### UNITED STATES ENVIRONMENTAL PROTECTION AGENCV WASHINGTON, D.C. 20460 

# FEB 0 1 1994 Mr. 

## Leonard Swatkowski Director of Engineering services Association of Home Appliance Manufacturers 20 North Wacker Drive· 

## Chicago, Illinois 60606 Dear Len: OFFICE Of AIR AND RADIATION

7 

## Attached is EPA's response to Dr. Clark Bullard's final repor.t for AHAM, 

## FIIAccuracy Analysis 

## of the ADL/ERA. 

## Model". The 

## report, which evaluated the draft ERA model, has been reviewed by 

## EPA and Richard Merriam at Arthur D. Little. The attached document summarizes our comments point-by-point for each of the issues raised in the report. The items we commented on include the approach taken for the**analys~s,** 

## the depth to which the issues were investigated, how such issues relate to the current version of ERA, and whether lessons learned can be utilized to achieve improvements to the model. The accuracy analysis evaluated the peer review version of ERA, which preceded the "official" release of Version 1.0. Version 1.0 had been released prior to your final report. Most of the issues raised**~n** 

## the report were relative only to the peerreview model. Version 1.0 had already addressed most of the concerns raised by the review. The peer-review of the. model by AHAM took place with virtually no interaction with EPA or the program's author. Further, the review was conducted as if. the program were a static, final product, rather than a developing entity for which peer-review, industry-expert inputs were desired. As a consequence, opportunities to resolve**misunders~andings** 

## by the reviewer and/or to alert the author to**~n** 

## obvious. problem· that could have been fixed almost instantaneously (for instance, the mistyped coefficient for R-141b) were lost. Unfortunately, these misunderstandings led to erroneous conclusions regarding the accuracy of the model. certain portions of the report, such as discussions on vacuum panel insulation and cycling losses, contain references to findings by manufacturers that seem to call the ERA calculations into question. These conclusions were drawn without presenting the actual data. without access to this data and the specific description of the conditions under which the data were obtained, we cannot respond definitively to claims that the available" data invalidate the model. UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON , D.C . 20460 

# FEB 0 1 1994 Mr . Leonard Swatkowski Director of Engineering services Association of Home Appliance Manufacturers 20 North Wacker Drive · Chicago, Illinois 60606 Dear Len: OFFICE OF AIR AND RADIATION

7 

## Attached is EPA's response to Dr. Clark Bullard's final repor. t for AHAM, 

## FIIAccuracy Analysis 

## of the 

### ADL/ERA , Model". The 

## report, which evaluated the draft ERA model, has been reviewed by 

## EPA and Richard Merriam at Arthur D. Little. The attached document summarizes our comments point-by-point for each of the issues raised in the report. The items we commented on include the approach taken for the analysi. s, the depth to which the issues were investigated, how 

## such issues relate to the current version of ERA, and whether lessons learned can be utilized to achieve improvements to the model. The accuracy analysis evaluated the peer review version of ERA, which preceded the lIofficial ll 

## release of Version 1.0. Version 1.0 had been released prior to your final report. Most of the issues raised**~n** 

## the report were relative only to the peerreview model. version 1.0 had already addressed most of the concerns raised by the review. The peer-review of the . model by AMAH took place with virtually no interaction with EPA or the program's author. Further, the review was conducted as if . the program were a static, final product, rather than a developing entity for which peer-review, industry-expert inputs were desired. As a consequence, opportunities to resolve**misunders~andings** 

## by the reviewer and/or to alert the author to**~n** 

## obvious . problem · that could have been fixed almost instantaneously (for instance, the mistyped coefficient for R-141b) were lost. Unfortunately, these misunderstandings led to erroneous conclusio· ns regarding the accuracy of the model. certain portions of the report, such as discussions on vacuum panel insulation and cycling losses, contain references to findings by manufacturers that seem to call the ERA calculations into question. These conclusions were drawn without presenting the actual data. without access to this da· ta and the specific description of the conditions under which the data were obtained, we cannot respond definitively to claims that the available · data invalidate the model.

## It was apparent that substantial company resources were expended in gathering in-house data or that experimental work was**con~ucted** 

## to address particular aspects of the 

# ERA program. If these, and other data from AHAM and individual manufacturers, were made available to EPA, we could evaluate it and use it to continue to strengthen certain sections of the model. I would like to recommend that be made available for this purpose. following data would be worthwhile: such, non-proprietary, specifically, access data to the AHAM round-robin compressor test.data for R-;34a and R-152a land other non-CFC refrigerants). This data contain test results for compressor internal temperatures, mass flows, and energy consumptions for at least two compressors; Detailed compressor maps for R-!34a and other non-CFC refrigerants;**~esults** 

## and descriptions of measurements relating to compressor cycling effects; Results and descriptions of vacuum panel insulation tests referred to in the Accuracy Analysis; Test data for energy consumption of a refrigerator/freezer at various operating conditions, including DOE standard test**co~ditions,** 

## and' typical kitchen conditions •. Such data should be accompanied by a complete set of ERA inputs. Using several**-se~s** 

## of . such data, the relative ability of the ERA model to deal with off-design· conditions could be addressed. In summary, our review of AHAM's critique indicates that these comments which had validity in an earlier draft of ERA have been successfully addressed, and that ERA provides a sound approach to evaluating refrigerator options. Of course, improvement is always 'possible and we look forward to further cooperation to continue to strengthen the model. Sincerely, 

# \\,. '-../

# J':;{~~~UP{~';{;i;C1-<?L Technology and SUbstitutes Branch Global Change Division cc:**R.Merriam~** 

## ADL Michael McCabe, DOE Jim McMahon, LBL .' 

## It was apparent that substantial company resources were expended in gathering in-house data or that experimental work was**con~ucted** 

## to address particular aspects of the 

# ERA program. If these, and other data from AHAM and individual manufacturers, were made available to EPA , we could evaluate it and use it to continue to strengthen certain sections of the model. I would like to recommend that be made available for this purpose . following data would be worthwhile: such, Don-proprietary, specifically, access data to the AHAM round-robin compressor test ,data for R-.134a and R-152a Jand other non-CFC refrigerants). This data contain test results for compressor internal temperatures, mass flows, and energy consumptions for at least two compressors; Detailed compressor maps for R-134a and other non-CFC refrigerants;**~esults** 

## and descriptions of measurements relating to compressor cycling effects; Results and descriptions of vacuum panel insulation tests referred to in the Accuracy Analysis; Test data for energy consumption of a refrigerator/freezer at various operating conditions, including DOE standard test**co~ditions,** 

## and typical kitchen conditions • . Such data should be accompanied by a complete set of ERA inputs. Using several**se~s** 

## of ' such data, the relative ability of the ERA model to deal with off-design ' conditions could be addressed. In summary, our review of AHAM's critique indicates that these comments which had validity in an earlier draft of ERA have been successfully addressed, and that ERA provides a sound approach to evaluating refrigerator options. Of course, improvement is always ' possible and we look forward to further cooperation to continue to strengthen the model.

cc : R. Merriam', ADL Michael McCabe, DOE Jim McMahon, LBL Sincerely,

# ~~~\**'7! ~'** **I7S ;L1A!** **L Jea~**  

## M. Lup1nabc1 Technology and Substitutes Branch Global Change Division

### A«uracy Analysis of Ihe :AOLIERA Model Prepared I", ASJOCi.tion of Home Appliance Manwaccurm NAECA 

### fisk """" Pre....... by . 

## alit BoIlanl_ 509 Welt Washin,lOft SII'CCt UrboN nlinoil61801 .ack&round . Thi.._ 

### was .......... u .... req.... ofol>c NAECA Tult """"ofol>c Anode .... of_ Applilncc**~ul_** hi. put 01 a

### lara.. 

# err"" by oI>c Tult _10 qUllllify oI>c-wn1y associued wiIh ..lima... ofCIlCrIl' .....p obWocd 

### udo. oI>c USEPA

_ ....... llllIyaia po..... (ollcERA po.....). Tho pro..... wasdewlaped by Anh ... D. UUIeIn<. (1991) ond wUl be used by I>ae in the 1998sww1&td-lCain. p-occal Tho ERA modd i. an i...,.oYcd ..moo ofoI>c.-1 uled by DoE In

# tenlI1. ollc 1993

_ (AD!., 1912) .Tho improve...... d.all mainly wioh .... u.... lnlaface. ond oI>c addilioo of mol.......... excbanJU1.lhcmaavc rtfriaaanu and new compressor modds lhat do noc rcqWre e&IorimrrAerIUlin, wi&b I panicularnew rdriJUllM. AHAM wk (on:e members. CIIlpnecn U'OIII &be ...

_ ....""Ifreear

### manulac:IUrin._ies. used .... ERA modd 10 perf""" ........._ reponed bore ond povidcd all .... neceutI}' InPUI dilL Purpose and itOpt For man)' Of the conservadon meaJW'Cllikel)' 10 be conlidmd by USDoE when ICllinlW 1998 NAECA eMIl)' efficienc)' aandards. adequate \tSI dall edit Mel cnabk manuilCtUl'allO pile lhe crodibilily ond eaui.,y of CIlCrIl' ..vi.... podiacd by oI>c ERA modd. Howevcr

_ ... Iial. orno 1051 da1a available for the tnC&SWU Ulled in Table 1..**~c:n** 

### DoE and 1,. .. ..:1' puda 10 chc NAECA IUlcmakinll'lll)' be forced 10rei)' I1most w:lul1vc1)' on mcdd·bua:I csDlJVI'':I fOllhc:le CDnlelVaDon InCISura. 'This report presenll results ofan effon 10 ellimue Ihe uncertainlia UIOCiated 

### with such model-based estimal:CL

I To"'_ ia pJr,is cwluioD 01 ... 011. model. ADL prootMtcd &hi AHAN TI* Force ...... i .... IIIcERA pnlI.-.n and inpul (del lIlICd ill !he USEPA', ORO Mldlipic .......Y' Rqon" 1992. SkanJ)' atW c:ompledan 01 the 11II1)'. n:pcwwd here. AHAN .. W«MOd ... USEPA _1IIouI ............... (1.0)

__ DA InOdd and

# uxI,"" 1U ... laW 'Oc:on&aiA ........**oI~CMI'** .. WIIion

...iewolIlrIcfta, tlut oonc IMl wouJd ........... )' aIw Ihc cmd

__ MIt nc:Ql 1 ft, 

## COIl&IieId" lIMa..,an. 1 • - a••**po~** •• to ••port by Clark Bullard A ••ociat•• "Accutaoy balyeb of tb_ ADL/BRA Kod.l l •

Background The report identified 80•• 

### ot the differencea between ERA and the 

### 1982 ADL/doe retrigerator/tr••zer .odel. Additional model features include: 1) incorporation of alternative refrlqoration cycles (dual-loop, Lorenz, aultiple control options for dualevaporator cyclee), 2) consideration of advanced**ins~lation** concepts, inclUding vacuu. panela, 3) various anti-sweat _ode options, 4) ettect. 

### ot door openings on cabinet loads, 5) more**co~plex** cabinet design8, inclUding repre.entation 

### at a co.pressor compart.ent, 6) enhanced**abilit~** to specity electrical energy use not associated with tane or the co.pressor, 7) additional compressor options, 

### 8) .ttect 

### ot variable 

### speed tans on enecqy use and heat exchanger pertor.ance, 9) and optional estiaation of heat transfer rates in each heat transfer regiae in the evaporator and condens8r.

purpO.8 aDd 800pe Test data have been obtained at the University of "aryland for gasket improve.ents, tor advanced insulations, for Lorenz cycle designs, and for alternative refrigerants and mixtures. In most instances, the ERA model 8ati.ates for energy savings were in agree.ent with the savings found in the meaaure.ents. The dualevaporator cycle (a auper set of the Lorenz cycle) is the basis of the standard design approach in Europe and in Asia. Comparisons between ERA analyees and laboratory measure.ents for a Chinese refrigerator using dual-evaporators were presented in the ERA Version 1.0 User'a Hanual. 

### Accuracy Analysis or Ihe ! ADLIERA Model Prepat<d fa<

Backcround . Association ofHome Appliance Manu{acQ,lrus NAECA 1....Fon:e Preporod by 

## autBullard A"o";'",, $09 Wea WuhinilOft S... UrI>ona OIinoiJ 61101



## nu. ....... wu IIRporod u .... ""1....oClhc NAECA TultFon:eoClhc ".eoci·....OC_ Applilnoe**~.r_** h 

### is ..... of llar,etc(f"" by Ihc TultFon:e 10 qlllAdIy ....

## -wnry woc:iucd with ulima...

### oC.....,. lI"'poWlDcd vllD,lhc USEPA**~**

# RIri,,,,,,,,, II1II)'111 

### po.,.., (Ihc ERA 

### po.,..,). The 

### po.,.., wu cIcwIoped by AM..D. Uule Inc. (1m) and wUI be vied by DoI!;" Ihc 199I.oandud·"";n,_' TIle ERA model is ..

### i...,..,.at venion oClhc model vied by DoI!;" KGin,Ihc 1993 ........... (AllL.**1982~** . The impfoYe......dul,

### mainly wioh ohe _ ;"oaf ....and Ihc 

### ooddilion 

### oC noulIiaont btu**~am.** alternative: rdriJUWI and 

### new carnpfUSOC' modd.1hat do 

### nee tequjre 

### cakJrimc::ea-ItSlin, widl. s-*ularnew

# rdriamnc. AKAM wi&: force membeR. 

### CDpnccn lrom

## _-.;or . .. 

## RlriacnlOl'_ ....ur_,_ies. vied ohe ERA model ..pod""" Ihc .... ___

..... and poYidcd alllhc......-y ;"poocdala. 

### PurpoH and .copt For many ofthe conservation mc.ut.ftS likely 10 be c:onsidmd by USDoE when Itldn, the 1998 NAECA eDa'J), efficienc), 1WMSanb, Idcquaae IC.a dati ubt and uabIe manwac:unn to JUlIe &be cndibility and c;:aWnl), of

### enc:rn .. vi,

n"pre:diacd b)' 1M ERA modd. HoweYCrIhcrc _1iaJc

### cw no I0Il daaa .vailable for &he mcaswu Us&ed in Table I,.**~ore** DoE and t. ......pIRia &0 chc NAECA JUlcmtJcina n'II)' be forced 10rei), aJmost e.u:lusivd)' on modd·buod**csci",, ~**  f«&hare conlaVuion measwu. 'nulrepan pRsentlfelUlli

### 01 an dfon 10 cllimaae Ihe uncertaintiCl UIONt.cd with such model·based**estirna~**

I To ...iII ..c"'''oI_ EAA.add, ADL ptO¥ided u.AHANTutFore. .......**~** ....**~** 6c ERA P'CII*" Iftd input flictMiDd

# ift., USUA', Dt.Ii Mv.kip&o ..... )'1 bpon. ill 1992.**~.,.,** CIIIIIIpIeIioIl 01 ... ."."..reponed""AHAM ..Wcwwd ..USUA ...". .....**~,....** (IJ)) ••ERAIIIOddMd'*" ..... . TMI .......MldIOCIOfUiII ........ oI ... o O¥W ..**~** •

...................._....ad ......... , .....wco"chn;",,· ... ,**~c 1rjw~**  ..."fOr\. 1 • - ••• pou•• to •• port by Clark 8ullar4 A ••oci.t•• "Accuraoy ADalrai. of tbe ADL/laA MOdel"

.ackgrouD4 The report identified 80•• of the ditterenc•• between ERA and the 1982 ADL/doa retriq8r&tor/tr••zar aodel. AdditionAl model featura. include: 1) incorporation or alternative retriqeration cycles (dual-loop, Lorenz, aultlple control option. tor dua}- evaporator cycl••), 2) coneideration 

### ot advanced**ins~lation** concepts, including vacuua pa. nels, l) various anti- s weat aode options, 4) ettect. 

### ot door openings on cabinet loads, 5) more complex cabinet designs, including representation 

### ot a co.pressor co.part ••nt, 6) enhanced**abilit~** to specity electrical energy use not associated with tana or the co.presaor, 7) additional**compr~ssor** optiona, 8) ettect 

### ot variable speed tans on energy use and heat exchanger pertor.anca, 9) and optional estiaation of heat tranafer rates in each heat transter regi.e in the evaporator and condenser .
Purpoae aDd .cope Test data have been obtained at the University 

### ot Maryland for gasket iMprove.enta, for advanced insulations, 

### tor Lorenl cycle**~esigns,** and tor alternative retrigerants and mixtures . [n most lnstances, the 

### ERA _odel eati••te. tor energy s avings were in agreeaent with the sav1nga tound in the Meaaure.ents. The dualevaporator cycle (a super set of the Lorenz cycle) 1s the ba sis of the standard design approach 1n Europe and in Asia. Comparisons between ERA analysea and laboratory .eaaure_ents for a Chinese rafrlqerator uaing dual-evaporators were presented in the 

### ERA Veraion 1.0 User'Q Manual,

# • tllm ovemcnts 

# · acuumitls

# ...... · 

# ......'" 

# ....... 

# ......... 

# · · on. 

# • """ 

# · llCOC n 

# · .., 

# ... Table 1. meaana 

# !, uS A

### 1imI>k 

# wiD_....... .....-of'l"""lifJlol .. __ ............ wiIh 11\ ERA_ot &7 .... Far.buccuenofri_._dlal .... -*I..- • ...,· weot2.00k_y•

# ..a I.lOk_y aftctlhc:dcsip**bu_~** 

# ..**~.**

............................ .-01 .. _..,. 1IIIIJ1la,_**~<Cllldudo** dlalu"", 01 Cl.2Ok_YCClllId be -.- Howe_if.... -.
_ ....

# _IlldaIIcnd_

.. -. S" ...yillIOk_y...... lhc:caia!Uod CO<IJY 

## 4si:ould ballld .. 

### 1ia

### to ..

........: 0< 611"<0.4 k_y.> 1loe _,io.1 k_y.lau u 

## diean,lool_ (oamillaIvoluo) f... CO<IJY ..

# win,. dlIl wuoluioodloiDally by Ibc-*l IWloe. 1llIa1a.· 

# ...-poIIIaIl_ wilen

__ ,_ .... 

### .-..apociaIIy_ .......

........ .. ClIlly _lD_ sipiflClllS r_ u"ERA -*I jaY"&" ' IOdiaplay ill 

## -aiav .... podi<lioo, 11UJ oampIc iUUIII'UCS 1M imponucc dkaowVw .... die' 'r6cc ...., .......

_**-*llD~lhc:....wL** ... •• ;

_ ..ybo lDIIJliflOd

_ and Ihoy ...y add In.

_ ..... 

