j ourna l ho me page: www.elsev ier .com/ locate /enbui ld
mpact of the optimization criteria on the determination of thensulation thickness
érôme Barrau ∗, Manel Ibanez, Ferran Badianiversity of Lleida, Applied Physics Section of the Environmental Sciences Department, 25001 Lleida, Spain
r t i c l e i n f o
rticle history:eceived 8 April 2013eceived in revised form 4 March 2014ccepted 5 March 2014vailable online 21 March 2014
a b s t r a c t
From the sustainable perspective, the optimum thickness calculations of the buildings envelope insula-tion materials published in scientific journals suffer a number of notable shortcomings. The most relevantare the short amortization time periods and the prevalence of economic criterion. The work presentedshows that an increase from 20 to 50 years in the amortization time period involves, in some cases, todouble the value of the optimum thickness. Moreover, the thicknesses calculated applying energetic or
environmental criteria for the optimization give, in some cases, results 10 times higher than the onesobtained using the economic argument. The type of insulation materials (especially their different char-acteristics at the manufacturing stage) and the calculation conditions (e.g. Degree-Days zone) also affectoptimum thicknesses determination.
Among all the solutions proposed to the energy problems inuildings, experts agree that building insulation is the least-costption for reducing energy consumption and CO2 emissions [1–4].
As a consequence, the determination of the optimum thicknessf the building insulation materials has been a subject of interestor many years amongst the scientific community [5]. The optimumnsulation thickness depends on a large number of parameters. Thecientific studies are primarily focused on analyzing the effect ofhe climatic parameters [6–11], the orientation [12,13], the thermal
ass [14], the fuels [8,10,15,16], and other parameters [9,17,18].The calculations of the energetic losses of the buildings are based
rincipally on single analytical models, but also, in some cases, onynamic methods [13,15].
The optimum thickness is straightforward determined through life-cycle assessment (LCA), basically balancing the initial invest-ent (insulation materials purchase and installation costs) with
he savings that can be made (lower running costs due to lowerransmission losses).
A first major drawback of these studies is the amortization timeeriod used for the calculations. The insulation does not wear out,oes not require maintenance and does not require replacing. But
the studies take values lower or equal to 30 years, with an elevatednumber of them using a lifetime of 10 years [8–10,13,16,17,19]. Thisis not consistent with the guaranteed material lifetime neither withthe lifetime of the buildings, defined as 50 years by most nationalbuilding laws [20].
The second major drawback of these studies is that the optimiza-tion criterion applied to determine insulation thickness is, in mostcases, the economic one. Even in the papers where energy savingsand/or the reduction of CO2 emissions [21–25] are included, theoptimum thickness is calculated considering only economic argu-ments. Nevertheless, the planet is facing huge environmental andenergetic problems and the energy needs of the buildings are oneof the responsible of this situation. Indeed, an analysis of the finalend use of energy in the EU-27 in 2010 shows three dominant cate-gories: transport (31.7%), households (26.7%) and industry (25.3%)[26]. A Life-Cycle Assessment (LCA) of the materials used in thebuilding, and specifically the insulation ones [27], allow calculat-ing the optimum insulation thickness from the environmental andenergetic point of views. Furthermore, calculating the optimuminsulation thickness with respect to the emissions of CO2 is consis-tent with the EU directives on the energy performance of buildings[28], which calculate the energy qualifications as a function of thisparameter.
