feb 008 write

The economic thickness of

insulation for hot pipes

8FUEL EFFICIENCY

BOOKLET

BEST PRACTICE

P R O G R A M M E

Th e v iew s a n d ju d g em en t s ex p ressed in t h i s Fu el Ef f i c i en cy Bo o k let a re n o t n ecessa ri ly

t h o se o f t h e D ep a rt m en t o f t h e En v iro n m en t , ETSU o r BRECSU.

Cover photograph courtesy of Courtaulds Fibres

THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES

1 INTRODUCTION 1

2 THE EFFECT OF INSULATION 1

3 THE ECONOMIC THICKNESS OF INSULATION 3

Basic requirements to estimate economic thickness 4

4 TYPES OF INSULATION 5

5 THE ESTIMATION OF ECONOMIC THICKNESS 6

Use of specially prepared tables 7

By customised tabulation 7

6 ADAPTING TO AMBIENT CONDITIONS 12

7 ACKNOWLEDGEMENT 13

8 SOURCES OF FURTHER INFORMATION 13

APPENDIX 1

Some useful conversion factors 15

APPENDIX 2

Tables reproduced from BS 5422: 1990 16

APPENDIX 3

Heat loss graphs for various materials and surface temperatures 25

Preformed rigid fibrous sections 26

Preformed rigid calcium silicate or 85% magnesia sections 36

Preformed rigid polyisocyanurate or polyurethane sections 46

Preformed expanded nitrile rubber and polyethylene foam sections 49

APPENDIX 4

Some basic heat transfer formulae 51

CONTENTS


1 INTRODUCTION

Th is booklet is con cern ed with th e econ om ic

th ickn ess of in su lat ion for h ot p ipes.

Con siderable am oun ts of data an d pract ical

advice is given , in ten ded for use both by

experien ced person n el an d as train in g m aterial.

Th e cost of in stallin g th e in su lat ion is offset

by th e large savin gs in fuel bills wh ich can be

ach ieved th rough in su lat in g p ipes. Th is booklet

explain s h ow to determ in e th e th ickn ess of

in su lat ion wh ich will resu lt in th e optim um

in stallat ion .

Th is booklet is con cern ed on ly with h ot

p ipes, alth ough th e in su lat ion of p ipes operat in g

below am bien t tem perature is also im portan t. In

part icu lar, p ipes form in g part of dom estic an d

n on -dom estic h eatin g an d h ot water system s,

an d process p ipework are covered. Th e

in form ation an d tech n iques for determ in in g th e

m ost econ om ic th ickn ess of in su lat ion is

con sisten t with BS 5422:1990.

Th is booklet is in ten ded as a brief gu ide to

th e econ om ic th ickn ess of in su lat ion for h ot

p ipes, an d th erefore referen ces are m ade

th rough out to th e exten sive docum en tat ion

available from th e in su lat ion in dustry an d th e

Brit ish Stan dards In st itu t ion (BSI).

Fuel Efficien cy Booklet 19 - Process Plant

Insulation and Fuel Efficiency- gives a broad

picture of th e use of in su lat ion for process p lan t

an d sh ould be read in con jun ction with th is

booklet.

2 THE EFFECT OF INSULATION

An y surface wh ich is h otter th an its

surroun din gs will lose h eat. Th e rate at wh ich

h eat is lost depen ds on m an y factors, but th e

tem perature an d area of th e surface are often

dom in an t; th e greater th e tem perature an d area,

th e greater th e loss. Addin g an in su lat in g layer

to a h ot surface reduces th e extern al surface

tem perature. Alth ough th e surface area m ay be

in creased if in su lat ion is added to a circu lar p ipe,

th e relat ive effect of th e tem perature reduction is

m uch greater an d a reduction in h eat loss is

ach ieved.

Con sider for exam ple, a 15 m m bore p ipe

run n in g th rough st ill air (at 20°C) carryin g a h ot

flu id raisin g its extern al tem perature to 75°C.

Th e h eat loss is about 60 W per m etre of p ipe

run . Th e addit ion of a 25 m m th ick layer of

stan dard p ipe in su lat ion would in crease th e

surface area by a factor of approxim ately 3.5,

but th e extern al surface tem perature would fall

from 75°C to aroun d 23°C. Th e overall effect

would be to reduce th e h eat loss from 60 W to

12 W per m etre run of p ipe.

Th e ‘avoidable’ cost in creases dram atically as th e

tem perature of th e process flu id in creases. If th e

h ot flu id was at 200°C, th e ‘bare p ipe’ cost

would be aroun d £10,000 per an n um . Th is level

of h eat loss is equivalen t to run n in g a 1 kW

electric fire n igh t an d day for m ore th an 25

years. It cou ld be reduced to £560 per an n um if

1

INTRODUCTION

Un wan ted h eat loss costs m on ey. Th e loss of

h eat from a 100 m run of bare 50 m m bore

pipe carryin g process steam at 100ºC, would

cost aroun d £3,000 per an n um if th e steam

was supplied by a gas boiler with a gas cost of

1p/kWh (approxim ately 30p/ th erm ). Th is cost

would be reduced to £250 per an n um if a 50

m m th ick layer of appropriate in su lat ion was

applied. Th us, an an n ual savin g of £2,750

would be ach ieved.


a 75 m m th ick layer of in su lat ion were used (th e

in su lat ion th ickn ess m ust be in creased as th e

pipe tem perature in creases, to en sure a su itable

extern al surface tem perature). In th is case, th ere

is an avoidable cost of £9,440 per an n um .

Th e use of in su lat ion on p ipes carryin g h igh

tem perature stream s is a n orm al an d accepted

pract ice. It sh ould n ot be assum ed th at an y

exist in g in su lat ion provides th e m ost effect ive

arran gem en t for avoidable cost reduction . In

m an y cases, th icker in su lat in g layers would be

well just ified. All h ot surfaces lose h eat an d, as

sh own in Fig 1, atten t ion sh ould be given to

valves, flan ges, etc., wh ich are often left

un in su lated for m ain ten an ce reason s. An

un in sulated valve loses about th e sam e am oun t

of h eat as 1 m of un in su lated p ipe of th e sam e

diam eter. Un in sulated flan ges, wh ich h ave a

sm aller surface area, lose about h alf th is am oun t.

Th us, a 50 m m valve carryin g process steam at

200°C would cost about £100 per an n um

with out in su lat ion , but on ly about £6 per

an n um with appropriate in su lat ion . Th e

operat ion of valves n eed n ot be affected by

in su lat ion an d it can be applied in easily

rem ovable sect ion s to ease m ain ten an ce. An

addit ion al ben efit is a m ore un iform m etal

tem perature with a con sequen t reduction in

tem perature in duced stresses in th e p ipework

system , wh ich can be a cause of leakage at join ts.

Alth ough som e form of in su lat ion is

n orm ally foun d on h igh tem perature p ipework,

low tem perature sm all bore p ipes, or p ipes wh ich

are used on ly in term itten t ly, are often

com pletely n eglected. However, as with valves

an d flan ges, th ere is a con siderable poten tial for

avoidable cost savin gs. For exam ple, th e

payback periods for 25 m m th ick in su lat ion on

15 m m pipe in a gas fired dom estic h eatin g

2

THE EFFECT OF INSULATION

1000 2

2000 1

3000 0.7

4000 0.5

(Payback period assumes that the total cost for the installation of the insulation is £2 per metre)

��

��

��

��

��

��

��

��

Lagged

flanges

Unlagged

flanges

Fig 1 Heat loss through unlagged flanges

Table 1 The Payback Period for Insula t ion on Dom est ic Cent ra l Heat ing Pipew ork

Num ber of Operat ing Hours Payback Period (Years)


in stallat ion , for wh ich th e operat in g tem perature

would be typ ically 60 - 70°C, are as sh own in

Table 1. Th e payback period is th e t im e taken to

recoup th e in it ial cost of an in vestm en t from th e

savin gs it produces.

