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2 Building nd Environment 42 (27) Net climtic impct of solid fom insultion produced with hlocron nd non-hlocron lowing gents Astrct L.D. Dnny Hrvey Deprtment of Geogrphy, University of Toronto, 1 St. George Street, Toronto, Cnd M5S 3G3 Received 6 July 26; received in revised form 28 August 26; ccepted 2 Octoer 26 The net climtic effect of incresing the mount of insultion in uildings through the use of hlocron-lown fom insultion involves three fctors: the greenhouse gs emissions ssocited with the energy used to mke the insultion; the climtic impct of lekge of the hlocron lowing gent from the insultion during its mnufcture, use, nd t the time of disposl; nd the reduction in heting nd/or cooling energy use nd ssocited greenhouse gs emissions. Recent studies nd ssessments leve the impression tht the use of hlocron-lown fom insultion hs strong net positive impct on climte, with the reduction in heting-relted emissions eing 2 1 times greter thn the CO 2 -equivlent hlocron emissions. This result pplies only to the overll impct of rther modest levels of insultion pplied to pre-existing roof or wll with negligile therml resistnce. It is pproprite to consider the time required for heting-relted emission svings to offset hlocron nd mnufcturing emissions for the ddition of successive increments of insultion the mrginl pyck time. For typicl lowing gent lekge rtes nd for insultion levels found in high-performnce houses, mrginl pyck times cn e in excess of 1 yers using hlocron lowing gents, ut re only 1 5 yers using nonhlocron lowing gents. With fixed thickness of insultion, the difference in heting energy svings using insultion with different lowing gents is generlly only few per cent, in spite of differences in therml conductivity of up to 66%. The net svings in CO 2 - equivlent emissions is lrger using non-hlocron lowing gents, with the reltive enefit of using non-hlocron lowing gents greter the greter the therml resistnce of the envelope element prior to dding fom insultion. r 26 Elsevier Ltd. All rights reserved. Keywords: Fom insultion; Polyurethne; Extruded polystyrene; Hlocrons; Emodied energy; Greenhouse gses 1. Introduction Building insultion cn tke the form of loose or spryon cellulose fires, fireglss or minerl fire tts, or solid or spry-on fom insultion. Solid fom insultion is widely used s externl insultion in commercil uildings, s it cn e fstened directly to poured concrete or lock wlls. It is lso sometimes used s n externl lyer in wood-frme uildings hving fire insultion etween the studs, s it cn spn the therml ridges creted y the studs. There re severl kinds of solid-fom insultion mterils: expnded polystyrene (EPS), extruded polystyrene (XPS), extruded polyurethne (PU), nd extruded Tel.: ; fx: E-mil ddress: hrvey@geog.utoronto.c. polyisocynurte ( PU derivtive). EPS is produced from ethylene ( component of nturl gs) nd enzene ( derivtive of petroleum). It egins s smll liquid eds comined with gseous expnding gent nd fire retrdnt. The eds re heted nd expnd, then llowed to set for 24 h, during which time the expnding gent diffuses through the wll structure nd, t some mnufcturing fcilities, is cptured for reuse. The eds re then reheted with stem in mould, cusing the eds to fuse together. XPS egins s crystlline polystyrene, which is melted under pressure. PU nd polyisocynurte re mde from polymeric methylene diisocynte nd polyohydroxyl, oth of which re derived from petroleum. A sustntil mount of energy, oth s process energy (for exmple, for heting the ingredients) nd s feedstock (petroleum nd /$ - see front mtter r 26 Elsevier Ltd. All rights reserved. doi:1.116/j.uildenv

3 L.D. Dnny Hrvey / Building nd Environment 42 (27) nturl gs), is required in order to mnufcture fom insultion. PU, EPS, nd XPS cn lso e pplied s spry-on fom insultion, which is prticulrly useful in retrofit pplictions, where often difficult-to-rech cvities need to e insulted. As with solid-fom insultion, some expnding gent is required. Fom insultion hs cellulr structure, creted through the expnsion of the expnding gent tht is dded efore the ingredients re heted. The expnding gent used in fom insultion cn e hlocron, pentne, wter, or CO 2, depending on the type of insultion nd its ppliction. Hlocrons re compounds contining cron nd one or more hlogen gses chlorine, fluorine, nd romine. Those contining chlorine nd fluorine re chlorofluorocrons (CFCs), those contining hydrogen, chlorine nd fluorine re hydrochlorofluorocrons (HCFCs), nd those contining hydrogen nd fluorine re hydrofluorocrons (HFCs). All three groups re greenhouse gses (GHGs), while those contining chlorine (the CFCs nd HCFCs) led to the depletion of strtospheric ozone s well. All uses of CFCs hve een lmost completely phsed out, s required under vrious interntionl greements to protect strtospheric ozone. They hve een temporrily replced y the HCFCs in vrious pplictions, including fom insultion, nd will in turn e replced y HFC or non-hlocron expnding gents in developed countries y 21. Developing countries re llowed to increse their use of HCFCs up to 215, fter which production levels cnnot increse, with phseout y 24. Lekge of expnding gents cn occur during the mnufcture of the insultion, while the insultion is in use, t the time of demolition of the uilding, nd if uilding deris including insultion is plced in lndfill fter disposl of the used insultion. The impct on climte of the emission of given mss of gs depends on the effectiveness of the gs in trpping het, on molecule-y-molecule sis, nd on the verge lifespn of molecules of tht gs in the tmosphere. As the mount of gs in the tmosphere decreses fter pulse emission, the het trpping decreses. The integrl (or summtion) of this het trpping over some ritrry time horizon cn e computed nd compred with tht for CO 2 ; the rtio of the two forms n index clled the glol wrming potentil (GWP). This is rough ut dequte mesure of the reltive contriution of equl emissions (in terms of mss) of different gses to glol wrming (see Hrvey [1] for critique of the GWP index). A trdeoff exists etween the reductions in heting energy use nd in CO 2 emissions on the one hnd, nd the emissions of hlocrons on the other hnd if n insultion with hlocron