
The biggest risk when working with asphalt is overheating the cable, Levergood said. Typically, hot asphalt can exceed 240°F (115°C), so the cables must be protected or the asphalt must be cooled to below the maximum temperature requirements of the cable.
Then there are pavers, which include bricks, flagstone, marble, tiles, and other types of stone or masonry. These are easier to install, Levergood said, since the cables are accessible even after installation is completed. The only real considerations for this application are to think about the thickness of the paver and how this will impact the reaction time of the heat, he said.
