Snowmelt system

Installation of a geothermal snowmelt system in Reykjavík

A snowmelt system is a form of snow removal used to remove snow and ice via embedded electric cables or hydronic tubing similar to indoor underfloor heating. Common areas for snowmelt systems are: driveways, walkways, parking areas, stairways, wheelchair ramps, loading docks, and around car washes. A snowmelt system is usually installed during the original construction in concrete, asphalt, mastic asphalt or under pavers. Retrofit electric systems can also be installed using saw cutting technology or on top of existing concrete, asphalt, or mastic asphalt surfaces if the existing surface is on grade.

Overview

Snowmelt systems prevent the build-up of snow and ice on walkways, patios and roadways, or more economically, only a portion of the area such as a pair of 2-foot (0.61 m)-wide tire tracks on a driveway or a 3-foot (0.91 m) center portion of a sidewalk, etc.. They function even during a storm thus improve safety and eliminate winter maintenance labor including shoveling/plowing snow and spreading de-icing salt or traction grit (sand). A snowmelt system may extend the life of the concrete, asphalt or under pavers by eliminating the use salts or other de-icing chemicals, and physical damage from winter service vehicles.

Systems are available in two broad types based on heat source: electric resistance heat or heat from a combustion or geothermal source delivered hydronicly (in a fluid). Arguably, electric snowmelt systems requires less maintenance than hydronic snowmelt systems because there are minimal moving parts and no corroding agents.

Most new snowmelt systems operate in conjunction with an automatic activation device that will turn on the system on when it senses precipitation and freezing temperatures and turn off the system when temperatures are above freezing. These types of devices ensure the system is only active during useful periods and reduces wasteful energy consumption. A high limit thermostat further increases efficiency when installed in conjunction with the automatic snow melt controller to temporarily disable the system once the slab has reached a sufficient snow melting temperature. Some building codes require the high limit thermostat to prevent energy waste. Though their total environmental impact depends on their energy source. Current systems are more cost effective in the long run than continual salt dumping and removal, and reduce waste by extending the life of the cement.

Operation costs

Operating costs vary by region, energy source (electric, gas, propane, etc.) used and costs associated. The American Society of Heating, Refrigerating and Air-Conditioning Engineers has standards intended to achieve satisfactory results and to minimize energy consumption from over sizing or over designing a system. Systems are typically designed to produce 70-170 BTU/sqft using ASHRAE guidelines by region. The time to melt snow from a surface varies by storm and how many BTUs the system is designed to produce.

Electric snowmelt systems

Electric snowmelt systems are composed of three basic components: heating cable, control unit and an activation device.

The heating cable is built to withstand harsh conditions to make it suitable for outdoor usage. The cable should be listed to UL standards by a Nationally Recognized Testing Laboratory and many consist of a single or dual conductor with a protective coating and/or insulation. Many cables are rated at 105 °C (221 °F) and produce 6-50 watts per lineal foot. Watts per square foot produced is determined by heating element spacing.

The control units are typically wall-mounted control panels and can be mounted in a NEMA enclosure. Control units vary by technology by using line and load terminal blocks, relays, activation terminals, transformers, as well as monitoring electronics.

Hydronic snowmelt systems

The heating element in a hydronic system is a closed-loop tubing made of a flexible polymer or synthetic rubber that circulates a mixture of hot water and propylene glycol (antifreeze). The fluid is warmed to temperatures of 60 °C (140 °F) to 80 °C (176 °F) to warm surrounding concrete/asphalt/concrete pavers and melt snow and ice. Technology for hydronic snowmelt systems is based on the same technology as underfloor heating systems.

The most crucial part of a successful hydronic heating system depends on proper tube spacing and layout. It is recommended to lay the tubes in a spiral or serpentine pattern to help distribute the heat evenly. Specification for spacing will vary between manufacturers. A faster rate of snowmelting will require closer spacing of tubing, typical spacing is 6”. Another heat factor is the amount of insulation used under the slab.