lowing gent is used. As well, the energy used to mnufcture the insultion (referred to s the emodied energy of the insultion) needs to e compred with the svings in heting energy. The emodied energy will increse in proportion to the thickness of the insultion s more insultion is dded, ut ech successive increment of insultion will sve less dditionl heting energy. Thus, t some point (depending on the climte nd the mgnitude of internl het gins), it will not e worthwhile from GHG emission point of view to increse the mount of insultion. The trdeoffs etween hlocron emissions, emodied energy, nd heting energy svings re the suject of this pper. 2. Chrcteristics of different kinds of fom nd non-fom insultion In this section, the properties of insultion relevnt to their net effectiveness in reducing GHG emissions re discussed Effectiveness in reducing heting nd cooling lods Het loss from uilding occurs through conductive het trnsfer in roofs, wlls, nd ground or sement floors; through conductive, convective, nd rditive het exchnge in windows; nd through uncontrolled exchnge of indoor nd outdoor ir through vrious lekge points in the uilding envelope. Conductive het trnsfer through uilding element vries inversely with the therml resistnce of tht element, s represented y the RSIvlue. 1 The RSI-vlue of pnel of insultion of given properties in turn vries directly with the thickness of insultion. Becuse het loss vries with 1/RSI, there re diminishing returns to successive increses in the thickness of insultion. This is illustrted in Fig. 1, which shows the decrese in reltive het loss s the therml resistnce of the insultion increses from RSI 2 ( miniml level of insultion) to RSI 1 (corresponding to U-vlue of.1 W/m 2 /K, s found in mny of the dvnced houses surveyed y Hmd et l. [2] nd Schnieders nd Hermelink [3]). Incresing the wll or roof RSI-vlue from 2 to 1 would reduce the conductive het loss through the wll or roof y fctor of 5. If insultion is pplied snugly etween the studs nd rfters (in the cse of lown-in, spry-on, or tt insultion), or s continuous lyer seled with culking in the cse of solid-fom insultion, then it is possile tht insultion will lso reduce het loss due to exchnge of indoor nd outdoor ir. This is potentilly significnt dditionl enefit of insultion, s ir exchnge cn constitute up to 4% of the totl het loss in leky uildings. This enefit is most likely to ccrue in the cse of lown-in cellulose or spry-on fom insultion, where the insultion cn esily fill the vrious smll gps nd irregulrities within the frming elements (studs nd 1 Following usge in Cnd, the term RSI will e used here to designte metric (système interntionl, SI) resistnce vlues. The resistnce is referred to simply s the R-vlue in Europe (where only metric units re used), ut in the USA nd Cnd, the term R-vlue refers to the resistnce in non-metric units. The reciprocl of the R- or RSI-vlue gives the U-vlue in the sme units.

4 2862 ARTICLE IN PRESS L.D. Dnny Hrvey / Building nd Environment 42 (27) Reltive Het Loss Advnced Houses: Wlls t R12 (RSI 2.1, U=.47 W/m 2 /K) Wlls t R2 (RSI 3.52,U=.28 W/m 2 /K) Roof t R32 (RSI 5.6, U=.18 W/m 2 /K) Wlls (R4,RSI 7.) Roof (R6, RSI 1.6) RSI Vlue, (W/m 2 /K) -1 Fig. 1. Het flow vs. therml resistnce for the rnge of resistnces encountered in insulted wlls nd ceilings. Het flow is reltive to the het flow t R12 insultion (RSI 2.1), which fits into 2 4 (38 89 mm) stud wlls. rfters), especilly t corners nd next to windows nd doors. Insultion, if pplied externlly nd comined with night-time ventiltion to remove het from the wll therml mss, cn e very effective in reducing or even eliminting cooling lods (prticulrly in uildings with smll internl het gins). For verge US climte conditions nd cooling equipment efficiency, McBride [4] estimtes tht the svings in electricity used for cooling due to insultion is 2 3% of the svings in heting energy use. A similr rtio is found for other countries with hot summers nd cold winters. For 1-storey house in Cyprus, dding 5 cm of polystyrene insultion to the roof reduces the cooling lod y 45% (nd the heting lod y 67%), while ddition of 5 cm of polystyrene insultion to the wlls reduces the remining cooling lod y out 1% (nd the remining heting lod y 3%) [5]. The solute svings in cooling energy use is out 6% of the svings in heting energy use. For 1-storey uilding in Tehrn, Sfrzdeh nd Bhdori [6] find tht 1 cm of insultion on the wlls nd roof (U-vlue of.38 W/m 2 /K) reduces the cooling lod y 14% (nd the heting lod y 55%), with the solute svings in cooling energy use out 2% of the svings in heting energy use. Insultion is prticulrly effective in reducing cooling lods in rid regions, where the mount of rdition reflected off of the ground onto wlls cn e lmost s gret s the mount of rdition directly striking the wlls. This in turn cuses the wll surfce temperture to e sustntilly greter thn the ir temperture, so tht the impct of insultion in reducing cooling lods is much greter thn expected sed on the difference etween indoor nd outdoor ir tempertures. Note tht, if the svings in on-site electricity use due to reduced cooling lods is 1/3 the svings in heting energy use, nd if the electricity is generted with n efficiency of 33%, then the svings in primry energy due to reduced cooling lods will e comprle to the svings in primry energy due to reduced heting lods Emodied energy Tle 1 summrizes vrious estimtes of the emodied primry energy of different insultion mterils on mss sis. There is remrkle disgreement mong lterntive estimtes, with Lenzen nd Trelor [9] giving n emodied energy for glss nd minerl wool tht is times tht of other estimtes, while McBride [4] indictes n emodied energy for XPS tht is 1 12 times less thn three other estimtes. However, there is no disputing the conclusion tht the emodied energy of cellulose insultion (recycled newsprint) is close to zero. Tle 2 summrizes vrious estimtes of the emodied primry energy on volumetric sis for different insultion mterils, long with therml conductivity (k) vlues. The emodied energy on volumetric sis increses directly with the insultion density, while the therml conductivity decreses with incresing density. Thus, pushing given insultion type to lower therml conductivity y incresing the