# f.- ........

# llllI_ (I'olwllld**B~I~).** 

### . 1loepaucilyotdlllCllllhc:dY ..**~_** 01

__ ...- impIicarign k ....... dIII_ otlhc: eqlllliono _lD.'I"Ill'itl' 

## caUcY u ..... 1liiy .. ya ..... boca IUbjcaod 10 riJOIOUI validalion. TheRIen iD 1M

## roIIowUtc

# .JIia'" IIMRCI 01 irrq IC)'

... _: \} .- ... In 

# Ihc:.........- opcciIIod U ............. ERAlIllldd; 2) • • DaNCe L 11**1iaERA'.eq...aoa.;ud3)lCnaIiudvc:N:lMlyClDiald~ERA"'"** 

# .._c:uea...... otlyp<l n .... '3

_ 110 qllllllif'lOd II

# dlia..,.... ...... 1acI: 01 daIa, lUll ICDC casa it was pouib&e IlO IIIC Iimiwd propic&uy dII:a fraID Ial 

### rar .. prac:ac:c ot ...... lyp<lot .......



## In. c:oM 11·I.1.QAkwa.. ·I'.Okww. 

### Z report atteapta 

### to abov bow**~lntl** ... HOOt.ted vitia any 

### analy.i. or alternative daalvna oan lead to 

### dlttlQUlty in interpretation. '!be 

### .-...pl. 

### ca.. atteapg to abow that the 

### uncertainty ..y ... Uy be •• 

### 1arta .. , or 1&l'9_ than, tb.. 

### enervr GOn8W1.ptlon dU'terence. . A n\label' of probl_ 'lith t.be arvu-nt pl'eaenbd. ara avldentz

- The unc.rtalnty aMily.i••••

### u.. that 

## u.e aocIel errOl'. "111 be**r.~,** 

### plu. or .1nua, without 

### ayate..tl0 behavior. 

### Unl••• a**~.l** baa no pIly.leal beata, or 1a vary poorly ••ecut.!, t.hl•

cannot be the ca.. vita. an analytically-baaed -. ... of ••tJ.aat:1hg' eDal'9Y coneu.ptlon•

- It t.be**.~t** pr_anted vere t.r\&e,**1~** would .pply ewn

aore 1M) to eKper1_nbll

_ ••

### u.r...nu, vbere**~lu"** -nervY**conauap~ione** 

# .1'..... urecl, .nd dUter..,.. taken. 

### Error. 1n



### ....ur.aent. 

# .1'. f.r aor. lik.ly to be**r~** 

### th.n 1n .naly•••• It i. 'known, of cour•• , that axperiaentAl ....ur_nu provide the ao.t r.U.))1 ....

### na of ...... i"" t.be perforMnce of • particular de.i9n.



### - The co...nt on 

### the .iM))Uity 

### to c1et....ine 

### energy ••vinqa due to

th. output of only t.hr ... ignUicant 

### tiqur.. i. aurpri.1ng. ".lDIing •**~ypic.l** anergy coneuption of 3 kWh/etay, the .. xi ... uncertainly in th. preciaion of the outpat can ))a 0.01, whieb i. only 1/3 of • 

### percent. The**~.n~** .adal provide. output 

### to thr .. deci .. l pl.ce., r ••**~lt1""** in .n unc:ertainty due to**outp~t** preai.ion of only 0.05' • Table I . O'......'ioa InCIU'II I . cd A ...........wiU ............ ....**........-~~** ...

# _·nocI·... wiIh .. ERA_otaICrQ .... For.

# _cut1Ofri_. __........_ pndIcII"-.Y.

_ ot2.00 kWlt,&y•

# ..a 1.10 kWhld.y Iftct .... dcsip bu_**~** I>

### buponIo.



### _ ................ .-ot..lIIICCnIiouylMlJ1ll. ____...... 

### vtapot G.2OkWlt,&YOOllId be IdIicwd. _vetil... ...-..in....._ .... _1IId..- .......

.......'''.lIy20.IO kWlt,&y. ................. .....,IIWopAI! 

### i>ouId lao IIId 1>110 to ... -=OcAl! · co.4kWlt,&y.> n.. ...... , tfUkWlt,&y . .............

### adIiMI_ (jIcmiAII ...... ) far aICrQ IlvUIp ..... WII oIuioodloitioll7 by .........._ -. 

### 'I1U II. · 

# _..-_w .... MII>oncdnI_ ....**-..~'_** 

### ....... . 

# __coIy_., ..... si...

## r_ 

# r_ II_ERA _ 11_ l ..dirpIoy III caIcuIIad 

## cDcru 

# '*pn ,eGg n 11IiI ......

## w- .... impononooot.................. ' ._ .......... ....,_

.........__.,ian.-:.doc ........ . ........

# -.Iopoo. ' ........ ......,..

..... ifiod arlllnulk, .... lIIO)' ... yodd ...**_~** r......___Cl'<nrllld BWIIRt,**1991~** n..poucityotdl&loo ....cllec:ri_ot__....... Iiu_....... impI....rjm, ..

### _dIoI_ot.............._ ...**~** 

### .......qy.vtap_, ..,....... breD 1Ubjc:acd 10 rilORlUl validalian. 'Ibad"cniD 1M

### rouowiat utJJII,a .......01 'um my

..._ : I) unccnoInlieo 1n .... ..,.......1pOCiIIod II ...... ., .... ERAIIIOdd: 2) • ,ICirw";'4 

# s. t '" ERA', IqUliona; and 3) laW

### iaad\tcnaMly ....**~** EllA 

### ,,'im;

.._ ...........otlypClllllld.3 CIIIIIOC "qlllOli/' ... 1I

# *"_duo., lIdtot...... lull

.....cues itWII pouiblc .... IimiW'.....,.;a.ydlla

# _........r.a...n ..... rar ....- ot_lypCIot....... 

### O......... oI __ 1op n.................. 1I,...;pcr..-. II ilboW' ......_ .... ' _CIA IdeociI)' I ' i I I 

### _ot...... , Eodoot_ .......__ -. __

## < .. ..__ .....ot 

### a

## n.___ .........2.1· U. O.A kwtt.tt ............... U . U .OkWliM. 2 fte report at.taapt. 

### to Mow bow u.noertalnt.i.. auooiat.ct .,1t.b any analr. i • 01' altarn.t.i.. ...ivna oan lead 

### to ditticult.y ln interpretat.ion. The e .... le 

### ca.. at.te.pt.a 

### to Mow that. the unc.rtainty _y ...11y be a. la.... a., 

### or l art_ tUn, t.b......

## rvv oonauapt.ion d1ft_ence . . A. n\&llber of probl_ vlth t.be ar"9\&Mnt. pr..... 

### t.ect ara avident,

- The uncertainty .naly.l. ..au.e. that. tbe .odel 

# .rror. vill be**ra~,** plu. or ainua, without .y.taaatio behavior. Unl••• a

aoctel 

### baa no phy.ical be.i., or i. very poorly 

### .xecuted, thi. cannot .,. the ca.. vit.b an analyt:ieally-beee4 ... ne of ..tiaatinq .....rvy COfta\aaPtion .

- If the**.~t** praaentad 

### ver. true, it would apply 

### .van

.ara ao to .xpar1aental .... ur_nb , wIMre abaoluta .... 1'9)" conau.ptione ar..... urad, and ditf_anoaa tak.n . trror. in



### .... ur...,..ta .r. far .or. likely to be randoa than 1n ana1y_•• It i. known, of eo\&r••, tbat axparlaantal .... ur... nta provide the .,.t. relbble ...,.. of a_ ••

ift9 t.M perforaanc. of • particular cle.i,n•

- Th. co... nt on the**nabllity** to detar-ina .nel'9Y •• vi....,. du. t.o th. output. of only thr... i,nificant flqur•• i •• urpri.lng. Aaeu.i..., a t.ypical en.1"9)' con.uaption of a kWh/day , th... xl .. Wlc.rtain1y 1n th. precl.ion of 

## ua. output can be 0.01, "bieb ia only 1/2 of a percant. The curr.nt. .odel provide. output to

three deci.. l pbce., r ••ult1ft9 in an u.ncertainty due to output preci.lon 01' only 0 . 05'•nonlinear simullMeOus equations ikscribin. the s)'llem) and klfcclS the nlw;s 0( Ihc OUrpUI variables (in ourcase we are primaril)' intereseed in the

### e"~1 on onl)' 

### One 0( chem. lhe enerv usc E).: Since lhesc input mus arc independenl. their effccts can be !he JaUIIAnI r.ance:naint)' ilpYe.n by. root-sum-squared equation. Given lhIt E·**E(~I, ~2**  .... a.) and liven &he unceruinties AaJ, Aa2, ••.

### 4~ on each or

## the independent 

### vuiabie.s, then &he unccnaint)' inE is 

### pen by 4E. 

### ll(aEf<l.,)6.,)2 + 

### «aEf<l'2)6x2I' + ... + 

### «aEf<l.,.)4x,J21l0

.S (I) In our case we wiD define.Ax wc:h thai we II'C**9~"** e:auin &bat the INC value olllliea wilhin Ihe nnlC 1:1: AL Then ...... is. 9.1 .. ch...:elhallb...:tual ..... 01 E lies widlin 1he RIll' E:I: 4E. If ...... unec:n&inties Ire normaJly disaibuted,lhe upper and &ower limiu ol. ma), be comideRd 10 be specified

## Ii 1he:l: 

### 20 .level. . . NOle 

## """""1. (I) 1ha.1bc "'ull will be dominaoed by

# die""" ..... Inside die 

### I 1_ .. eocb Is aqUlRd. It is Ihe.rdCR possible to limit the anaI)'siSIO the Nlatlvd)' few larae It:I'mIt and 10 ipcn the Oft aumuous ImIJIer ones. For example lhc awn 01. 1011i aror due 10 0ftC 01 &he: inpuu plYl • twenIY-one I" mon wiD result in onl)' an 11 .. cnor on 

### Eo «he ann-w CRUD usc.1**~Cft** • aaention was focused on obWnin& lCCurate estimlte:s ol

## on!)' the 1arJcJIIet!"'contriburin,IO &he: llftOetUinl)'• 'Ibis kind ofanaI)'sis is caUcd -sinJle.sampIi unccnainc)' analysis- bc:ca... il ddinc.I dM: nnp: widl.in which the resull wil11ie, eYen ifonl)' • few musurtmenll and variablcs., arc involwd." 

### ne rault is &berefCR very conscr:vaDvc, mainl)' 

### bec:.use not enoup data ckill flX'mean values 10 be

## known.' To dc:f'iDe. more raJislic: rule on E woukl RlQuirc tWO Ihinp: 1) mcncateNivc dllaon NCACrCYl;ODsavin. desiJns 10 pennil aceunte: estinwion ollbe mean values the paramtler1 dcIc:ribin.1he improved s)'Slems; and 2) a MoniC Cltk> analysis in wMch hunchds othypothetic:al .driJQ"&1On -c:onscructcd- from inputs aj randomJ)' scJc:ctcd from "blns" conLainina values in d'le ran,e ai:t 4xj. The resuhinc Ej would lie within a much narrower ruae Ihan E t 4E iflhecrron combi"Cd 1011 k» eancel one**ano~.** We will lake the simpler root.aum·s4uaftd IpptOKh IXUlincd above. 11 is ,tnerally nol advisable: 10 IWt widt • Monle 

### Cu10 analysis; 11 is bencr 10 kim (ant v-hach IOUrtCI of UDCCIUinl)' are lhe most imponanllo model. 

### ) n.c combiDCd CIJCI' is .iwal by 1102 • 11(1 2») 4 Fa". ckaai!c4**eJ~** 0( .. is k;ftd" UftCtI\I11lt1 anaI)'IiJ _It J, MoIIat, ·Dacribifta uncenainIiu .. u.pe:rilftt.Wl ralillLl-,**~,wIllfl/TMr_** ONIFI_ S,""c.l9U: 1:3·11; or S.J. Kline MIl F.**A.~,** "Ducribin. uncuWnIicJ if! siftllt;·..,&e upui ..... ", ",,,•. Lt,., 3-1.

# '.1AIr)' its)'
, It ill 801 .. nlUCtY";wc u. tfOf1t Code IMI,sis in wtWdl •• ifI9W ...en ... thtir b.ftIM .... ift ... -.nner "'.1 Lhe cmn adckId. 1llc Jt'PIOJ'h uxd here IICCOl.lnU 

### r«. ria'" "- awca oIllnCCftady ate iIldcpmdea4 and M. ttlad'orc unlikel)' 10 add io. wcw.c;uc ...... 3 DOft1jnc.ar simultaneOUS equldons describin, the s),stcm) and IIlcclS &he**val~** 0I1he oulput variables (in our case 

### we are primarily inlc.rutcd in the

### clf~1 Oft only 

### One 01

### them. the Cfta',y 

### ..se E). : Since IheJc input crron are indcpcn6cIU, their dl'"ccu can bc.1ddcd.: che**~kant** .anocnailUy is 

### Jiven by a rooc·sum-lQuamI equadon. Given Nt E • £(x•••" . .. a.) and 

### siven &he:

### unoctUint~s MI, &"

_. 4 ..

### on each 01

### ~ independent vwiabka.1hea chc unocnailUy iaEiI

### pen by <Y! _ 

### H(afJax,)As,I' • (afJax2JAs,I' • ... • (afJallal4&oI'lIG.S (I) In our cue

### we wiU define**~** IUCh Ihal 

### we In**9~.** ccnain 

# "* lhc.1IIW Vllue 01 x lica wilhin the ranee

.. :t: 4x. Then lhere is.95..chance thallhc lC'tuaJ value ofBliu wilhin Ihc ranpB:t: AI!.. II Ihesc unccrWnOCSII'C nonTIIlly disaibutt.d. lhe upper and lower Umiu d. may be oon&idered 10 be specified Ii dle t 20 . level. . NOlO from."I. (I)

# ,hi, dle .... 11 will be domi",1ed by !he .............. In&ide die ( 

### 1_ each I, tqUlRd. ItiJ Ihctd'ort possible to Iimillhc anaIylislO the rc1advd)' few

# .,e IC:Im&. and 110 ipen Ihc InCR 

### aumcrous smaller

### ones. For

### cJWnple Ihc IWD of. 10.cmJr_ to 

### one olthe inPUli 

### plus
- rwcnt)'oQOC**1~** enors will mull In only an 111ft cmJr on 

### E.1hc unual eoerl)' UIC,'**~ore** - UtnOOn 

### was: locused on obWnina ICCURiC esaimalCs 01 

### on!y thc 

### larJesa tams

### conaibuD"I 10 thc**~** 1I<I<lefUil1l)l. This kind ofonalysis I, ealled "sin&le.sampit**u~ll**.. y analysi'" __ .dc/iaadle .....wi.... which &he result willlic, even ifonly I few mc.asumnenu and variablel Xi are inYOlwd.4 The:**~I** is dlcRfcn**vtr)'tonK~IDYC.** mainly __

### ..se noc enou,h dall Uisl ftwmean values 10 be

## known.' To dcfiat. more: rulistM: ranac on E would 

### require tWO Ihinp: 1) mcnuleft&iyc dillon Ihccaa'JYcooservin,desians 10 pc:rmiIICCURee cuimarion oIlhc mean valuuollhe**~tcn** dacribinalhc improved systc.nu; Ind 2) I MonIC Cuk» anaI)'Iis in which hunchdsofh)'pOlhc.:tk:aJ refriJCn1Cn Wa'e -c:onsCNCled" from inpuu Xi l'MdomIy selected from -bins" oonwnlna vaJuu In 1M ranae xl:t: 4xi. 

### The rcsultinc E i would 

### Itt. within I much 

### narrowerran,e than E t 4E lflhc: emn**c:ombi~** IOU 10 C&f'ICCI onc**ano~ .**  We will like the simpkr l'OOloaum.sqUlRd Ipproch c.ulined above. II Is 

### aenenll)' not adYisabk 10 Iwt with I Monle 

### Cu10 analysll; it 

### 1s ben« eo kim 

### rU'll 'l'hM:h IOW'OeIof unc:cnaintyare the moSi imponlnllo model.

J**n..~cnaritli",,,,"02** .11(12)1 • Far .....**lc4c.~** ofdtil ki"lld

## WICCftIi ,., IMIpiJ IDe It. J. MolfM. 

### "DcIc:riWftc**~** 

### .. capcri......**~u· £qu~TItN".,_**  FIlM

### xittlt. INl: 1:3. 17;.S, J.

# KJ._ F. A.1t4cOiMcd**~.~ "sI",tc.--"CJpctu..-'II.c"&,** **,, )..I** **~** I''', • , It ill ••nIUCf\I.ci.c u. WOf1I cue ..-l)'liJ in ..wct. .. &.pull. -:cn ...1hcit UftMC ....... ..ct. • 

# ........•'_cnon Iddod. 'Tbc**~** ttICd IIcrc 1ICCCIWIi.l1. Mfa ..r.a.1OWCCI oIl1fC..... , 1ft ! 1 f .. &lid 1ft IhcIeIcft Wltacl, 10 df ;' . WOI1I.caIC 1UWICf, 3AppllCl.ion 10 conlIn_lion opllons



### . To

## aramalt &he**YnCCttIi~** 

### rc1&l:in,IO' panjcular conscrvacioa opUon, we 

### .riu ilftCR lei'" chc moment lbe

_ 01 ............ Oft potUn<ICn dcsalbinl 

### pons 0I1hc.,. ..... dw ... nat _peL For cumpJe in chc ease 0(addina VlCWm panels, only 

### pan 01 &he foam is Whu b**ftleYU!'_~!he** .caney of !he model is how 

## wen Ihc mtItl valua of&he: repIaoDd foIm lind Iht VICWm p&nd are .

_ III tile C&IC 01 RII 

### r .... il milht be 111* dw Ihc Il>o:rmoIcondllcdvilY k and tile rwdliq R·



### ...... r ... dlo 1pud known, due 10 

### yean 01 uperience and CIlWIIi ........,01 olIi.lllIIaiaI. I. 

## e... il"&hI be bIe lO ....me dw tile _lIIIIo< Is

__ parca """""l'. III dw .... lbe on!)'...-alnlY inlnldnl:cd by dlo ..placement oIf .... by._ puds -.Id be

_ •

. usocWed wilh Ihc ......... condIIc:dvilY and dlicknesl 01 dlo

__ ........ _ 01 .... Iact 01 euensivc 

### Don, and such untenlincies are 1nIJ)'KId usin. the sinJle·1ImpIc mcchods desc:ribc:d 

# _. Forotbtrconservalion fnUSW'CS, howcver,lhen: CXl$u aubalnlial wae:cnain«y aboullbe mean values 0I ......t<n dcs<:ribinl!he bue C&IC 

### dcsiln.**~Ies** Inc:IIIdc beat

### udIIn&" «lIld_and pskct bcallcaks. Dcspire)'CUS of

### tesM' and an&Iysis. unoauindc:s remain due**1O~,** limiWions and &he lid; ofS&&ndIrdized 1e&IS. For oonsavllion DUI6ftI inYolvin. thcIc componeIiu. unccnainliel in the bile cut arimates IR considc:nld cxpllcidy. In !he followift, wbsections the mnsavation meuum Ire an&Iyzed individually ftKaU Ihft:c: eypes of



# ...... -=: I) WlCCIUindes in !he inJ'll" spc<ifoed by!he .... O( dlo ERA -.; 2) Ul<l11!JlCic>!!**ta>bc!ldedinERA~cq** ...lio<lI; ond3) ...... i_llyomia.cdrr-ERAcq........ Type I ......

_ quantified W'heR possible, while ,he CKhen are discusMd in quaUwivc ICf1nL Guild kUI luk • The: ERA model allows dw: user 10 input I plkel htat 

### kak. and k includes I c:ak\IIationaI assist fcabln: D c:Uallaac thai fil'R from infonnation aboul d'le ,uket mI&CriaI Md pomc:vy. 1)pical values for 1hc: main puwneun affcctin& this**c:aku~alion** are Ihown bcbw: O •• tet H.at Leak Measure.ents pertoraed at The**Unlver8i~y** 

### ot Maryland for a series of**gaske~** .odificationa co.pared favorably with tho predictions made usinq ERA and the gasket heat leak reductions given by Flynn et al. Intern,' Clliposcd width lntemal heal nnsfer c:odf.c:iall c.binet skin lhkknc» CuIcet olIickncss CT.IlH 0.25 

### <m S.U 1.0WJm2'C l.30to.31 ... 0.43to.I3 ... The calculation aesiat feature tor gasket**hea~** leak determination was not included 1n ERA Veraion 1.0. The authors 

### ot**~his** document agree with the general findinga of the**~ccuracy** Analysis in**~his** area. Since the feature was re.oved prior to the completion 

### ot the 8ubject report, .oat. of the discussion is not relevant to the current version of the .odel, An ERA simulation was conduclal usin, ahc.sc vaiKS. Ie IhowaS Ihu the ERA-calallatal hell hnucr is

_ ...<d by dlo

# r"" ''''' ....... and dill Ihc '""pi< ctrca 0( all dlo is abdIr2.6S,

........ IS kWlVy for.**buc~** .. II <.bi< 

### rooc model Thu< .....11.... hilbIy 

### pea for 

### sevaal IUIOQL. FU'SI, condUCDon 

### duoup the eabincl nan,c is modeled in ERA, whUe conduction 

### IhrouJh Ihcdoor flan,c is appucntly iJ,lMRd. Second. the ERA modeldoa DO( allow the '*let 10 specify chc InOSl impon.w faccon alTCIClin, plkel 

### rtpon heat &uk,**~y** chc ft1ali\'C posicions ofchc ,asku and 4 Appllcalion 10 

### nnsenatloa GplionJ To CIIimaIe Ihc 

### ync::cn,aincy rtlaJinllO I pu1ieuJar c::on.scnUon opion, we 

### Wiu lanore for &he. moment

...._ of_ on ponrntI<n dclCriblnl pons ofoho 1)'_dw ..."'" -,cd. For cumpIe in die.,.,.of-...Vl<Wm panels, only put ofoho 10111\ is ",pIIocd. WIw is 

### n:leYll!'. !" die 

## ocancy ofdie model is how wdllht ....... volues of Iht ",pIoood loom IOd die v_ """" ... bowl>. ladle.,.,.ofRII I....b ...,hI I>< UJ\ICd dw oho _ cooduaivi<y t ond oho 

### n:suIUo& R · vol ..for .... will """"knowo, doe 10 yean of..,.n.-1OdWCNi..leilia, of IhiI mMCriaI. .. 

## r.a ... ""l>< ....... bIe lO .....me dw Iht_YOIot ,,__

## """"ocancy. Ia 

### 111M .... Ihtooly...........,_ I»'Iht "'........of'-0 

# 1»'_-"_1><_ .

. "WI'''' willi oho lhtrmtlconducdvity ond dUckncsI of Iht_ pond&. _ of Iht Itct of CAlCnSivc acini and**~** IUCh Iotncenaincies**~** analyud uUnI the 

## siftase·umpae mechodJ described tbovc . Rwochc:rconJClYuion mtUUrCS, howcver,lhcrc u.iIu IUbaanrial unccnainly aboul &he mean values ofportmtlCtl dclCribln, die buc.,.,. dc'i&n. 