Like electric snowmelt systems, hydronic snowmelt systems must be installed in the base surface material (sand or compacted, crushed stone). Ensure the subgrade is well compacted before beginning tube installation because uneven settlement may damage the tubing. Tubing can be fastened with cable ties to either the re-mesh, re-bar or below slab insulation.

Hydronic tubes should not be placed directly on top of solid bedrock; this will cause the heating tubes to conduct heat into the earth.

Activation Devices

There are a number of activation devices used for snow melting applications. Some activators are a simple manual timer that activate the system to stay on for a specified time period while others sense temperature and moisture or just temperature conditions to automatically activate the snow melt system. Automatic devices can be aerial-mounted, pavement mounted or gutter mounted. High-end activation devices feature: adjustable temperature trigger points, adjustable delay off cycle, and upgradeable remote activation. The activation device enables the snowmelt system to run 100% automated.

Self regulating Trace heating cables automatically regulate the amount of heat supplied so that only those parts with temperatures below the set point are heated.

Careful placement of the sensors is important to have an effective result when using these activators. Activation moisture sensors should be placed in a location where they will effectively collect any moisture from a snow storm and in a relatively close proximity to the area to be free of snow and ice. Temperature sensors are installed outside to sense the same temperature conditions that the surface that the snow melting system will experience. Other activators, such as manual timers or switches can be installed in a convenient location.

New installations

The installation of snow melt systems is accomplished during construction of the walkway or roadway with the spacing of the cables or tubing based on the system design. There should be a minimum of 3” and max 4” of substrate covering the heating cables for new concrete applications. Concrete mixture must not contain sharp stones as these may damage the cable. The concrete should be allowed to set for 30 days before the heating cables are turned on. For this reason, the best installation time is during summer months.

System installation specifications beneath asphalt may vary between each manufacturer. The cable can be laid out on the base surface (usually a sand bed), and covered with 1/2" sand. The asphalt is then hand shoveled onto the heating cable and base surface.

Insulation below the cables or tubing is recommended, but not required. One-inch rigid insulation can be installed underneath the base surface, or it can be laid on the base surface and the heating cable can be secured on top of the insulation.

Some installations involve two layers of asphalt. For this installation, a base layer of asphalt (1" thick) is placed down first. Heating cables are then installed and secured to the surface of the base layer. Once the heating cables are installed, a second layer of asphalt is placed over the heating cables and the first layer, embedding the heating cables within the slab.

Installing a snowmelt system under brick pavers is achieved by placing the heating cables on the base surface over 1/2" of sand. The heating cables are then covered with 1/2" of sand and the pavers are installed as normal over the sand bed.

Retrofit installations

Retrofit installations are possible with electric systems by cutting grooves 11⁄4" to 11⁄2" deep and between 1/4" and 3/8" wide into the asphalt or concrete, inserting the cables and sealing the grooves with backer rod and a special caulking or sealant at the surface of the groove.

Notable installations

See also

References

  1. ↑ http://www.massmoments.org/moment.cfm?mid=230
  2. ↑ http://iceland.vefur.is/iceland_nature/geology_of_iceland/geothermal_heat.htm
  3. ↑ http://www.flickr.com/photos/canadianveggie/2636012834/
  4. ↑ http://internationaltravelchick.com/2012/03/15/oslo-norway-beyond-the-heated-sidewalks/
  5. ↑ http://tommyimages.com/Stock_Photos/Scandinavia/Norway/Norwegian_Architecture/slides/Norway_04_E_1_25-Heated_Sidewalks.html
  6. ↑ http://www.treehugger.com/sustainable-product-design/are-holland-michigans-heated-sidewalks-intelligent-infrastructure.html
  7. ↑ http://www.oakpark.com/News/Articles/1-22-2013/Sidewalks-on-Marion-Street-heat-up-at-a-hefty-price-for-Oak-Park/
  8. ↑ "Heated sidewalks in the future?". CTV News. Retrieved 2013-12-17.
  9. ↑ http://www.rampheatingrepair.com
Wikimedia Commons has media related to Snowmelt system.