density (in order to reduce the spce requirements) increses the emodied energy for given RSI increment (s well s incresing the cost). The polystyrene therml conductivities given in Tle 2 re for pentne-lown commercil product clled Neopr s (ville in Europe in smll quntities) tht contins low-e coting to minimize infrred rditive trnsfer within the insultion mtrix. This reduces the therml conductivity y 1 15% (see The resistnce of lyer of thickness D is given y RSI ¼ k=d. (1) From this, the thickness of sl with RSI 1. cn e computed, nd from tht the emodied energy of n RSI ¼ 1. sl cn e computed using the volumetric emodied energy. These emodied energies re given in the lst column of Tle 2. To compre the svings in CO 2 emissions resulting from dditionl insultion with the CO 2 emissions ssocited with mnufcturing the insultion, the kinds of energy used to mke the insultion, the kind of energy used for heting, nd the sources of ny electricity used for heting or mnufcturing need to e considered. Tle 3 gives the rekdown of primry energy inputs for the mnufcture of polyisocynurte insultion in Cnd. Aout onequrter of the primry energy input is col, which hs lmost twice the CO 2 emission fctor of nturl gs (92 vs. 55 kg CO 2 /GJ). Thus, if the heting energy tht is sved is nturl gs, the pyck time for CO 2 emissions will e 17% longer thn the energy pyck time if we pprox-

5 L.D. Dnny Hrvey / Building nd Environment 42 (27) Tle 1 Emodied primry energy (GJ/t or MJ/kg) of different insultion mterils ccording to vrious pulished estimtes Chen et l. [7] Adlerth [8] Lenzen nd Trelor [9] Petersdorff et l. [1] McBride [4] Cellulose Fireglss Polyester 53.7 Glss wool Minerl wool Polystyrene Polyurethne 137 Ure formldehyde 78.2 Energy use t the mnufcturing fcility is 4% electricity, 6% nturl gs. The mount of primry energy used to generte electricity is estimted here ssuming the powerplnt trnsmission efficiency to e.33. Energy use is entirely electricity, converted to primry energy ssuming powerplnt trnsmission efficiency of.33. Computtion of MJ/kg requires the fom density, ssumed here to e 3 kg/m 3. Tle 2 Emodied primry energy for 1-m 2 insultion pnel with n RSI vlue of 1, computed from emodied energy per unit volume nd therml conductivity Type of insultion Density (kg/m 3 ) Emodied energy Conductivity (W/m/K) Emodied energy (MJ/m 2 /RSI) (MJ/kg) (MJ/m 3 ) Cellulose Fireord Polystyrene Polyurethne Minerl wool Minerl wool 4 Fireglss 16.5 Fireglss Emodied energies (s MJ/m 3 ), densities, nd therml conductivities re from Petersdorff et l. [1] nd re used to compute other entries, except for polystyrene therml conductivities (which re from BASF) nd emodied energies in the lst two rows (which re from Norris, [11]). Assumed here. Tle 3 Energy nd feedstocks used to produce 1 kg of polyisocynurte insultion in Cnd Input Used s feedstock Used s energy Mss (g) Energy (MJ) equivlent (MJ) Oil Nturl gs Col Other Totl Totl emodied energy (MJ) Feedstocks hve een converted to energy equivlents using 1 gm oil ¼ 42 kj nd 1 gm nturl gs ¼ 5 kj. Source: Frnklin Assocites [12]. imte the emodied primry energy s 75% nturl gs, 25% col. For fireglss nd XPS insultion mnufctured in the US, McBride [4] indictes tht 4% nd 1%, respectively, of the energy inputs re s electricity. If the electricity is generted from col with genertion trnsmission efficiency of.33, nd the heting energy tht is sved is nturl gs, then the pyck times for CO 2 emissions will e 45% nd 67% longer thn the energy pyck times. If the focus of interest is the depletion of non-renewle energy supplies, rther thn emissions of GHGs, then the use of nturl gs nd oil s feedstock (in ddition to their use s n energy source in the production process) should e tken into ccount. As seen from Tle 3 for polyisocynurte mnufctured in Cnd, considertion of feedstocks roughly doules the computed emodied energy of the insultion. Given the similrities mong different kinds of fom insultion, roughly comprle fctor should e pplicle to other types of fom insultion Hlocron emissions nd therml conductivity of fom insultion Tle 4 lists the CFC, HCFC, HFC, nd nonhlocron expnding gents tht hd een used, re used, or could e used in vrious kinds of fom insultion except EPS (which uses pentne). Also given is the GWP of the

6 2864 ARTICLE IN PRESS L.D. Dnny Hrvey / Building nd Environment 42 (27) Tle 4 Blowing gents used for polyisocynurte, polyurethne, nd extruded polystyrene insultion, nd the glol wrming potentil (GWP) of the lowing gent reltive to CO 2 over 1-yer lifespn given Type of insultion Originl lowing gent HCFC lowing gent HFC lowing gent Non-hlocron lowing gents Polyisocynurte CFC-11 Pentne, cyclopentne GWP ¼ 468 GWP ¼ 713 Polyurethne (PU) CFC-11 HFC-245f Pentne, CO 2,CO 2 /H 2 O (for spry foms) GWP ¼ 468 GWP ¼ 713 GWP ¼ 12 Vrious isomers of pentne (GWP ¼ 7) HFC-227e GWP ¼ Extruded polystyrene (XPS) CFC-12 HCFC-142 HFC-134 Pentne (GWP ¼ 7), CO 2 (GWP ¼ 1) GWP ¼ 172 GWP ¼ 227 GWP ¼ 141 HCFC-22 HFC-152 Cyclopentne/isopentne lends GWP ¼ 178 GWP ¼ 122 Source: Ashford et l. [13]. hlocron expnding gents. The following dditionl informtion is tken from Ashford et l. [13] except where indicted otherwise: Polyisocynurte is mde with norml pentne nd cyclopentne/isopentne lends in North Americ nd Europe. PU is mde using in developing countries, while in developed countries the use of is limited to smller contrctors using spry fom. For solid PU in uilding pplictions in developed countries, pentne hs rpidly gined widespred use. The use of pentne (or other hydrocrons) in polyisocynurte nd PU requires significnt re-engineering of production sites nd worker trining to prevent explosions, therey entiling costs tht cn e prohiitive for smll- nd medium-sized enterprises in oth developed nd developing countries. Supercriticl CO 2 hs een used for some PU spry fom pplictions in Jpn. A wter/ CO 2 mixture hs een used in Europe, with 1 2% mrket shre y 2 [14]. XPS is mde using HCFC-142 nd HCFC-22 in developing countries, nd these HCFCs continue to e used for XPS in North Americ. However, in Europe (where HCFCs re eing phsed out erly), CO 2 is used lone in XPS or s co-lowing gent with hydrocrons. The use of CO 2 is techniclly chllenging nd requires sustntil new investment for mny product