3 THE ECONOMIC THICKNESS OF

INSULATION

Th e exam ples presen ted in th e previous Section

give an in dicat ion of th e cost savin gs wh ich can

be ach ieved by th e use of in su lat ion to preven t

th e un wan ted dissipat ion of h eat from pipework.

For a given p ipe an d process con dit ion s, th e rate

of d issipat ion is depen den t on th e th ickn ess of

th e in su lat in g layer an d its th erm al perform an ce.

In m ost cases, th e m ost im portan t aspect of

th e in su lat ion ’s th erm al perform an ce is th erm al

con ductivity, a ph ysical property wh ich relates

th e rate at wh ich h eat is con ducted th rough a

m aterial to th e tem perature d ifferen ce across th e

con duction path . For th e sam e th ickn ess of

in su lat ion , h eat losses are reduced as th e th erm al

con ductivity reduces. Th e effect ive th erm al

con ductivity of an in su lat in g layer m ay depen d

on th e applicat ion procedure sin ce th is m ay

in fluen ce, for exam ple, th e exten t of voids or

bin der m aterial. Operat in g tem perature also

affects th e value of m an y in su lat in g m aterials’

th erm al con ductivity (see Section 4 ‘Types of

in su lat ion ’).

Oth er factors in fluen cin g th erm al

perform an ce in clude surface propert ies wh ich

affect losses due to radiat ion . For exam ple,

radiat ion losses can be reduced by th e addit ion

of a sh in y m etallic skin to th e in su lat in g layer.

Th e ben efits of such an addit ion depen d on

actual con dit ion s, but a 10% reduction in overall

h eat loss would n ot be un typical.

Man ufacturers of in su lat ion n orm ally

provide in form ation on th erm al perform an ce

wh ich avoids th e n eed for com plex h eat tran sfer

calcu lat ion s. Th e data, wh ich are n orm ally

referred to as ‘U’ values, give th e h eat loss per

un it len gth of p ipe for a ran ge of p ipe diam eters,

process stream tem peratures an d in su lat ion

th ickn esses. Wh ilst such data are usefu l for

est im ation purposes, it is im portan t to n ote th at

th e values are based on specified extern al

con dit ion s (often qu iescen t air at 20°C). Som e

caution m ust be exercised if th e actual

applicat ion con dit ion s vary con siderably from

th ose used to establish th e ‘U’ values.

It would be possible to reduce dissipat ive

losses from pipework system s to effect ively zero

by an appropriate ch oice of m aterial an d

th ickn ess. Th e cost of operat in g a h ot p ipe is

th e cost of th e h eat loss, p lus th e cost of an y

in su lat ion . In gen eral term s, th ere is a cost

pen alty associated with in creased th ickn ess an d

im proved th erm al perform an ce. Alth ough

h igh er expen diture resu lts in greater cost

savin gs, th ere is a poin t at wh ich in creased

expen diture to im prove th e level of in su lat ion

can n ot be just ified by th e addit ion al savin gs

wh ich would arise.

Th e com bin ed effect of in creased

expen diture due to in creasin g th e th ickn ess of

th e in su lat in g layer, an d in creased cost savin g,

for a specific set of operat in g con dit ion s, is

illustrated in Fig 2. Th e m in im um cost sh own is

th e lowest com bin ed cost of in su lat ion an d h eat

loss over a given period of t im e (th e evaluation

period). Th e m in im um cost occurs at a

part icu lar th ickn ess of in su lat ion , referred to as

th e ‘Econ om ic Th ickn ess of In su lat ion ’. In

pract ice, th e curves are less sm ooth because

3

THE ECONOMIC THICKNESS OF INSULATION


4

m an y types of in su lat ion are available on ly in

certain th ickn esses. Non eth eless, th e prin cip le

st ill applies.

Basic requirements to estimate economic

thickness

Most of th e in form ation wh ich is n eeded to

estim ate th e econ om ic th ickn ess of in sulation

follows from Fig 2. In particular, data are required

wh ich allows th e cost of h eat loss from th e

pipework system over th e evaluation period, an d

th e cost of in stallin g in sulation to be determ in ed.

Both th ese item s n eed to be establish ed for a

ran ge of in sulation th ickn esses. In BS 5422:1990,

th e m ain referen ce for th is booklet, evaluation

period is defin ed as th e total n um ber of operatin g

h ours over wh ich th e in vestm en t is to be assessed,

i.e. it is th e product of th e an n ual operatin g h ours

an d th e life of th e in vestm en t in years. An n ual

costs ten d to be m ore m ean in gful th an evaluation

period costs. Con sequen tly, in an y an alysis of

econ om ic th ickn ess, th e determ in ation of an n ual

costs is recom m en ded, th e evaluation period costs

are easily establish ed from th e an n ual data.

Ideally, th e life of th e in vestm en t would be based

on th e useful life of th e in sulation , but often

com pan y policies regardin g in vestm en t criteria

require a m uch sh orter period to be used. Th e

data required for th e com plete an alysis of

econ om ic th ickn ess can be sum m arised:

1 To determ ine the annual cost of heat loss per

metre run of pipe

Data requirem en ts:

■ Th e cost of fuel (In th e n orm al un its of

purch ase, e.g. pen ce/ th erm )

■ Th e boiler efficien cy (%)

An n ual operat in g period (h ours)

■ Heat loss per m etre run of p ipe

(Watts/m etre) wh ich depen ds on :

Pipe size

Operat in g tem perature

Type an d th ickn ess of in su lat ion

Am bien t con dit ion s

(Meth ods to est im ate th e h eat loss from

th ese data are given in Section 5)

2 To determ ine the cost of insulation


■ Cost of m aterial (£ per m etre of p ipe)

■ Cost of an cillary m aterials (£ per m etre of

p ipe)

■ Labour costs (£ per m etre of p ipe)

3 To determ ine the evaluation period


■ Th e in vestm en t life (years)

■ An n ual operat in g period (h ours)

THE ECONOMIC THICKNESS OF INSULATION

Insulation

cost

Lost heat

cost

Total cost

Co

st

(£)

Min

imu

m

co

st

Fig 2 Econom ic thickness of insula t ion


5

Th e an alysis to determ in e th e econ om ic

th ickn ess of in su lat ion can be carried out from

first prin cip les usin g basic data. Th is procedure

can in corporate both th e exact detail of an y

part icu lar applicat ion an d th e stan dard com pan y

m eth od for assessin g poten tial in vestm en t. For

exam ple, Discoun ted Cash Flow (DCF)

tech n iques are em ployed by som e organ isat ion s.

At th e oth er extrem e, tables of econ om ic

th ickn esses based on typ ical values of costs, etc.,

h ave been prepared. Th e use of such tables m ay

n ot provide th e optim um solut ion for a

part icu lar case, but th ey would n orm ally provide

a better an swer th an an arbitrary ch oice of

th ickn ess.

Before th e m eth ods of ach ievin g a value for

econ om ic th ickn ess are con sidered, it is usefu l to

con sider briefly th e types of available in su lat ion .

Th erm al perform an ce an d in stallat ion costs are

affected by th is ch oice.

4 TYPES OF INSULATION

In su lat ion m aterial is classed as:

■ Inorganic - based on crystallin e or am orph ous

siliceous/alum in ous/calcium m aterials

■ Organic - based on h ydrocarbon polym ers in

th e form of th erm osett in g/ th erm oplast ic

resin s or rubbers.

Th e in su lat ion m aterial can be eith er flexible or

rigid, both types of wh ich are available in

preform ed p ipe sect ion s. Table 2 lists th e

com m on types alon g with relevan t details.

