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InsulateTRANSCRIPT
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The economic thickness of
insulation for hot pipes
8FUEL EFFICIENCY
BOOKLET
BEST PRACTICE
P R O G R A M M E
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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
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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
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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.
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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)
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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)
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
Data requirem en ts:
■ 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
Data requirem en ts:
■ 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
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
THE ESTIMATION OF ECONOMIC THICKNESS
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
8
THE ESTIMATION OF ECONOMIC THICKNESS
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 )
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
9
THE ESTIMATION OF ECONOMIC THICKNESS
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
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A B C D
THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
THE ESTIMATION OF ECONOMIC THICKNESS
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
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
THE ESTIMATION OF ECONOMIC THICKNESS
( )
( )
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
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14
THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
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16
THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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))
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
17
TABLES REPRODUCED FROM BS 5422: 1990
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
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))
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
18
TABLES REPRODUCED FROM BS 5422: 1990
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
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))
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
19
TABLES REPRODUCED FROM BS 5422: 1990
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
1 Outside diameters are as in BS 3600. The same thickness of insulation would be used for copper pipework ofapproximately sim ilar outside diameters.
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
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))
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
20
TABLES REPRODUCED FROM BS 5422: 1990
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 )
Th ickn ess of in su lat ion (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
Flat surfaces 34 37 40 43 45
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
Outside diam eterof copper p ipe(in m m )
Th ickn ess of in su lat ion (in m m )
Th erm al con ductivity at +40ºC (in W/(m .K))
Th erm al con ductivity at +40ºC (in W/(m .K))
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
21
TABLES REPRODUCED FROM BS 5422: 1990
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
Flat surfaces 20 22 24 24 25
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
Outside diam eterof copper p ipe(in m m )
Th ickn ess of in su lat ion (in m m )
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
Flat surfaces 23 25 25 29 31
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
Outside diam eterof copper p ipe(in m m )
Th ickn ess of in su lat ion (in m m )
Th erm al con ductivity at +40ºC (in W/(m .K))
Th erm al con ductivity at +40ºC (in W/(m .K))
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
22
TABLES REPRODUCED FROM BS 5422: 1990
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 )
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))
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
TABLES REPRODUCED FROM BS 5422: 1990
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 )
Th ickn ess of in su lat ion (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
Th erm al con ductivity at m ean tem perature (in W/(m .K))
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
24
TABLES REPRODUCED FROM BS 5422: 1990
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.
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THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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
![Page 29: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/29.jpg)
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
![Page 30: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/30.jpg)
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
Graph 2 Heat loss for pipes w ith surface tem perature of 75ºC 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 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
![Page 31: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/31.jpg)
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
Graph 3 Heat loss for pipes w ith surface tem perature of 100ºC 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 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
![Page 32: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/32.jpg)
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
Graph 4 Heat loss for pipes w ith surface tem perature of 150ºC 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)
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
![Page 33: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/33.jpg)
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
Graph 5 Heat loss for pipes w ith surface tem perature of 200ºC 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 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)
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
![Page 34: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/34.jpg)
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
Graph 6 Heat loss for pipes w ith surface tem perature of 300ºC 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 pipe7588100125150
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)
![Page 35: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/35.jpg)
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
Graph 7 Heat loss for pipes w ith surface tem perature of 400ºC 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 pipe7588100125150
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)
![Page 36: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/36.jpg)
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
Graph 8 Heat loss for pipes w ith surface tem perature of 500ºC 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 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)
![Page 37: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/37.jpg)
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
Graph 9 Heat loss for pipes w ith surface tem perature of 600ºC 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 pipe7588100125150
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)
![Page 38: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/38.jpg)
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
Graph 10 Heat loss for pipes w ith surface tem perature of 700ºC 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 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)
![Page 39: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/39.jpg)
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