### EwI1>Ica ioclude bctlexdIanccr __ond pskClbctt leaks. 

### DuP" yean of......, ond tIItIysI.. ....,..".,... """"'due 10 ............. IimiuDans ond!he Itct of 1WIdtrdi* ...... Foroon....tdoa .........in.:w.... .- .............. ..x:naincics in she bue

### c:uc c:a:imllu**~** c:onsidm:d aplleidy. Ia !he foUowin, subscccions the COfIKn'.cion meuum IN analyzed wlMdua11y for all thftC Iypc. of aror -. I) _ in Iht**inPUII~""** I»' oho utcrof .... ERA -*I; 2) 

## ""IfI!Pdon!

ph 1+c' in ERA'I cqu.aDonS; and 3) ICmlS inadYcnc.ndy omiadfrom ERA Iqutions. T)'pe I 

### cmn IfCquantified where possibk, whik the O&htn aR**diK~** in q&aaUwivc amn&.. Otsk..... \ kit • The ERA aoodd 0I1ows .... UI<1I0 input I 

# ,,"'et hallcak.1Od k ioclude. I caIaaIttiontI wi" I..... 10 c:alcuJlIC IhII fil\R from inf'onnIciotIltou Ihc lukc:t alIICriaI and 

### pornccry. 1)picU values for Iht main parwncrcrs Iffcctinllhis c:ak:u! .. ion are Ihown bdow:: Intern,1 exposed width lnlCmll hell nn.s(cr codflCictll Clbin« akin Ih"kneu Gukct Ihi<tJIcu CT.9H O .2.1tm S.U 1.0W!m2"c I.JO±0'31 awn 0,4UO,13 ... An ERA aimuladoa was condllClCd usin, Ihesc ftlucs. k Ihowcd MilleERA-caScuIucd heal nnsfcr is doni...... I»' .... 

### r .... ,""...."..tnd Iht,!he """....

### etr"" oftil die _ ..... II**_1.6~**•

...lboul IS kWll/y for I buctine II cubic '- model Thuc """" ..

### hi&bIy ""POCO for ttVcroI

........ FIno. _UCDon duou&lo!he ttIN .. , fltnCC is moddod In ERA. while

# --&II

die door flan,C ia appuemly iancnd. Second, the ERA model doc:a.,. aUow the u.acr 10 specify Ihe J:nOiSI: important flClOfS 

### atrc:ain, pskcl R&,ion heal kat,**~y** the R1aDVC poa.idons 01 the pskct Iftd 4 

### a••tet aeat Leak H

easure.ante pertoraed at The Univeraity of Maryland for a series of 9asket .odification_**co.~r.d** f.vor.bly w ith tho predictions made usinq ERA and the qaaket heat leak reduction. given by Flynn et a1. The ca lculation aa.iat f.ature tor gaaket heat l eak**deter~lnation** was not included in ERA Veraion 1.0. The authors of thi s**docu~ent** agree with the general finding. of the**~ccuracy** Analysis in thi a ar... Since the feature was re.oved prior to the completion of the 8ubject report, .oat of the discussion is not r elevant to the current vereion of the aod.l.fllIlaes. Illppears chit ERA Inemp" 10 lCCOunl rOf mosl 

### of chc**~I** pin 

### dln>up chc edae Rpon &I direa heal nnsru 

### dvoup &he pskc:t. while in rlCl conduaion WOuah Ihc: Ihc:cl mew 

### flances is Ihe c:ridcal rlaor. . flynn., tI. aI. (1992) confinncd this rlCl by dcrnonsnlina 

### dvouJh r"'de elcmM1 moddina lhII" is Ihc iaIcncCion berwcen the Olna" Ind the alSktl, ,..her chll'l the dimensions 01 tilher. &hal determine the

..... _or"""'" doorod.... ,.,.. ERA 

## only .. low..... _10

_ ...... di_ 

## or..... llonaalll4 lOchul•• 1heV in......-I. die _y._ by f1yoa The 

## _orBouJhtoo (1992) IIl4 olIal

## or fly••• '" (l992liadi<OlColIal oIq>1ydllnJin.pskOI

_ could yl<1d ..vi 0< leu ...... dlc predi<tod by ERA. dependln. OIl dlc olenl1O which .... lIan aude pII' 

### oda. orthe pskOIln1O dlc 

### rdri& If .. die ERA

.................... die pskOI helt leak cal In f )'Idd -..... 1 .. far die

_ ..... Iha'e is no puuucc lhu c:ak:ulltions of

## cncto IlYina. due 10 rodcIip will be canu:L For cumpk ir die st<d lIan•• procrude. pili pske•• moll of .... heI. will nvd .......h .... lIan•• 1Il4 

### wum .... in e.poaod sudsc:eor p.lttL On dlc othu hIIl4 if .... lIan••

# _nola ha1fway"""", dlc 

# .uke intcmaJ ..poaod sud... 

## or.... psltet will be: tllIlCh _.1Il4 die ..... _or"""", .... pskc:1 iudfwiD be maach lIraer. The cnul)' IIviAas due 10 thulina 

### aaKct 1DlIeria1, ill**in~** expoaod width. or .... lIan.. thickness will diller ....

## dy·amon._.....; which CIMOI be: dis••

### JUished by ERA. ERA uscn mull also belWare: o( other intenlCdOAS besides IbOse Iddrascd by Aynn,eL 11.·(1991), who c:onoenaalCd mainly on the ellC:nllG which die lukclovatIppcd chc cnda of chc: mccaI flanacs. Ileal kab """."' .... Jlsl<et 1Il4 .... _ metal 

### na.... may be:..-lOd by .... paence of mullion hwcn and M?'Swe&I hulen, which an: modeled tude., c 

### .teocIy in ERA. 

### Abo. tine· dimensional heal nnd'u 

### oc:aan w.hcR:ver lhe &heet mew door

### cw c:abinc:I akin pocrudes inIo Ihe cold interior 10 provide ror the mlpeQc door sui.. The will heal nnd'cr C1QuuionI in ERA do noc ICCOWlI for chis 3·0 etrea, which will lower the lempenlure or the WICf skin and Ihcft:by**~uce** 2·0 heal

_ ..........h .... w"l. 

## , Since ERA Ippan:nlly llno,:" conduction 'ItvouaJI\he door nanae,. tNdc: appt'OIC:h 10 modelin. thi.t d'fect usial ERA would be 10 Idd this vllue to the uscr·spc:clfied pskct hell leak, and t.aIC ahat inslCld 

## or.........Wiona1 ....... AnoIher puhway far ..... Jlin ...... '" .... 

### pet ..,.,.. air WUtnllion, II also 

### iJnarod In .... ERA modeL ManufaChftn**~pan** that this flttOr is hl.h1y vlrilb&e, and ClOnIritiucea**lian~andy** &0 the IOC&I psltet· ..,.,. heal pin

## or 20 10 2.5" 

## or .... cabinet hell ...... (Nole olIal dlis ............ wu applicable to 1990-viftl.lIC Qbincu; it c:ouad be p«lpOl'UonItely1lrJa' for 1993 or vltr.Nn't-plnCl cabinets in Ihe (UUlR.) A c:rudc: wlylo .e:tOUnl for.it infilnlion usina the ERA model would be 10 5 ftMI,a. Illppears thll ERA Inempcs 10 IOCOUnl (ew mosl of Ihe**~I** pin 

### du'ouah the**~** cdae 

### «pan ..diRQ heal tranS(er

### thro&Iah the psbl. while in (ecl cond.acUon 

### Ihrouah 1M shctI meW 

### ftances is &he aiDe" (ector. . Rynn. ...... (1992) confi nnod thi. raa by _ . .. dn,_1lI r.....

## dcmon'..-un' dill iI is ....**~** berwoen &he ftanlCS Ind 1M 

### ,uht.nther than Ihe dimcftIion, 01 tilha', ...cktaminc Ihe _nnsfcr_'hllltdoorq ......... ERAooIy .. IowIIht_lOdIM.....di--...of.... · 1Ian.., MIl psIceO. .....chan,ollltit in...........I.....way. __ by F1yaa, ..... _ The -"**ofllou~'"** II. (1992) MIl dill ofRyn. . ... II. (1992) _doll d .... ydIMliall.sUI dimauioos _III yield llYin" paleror 1cII ................... pnodiaod by ERA. dcpendln' .......

...... 10 which ....

### fIan....,..,.....PU' ........

### or ,he .......inlO .... 

### ..tri&craa. Ifos ....

## E!\A

......................dIe .......hea,IcaIt .............. .,.I. raa yIdd .............1 .. fordle_cue.**~"no** I"uanuc lhM caJcu.l.donI ofCftCtp savin,s d&ae 10 ftIdcIip will be c:aftICt, Forcaunpk if die ..... 

### fIan,. poaud<. pall lilt ......'. ... 11

## or liltheal wiU .....**~,h** .... 

### fIan,. MIl wum lilt in......... 

### posed 

## surf_or lilt psllco. On dlelllhu hood iflht 

### fIan,< ......._ halfwoy ......1lI die psII., .... in,emd .. posed III/face ofdie psIIo, wUlbe ......._ . MIl die ..... nnsfcr

### dvouIh Iht pskt:1 i&selfwiD be 

### much tar,er. The 

### enu,y uvu.as due 10 

### chanpn,**~** pstetmaICriIl, ill**in~** exposed widlll. ......

### fIan .. llIickna, will diff., ...... y......,_.....:wIUch _ be dis........... by ERA. ERA uscn must also be awlUC 0(0Ihcr in1CnCliotis besides**~** IddruIed by Ryan. ct. 11"(1991), who conccncn.led mai nly Oft Ihc ClIe'" 10 whkh me ,ukel overtipped 1M ends of Ihe maaI nan,e:s. HUlIats 

### -Ill lilt ","'MIl lilt ....... 100II 0.....ma, be..-1111 by Iht __of

........h<IIen MIl**an ,** 

## .............. wllict> ...

### modeled • did lIy in ERA. Alto, ...... dimensional.,... 

### nII.ru ......

## w . _,he....... mew door .........dIin**~** inIO ...._ inlerior CO provide (or Ihe tnlpeQe door seal . ,1bc wall heal nnd'c:rc:q1oWionl inERA do noc &lCOWlt for &his 3-D effea, which will lower the**,cmpenlu~** o( lht ",Ucr akin and &heRby reduce l ·D hell nnsfcrlluou'h .... w"l. 

## , Since ERA Ippuently I,no,:"conduclion ' Itvou&t i the door flInae, a crude appcoKh CO modcLin. &h4 

### ctrect usin& ERA would be 10 add this value 10 Ihe USCNpedicd

# ,askea hclllak, and laIC that instc&d ofdie ............. wilL

_ puhwo, for .....pin 

### IIuouIh lilt ........, ........ airWU........ Is ....i&1IOftd1a lilt ERA model. ManuflCtUftt'S 1'tpcr1 d\II d ds (1C1Of' is hi,hly varilble.1nd conaibuca**Iip~lCMdy** CO the lOW

......,............. pi.

### or20 "'l.\"

### or ..... cabincl ..... 1oad. (NoIc doll dois po 

# "'0._ appIicaI>Ic 10 I99().Yi.....cabineos; il ooulllbe ............... 

### y.....ror 1993 ...............1 c:abinca in abe (Ulurc.) A CNdc WI'11O tce:QUn( fer lir infilncion

# usin. the ERA modd would be 10 

## sspecify 50mC "equivalent number ofdoor-opcnin&s." NcMt; also thai healleab occwin& on Ihe DoE ItII involve rellovdy cIty!ilen= air. while in accual refri&a?aon Ibc: 'infilD'llin& air wiU be sc:meWMI cooler but weU" tberdJy incrc.uin& defrost enc:rp. 1bc reporu by Flynn .... aI. and Bou&Jl1Oll<t. aI. wall

_ 00 .._ aimod .. iIolaliJI•

............ ..... 1caIts _lilt ranaindtr '" lilt

__ 1bc 

### mon: typicaIlilllllioo. _. is dill. will

_ .. ..,.;,. eabincI and ................ 

### ERA paliaIoo. One nmafac:Nm'did Ibis. usine Ihc ERA cakulacional wist I) quaalify cbc pskcl·rqjon tXlnIribulion. 

### aM COCIlpU"Cd the K)Ia1s. The results arc shown in Ibc: Table below.

## ~ix'

'opMounl 15 Cu. Fe

le·By·, 20Cu. Fl. ·uy· 24 Cu. 

### Ft. UUJ<"'Cabincl and S_

. (FuUy modclod) :Whldau \ •

Vacuum p8AC'1 la.sulaUon A quMDlltive anaI)"is w.inl ERA was conduacd by one manufacc.nt fot a pan:icu.... c:onfieuratioa of**'¥acu~** panels in a refri&enaor hlvinll baseline enerl)'conaumptian of616 kWbty. Enc:rl)' savines 01106 kWhly dut 10 Ibc: vacuum panels wuc estimalCd by &he model UnctN1ntits aboullhe enclosure lhic:kness (t 18'11» and panei ...illivily (t 10'11» combined .. pIau dlC ..suI! in lilt foUowinlnnae: 97 < l06 < IlS kWh/y. This preliminary result was based on the: assumption lhallhc mcM value.**ol,~** (OlIn raiadvity (R. 

### O.sa mz-eC/W<rn) 

### was known wilb pcrl'CCI ca1I1nl)'. 

## Wt.ue thia ma), arauabay be INc fot Rli foam (individual panels rnly vary 10 manuflCunnllOlerMc:ca etC. bullhc mean Is b)' 

### now well known) Ihc wne may IK\II be INC for non·CfC foams. If

### DoE wac 10 limply UK I ICSI raWt

## e", a acw (R14lb) roam 10 eakullte CncfCY savines. Ihc. Input value oIk 

### mlJhc be in aror by as nKatb as:ilor. bceause 01**~I'''nknown** dirrmnces between labonklry apccimtftl Md ICWII bIowinalfOUftd vaewm pInels; Ihc cS;trcrence between labcnlOlY ICII tempctMuru(1s-F) and acwa1lCmpmluresof' foam in I ftfriaenlOt apertunl in I goeF test ehamber; etc. Flt:k:WiRe Ibis uncuWnI)' iNa bach &he bue-casc Ind vlCuum-pltlCl refriltnlOl'chanlcs the result drwnIUea1ly 10 7S < 106< 137 kWhI)'.

6 Vacuua .8.el ID8ulatioD Property Uncertalntl... The discussion about uncertainties in foaa r-value does not apply to £RA per-ss; indeed, the argument raised would apply to any aodel, or to any interpretation of the results of a aeasure••nt. With any new .aterlal or technology one must make an a••u.ptlon about what i. known and then attempt to evaluate the consequence. of the as.u.ption. A model. itself. cannot deal with uncertainti•• in a••u.ptions. This .ust be addressed by the evaluator. reqardle •• of the tools employed to reach a conclusion. Bimetallic Effect. The DOdel i8 based on the pre.ise that good design practice i. tollowed. It 1. a•• umed that a •• nulacturer would not produce and Market a product**~ith** a slqnificant infiltration due to door warping_ No model can take such a situation into account. Hence, the Coamant would appear to apply to a product that would never be aanulactured. 5pCCify IOITIC "equivalent numbcroCdoor-openin"." Noc(aJso dw heat kaks ocewin,OQ &he DoE ItR involve .cllcivdy dry 9Q-F air, while in Ia,* .cfri,aUon Ihc'inrdauin, a1r";U be ICmCwhat cooler bu weller &henby hw:rus"', defrost cnerU· 

# The..,.... by F1YM.eL a1. and .,...",... eL a1. ..... _ onllbanlory "udia aimed 

# "looIOIin, psI<cI........... 1eoIts 110m IlIc nmaIncIer <II IlIc ___ Tho _ typlcallilllldon. __ • ilihal a manWlCNrCI' will k:St II) entire cabinet and**~** Ihc taadllD Ihc ERA PI f cd One 

## ......r ........ did dIis, I&Sin,llIc ERA caIc:.1OIionaI will ..

### -"'Y.... psI<cI• 

### ..pon

# oonori_. ood 

### """PO"'d Ihc: IOIIIs. The .... Iu ...oIIown 10 Ihc: Tobie below.

Vacuum panel hl$ulltJon A qano",ove an.aIysiJ

# usin, ERA was conduac:d by one manulaaurt:r 

### lor, puOcutu- confilYnlioa 01**vtcu~** panels in.rdri,cruor htvin,. baseline tnc1,yeonsumpdoft 01616**k~.** Eftc::ray pvinp of 106**k~** due 10 the Vltuwn panels WCR estimated by &he model Unccnaintics.bout &he enclosure lhic:kness (t 18")and panel**"si~IYioy** (t lOt.) __ 10 pIKo die _10 IlIc followin, ""PO: 91 < 106 < liS kWh/y. This p.clirnirwy IUUlc WIS based on &he assumption Ihat 1M meM value 

### ot..,.. (OlIn rt.Siadvic.y (R • (lSI 

### mz..C!W<m) was known whh perfCCt ccnaitu)'. 

## 'lihUe d\1a 1M)'**UJ~),** be INefor RII lOAm (i,.,ividual panels lTIIy vlrJ due 10 manultaurin,lOknnca

### cae. bulihc mean I,by now well known) &he same may IlOl be INC (or non·CfC (oams.. If

### DoE were to limply UJC llIbanIory IeSl res¥il for. .w(RI.lb) foam eoealculatc ena-p uvin,I.1hc input value oIk ml,hI be in aror by u......c:h u:t 10'11 bccawe t1 )'Ct·unknown diffCRncc.s bctWCCtlYbonkW)' apccimeas and aa»&I

# blow"" around YICllUl1l**pond~** .... cliff ..."", bet..... l.bcn..,. .... _ ....(75'f) and

# """'oem.,........ 01 ' 

## ro.m in.rdrip1ltoropctatin, In. 9()'tF lUI (lumber, etc.. FanoriD,lhb unccnaincy Wo boIh &he buc-cuc and VItUum-pand rcfri,ustor (hao,es the result dnmItlcaUy 10 1.5 < 106 < 137 kWhI)'. 6 Vacuu. .aDe1 IDau1atioD Property UncertalntJe.. Th. di.cu••ion about uncertainties in foab r-value doe. not apply to ERA per-.e; indeed, the argu.ent raised would apply to any .odel, or to any interpretation of the res ult. 