Certain types of in su lat ion can be applied by

sprayin g an d th is m igh t be appropriate for large

pipes. Of th e in su lat in g m aterials listed in

Table 2, m in eral wool an d polyureth an e rigid

foam can be applied in th is way. Oth er

in su lat in g m aterials with a spray applicat ion

option are verm icu lite (m axim um tem perature

1,100°C) an d alum in o silicate (m axim um

tem perature 1,260°C). A bin der m ay be

required.

Th e th erm al con ductivity of in su lat in g

m aterials varies con siderably accordin g to th e

type of m aterial, its den sity an d operat in g

tem perature. Table 3 gives a represen tat ive

select ion .

TYPES OF INSULATION

Min eral Wool (Glass) 230 15 - 100

Min eral Wool (Rock) 850 80 - 150

Magn esia 315 180 - 220

Calcium Silicate 800 190 - 260

Polyureth an e Rigid Foam 110 30 - 160

Polyisocyan urate Rigid Foam 140 30 - 60

Ph en olic Rigid Foam 120 35 - 200

Polyth en e 80 30 - 40

Syn th etic Rubber 116 60 - 100

Table 2 Insula t ing m ateria ls ava ilable in preform ed pipe sect ions

Materia l Approxim ate Maxim um Norm al Bulk Densit y kg/m3

Tem perature ºC


Service tem perature is an obvious criterion

for th e select ion of an appropriate m aterial, but

oth er factors relat in g to th e operat in g

en viron m en t m ust also be taken in to accoun t.

Th ese in clude in tern al or extern al use, required

surface fin ish , structural stren gth con strain ts an d

accessibility. Alth ough m aterials exist to sat isfy

all com m on requirem en ts, it is im portan t to

n ote th at th e econ om ic th ickn ess varies

accordin g to type because of d ifferen ces in

propert ies an d costs.

Furth er details about in su lat ion m aterials

can be foun d in th e TIMSA Han dbook (available

from Th e Th erm al In su lat ion Man ufacturers an d

Suppliers Associat ion , PO Box 111, Aldersh ot,

Ham psh ire, GU11 1YW) an d BS 5970: 1992.

In su lat ion for p ipework is also d iscussed in Fuel

Efficien cy Booklet 19 - Process plant insulation and

fuel efficiency- wh ich gives gen eral in form ation

on in su lat in g a ran ge of process p lan t an d m ore

details of surface fin ish es an d gen eral good

pract ice.

5 THE ESTIMATION OF ECONOMIC

THICKNESS

Th ere are th ree differen t m eth ods of est im atin g

econ om ic th ickn ess. Th e first uses specially

prepared tables based on assum ption s about

every item of data required to est im ate econ om ic

th ickn ess. Th e assum ption s are reason able for a

wide ran ge of applicat ion s an d th e tables are

easy to use. However, th ere is a m argin of error

with th is m eth od, because specific details can n ot

be in cluded. Th e secon d an d m ore accurate

m eth od is th e form ulat ion of custom ised tables

wh ich do take accoun t of specific details an d

wh ich th erefore provide a greater degree of

con fiden ce. Th ese two m eth ods will be described

in detail in th is Section

Th e th ird m eth od of est im atin g econ om ic

th ickn ess is an algebraic solu t ion . Th is requires

m ath em atical m an ipu lat ion skills, but it h as th e

least n um ber of assum ption s an d is th e m ost

flexible of th e th ree m eth ods. It sh ould on ly be

attem pted if a very precise value of th ickn ess is

n eeded, an d often th is is n ot a requirem en t

6

THE ESTIMATION OF ECONOMIC THICKNESS

Table 3 Therm al conduct ivit ies of insula t ing m ateria ls

Calcium Silicate 210 0.055 0.058 0.083

Expan ded Nitrile Rubber 65 - 90 0.039 – –

Min eral Wool (Glass) 16 0.047 0.065 –

48 0.035 0.044 –

Min eral Wool (Rock) 100 0.037 0.043 0.088

Magn esia 190 0.055 0.058 0.082

Polyisocyan urate Foam 50 0.023 0.026 –

Material Den sity Th erm al Con ductivity W/(m .K)

kg/m3 Tem perature ºC

50 100 300


because m an y types of in su lat ion are available

on ly in certain specific sizes. For th is reason , th e

algebraic m eth od will n ot be described in th is

booklet. For a m ore detailed explan ation of th e

tech n ique, referen ce can be m ade to Energy

Efficiency for Technologists & Engineers; Eastop &

Croft, publish ed by Lon gm an Scien tific &

Tech n ical; ISBN 0-582-03184-2.

Use of specially prepared tables

Tables of th e econ om ic th ickn ess of in su lat ion

for various types of applicat ion are in cluded in

BS 5422:1990. Values of th e econ om ic

th ickn esses h ave been tabulated for appropriate

ran ges of p ipe sizes, p ipe surface tem peratures,

(n orm ally th e process stream tem perature), an d

in sulat ion th erm al con ductivit ies. Th ese tables

h ave been reproduced in th is booklet in

Appen dix 2 as follows:

■ Non -Dom estic h eatin g an d h ot water

services

Heatin g - solid fuel boiler Table 8

- gas-fired boiler Table 9

- oil-fired boiler Table 10

Hot water services Table 11

■ Dom estic h eatin g an d h ot water services

Heatin g - h eated areas Table 12

- un h eated areas Table 13

Hot water services - h eated areas Table 14

- un h eated areas Table 15

■ Process p ipework Table 16

Th ese tables provide th e easiest m eth od of

determ in in g th e required value of econ om ic

th ickn ess, but th e con dit ion s of th e applicat ion

un der con siderat ion sh ould reason ably sat isfy

th e assum ption s used to derive th e tabulated

values. Use th e tables in th e absen ce of an y

applicat ion data, but if data are available, th ey

sh ould be ch ecked for con sisten cy with th e

assum ption s. Un less oth erwise stated in Tables 8

to 16, am bien t con dit ion s are st ill air at 20°C.

Table 4 sh ows th e fuel costs an d evaluation

period used to derive th e tabulated values for th e

th ree applicat ion categories, n on -dom estic

cen tral h eatin g an d h ot water services, dom estic

cen tral h eatin g an d h ot water services an d

process p ipework. Fuel costs are expressed in

pen ce per usefu l MJ. Th is is th e cost of th e fuel

in pen ce per MJ divided by th e efficien cy of th e

boiler.

Table 17 gives th e usefu l cost of h eat for

com m on fuels over a ran ge of fuel prices,

expressed in th e n orm al purch ase un its, based

on typ ical boiler efficien cies. For a part icu lar

purch ase price, th e usefu l cost of h eat can be

obtain ed direct ly from Table 17. In su lat ion costs

are expressed in a part icu lar way wh ich is

described below. In gen eral term s, th e econ om ic

th ickn esses h ave been derived for est im ates of

fuel, in su lat ion an d in stallat ion costs wh ich will

apply in 1995.

By customised tabulation

If th e data relat in g to a part icu lar applicat ion are

sign ifican tly d ifferen t from th ose form in g th e

assum ption s used to derive th e tabulated values

of econ om ic th ickn ess (Tables 8-16) a calcu lat ion

specific to th e applicat ion m ust be perform ed.

Th e m ost straigh tforward m eth od of calcu lat ion

is to create a table wh ich sh ows th e total cost,

i.e. th e cost of th e h eat loss p lus th e in su lat ion

costs over th e evaluation period, for a ran ge of

in su lat ion th ickn esses. Th e th ickn ess wh ich

results in th e m in im um total cost can th en be

selected.