lines. For spry foms, the choices re HFCs, hydrocrons, or CO 2. Hydrocron lowing gents rise sfety concerns (the risk of fire), ut the hzrds cn e eliminted during the mnufcture of solid fom ut not yet with spry fom. CO 2 -lown spy foms suffer from low density nd high therml conductivity compred to HFC foms. The uilding style in mny countries lends itself to the use of spry foms in retrofit pplictions, such s upgrding flt roofs in Spin. Spry foms re the lest expensive (out hlf tht of XPS or EPS when ccounting for lour costs), so more insultion cn e done for given udget. HFCs re expensive nd so re used only where they re perceived to e solutely necessry. The first HFCs to e ville for fom insultion were HFC-134 nd HFC- 152, which were used in XPS, either lone or co-lown with pentne. HFC-152 leves the fom quickly, while HFC-134 is long-lived in fom. Systems with it cn mtch the therml conductivity of HCFC-142. HFC-227e, HFC-245f, nd re more recent products, which cn e used in PU. The GWPs of HCFCs used in insultion rnge from out 7 to 23, while GWPs of HFCs used in insultion rnge from out 12 to 14. The lowing gent cn lek into the tmosphere during the production of fom insultion, during its use, nd t the time of disposl. There is rough consensus in the literture concerning the rtes of emission of lowing gents from fom insultion, s summrized in Tle 5. Lekge rtes during mnufcture pper to e sustntilly greter for XPS (out 25%) thn for PU solid fom (5 12.5%) or for PU spry (5 15%). Lekge rtes during use re lso highest for XPS (.75 4.%/yer) nd lowest for PU solid fom (.2.5%/yer), with the estimted lekge rte of PU spry ( %) overlpping the lower prt of the estimte rnge for XPS. PU solid fom cn e mnufctured without fcings, or with tri-lminte fcings (luminium foil/krft-pper/luminium foil, ech 7 mm thick) on oth sides [14]. Lekge rtes will e lower in the ltter cse. A portion of the lowing gent remining t the end of the life of the insultion will e emitted to the tmosphere, depending on the method of disposl. If the uilding is demolished nd the insultion plced in lndfill, then essentilly ll of the remining lowing gent will rech the tmosphere (cteril degrdtion is thought to e negligile). If the insultion cn e seprted from the uilding deris nd incinerted, essentilly the entire

7 L.D. Dnny Hrvey / Building nd Environment 42 (27) Tle 5 Comprison of ssumptions concerning rtes of emission of lowing gents used in fom insultion Type of insultion Emission up to point of disposl Reference Mnufcture or ppliction (%) lowing gent is destroyed. However, unless uildings re constructed with the intention of eventully seprting nd recycling the insultion, doing so will e very difficult. As well, some of the lowing gent remining t the time of demolition will e relesed to the tmosphere during the demolition process (Hrnisch et l. [15] ssume relese of 2%). Fom insultion cn lso e recycled, either y recovering the rw mterils (y, for exmple, glycolysis) if the chemicl composition of the fom is known, or cn e shredded nd used in the production of pressed ords if it is not dmp [17]. Fom insultion mde with hlocron expnding gents tends to hve much lower therml conductivity thn fom insultion using non-hlocron expnding gents, or thn most non-fom insultion. This is due to the lower moleculr conductivity of the hevy-moleculrweight hlocron lowing gent. However, s the lowing gent leks over time nd is replced y ir, the therml resistnce of hlocron-lown insultion will decrese. The rte of decrese in the hlocron loding, nd hence the rte of increse in therml conductivity, depends on the type of lowing gent used nd the thickness of the insultion pnel (thicker pnels experience smller reltive loss). In spite of lekge, hlocron-lown fom insultion provides greter long-term resistnce to het loss thn non-hlocron-lown insultion for given thickness. This is illustrted in Tle 6, which compres the therml conductivity of 5-cm thick lyer of XPS insultion t the time of mnufcture nd fter 1, 2, nd 5 yers for different lowing gents, s modelled y Vo nd Pquet [21]. Also given re the therml conductivities verged over 5-yer life. The long-term therml conductivity of 5-mm thick XPS pnels is out 13% less using HFC-134 thn using CO 2. Tle 7 gives long-term Use (%/yer) Totl (%) XPS Hrnisch et l. ([15], Tle 9) XPS Ashford et l. ([16], Chpter 7) PU using HFC Ashford et l.([16], Chpter 7) PU using HFC-277e, 245f, 365mfc Ashford et l. ([16], Chpter 7) PU Roof pnels Hrnisch et l. ([15], Tle 23) PU pnels.2 1 Krähling nd Krömer ([14], Tle 3) Generic PU Pnels in Hrnisch et l. ([15], Tle 9) PU Spry Ashford et l. ([16], Chpter 7) PU Spry 5 (1st yer diffusion) Krähling nd Krömer ([14], Tle 3); Krähling et l. ([17], Tle 7) Totl emissions hve een computed ssuming 5-yer lifespn. Assumed to e liner rte of emission s frction of the initil loding y some sources, ut ssumed here to pply to the nnul decrese in the mount remining t the strt of ny given yer. First row is for continuous pnels, second row for discontinuous pnels. therml conductivities for spry nd solid PU insultion using different lowing gents s given y Krähling nd Kro mer [14]. For given lowing gent, the therml conductivity is out 3% less for solid fom thn for spry fom. As noted ove, the rte of lekge of the lowing gent from fom insultion depends on the thickness of the insultion pnel. Tle 8 gives the initil lowing gent loding nd the loding fter 5 yers for XPS pnels of vrious thicknesses, s computed y Vo nd Pquet (24). Also given re the verge nnul rte of loss of lowing gent over 5 yers nd the initil nd finl therml conductivities (results hve een djusted to give n initil conductivity of.27 W/m/K). Annul rtes of loss rnge from 3.8%/yer in 25-mm ords to.74%/yer in 1- mm ords. This spns the rnge of nnul losses given in Tle 5 for XPS. 3. Assessing the trdeoff etween emodied energy nd reduced heting energy use In this section we exmine the trdeoff etween incresing emodied energy nd decresing heting energy use due to decresing conductive het loss s the thickness of insultion is incresed. As noted in Section 2.1, incresing insultion my provide dditionl heting energy svings through reduced envelope ir lekge, s well s svings in cooling energy. These re not considered here, ut could s much s doule the enefit of incresing insultion thickness. The time required for the energy svings of n energyefficiency (or renewle energy) feture to offset the emodied energy of the feture is referred to s the pyck time. Pyck times for insultion cn e