Within this framework, Ostermeyer et al. [29] adapted with-
out major changes the simplified method presented by Petersdorffet al. [30], originally designed to calculate the optimum insulationthickness from the economic point of view, in order to considerenvironmental parameters. The authors showed that the insulation
A area (m2)Cf economic cost of the fuel (D/J)CO2 cost in emissions of CO2 (kg of CO2)Cp heat capacity (J/kg K)E cost in energy (J)fu use factorHDD annual Heating Degree Days (◦C day)i intermittence factorKf environmental cost of the fuel (kg CO2/J)N lifetime (years)q annual heat losses (J)R thermal resistance (m2 K/W)ren air change rate (ren/h)T temperatureU thermal transmittance (W/m2 K)V volume of the building (m3)Vins volume of the insulation material (m3)VR ventilation rate (m3/s)x insulation thickness (m)
Greeks� density (kg/m3)� heat conductivity of the insulation material (W/mK)� efficiency
SymbolsD economic cost (D)
Subscritsa annualb base, comfortair aircow complete opaque wallsins insulation materialLCA Life Cycle Assessment; Fabrication and installation
phase of the materialsmax maximummin minimumow opaque walls, without the insulation layeru unity of insulation material (m3)USE use phase of the buildingvent ventilationw windowsy0 inversion in the insulation material and installation
tmmoittei
df
•
q = qcow + qw + qvent (2)
at year 0
hicknesses obtained from the environmental criterion of opti-ization, taking into account the life cycle of the materials, areuch higher than the ones obtained from the economic criterion
ptimization method, that only consider the use phase of the build-ng. Their study is limited to mineral wool insulation material. Sohe impacts, on the optimum thickness, of the parameters relatedo the fabrication of the insulation materials, such as the energymbedded and the emissions of CO2 related to this process, are notncluded.
The present authors believe that the issues mentioned aboveeserve more attention. Therefore, this work is written with theollowing objectives:
To show the relevance of the building and materials lifetime whenthe optimum insulation thickness is determined.
dings 76 (2014) 459–469
• To show that the economic optimum thickness values disagreewith optimum thicknesses based on energetic or environmentalcriteria.
• To check the impact of some relevant parameters, including theones related to the fabrication process of the insulation materials,in the determination of the optimum insulation thicknesses.
2. Methodology
When considering the economic optimization of the insula-tion thickness, the only properties of the materials needed arethe thermal ones (thermal conductivity and, for some methodol-ogy of calculation, heat capacity), which influence in the use phaseof the building and their running cost. When assessing the wholelife-cycle of the building for the calculation of the optimum insula-tion thickness from the energetic or environmental point of view,it is necessary to take into account the energy embedded in theinsulation materials and the emissions of CO2 related to the fab-rication process. In this paper, with the aim of making easier theunderstanding of the results, the environmental impact is only eval-uated through the CO2 emissions, although some building materialsdatabase give more parameters associated to this criterion.
The main goal of this study is not to calculate highly accurateoptimum insulation thicknesses but to demonstrate the limitationsof the usual way of doing it in relation to, on the one hand, theinsulation materials and buildings lifetime and, on the other hand,the optimization criterion selected. In order to focus the work onthis objective, the simplified analytical procedure described belowwas applied and the studied conditions were voluntarily limited. Sothe results may not be evaluated by themselves, but in comparisonwith values obtained by the other insulating materials.
The hypotheses used for the model are the following:
• House dimensions 9 × 6 × 2.5 m3
• Floor and ceiling adiabatic (dwelling located vertically betweentwo equal housing characteristics and occupation).
• Optimum insulation thickness determined by the building heat-ing demand.
• Ventilation losses included• Solar gains and internal heat sources not included• Efficiency of 90% for both biomass and gas space heating systems• The global warming potential of the greenhouse gases emis-
sions during the fabrication process of the insulation materialsis expressed trough the carbon dioxide emissions, as the databases do not offer the total greenhouse gases mixture for all theconsidered insulation materials.
In order to evaluate the optimum thicknesses of insulationmaterials, the methodology determines the balance depending onoptimization criterion, for different working conditions (Fig. 1).