7



8


Fuel: Solid Fuel 0.38Gas 0.57Oil 0.67

Applicat ion : Cen tral Heatin g 20,000Hot water services 40,000

Table 4 Fuel costs and eva luat ion period used to derive the econom ic thickness Tables 8 - 16

Fuel Cost Evaluation Periodpen ce per usefu l MJ h ours

Dom estic cen tral h eatin g an d h ot water services

Non -dom estic cen tral h eatin g an d h ot water services

Fuel: Gas 0.76

Applicat ion : Cen tral Heatin g 17,000Hot water services 9,000

Notes: (1) Each evaluation period is based on a typical interm ittent operation for the number of hours shown over a five year period (e.g. continuous non-domestic operation for five years = 40,000 hours)

(2) Deduced from data in BS 5422:1990

Process p ipework 0.6 (2) 40,000

Fig 3 Exam ple of t able needed for custom ised tabula t ion

Th ickn ess of Heat loss Cost factor Cost of h eat lost over In stalled cost Total costin su lat ion evaluation period of in su lat ion

(m m ) (W/m ) (£/W) (£/ lin ear m ) (£/ lin ear m ) (£/ lin ear m )


9


A table of th e type sh own in Fig 3 is

required. In form ation described in Section 3,

‘Th e econ om ic th ickn ess of in su lat ion ’, m ust be

available to com plete th e table. Th e m ean in g of

th e h eadin gs an d th e m eth od of calcu lat in g th e

relevan t values are as follows. Each h eadin g h as

been assign ed a step n um ber, used to clarify th e

worked exam ple given on Page 9.

Thickness of insulation (Step 1)

Th e table is com pleted for a ran ge of

possible in su lat ion th ickn esses. If n ecessary, th e

first en try can be bare p ipe, i.e. in su lat ion

th ickn ess equals 0 m m , an d successive en tries

m ade for each of th e available th ickn esses of th e

selected in su lat ion . Altern atively, th e tabulated

values of econ om ic th ickn ess can be used as a

guide to th e approxim ate value an d a ran ge of

th ickn esses aroun d th is value used in th e table.

Heat loss (Step 2)

Th is is th e rate of h eat loss, in watts, per

m etre of p ipe. It depen ds on th e process stream

tem perature, th e p ipe diam eter, th e in su lat ion

th ickn ess an d am bien t con dit ion s. Th e h eat loss

can be determ in ed con ven ien tly from pre-

prepared graph s (Graph s 1 - 25) wh ich give th e

h eat loss for a ran ge of in su lat ion types an d

th ickn esses, p ipe diam eters an d tem peratures.

For presen tat ion al con ven ien ce, th ese graph s are

reproduced in Appen dix 3. Table 5 sum m arises

con ven ien tly th e con ten t of each of th e graph s.

Use Table 5 to select th e appropriate graph for

th e part icu lar in su lat ion type an d p ipe

tem perature relevan t to th e applicat ion un der

con siderat ion . Th e use of th ese graph s is

illustrated in Graph 3 wh ich is based on a p ipe

tem perature of 100°C in su lated with perform ed

rigid fibrous sect ion s. Th e dotted lin es sh ow, for

exam ple, th at a 50 m m bore p ipe with 50 m m of

in su lat ion would lose h eat at 20 W/m ; th e sam e

pipe with out in su lat ion would lose h eat at 240

W/m . In a sim ilar way, th e value of h eat loss

can be determ in ed for an y com bin ation of p ipe

bore an d in su lat ion th ickn ess. If con dit ion s are

win dy, refer to Section 6.

Cost factor (Step 3)

Th e cost factor is th e cost in poun ds of on e

watt of h eat loss per m etre of p ipe over th e

evaluation period. It depen ds on th e evaluation

period an d th e cost of usefu l h eat. Th e stages in

determ in in g th e cost factor are:

i) Determ in e th e n um ber of MJ of h eat wh ich

are lost per m etre of p ipe over th e evaluation

period if th e rate of loss is on e watt/m etre.

A watt is a jou le per secon d. Th erefore, if

th e evaluation period is expressed in h ours,

th e n um ber of jou les wh ich are lost with a

on e watt h eat loss is:

evaluation period x 3,600

A m egajou le (MJ) is 1,000,000 jou les

(106 jou les), th erefore th e n um ber of MJ lost

with a on e watt h eat loss is:

evaluation period x 3,600 / 106

ii) Determ in e th e cost factor wh ich is th e

product of th e cost of usefu l h eat in pen ce

per MJ an d th e n um ber of MJ lost, i.e.,

cost x evaluation period x 3,600 / 106

Th e result sh ould be divided by 100 so th at

th e cost factor is expressed in £/W

Th e two stages can be com bin ed in to a sin gle

form ula:

Cost factor = pen ce x evaluation period x 36MJ 106

A B C D


Cost of heat lost over evaluation period

(Step 4)

Th is is sim ply th e total value of th e h eat lost

per m etre of p ipe, for th e part icu lar th ickn ess of

in su lat ion , over th e evaluation period. Th e h eat

loss colum n gives th e loss in watts per m etre an d

th e cost factor gives th e cost in £/W for th e

evaluation period. Th erefore, th e cost of h eat

loss is given by:

Heat loss x Cost factor

Installed cost of insulation (Step 5)

Th is is th e total cost of th e in su lat ion per

m etre of p ipe in clusive of th e cost of th e

in su lat in g m aterials, th e in stallat ion cost, surface

fin ish , fixin g m aterials etc. Th is cost m ust be

determ in ed for every th ickn ess of in su lat ion

con sidered.

Total cost (Step 6)

Th is is th e sum of th e cost of h eat loss over

th e evaluation period an d th e in stalled cost of

in su lat ion .

10


50 1 11 24

70 21

75 2 12 25

100 3 13 22

145 23

150 4 14

200 5 15

300 6 16

400 7 17

500 8 18

600 9 19

700 10 20

Table 5 Sum m ary of heat loss graphs (Appendix 3)

Pipe Surface Graph Num ber

Tem perature (ºC)

In su lat ion Type

Insulation Types A: Preformed rigid fibrous sectionsB: Preformed rigid calcium silicate or 85% magnesia sections (magnesia sections up to

300ºC only)C: Preformed rigid polyisocyanurate or polyurethane sections (polyurethane sections up to

100ºC only)D: Preformed expanded nitrile rubber and polyethylene foam sections


Ex am ple:Th e followin g exam ple sh ows th e use of th e

custom ised tabulat ion m eth od for est im atin g

econ om ic th ickn ess.

A n on -dom estic h eatin g system uses steam at

sligh t ly over 100ºC supplied th ough 50 m m bore

pipes. Th e steam is supplied by a gas boiler wh ich

is 70% efficien t an d th e cost of gas is 28 pen ce per

th erm . Preform ed fibrous in su lat ion m aterial

(th erm al con ductivity - 0.055 W/(m .K) ) is to be

used. Th e total cost of in stalled in su lat ion for the

various th ickn esses available from th e

m an ufacturer is as follows:

19 m m th ickn ess £1.40/m

25 m m £2.00/m

32 m m £2.30/m

38 m m £2.90/m

50 m m £8.40/m

Th e evaluation period is 22,000 h ours (5 year

in vestm en t life with 4,400 h ours of operat ion per

an n um ) an d th e p ipework can be assum ed to run

th rough st ill air at 20ºC.

St ep 1 Th ickn ess o f in su la t ion

For th is applicat ion , Table 9 in dicates th at th e

econ om ic th ickn ess is 37 m m (tabulated results for

a p ipe with an outside diam eter of 60.3 m m are

th e closest to th e proposed applicat ion ).

Con sequen tly est im ates aroun d th is th ickn ess are

likely to be required an d th e first est im ate of

econ om ic th ickn ess sh ould be 25 m m . Th e values

for each of th e colum n s of th e est im atin g table

can n ow be evaluated.

St ep 2 Hea t Loss

Graph 3 is th e appropriate h eat loss graph for th is

applicat ion . Th is sh ows th at a 50 m m bore p ipe

with 25 m m of preform ed fibrous in su lat ion

would lose h eat at th e rate of 30 W/m .