8 2866 ARTICLE IN PRESS L.D. Dnny Hrvey / Building nd Environment 42 (27) Tle 6 Therml conductivity (mw/m/k) of 5-mm-thick XPS pnel, with density of 32 kg/m 3, for vrious lowing gents t vrious times since mnufcture Blowing gent Time (yers) Averge CFC HCFC HFC HFC HCFC CO Source: Vo nd Pquet (24, Fig. 11). Tle 7 Long-term therml conductivity of spry nd solid PU fom insultion lown with different lowing gents Blowing gent Sprys 29 3 Wter/CO 2 35 Solid HC- 24 Source: Kr hling nd Kro mer [14]. computed sed on the svings in heting energy nd the emodied energy in the full thickness of insultion referred to here s the overll pyck time or sed on the dditionl svings in heting energy nd the dditionl emodied energy when n extr increment of insultion is dded. In nlogy to economic cost/enefit nlysis, the ltter will e clled the mrginl pyck time. Becuse the solute reduction in het loss with successive increments of insultion decreses s more insultion is dded (s seen from Fig. 1), the mrginl pyck time is longer for given increment of insultion the greter the pre-existing insultion level. At ny level of insultion, the overll pyck time is less thn the mrginl pyck time. The overll pyck time is useful indictor of the vlue of given mount of insultion, while the mrginl pyck time is useful in deciding when (on lifecycle energy sis) to stop dding more insultion: the mount of insultion should not e incresed eyond the point where the mrginl pyck time equls the expected lifespn of the insultion. Fig. 2 gives overll nd mrginl pyck times sed on the primry energy needed to mnufcture (ut not trnsport or instll) vrious kinds of insultion for climte with 4 heting degree-dys (HDDs) nd heting-system efficiency (Z) of.9. A climte with 4 HDD pertins to regions with modertely cold winters, such s Toronto or Zurich (heting nd cooling degree-dy dt for smple of 77 world cities re given in Hrvey [18]). The svings in heting energy is computed s Svings ðjþ ¼HDD DU=Z, (2) where DU is the difference in U-vlues with nd without fom insultion (or with nd without given increment of fom insultion) (U-vlue ¼ 1/RSI-vlue). Fig. 2 gives overll pyck times reltive to n uninsulted rick or msonry wll with n RSI-vlue of.5. Even for the most Conductivity (mw/m/k) Tle 8 Initil lowing gent lod (per cent y mss) nd fter 5 yers for XPS insultion pnels of vrious thicknesses when lown with HCFC-142. Thickness (mm) BA loding (%) Rte of loss (%/yer) Conductivity (mw/m/k) Initil After 5 yers Initil After 5 yers Also given re the verge exponentil rte of loss nd the initil nd finl therml conductivities. Source: Vo nd Pquet (24), Fig. 16 for residul BA lodings, with initil nd 5-yer conductivities inferred from these lodings nd their Fig. 12.

9 L.D. Dnny Hrvey / Building nd Environment 42 (27) Energy py ck period (Yers) Reltive to RSI.5 Energy py ck period (Yers) Reltive to RSI 3. Mrginl Energy Py ck Period (Yers) c Minerl Wool High Low Polystyrene High Low Minerl Wool High Low Minerl Wool High Low Polystyrene High Low Polystyrene High Low Polyurethne High Low Cellulose Polyurethne High Low Polyurethne High Low Cellulose Finl RSI Vlue energy-intensive insultion, the overll pyck time is less thn 2 yers for n RSI of up to 1. An lterntive se cse is wood-frme structure with internl insultion giving n effective RSI-vlue (including therml ridges) of 3.. Fig. 2 gives the overll pyck times when externl insultion is dded sufficient to ring the totl RSI to vlues rnging from 4. to 1.. The overll pyck time for the dded externl insultion when sufficient externl insultion is dded to ring the totl RSI to 6.7 (out the most tht hs een done for wlls) is 3 6 yers for polystyrene nd 5 8 yers for PU, depending on the efficiency of the mnufcturing process. Fig. 2c gives mrginl pyck times, sed on the lst RSI increment of 1. dded. When the RSI is incresed from 9 to 1, the pyck time for this increment is s lrge s 34 yers, ut insmuch s this is less thn the expected lifetime of the insultion, incresing the RSI to s high s 1 using the most energy-intensive fom insultion is justified on lifecycle energy sis with 4 HDD climte. However, RSI-vlues s lrge s 1 hve een used only in roofs which, if flt could e insulted to this level using continuous ed of cellulose insultion, which is much less energy intensive. 4. Assessing the trdeoff etween hlocron emissions nd reduced heting energy use The climtic trdeoff involved in hlocron emissions nd reduced heting energy use will e ssessed here in three wys. For the first two re sed on the overll nd mrginl pyck times computed for emodied energy, with the frctionl rte of lekge nd long-term therml conductivity of the insultion ssumed to e independent of the thickness of insultion. In the third method, the frctionl rte of lekge is ssumed to e smller the thicker the insultion, nd s this leds to lrger verge lowing gent loding over the lifetime of the insultion, the verge therml conductivity is smller the thicker the insultion. One cn expect these ssumptions to reduce the increse in mrginl pyck time s the thickness of insultion increses Results s the thickness of insultion is incresed with fixed rtes of lekge Results for polyurethne fom For PU fom cses with fixed rte of lekge of the lowing gent, we ssume n emission of 8% during the mnufcture of solid fom insultion, emission of.2%/ yer or.5%/yer of the lowing gent remining t the strt of ech yer over 5-yer lifespn, nd complete destruction or recovery of the lowing gent remining fter the 5-yer lifespn. These emission ssumptions result in 16.8% nd 28.4% of the originl lowing gent eing emitted to the tmosphere over period of 5 yers for the.2%/yer nd.5%/yer cses, respectively. As Fig. 2. Vrition in the overll energy pyck time s the totl RSI is incresed from ().18, ().5, or (c) 3. to vlues s lrge s 1., nd (d) vrition in the mrginl energy pyck time when the RSI-vlue is increse y 1. to the indicted finl vlue. Energy pyck times re for climte with 4 HDD nd heting system efficiency of.9, nd re sed on the emodied energies given in Tle 2.