### ot a .. aaur•• ent. with any new ••terial or t echnoLogy one must 

### make an 

### a••uaption about what 

### 1. known and then atteapt to evaluate the conaequence. 

### ot the a.euaption . A .o4el , it.e1!, cannot deal with uncertainties in aaauaptiona . Thi. aus t be addressed by the .valuator, regardle•• of the tool . eaployed to reach a concluaion. Bimetallic Effect . The DOdel 

### 1_ baaed on the pre. i se th at good de a lgn practice 1. tollowed. It i •••• u.ad that a aanu fac ture r w

ould not produce and a arket a product with a significant i nfiltration due to door warping. No aodel can take s uch a si tuation into ac count . Hence, the coa.ent would appe ar t o app ly t o • product that would never be .anufactured .Comparison ofthese results illustrates another polemial 

# source of error. careless cxD'lpolation of' limited test data by !he analyst running the ERA model. The 

### ± 10% uncertainty on foam conductivity may be reduced considel'bly over time IS more is learned about the PfOCCiS o(t,*,""& &rooM vacuum panels. the tempenlure dependence ofk·values,.nd 

### otl:Ieicharactcrislics offoams made.with non.CFC blowing agenls. Until these uncertainties are resolved. the uncenainty analysis must address all thIce parameterS (panet resiStivity; enclosure thicknciS; (OlIn resistivity); the laner C&M0l be neglected as in the case of

### RII-blown foam. Other uneenaintiC5 unique to vacuum PlIletS cannot be analyzed quantiative1y using the ERA modet. For eumple the "bimetallic effect" ofa vacuum panel in I door may cause $OIT)C warping of the,door and lead to increased air infiltration. Data from-one manufaetura' indicates the existence of such an effect. but much more dall would be requimS to quantify iL The ERA model would then need to be modified 10 account for the resulting infilD"lrion through the psket region. Heat leaks through the gasket region are also underestimated by the ERA model. as described in the previous section. It was suggested that an estimate ofheat conduction through the sheet metal door flange could be included in the user-specified gasket heat leak. However if this were done. and themodel were then used to estimate energy savings doe lO vacuum panels. the energy savings would be overestimated because heat flux through 1he flange would incrusc. The vacuum panels (or any other kind ofinausod wall insulation) would increase the temperaNrc of the: sheet metal to a level approaching approaching thll ofthe test chamber. while the tempcranm inside the refrigcr&tor Rmaincd coostanL The higher temperature differential would cause more hwlO be**~ferred** through the flange than in the base case without vacuum panels.**~1iminary** tests conducted by this manufacturu for four**~figurations** showed that**ERA-p~cted** enClJ)' savings exceeded measured energy savings by**18~.** 20$, 47111 and 60%, respectively. Pan ofthese differences may be .tttibutable to )-0 effects such as flange hea11eaks not modelled by ERA, while the rest. is probably .nribullble to the**faeto~** quantified above. 

## 'J11is kind ofthree-dimensional effect, ignored in ERA, tIft'be analyzed usin. I much more C()mplex finite-diffCRnce model. One**manufacnu~r** did so for (WO configurations and found thll ERA underpredicted enerlY savin,s by 73*, and 74%. respecdvely. A Iabc:ntory lest was then conducted for one ofthe refrigerators, and the ICtual savinas were Ictually 60'11 puter than predicted by ERA. The**~son** here is thlt more accunle 3-D models cin lUide Ihe placement of vlCuum panels 10 maximize 3- D enerlY $lviogs Ind minimize 3-0 energy losses. The fact remains. howeva-.l.hat the crude assumptions in lhc ERA model may combine with uncenain input panmctcrs 10 peatly overcsti.mlle or underestimate the energy**saving~** achievable with vacuum panels.

7 Srfect of Improved. Insulation on Gasket Heat Leaks. In principle, improved cabinet heat flow resistance would result in increased temperature.driving forces across the gasket regions. However a simple calculation shows that the increase would be nearly unmeasurable. For example, it a 2-inch r-S foam section were analyzed with air-aide heat transfer resistances of 0.67 and 1.0 hr-ft2-op/Btu on the outside and inside surfaces, respectively; and with the gaSket heat leak corresponding to.20' 

### ot the total cabinet heat load, and with 50' of the gasket heat leak due to mstallic conduction across the cabinet flange (not inclUding the door), dOUbling the net resistivity of the inSUlation without increasing the thickness (a very conservative assumption) would increase the cabinet heat load due to increased gasket heat leaks a maximum of 1/2 ,. Hanufacturer Measured Savings. The statement is offered that a manutacturer determined that ERA overestimated energy saving from a vacuum panel by IS' to 60'. This can in no way be related to the discussed effect on gasket heat leaks. The authors of this document are not able to ·comment on the statement regarding measured and predicted savings, since a description of the refrigerator test was.not provided, and the model inputs have not been included. This problem is confounded by a subsequent statement that,another manufacturer round that ERA under-predicts energy saving due to vacuum panels. Again, no data, or description of the situation, were provided in the report. Three-Dimensional Effects. The report refers to the "crude assumptions" in the ERA model concerning multi-dimensional heat transfer efrects associated with vacuum**pan~ls** placed in roam composites. In order to retain analysis tractability, a relatively straightforward procedure was in fact adopted by ERA. However. considerable efforts were made to capture the major physical effects**as~ociated** with multi-dimension heat flow. Results of**compariso~s** of ERA predictions for three-dimensional foam-panel composite geometries with those obtained by finiteelement codes have been presented in the ERA User's Hanual. Two sets or finite-element analyses were provided by ORNL; both situations are discussed and tabulated in the User's Manual. For these situations, the agreement between the two models was within a few percent over most of the geometries considered. A further confirmation of the adequacy of the general approach adopted by ERA has been given to us by an independent manufacturer of inSUlating products, who stated that the ERA. model predictions were essentially the same as generated with the manufacturer's finite element codes, see attached letter from stan Rusek or Owens Corning. Comparison orthese results illustrates another pc)(cmial sourceof error. careless txaapo.iation of ' limited test data by !he analyst running the ERA model. The 

### ± 10% uncenainty on foam conductivity may be reduced consider.bly over lime as men: is Ieamed about the proceuof't'*1ling arouhd vacuum panels. the lCmpenture dependence ork-vaJues••nd 

### otl:Ieicharacteristics offoams made.with non-CFC blowing agents. Untillhese unccnainti es are resolved. the uncenainty analysis muSt address all thIceparameters (panel resiSlivity; enclosure thickneu; faun resistivity); the laller caMOl be neglected as in the case of RII-blown foam. Other uncertainties unique to vacuum panels cannol be analyzed quantitatively using the ERA modeJ. For example the "bimetallic effect" ofI vacuum panel

# u:.. door may cause $OITlC warping ofthejljoor and lead to increased air ihfila-ation. Data from-one manuflCtUR:r indic. llts (he existence ofsuch an effect. but much more data would berequimS toquantify iL The ERA model would then need to be modified to account for the resulting infilD'ltion through the psketre&ion. Heat leaks through the gasket region are also underestimated by the ERA modeJ. as described in the previous s.ecoon. h WIS suggested that an estimate of heal conduction through the sheet metal door_ flange could be included in the user-specified gasket heat leak. However ifthis were done. and the model were then used to estimate energy savings due to vacuum panels. the energy savings would be o\lerestimated because heat flux through tile flange would inausc. The \I.euum plnels (or any other kind ofincreased wall insulation) would increase the temperature ofthe sheet metal toa level Ipproaching approaching that ofthe teSt chamber. while the temperartm inside the refrigerator remained constanL The higher temperature differentiaJ would cause ID)te hell to be**~ferrcd** through the flange than in the base case without vacuum panels.**~liminuy** tests conducted by this manufacrlR[" for four <\Oflfigurations showed thar ERA-pn:dicted enClJ)' $lvings exceeded measured energy livings by**18~,** 2M1. 41... and 60%, respectively. Pan of\he.se differences may be attributable 10 3-D effects such IS flange heat leaks not modelled by ERA, while the**res~** is probably ltoibutable to the factors quantified above. 

### 'J'!lis kind ofthree-dimensional efrect. ignored in ERA, can·be analyzed usina a much more cpmplex finilC-diffeRRCe model. One**manuraclLlI~r** did so for lWO confiaurations and found thu ERA underprediCted enerlY savin,s by 13... and 74% . respec::lively. A Iabon.tory test was then conducted far one ofthe refrigerators, and the actual savinls were actually 6QII, JfWeI' lhan predicted by ERA. The 1c.s:son here is that more accURte 3-D models cin CUide the pltcanenl

### otvacuum panels 10 maximize 3- D eneJ"1Y $lviniS Ind minirNzt 3-0energy losses. The fact remains, however.wt the crude assumptions in the ERA model may combine with unoenain input panmetc:rs 10 &J'CIlly overcsti. mate or underestimate the energy**saving~** achievable with vacuum panels.

7 Bffect of Improved. Insulatjon on Gasket Heat Leaks. In principle, improved cabinet heat flov resistance would resulL in increased temperature .driving forces across the gasket regions. However a aimple calculation shows that the increase would be nearly unmeasurable. Por example, it a 2-inch r-8 foam section vere analyzed with air-aide heat transfer resistances of 0.67 and 1.0 hr-ft2-o F/Btu on the outside and inside surfaces, respectively; and with the gasket heat leak corresponding to . 20' of the total cabinet heat load, and vith 50' of the gasket heat leak due to metallic conduction across the cabinet flange (not including the door), doubling the net resistivity of the inSUlation without increasing the thickness (a very conservative assumption) would increase the cabinet heat load due to increased gasket heat leaks a maximum of 1/2 ,. Manufacturer Heasured Savings . The statement is offered that a manufacturer determined that ERA overestimated energy saving from a vacuum panel by 18' to 60\. This can in no way be related to the discussed effect on gaSket heat leaks. The authors of this document are not able to · comment on the statement regarding measured and predicted savings, since a description of the refrigerator test was . not provided, and the model inputs have not been included. This problem is confounded by a subsequent statement that ,another manufacturer found that ERA under-predicts energy saving due to vacuum panels. Again, no data, or description of the situation, were provided in the report.**Three-Di~nsjonal** Effects. The report refers to the "crude assumptions" in the ERA model concerning multi-dimensional heat transfer effects associated with vacuum pane.ls placed in foam composites. In order to retain analysis tractability, a relatively straightforward procedure was in fact adopted by ERA. However. considerable efforts were made to capture the major physical effects**as~ociated** with multi-dimension heat flow. Result6 of**compariso~s** of ERA predictions for three-dimensional foam-panel composite geometries with those obtained by finiteelement codes have been presented in the ERA User's Hanual. Two sets of finite-element analyses were provided by ORNL; both situations are discussed and tabulated in the User's Hanual. For these situations, the agreement between the two models was within a fev percent over most of the geometries considered. A further confirmation of the adequacy of the general approach adopted by ERA has been given to us by an independent manufacturer of insula, ting products, who stated that the ERA model predictions were essentially the same as generated with the manufacturer'. finite element codes, see attached letter from Stan Rusek of OWens Corning_AUernative refrigerants and mixtures The thermodynamic property dall used by ERA are the CSD equations ofSlite obtained from NIST REFPROP 3 program (Morrison and Mclinden. 1986). They could be. si,nificut $Ourcc of unccrIIinry because they are relatively crude equations requiring only 'minimal

### CJlpcrime~ data.. .. 1bey were used in ERA because unlike other more aecUJate equations ofsUte they can easily combined to approximate the properties ofmixtures. However ERA uses them for pure fluids as well. Prdiminuy comparisons have shown thai the latent enthalpy ofR-I34a JRd.icted by the CSD equations ofstate to contain to vuy by about I 104'11 from the Manin-Hou and Bcncdict-Webb-Rubin (BWR) equations.6 Similar discrepancies are found in the near-superheatrecime..The mlgn1lUde of these errors were**c::onr~** by N1ST (Gallagher. 1993) who estimated that: the CSD equations estimate the vapor pressure curve quite ICCUflltely**(:to.2~):** for went enthalpy cm:n in the**3-5~** range lie entirely possible; ant**~at** the NlST BWR**~ualions** an: the most accwate forR-I34a. Thtnfore the only way to remove this source of uncertainty from 

### me model is 10 replace the CSD equations ofstate by the NlST BWR equations when simulating systems using R· J34a. Similar errors may exist for other pure**re~gerants.** Note that this aror lends not to be nndomly distributed about a mean. but inlroduces a clear bias in the positive direction. The dircc:tion may be different for other refrigeranls. '



### . . 1be inaccuracy ofthe latent enthalpy dill for R·l34a will propapte through the ERA model k) affect its estimates ofannual energy use almoSt proponionately. 1bat is. a 

# 1., error in latententhalpy at the evaportlor temperature will cause ERA to alter the run time and hence the: enercY use 

## bY an equal amount. There will be some socond-order effects in the compressor model and due lO the way in "bi<:b ERA lwldles cYCling losses. bUf these lie probably insiinificant compared to the I'll error in annual energy use that could resull from inaccuracies in the property cWa al the evaporating 1IC11lpCf'UUre. Similarly. a 4'11 mor in Iitent enthalpy at the condensing temperature will alter the**~T** at the condenser (and therefore the EER) 

### as lhe model holds the user·specified values ofVA and**~bcoo1ing** constant. AdditiQnaJ elJOlS will be introduced when ERA is used 10 sim':l1lle mixtures ofrefri,eraRts. The interaction coefficients in the NIST property routines are intended 'D aocounl for such facIOt'S as zcotropic behavior. No quantitative analysis of the associated unccnainty 

## c:ouid be conducted. however. becauseofa lack ofdati onJll.e uncenainty ofthe interaction eoefficienlS lhemselves, 

### Ind on latent enthalpy and other key properties oflhe**rerrig~nts** mDStlikely 10 be used in mixlures for refrigerator-freezers. 6 Forcumple II I c.ondensin, cempcralul'C of IJI)-F Ihe eSD OQlIIUonJ' vllue for latent enthalpy is aboul4'1l '-Iu Ihan value liven by the Mlrtin·Hou equauoru: ofstile. At an ev.pomin'lempclSUlR: of -2O"F the em;If is Ibo 8**&l~erDetiv.** 

### aetrigeraDt. an4 ,ixtur•• The characterization of the MIST-developed CSD equation of state as being "relatively crude" .is unfortunate. Although the required coefficients can be estimated on the basia of "minimal experimental data",·thera ia no reaeon to believe**tha~** thia was the case. The sam. level of experimental underpinning for the coefficients is available for the CSD equation of state as for any other, inherently more parameter-intensive equation of.state. As shown in the NIST REFPROP documentation, a very large number of experimental data values were used to establish the coefficients. 

### ERA relied exclusively on the CSD equation 

### ot state (EoS) tor several reasons: 1) the same EoS would be applied to all refrigerants and refrigerant blends. 2) an extensive analytical and experimental effort was underway at NIST and elsewhere to retine the CSD EoS in support 

### ot the on-going assessment of the potential for alternative refrigerants, and 3) there was no apparent need to increase the complexity of the model by . utilizing more than one EoS. Considerable discussion is afforded in the report to."errors" in certain property predictions of R-134a. However, no quantitative attempt is made to put the uncertainties associated with property predictions in**perspective~** The report raises the issue of an error of 4\ in the calculated latent heat of R-134a at condensing conditions. To explore the consequences of such an error, an analysis has been carried out (using MUltiple Pathways run D 1993) Where the calculated latent heat was artificially reduced 

### by 4\. The calculated effect on annual energy consumption was only 0.4\ (3 kWh/year). Some very careful experimental studies have been concluded at ORNL to determine the energy consumption of refrigerator/freezers using various refrigerants; The ERA predictions for energy-use 

### differences associated with R-134a and R152a (compared to 

### R-12) are all within the. range of energy differences reported by ORNL. Allemalive refrigeranls and mixtures The lhennodynamic propcrt)' dati used by ERA are lhe CSD equations of Stile obcained from NlST REFPROP 3 propm (Monisonand McLinden. 1986). They could be a lilnLficanllOuree of unccnainly because Ihey are relalively crude equalions tequirinl only ·minimal

### experime~ da1a.. . . They were used in ERA because unlike oIhet more 

### acc:un.1C equations ofstate Ihey can be easily combined 10 3pproximale the properties of miXIW't$. However ERA U5tS !hem for pure fluids 

### as well. Preliminary comparisons have shown 

### Ihai the latenl enthalpy ofR-l34a predicted by !:he 

### esD equarions ofSlate 10 contain to vary by ,belli**1104~** from the Martin·Hou and**Bened.iet We~Rubin**  (BWR) equations.' Similar dise:n:pancies 

### are foWid in !he near·superheat

### re&ime. . The mlpitude of these crrcws were**con~** by N1ST (Gallagher, 1993) who c.stimatl:d IIlat: the aDequations estimalC the vapor pressure curve quile ac:cut1lCly**(±O.2~) ;**  fel" laIenl enthalpy 

### em:n in the**~5~** range are entift: ly possible: ant 'tat the NlST BWR equations are 1he most accurate for R· l34a.**Thcrefo~** the only way 10 remo\le this soW'Ce ofuncertainty from lhe model is toJt:pllce the 

### esD equations ofstate by the NlST BWR equations when simulatinl systems uMl R-l34a.. Similar mon may edst for other pure**re~gem\lS .**  Note that this error ICnCls nO( 10 be nndomJ)' distributed aboula mean, but introduces I clear bias in the positive direction. The direction may be**di!f~t** for Olher**~frigerants .**  The inac:cUt1cy ofelle lalenl emhalpy dati for R-l34a will propapte

### throuah the ERA modal 10 affect its csamates ofannual enellY use almost propontofl.l.lely. 'Iblt is. a 1**~** error in latententhalpy at the evapcnlOr temperature will cause ERA to aller the run lime and hence the eftCO' use 

## bY an equal amounL 

### There will be some second-orderelTects in the compressor model and due 10the way in wbich ERA handles cYcling losses, bulthese are probably insiinificant compared ro the 1**~** enorin annual cntr'JY use that could result from inlccuracies in lhe 

### popeny data at the evaponlinl 1CmpCtUUre. Similarly, a**4~** enor i n latent enthalpy at thecondensin& temperaNre will alter the 4T al the condenser (and thererore the EER) 

### as the medel holds the user-specified values ofUA and**~bcooling** COnSWlt.**Addi~naJ** errors will be introduced when ERA is used 10 simuJaIC mixtures ofrdrileranu. The intenCtion coefficientJ in the NlST property roulines are intended 10 account for such fa<:tot'S as ZCCItI'q)ic behavior. No quantitative analysis of the associated unccnainty 

### c:ou.ld be conducted. however, beauseofa lack ofdata on.Jlte uncenainty ofthe intcnction oocfflCienlS lhemsdves,

# and on latent enthalpy and Olher key properties oflhe**mri&~nts** most likd)' 10 be used in mixtures for rd"ri&tnlor-freezers.

, Feruample II.condensin. Itmpctatl1te of tlO"F ahe CSD eqloll1ions' ....**I~** lot IMetU. e:nthllp), is Ibouc

# ."larJet Iban the vthole ,iYeJI by

### u.e Mlnin·HCKI equationsol Slate. At an enpoBliD,temperaa.we 01 -2O"F

### u.e cm:II' is., 8 

### alternative •• friqeraDta aD4**~izture.** The characterization 

### ot the NIST-developed CSD equation of state as o.ing "relatively crude"**~s** unfortunate. Although the required coefficient. can be estiaated on the basi. of "m1nimal experi.ental data", · tbere i8 no reason to believe that this was the ca... The sa•• level of .xperim.ntal underpinning for the coefficients is available for the CSD equation of state as for any other, inherently .ore para.eter-intensive equation ot . state. As shown in the NIST REFPROP docuaentation, a very large number of experimental data values were used to establish the coefficients. ERA relied exclusively on the CSD equation of .tate (EoS) for .everal reasons: 1) the same EoS would be applied to all refrigerants and refrigerant blends, 2) an extensive analytical and experimental effort vas underway at NIST and elsewhere to retine the CSD EoS in support of the on-going assessment of the potential for alternative refrigerants, and 3) there was no apparent need to increase the complexity of the model by . utilizing more than one EoS. Considerable discussion is afforded in the report to "errors" in certain property predictions of R-13.a. However, no quantitative attempt is made to put the uncertainties associated with property predictions in perspective : The report raises the issue of an error of ., in the calculated latent heat of R-l34a at condensing conditions. To explore the consequences of such an error, an analysis has been carried out (using "ultiple Pathways run 0 1993) where the calculated latent heat was artificially reduced by.'. 

