Hydronic snowmelting essentials

Here Phc News begins a two-part article about the basics of snowmelt system design and installation, with a focus on the need for careful consideration about and the use of inhibited propylene glycol solutions. Part one introduces the snowmelt system and its various forms and uses.

We all know that during winter, sleet, snow and freezing rain lay down the challenge for safe movement outside. As professionals in the business of designing or installing hydronic snowmelt systems, one of your key challenges is overcoming building owner reluctance to install a system.

Granted, it’s not inexpensive. But there are benefits that help to sway the decision. These include convenience, environmental enhancements (no salts, cinder and chemical de-icers), and the greatly reduced labor and hardware costs that are otherwise needed to remove snow and ice. Ice-melt chemicals can kill nearby plants, increase building cleanup as they’re tracked inside and, over time, seriously degrade floor surfaces, concrete and asphalt. In essence, using radiant heat is a “greener” approach to melting snow and ice.

Snowmelting is the radiant heating of outdoor surfaces. The most common method is the use of tubing embedded inside concrete or asphalt surfaces to distribute warm fluids. The end result: pathways, driveways and other areas remain dry and clear. For commercial applications, especially those deemed critical areas -- hospital and senior housing entry areas, helicopter pads, delivery and handicap access ramps, etc. -- radiant heat can prevent injuries and saves lives.

Another advantage is the proactive prevention of liability claims and added safety overall. Given today’s litigious society, snowmelt systems don’t cost money; they save it. The cost of the system is more than returned with one avoided lawsuit. And, some insurers recognize the value of these systems, rewarding building owners with reduced insurance rates.

Examples of snowmelt systems

The most common pipe material used to distribute warmed fluid solutions are cross-linked polyethylene (PEX) or synthetic (EPDM) rubber. Because the fluids are exposed to freezing temperatures in the mass that surrounds them, it’s widely known that to prevent freezing, inhibited (corrosion-protected) glycol solutions are used. Common snowmelt applications include:

• Helipads. Hospital helipads are excellent examples of places needing to be safe and snow-free. With space becoming more and more precious, many hospitals are forced to install helipads on the building roofs. These rooftop helipads can become extremely dangerous when coated with ice and snow.
• Sidewalks. By making walkways convenient and more inviting to the passerby, sidewalk snowmelt systems can increase business and decrease liability. Customers are more likely to shop stores with clear sidewalks.
• Stairs. Pedestrians can travel in relative comfort and safety. The spacing of tubes for stairs varies according to application, but they are usually installed with two lengths of tubing in the tread and one length in the riser.
• Car washes. Water is always present in car washes, but property owners can keep car washes open and ice-free. Tubing for car washes is always installed in a concrete slab. The control strategy for car washes is simple. Either air temperature or slab temperature can be monitored. If the temperature of the slab or the air drops below 35°F, the system is turned on. When the temperature rises above 35 F, the system is turned off.
• Hospital entrances. Tube spacing for hospital entrance ramps usually are set closely at 6" on center. Further, these systems are idled, or operated at a reduced output, to decrease system lag time (the time required for the system to reach operating temperature and start melting snow). When the sensors detect freezing precipitation, the system then operates at full output.
• Parking garage ramps. Snow-melting systems ensure cars driving in from the street can safely negotiate up and down parking garage ramps.
• Loading docks. Snowmelting systems ensure that the goods can be easily moved in and out of a facility.
• Large area “hot pads.” Instead of heating the entire area exposed to winter elements, it may be more cost effective to operate a snowmelt system on a smaller area where shoveled snow can be piled on. This technique is most commonly used for airport runways and large parking lots. Typically, tubing for hot pad slabs is spaced at 4" to 6" on center to accommodate a large amount of snow. Hot pads are usually operated manually, activated whenever the need arises.

Know your system

If you find yourself at work on a snowmelt system without inhibited glycol in it, there are key steps to take to ensure that you aren’t introducing good fluid into a bad system. Factors that cause excessive fluid degradation include: operating temperature; the amount of air or dissolved oxygen the fluid is exposed to; system age; the materials of construction; and the quality of the heat transfer solution, including proper dilution and maintenance, to name a few.

The use of a poor quality glycol fluid can lead to serious corrosion problems. Any glycol can provide freeze protection, but only a properly formulated glycol, at the right concentration level and with industrial strength corrosion inhibitors can keep corrosion in check. All glycols can introduce the potential to thermally degrade or oxidize even when left alone in their original sealed container. Degradation proceeds even more rapidly when glycols are used within an operating system.

Many system owners learn the hard way that not all glycols can provide long-term protection of system components from corrosion. The old adage, “Do it right the first time,” holds true since it always costs more to correct a serious corrosion problem than it is to prevent one from happening.

The industrial inhibitor packages used in products like Dow Chemicals dowfrost propylene glycol based fluids and dowtherm SR-1 ethylene glycol base fluids are specially formulated to help prevent corrosion in two ways. First, the corrosion inhibitors “passivate” the surfaces of the metal, so they are less susceptible to corrosion. Second, the inhibitors buffer the organic acids formed as a result of glycol oxidation to keep the fluid from becoming acidic.                   

End of part 1. Part 2 to continue in the March issue of Phc News. Part 2 of this article looks in greater detail at the need for inhibited glycol solutions when installing snowmelt systems. It also examines the type of heat losses that will occur, how to anticipate the influence of heat loss, basic types of operation and control, and cost of system operation.