10 2868 ARTICLE IN PRESS L.D. Dnny Hrvey / Building nd Environment 42 (27) Tle 9 Input nd computed intermedite prmeters used to compute the time required for svings in heting energy CO 2 emissions to completely offset the GHG emissions ssocited with the mnufcture of polyurethne solid fom insultion nd ssocited with the lekge of three different lowing gents into the tmosphere Prmeter Blowing gent (BA) third cse, 1% of the remining lowing gent t the end of life is ssumed to e emitted to the tmosphere. Tle 9 gives the GWP, mount of lowing gent used, nd the fom therml conductivity for solid PU fom mnufctured using,, or n- pentne s lowing gents. From these prmeters, nd given fom density of 32.5 kg/m 3, the emodied energy nd mss of lowing gent used in 1 m 2 of fom with n RSI-vlue of 1. cn e computed, nd re given in Tle 9. Assuming the energy used to mnufcture the fom to e one-qurter col nd three-qurters nturl gs, with emission fctors of 92 nd 55 kg CO 2 /GJ, respectively, the CO 2 emission ssocited with the mnufcture of the insultion is s given in the fourth lst row of Tle 9. Given the initil BA lodings, GWP, nd totl lekge, the CO 2 equivlents of the BA lekge cn e computed nd re given in the lst two rows of Tle 9 for.2%/yer lekge rte,.5%/yer lekge rte, nd complete end-oflife emission cses. Figs. 3 5 give the numer of yers required for the svings in heting energy CO 2 emission (resulting from the ppliction of the PU fom insultion) to completely offset the equivlent CO 2 emissions ssocited with the mnufcture of the insultion nd with lekge of the lowing gent for the.2%/yer,.5%/yer, nd complete-emission cses, respectively. Heting energy svings re computed using Eq. (2), ssuming 4 HDD nd heting efficiency of.9, then converted to CO 2 emissions ssuming the energy used for heting to e nturl gs. Results re given for fom insultion sufficient to give totl RSI rnging from 4. to 1., eginning with n initil RSI-vlue of either.18 (Figs. 3 5, corresponding to 2-cm Dougls Fir shething),.5 (Figs. 3 5, corresponding to rick wll) or 3. (Figs. 3 5c, corresponding GWP Kilogrm of BA used per kg of fom BA density (kg/m 3 fom) Insultion conductivity (W/m/K) Are of RSI-1 pnel (m 2 ) produced from 1 m 3 of fom Fom mss (kg/m 2 /RSI) BA mss (kg/m 2 /RSI) Fom-emodied energy (MJ/m 2 /RSI) CO 2 from mnufcture (kg/m 2 /RSI) CO 2eq of BA emission (kg/m 2 /RSI) for.2%/yer lekge over 5 yers, % therefter CO 2eq of BA emission (kg/m 2 /RSI) for.5%/yer lekge over 5 yers, % therefter CO 2eq of BA emission (kg/m 2 /RSI) for 1% emission In ll cses, the fom density is ssumed to e 32.5 kg/m 2 nd the emodied energy 137 MJ/kg. Fom density nd emodied energy re tken from Tle 3, while fom conductivities nd lowing gent GWP nd loding re tken from Hrnisch et l. [15], emission during mnufcture is 8% of the initil loding, emission t disposl is % or 1% of the remining lowing gent, nd emission during use is either.2%/yer or.5%/yer over period of 5 yers. to pre-existing fireglss insultion tts etween 38 mm 89 mm studs). Also given re mrginl pyck times, sed on RSI increments of 1. up to finl RSI-vlue of 1. (Figs. 3 5d). As seen from Figs. 3 5, pyck times re lrgest using, with the pyck eing out 75% s lrge using nd 2 25% s lrge using. For.2%/yer lekge using, the overll pyck time is out 1.3 yers when PU is used to increse the totl RSI from.18 to 1 (Fig. 3), out 3.6 yers when PU is used to increse the totl RSI from.5 to 1 (Fig. 3), nd out 2 yers when PU is used to increse the totl RSI from 3. to 1 (Fig. 3c). For finl RSI-vlue of 6.5, the mrginl pyck time is out 25 yers, while for finl RSI-vlue of 1. (otined in the roofs of some low-energy houses), the mrginl pyck time is out 65 yers using, 5 yers, nd 25 yers using (Fig. 3d). If the lekge rte during use is.5%/ yer rther thn.2%/yer (Fig. 4), the pyck times re incresed y out 4% (so, for exmple, mrginl pyck times for re out 35 yers t RSI 6.5 nd out 9 yers t RSI 1). However, for PU lown with, the mrginl pyck t n RSIvlue of 1. is only 25 yers, nd verge pycks (sed on the totl thickness of fom insultion) re 8 yers nd 1.4 yers if the strting RSI-vlues re 3. nd.5, respectively. These pyck times re lrgely independent of the ssumed lekge rte, ecuse they re dominted y the emodied energy of the insultion. Finlly, if 1% emission of the lowing gent remining t the end of life occurs, pyck times for nd re out 3 times longer thn for the.5%/ yer cse.