On the one hand, the annual costs associated with the use phaseof the building are calculated. For this, it is necessary to assess theannual costs in terms of energy during this phase, which is theannual energy consumption (EUSE):0
EUSE = q
�(1)
where � is the efficiency of the heating system and q is the annualheat losses, which take into account the losses through the com-plete opaque walls (qcow) and the windows (qw), and the ones dueto ventilation (qvent).
with
qcow = Ucow · Acow · HDD · fu · i · 86, 400 (3)
J. Barrau et al. / Energy and Buildings 76 (2014) 459–469 461
Material sdataba ses
INPUTCalculations setting s (C F1, 2, 3,…10 )
Insula ting material (Mineral wool , Polyure than e, Wood fibe r, Cork )Lifetime (20 and 50 year s)
Energe tic Balan ce (23 )Econo mical balan ce (24 )
Environ men tal ba lan ce (25 )
USE FAB RIC ATION
EACV CO2 LCAEACVConsu mo energét ico
EUSO
Heat losses (q)
CO2 US E€USE
Heatin gsystem
effici ency (
Fuel (Kf, Cf)
xCO2
ELCAEnergy consu mption
(EUSE) € LCA
x€
thickness calculation diagram.
q
a
q
ufitb
t
H
max
wa
r
V
i
U
w
R
Table 1Fuel data applied [31–34]. The Lowest heating Value (LHV) of the fuels are includedin the parameters Cf and Kf .
Kf Cf
kg CO2/MJ D/MJ
xE
Fig. 1. Optimum insulation
w = Uw · Aw · HDD · fu · i · 86, 400 (4)
nd
vent = VR · �air · Cpair · HDD · fu · i · 86, 400 (5)
and i are, respectively, the use and intermittence coefficients. Therst one is related to the number of heating days per month andhe second one to the number of hours of heating per day. As theuilding considered in this paper is a house, fu = 1 and i = 0.85.
The annual Heating Degree Days (HDD) are calculated throughhe following equation:
DD =365∑j=1
(HDDj)
⎧⎨⎩
if(
Tmax − Tmin
2
)j
< Tb then HDDj = Tb −(
T
else HDDj = 0
ith Tb the comfort temperature (considered 18 ◦C in this work)nd ((Tmax − Tmin)/2)j the mean air temperature of day j.
The ventilation rate VR (in m3/s) is given by the air change rateen (in ren/h) and the volume V of the building:
R = ren · V
3600(7)
The thermal transmittance of the complete opaque wall (Ucow)s given by its thermal resistance (Rcow):
cow = 1Rcow
(8)
ith
cow = Row + Rins (9)
− Tmin
2
)j (6)
Gas 5.7 × 10−2 1.58 × 10−2
Biomass 0 0.94 × 10−2
Row is the thermal resistance of the opaque walls without the insu-lation layer, and Rins is the thermal resistance of the insulation layer,that depends on its thickness (x) and its thermal conductivity (�):
Rins = x
�(10)
So the annual cost in terms of energy during the use phase (EUSE)is:
EUSE =
[(1
Row+ x�
)· Acow + Uw · Aw + VR · �air · Cpair
]· (HDD · fu · i · 86, 400)
�(11)
From the economic and environmental point of view, the annualcosts during the use phase (DUSE and CO2 USE) are:
DUSE = EUSE · Cf (12)
and
CO2 USE = EUSE · Kf (13)
462 J. Barrau et al. / Energy and Buildings 76 (2014) 459–469
Table 2Insulation material data applied [35,36].
Fabrication and installation costs Thermal conductivity
Du (D/m3) Eu (MJ/m3) CO2u (kg CO2/m3) � (W/m K)
Mineral wool (MW) 77 900 30 0.04
Ca
atc
E
D
C
NEte
E
D
C
(g
n
V
amf
E
C
D
tt
TC
Polyurethane (PUR) 216 4320
Wood fiber (WF) 211 2124
Cork (C) 192 234
f and Kf are the conversion factors from energetic to economic costnd from energetic to environmental costs, respectively (Table 1).
On the other hand, the energetic, economic and environmentalnnual costs associated to the fabrication and the installation ofhe insulation materials (ELCA, CO2 LCA and DLCA, respectively), arealculated as follows:
LCA = Ey0
N(14)
LCA = Dy0
N(15)
O2 LCA = CO2 y0
N(16)
is the lifetime of the building and the insulation materials, andyo, Dyo and CO2 yo are, respectively, the costs of the investment inhe insulation material and installation at year 0 from the energetic,conomic and environmental point of views.
y0 = Eu · Vins (17)
y0 = Du · Vins (18)
O2 y0 = CO2 u · Vins (19)
The unitary costs of the insulation materials for the energeticEu), economic (Du) and environmental (CO2 u) optimizations areiven in Table 2.
