HYDRONICS By La nc e M a c N e v i n
broad appeal of snow and ice A brief history
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ollowing another crazy long winter across North America, spring and early summer brings the opportunity to help your customers prepare for next winter by equipping them with hydronic snow and ice melting (SIM) systems.
Photo: NIBCO
Winter precipitation is unpredictable and dangerous, and snow and ice increase liability and are expensive to remove, which is why many home and business owners are warming up to hydronic snow and ice melting systems.
Hydronic systems to melt ice and snow were pioneered in the 1940s. These early systems used wrought iron or steel pipes embedded in concrete. Perhaps not surprisingly, they often rusted out, some very quickly. Most modern SIM systems use flexible PEX or PE-RT tubing, the same as used for radiant heating systems. In fact, some people think of SIM systems as outdoor radiant heating systems.
For instance, a hospital entrance in Edmonton that is expected to keep up with 100 per cent of expected snowfalls in that frigid location may be sized to output 300 BTUH/ft2 under worst case conditions. This doesn’t mean that the system will always require 300 BTUH/ft2, but the designer might want to specify the system to meet that capacity when needed for a critical facility. On the other hand, a residential driveway in Hamilton, Ont., might be sized for lower output, even as low as 75 BTUH/ft2. A system of this capacity might not keep up in a historical blizzard, but it will catch up and leave a dry surface a few hours later. Designing for a lower capacity can reduce the mechanical system costs (e.g. b l circulator) significantly. And who needs a perfectly snow-free boiler, driveway in the middle of a blizzard, when the roads are impassible?
MATCHING TO THE LOAD AND EXPECTATIONS Environmental factors that affect SIM heat loads include the air temperature when snowing, rate of snow fall, snow density, wind, humidity level of the atmosphere, and even the “apparent sky temperature.” With so many variables, the most difficult design issue is estimating loads. It’s a lot like predicting the weather, and we see how often meteorologists get that correct. Heating loads for these outdoor systems can be in the range of 50 to 300 BTUH/ft2, including reverse loss and edge losses to the cold ground. This is a big range of loads, which also depends upon the project location and customer requirements, and impacts initial installation costs.
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Once the estimated loads are known, then hydronic calculations such as flow rates and head loss are straightforward for experienced hydronic experts. Plastics Pipe Institute has a free online software tool for several types of piping calculations at www.plasticpipecalculator.com. Just make sure that antifreeze is selected when calculating flow rates and head loss. To start a design, work with local hydronic designers who have previously supplied systems in your locale and ask them what output they recommend for a given application.
Photo: Klimatrol
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