St ep 3 Cost Fa ct or

Table 17 in dicates th at th e usefu l cost of h eat for a

gas boiler with 70% efficien cy an d a fuel cost of

22.16 p/ th erm is 0.30 p/MJ an d for a fuel cost of

29.54 p/ th erm th e usefu l cost is 0.40 p/MJ. In th is

part icu lar applicat ion th e gas cost is 28 p/ th erm an d

th e usefu l cost of h eat m ust be est im ated. Sim ple

proport ion ality can be used; for th is applicat ion , th e

usefu l cost is given by:

0.30Usefu l Cost = 22.16 = 0.38 p/MJ

Th e evaluation period is 22,000 h ours an d,

th erefore, th e cost factor is given by:

Cost Factor = 0.38 x 22,000 x 36 = 0.30 £/W

106

Note th at th e cost factor is th e sam e for all

in su lat ion th ickn esses.

St ep 4 Cost o f h ea t los t over eva lu a t ion

p er iod

Th e product of th e cost factor an d th e h eat lost.

Th erefore:

Cost of h eat = 30 x 0.30 = £9.00/m

St ep 5 In s t a l led cost o f in su la t ion

Given as £2.00/m

St ep 6 Tot a l cost

Th e sum of th e cost of h eat an d th e in stalled cost of

in su lat ion (Step 4 + Step 5), i.e.:

Total Cost = 9.00 + 2.00= £11.00/m

Sim ilar calcu lat ion s are used for all th e oth er

th ickn ess values an d th e resu lts h ave been tabulated

in Table 6. Th is sh ows th at th e m in im um cost

occurs with an in su lat ion th ickn ess of 38 m m an d

th is sh ould be th e th ickn ess selected. Note th at in

th is exam ple th e tabulat ion m eth od gives

approxim ately th e sam e value of econ om ic

th ickn ess as given in th e pre-prepared tables. THIS

WILL NOT BE TRUE FOR EVERY APPLICATION. It

m ust also be rem em bered th at th e values for Total

Cost are h eavily depen den t on th e in vestm en t

criteria of th e organ isat ion .

11


( )

( )


6 ADAPTING TO AMBIENT CONDITIONS

All th e procedures in dicated above h ave beenbased on am bien t con dit ion s of st ill air at 20°C.Air m otion , wh ich in m ost pract ical applicat ion swill be due to win d, an d a d ifferen t am bien ttem perature, can h ave a sign ifican t effect on th erate of h eat loss an d, con sequen tly, th eecon om ic th ickn ess of in su lat ion .

Win d speed can h ave a large effect on th e

h eat loss from bare p ipes as sh own in Table 7.

Th is gives m ult ip lyin g factors for bare p ipe h eat

losses com pared with th ose in st ill air con dit ion s

sh own in Graph s 1 - 25.

Th e factors for h igh , m edium an d low

em issivity surfaces refer to th e n ature of th e

outer surface of th e p ipe. As a gu ide, a pain ted

surface would n orm ally h ave a h igh em issivity,

oxid ised steel a m edium em issivity an d polish ed

alum in ium a low em issivity.

If th ere is n o data on typ ical win d speeds,

th e followin g values are recom m en ded:

Sh eltered situat ion s 1 m /s

Norm al situat ion s 3 m /s

Exposed situat ion s 10 m /s

Fortun ately, for in su lated p ipes th e effect of

exposure to win d speed alon e will n ot n orm ally

in crease th e h eat loss from a well in su lated p ipe

by m ore th an 10% even in exposed con dit ion s.

Th is is because th e th erm al resistan ce of th e

in su lat ion is th e dom in an t factor in determ in in g

th e rate of h eat loss.

12

ADAPTING TO AMBIENT CONDITIONS

25 30 0.30 9.00 2.00 11.00

32 26 0.30 7.80 2.30 10.10

38 23 0.30 6.90 2.90 9.80

50 20 0.30 6.00 8.40 14.40

Still Air 1.00 1.00 1.00

1 1.35 1.44 1.58

2 1.65 1.81 2.11

3 2.00 2.25 2.72

5 2.60 3.00 3.86

10 4.00 4.75 6.32

Table 6 Exam ple of econom ic thickness determ inat ion by tabula t ion

Table 7 W ind speed correct ion factors for heat losses from bare pipes only

Win d Speed (m /s) Mult ip lyin g Factors

Th ickn ess of Heat Loss Cost Factor Cost of Heat In stalled Cost Total Costin su lat ion Loss of In su lat ion

m m W/m £/W £/m £/m £/m

High Em issivity Medium Em issivity Low Em issivity

Surface Surface Surface


Variat ion s in am bien t tem perature also affect th e

rate of h eat loss, wh ich in gen eral is proport ion al

to th e differen ce between th e p ipe (flu id)

tem perature an d th e am bien t tem perature. For

exam ple, if th e average am bien t tem perature is

10°C as opposed to 20°C, an d th e p ipe

tem perature is 150°C, th e rate of h eat loss will be

7.7% (10 ÷ 130) greater.

For outdoor in su lated p ip in g in th e UK, a

rough guide would be to in crease th e st ill air,

20°C am bien t, h eat loss rate by 15% - 20% to

take accoun t of th e lower air tem perature an d

exposure to win ds.

It is n ecessary to em ph asise th e im portan ce

of claddin g or sealin g outdoor in su lat ion to

m ake it waterproof as far as possible. Th e h eat

losses from wet in su lat ion will far exceed th e

h eat losses th rough dry m aterial.

7 ACKNOWLEDGEMENT

Th e Departm en t of th e En viron m en t is gratefu l

to th e Brit ish Stan dards In st itu t ion for

perm ission to reproduce m aterial from BS5970:

1992 an d BS 5442: 1990.

8 SOURCES OF FURTHER INFORMATION

■ British Standards:

Th e followin g Brit ish Stan dards con tain furth er

in form ation on th erm al in su lat ion , its

specificat ion an d sources of supply:

BS 5422:1990 - Method for specifying thermal

insulating materials on pipes, ductwork and

equipment (in the temperature range -40ºC to

+700ºC)

BS 5970:1992 - Code of practice for thermal

insulation of pipework and equipment (in the

temperature range -100ºC to +870ºC)

Copies of th ese Brit ish Stan dards are available

from :

Brit ish Stan dards In st itu t ion

Sales Departm en t

Lin ford Wood

Milton Keyn es

MK14 6LE

■ Insulation Suppliers:

TIMSA Han dbook: The Specifiers Insulation Guide

1992

Copies of th is publicat ion are available from :

Th erm al In su lat ion Man ufacturers an d Suppliers

Associat ion

PO Box 111

Aldersh ot

Ham psh ire

GU11 1YW

Tel: 01252 336318

■ Energy Efficiency Best Practice programme

publications:

Copies of literature applicable to in su lat ion an d

to en ergy efficien cy in in dustry in gen eral are

available from :

En ergy Efficien cy En quiries Bureau

ETSU

Harwell

Didcot

Oxon

OX11 0RA

Tel: 01235 436747

Fax: 01235 433066

■ The latest news in energy efficiency technology

Energy Managementis a free journ al issued on

beh alf of th e DOE wh ich con tain s in form ation

13

SOURCES OF FURTHER INFORMATION

14


SOURCES OF FURTHER INFORMATION

on th e latest developm en ts in en ergy efficien cy,

an d details of forth com in g even ts design ed to

prom ote th eir im plem en tat ion .

