Page 260 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

HEAT TRANSFER, INSULATION, AND FREEZE PROTECTION

5.44 CHAPTER FIVE

FIGURE 5.20 Frost penetration beneath pavement: 100 pcf base material.

in a pipe (for example, by increasing the viscosity of number 6 fuel oil). Heat tracing used for
domestic hot water temperature maintenance is discussed in Chap. 9, “Plumbing Systems.”
This section will be concerned with freeze protection. Other aspects of this subject are
outside the scope of this book.
There are two broad classes of heat tracing methods, electric and fluid. Electric heat
tracing systems convert electric energy into heat. Fluid methods generally utilize water or
steam at an elevated temperature to transfer heat from one pipe to another. Fluid heating
media are usually contained in a small tube or pipe directly attached to the pipe being pro-
tected. Of the two fluids, steam is the more prevalent method of heat tracing.
Steam is more costly to install and maintain than electrical resistance. Periodic steam
leaks and failed steam traps waste energy and require constant maintenance. In addition, a
steam tracer produces 2 to 10 times more heat than is actually required for most applica-
tions. Choosing the most appropriate and cost-effective option for any specific application
involves many factors. If both systems are available, Table 5.13 can be used as a checklist
of the most important information needed to decide which option to choose. In general, if
steam is not present in sufficient quantities to provide the necessary heat, it is almost always
more practical and far less costly to use electric heat tracing.

ELECTRIC HEAT TRACING

General
This type of system consists of a heat-producing conductor (or cable), a controller to sense
the temperature of the air or pipeline, and a relay to turn on the current. As the electricity
flows through the cable, the resistance of the conductors causes the wire to become hot.
There are three general categories of heating cable. The first is mineral insulated, series
circuit-resistant cable, which has a constant heat output for its full length. It has a metal sheath
for cable protection. It is used when close temperature control is necessary, the liquid (or pipe)
may reach a very high temperature, protection from physical abuse is required, the cable
may be placed in a wet or moist environment, or close supervision of the system is needed.

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