To prevent pipes and tanks from freezing, heater cables are installed under the insulation. Insulation slows but does not stop heat losses from the pipe or tank to free air. In a freeze protection application, watt densities are selected to make up for those losses. Typically, self-regulating heater cables are used in this application, although in some applications mineral insulated heater cable can be a better choice.
Self-regulating heaters in this application do not require external controls, but they are recommended for enhanced energy efficiency and lower operating costs. The simplest and lowest cost design is to use ambient sensing controllers that can turn on a heater or group of heaters based on outside air temperature.
For more precise control and maximum energy efficiency, pipe sensing controllers are the best option. With pipe sensing control a separate sensor is required for each unique flow condition. While this makes the design and installation process more complex, it offers the best long term performance.
Process Temperature Maintenance
Process temperature maintenance typically refers to keeping product in pipes or vessels at a temperature higher than ambient temperatures. In commercial application viscosity control for grease lines and fuel lines is the most common requirement. Industrial applications include chemical and pharmaceutical manufacturing, refineries, as well as food and fragrance processes.
Both self-regulating and mineral insulated heater cables are used, depending on the unique design requirements. What are the maintained temperatures? What are the exposure temperatures during normal operations? Are pipes subject to steam cleaning? How long are the pipe runs? All these questions help determine the proper heater cable. IEEE recognizes three types of process temperature applications, and the choice of control and monitoring is driven by type. Type I applications are those where the product simply needs to be maintained above a certain minimum temperature. Type II requires processes to be maintained within a moderate range, and Type III requires temperatures to be maintained within a tight range, often with redundant controls and heat tracing.
Pavement Snow Melting
Mineral insulated heater cables can be imbedded in paved surfaces to provide snow and ice free surfaces for walkways, driveways, loading docks, and parking ramps. The type and construction of the pavement, heater depth and spacing, and desired watt density all factor into system design.
ASHRAE references three classes of snow melting: Class I, for residential walks and driveways; Class II for commercial walks and driveways; and Class III for areas such as toll plazas and hospital emergency entrances. IEEE uses two categories, non-critical (convenience) and critical (essential).
Local weather requirements also need to be considered. AEF Sales has designed and provided snow melting systems from the Moscow World Trade Center to the Top of the Rock Observation Deck in midtown Manhattan, offering a variety of snow detection and control options.
Roof and Gutter De-Icing
Roof and gutter de-icing applications are primarily designed to maintain melted flow paths at roof edges, gutters, and drains to mitigate formation of icicles and ice dams. Installations can range from small scale residential to large scale commercial, industrial, and museum applications. Pictured are skylights at the Metropolitan Museum of Art, where AEF Sales has provided several thousand feet of heater cable.
Controls for roof and gutter de-icing range from manual control with timers to ambient sensing thermostats for small to large systems with multiple probes to detect falling snow, freezing rain, and water in gutters.
Articulated controls allow different parts of a structure to be controlled individually for maximum efficiency. South and west exposures typically benefit more from solar gain than north and east exposures. In densely constructed areas like Manhattan the patterns of sun and shade are affected not only by direction but by the adjacent structures.
Heater cables can be installed under stone, tile, marble, and ceramic floors. In most cases the design goal is to provide a comfortably warm floor surface. For residential applications such as bathrooms and kitchens, keeping the floor at a temperature above 82F (the typical skin temperature on the sole of the foot) provides a pleasantly warm walking surface.
In commercial applications, floor heating is used to offset heat losses through the floor to an unheated area below (such as a parking garage) or in some cases as a primary source of heat, as in the lobby of 30 Hudson Street in Jersey City, shown to the left.
Watt densities vary depending on the application and need to factor in the NEC maximum of 16.5 watts per linear foot of heater cable. Controls can be floor sensing or a combination of floor and ambient room sensing. Heater cable can be imbedded in concrete slab, in mortar setting bed, or beneath an existing concrete deck.
Hot Water Maintenance
Self-regulating heater cables specially designed to maintain temperatures on domestic hot water lines are often used to replace hot water recirculation systems. Heater cable requires less space -- there are no recirculation pumps or balancing valves -- and does not require periodic maintenance.
Heaters are color coded based on the temperatures they are designed to maintain. The insulation thicknesses used varies with pipe diameter to allow heater to provide a stable pipe temperature, with the heat produced by the cable offsetting heat losses through the insulation. AEF Sales stocks hot water maintenance cables for 105F, 115F, 125F, and 140F applications.
AEF Sales offers heater cable and heating pads for tank and vessel heating. Heaters are used for freeze protection and viscosity control, or to prevent crystallization (with products such as caustic soda).
The tank material, dimensions, orientation, supports, and insulation type and thickness all play into the heat loss calculations. The product in the tank, whether or the tank is agitated, fill ratios, and the tank surfaces available for installation of heaters are also important factors.
Heat trace design software is used to determine the optimum heater and control selection for each unique application.