### The calculated etfect on annual energy consuaption was only D•• ' (3 kWh/year). Some very careful experimental studies have been concluded at ORNL to determine the energy consu.ption 

### ot refrigerator/freezers using various**refrigerant8 ~**  The 

### ERA predictions for energy-use difterences associated with R-134a and R152a (compared to R-12) are all within the. range 

### ot energy differences reported by ORNL.The ERA model's ability lolkaJ with IlUeu\llliye**rcrfi8efa/ll~** lind lllilllme5 is rurther limited hy inadequacies in the compressor models (see below). Re,liable results can probably only be based on maps ofcompressor calorimeter da" oblained with Ihe rerri,e"nt or blend in question. Lorenz cycle Efforts &0 oondIJClan uncenainty analysis or the Lorenz cyde reature or the ERA model belan with a simple allempt 10 compare model resulls lO the resulu or I Ie.St conducted by one manuracturer usin,l .mL.rure 0(**6S~** R22 and**3S~** R 141 b. The enerIY savinas e.stirnated by ERA wm: discarded as not credible because the program prcdk:ted tempc"turt ,!ides or**o~y O.~C**  and 

## l.re (or the condenser and evaporalor. respective)y. These differed lTutly ITom.lhe a1ides oC30oC and 37°C predicted by the REFPROP pro"..m from NIST. The Task Force member conductinl**t~e** analysis reponed thll the Itsuhs did change when the intCflcdon coefficient Crom REFPROP WIS entered inlo the ERA program. A second**Ipp~nl** error in the ERA program WIS discovered when cxaminin, the d(cci or heat c:xchanacr aeomc:try. To fully exploil the lhennodyn.mic benefits cI 

### me Lotcnzcyclc,a C:OUntc:rf1ow heat exchlnger is: rcquim:l. HOft¥trdue 10 the difficullY.or tchieving th(s 1011 in pncdce given &he**pee:klgin~** conSlnIinu in rcCriacIIIOf/frccl(:rs. an .ttempl w.s made tocompaR ERA's e5rimales of IIIC performance or crossrJow.nd counterflow desians. The slanin, poinl was input file 86_0SLRZ..ERA which was used by USEPA (1992) in its "multiple palhways" report on superefficient**~fri'Ullon,** Strangely. thai inpul file specified crossnow ralher than counlernow hcat·exehan,cn. When the inputs wm: chlnced 10 counterflow and lhe prolT&m re·run, the resultin. esrimlte orenern use was identic:01I. BOlh oC these findinas Indlclle the prtsence ofII lust one serious enor In Ihe ERA prolJam. or al. minimum I serious problem with the user interface that would allow ellpcrienc:ed desiJllCf 10 mike dill inpuc errors Ihac would**le~** 10 such enoncoos results. The error{s) In the propwn milhl concelYlbly have I common cluse. because In lhe absence of. lemperature elide one would expccl to sec no sicnificani difference between the pcrformanc:c oCcrounow and counlerflow .eomcrries lllhe . specified desisn condidon (minimal superheat or sub!:oolinS). Becluse or these problems with ERA's ability to properly model the behavior of milllures and lhe effect ofcounterflow helt exchll1'u ,eomelries. the unctnaint)' In.lysis wu terminated II this point.**The~** is also cause Cor

### concern about approximations made by ADL in calculatin, lhc dTecliveness of heal ellchangers in the Lorenz cycle. 'The equalion CorerCectiveness depends ailicall)' on the ratio or heal capacities (prodUCl ofm.ss now and specific heal) oC**~hc:rt.rri&eranl** arid air strelmst ERA 9 Lorena Cyole R-22+R-J4Jb Hlxture. The'report authors are correct in their assessment of the inability of the reviewed .odel to handle this mixture .. This circu•• tance resulted frOM an incorrect typing of one of the CSD coefficients for R-14Ib. This haa now been corrected. The problen was with an incorrect digit in the program, rather than with the inherent accuracy of the CSD equation of state used to calculate the properties of the mixture or with the model approach. Heat Exchangor Goometry. The report discusses an apparent error in ERA's treatment of heat exchangers. There are a great many diffiCUlties with the report in this area:

- The report states that the**~odel predict~d**  the sftme

energy use for both counter- and crosa-flow heat exchangers for input file B6 OSLRZ.ERA**us~d** in the draft Hultiple pathways analyeis. -PhysJcs**dem~nds** that the syste. performance be largely insensitlvp. to the type of heat eXChanger [or the particular situation exaMJned.**8eCftUA~** of n high air flow aeroao tho hent eXchanger, the air tPlIlperature chnnq8 was only 2'·C. Froll the viewpoint of the reCriqerant,' the air-aide of the heat exchanger would look like an infinite heat source. thereby elimlnatinq any possibility for diffetences 1n heat transfer relatinq to qeo.etty (neglectinq other realworld effects such as poor M1xing, and pressure drops). For Hultiple pathways case 86 06LRZ.ERA a SMall gain in efficiency occurs with a countet-flow evaporatot, even with the high air flow rate: however, this qain is**l~rgely** offset during that portion or the cycle when the refrlgflrftnt Is dlrpctert throuqh tho frEO'"7.er to nchiev.. temperature conttol.

- A "cause Cor concern" is raised in the rei rt relative to the

Modells treat.ent of heat exchanger effecl.veness calculations. The overall discussion revolves about the change in heat capacity ratio of the heat**e~ch"nqlng** streams alonq the heat eXchanger. where the reviewer staten that ERA uses the averag_ specific heat for the**refrlq~rant,** calculated fro. refriqer"nt inlet and outlet enthalpies and te.peratures. This Is exactly what ERA doe. not dol Because the refrigerant properties do chang_ throuqhout the heat transfer process, the heat exchanqer**i~** subdivided into a lIi,nillu. oC three .reqions: superheat, two-pha8e, and liquid. l"he ERA moders ability It) ticAl willllllteltuU;ve rcrri,C.rIIlLJ Mel ..,i. lt!u,e,t; is runha li mited hy inadequacies in the COI'1lpt'CSSOf models (see bdow). Reliable: rWJlucan probably only be: bl.scd O'n maps 01 compressor calorimeter dal' obt.ined with the rt.fri&erlnt or blend in question . Lortn:r. (yclt Erroru 10 conduct an uncenainlY anllysil orthe Lorenz. cycle rCll\u'e or the ERA model beaan with a li

mple. anempt 10compvemockIltSults &0 the ltSuhs O'r a lest eond...acd by one manllrKtlftl' IIsin& a

.mixture**oI65~** 1U2 and**3S~** R141 b. The ene:rIY uvin,s estlnwed by ERA**~** discarded U nGI credible because the proJBfTI predk:ted temper1.ture Iiides ofO'nly 

## o , rcand 

## I .rc(orthe: condenser and evaporator, respectively. Thesc differed &Tully rrom.the l!ides or30°C and 370C predicled by the REFPROP proanm from NIST. The Task Force member oonductin&**I~e** analYJIJ**~poncd** thll the RSllhs did**~** chance when the-Intenclion coefficient rrom REFPROP WII entend InlO' the ERA prO'gram. A second 'ppmnl error in the ERA pro&Tam was discovc.rcd when cuminin& the effce' ofhea' e.chan," ,comeny. To lully exploit the Ihc:nnodynamic: benefits d the.**Lon:n~cyd~** a oounttrllow hUlu,chinler 

### ts lUluircd. Howevtrdut 10 the: difficullY.ofachicYin& thi. s ,Oil in pncticc &iYen the pacb&in& conscralnll in rt.lriacrltor/rruz.crs. an IlIcmpl was made. to' comparc ERA', estimates orthe**pc.rf~** 0(crossflO'w.nd counterflow desians. The. slanini poinl WlS input me 86_0SLRZ.ERA which was used by USEPA (1992) in its "mufliple palhw.ys" Rpor1 on JuperefflCienl rWi,eRTOf'I. Su.nSCly. thai input file specified aonnow ralher tllan counterflow hUI'exchan,c:n. When the inputs were ch.nled 10 counlerflow and the proaram re-run. the resuldn, esrimalc: orener.,. Ute was 

# _bc:II. Both ofthese findln&! Indlcate.lhc presence orll leasl one: seriOIlJ cnor In the ERA propam, or at. minimum a serious problem wllh the. user inlerface thai would .1I0w upericnced desicnct 10 make data input enon Ihll would lea,d 10 such erroneous results. The. erroril) In the propvnml&ht conceivably have a common c.use, bec'lIscln lhe abscnce O'r I Icmpetarure ,Iide one would eXpClCllo see no si,nific'nI dirrert.nce between the pcrfonnance orcl'Ounow.nd countc.rllow ,eomctrie.S lllhe specified desia" condition (minim.1 supelMII or subtoolinl). Bec.use or lhese problems with ERA'J .bililY10' properly modellhe behavtoror milillUteS 1M lhe dTcct ofcounterflow hell exchancu ,eomttries,lhe IInctnainlY tnllY1ls was laminlled II this point. 1'1lere Is also cause (otconcem aboU1**.ppro~lmllions ~**  by ADL In Clkilialin, the effectiveness of heat exchineen in the**l.ortn~** (),de. Tbe equalion f oreffeccivc:ocst depends citially on Ihe rlrio or heal apacilies (product ormass now .nd specific heat) ofthc..'ferrlcertni anCi air Streams, ERA 9 Loren. Croie R-22+R-l'lb HiKture . The ' report authors are correct in their aaaess_ent of the inability O'f the reviewed _O'de1 to handle this mJxture. Thi. circu••tance re.ulted fro. an incO'rrect typing of one of the CSD coefficient. for R-14tb . This haa nO'w been corrected. The proble. was with an incorrect digit in the progra_, rather than with the inherent accuracy of the CSD equation of state used to calculate the properties of the mixture or with the Model approach. Heat Exchangor Coomotry. The repO'rt dIacu8s8M an apparent error in ERAI. treatMent of heat exchangers. There are a great many difficulties with the report in thi8 area:

- The report atates that the**~odel predict~**  the 8ame

energy use for both counter- and cross- f10w heat exchangera for input file 86 OSLAZ.ERA u8pd in the dratt Hulttple pathway. analysis.
- rhysJcs**dem~nris** that the syste_**perlor~ance** be largeJy**insen$ltlv~** to the type of heat eXChanger (or the p4. rtlcular .Jtuation eKa.Ined. 8ecl'l. u". or III high air f low across t.ho hOl'llt exchanger, the air tplilperature change vaa only 2 "C. Fro. the vlevpoint of the retrigerant. the eir-side of the heat exchanger would look lik_ an infinite heat sourc., thereby eli_inating any po.sibility for ditferences in heat transfer relati"9 to geo••try (neqlectlnq other reolworld eftects such as poor**~ixi ng** **,** and pr.s.ure drops). For Multiple pathway. case 86 06LRZ.ERA a ••all gain in efficiency occurs with a counter-flow evaporator, even with the high air flow rate; however, this gain i.**l~rgely** offset during that portion or thA eyclp when tha**re(rlger~nt** I. dirpcterl throuqh**th~** rrpP7.er to IIIchlev.**te~perature** control.

- A "cause for concern" is raised in the rOI rt. relatIve to the

modell.**treat~ont** of heat exchanger etCecl.veness calculations. The overall discus.ion revolvea about t.he change in heat capacity ratio 

### at the heat exchftnging streams along the heat exchanger, where the reviewer staten that ERA U8es the average .peclfio heat for the**refrt~prant,** calculated tro. refriqerl'lnt inlet ftnd outlet enthalpies and teMperatures. This Is exactly what BRA does not dol Becau•• the retrigerant properties dO' change throughout the heat**tran~fer** process, the heat exchanger**i~** subdivided into a .ini_u. oC three reqions: superheat,**two-pha~e,** and liquid .c:UcuJalCS: dlis nOo usin. an**lIl'r'41~** specmC hut wh'ch it dc1ctmi.nes frotn**refri~ClMt** inlca and oudet enthaIpies and lcmper1luteS. However the acwaI value

### ol&h~)pcdrlC heM CIIIl 

### Vvy by as much as I (aaorolseven or more 

### ttvou,tt &he heal uch&nau (Conidia and Vineyard. 1992), dcpcndin. on 1hc refriaa-**milll~** sdectcd. This in M'n lITecu the nrio 01 heat CIpICities by &he IIdIC (ICW. I(JI!e dfec::tiYcness ofthe heat c:xchanacr is amaIl, this error in Ihe rMio 01 hell c:apKWe& wiU hive oN)' I

_ eIf""",,1hc**~1Oll** 

## _aossIlow IIId _taflow daips. On .... __ it .... elfc<O...... is 1-.1lIbstonliII ann may be inlrOll_ .... --.or.....now IIId 

## _,.....,nes.**OIhcr~yin,,,,u"'9'ions** made in .... ERA modd 

### wi abo

_ 

# -.1 ......... or cncrI)' .....p lCiliev.ble lhrouahlhc LoRu cycle. They _Id,,"ifiod ill .... U

_ (ADL, 1992); Ihcy ... nOlldcnlSodiAdtIIil

__lelhc _oncylllOlysil

__ UIO catlicr N&e few the rusons stated above. For exampk. &he heal ll'InIfer carrdaOons UICld 10 Cllculaee condUlCW'a wert a'i.U.IU)' determined for 

### pure OWds. and ahoWd not be UMld (or RfriJUMI mixuu bc:cIUIC 

### they ue known lObc:havc VU"J dilferuaJ)'. FiNIIy Ihc ERA pro...... Ulna .... 

### ,..pr deli .. prollkm 

### "oed'M willi LoRu cyc:Ic I<fri....... - cabinet kmpenl\lrt: 

### conm. UCVlponlOf 

### uas arc apcimizcd for I 

### pII1icuIar desip openriAa condilion. companmenllrmpcn.lUiU cou'd noellC) (c:oId) kvell dw would Wille eftCI'I)' 01 (w-m) levels thI1 would spoil food, depe.rv:tin. on climale and door-opc.ttin. condiDoni experienced under aclUaI

# _in. coadilionL 8o<h**orERA'~** ' ....... ""lions, iAvoIviJw Ihc dilCharae or

_ '"' 10 &be &all food axnput.mcnt or b)"pUlinl pan ollhe cvapc:nItM 

### area. would wuc

## cncru rdaIi.e 10 Ihe aominal condition II which she evlponlOn wen: desipcd 10 opcnIC. Varlablt·.pttd comprtuOri RCtOaM devdopmenu in c:lecaic moIOI' IedmoIop ha't'C CIUICd b: opponr.anicy (CIt _. VIriab&ospeed drives on eomprr.uan as wcllu &he (ans that move air ova' heal**exc~acn.** A vuilble-speed compmsar could eliminale eyelin, k»ucl, rnck toIds indUOCld by IaII&C plueml and 

### c1imItc. and inc:ra.se opcnanC cmciency by R:ducin. c:ondt, ...n.le:rI1flCRbUU and Iftaasinl cvapc:nIift. 1CmpUIIl,ftS. Thai is one ruson fot dtvc!opinllh: capabilll)' (or modcIin'lUdI equipmraL . A ICClOnd 

### reason K dcvdopin. benet WI),S of mcdclina 

### coo.+ Sian is 10 be able 10 pndiet I!iWA 

### coo.+UiC.I"s pa10rmancc with 

### alurnative rclrilcnntl. Sinoc canpraIOt map equatigu 

### are boch COli4Awoc, and rdripanl·SpcciftC.1he ERA model indudc:I**rwoCMher~lOI"moddL** 80ch RIQUiR; Ihe YSCI' 10 inpul such ph)'wl patllY'Clc:n u displlcemtnl volume and Ipecd (rpm), which arc acedcd 10 

### Fftdict how. panicuw compressot will pa(onn with. vlrilbSc-spc:c:d drive. 

### c:w wich an &hemItiYe rdri.cnnl havin. I differenl specifIC YOIume and other Ihennod)'namic propc:nia. 10 Single node.**~ro** u.ed in the vapor and liquid region., where the refrigerant .pecific heata are ••••ntially constant. Across the two-pha.e r.gion,. the r.trigerant-aide h.at transfer coeftici.nt do.inat•• the ov.rall h.at .xchange; hence, an averag_ apecitic h.at can be reasonably applied in the two-pha.e region by utilizing only on. nod.. Howev.r, the user is given tbe opportunity to u•• an unli.it.d nuaber at subdivi.ion. in the tvo-pha•• region to deal vith th. effect. at changing properti... The heat exchanger etf.ctivene•• concept i. Uled a. part of the .n.rgy balance across .ach individual node,**~here** the properties can be reasonably conaidered aa conatant, rather than across the entire heat exchanger a. appar.ntly under.tood by the reviever. The author ot ERA has found that calculations pertor.ed with only one node specitied tor the tvo-pha•• region ot the heat exchanger. generally yield nearly identical result. to those obtained**~hen** three or acre n04e. are apecifi.d. Selection of the level of preci.ion in this psrt ot,the calculation i. lett to the proqraa u.er, although the detault .election is one node 1n the tvo-pha.e region. Heat Transrer Correlatlon.. A**~riet** co..ent i. aade in the report about the adequacy of heat transter correlationa uaed tor aixed refrigeranta. In aoat inatance., the heat transter r.sistance ia dosinated by the air-side, especially in the twophase region Where the aixture heat transfer correlations are least certain. The uncertainties ari •• , at lea.t partially, trom composition non-equilibriua ettecta betveen the liquid and gas along the retrigerant path length vhere complicat.d vapor slip conditions .ay occur in the evaporator, end where the effects of "non-condensible.- aay degrade the retrigerant-side condensing heat transter. aecause the refrigerant-.ide h.at tranat.r rates are high relative to the air-.ide, even in the pre.enc. of degradation. due to non-equilibriu. eftect., the net ettect on overall heat exchanger ettectiveneaa i. nor.ally ••all. The effect. ot an uncertainty in the tvo-pha.e heat transfer correlationa have been explored tor a .ixture ot 20\ R-22
- 50' R-152a
- 30\ R-123 (ca.e A8 05LRZ.ERA). A.su.ing that the calculated evaporating heat-tran.ter coefticient i. 10o, too high incre••ea the calculated energy conluaption by 2.5\ (ll kWh/year). Si.ilarly, esauaing that the calculated condensing coefficient i. 100' too high incr••••• the calculated energy consuaption by l' (5 kWh/year). Cablnet re.perature Control. The diacu•• ion in the Accuracy Analyaia liaita ERA'. control concepta to tvo ecenarios which would presua.bly vaate energy. It ia in tact true that non-ideal performance will be obtained for otf-delign operating conditions_ The**.od~l.doe.** indeed atte.pt to deal with the effecta of 011- design operation by the varioua .control- option., rather than ·skirting the issue.- One ot the options involve. te.perature float. For exaaple, it no atte.pt were .ade to provide active control, the .odel vill eBti.ate the resultant chang_ in cabinet teaperature. Hence, the aodel i. in fact not ba.ed on the calculaaes W5faOo usin, an lIlIU4It. 

### 5pCdrw: hw which it**~5** from**rdri~** Wd and OIoIdec ctaCbaJpie:s and &cmpUI1W'CS. However lhe KCUII value 01dliI1pcc:if1it hc.u CoM 

### Vt"y by as much IS a

_ cl ......or mon: ohroup doe hC&ICAdlanau (ConIdia ud VioqIrd. 1992).

