AR No. ____ - Insulate Pipes
Estimated Gas Energy Savings = **.* MMBtu/yr
Estimated Gas Cost Savings = $***/yr
Implementation Cost = $***
Simple Payback = *.* years
Recommended Action
Pipes located in the _______ area should be insulated to reduce heat losses and associated energy
costs.
Background
Measurements of uninsulated pipes were taken during the site visit. This information is
summarized in the table below.
**** CUT & PASTE SPECIAL THE "SITE_SHEET" TABLE FROM THE
INSPIPES.WB1 FILE HERE. ****
****INCLUDE ANY ADDITIONAL INFORMATION THAT MAY APPLY HERE ***
Anticipated Savings
The annual energy savings, ES, and energy cost savings, ECS, which could be realized by insulating
pipes, can be estimated as follows:
(

)  L  UH
ES  HL b HL i
EFF  C
ECS  ES  avoided cost of natural gas
where
HLb
HLi
L
UH
=
=
=
=
EFF =
C =
heat loss rate from bare pipe, Btu/h ft
heat loss rate from insulated bare pipe, Btu/h ft
pipe length, ft
annual time during which pipes are heated and heat loss does not contribute to space
heating, h/yr
efficiency of the heat supply, no units (assumed to be 80%)
conversion constant, 1,000,000 Btu/MMBtu
The 3E Plus Insulation Thickness Computer Program developed by the North American Insulation
Manufacturers Association is used to determine the heat loss from the bare and insulated pipes. The
program determines the most economically attractive thickness of a selected insulation type and
determines the heat loss from the pipe diameter, temperature, orientation, and other data related to
the heating system and economic criteria used at this facility. A summary of the heating system,
economic, and technical data used to determine the heat loss and most economically attractive
insulation thickness specifically for this plant is presented in the table below.
Summary of Heating System, Economic, and Technical Data
TECHNICAL DATA
Emittance of Outer Jacketing
0.10
Wind Speed
0 mph (indoors)
Emittance of Existing Surface
0.80
Additional information on the calculation routine used in the program is provided at the end of this
analysis. As an example calculation, the approximately ____ feet of uninsulated ___" diameter pipe
in the _______ area was measured to be _____F during the site visit. This area is not heated for
___ hours annually (the unheated hours are used because the bare pipe provides some space heating
to this area. Insulating the pipe will require some additional space heating.) From the 3E Plus
program, the heat loss from the bare pipe is ___ Btu/h ft. The suggested insulation is ___" of
___________, which costs about $___/ft installed. The heat loss from the insulated pipe is ___
Btu/h. Thus,
ES 
(****  ****)(***) (***)
 *,*** MMBt u/yr
(***)( 1,000 ,000)
ECS  (*** MMBtu /yr)($***/ MMBtu)  $***/yr
The energy and cost savings for other bare pipes in this plant are listed in the table below.
Summary of Energy and Cost Savings
***** CUT & PASTE SPECIAL "SAVINGS" TABLE FROM INSPIPES.WB1 ****
As shown in the table, the total energy savings are ____ ccf/yr and the corresponding cost savings
are $____/yr.
Implementation Cost
The installed cost of the insulation costs1 and simple payback are given in the table below.
*** CUT & PASTE SPECIAL "IMPLEMENT" TABLE FROM INSPIPES.WB1 ***
From the table, the total installation cost is $____. The cost savings of $_____/yr will pay for the
implementation cost in about ___ years.
Equations for Heat Loss From Pipes
The 3E Plus Insulation Thickness Computer Program developed by the North American Insulation
Manufacturers Association is used to determine the heat loss from the bare and insulated pipes. For
pipes, the heat loss per unit of outside surface area is given by the following equation:
1
From R. W. Means Company, Inc., CostWorks 2000 Software, R. W. Means Company, Inc.: Kingston, Mass.
Q
t t
 P S
A R  RS
with
R  r2
where
Q/A
tP
tS
R
r1
r2
k
Rs
ho
=
=
=
=
=
=
=
=
=
r 
ln  2 
 r1 
k
and
Rs 
1
ho
heat loss per unit of outside surface area, Btu/h ft2
process temperature, F
outer surface temperature of insulation, F
thermal resistance of insulation subsurface (conduction only), F ft2 h/Btu
inner radius of insulation layer, ft
outer radius of insulation layer, ft
thermal conductivity of insulation subsurface, Btu/F ft h
thermal resistance of insulation surface, F ft2 h/Btu
surface heat loss coefficient, Btu/F ft2 h
The surface resistance on the process temperature side is assumed to be small in comparison to the
other resistances so that it can be neglected. The conduction resistance R is a function of
temperature because k is temperature dependent. The surface resistance Rs represents the combined
effects of radiation and convection heat loss. To calculate Rs, a variation of the Heilman equations
is used. The equation is presented in ASTM C680. The combined convection and radiation heat
loss from the pipe surface is calculated as follows:
Q
t  tA
 S
A
Rs
or
Q
1
 ε σ ( T S 4 - T A4 )  C  
A
 D
where
tA =
T =
ε =
0.2






1
1
( TS  TA
2



) 

ambient temperature, F
temperature in degrees Rankine, R = F + 460
outer surface emittance, no units
0.181
( t S  t A ) 0.266
1  1.277 V
σ =
C =
D =
V =
Stefan-Boltzman constant, 1.714 x 10-9 Btu/ft2 h R4
constant depending on pipe orientation:
C = 1.016 for horizontal pipe
C = 1.235 for vertical pipe
outside diameter of last insulation layer, inches (if D > 24", then D = 24")
wind velocity, mph
Since the surface resistance depends on surface temperature in a nonlinear manner, some type of
iteration process is necessary. A back substitution method is used until the routine converges.
Within the iteration loop, the thermal conductivity of the insulation material is continuously
updated.
For the bare pipe case, the resistance of the pipe walls is not neglected. Geometrical data for
Schedule 40 pipe and the conductivity of steel are stored in the program. The resistance of the pipe
walls is calculated and then used to iterate on the surface energy balance.
The thermal conductivity k is calculated by integrating the thermal conductivity equation from the
hot face temperature to the surface temperature. This requires an initial guess of the surface
temperature. Each time the program iterates, the surface temperature is recalculated and a new
thermal conductivity is calculated.
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