11 L.D. Dnny Hrvey / Building nd Environment 42 (27) Pyck Period (Yers) Reltive to RSI.18 to RSI.5 to RSI 3. Mrginl Emission Pyck Period (Yers) c d If the pyck time for the ddition of n increment of insultion is greter thn the expected lifetime of the insultion, then the increse in the mount of insultion is counterproductive from climtic point of view over the lifetime of the insultion increment, the svings in hetingrelted CO 2 emissions is less thn the CO 2 -equivlent of the hlocron emissions. Bsed on these results, it is seen tht the net climtic enefit of hlocron-lown fom insultion cn e quite smll, nd tht when used to uild the totl RSI-vlue up to the levels of wll insultion used in low-energy houses (RSI 6.5), hlocron-lown fom insultion is counterproductive from climtic point of view if, s is normlly the cse t present, there is complete loss of the remining lowing gent t the end of 5-yer insultion life. An lterntive wy to view the impct of vrying mounts of insultion nd of different lowing gents is to plot the vrition in net emission reduction vs. RSI, where the net emission reduction is the svings in nnul heting-relted emissions minus the CO 2 (or CO 2 -equivlent) emissions ssocited with the emodied energy nd lowing gent verged over the lifetime of the insultion. This is shown in Fig. 6 for lekge rte of.2%/yer. For hlocron lowing gents, net sving peks t some intermedite RSI-vlue nd then declines; the mximum net sving occurs t the RSI-vlue where the mrginl pyck time is equl to the lifespn of the insultion. For, the net sving increses with incresing RSI-vlue over the rnge (2 1) considered here Results for extruded polystyrene The lekge rte from XPS insultion (.75 4.%/yer ccording to Tle 5) is sustntilly lrger thn from PU solid-fom insultion (.2.5%/yer), the GWPs of the hlocron lowing gents re out twice s lrge (18 23 vs. 1 11), nd the therml conductivity is out 3% greter (so less heting energy is sved for given thickness of insultion). As result, the pyck times for XPS re sustntilly greter thn for PU solidfom insultion. Pyck times re given in Figs. 7 nd 8 for lekge rtes of.75%/yer nd 4.%/yer, respectively, with complete recovery of the remining lowing gent t the end of life, nd dditionl ssumptions nd intermedite results s given in Tle 1. Aout 9% of the initil lowing gent hs een emitted fter 5 yers in the 4%/yer cse, so the results for this cse re lmost the sme s if complete emission of the remining lowing gent hd een ssumed. In uilding from RSI.18 to RSI 1, Finl RSI Vlue, (W/m 2 /K) -1 Fig. 3. Vrition in the overll pyck time for equivlent CO 2 emissions s the totl RSI is incresed () from.18, () from.5, or (c) from 3. to vlues s lrge s 1., nd (d) vrition in the mrginl emission pyck time when the RSI-vlue is incresed y 1. to the indicted finl vlue. Emission pyck times re for polyurethne insultion using either,, or s lowing gents, for climte with 4 HDD, for heting system efficiency of.9, 8% lekge t the time of mnufcture,.2%/yer lekge during use, nd no relese of the lowing gent remining t the time of disposl (fter 5 yers of use).

12 287 ARTICLE IN PRESS L.D. Dnny Hrvey / Building nd Environment 42 (27) to RSI.18 to RSI.5 to RSI 3. Mrginl Emission Pyck Period (Yers) c d to RSI.18 to RSI.5 to RSI 3. Mrginl Emission Pyck Period (Yers) Finl RSI Vlue, (W/m 2 /K) -1 Fig. 4. Sme s Fig. 3, ut for.5%/yer lekge of the lowing gent during use c d Finl RSI Vlue, (W/m 2 /K) -1 Fig. 5. Sme s Fig. 4, except for complete relese of the lowing gent t the end of use.

13 L.D. Dnny Hrvey / Building nd Environment 42 (27) Net CO 2 Emission Svings (kg CO 2 /m 2 /yr) Net CO 2 Emission Svings (kg CO 2 /m 2 /yr) Net CO 2 Emission Svings (kg CO 2 /m 2 /yr) c Totl RSI Vlue, (W/m 2 /K) Fig. 6. Net nnul CO 2 -equivlent emission svings for PU fom with.2%/yer lekge, strting from () RSI ¼.18, () RSI ¼.5, nd (c) RSI ¼ 3.. Net emission svings re the svings in heting-relted emissions (ssuming nturl gs furnce t 9% efficiency nd climte with 4 HDD) minus the totl emodied-energy nd lowing gent emissions verged over n ssumed insultion lifespn of 5 yers. The upper curves for nd ssume no relese of the remining lowing gent fter 5 yers of use, while the lower curves ssume complete relese. the overll pyck times re 3 5 yers using HFC-134 nd 5 8 yers using HCFC-142 (depending on the lekge rte). However, the mrginl pyck times t RSI 1. re yers for HFC-134 nd yers for HCFC-142! At more modest RSI of 6.5, mrginl pyck times re still 6 1 yers for HFC-134 nd 9 16 yers for HCFC-142. For CO 2 -lown XPS, the mrginl pyck time t RSI 1 is out 2 yers, most of which is relted to mnufcturing emissions Results for spry-on polyurethne fom Spry-on fom insultion hs the dvntges tht it cn e pplied in difficult-to-rech situtions, cn fill irregulr voids, nd cn form n effective sel ginst ir flow, therey reducing het losses due to exchnge of inside nd outside ir s well s reducing conductive het loss. Fig. 9 gives overll nd mrginl pyck times for spry-on PU insultion using,, nd wter/ CO 2 s lowing gents, in ll cses ssuming 5% lekge during ppliction, 1.2%/yer lekge during use, nd complete recovery of the remining lowing gent t the end of 5 yers. Fig. 1 gives pyck times ssuming complete emission of the remining lowing gent. Additionl ssumptions nd intermedite results re given in Tle Assuming complete end-of-life recovery, the mrginl pyck time is 5 7 yers t RSI ¼ 6.5 nd yers t RSI 1 using the hlocron lowing gents, ut is only 2 yers t RSI 6.5 nd 47 yers t RSI 1 using wter/co 2 mixture s the lowing gent. The hlocron pyck times re lmost douled if complete emission of the lowing gent tht remins t the end of the insultion life occurs PU mrginl pyck time when lekge rte depends on thickness The ove results re sed on lekge rte tht is independent of the thickness of the fom insultion. In relity, the frctionl lekge will decrese the thicker the insultion, nd this decrese will offset to some extent the declining mrginl enefit of greter thicknesses of insultion. This in turn will cuse the mrginl pyck time to increse more slowly s the thickness of insultion increses. Bsed on the dt presented in Tle 8, it will e ssumed here tht the rte of lekge during use is given y R ¼ :5 ð4=hþ, (3) where H is the thickness of insultion in cm. This produces the rtes of lekge shown in Fig. 11, which rnge from 1.2%/yer for totl RSI of 1. to.1%/yer for totl RSI of 1 if the uninsulted cse hs RSI ¼.18. At given RSI-vlue, the rte of lekge is smller the more of 2 The H 2 O/CO 2 loding when used s lowing gent is not known, nor re the proportion of H 2 O nd CO 2,soCO 2 loding out hlf tht when used s lowing gent in PU is ssumed.