The volume of the insulation material (Vins) depends on its thick-ess (x):
ins = x · Aow (20)
So the energetic, economic and environmental annual costsssociated to the fabrication and the installation of the insulationaterials (ELCA, CO2 LCA and DLCA, respectively) can be expressed as
ollows:
LCA = Eu · x · Aow
N(21)
O2 LCA = CO2 u · x · Aow
N(22)
LCA = Du · x · Aow (23)
N
In Eqs. (11)–(13) and (21)–(23), the insulation thickness (x) ishe only unknown value and so we can combine the parameters ofhe use phase and the ones of the LCA phase in order to make the
able 3alculation settings. The calculation settings for CF2 to CF10 are the same than CF1, excep
Parameter Unit Base Variations
CF1 CF2 CF3 CF4
Uow W/m2 K 1.5 3 0.5ren ren/h 1
HDD ◦C day 3199 2083
Windows % 25
U Windows W/m2 K 3.5
Fuel [−] Gas
380 0.02378 0.0426 0.045
annual balance from the economic, energetic and environmentalobjectives.
In the economic analysis, the interest has not been includedintentionally in the calculation in order to reproduce the sameprocedure for each criterion.
Ea = EUSE + ELCA (24)
Da = DUSE + DLCA (25)
CO2 a = CO2 USE + CO2 LCA (26)
The minimum value of annual costs, relative to the energetic(Ea), economic (Da) and environmental (CO2a) point of view, cor-responds to the optimum insulation thicknesses for each of thesecriteria (xE, xD and xCO2, respectively).
The optimum thicknesses of the insulation material, through theenergetic, economic and environmental criteria, are calculated in10 calculation settings (Table 3). These scenarios include changesin several parameters to evaluate their impact on the differencesamongst economic, energetic and environmental optimizations.
For each calculation setting, the methodology is applied combin-ing 4 insulation materials (Table 2) and 2 building lifetimes (20 or50 years). Materials with significant different characteristics dur-ing the fabrication phase have been chosen in order to evaluatethe impact of each parameter on the optimum insulation thicknesscalculated.
3. Results
3.1. Economic optimum insulation thickness
The calculation methodology is applied to reproduce traditionalresults previously reported in the literature of economic insulationthickness optimization. These previous reports are mainly based inshort lifetimes of the buildings (around 20 years) and the commoninsulation materials. These well-known results are used as refer-ence ones. In Fig. 2, the optimum insulation thicknesses obtainedfor the four insulation materials studied, which represent differentbackgrounds and manufacturing processes, are presented.
The values reported are larger than the usually applied in Span-ish buildings. Moreover, Fig. 3 shows the fac ade thermal resistance
values obtained by the economic optimization versus minimuminsulation values given by the building standard (CTE [20]).
In some cases, the economic optimum thermal resistance foundis 6.5 times larger than the one required by the CTE. The Spanish
t when a value is presented in the table.
CF5 CF6 CF7 CF8 CF9 CF10
31128
50 501.8 1.8
Biom.
J. Barrau et al. / Energy and Buildings 76 (2014) 459–469 463
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
CF1 CF 2 CF 3 CF 4 CF 5 CF 6 CF 7 CF 8 CF 9 CF10
Econ
omic
opt
imum
thic
knes
s x €
(m)
Calculation settings
MW
PUR
C
WF
Fig. 2. Optimum insulation thickness. Economic criterion; lifetime: 20 years.
0
1
2
3
4
5
6
7
8
9
10
CF1 CF2 CF3 CF4 CF5 CF6 CF7 CF8 CF9 CF10
Ther
mal
resi
stan
ce (m
2 K/W
)
ulati
MW PUR C WF CTE Min. values
insul
sb
dvcraiot
3
ea2
b
Therefore, the results presented in the following sections are basedin these 50 years period optimizations.
Table 4Comparison of economic optimum thicknesses for lifetimes of 20 and 50 years.
