economic thickness of insulation

8/9/2019 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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economic thickness of insulation

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