# *J>endIn,'"' doe rdriJCIMC mixture sdec:cc:d. This ia IUm affects &he ...Iio01 heal. c:apKilia by 1M same Caca. 1(Jhc: dfcaivcness ofthe hwcuNnI"Is.unall. this emv.the nIIio 01 ht.aI: capIICiIia; will hi...onI, I ....udr ..... doe-...;...beIwcaIa1>5SIIowud_........ Oodoo __ifdoc drcai_is Iarp. subsWllial emn may be Inroducod inoo __cl

## "'!"'I- ud

_ ....o ...

ks. Oobcr simpliCyin,assuml'lions mooIe 1ft doe ERA 

### model will also iIoa-ooIo.cc _I ............ claaJ)' savinp ochicv.bIc oIvooop doe L-oreo& <)'Cle. They _1IIeo1ilicod 10 ....V...._ (ADL. 1992); doey an: "'_lacltlallha< _ ..doeacc:onoy .... ysUwu_u .. earlier IUIC ror the reasons stllCd aboYe. For cXlmpk. 1:he heal transrer carrdadonl UICId to Qkulue oondUCIMCC 

### were ori,inaUy dclermined ror pure Oulda. and IhoWd notbe UICId ror n:trl,ennt aUbIrU bccIUIC lhc)' R known 10 behave vuy differently. Finally doe ERA 

# pro...,.. skins doe -.jorlltsian problem "rei'*, willo L-oreo&O)dc

# ..rrI.......-- cabinet tempcnNftconaol. IfCYlporMOr ftU _ opcimized ror I p.nicul.- cksip opauiAa condilion. cocnp&nmcnl tcmpmNl'tS**~Id** noalta (eoId) IeveII dw would WIlle

### cnc:rv or (WInn) 

# _Is..... _Id spoil (ood. dcpendlft, ...**<~ma**..ond doot..... 'CIOIIdiIions uperiaoood _

......opcr1IinaClOlldioionL 80010 clERA",'conllOl'

### o9Iioos. 

## iovoMna Ihe diJdoItp cl,.,...,.

### W10 &be fRsb fco1 c:ompuuntnl 01 bypusin, pan cllbcCyapcrum- lIP.would Willi. --0rdMive 10

_ QOftnaI condidon .. which aM CVlpotllOn**~** de5i"" to opcrI& Variable-lIMed comprHlOrt RCCCDl ciadopmcMS in dccG'it moIOf'tcchnoIol)' have: cra&cd Ihc**~** 

## ror

# uain. variablespc:cd driva on compteuon as Mil u Ihc rlll5 mat move air CMr heal CKtupn. A vuiablc-&pced c:ompra.sor CI:Mdd eliminatc t)'Ciinllosscl. InCk toIdl induood by 

### u.uae putcml lAd dirNJe. lAd inc:ft:uc opcncinl dflCicncy by tt.eNtin, c:ondcloam, IenlfCI'IIWU and lnaasin,cvaponQn,

_ ..... Thoois """ ....... (a< dcYClopin,oll: oapobiIloy (a< .-ainl_equlpmeaL . A ICCOnd 

### rcuon I devdopin, benet WI,I 01 moddinc**~** is to be 

## .we 110 predia a aivea

............ SpalOnnanco wido ........."'rcfri........ 

### s;,..,. __**~** 

### ... boch

............ ond .... riaenno·spccUoc. doe ERA 

### model indooda __.........""modcIL Bodo ftqIIio< ..........

# OJ"""" such pIIysi<a1 .,.,.,...0...as**di~** ....... ond Jpood (rpml. _ .. ac:cdcd 10 pmd-':' bow a puUcular compR:UOf' will pcdonn wi&b avllrilWc·spc:ed dri.... or wilt. 1ft ahcmaIivc rdriaawn hiyin,adiffCftNI spociriC: volume and ocher Ihamodynamic: popc:n:ia. 10 Single node. iro u.ed in the**vapo~** and 11quid reglon.,**wh.~.** the refrigerant .peclfic haat. are ••••ntially conat.nt. Acroe. th. tvo-ph••e region, . the retriger.nt-aid. heat**t~ansfer** coettici.nt do.in.tea the overall heat e.change; hence, an averag•• pecitic he.t can be rea.on.bly applied in the two-pha.. region by utllizing only one 

### nod.. Howev.r. the user i. glvan the opportunity to u•• 

### an unli.lta4 nuaber of subdivi.ion. in the tvo-ph••e**r~lon** to deal with the ettecta ot changing propertie.. Th. h.at exchanger .tf.ct. iven... concept i. uaed a. part 

### at the .n.rgy balanc. acros. each ind1vidual nod., vhere the properti•• can be reaaonably con.idered a. conatant, rath.r than**ac~oa.** the entire he.t eXChanger aa apparently under.tood by the r.vi.wer. Th.**autho~** of 

### ERA ha. found that calculatlon. perfor.ad with only one node sp.cified tor the tvo-phaa. region of the heat exch.nger. g.nerally y1eld n.arly identical r ••ult. to tho.e obtained vh.n three or .ore nod•• ar. apecifi.d. s.l.ction of the level of preci.ion in this part of the calculation i. lett to the progra. u••r, although the d.fault .el.ction i. one node in the two-pha.e r.gion. Heat Tran.r.r**Cor~elat1on..** A**~riet** co...nt ia .ade in the report about the adequ. cy ot h.at t . ran.t.r correlatlona ua.d tor .ixed refrigerant.. In .o.t in.tance., the h.at transfer re.istance i. do.inat.d by the air-aide, e.pecially in the twophase region vher. the aixtur. h.at tranat.r**cor~.lations a~e**  least certain. Th. uncertainti•• ari••, at lea.t partially, fro. composition non-aquilibriu. eff.cta betw••n the liquid and gaa alonq the retrig.rant path lenqth where co.plicated vapor slip conditiona .. y occur 1n the .vaporator••nd vh.r. the .tfects of "non-cond.n.ibl.a- .. y degr.de the refrigerant-aid. conden.inq heat transt.r. Becau•• the r.frig.r.nt-aid. h.at tran.t.r rates are high r.lativ. to the air-.ide , ev.n in the pre••nce of degradation. due to non-equilibriu. etfecta, the n.t .tt.ct on overall heat .xchang.r etf.ctiv.n ••a i. noraally •• all. The etfect. of an unc.rtainty in the tvo-phaae heat transf.r correlationa have be.n**explo~.d** tor a**.1xtu~.** 

### ot 20' R-22
- 50' R-152a
- lOt R-12l (ca•• A8 05LRZ.IRA,. A.su.lnq that the calculated .vaporating h.at-tran.f.r coeffici.nt i_ 10o, too high incre••e. the calculatad energy con.u.ption by 2.5' (11 kWh/year). Si.ilarly, .aau.ing that the calculated cond.nsing coefficient i_ 10o, too high incr••••• the calculated energy conau.ption by 

### l' (5 kWh/y .. r,. Cabinet Te.parature COntrol. The diacua.ion in the A ccuracy Analysis li.ita 

### ERA'. control conc.pt. to two .cenarioa which would presuaably vaate**.ne~gy.** It i. in fact true that non-idea) pertor_ance viiI be obtained for otf-d ••ign operating conditions . The .od . el do•• ind.ed att••pt to deal with the .ffecta of of(- design operation by the various -control- optiona, rather than -skirting the i ••u•• - One of the optiona involv•• t •• perature float. For .xa.ple, If no att•• pt vera .ade to provide active control, the .odel will eati.at. the re.ultant change in cabinet temperatura. Hence, the .odel i. in fact not baa.d on theCompressor raJing poitllmot:kJ The nling poim model requiru 1he user to input the**~R** only &l: a single rating point, and then proceeds 10 calculaic its performance throuJ.h!:tut lhe 'map' Rngc or. CYl.pcntinllnd condcnsinl preSSUfcS. However these alculations are baSed on cmpirieal com:lations obtained for compressors using R·I2. Since the slopes ofthe" c:ompusor performance maps vl!Y.. significantly fordiffcrent refrigcaal'lls. one would not expect the ERA ratin, point modd 10 yield accuralc ruults for anything bul R·l2. One Task Force member simulalCd IWO refri,trIJOIS using an ICN&1 c:omprusor map obtained with R-l34a. and rqated the limuIations usinl the ERA nting point modd. Thc energy requirements predicted by the rating poinl model**~.5'5** and S*' lower Ihan those predicted using the map-based modeJ. II is**~ffieulllO** dnw acenmliud c:onclusion from this limited infoonation. However it is clear that Ibis data, shown in the IIbJe below. provides no evidence that the rating point**mode~** is as IlXUnte IS mort. widely cc:eptcd map-based models. 

### • RunJime**vpmu:I.~'ly ~=><**  En...v 

# .. B,uII> Top_Mounl 19 Cu. Fl. !Compressor 1.0 ".0 6<il 4.7, 

### mao incthocl 

## ,lUbJla pom' U.Y" 

# ,

# ... 0" '.IZ model**~~.~:oY::"··** 21 Cu. Fl. I Compressor 1.0 '9.' 

# oz. 

# ,.u, maD 

## melhod :Rattng potnt 0.9Z0 '1.0 77. '>.43·, model Comprusorphysical model ADL's documentation ofthe t::ompR.SSOr physical model was**~viewed** by Task Force memberS who design compressors. in anticipation ofc:ondlKtins a detailed accuracy analysis. The ERA model requires the user to specify. among other paruneters. an "isenlrOpic compression cfF'lciency" which appears 10**~rer** to a pamnete:r kno'Nn**j~** the indusay as "pUlOn work isentropic compression efficiency". This puamtter·cquaJs the mndard "isentrOPic compressor efficiency" defined in Ihennodynamics (txU, modified fo! motor losses and friction and windage 

### losSes. In addition, the ERA model demands thil the user specify input paramet.en Ihat differ from the slltldard pantnCleJ'S familiar to designers (Col. motor-pump etrM:icncy. can Joss as pm:ent ofpower; discharBe line loss). Because ofthe induSO')"s unfamiliarity with these puameta'S and resullant lack ofreliable dati. Task Force mcmben concluded that dle uncenainry on Ihesc inpul 

### parameters would inaoduoc an inlOleRbie amount

## orenor into the ERA simulation. They SUUested that a D'I(R accurate



### . 

# - . approach would be 10 simply specify the standard "isentropic compres$Ofefficiency" as the input pamnc:ter that would be used 10 calculate the power required. pr••ise that the**~renz** cycle, or the .ore general two-evaporator cycl., will behave in an ideal manner. It is precisely for this r.ason that a number of candidats "control" options (including no contrOl) are offered for exploration by the user. Variable 8p.ed coapr•••ora (page 10) The authors of this docuaent agree with the general statements made 1n this area of the report. In particular, a compressor map should utilized whenever available. This is consistent with the philosophy that experi.. ntal data should be utilized to the degre. possible to a••••s the pro.ise of a particular technology. The introduction to this section of the report provided soae very helpful background, useful towards putting the three co_pressor models into perspective. Amplification 

### ot the discussion is given belov for each of the three models. Compressor Rating IIodel (pg 11). The compressor rating model was designed as an intermediate analysis approach between the more data-dependent "physical aodel" and the more directly-applied "aap model" in which. the Task Force members rightfully have the most confidence. It was intended as a means of estimating the behavior of a compressor where only a minimum at performance data are known •. The necessity for such an approach is clear when the potential performance of a significantly new situation is to be estimated. For example, if no daea exist tor a refrigerant blend, and the analyst wishes to explore whether the blend 

### might have 80ae promise, then some means must be available to estimate how the compressor will behave with the blend. Although correlations.are an important part of the rating-point model. various thermodynamic relationshiV8 also form part of the algoritn.s used. For example, the effect on the net pumping rate of refrigerant ga.·density at the suction port is taken into a-ccount. Developaent of the correlations used in the rating-point model was based on two sets of detailed co.pressor temperature and performance data provided to ADL by AHAM for R-12 refrigerant. Data of the same nature and quality were not available to us for other retrigerants. Compressor Physical Hodel. The compressor physical model closely follows the approaches used by MIST and ORNL in their detailed heat pump models. By breaking down the overall efficiency into individual factors rather than looking at the compressor as a "black box," the physical model attempts to allow the analyst to focus on the potential value of a component change. For example, the potential value of a higher efticiency motor on the refrigeration system behavior can be estimated. A back-of-theenvelope**app~oach** may suggest simply comparing the motor efticiencies and then scaling the compressor efficiency (tor example, modifying the map), but this would fail to account for the etfects of motor inefficiency on suction gas heating which the**physica~** model attempts to take into account. Compressor raJing poilllmot:kl The rating poiO[ model requires 1he USU 10 input the**~R** only at 1 single nting point, Ind then proceeds 10 calculaic its performance**throu~ut** lhc 'map' ranee of. evapcnona and condensing**ss ure** **s.** However these c:a1culations are baSed on cmpiric:aI com:lations obWned for c:ompressors usine R · I2. Since the slopes ofthe'c:ompre.ssor performance maps vl!Y. significantly for different reirigtl a rus. one would not expca theERA raona poinl model 10 yield accurate results for anything but R ·l2. One Task Force member simulalCd IWO refrlcc:rators usin g an acN&l compn:ssor mapobWned with R·l34l. and rqaled the simulations usinalhe ERA rating point model. The energy requi rements predicted by the ruin, painl mockl were. 515 and 81JJ lower than those: pn:dic:tcd using the map-based modeJ, II is**~fficu1t** to draw &.encraliudc::oodusion from this limited information, However it is clear that this dlla. shown in the table below, pvvides no evidence thatme min, point**mode~** is as ICalrate IS**~** min, widely KCCpICd map-t.sed models.

Compressorphysical model ADL's documentalion ofthe**~** physical model was**~vlewed** by Task Fon::e memberS who design compressors, in anticipation ofc:ondlKtin, a dc:LaiIcd accurac:y analysis, The E.RA model requires the user to specify. amonl other parameters. an "isernropic compression effi ciency" which appears 10 refer to 1 pan.metc:r known**j~** the indusay as -pislOn work isentropic compression efficiency". This puameter'cquals the sLandard "isena-opic: COfnJftSSOf efnciency" defined in 1hermodynamics ItltlS, modified**fo~** motor losses and f"riction and wind1le 

### losSes. In addition, the ERA model demands 

### !hi, the user specify input panmc:tcn tIw differ from the standard pamnelers familiar to desianm (e.g, mocor·pump etrM:imc:y. can loss as pm::enl ofpower; clischarJ;e line loss), Because ofthe ioousuy's unfamiliarity wilh the$C parltnQcn and rtsulWIIlKk ofrtllable data.Task Force mcmben concluded that the uncauimy on these input 

### panmetets would 

### inaoo.uoe an inlOleRbIe amoum oferTOI' intothe ERA simulation. They suUested thaI & IIlCR aocw-ate approach would be 10 simply specify the

### s~ "isenaopi;'""compressor effickncy" as &he input

### ~ panmc:ter mat v.ould be used 10 cak:ulile the powu requited. pre. iae that the**~renz** cycle, or the .ore general two-evaporator cycle , will behave in an ideal manner. It is preci••ly for this rea.on that. number of candidate "control" options (including no control) are otfered tor exploration by the user. Variable Speed coapre•• or. (page 10) The authors of this dOCUAent agree with the general atateaeata aade in this area of the report. I . n particular, a co. pressor map should**~** utilized whenever available. This is consistent with the philosophy that experi.. ntal data should be utilized to the degre. possible to a8••• a the pro.ls. of a particular teChnology . The introduction to this section of the report provided soae very helpful background, useful towards putting the three coapressor models into perspective. Amplification of the discussion is given below for each of the three models. Compressor Rating Nodel (pg 11). The co.pressor rating model was designed as an intermediate analyais approach between the more data-dependent ·physical model" and the .ore directly-applied "aap model N 1n which the Task Force members rightfully have the most confidence. It was intended as a aeans of estiaating the behavior of a compressor where only a m inimum of performance data are known. , The neces.ity for such an approach is clear when the potential performance ot a significantly new situation is to be estimated . For example, if no dat-a exis t for a refrigerant blend, and the analyst wishes to explore whether the blend .ight have soae promise , then some means m ust be available to estimate how the compressor will behave with the blend . Althouqh

### ~orr**elations are**  an important part of the rating-point .odel, various thermodynam ic relationshivs also form part of the algoritn.s used. for example, the effect on the net pumpinq rate of**~efrigerant** gas dens ity 

### at the suction port 

### is taken into a'

ccount. Development of the correlations used in the rating-point model was based on two sets of detailed compressor temperature and performance data provided to AOL by AMAH for R-12 refrigerant. Data of the Game nature and quality were not available to us for other refrigerants .**Co ~p** **ressor** Physical Hodel. Th. compressor physical model closely follows the approaches used by MIST and ORHL in their detailed heat pump models . 

### sy breaking down the overall etficiency into individual factors rather than looking at the compressor as a "black box," the physical aodel attempts to allow the analyst to focus on the potential value ot a component change . For exam ple , the potential value ot a higher efficiency motor on the refrigeration system behavior can be estimated. A back-of-theenvelope appr , oach may suggest aimply comparing the motor efficiencies and then scaling the compressor efficiency (for example, .edifying the map), but this would fail to account for the effects of motor inefficiency on suction gas heating which the**phY8ica~** model attempts to take into account.In CClI'I#ISI co power input. the**c:om~uor** man flow ralC is compulCd'ln ERA', "compn:5IOr physical model" iD a nK:h mcnsD'ai.htforwwd manner. II**r~.·diri:aI)'** from Ihc ..,.1pCCificld YlJllClol displK:emcnc. clcuancc volume. rpm and. Ra-lion between YOIlIIDC:II'k and praIIn raIio &hal is bud·wind inca the 

### P'O,ram. This lypCoimodd pllca.motIold'Je burden c:. &be**_tq~_** . supply &he CDmlCC inputs. bullhm are Slill uftCCl'tlinlies about Ihc KaI'IC), of chc votumeuic cffidcnc:y fonnula and iu app1icabilil)' 10 alternaQve rcfriaaws. Tb:'l paIC8 UftCIa1ainry. hoW'CWl'. is lied in&o

.... wrandy complex heotlnllSi« phenomcoa lIlIloccurlNido .... CCll1lp<uarllldl_ ....... ollhcllECionlincandlhcsuaionponoilhet)'lindcrlucll(iDarciproctdn, 5 Ie).**~ERA** model docs not claim 10 be able 10 simulate lOW)' vane 0CIdIpI'aICln.

_ ADL

_ EPA .. publilllcd diu vllidWt, eiohcr ....jI/lyIil:aI_o. ......... paio, 

# _.I.......pIe by.ilemptin' ....prod "" .... _ _ til... C<lI"oditillllS. This Is tIte mlnimalllllOWltofnlidalioll_i1oc1 bcf<n 

### sud>..;.w.eoUId be substit..... for mIpI for c:onswu·speed opuarion with alternadve refriaennq, If IUCh

_ wen avaiJablc, il 

# ali'" be .......bI .....pea tIte 

## ""ysica! and ..... , poin'nakIs ...... 

## _y-" _opcratico II oondilions u'niflcandydilf ....'flom .... lIO'F ambient ....... __ inIec laaperacurcs on which Ihc pcrfcnnancc maps buod. 

### Jiowcva'. before uain. JUdt IIIOdcq, 

### io JII<dics dI. cfI«U tilv_.·speed operatiOll....... 

### sIIooIId be

_ vtdlduion

_ ..... C<lI"oditiOlls -.. tIte ................. heotlnllSier(orid .... doody·..wed ""'"

_ windin,s and friction Ioucs) ma), differ paLl)' from chc ruU·1oed 

### cue. 8a::Iusc ollbesc dcf.cicncics in the tlrin, point and pItJ)'5QI 

### mode1&. &he Talk FoR:c maDbc:n uYC DO confidence in !hem. In the .bsence fA Udllin' data it is ftICIOIDDenlSed lhIa nciIhc:r model be uet 10 

### ptocIicI tIte JIOW". 

### nws 

## now u. IlIOCtioo 

### tII

__ prapenIea .. __ op«d In tile meantirot UmulstiOllS in,olvln, alla1IIlI .. mri o. variabIe.speed_ OlIIh' .. be bued 011 .... ""'p'bued model usin, dw

_ I spcc:ific mri,ClW (.. blond) ..