Copies of En ergy Man agem en t can be

obtain ed th rough :

Em ap Maclaren Lim ited

Maclaren House

19 Scarbrook Road

Croydon

Surrey

CR9 1QH


SOME USEFUL CONVERSION FACTORS

15

APPENDIX 1

Conversion factors for units used in this booklet

SI Im perial

Tem perature ºC x 1.8 + 32 = ºF

Len gth m m x 0.0394 = in

m x 3.2808 = ft

Volum e litres x 0.2200 = gal

Weigh t ton n e x 0.9842 = ton

En ergy GJ x 9.4782 = th erm

Heat flow rate W/ lin ear m x 1.0400 = Btu/ ft h

Th erm al con ductivity W/m K x 6.9335 = Btu in / ft2h ºF

Th erm al con ductan ce W/m2K x 0.176 = Btu/ ft2h ºF

For h eavy fuel oil th e n um ber of lit res in ton n e = 1,020

Medium fuel oil th e n um ber of lit res in a ton n e = 1,040

Gas oil th e n um ber of lit res in a ton n e = 1,180

16


TABLES REPRODUCED FROM BS 5422: 1990

APPENDIX 2 TABLES REPRODUCED FROM BS 5422: 1990

Table 8 Econom ic thickness of insula t ion for non-dom est ic heat ing insta lla t ions

served by solid fuel-fired boiler plant

17.2 14 17 20 23 17 21 24 26 22 25 28 32

21.3 15 18 22 24 17 22 25 27 23 26 30 34

26.9 17 20 23 25 20 24 26 28 24 28 32 35

33.7 17 21 24 26 20 25 27 31 25 29 34 37

42.4 18 22 25 27 21 25 28 32 25 31 35 39

48.3 18 23 25 28 22 26 29 33 26 32 36 41

60.3 19 24 26 29 23 27 31 35 27 33 38 43

76.1 20 24 27 31 23 28 33 36 28 35 40 45

88.9 20 24 28 32 24 28 33 37 29 36 42 46

114.3 21 25 29 33 25 30 35 39 31 37 44 48

139.7 22 26 30 34 25 31 36 41 31 38 45 50

168.3 22 26 31 35 25 32 37 42 32 40 46 52

219.1 22 27 32 36 26 33 38 43 33 42 48 54

273.0 23 27 33 36 26 34 39 44 34 43 49 55

Above 323.9 23 28 34 38 27 35 42 47 35 45 53 60

an d

in cludin g

flat surfaces

1 Outside diameters are as in BS 3600. The same thickness of insulation would be used for copper pipework ofapproximately sim ilar outside diameters.

Hot face tem perature (in ºC) (with am bien t st ill air at +20ºC)

+ 75 +100 +150

0.025 0.04 0.055 0.07 0.025 0.04 0.055 0.07 0.025 0.04 0.055 0.07

Outside diam eterof steel p ipe onwh ich in su lat ionth ickn ess h asbeen based (in m m ) 1

Th ickn ess of in su lat ion (in m m )

Th erm al con ductivity at m ean tem perature (in W/(m .K))


17


Table 9 Econom ic thickness of insula t ion for non-dom est ic heat ing insta lla t ions served by

gas boiler plant

17.2 17 22 24 26 20 24 27 31 24 29 34 37

21.3 18 23 25 27 22 25 29 33 26 32 36 39

26.9 20 24 26 29 23 27 31 34 27 33 38 42

33.7 21 25 27 31 24 28 33 36 28 35 40 44

42.4 22 25 29 32 25 30 34 38 30 37 42 47

48.3 22 26 30 33 25 31 35 39 31 38 44 48

60.3 23 27 32 35 26 32 37 41 33 39 46 50

76.1 24 28 33 36 27 34 39 43 34 42 48 52

88.9 24 29 34 37 28 35 40 45 35 43 49 53

114.3 25 31 35 39 29 36 42 47 36 45 51 56

139.7 25 32 36 41 30 37 43 48 37 47 53 59

168.3 25 32 37 42 31 38 45 50 38 48 56 61

219.1 26 33 38 44 32 40 46 52 40 51 58 65

273.0 27 34 40 45 33 41 47 53 41 52 59 68

Above 323.9 27 36 42 47 34 43 51 58 42 54 63 72

an d

in cludin g

flat surfaces



+ 75 +100 +150

0.025 0.04 0.055 0.07 0.025 0.04 0.055 0.07 0.025 0.04 0.055 0.07

Outside diam eterof steel p ipe onwh ich in su lat ionth ickn ess h asbeen based (in m m )1




18


Table 10 Econom ic thickness of insula t ion for non-dom est ic heat ing insta lla t ions served by

oil-fired plant

17.2 18 23 25 28 22 26 29 33 26 32 36 40

21.3 19 24 27 29 23 27 32 35 27 34 38 43

26.9 21 25 28 32 24 29 33 36 29 35 41 45

33.7 22 26 29 33 26 31 35 38 31 37 43 47

42.4 23 27 32 35 26 32 37 41 32 39 45 50

48.3 24 28 33 36 27 33 38 42 33 41 46 51

60.3 25 29 34 37 28 35 39 44 35 43 49 52

76.1 25 31 35 39 29 36 42 46 36 45 50 55

88.9 25 32 36 41 30 37 43 48 37 46 51 57

114.3 26 33 38 43 31 38 44 49 39 48 54 60

139.7 27 34 39 44 33 41 47 51 41 50 57 63

168.3 27 35 41 45 33 42 48 54 42 52 59 66

219.1 28 36 42 47 34 43 51 56 43 54 62 69

273.0 29 37 43 48 35 44 52 57 45 55 64 71

Above 323.9 31 38 45 52 37 47 55 62 47 60 69 77

an d

in cludin g

flat surfaces



+ 75 +100 +150

0.025 0.04 0.055 0.07 0.025 0.04 0.055 0.07 0.025 0.04 0.055 0.07





19


Table 11 Econom ic thickness of insula t ion for non-dom est ic hot w ater services

17.2 17 21 24 27 20 24 28 32 22 27 31 34

21.3 18 22 25 28 22 26 30 34 23 28 32 36

26.9 20 23 27 29 23 28 32 35 24 29 34 38

33.7 20 24 28 31 24 29 33 37 26 31 36 40

42.4 21 26 30 33 25 31 34 39 28 33 38 42

48.3 22 27 31 34 26 32 36 40 29 34 39 43

60.3 23 28 32 36 27 33 38 42 30 36 41 45

76.1 23 29 34 37 28 35 40 44 31 37 42 47

88.9 24 30 35 38 29 36 41 45 32 38 44 48

114.3 25 31 36 40 30 37 43 47 33 40 46 51

139.7 25 32 37 41 31 38 44 50 34 41 47 54

168.3 26 33 38 42 32 39 45 52 34 42 51 56

219.1 26 34 39 44 33 41 47 55 35 44 53 59

273.0 27 35 40 45 34 42 51 57 36 45 55 61

Above 323.9 29 36 42 50 35 44 54 61 40 51 59 65

an d

in cludin g

flat surfaces


Water tem perature +60ºC)

Solid Fuel Gas Oil

0.025 0.04 0.055 0.07 0.025 0.04 0.055 0.07 0.025 0.04 0.055 0.07





20


Table 12 Econom ic thickness of insula t ion for dom est ic cent ra l heat ing insta lla t ions

in heated areas

10 17 18 19 20 27

12 18 19 20 21 29

15 18 19 21 29 31

22 20 29 30 32 33

28 21 30 32 34 35

35 22 32 34 35 37

42 22 33 35 37 39

54 23 35 37 39 40

Flat surfaces 29 31 34 36 38

Water tem perature of +75ºC with am bien t st ill air tem perature of + 20ºC

0.025 0.030 0.035 0.040 0.045

Outside diam eterof copper p ipe(in m m )


