FREEZE PROTECTION DESIGN PROCEDURE

1. TEMPERATURE DIFFERENTIAL
Determine the temperature differential to be maintained by subtracting the ambient temperature from the fluid temperature to be maintained. (TF -TA). Typically, for pipe freeze protection applications, the pipe temperature should be maintained at 40°F. Pipe temperatures should be maintained at 110°F for clog prevention of grease disposal lines and 40°F for viscosity maintenance of fuel oil lines.

2. HEAT LOSS
Use Table 1 to look up the heat loss associated with the pipe diameter and thickness of insulation. If a rigid insulation such as calcium silicate is used, the pipe heat loss should be increased to that associated with the next larger size. Insulation should also be oversized when using any cable other than the standard self-regulating HSR, without overjacket. This will compensate for the space of the heating cable. As an example, you would use 2-inch pipe diameter heat losses for 11/2 inch pipe heating application if rigid insulation were used. Heat loss figures from Table 1 include a 10% safety factor.

Another Table

3. ADJUSTMENTS TO HEAT LOSS VALUES
The heat losses in Table 1 are based on glass fiber insulation. If other insulations are used, multiply the heat loss value by the correction factor (shown in Table 2) for your insulation.

Heat losses are based on outdoor applications with 20 mph wind. If piping is used indoors, multiply heat loss values by 0.9.

4. DETERMINE CABLE P0WER
Using heat loss determined above, select appropriate cable from Performance and Rating Data chart. For heat loss in excess of 20 W/ft, use multiple cables. For example, for heat loss of 23 W/ft, use two 12 W/ft cables. Cable power may exceed heat loss by up to 50%. It is also possible to spiral cable on pipe such that the power applied to the pipe exactly matches the pipe heat loss. For example, for heat loss of 13 W/ft, a 10 W/ft cable can be spiraled on the pipe such that 1.3 feet of cable are wound on every foot of pipe, resulting in exactly 13 W/ft being applied to the pipe. However, spiraling requires significant extra labor to install and significant clearance around the pipe.

EXAMPLE