.... pan;eu1ar ....ti_ speed bein, simuls..... . Rtdudnc e)'dln. losstS C)clin,losscs ...... ""'.... by die EP.A model u ...... of slmlll.tioo. ""- tile model ia sa OP" xnalyu only one conKlVotioo .-... almed.t rocI 

# sucll_, • chocl: valve 1IlIl_ IftVCN &he Rfri,cnnllrom mipatin, 10 chc cvapcnlOtdurinc 1M cft'-qdc.7 OlberapproachcllO 

# _in, with cycJin,losses 

### (c." rocIucin, tile _,.)...- be

# simu_ by EllA. 11tc ERA model slmlll".s stellly·

__ II

_ 

### daian conditioos. ., then

_ widt cycJin,losses by .pplyin, tiOll IIC......... by ADL (1m) """' ...port by J.....n cL aI. (1990). Iflhc: COtI'CCtion f-etor formulae wcrcc:ridibtc. it would makc sense 10 uaminc the acnsiti...it)' 7 0..01' 1"0 _va**~Id** be depcAdifti 011 'IWtIetJw. ee.paaor b."*'YOI'**nc~** 1rpe. 12 Several ••jur probl •••**wi~h** the physical .04el are well known: 1) the .hell 10•• i. not directly calculated, but i. expre••ed aa a function of the work input, and 2) the .odel has no applicability to rotary co.pre••or.. 

### An additional probl •• with the phy.ical .odel ie the larg. nuaber of input. required, .any of which .ay not be well known. Hovever, for tho.e eituation. where the alternate .odel ••ay not be u•• ful, the phy.ical aodel can be uaed in conjunction with the rating-point .odel. Por exa.ple, the rating-point**~.l** will output ••ti .. t.d value. required •• input. to the phy.ical .od.l (pi.ton work i.entropic efficiency, .otor 10•• , .h.ll 10•• , cl.arance volu-e, etc). If the•• values are enter.d into the phy.ical aod.l, 'the .... ey.t•• etficiency will be calculat.d. Than the affecte of i.prov.d .otors or ditferent rotational .p••d. can be e.ti_ated. It the .otor etticiency i. known to decr.a•• with decre•• ing .peed, this effect can be directly .pacified. A reco ... ndation i ••ade in the r.port '(page 11) that the phy.ical .odal be replac.d by a .i.pla overall ".tandard isentropic coapr•••or .ttici.ncy.N Thi. would •••• to be a major step backward•• ince it could not deal with the ettects 

### ot suction ga. teaperatur. on puaping rat. or with the potential impacta 

### ot i.prov.d coapr••aor co.ponents. E ••• ntially all compresBor .adaiB publiahed in the pa.t 10 to 20 years have atteapted to ba.a the calculations on conditions at the suction port rather than on conditions at the entrance to the co.pressor can. Rel.tJonsh1p or the Thr••**~od.Js.** A.**~t.ted** earlier, the authors are in agr.... nt with the con.en.ua that tha co.pressor map aodel is to be .trongly pr.t.rred, where _uch .ap data are available. However,**th~r.** ViII be .any in.tance. wh.r. aap data. are not known. In this in.tance, tha analysts can: 1) request that a co_pres.or aap 

### be obtained for the refrigerant and operating condition. 

### ot int.r••t, or 2) u.e a aethad that provides a reasonable approxi.ation 

### ot the behavior of the COmpressor in the particular situation, or J) do nothing. It would seem useful to do initial studi •• using available approxi ••tion tools, and then it the situation looks inter.sting, follow up with tests. Reduoing Cyoling LO•••• The authors agree with the Ta.k Force'. general findings that the correction factor 

### tor cycling behavior has a very alia experimental basi. indeed. Given that a broad.r**expe~i.ental** data ba.e i. now available, the analyai. could, in principle, be**stren9th~n.d.** Several point. rai.ed in the revi.w d••erve additional clarification. ERA does not att••pt to account for cycling 109ses as part 

### ot .ach .iaulation. This i. a user option. If the model i. used •• a tool tor looking at the eftecta of cha.nges in certain para••tera, the an.lysia can assu•• steady atate operation for both .ituation. of inter.at: it the sa .. analyses are carried out uaing the cycling los.es, the ditterence between the estimated energies associated with the two**desi~ns** will be essentially the sa.e as**calc~lated** a.su.ing staady state In c:onuasllO power input, the

## c:ompteSSO'r rna" flow ra'e is compulCd 'Jn ERA', "COfnpRAOt physical modd" ill I**~** moftllni.htfOfWU'd fPIMC:I'. II**r~. diRaly**  ftun che Yrcr. 1pCIC:ifiod YlJucso( disp' 

### "'c:nc. clc:uanec volume. 'Pm and I rt:"tion between YOIumeait:**~** Ind praIUR,rado &bar iI bud·wind inca the PfOJI"Itn. This Iypeolmodd pllca.mottO(&he burden on &he '*I'lQ_ . supply !:he CCJmlCI inputs. bullhere: _1Ii1l uhOClUindc:a lbout &he.:cuney 0I1hc voiumc:uic cfficienc:)' !emula 1M iu appticlbility 10 aJtemldve rt:friJCfMU. Tb:'I paIC8 unca,.;,uy, howcYa'. i& lied into 

# "curand, compIea hAl tnnsf"phenomcoa lIIIt .......iNido ............. Ihdl_ ..exic of......... Uno and the .....1on port ofthe C)'1Utdcr luclt(I...... procodn, II**~ ~**  EllA model doa not cllim 10 be able 10 limulaae lOW)' vane CIDIIIp'eIIG'I. NeitherADL 

### n ...EPA**~**..pttblilhcd dau

### vllidatin, .. tIter .. 

### JIIIYIi<aI .................paiol 

# ........'.u....pIe b)< aitcmptin,", .. prod"", ........... """,,,,, ..__ of_ conditiOflS . This Is the minimal """""I.(Valldation toqUitOd bel...sucII 

## mtideIs eotlId be .. bAil.ted for maps fCl' COIIlwn·speed opuarion whh altem.dve Rfri..... 1I. IIIU1Ch da&I wac IVIiIabIc. it 

# ali"" be ....... bI. 10 capea the physical .... ratin, poinl.-..", man:

# _y_ _opentionII conditions d'n1fi<and'dill' .... lfIoat ..9O'F _ ';"andtofripnot inIec Iel'apet'lNI'CI on which the performance: maps_bucd. Howcva'. before ""'" JUdt 

### IDOdclf

### io ptodia tit. dlecu ofvlriobl, ·speed opention.....s/IotjId be _ va/itIuiott ....._ ... conditions _so tItC __ un hAl tnnsfer(and ..doody·..wed ..... Ioa ........_ 

# wittdin" and friction 10.... ) may differ ..... dy ftom the '.IHood ..... Because 01 dlesc defkienciel in the rlOn, poinl and

### ~1sicIJ rnodd&. &ht Tuk

# Fc.cc mtmbc:n uYC DO confidence in &hem. In the Ib$ence 0(viUdlUn, cia.. it is ftICIOIDDtnISod lhMl'IeihrIDDIkl be UDd 10 

### prodia the 

### power...... 

### now ... an hell loa

### u. '1IIIClion of..m,aw praponIea OI...,.ator 

### ..,...t In the meantimt simulations Involvln, allCmIdvc refripnnlS 01 variable.speed __ OII,hl "'be bosed on the map-based model ttSin, dill _ 

# '01"**~fic** refri,aw (or blond) u !he pa1icu1ar

### rocaaonal speed beinl simulalCd. 

### Rtdudnc e,dln. Iou" Cydin, 10SSCl 

### are esDmalid by 

### the EP,A model U I pattor ..s1mulldon. However &he model 

### ilia Dp II) anaJ)'U only 

### one c;onsuvation meuW"taimed It

### redudna 1Udl1oIaa: I chcItk valve &hal would

.......thetdri'..... ftomml... tin' ..tlteev_duri.....oII-cycIe.' Oth«_hAlO doaIiII, with cyclin,losses ( . ... reduciIt, the refri_

### -te)... - be .....1ated b)< ERA. The ERA __ sinwl.. cs steady·.....opention II SIIIIdanI desi..conditions. II then deals with cyclin,iosses b)< "'piyin'a ...... tioa

# r.,,,... lIken b)< ADL (1992) ftom. "'port b)< J..... n ... xl . (1990). Ifthe c:oncction (.c1Cr formulae 

### were cftdibSe. iI would make: Knst 10 eumine: the scnsilivily Sevaral .ajur proble•• with the phyeical .odel ara veIl known: 1) the .hell 10•• i. not directly calculated, but 1. expre••ed a. a function 

### ot the work input, and 2) the .odel ha. no applicability to rotary c08pre••or.. 

### An additional proble. with the phyaic.l _odeI i. the l.rg. nuaber 

### ot input. requir.d, .any ot which ••y not be veIl 

### known. Hov.v.r, tor tho•• eituation. where the alternate .od.l•• ay not be u••ful, the phyaical aodel can be used in conjunction with the rating-point .od.l. Por axaaple, the rating-point .od.l will output ••ti.. tad v.lu.. required a. input. to the phy.ical aod.l (pi.ton vork i.entropic .tticiency, .otor 10••, .h.ll 10••, clearance volu.e, eto). It the.e values are enter.d into the phy.ical aodal, the .... ey.te. etticiency w

i ll be calculat.d. Then the ettect. 

### ot iaproved actors or ditterent rotational epe.d. c.n be ••tiaated. It the .otor etticiency i. known to d.cr•••• with decr. a.ing epeed, this effect can 

### be dir.ctly .p.cified. 

## , A reco... ndation i. aade in the raport (page 11) that the phy.ical aode1 be r.plac.d by ••iapl. overall ".tandard is.ntropic coapr•••or .ttici.ncy.- Thi. would aee. to be a major step backward. alnc. it could not deal vith the ett.cts 

### at suction ga8 temp.ratur. on puaping rate or with the potential impacta of iaproved coapr•••or coaponante. E •••nti.lly all compressor aod.l. publiahed in the paat 10 to 20 years have 

### atteapted to ba•• the calculations 

### on conditione at 

### the suction port rather than on condieiona at the entrance to the co.pressor can. 

### Relationship oL the 

### Thr..**~od.J. .**  Aa _toted •• rlier, the authors are in .gr.... nt 

### with the con••n.us that the co.pre.sor .ap aodel i8 to be .trongly pr.f.rred , where .uch ••p data ara available. HOlJever, 

### the. r. v111**~** liany ihatanc•• where 

### up data . are not known. In this instanca, the analysts can: 1) request that a**co~pre**

### •• or aap be obtain.d tor the r.frig.rant and operating condition. 

### at inter ••t, or 

# 2, u•• a ••thad that provides a reasonable .pproxiaation of the behavior of the COmpressor in the particular aitu. ' tion, or J) do nothing . It would seea usetul to do initi'al stucU.s uBing available approxi••tion tools, Dnd then if the situation looka interesting , follow up with tests . ReduoiDg cyoling LO•••• The authors agree with the Task Force'. general tindings that the correction factor tor cycling behavior has 8 very .li. experimental baai. ind•• d. Giv.n that a broad.r exper,iaental data base ia now availabl., the analys is could, in principl e, be strengthen.d. 

### , Several pointe raie.d 1n the rev!.w d••erve additional clarification. ERA does not otteapt to account tor cycling losses as part 

### ot ••ch aiaulation. Thi. i . a user option. It the model 1. u•• d •• a tool tor looking at the ettecta of changes in certain para••t.ra, the an.lysis can .S5U•• steady atate operation for both .ituation. 

### ot int.reat: if the sa•• ana lyses are carriad out using the cycling 10sse8, the ditference betveen the estimated energies associated with the two design. will be essentially the saae as**c.lc~l.ted** .88U.in9 st••dy stateofrnodd mullS 10 uncc:rtI.inry in d\c: input variables rdacin, \0 Ihc. eomaion flClOR. This type of analysis 

### c:annoc bcdone in miscue because the ClOr1'CCtioft flClOl' isnol III CIIimates of CYClln.)oucs arc pout,**iftc:onsi~t** wi ... dal.l provided by rchiFMor ""U".f8CWWL ERA's; qclin,loss com:ction flClOl'is COUIp)ICd oIl't11l'O pu1J. The 

### r is iaIc:ndocI capGft the elfoct

## orrdri,,,,,,, mi by

# _In, COP by 1.I1i 

## orqoela ............ 

## 1, u oppIiod 10 a11 ..

## m' dial do ... -.In.

_ val Tho 

## or ollis aror

## uobvioosly 'i 1 ' ... oil<

# q""" orrdria<nnt chup dial

# ml_ it

# wiIl_ ..., tipiIl<udy_,

__I ADL_idelllOjoali_ for 

### opplJiollhi. v oD**..mea-"~** 

## or chup. Moroo.er, ...... 

## unojllSlifo<alioo lor oppIyio, 

## r_ .. refriacnatequlJlPOd wi...

.....,. YL 

### ..aprocalin, <doi"" lion. RowieI ...... h1p'lide and it for .... rdri ...... (whidl di ....... ln .... oil cbi .. oil< aIr:qolo) 10 YlIpClria lOll oil< on-c:yck (illllJSI wail for the can to heal up). Since ERA ipora IUCh 

### rM*:in u ClUCiIP MY &bcrmaI IIIUI iI cannot model mis dirrCftftCC. and Ihe com:uion fICa cannot be. ahcnd bj

_ UICI' 10 IlXlOWl& f« Ihe plCsence of. rtllU')' cornprusor. AHAMTuIt

### foIt:c memben indic:aAed &hal noODll'llCtion CICIoI'''' il 

### to 

### tit dNllIimi (dtlAj C)'dc) .... bemdible. 00 lIlcomical 

### aIone. .... ...-.arordue .. Id'ri_ ......... IDUl iDausc u run arne dcc:rascI. To Uluscnte chis effect OM InIftUfM:lW'a' proWled e.pa.iI In'll



### ... _n, measured COP 

## ra< Id'ri........ M 401i < ...lime < 601i and 4.l mlo < C)'dc ....**<1~min.** ",.,. ..... Iu_ dmealfecled .... 

### ·qo<lio'iooICGi...... _ .. c::oncIillions by IK f«f'Cciprotll"" compiIC,son and by u muc:b II 100ft for I'OIIriu. Qeut'11bt etroct

## orNllIime cannoI be ianoreclu;" ERA 

### modteI. """- .... __ .....,.llIld 

### ..aprocalin,

_ ... """_ r&ClOn

_ ..... Id'ri_ mpalion ...y ..... _ 

### dTeeu on cyc:1ia,lossu. 1be

_ 

### pan

## orihe CJ<lin, e:emclioo 

### opplicl only .. _ 

# bovln,.

_ wi... I' acouaIly inaaIa .... COP.s. 

# r_ ordoily CJ<101O ",,"*h "iii i 

# '.,Iy.... b'pocIlmcaI

_ oil<

_ in CJ<tin, frequencJ'_binet wi 

### ,IIlc!'"a! ..... 

## or

_ ,cIt 1ooId cvaporalin, and condelllin' ............... " conapondina .. oIl< 

## or''-..,...s , COUlpIeucr opcralin, <:OntinUCMally with no c)'CIWt' Iou. ADL aua a wio fA Catnot COP'SlO IdjUli

....... uaICOPror ........... ln ..

# --.'ond_Iin'_ Apia,ADLoIraallO judjcMion 

## ra< 'l'plyln,1O all 

### rdri_ quanli""' .. wi"'lioo olloaved by 

### J_ al. (1990);" .....,10 ..perimenlal_", , ................. 

## orllllllnowo

_ ...... To lOa 

# effie.., or oil< ERA 

### coneaion

## r ra<.)'IICmS .qulJlPOd widl 1OII'

### valve. .... _

_ panded by addln, "'"wi ..........

### rri,....... wi 

## .....,.........-a.

• 1lliI .... II'" diftlaI, 

## rfOnl" ttIetalu 10

__

# .Ie**c~** fCIIClr1lOd J......

### ~a. aI. (1990). IJ operation. On the other hand, the ability or the eodel to evaluate the value 

### ot a shut-ott valve a. a con.ervation eeasure is clearly in que.tion. A significant experi.ental data bas. is reported to have been developed by a aanutacturer 1n an atteept to evaluate the cycle 10•••ode1. Such data, which have not been available heretotore, could be used to develop i.proved algorltn.a tor this etfect or to show that no aiapla a190ritha i. t ••• lbl•• 0(modeJ ruullS 10 uncenainry in &he input ...ariabks rdadnllO &he conecUon fKIGn. nb t)'pC of analysis cannot be done in !his cuebcceuse &he correc1ion fKtar is ncx c:ndibk. au 

### eai.mMes of q'diD,losscs**~** IJ"OUI, iooonsiucni wich data provided b)' rcbi.........

### ..r.a.nn. ERA" c:yclin,1ou eomaion (r.aorls

## cw...,...s 011_

### puu. The 

## rnt .. iaceIldod to**~** 1M dTa:lorldria""'" mipdoa by_1II1cor by 1. 1._dIc_ofqoeleo .....

## IIour.· hil applied '"all

## rem_1hoI do ...-.In I _ valve. The ___ofdIU_ iI_y I I 01 die qlllllCily 01 Idrip:nnt cbarp IbaI mipa. k 

### wW _ ... "frJ ".,.- ..IY_I "'"-- ADLpnwideloojullificacioo bappM dU.v......a11**~** ....,....of 

# -... --.r.dIcn: II 110jUIIiIIcaIioo for 1ppIP,1 die _ 

## r_..**~** oqllipped willi

.....,. .... n:cipnulinl

### c6mFrcu.... _ hi.. I hlah·aide...,., UId III111aIaap blhe Itfri...... (whidl diuol_1oIhe 011 

### durina die a/r-qclo) 10 VIpClria UId ......

## drculadnaduria& die on-cyclc (ilftI.IlC wah for she can 10 heal up). Since ERA iporca IUdt (1CIOfI U COG" ICJI' 

### &hamal INSI it cannot model chis dirrera'ICe. and 1M 

### c:cm:caion (ICIOI' cannot be alt&nd 

### bY che. UI«IIO IIiCICIOWI& (or the presence of. rotary COMpIUSOI". AllAM Task Fa« ...-.lndicIIod IhoI no """"""'"

# * .. IhoI I. I • iI,ofNO iaa

## (...y q<1o) <&/I be mdible. On

# dIoortcicaI--" aIone.lhe 

### pea .........due ..__......... aastiaaease as nan time: dec::IuIea. To ilNMnle this dYea OM lInIftulaawuprovWcd upaimeftW



### __ I ..... _COPr ..

# _n:fri....-..**~<_<~Uld4S** ...<q<Io ....pb <75miA. ",... ..... luahowed ........ dmealrClOd ..·C)'CUoIIoaa ..., . ___

### iliac oonditions by lcw,**forred~'CDqllrsscnllnd** byu nwdlllIloow. fotlWria. C'ICIItylbc dl"ca oINnUmeClMOC be 

### Ian<nd IS III Ihe ERA**~** _Ihe¥IriIIion __lad m:ipo<aUnl """"""'"

## _1hoIr ...... _Ibao

# n:fri_ mipuioo ... 

## y

...._ dYoc:u on c)'Clil'lossc:s. 1bcaocond pan or !he q<11II1_apptiaonly 10 _ havIolI

# _vol... IIIC1U111y _IheCOP IU r........oIdoiCyq<le ..**~** U)II i , ' l'Iylhc b)pochaicaI_lo_ dIc ........ lnq<tinlfroqu<ncycombinctwilhlhe.lhc!-I ....oflhe_--..._ cvapcndnl and condcnsl.I ..............

## ",1eYCIJ oonapondina ..die 

### cue**of.'-~** COiDpWCll' operaIin, continYOully wilh nocyelln,lou. AOLutcI. ruloolClrnoc 

### COP's 10 idjYM dleaaualCOPforlhc<hlnaeinn-",land-.u.l_ Apia,ADLoII"cnoo jlRifi"Ii"" r"applylllllO a1lldri....-Ihe__.....,**ti~,_** by 

### J_..II. (19110) ill I 

### linalo .. pcrimenlll_............ _ cochIn...of ......... ___ To ... die cIfi<a<y 0I1he ERA _ion r_for._ oqIIipped _._valve,dIe_ dtIaitted IboYc were upended by addin,. s1MalOtT valve 10 &he ICfriaaucnwI.t. ro&.wy a:IIInpn .. au. operation. On the other hand, the ability or th• .odel to eivaluate the value or a ahut-ott valve • •• con•• r vation aeasure s Clearly In que.tion . A .i9nifi cant experi..nta l data baa. ia reported to have been**~eveloped** by ... nutacturer in an atteapt to evaluate the cycle 011 1 .ad.i. SuCh data, which have not been available heretofore cou d be uae4 to develop iaproved algorithaa 

### tor thi. ettect or ' to .how that no .iaple algoritha i. teaalble.Subslantial energy savinls were**IChic~,** but t)'clinl performance was loll wone Ihan**~)'-SUIte.** 

### In conQ'UI the ERA comction (atlon, computed (or lhese umc rdrilCfalOtl, pttditud a**I·;J~** UtutdSe in COP over the SlCId)'-Sll1e value. Bc:cuase ofthese obvious de(ecu in Ihe suuctlart of &he cqu'alions dealinl wilt! cyc1inl knse$,me ICQInC)' nyul wu terminated II &his poinI. Dual I .. porator ERA .......... die dual ...pont«.yaem as I special case d .... 