14 2872 ARTICLE IN PRESS L.D. Dnny Hrvey / Building nd Environment 42 (27) to RSI.18 to RSI.5 to RSI 3. Mrginl Emission Pyck Period (Yers) c d HFC-134 HFC-134 HFC-134 HCFC-142 HFC-134 CO 2 HCFC-142 CO 2 HCFC-142 CO 2 CO Finl RSI Vlue, (W/m 2 /K) -1 Fig. 7. Sme s Fig. 3, ut for XPS fom insultion with.75%/yer lekge of the lowing gent during use nd other ssumptions s given in the min text. to RSI.18 to RSI.5 to RSI 3. Mrginl Emission Pyck Period (Yers) HFC-134 HFC-134 HFC-134 HCFC-142 HCFC-142 CO 2 HCFC-142 HFC-134 CO 2 CO 2 CO Finl RSI Vlue, (W/m 2 /K) -1 Fig. 8. Sme s Fig. 3, ut for XPS fom insultion with 4.%/yer lekge of the lowing gent during use nd other ssumptions s given in the min text.

15 L.D. Dnny Hrvey / Building nd Environment 42 (27) Tle 1 Sme s Tle 9, except for XPS solid fom insultion Prmeter Blowing gent (BA) HCFC-142 HFC-134 CO 2 GWP Kilogrm of BA used per kg of fom BA density (kg/m 3 fom) Insultion conductivity (W/m/K) Are of RSI-1 pnel (m 2 ) produced from 1 m 3 of fom Fom mss (kg/m 2 /RSI) BA mss (kg/m 2 /RSI) Fom-emodied energy (MJ/m 2 /RSI) CO 2 from mnufcture (kg/m 2 /RSI) CO 2eq of BA emission (kg/m 2 /RSI) for.75%/yer lekge over 5 yers CO 2eq of BA emission (kg/m 2 /RSI) for 4.%/yer lekge over 5 yers In ll cses, the fom density is ssumed to e 22.5 kg/m 2 nd the emodied energy 127 MJ/kg (sed on Tle 2). GWPs re from Tle 4, fom conductivities re verge vlues from Tle 6, nd the lowing gent frction is from Tle 8 (for HCFC-142 nd ssumed to pply to other lowing gents). Emissions during mnufcture nd use re ssumed to e 25% of the initil loding nd either.75% or 4.%/yer, respectively, sed on Tle 5, nd no emission of the remining lowing gent is ssumed. the totl RSI tht is ttriutle to the solid fom component of the wll ssemly, s this implies greter thickness of solid fom insultion. The reltionship show in Fig. 11 ssumes tht greter RSI is otined y using thicker fom pnels, rther thn y comining 2 or more pnels in lyers. Fig. 11 shows the totl lekge frction over 5-yer lifespn, including emissions during mnufcture ut ssuming no end-of-life emissions. As incresing mounts of PU insultion re used, sufficient to increse the totl initil RSI from 1. to 1. strting from n uninsulted shething with RSI ¼.18, the totl emission decreses from 48% to 12%. Thus, s the thickness of insultion increses y fctor of 12 (from 1.7 to 2.6 cm), the totl hlocron emission increses y only fctor of 4. If solid fom insultion is pplied to preexisting insultion, the emission frction t ny given totl RSI-vlue is lrger the greter the strting RSI-vlue, s this corresponds to thinner sl of fom insultion. Thus, for totl RSI of 4., the emission frction is 43% for pre-existing RSI of 3. nd 19% for pre-existing RSI of.18. These results should e regrded purely s n illustrtion of how importnt to overll emission the dependence of lekge rte on insultion thickness could e, s the specific numers depend on the ssumed reltionship etween fom thickness nd nnul lekge, s well s on the ssumed emissions during mnufcture nd disposl. The verge therml conductivity of the insultion is given here y K ¼ K o þ :5DBA f, (4) where K o is the initil conductivity (t full BA loding), nd DBA f is the decrese in the lowing gent loding expressed s frction of the fom mss. For K o ¼.22 W/m/K, K t the end of 5 yers rnges from.249 W/m/K for 2-cm lyer to.227 for 22-cm lyer. However, the smller K for thicker sl hs very little effect on the mrginl heting energy svings compred to the vrition in 1/RSI. Fig. 12 compres the resulting mrginl pyck times for PU insultion lown with either HFC-142 or. Shown re cses with lekge rte fixed t.5%/yer nd therml conductivity of.21 W/m/K (HFC-142) or.22 W/m/K (), for lekge rte given y Eq. (3) ut fixed conductivity, nd for lekge rte given y Eq. (3) with conductivity given y Eq. (4). Accounting for the decrese in lekge rte with incresing insultion thickness reduces the mrginl pyck times y out 5%. This is consistent with BA gent ccounting for out 7% of the totl greenhouse heting (including emodied energy) t RSI ¼ 1, nd reduction in this contriution y out 7% with thickness-dependent lekge rtes. Allowing for the increse in therml conductivity s BA leks hs negligile effect on the mrginl pyck times Comprisons with fixed thickness of insultion In the preceding discussion we hve compred pyck times nd net emission svings s the RSI-vlue is incresed for different kinds of insultion nd with different lowing gents. Insultion with lrger therml conductivity needs to e thicker in order to provide the sme RSI-vlue. However, in some situtions (prticulrly involving renovtions), the totl thickness ville for insultion is fixed. In this cse, use of insultion with lrger therml conductivity results in smller RSI-vlue. However, if the lower therml conductivity is due to the use of non-hlocron lowing gent, then CO 2 -equivlent emissions ssocited with lekge of the lowing gent re gretly reduced or eliminted ltogether. This trdeoff is ssessed here.

16 2874 ARTICLE IN PRESS L.D. Dnny Hrvey / Building nd Environment 42 (27) to RSI.18 to RSI.5 to RSI 3. Mrginl Emission Pyck Period (Yers) c d Wter/CO 2 Wter/CO 2 Wter/CO 2 Wter/CO Finl RSI Vlue, (W/m 2 /K) -1 to RSI.18 to RSI.5 to RSI 3. Mrginl Emission Pyck Period (Yers) c d Wter/CO 2 Wter/CO 2 Wter/CO 2 Wter/CO Finl RSI Vlue, (W/m 2 /K) -1 Fig. 9. Sme s Fig. 3, ut for spry-on polyurethne insultion with 1.2%/yer lekge of the lowing gent during use, 1% cpture of the remining lowing gent t the end of 5 yers of use, nd other ssumptions s given in the min text. Fig. 1. Sme s Fig. 9, ut ssuming complete relese of the remining lowing gent fter 5 yers of use.