Embedded systems: A radiant concept
Snow and ice melt basics.
February 2, 2014 by Mike Miller
SNOW. It is part of nature’s beauty, especially in Canada. But for commercial and institutional facilities, it is a cumbersome winter guest. Building owners and facility managers are well aware of the importance of proper snow removal for safe and easy access, prevention of slip and fall injuries and protection from potential lawsuits.
The conventional methods of snow removal – plowing, shoveling, salting and sanding – can impose a great financial burden every year. The cost is not just for the labour and materials associated with the removal, but also the wear and tear on the surfaces in and around the structure. Traditional snow-removal methods can even be an environmental challenge if chemicals are used that are either tracked into the building by guests or absorbed into the ground during the spring thaw.
Hydronic snow melting has been gaining traction on commercial and residential properties in recent years. It has been found to help reduce both annual maintenance costs and environmental concerns.
Just like a radiant floor heating application, these systems circulate a warm water/glycol mixture through crosslinked polyethylene (PEX) tubing embedded in the ground. This is the same PEX tubing you use in a radiant floor heating system to heat a residential or commercial structure. The technology has been proven effective for more than 40 years in North America and even longer in Europe.
Embedded hydronic snow melting systems can be effectively used in any exterior area, including stairs, sidewalks, driveways, parking lots and ramps, loading docks, building entrances, wheelchair access ramps, hospital emergency entrances, and helipads on building tops. Almost any area that accumulates snow or ice can benefit from a snow-melting system.
BEING IN CONTROL
When it comes to controlling the system, there are several options to choose from, such as automatic, semi-automatic, manual and idling.
Fully automatic system: a sensor is placed in the ground to detect when snowfall begins. The sensor sends a signal to the heat source to activate the warm liquid flow through the radiant tubing. Once the snowfall stops and the sensor is dry and clear from snow and ice, the sensor sends a signal to stop the water flow and shut down the system. This energy-efficient method of controlling a snow melt system is typically the most economical as it runs only when needed.
Semi-automatic control: a manual intervention is required to start the system, but a timer is also included that will operate for a preset amount of time and then shut the system off when it times out. This could cause the system to be started too late and when the timer stops, the system could shut off too early or too late – both undesired outcomes.
Manual control: the system turns on and off with the flip of a switch. While this is by far the most cost-effective option to install with a snow-melt system, it generally costs more to operate. The human interface requirement typically does not align with that of perfect timing to start or stop a system when compared to the fully automatic system.
Idling: Another option is to idle the system at a preset temperature, typically 22F to 28F (-5C to -2C), to ensure it can ramp up quickly in the event of snowfall. This option is often useful in critical areas that must remain snow and ice free, such as walkways or entryways to buildings. The idle option can be used with either automatic or semi-automatic controls.
DESIGN AND INSTALLATION CONCEPTS
Designing an effective snow-melting system requires consideration of several factors, including Btu/sq.ft./hour load requirements, snowfall rates, snow density, snow temperature, outside temperature, wind speed, tubing size, and tubing spacing. All these factors help the designer and installer create a system that will be the most efficient and effective for the project at hand. As the installer you will need to consider a number of options:
Installation method: There are several different methods for installing the PEX tubing, including tie-downs to wire mesh or rebar, or stapling to rigid foam.
Tubing type: When choosing the type of PEX to use it is important to use tubing that includes an oxygen barrier. This is because oxygen can migrate through PEX walls that do not have a barrier and corrode the ferrous components such as the boiler and pumps, in a hydronic radiant system. It is possible to use a PEX product without an oxygen barrier in a hydronic radiant application, but the system design must ensure that there are no ferrous components, or that such components are isolated from the tubing to prevent corrosion and damage.
Heat source: The heat source for snow-melting systems can vary from traditional modulating-condensing boilers to solar, geothermal and even waste heat.
In terms of control human intervention is not always a good thing as was discovered at a school with a snow melt system in its playground. The system has basically the same setup as a commercial sidewalk or residential driveway snow melt system, but with a slight variation. A layer of soft material was applied on the concrete substrate to cushion the play area. The fully automatic system employed a sensor to detect falling snow and activate the boiler, which activated the system (as described above). When the system was first installed, a school official turned the system off during the winter break. It snowed quite a bit during that time and with the system off, the snow accumulated and had to be shoveled off.
Lesson: Let the system function as it is designed to.
Fully automatic systems need to be turned on for the
entire season if the user is to reap the benefits.
Mike Miller is director of business development, Canada, with Uponor Canada Ltd. and vice chair of the Canadian Hydronics Council (CHC). He can be reached at firstname.lastname@example.org.