(e50/e20)mean (e50/e20)max/(e50/e20)min
Calc
Fig. 3. Thermal resistance calculated from the optimum
tandard does not approach the optimum economic efficiency onuilding insulation investment.
Figs. 2 and 3 also show that the insulation material selected isefinitive in the optimum thickness obtained. Some materials givealues triple than others due to different thermal conductivities andosts. For example, as mineral wool is cheaper than the other mate-ials, the optimum insulation thicknesses obtained for this materialre much higher than for the other materials. Furthermore, evenf both materials have similar prices, as the thermal conductivityf the polyurethane is lower than the one of the wood fiber, thehicknesses for the first one result lower.
.2. Optimum thicknesses dependence on lifetime
The methodology for evaluating optimum thicknesses based onconomic criterion is applied for different lifetime of the building
nd insulation materials. Fig. 4 shows the results when lifetimes of0 and 50 years are applied.
From Fig. 4 and Table 4, it is derived that a thickness increaseetween 50% and 100% is needed to obtain the best economic
on settings
ation thickness. Economic criterion; lifetime: 20 years.
performance when the lifetime is increased from 20 to 50 years,with an average between 60% and 90% depending on insulationmaterials. Also, for a given insulation material, the maximum dif-ference among calculation settings varies from 1.3 to 1.6 (Table 4).Lower energetic demand calculation settings (CF3, CF4 and CF10)are less sensitive to the lifetime.
Most European codes propose a life span of 50 years for build-ings and the same period is guaranteed by insulate manufacturers.
464 J. Barrau et al. / Energy and Buildings 76 (2014) 459–469
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
CF1 CF2 CF3 CF4 CF5 CF6 CF7 CF8 CF9 CF10
Econ
omic
opt
imum
thic
knes
s x €
(m)
set
MW; N=20
MW; N=50
PUR; N=20
PUR; N=50
C; N=20
C; N=50
WF; N=20
WF; N=50
conom
3
tsdrttCitesntata
Calculation
Fig. 4. Optimum insulation thickness. E
.3. Comparison of optimization criteria
Once demonstrated the impact of the lifetime of the buildings,his study analyses the influence of the optimization criteria. Fig. 5hows, for wood fiber, the optimum thickness values obtainedepending on the economic, energetic and environmental crite-ia in each calculation scenario. Table 5 presents, for each material,he ratio between alternative and economic criteria. For calcula-ion setting 9 (CF9), the fact that the fuel is biomass means thatO2 emissions during the use phase of the building are zero. It
s therefore impossible to calculate an environmental optimumhickness in this calculation setting. Results show clearly that theconomic criterion offers lower thicknesses than the others for allcenarios. The ratio between energetic and environmental thick-esses varies depending on insulation characteristics – optimum
hicknesses from an energetic perspective are higher than fromn environmental point of view for polyurethane and cork whilehe reverse results are found for mineral wool and wood fiber –nd calculation settings. For wood fiber, environmental thicknesses
are larger or smaller than energetic ones depending on the con-figuration evaluated. The largest differences are reported for corkthicknesses where environmental and energetic optimum thick-nesses reach values, 16 and 13 times higher respectively, than theeconomic ones. Mineral wool and polyurethane give the lower dif-ferences between criteria.
It was reported previously that optimum thicknesses based oneconomic criterion show important differences depending on insu-lation material. Large differences between materials are confirmedfor environmental and energetic criteria. The characteristics foreach calculation setting has a larger specific weight in the optimumthickness determination (from the economic, energetic or environ-mental criteria) when, in the materials manufacturing stage, thecosts (economic, energetic or environmental) are lower (Figs. 6–8).This is due to the fact that, when the costs at the manufacturing
stage are high, the impact of this phase with respect to the use oneis higher. That implies a decreasing impact of the calculation sett-ings (associated to the use phase of the building) on the optimumthickness.
CF6 CF7 CF8 CF9 CF10
on settings
x€
xE
xCO2
) and environmental criterion (xCO2). Lifetime: 50 years. Material: Wood fiber.