Table 13 Econom ic thickness of insula t ion for dom est ic cent ra l heat ing insta lla t ions

in unheated areas

10 19 20 21 32 34

12 20 21 22 32 34

15 21 22 32 33 35

22 22 32 34 35 36

28 23 34 36 36 36

35 24 35 37 38 39

42 25 37 38 39 40

54 26 37 38 39 40


Water tem perature of +75ºC with am bien t st ill air tem perature of -1ºC

0.025 0.030 0.035 0.040 0.045



Th erm al con ductivity at +40ºC (in W/(m .K))



21


Table 14 Econom ic thickness of insula t ion for dom est ic hot w ater system s in heated areas

10 13 14 14 14 15

12 13 14 14 15 16

15 13 14 14 16 17

22 14 15 16 17 18

28 14 15 16 18 19

35 15 17 17 19 19

42 15 17 18 19 20

54 16 18 19 20 21


Water tem perature of +60ºC with am bien t st ill air tem perature of + 20ºC

0.025 0.030 0.035 0.040 0.045



Table 15 Econom ic thickness of insula t ion for dom est ic hot w ater system s in unheated areas

10 14 15 16 17 18

12 15 16 17 18 19

15 15 17 17 19 19

22 16 18 20 20 21

28 17 19 20 21 30

35 18 20 21 22 31

42 19 20 22 23 32

54 20 21 23 33 34


Water tem perature of +60ºC with am bien t st ill air tem perature of -1ºC

0.025 0.030 0.035 0.040 0.045






22


Table 16 Econom ic thickness of insula t ion for process pipew ork and equipm ent

17.2 28 31 35 38 41 45 49 52 56 59 52 57 61 66 70

21.3 29 33 37 40 43 46 50 54 58 62 55 60 65 70 74

26.9 31 35 39 43 46 50 54 59 63 67 59 64 69 74 78

33.7 33 36 40 44 48 52 56 61 65 69 61 66 72 77 82

42.4 36 40 45 49 53 56 61 67 72 77 67 73 79 84 90

48.3 38 42 47 51 55 59 64 70 75 80 70 77 82 88 95

60.3 41 45 50 55 59 63 69 75 81 86 76 82 89 96 102

76.1 42 47 52 57 62 67 73 79 85 90 78 86 94 101 107

88.9 44 49 54 59 64 70 76 82 89 94 83 90 98 105 112

101.6 45 50 56 62 66 73 79 85 91 97 85 93 101 109 116

114.3 46 52 57 63 68 76 80 87 93 99 87 95 103 111 118

139.7 49 54 60 66 71 78 84 92 99 105 94 102 110 118 125

168.3 52 58 64 70 76 83 90 98 105 111 101 107 117 126 134

219.1 54 60 67 74 80 87 95 104 112 119 105 114 124 133 142

244.5 55 62 69 76 82 89 98 106 115 122 108 117 127 137 146

273 56 64 71 78 84 94 100 110 118 126 113 120 132 142 151

323.9 58 66 73 80 86 94 104 114 123 132 115 123 135 145 154

355.6 59 67 74 81 88 97 107 116 125 134 116 125 137 147 156

406.4 62 69 76 83 90 100 109 118 127 136 118 128 140 150 159

457 63 70 77 84 91 102 111 120 129 138 121 132 144 154 163

508 65 72 79 86 93 105 114 123 132 141 124 134 146 156 165

Over 508 72 78 87 98 105 113 124 133 142 151 127 137 151 161 170

an d in cl. flat

surfaces

Hot face tem perature at m ean tem perature (in ºC) (with am bien t st ill air at +20ºC)

+100 +200 +300

0.02 0.03 0.04 0.05 0.06 0.03 0.04 0.05 0.06 0.07 0.03 0.04 0.05 0.06 0.07

Outside diam eterof steel p ipe (in m m )




23

17.2 64 69 74 79 83 76 81 8691 95 89 93 98 103 107 99 104 109 114 119

21.3 68 73 78 83 88 81 86 9196 101 93 98 103 108 113 105 110 115 120 125

26.9 73 78 83 89 94 87 92 98103 107 100 105 110 115 120 113 118 123 128 133

33.7 76 81 87 92 97 89 95 100106 111 103 108 114 119 124 116 121 127 132 137

42.4 83 89 96 102 107 99 105 111 117123 114 120 126 132 137 128 134 140 146 152

48.3 87 93 100 106 112 103 109 116 122128 119 125 132 138 143 134 140 146 152 158

60.3 94 101 108 115 121 111 118 125 132 138 128 135142 149 156 144 151 158 165 172

76.1 99 106 114 121 127 117 124 132 139 146 135 142149 156 163 152 159 166 173 180

88.9 103 110 118 126 133 123 130 138 145 152 141 148156 163 170 159 166 174 181 189

101.6 106 114 123 130 138 126 134 142 150 157 145 153161 169 177 164 172 180 187 195

114.3 109 116 125 133 140 129 137 145 153 160 149 157165 173 181 167 175 183 191 198

139.7 116 124 133 141 149 138 146 155 163 171 158 167175 184 190 179 187 195 204 211

168.3 124 132 142 151 159 147 156 165 174 182 170 178 188196 205 191 200 209 218 227

219.1 130 140 151 161 171 156 166 176 186 195 180 190 200 210220 203 213 223 233 243

244.5 135 145 156 165 175 161 171 182 192 201 186 196 206 216226 210 220 230 240 250

273 139 149 160 170 180 166 176 188 198 207 191 202 213 224 235 217227 238 248 258

323.9 142 153 164 174 184 171 181 193 202 212 196 207 218 229 240 223 233 244 254 264

355.6 146 157 168 178 188 177 185 197 206 216 201 212 224 235 245 230 240 251 261 271

406.4 149 160 171 181 192 181 189 202 213 223 207 218 230 241 252 234 245 257 269 279

457 153 165 176 187 198 187 196 209 220 231 213 225 238 250 261 242254 266 278 289

508 155 168 179 191 202 191 200 213 226 237 218 231 244 256 267 248260 273 285 296

Over 508 158 171 182 195 205 194 207 218 230 239 228 240 250261 270 257 271 279 293 304

an d in cl.

flat

surfaces

0.04 0.05 0.06 0.07 0.08 0.05 0.06 0.07 0.08 0.09 0.06 0.07 0.08 0.09 0.10 0.07 0.08 0.09 0.10 0.11


Table 16 Econom ic thickness of insula t ion for process pipew ork and equipm ent cont ...

Hot face tem perature at m ean tem perature (in ºC) (with am bien t st ill air at +20ºC)

+400 +500 +600 +700Outsidediam eterof steelp ipe (in m m )


Note: For thicknesses in bold type, the outside surface temperature is likely to exceed 50ºC if a low em issivitysurface is used, i.e. bright metal



24


Table 17 Fuel cost com parisons: cost of heat rela ted to fuel price

Cost of h eat Fuel oil at Natural gas at Solid fuel at Solid fuel at Electricity at 70% efficien cy 70% efficien cy 55% efficien cy 70% efficien cy 100% efficien cy

pen ce/usefu l pen ce/ l pen ce/ th erm £/ t £/ t pen ce/kWhMJ

NOTE 1: The first column shows the basic costs required for economic thickness calculations. The range covers both past prices and possible future price increases.

NOTE 2: The efficiencies given in the column headings indicate the values assumed in the calculations; they do not represent the actual operating efficiency. In practice the system efficiency for a particular application may be considerably lower than the values given.

