economic thickness of insulation
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%utline of Presentation
• Primary reasons for Insulation
• What is Economic Thickness of Insulation (ETI)?
• Affecting factors in ETI
•
Procedure for Calculating Economic Thickness of Insulation• Case Study No !
• Sim"lified #ormula for $eat %oss Calculation
• Case Study No &
• Conclusion• 'eferences
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Primary reasons for Insulation
To consere energy
To reduce heat loss or gain
To assist in maintaining a "roduct at a constant
tem"erature
To "reent condensation
To create a comforta*le enironmental condition
To "rotect "ersonnel ie Safety
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What is Economic Thickness of Insulation (ETI)?
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Affecting factors in ETI
i Cost of fuel
ii Annual hours of o"eration
iii $eat content of fuel
i +oiler efficiency
,"erating surface tem"erature
i Pi"e diameter-thickness of surface
ii Estimated cost of insulation
iii Aerage e."osure am*ient still air tem"erature
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Procedure for Calculating Economic Thickness of Insulation and Case Study No. 1
• To e."lain the conce"t of economic thickness of insulation/ 0e 0ill use an e.am"le ('efer Ta*le) Consider
an 1 *ar steam "i"eline of !21 mm diameter haing 345meter length We 0ill ealuate the cost of energy
losses 0hen 0e use !6/ &6 and 76 insulation to find out the most economic thickness
A ste"5*y5ste" "rocedure is gien *elo0
• ! Esta*lish the *are "i"e surface tem"erature/ *y measurement
• & Note the dimensions such as diameter/ length 8 surface area of the "i"e section under consideration
• 7 Assume an aerage am*ient tem"erature $ere/ 0e hae taken 74 9C
• : Since 0e are doing the calculations for commercially aaila*le insulation thickness/ some trial and error
calculations 0ill *e re;uired for deciding the surface tem"erature after "utting insulation To *egin 0ith
assume a alue *et0een :4 8 23 9C/ 0hich is a safe/ touch tem"erature• 3 Select an insulation material/ 0ith kno0n thermal conductiity alues in the mean insulation tem"erature
range $ere the mean tem"erature is !!! 9C and the alue of k < 44:: W-m& 9C for mineral 0ool
• 2 Calculate surface heat transfer coefficients of *are and insulated surfaces/ using e;uations discussed
"reiously Calculate the thermal resistance and thickness of insulation
• = Select r& such that the e;uialent thickness of insulation of "i"e e;uals to the insulation thickness
estimated in ste" 2 #rom this alue/ calculate the radial thickness of "i"e insulation < r&5r!
•1 Ad>ust the desired surface tem"erature alues so that the thickness of insulation is close to the standardalue of !6 (&3: mm)
• Estimate the surface area of the "i"e 0ith different insulation thickness and calculate the total heat loss
from the surfaces using heat transfer coefficient/ tem"erature difference *et0een "i"e surface and am*ient
• !4 Estimate the cost of energy losses in the 7 scenarios Calculate the Net Present @alue of the future energy
costs during an insulation life of ty"ically 73 years
• !! #ind out the total cost of "utting insulation on the "i"e (material la*or cost)
• !& Calculate the total cost of energy costs and insulation for 7 situations
• !7 Insulation thickness corres"onding to the lo0est total cost 0ill *e the economic thickness of insulation$
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Total cost is lo0er 0hen using 2" insulation thus it is
recommended.
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Sim!lified ormula for #eat $oss Calculation
S < B!4 (TsTa)-&4D . (TsTa)
• S < Surface heat loss in kCal%hr m2
• Ts < $ot surface tem"erature in &C
• Ta < Am*ient tem"erature in &C
• Total heat loss-hr ($s) < S ' A
• Annual heat loss in monetary terms ('s) < $f #uel cost
('s-kg)
• FC@ < Fross Calorific alue of fuel kCal%kg
• G * < +oiler efficiency in H
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Case Study No. 2
(. Steam "i"eline !44 mm diameter is not insulated for!44 m length su""lying steam at !4 kg-cm& to the
e;ui"ment #ind out the fuel saings if it is "ro"erly
insulated 0ith 23 mm insulating material
Assumptions:
• +oiler efficiency 14H
• #uel ,il cost 's!3444-tonne
• Surface tem"erature 0ithout insulation !=4 9C
• Surface tem"erature after insulation 23 9C
• Am*ient tem"erature &3 9C
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Existing System : (i.e. Without insulation)
• S < B!4 (Ts Ta)-&4D (Ts Ta)
• Ts < !=4 9C
• Ta < &3 9C
• S < B!4 (!=4 &3)-&4D (!=4 &3) < &344 kCal-hr5
m&
• S! < S
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Modified System:
• After insulating 0ith 23 mm glass 0ool 0ith
aluminum cladding the hot face tem"erature 0ill *e
23 9C
• Ts 23 9C• Ta &3 9C
• Su*stituting these alues
• S < B!4(235&3)-&4D (23 &3)• < :14 kCal-hr m&
• S& < S < E.isting heat loss (:14 kCal-hr m&)
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C)NC$*SI)N
• The a""ro"riate insulation must *e selected on the
*asis of tem!erature thermal conducti+ity and
other limiting factors that might limit a!!lication
• In any case insulation means less fuel consum!tiontherefore less emission
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,EE,ENCES
! 000*eeindiain
& Thermal Insulation and 'efractories 5PC'A
7 $and*ook on 'efractories *y NNandi/ Tata
JcFra0/ Ne0 elhi/ !1=
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T)"N*
+%,
1$
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