After the general layout of the system has been made and the site
and application conditions have been determined, size the system
carrier piping assuming a 2 percent heat loss from the supply line
at maximum flow.
Select one particular type of system configuration which is
relatively low in first cost and is approved for use with the site
and application conditions identified, to use as a model in making
the economic analysis.
Determine separately, for each section of the system, the installed
cost per foot of the system configuration with each of the
applicable combinations of insulation thicknesses shown in Table 3.
A section can be considered as any portion of the system in which
the conditions that affect heat loss are similar--e.g., pipe size,
tunnel shape, cover type. The cost of all components, other than
valve vaults called for in the selected system should be included
in the cost estimate. If only one pipe is to be installed (i.e.,
either a supply or return, but not both), use only the appropriate
column from the table for that type of pipe.
Determine the annual owning cost per foot of each section of the
system with each of the different thicknesses of insulation called
for in Table 3, using the following equation:
Installed Cost ($/ft)
Owning Cost ($/ft-yr) =
*Series Present Worth Factor
*The series present worth factor is the reciprocal of the
capital recovery factor.
The series present worth factor can be obtained from any set of
interest tables, given the annual interest rate (or rate or return)
and the number of years over which the cost is to be amortized
(i.e., the economic life of the item). Use an economic life of 25
years and a discount rate as published in National Bureau of
Standards (NBS) Handbook 135, entitled Life Cycle Cost Manual for
the Federal Energy Management Program.
Calculate the heat loss per linear foot separately for each pipe in
each section of the selected model system, assuming the various
thicknesses of insulation called for in Table 3, using applicable
calculation procedures in para. 188.8.131.52.