J. Barrau et al. / Energy and Buildings 76 (2014) 459–469 465
Table 5Optimum thicknesses comparison depending on optimization criteria: Economic (D), energetic (E) and environmental (CO2). Lifetime: 50 years.
Mineral wool (MW) Poliurethane (PUR) Cork (C) Wood fiber (WF)
Fig. 6. Optimum insulation thickness as a function of costs in the manufacturing stage. Energetic criterion. Lifetime: 50 years. Calculation settings CF1 (HDD = 3199 ◦C day),CF4 (HDD = 2083 ◦C day) and CF10 (HDD = 1128 ◦C day).
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 50 100 150 200 250 300 350 400
Envi
ronm
enta
l opt
imum
thic
knes
s x C
O2
(m)
CO2u (kg CO2/m3)
CF1
CF4
CF10
MWC WF PUR
Fig. 7. Optimum insulation thickness as a function of costs in the manufacturing stage. Economic criterion. Lifetime: 50 years. Calculation settings CF1 (HDD = 3199 ◦C day),CF4 (HDD = 2083 ◦C day) and CF10 (HDD = 1128 ◦C day).
466 J. Barrau et al. / Energy and Buildings 76 (2014) 459–469
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0 50 100 150 200 250
Econ
omic
opt
imum
thic
knes
s x €
(m)
€u (€/m3)
CF1CF4CF10
MW C WF PUR
F turing(
toFglt
4
ctrd
FC
ig. 8. Optimum insulation thickness as a function of costs in the manufacHDD = 3199 ◦C day), CF4 (HDD = 2083 ◦C day) and CF10 (HDD = 1128 ◦C day).
The figures show that there are general trends for each calcula-ion setting. However, the parameters used in the x axes are not thenly ones that have an impact on the optimum insulation thickness.or the environmental and economic criteria some changes in theeneral trend are found depending on material. As an example, theower thermal conductivity of polyurethane changes the shape ofhe curves.
. Discussion
In the previous sections a description of optimum thicknesses
alculation depending on criteria is presented. The goal of this sec-ion is to detect parameters that allow establishing a quantitativeelationship between optimum thicknesses calculated through theifferent optimization criteria.
stage. Environmental criterion. Lifetime: 50 years. Calculation settings CF1
4.1. Parameters in the manufacturing stage
Figs. 9–11 show the relations between, on the one hand, the dif-ferent optimum insulation thicknesses depending on criteria and,on the other hand, the characteristics parameters for each of thesecriteria in the manufacturing process.
It is concluded from Fig. 9 that there are no great differencesbetween thicknesses in most configurations when environmentaland energetic criteria are applied. Meanwhile, when the spe-cific weight of energetic consumption in the manufacturing stageincreases in relation to emissions in the same life cycle stage, theenergetic optimum thickness decreases in relation to the envi-
ronmental one. Furthermore, for each insulation material, therelation between optimum environmental and energetic thick-nesses depends on the calculation settings in different grade. Asan example, cork manufacturing low CO2 emissions and energetic
20 25 30 35
MJ/kg CO2)
CF1 CF4
CF10
MWWF
50 years. Calculation settings CF1 (HDD = 3199 ◦C day), CF4 (HDD = 2083 ◦C day) and
J. Barrau et al. / Energy and Buildings 76 (2014) 459–469 467
onsumption imply that costs in running consumption of build-ngs play a major role in the optimum thicknesses calculations.his major dependence in building consumption is related withhe thicknesses variability among the different calculation sett-ngs. The wood fiber case is similar but the slightly higher energyonsumption in the manufacturing stage damps the calculationetting effect. Instead, the polyurethane manufacturing is highlynergy consuming with large CO2 emissions associated. In this case,he manufacturing stage has a large weight in the determinationf optimum insulation thicknesses. These counterbalanced effectsxplain the results in Fig. 9, where there are not relevant differ-nces between optimum thicknesses for the three configurations
tudied.
