Heat Trace Cables Embedded in Concrete Pads
on Tue, 03/08/2016
These mineral insulated heat trace cables allow the creation of heated concrete pads that utilize moisture sensors connected to a control panel to minimize the use of electricity. The sensors have a small heating element that melts any nearby snow into water, which a moisture sensor then detects and subsequently transmits a signal to the control system to activate the heat trace cables.
In addition to the convenience of automatic snow detection, this sensor based system is highly energy-efficient and optimized to make the best use of available power. Depending on the rate of snowfall, the resting heat cable system could save up to 60 percent of normal heat cable electricity costs. Also, parameters in the control panel cause the circuits to gradually activate to avoid the surge of electricity that would be caused if all circuits activated at once.
The paving guidelines for mineral insulated heat trace cables include adequate drainage, clean paving areas free of roots or other obstructions and adequate concrete thickness to support the desired load - e.g. 4 inches for pedestrian walkways and 6 inches for supporting motor vehicles. Expansion joints in concrete are an additional concern that must be provided for larger areas or changes in slab thickness.
As a fairly high-wattage system, all electrical system including switches, circuit breakers, and controllers must be capable of breaking both sides of the line on ungrounded circuits. Automatic control is available but not necessary for every system. When manually activating the heat trace system, an indicator light is recommended to signal wheter the system is on or off.
Electrical and paving contractors installing the cables must be extra careful to avoid damage from sharp objects normally present on construction sites. The heat trace cables must be treated with special care when shipping and unloading and be embedded at least 2 to 3 inches below the final concrete surface.
Mineral insulated heat trace cables come in two different sizes, "K", with a smaller diameter and "B", with a slightly larger diameter. In general the cables are utilized for their tough exterior that is able to handle high temperatures and harsh conditions that standard polyolefin coated self-regulating heat trace cables would fail under. These conditions include piping exposed to extremely high temperatures such as steam cleaning, food processing applications involving high heat and crude oil that must be regulated at a high temperature. Embedding the cables in concrete or asphalt is also possible due to their tough exterior.
Manufacturing Facility Fixes Walkway
In one instance, a manufacturing facility in Wisconsin utilized heated concrete pads to alleviate the negative effects of excessive snow and ice buildup on the walkway leading to its building entrance. The project engineers created modular and energy efficient heated concrete pads that allow the facility to replace damaged portions of the walkway as necessary without extensive reconstruction, and a sensor in the concrete detects snow and automatically turns the heating system on when needed.
Priop to installing these concrete pads, the facility was experiencing an excess of snow buildup, which in some cases could block the entryway to the building. Additionally, snow damages concrete over time when water from melted snow makes its way into cracks and crevices in the concrete and refreezes, cracking and popping the concrete and causing premature aging. The ice and snow accumulated on the outside of the building also created a dangerous environement, causing employees and vehicles to lose traction. In one instance, a vehicle lost control and physically impacted the side of the building.
The solution for these ice and snow-related problems was first to tear out the entire original concrete walkway leading to the facility. The replacement walkway was made up of 10-foot by 10-foot individual pads extending approximately 90 feet from the parking lot to the entrance of the building. Each pad was equipped with mineral insulated heat trace cables embedded in the concrete at the time it was poured. The cables were wire-tied to rebar mesh inside of each concrete pad in a pattern designed to evenly distribute heat throughout the entire area.
The heat cables are powered by a control system operated by a snow sensor that automatically detects the presence of moisture near the concrete and triggers the system to activate it. When the concrete was poured, a small housing for the sensor was included. With a minimum of 30-watts-per-square-foot required to effectively melt snow on concrete, this system requires approximately 27,000 watts of power to operate. The moisture sensor incorporated in the system plays a large role in regulating excessive power usage. Prior to the installation, the facility managers were concerned about the need to replace the entire system in the event of a failure or damage to the cables. The engineers recommended 10-foot by 10-foot concrete pads so that none of the heat cables had to pass through an expansion joint, thus allowing each pad to be individally replaceable. This modular design is not very common in the industry, although it allows far more flexibility for repairs or future expansion.
The modular design also creates increased durability for the heat trace cables. The most common point of failure for heat trace cables is in expansion joints between pads of concrete, but the lack of cable pasing through expansion joints due to the modular desing completely eliminates that risk. The project engineers could have specificied a 20-foot by 10-foot concrete pad design, but opted for a smaller size to increase the durability of the heat trace cables.
After the successful installation of this energy-efficient automated heat trace cable system, the manufacturing facility no longer has problems with the excess snow and ice buildup. The system automatically activates any time snow accumulates, melting the snow and ice and clearing the path for safe pedestrian access. The facility also benefits from the energy-efficient design of the control system and the option to individually replace each concrete pad if needed.
Additional applications for concrete pads heated with mineral insulated heat trace cables include truck stops where employees would normally have to lay down on slabs of frozen concrete to perform maintenance on their trucks. A thicker concrete pad is poured to absorb the weight of the heavy machinery, and heat trace cables can be included to provide a warmer surface for employees as well as melt any ice or snow that trucks can deposit onto the concrete.
In some open-pit mining operations, ambient temperatures can become extremely cold and create a dangerous environment for workers maintaining large machinery. Heated concrete pads in this application can be so effective that they raise the ambient temperature of the space surrounding the concrete.
Another example is an airport hangar with a large sliding door mounted to metal tracks that would freeze and stick during winter months. A heated concrete pad was installed below the door and the heat radiated up onto the track to melt any snow or ice that accumulatesd, allowing the doors to freely open and close even in the coldest of conditions.
Mineral insulated heat trace cables have the resiliency to offer these convenient solutions in applications that would damage standard self-regulated heat trace cables. Combined with a moisture sensor and automatic control system, concrete pads with embedded mineral insulated heat trace cables can provide unique alternatives where snow, ice or low temperatures cause undesirable conditions.
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