0.30 7.89 22.16 38.4 58.61 1.08

0.40 10.52 29.54 51.2 78.15 1.44

0.50 13.15 36.93 64.0 97.68 1.80

0.56 14.73 41.36 71.7 109.40 2.02

0.60 15.78 44.31 76.8 117.22 2.16

0.64 16.83 47.27 81.9 125.03 2.30

0.68 17.88 50.22 87.0 132.85 2.49

0.72 18.94 53.18 92.1 140.66 2.59

0.76 19.99 56.13 97.2 148.48 2.74

0.80 21.04 59.08 102.4 156.29 2.88

0.84 22.09 62.04 107.5 164.11 3.02

0.88 23.14 65.00 112.6 171.92 3.17

0.92 24.20 67.96 117.7 174.74 3.31

0.96 25.25 70.91 122.8 187.55 3.46

1.00 26.30 73.87 128.0 195.37 3.60

1.04 27.35 76.82 133.1 203.18 3.74

1.08 28.40 79.77 133.2 203.66 3.89

1.12 29.46 82.73 143.3 218.81 4.03

1.16 30.51 85.68 148.4 226.67 4.18

1.20 31.56 88.64 153.5 234.44 4.32

Th is Table is based on Table 36 in BS 5422: 1990. The colum n h eaded ‘Fuel oil at 70% efficien cy’ h as

been recalcu lated an d is n ot taken from th e Brit ish Stan dard. Copies of th e origin al docum en t can be

obtain ed by post from Brit ish Stan dards In st itu t ion, Sales Departm en t, Lin ford Wood, Milton Keyn es,

MK14 6LE.


25

A wide variety of p ipe in su lat ion products is

available from m an y differen t com pan ies. Th e

h eat loss graph s are based on four com m on

product types, wh ich are given below.

■ Preform ed rigid fibrous sect ion s (in cludin g

rock an d glass fibres) (Graph s 1-10)

■ Preform ed rigid calcium silicate or (up to

300°C) 85% m agn esia sect ion s.

(Graph s 11 - 20)

■ Preform ed rigid polyisocyan urate or (up to

100°C) polyureth an e sect ion s

(Graph s 21 - 23)

■ Preform ed expan ded n itrile rubber an d

polyeth ylen e foam section s (Graph s 24 - 25)

APPENDIX 3

HEAT LOSS GRAPHS FOR VARIOUS MATERIALS AND SURFACE TEMPERATURES

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

26

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS

Graph 1 Heat loss for pipes w ith surface tem perature of 50ºC w ith varying insula t ion thicknesses

500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10

Insulation thickness (mm) 63 50 38 32 25 19 Bare pipe7588100201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

27

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

28

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

29

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

30

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

31

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

32

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

33

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10

Insulation thickness (mm) 63 50 38 32 25 19 Bare pipe7588100125150N

om

inal b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

34

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

35

PR

EFO

RM

ED

RIG

ID F

IBR

OU

S S

EC

TIO

NS


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10

Insulation thickness (mm) 63 50 3832 25 19Bare pipe7588100125150N

om

inal b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

36

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10

Insulation thickness (mm) 63 50 38 25 Bare pipe7588100

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

37

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

38

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

39

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

40

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

41

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10

Insulation thickness (mm) 63 50 38 25 Bare pipe7588100125150N

om

inal b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

42

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

43

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


100N

om

inal b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

44

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


100

No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

45

PR

EFO

RM

ED

RIG

ID C

ALC

IUM

SIL

ICAT

E O

R 8

5%

MA

GN

ES

IA

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


100

No

min

al b

ore

(m

m)

10 20 30 40 50 60 7080 100 200 300 400 500 600 8001000 2000 4000 6000 8000 10000W/m

Btu/ft h 20 30 40 50 60 70 80 100 200 300 400 500600 800 1000 2000 4000 6000 8000 10000

Heat loss

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

46

PR

EFO

RM

ED

RIG

ID P

OLY

ISO

CYA

NU

RAT

E O

R P

OLY

UR

ET

HA

NE

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10

Insulation thickness (mm) 63 50 38 25 19 Bare pipe7588100

201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

47

PR

EFO

RM

ED

RIG

ID P

OLY

ISO

CYA

NU

RAT

E O

R P

OLY

UR

ET

HA

NE

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

48

PR

EFO

RM

ED

RIG

ID P

OLY

ISO

CYA

NU

RAT

E O

R P

OLY

UR

ET

HA

NE

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

49

PR

EFO

RM

ED

EX

PA

ND

ED

NIT

RIL

E R

UB

BE

R A

ND

PO

LY

ET

HY

LE

NE

FO

AM

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss

TH

E E

CO

NO

MIC

TH

ICK

NE

SS O

F IN

SU

LATIO

N F

OR

HO

T P

IPE

S

50

PR

EFO

RM

ED

EX

PA

ND

ED

NIT

RIL

E R

UB

BE

R A

ND

PO

LY

ET

HY

LE

NE

FO

AM

SE

CT

ION

S


500450400350300

250

200

150

125

100

80

65

50

40

32

25

20

15

10


201816

1412

10

8

6

5

4

3

21/2

11/211/4

3/4

1/2

3/8

1

2

No

min

al b

ore

(in

ch

es)

No

min

al b

ore

(m

m)

1 2 3 4 5 6 7 8 910 20 30 40 50 60 70 80 90100 200 300 400 500 600 800 1000W/m

Btu/ft h 2 3 4 5 6 7 8 9 10 20 30 40 50 60 70 80 100 200 300 400 500 600 800 1000

Heat loss


51

SOME BASIC HEAT TRANSFER FORMULAE

Th e various m eth ods of est im atin g th e econ om ic

th ickn ess of in su lat ion h ave m ade reason able

assum ption s about th e am bien t con dit ion s.

Sin ce th ese can h ave a sign ifican t effect on th e

rate of h eat loss, an y serious divergen ce from th e

assum ed con dit ion s sh ould be an alysed as an

in dividual case. Th is requires th e use of basic

h eat tran sfer equation s. Th ere are m an y

stan dard texts on h eat tran sfer wh ich give

com plete details but th e basic equation s are:

an d

Wh ere:

Q = h eat loss per m etre len gth of p ipe (W/m )

U = Overall h eat tran sfer coefficien t (W/m2)

t1 = pipe surface tem perature (°C) -

APPENDIX 4 SOME BASIC HEAT TRANSFER FORMULAE

Q = U (t1 - tm) . . . A1

1 = 1 + ln (ri/ ro) . . . A2

U 3.142dih 6.284 k

Table 22 Varia t ion of outer surface coefficient w ith tem perature d ifference betw een surface and a ir

for various outer d im ensions of insula t ion

Outer d iam eter

in su lat ion (in m m )

High em issivity surface Low em issivity surface

1 2 5 10 1 2 5 10

NOTE: The above figures refer to the outer surface of the insulation

approxim ately equal to process stream

tem perature

t2 = outside tem perature of in su lat ion

tm = am bien t tem perature (°C)

r i = radius of outer surface of in su lat ion (m )

r0 = outer radius of p ipe (m )

d i = diam eter of outer surface of in su lat ion (m )

h = surface h eat tran sfer coefficien t (W/m2K)

k = th erm al con ductivity of in su lat ion

(W/m .k)

Th ese equation s are used to fin d th e h eat loss

per m etre len gth of p ipe. Th e overall h eat

tran sfer coefficien t, U, is determ in ed first by

solvin g equation A2. Equation A1 th en gives th e

required value. Th e problem is determ in in g a

suitable value for h , th e surface h eat tran sfer

coefficien t. Th is can be don e from first

prin cip les (see an y stan dard text on th e subject)

or Table 22 can be used to give an approxim ate

value.

40 8.0 8.4 9.1 9.7 3.4 3.9 4.7 5.4

60 7.6 8.0 8.7 9.3 3.1 3.5 4.2 4.9

100 7.3 7.7 8.3 8.8 2.7 3.1 3.8 4.4

200 7.0 7.4 7.9 8.4 2.4 2.8 3.4 4.0

Vertical flat surface 6.6 7.0 7.5 8.0 2.0 2.4 3.0 3.6

Outer surface coefficien t, h (in W/(m2.K))

Tem perature d ifferen ce (t2 - tm) (in K)

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19 Process plant insulation and fuel efficiency

20 Energy efficiency in road transport

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