In Fig. 10 it is drawn that optimum environmental thicknessesre always higher than the economic ones (from 2 to 8 timesarger). The ratio between optimum thicknesses decreases when
the CO2 emissions in the manufacturing stage increase in relationto the economic cost of materials. Furthermore, the previous dis-cussion about the contribution of the manufacturing stage in Fig. 9is extended to Fig. 10.
Fig. 11 shows that the energetic optimum thicknesses are alwayslarger than the economic ones (from 2 to 12 times larger). The ratiobetween optimum thicknesses decreases when the energy con-sumption in the manufacturing stage increases in relation to theeconomic cost of materials.
4.2. Building envelope parameters
Fig. 12 presents the relationship between the optimum thick-nesses and the UA values for opaque enclosures. This value is theproduct of the thermal transmittance of the complete opaque walls(Ucow) by the area of these walls (Acow). The UA value is not climate
15 20 25
(MJ/€)
CF1
CF4
CF10
W PUR
years. Calculation settings CF1 (HDD = 3199 ◦C day), CF4 (HDD = 2083 ◦C day) and
468 J. Barrau et al. / Energy and Buildings 76 (2014) 459–469
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25
Opt
imum
thic
knes
s (m
)
UAcow (W/K)
x€
xE
xCO2
Fig. 12. Optimum thicknesses in front of opaque envelope UA values. Energetic, economic and environmental criteria. Lifetime: 50 years. Materials: Mineral wool,polyurethane, wood fiber and cork.
F l crite
dicdlt
ttrspt
tc2
ig. 13. Optimum thicknesses distribution. Energetic, economic and environmenta
ependent so it is a good enclosure characteristic to compare build-ng envelopes. The figure considers all the insulation materials andonfigurations studied for a lifetime of 50 years. From the plot it iserived that economic optimum thicknesses are closely linked to
arge UA values. Therefore, largest heating losses are expected fromhis criterion in front of energetic and environmental approaches.
We can observe that, even when the calculation methodologyakes into account the LCA of the materials, the general trend ofhe curve is similar to the traditional one. The energetic and envi-onmental optimization criteria lead to the lower UA values ando, the best envelope characteristics. The influence of the materialsarameters on the manufacturing stage adds some dispersion tohe data graph.
Fig. 13 shows the optimum thicknesses distribution for each cri-erion for a lifetime of 50 years. Attending to the three optimizationriteria, most of the optimum thicknesses are in the range from00 to 300 mm (27%). But in the economic evaluation most results
ria. Lifetime: 50 years. Materials: Mineral wool, polyurethane, wood fiber and cork.
(42%) are in the range from 100 to 200 mm. However, applying theenergetic and environmental criteria, the highest percentages (28%and 44%, respectively) are for thicknesses above 1 m. We can alsoobserve that 100% of the economic optimum insulation thicknessesare below 500 mm, whereas, for energetic and environmental opti-mization criteria, respectively 48% and 61% of the thicknesses arehigher than 500 mm.
5. Conclusion
A simplified method is used for the determination of the
optimum insulation thickness for the energetic, economic and envi-ronmental criteria. The need of including some changes in themethodology to calculate these values is shown. This paper demon-strates that:
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J. Barrau et al. / Energy an
1) a thickness increase between, on average, 60% and 90% isneeded to obtain the best economic performance when thelifetime is increased from 20 to 50 years.
2) the optimum insulation thickness calculated trough the ener-getic or environmental criteria results, in some cases, 10 timeshigher than the one calculated trough the economic criterion.The increasing concern of these aspects in the whole soci-ety and, in particular, in the efforts for reducing the buildingimpacts, suggests that the governments will have to weigh up,in the future regulations of this sector, the 3 optimization crite-ria considered in this study as a function of their priorities.
3) the influence of the parameters associated with the manufac-turing phase of the insulation materials on the determinationof the optimum thickness is very high: Increasing values of thecharacteristics parameters of this manufacturing phase impliesa decrease of the impact of the calculation settings, associ-ated with the use phase of the building. Furthermore, for agiven calculation setting and a similar thermal conductivityof the insulation materials, the optimum insulation thicknessobtained for different insulation materials varies from 3 to 10times depending on the optimization criteria.
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