Graph 11 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 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
![Page 40: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/40.jpg)
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
Graph 12 Heat loss for pipes w ith surface tem perature of 75ºC 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 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
![Page 41: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/41.jpg)
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
Graph 13 Heat loss for pipes w ith surface tem perature of 100ºC 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 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
![Page 42: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/42.jpg)
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
Graph 14 Heat loss for pipes w ith surface tem perature of 150ºC 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 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)
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
![Page 43: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/43.jpg)
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
Graph 15 Heat loss for pipes w ith surface tem perature of 200ºC 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 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)
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
![Page 44: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/44.jpg)
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
Graph 16 Heat loss for pipes w ith surface tem perature of 300ºC 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 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)
![Page 45: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/45.jpg)
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
Graph 17 Heat loss for pipes w ith surface tem perature of 400ºC 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 25 Bare pipe7588100125150
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)
![Page 46: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/46.jpg)
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
Graph 18 Heat loss for pipes w ith surface tem perature of 500ºC 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 25 Bare pipe7588125150175200
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)
![Page 47: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/47.jpg)
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
Graph 19 Heat loss for pipes w ith surface tem perature of 600ºC 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 25 Bare pipe7588125150175200
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)
![Page 48: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/48.jpg)
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
Graph 20 Heat loss for pipes w ith surface tem perature of 700ºC 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 25 Bare pipe7588125150175200
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)
![Page 49: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/49.jpg)
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
Graph 21 Heat loss for pipes w ith surface tem perature of 70ºC 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 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
![Page 50: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/50.jpg)
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
Graph 22 Heat loss for pipes w ith surface tem perature of 100ºC 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 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
![Page 51: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/51.jpg)
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
Graph 23 Heat loss for pipes w ith surface tem perature of 145ºC 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 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
![Page 52: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/52.jpg)
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
Graph 24 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) 38 32 25 19 13 9 Bare pipe50
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
![Page 53: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/53.jpg)
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
Graph 25 Heat loss for pipes w ith surface tem perature of 75ºC 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) 38 32 25 19 13 9 Bare pipe50
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
![Page 54: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/54.jpg)
THE ECONOMIC THICKNESS OF INSULATION FOR HOT PIPES
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)
![Page 55: Feb 008 Write](https://reader034.vdocuments.mx/reader034/viewer/2022051218/5695d4e71a28ab9b02a33a52/html5/thumbnails/55.jpg)
The Government’s Energy Efficiency Best Practice Programme provides
impartial, authoritative information on energy efficiency techniques and
technologies in industry, transport and buildings. This information is
disseminated through publications, videos and software, together with
seminars, workshops and other events. Publications within the Best
Practice Programme are shown opposite.
Further information
For buildings-related publications For industrial and transport
please contact: publications please contact:
Enquiries Bureau Energy Efficiency Enquiries Bureau
BRECSU ETSU
Building Research Establishment Harwell, Didcot, Oxfordshire,
Garston, Watford, WD2 7JR OX11 0RA
Tel 01923 664258 Fax01235 433066
Fax 01923 664787 Helpline Tel 0800 585794
E-mail [email protected] Helpline E-mail [email protected]
Energy Consumption Guides: compare energy use in specific processes, operations, plant and building types.
Good Practice: promotes proven energy efficienttechniques through Guides and Case Studies.
New Practice: monitors first commercial applications of newenergy efficiency measures.
Future Practice: reports on joint R & D ventures into newenergy efficiency measures.
General Information: describes concepts and approachesyet to be fully established as good practice.
Fuel Efficiency Booklets: give detailed information on specific technologies and techniques.
Energy Efficiency in Buildings: helps new energy managersunderstand the use and costs of heating, lighting etc.
© CROWN COPYRIGHT REVISED 1993 REPRINTED 1996
Titles in th e Fuel Efficien cy Booklet series are:
1 Energy audits for industry
1B Energy audits for buildings
2 Steam
3 Economic use of fired space heaters for industry
and commerce
4 Compressed air and energy use
7 Degree days
8 The economic thickness of insulation for
hot pipes
9 Economic use of electricity in industry
9B Economic use of electricity in buildings
10 Controls and energy savings
11 The economic use of refrigeration plant
12 Energy management and good lighting practices
13 W aste avoidance methods
14 Economic use of oil-fired boiler plant
15 Economic use of gas-fired boiler plant
16 Economic thickness of insulation for existing
industrial buildings
17 Economic use of coal-fired boiler plant
19 Process plant insulation and fuel efficiency
20 Energy efficiency in road transport
Fuel Efficien cy booklets are part of th e En ergy
Efficien cy Best Pract ice program m e, an in it iat ive
aim ed at advan cin g an d prom otin g ways of
im provin g th e efficien cy with wh ich en ergy is
used in th e UK.
For copies of Fuel Efficien cy booklets or
furth er in form ation p lease con tact th e addresses
below.
Overseas custom ers p lease rem it £3 per copy
(m in im um of £6) to th e ETSU or BRECSU
address with order to cover cost of packagin g
an d postin g. Please m ake ch eques, drafts or
m on ey orders payable to ETSU or BRECSU, as
appropriate.