(Btu/hr-ft)
(W/m)
100
90
90
80
Total Insulation
80
Total CEGS - 02695
70
70
60
60
50
50
Supply Insulation
Supply CEGS - 02695
40
40
Return Insulation
30
Return CEGS - 02695
30
20
20
10
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
J
1988
1989
Figure 12. Heat losses from the MTHW individual conduit system.
for a portion of the study period for the individual
Here the average temperature difference between
conduit site are shown in Figure 12.
the outside of the conduit and the undisturbed soil
temperature at the burial depth is only 3.4C
(25.8F). This can be compared to a temperature
LTHW preinsulated system, site 1
difference of about 36.7C (66F) at the common
On the LTHW system at Site 1, the temperature
of the supply during the study period averaged
conduit site. The primary reason for this much lower
85.5C (185.9F) and the return averaged 81.2C
temperature difference at the individual conduit
(178.2F) for the same period of time. The relatively
site is the increased insulation thickness at that site.
small temperature difference between supply and
Because the thermal resistance of the insulation is
return must be attributed to the mass flow rate
much larger at the individual conduit site, the ther-
being in excess of what is required. It is not known if
mal resistance of the soil becomes a much smaller
this resulted from an error in design or from the
fraction of the total, and thus the corresponding
substitution of a larger pump in the construction
temperature drop across that resistance decreases.
process. The temperature of the outer surface of the
The heat losses for the individual conduit system
FRP jacket averaged 43.6C (110.5F) for the supply
were calculated by the insulation and CEGS-02695
and 42.4C (108.3F) for the return. The undisturbed
methods described earlier. As in the calculations for
ground temperature at approximately the same
the common conduit site, the thermal conductivity
depth as the centerline of the pipe averaged 25.5C
of the soil was taken as 1.08 W/m-C (7.5 Btu-in./
(77.9F). Here the average temperature difference
hr-ft2-F) for the CEGS-02695 method. The average
between the outside of the jacket and the undis-
of the heat loss values computed by the two meth-
turbed soil temperature at the burial depth is 17.5C
ods is 74.7 W/m (77.7 Btu/hr-ft). The highest of the
(31.5F). This can be compared to a temperature
methods (Insulation Method) was approximately
difference of about 36.7C (66F) at the common
7.5% greater than the lowest (CEGS-02695 Method).
conduit site and 14.3C (25.8F) at the individual
Again, considering the difficulty involved in mak-
conduit site. As with the individual conduit site, the
ing thermal measurements of this nature, we be-
primary reason for this much lower temperature
lieve this agreement is very good. The heat losses
20
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