Page 261 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

HEAT TRANSFER, INSULATION, AND FREEZE PROTECTION

HEAT TRANSFER, INSULATION, AND FREEZE PROTECTION 5.45

The second type is constant wattage, parallel circuit-constant resistant cable. It should be con-
sidered for use when long runs of cable are required, the length of cable is not known, or close
monitoring is necessary. Care must be exercised so as not to exceed the temperature rating in
use. The third type is the self-regulating, parallel circuit-variable resistant cable. It could be
used when the liquid has a wide temperature range, the length of cable is unknown, or liquid
temperatures will not exceed 185°F. All three of these cables are suitable for freeze protection.
In order to design and specify an efficient and cost-effective system, the following infor-
mation should be obtained or calculated:
1. Minimum temperature of the fluid to be maintained
2. Ambient temperature of the area where installed
3. Wind velocity of the area where installed, if outdoors
4. Pipe or vessel size and material
5. Tolerance of components allowed
6. Type and thickness of insulation over heating cable
7. Whether monitoring of operation will be required
8. Whether an alarm or enunciating of alarms will be required in the area in which the
cable is installed

TABLE 5.13 Checklist for Steam and Electric Heat Tracing

Electric Steam
Preexisting project constraints
Heat tracing recommended in company engineering practices (Yes/No)
Other
Project design phase criteria
Total feet of traced pipe
Cost of electricity, $/kWh, and steam energy ($/1000 lb)
Estimated annual maintenance cost per foot of tracing, $/ft
Number of heat-tracing circuits required
Needed accuracy of temperature control, degrees
Temperature control cost per circuit for needed accuracy, $
Cost of monitoring one circuit in distributed control system, $
Design time per circuit, h
Design tools available for engineers (Good, Fair, Poor, None)
Capital cost of steam capacity, condensate return, etc., $
Capital cost for required electrical power, $
Other
Project installation criteria
Labor cost to install tracing and accessories, $/ft
Training time per plant laborer, h
Labor and overhead costs, $/h
Total installed heat-tracing costs, $/ft
Other
Project operation criteria
Annual maintenance required, h/ft
Annual cost for replacement parts, $/ft
Annual energy cost, $/ft
Total annual maintenance cost, $
Total annual operating cost, $
Other

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