### LaRno Clde.Iuq>io.

_ cvaponIOI1 io saics and simply elimi..,;., .... d dle io_ The pani<lIIaT 0001" .._ c:onsidcrcd in IhiI analysis has no air exchanlc beIwcen Ihe c:urp.nmc:n1S..and wumcs The 

### JIrimarY""" d .._ ·COIl ........ io Ihis case would be .... 

## climinuioo ofdle 

### ewponwrfan 

### power • 'and she compreuor CIlCIJY 10remove IIw heal from the c:abineL 

## ne only other poce:ntill for c:onsavinl ener&Y would seem $0 be savinls in deffOSl enerJ)', si.nce no humid air from che fresh (ood c:ompartrne!'ll would contact the freezer ,cvaporllOl'. Howevu.ueh savinls would nat be observed on the DoE lesl, or in**simulali~s** ofdosed-dooropcn.lion. It appcan IMI ERA is unable 10 model ochctdual-eVlpcnlOl" c:onfiluralions NI miahl elpk)il other lyptS ofenero conservacicm opporrunilies. 1be b&Je ease refriacra11X' for Ibis experimenl 

### wu usumed 10

### haw. &inJIc cvapora&ar, and IUbjeclao chc foUowina uncauinties. The**cond~** or U·value (or**~pIwe** opauion was**u~ '9a~**  Down within:t**I~.'** The voh,lmerric: air flow rue CNtrme cvaporat« is also known wilbin 10., and the CVlponalX' fan power wiThin**S~.** The tombi.ned effect cllhac evtporllOt-apccific unocnain• ., _"lcd llvoup .... model 10 prod""" Ii 0.73" uncauinly io ERA'• .,lima.. d cneraY lISC. The cb.aa1 evapcn1Ol' S)'1&Cm conLains none ollhe aforemcntionod componc.nu. which wen: repLaced by IWO lillie evapcnu:n dermed in Iem'IS oIlhcir condut&ance.s and Ihdt 

### areu. To ensure dw the cabin« lelDpen.nues wUlpU'Ible berwccn Ihe**linl~'** and

### 4Pal-cvapontor simulalionl, die lRU ofthe IWOeVaporalors were r'•fined 10 achieve Ihc 

### proper acmpencum in eac:b compuanenllNXla' doleddoor conditions in a 

### 9C1'F envilVNnCnl. IO ERA', calculational will menus were UIOd 

## .0 c:aIculaIe Ihe condlM:tantes o( these nllunl-dratt cvapcnlOn, which: art: usumcd 10 be known only within :tIS"

, Aa&*lyll)'PQI evaponlOfcaklrinMIlu it allIe**IOcompuc.~** wilIIia ± ,'10............ waJue iI.cn dill"cult 1Olkat:rm.ine. Since acOOc:nDltypC 01 -oM lilt", to iii ... ror -.&if: ill ia 10 tcDJWC !be ar.IUlC valua. 10 11MI u:aumpOon Irlelpl 

## u.c e-eray 

### pon;o.. 01 ft )'111. 1M IfUI**~y** Wo the COlI 1\rcnrquircd Ift:II miJht be IUbufMiaIIJ -au or 1u .. 1M value prMicIId'J EllA. Ilia ...... to .......

.... pi:I 10 pnx:eed and yield JCrflC wicht inlO 1M taISN.,iI, 01-*1 f'talkl1O'" JIIIIIM'&f. Howc\ICI it rec:osltiJ.ca fIIllheClDlt ditrClaC between asinate• .,.,.. Md dlaaI• .,'9Qn&Ol' wiD ftlqUifta dNiIIDd Cl*_)'IiI 

# ..,...,.. 14 Dual-.vaporator The review retlect. a caretul atte.pt to exa.ine the uncertainties with aodelinq 8 dual-evaporator Bystem. It provide. a quantitative eetimate 

### ot the level 

### ot uncertainty in the analyeie. Several co"ent. are provided below relative to so•• of the points rai.ed in this part of the Accuracy Analysis:

- As the reviewer stated, the .avings in defrost energy can not

be applied to the, DOE test. Clearly, this is because of the specification of the te.t procedure. However, the potential benefit relating to reduced defrost requirements during actual operation can 

### be eetimated u.ing the ERA door opening algorithme.

- The dual-evaporator aodel wa. added to acco ..odate designs

currently in vide u.e 1n Europe and Asia.

- The report atate. that the greatest uncertainty in a dualevaporator cycle i. a••ociated with temperature control. This is, in fact, a major difficulty .ssociated with this type of design. Cabinet te.perature variations acceptable in portions or the Asian market would likely be intolerable in the American .arket. The report err. in .tating that ERA ignores the proble•• Several .eana of addre.slng the proble. are built into the model: 1) allow a cabinet te.perature drift in one of the cabinet sections and report the change in te.perature, 2) assume the use of • valve (801enoid contrOl) to divert the refrigerant to only one evaporator at a ti.e, 3) use a control means such a. a refrigerant valve to allow refrigerant flow through both evaporators over most of the cycle, and then divert 1t past one of the evaporators during another portion of the cycle, or 4) calculate the evaporator .izes that would be required to •• intain temperature control. Option 1 reports the cabinet temperature. that would be achieved without control. Options 2 and 3 represent active control situations. In fact, option·J is used in one of the .ost popular refrigerator/freezers now .arketed in China; energy use associated with the solenoid valve i. considered by ERA. Option 4 i. added only for research purposes. It is intended to provtbe so•• insights into the variation of required evaporator areas with operating conditions • Subs&antial CllUIY "Yin,s wett**ac:hie~.** bul c),clin, perfonnancc was ltill WOlle \han S&eady
-ualt. In conaut the ERA ton'CCdon ("tors. compuled for these limemri,eralOtl, pR:diclClCi a I·, ..**~** in COP averlhe lleady-ualC value. Bc:cau.It of!htseobvious de(c.c:u ill sbc 1INCI\ft d the equlEionl dc.alill, with eyel.." Iouc$, &he**~** analysil 

### was aaminalCd "&his poin&. 

### Dual enporalor ERA _ .... d.oI ... 

### po.."or.Y*"''''**~** 

### ....0I .... l.cm>z qdc, .....,_

_ io scri<I and simply diminalin, one 0I1he 

### to_ The panlcular

# 000/",,_ oonsidcnd 

### to dIia analysis has no air ""han,e _Ihe IWO 

## _u, ·and......,.. The primIry _ 01 .... 1)'·"""..... doo 

### to dIia ....-.Jdbe ....

## dimlnadoa orIhe CVIjlOIVOfr.. ,.,...... •

·..-Ilhecompttuorena'J)' 10 rtrnOYe dw heal from lbtc:abincL The anly other JIO'CIlDIl (or consavin, enerJ)' would seem $0 be savin,s III defrost enaJY. since: DO humid a1t from Ihe frtah (ood**oompanmc:~t** would IXMllaCi VIe freezer. ev.pon&or. However sUch uvin,s would not be observed on the DoE leSt. 01 in**"mullti~s**

## or**doliCld~opendon .**  It appean WI ERA it unable 10 _Iochuduol<:vapO.. "Ofc:onfi'........ilia, 

### mlllU "ploil0Iher 'yp<S 0( CIICIJl' cooscrvllion opportunities. 1be buccase rcf'ripalOl' for chis e.xpcrimenI 

### was usumed 10 haw. unakevap:naor. and IUbjca 10



### ....roUowin,IIIICGlIi..... The COfIducIancc,Of

### U ·..a..ror .....ptwc opcnoioo 

### was ..**~** 

### 19.\1< Down within %IOtt.' The YOIumeaic: air now me 01« &he evaporaaor iJ abo tAo"", wicbin 10.. and Ihc 

### evaponlOfran power 

### w hhin 5t.. The comIJincd 

### ell'...

# 01_cv_ ....spoci/ie """",,",liespropaplCd ,,,",,,'" Ihc model ..pod.....

### ±O.73t. 1IIIOCftIi0'Y In ERA" CI"",,01 -0 ..... The dual ev.porator ly5&Cm conwns none d the aforemenDonocl compontnu. whicb 

### were rep1lced by 

### cwo 1IIDc: evaporIIcn defined in tamSoIlhcirconduccancu and Ihci.r &raJ. To**~** &hal Ihe cabinel Iempc:n.NttI 

### were**t':"l~ble** berwoen Ihc sin,k- and 4P&J-cvaponaor simulalioo.. die arcu otthe 

### cwo riaponlcn 

### were t'.fined to .chieve che 

### proper**~IUI'U** in ach ccmpllU'l'leftl under ebcddoorc:ondiUons in.

### 9O'F envirvnmenl.IO 

### ERA'. caIeu1ational aui.at meft", 

### were &&IOd aOealcuJaae the c:andrx:WlCCS ofthelC natural-drU1 cv.ponaon. whidlare usumed to be known oNY withln %15.
t**Aa.l1'1.t)'piellcV.ponuwc./loriMaud"'lOconpuc.~""t'ft**. ...........

## vaa. ..... difrCuklOddaminc.**Siocc.dilrcn.t1)1lCoI~WOIIId"tClO** .....**tOl"~kil"""** 10 c:.pIIC Ill&: ItJiIDhII& ,.w., 10**na.~** _Ie- -CMtI'1 ponioA 01" MIl,... ...**~.,......w.,** -.0 lheODll**~** 

### ne.......lfta rN ...**bc~l,** .. Ff• 

### ...rtct ..."-,,,..........,EaA. 11 ......10 ....... ItIIIIyUt IOpnIC*Id -S '1tdd tome -iaN Wo .1aUiIiYil,oI.add1Caka 10

## ad..,...,. Hawrnct k**~** 

# "1IIe**~ctjffCIUCC** between

## '1inJIc.,,,,,,.....**~...,.IY*IN**

# will,.,.. deWW a. .. ,.. 

# ..,...... 14 

### Dual-avaporator The review reflecta a careful atteapt to exa.ine the uncertaintie. with aodelinq • dual-evaporator ayate.. It providea a quantitative e.tl.. te of the level of uncertainty i n the analyei•• Several co... nta are provided below relative to so•• of the points rai.ed in this part of the Accuracy Analysis:

- As the reviewer .tatad, the .avings in detroat energy can not

be applied to the
- DO£ te.t. Clearly, this i. because of the specitication of the teat procedure. However, the potential benefit relating to reduc.d defrost r equire.ants during actual operation can be a.tiaated uainq the ERA door opening algorithaa.

- The dual-.vaporator .odel was added to accoaaodate desi9ns

currently in vide uee 1n Europe and A .ia.

- The report .tate. that the gr.atest uncertainty in a dual-

evaporator cycle i. a•• ociated with te.perature control. This is. in fact, a .ajor difficulty a.sociated with thi s type of design. cabinet t •• perature variationa accept able in portions of the Asian aarket would likely be 

### i ntolerable in the American

. arket. The report err. 1n .tating that ERA ignore. the proble•. Several .ean. at addr••• ing the probl•• are built into the model: 1) allow a cabin.t t •• peratur. drift in one at the cabinet .ectiona and report the change in te.perature, 2) assume the use 

### at a valve (.01en01d control) to divert the refrigerant to only one evaporator at a ti.e, 3) u.e a control means s uch a. a refrigerant valve to allow refrigerant flow through both evaporators over .ost ot the cycle, an4 then di vert it pa. t one of the evaporator. during another portion of the cycle, or 4) 

### calculate the evaporator .ize. that would be 

### required to .aintaln te.perature control. Option 1 reports the cabinet t •• perature. that would be achi.v .d without control . Options 2 and J 

### represent ac tive control .ituationa. In fact , option ·3 is used in one ot the .oat popular refrigerator/treezers now .arketed in China; energy uae associated with tha aolenoid va Iv. i. conaid.red by ERA_ Option 4 

### i. added only for researcb purpo.... It is i ntended to provth. so.. insights into the variation of required evaporator area. with operating condition•.because ofthe relalive difficulty ofthe calorimetty Jiroblem. This produced I 

### ± I.S% uncc:naincy in energy usc. The. energy savings associated with eliminadnllhc fan were approxima1cly 13lJt. ConsiderinllMi. . uncertainties, the savings an: estimaled in Ihis Quanlilative analysis 10 lie wilhin the l1-IS'II ange. However, this quanlitative analysis may not Iddrus the most imponant sources ofunce:rtainty. For eumple the arus ofthe plltc-slyle static evi.pon.lOR azc much pcau:r rhan the area of' abc ibnatc rorecd-dtaft evaporator. If !he resultinl.chara;c**ri:qu~menu** an: also proportionately larger. cycling losses due 10 rcf'rigcrant migration will also increase. The greatea unceruinty, "ho'NevCt, is associitocI with the lempc:nrurec:Onlrol protkm, which the ERA model ignoJeS. OveTOOming this problem wUI cc:rtainly make &he system more costly. for example by adding the CQSt ofrefrigenru switching YalYes, 

### SCflsOrs and CO'IIroUers 10 &he CXttl cost ofevaporator swface areas. It may also increase energy Kquu-emcnts, dependina: on the centrol option chosen. For examplc exchanging air between the companmc:nts may erode dcfrostinS savings, fans mia}" be Deeded 10 prevent SD"&tification, and pulldown requirements might demand a wger**oomp~** thereby shonening the duty cycle. Conclusions and**recomm~ndatlons** This report dcsaibcd both the qUlliwive quantiwive aspectS ofthe accuncy analysis**~uc~** for the COI'Ise:rvation options Jisted in Table I. The options were selccted because there is inadequate lest dala a'Yaiiabie (0 validale lhe pans oflhe ERA modd used to calculale energy savings. For a few ofthese coosenoation"options. limited amounts oftest dati were povidcd by manufacturers on a COnfidential basis. In 

### sOme cases it was possible to conclude. based on this adminedly sparse and confKlcntial dall, that cen.ain parts ofthe ERA program must be improved befon: they can be used 10 accun.1ely predict energy sa'Yings associated with ccnain conservation options. Except for the psket heat leak and VICUum panel insulation aniIysis, the quantitative pan of the analysis could not be completed because of erroneous assumptions and omi.ss:i&lfIs in the ERA model itself. The findings tq)Of1CIoo .hove ltad to the following conClusions and recommendations: Estimatcs ofenergy sa'Yings obtainable from pskCl improvements should be detenninocl di.recdy by experimenL ERA's calculational assist yields ruulu that fail to agree with published dati and"**e~perimcnts** conducted by manufactllrCrS, and may lead &0 em:n of

### sen.**or~'.** ERA's estimates ofeneTlY saYings due 10 YICUum panel insulation may be· in cnor by ±1Qtl, due 10

### unc~nties about

### cnclosu~ thickness and and panel teSistivity alone. CMclcss use 

### of. laboratoryreported k·Yalues for non·CFC foam can iDCI'tISC these arors**IO±~"** ERA's failure IOdca.l with 3-D effccts Ippan:ntly led to even IIUlCt errors in tests conducted by one manufac(ura". CODolu.iona and aeco ..endatioD.

- Agree, The calculation assist routine was already deleted from

Version 1. O.

- Comparisons of ERA predictions and finite element models show

excellent agreement. Data are not presented in the review which substantiate its claims. because ofthe relative dlrficuhy ofthe calorimetry p · roble.m. This produced.

### ± 1.S'II uncenaioty in energy use. The energy savi nes associated with e1imin.i.dn, the: fan were approxima1cly**13~ .**  Considcri.n,**~** . uncertainties, the savincs are estimated in this qu&.uiwive analysis 10 lie within the Il·lS-'l1I1lCHowever, this quantitative analysis may noc addrus 

### tt.c most imponant sources ofunc:erWnly. For example the. areas ofthe platCostyle swiceviporltors are.Duch JrC&'Cf &han the aru ofthe sinllc forced4Bft evapontor. Ifthe rcsuhing.char&e ftiquimnents**~** also proportionalCly lar&cr, cycling losses due to refrigcn.u nUaration will also inause. The peatea uncena.inty, · howcvO'. is associited with the lemperarure concrol problem. which the ERA modd ignores. Overcoming this problem will certainly make the system 

### rrw:m costly, for example by &delin, the COSt ofrefrigerant switching valves, sensOrs and CO'Ib'OUen to me eXIrII COSt of' evapontor swface IJUS.. Itmay also incru.se energy requirements, depending on the control option chosen. For example exchanging air between the compartments may erode defrostinJ savin,s, fans miahl be • needed to prevent slratification, and puUdown requirements miibt demand • larger compressor thereby shoncning the duty cycle. Conduslonl and**rtcomm~ndalions** This report dc:saibcd bach the quaJiwive 

## an4 quantiwive ISpCCtS ofIhe accww::y analysis**~uct.ci\** for the conservation options listed in Table 1. The options were selected bc:cau.se lhere is inadequate lestdallavailable 10 validate the pans ofthe ERA model used tocalculate enerzy savingS. For a few ofthese conservation·options. limited amounts oflest data were pl)'YMkd by manufacturers on a confidential basis. In 

### sOme cases it was possible to ooochxtc. based on this admiRedly sparse: and confidential dill, that cena.in partS ofthe ERA program must be improved belen they can be used to accun.tely predict energy savinp lS$OCiated with ccnafn conservation options.. Except for the psket heatleaic and vacuum panel insulation aniIyJis. the quantitative 

### pan ofthe analysis could not be completed bectuse oferroneous assumptions and**~** in the ERA model itself . The findlnls**~** .bove ltad to the following conClusions and recorrvncndations: Estimatcs ofenefgy savinls obcainable from pskCl improyemcnts should be dettnnined directly by experimenL ERA'I calculational assist yields results that fail CO acree with published data and ellperiments conducted by manufacturers, and may lead co em:n ofSOtI or mea.• ERA's estimates ofcnerlY savin" due to vlCuum panel insulation ma)' be in error by**%I~** due to

### u~nties about encloslR thickness and and panel rc.siscivh:y alone. Cardess usc 0(laboratory· reported k·values for non·CFC foam can iDCftUC these emm 10% SOtI. ERA's failure tode&l with 3·0 effects apparently kd 10 eveR laracr errors in IeSts conducted by one manufacturer. - Agree. The calculation assist routine was already deleted tro. Version 1 . 0.

- Coapar!sons or ERA predictions and tinite element .odels show

excellent agreement. Data are not presented in the review which substantiate ita c laims.- This suggestion was already incorporated into version 1.0.

- This suggestion was already incorporated into Version 1.0. - ERA calculations show the effect of errors on energy

consumption ot**les.~than** 0.5'.

- The _odel should 

### be strengthened, revised or abandoned; based on

in-depth review ot,additional data. strongly. ERA allow••everal control strategies to be to control cabinet temperature. 

### tor a dual-loop It will also show the reault. it no atrategy 1s used. The ettects of environ.ent and door openings on cabinet loade are explicitly modeled. Data i. not presented by the reviewer to support this claim.

-**~gree.** The Ilap model is preterable. In cases where data 1s not

available, however, the other models allow a first-cut analysis to be pertormed. - A mistyped CSD coefficient was fouhd and corrected for R-141b. The

corrected model predicts the expected glide. The reviewer seriously _is interprets the approach used in ERA.**~he** model allow. the vapor, liquid, and two-phaae regi ... in the heat

exchangers, and the retrigerant required properties, to 

### be .odeled in .s many**se~ents** as the user de. ires.

- Disagree

employed systell. The NIST Ihermodynamk: propc.ny routines used by ERA may lead' to errors in eneJlY use exceeding 1'" for R-I34a. More aocurale routines are available from NIS'F in Idenlical fonnal and 

## mould be used for aU R-l34a simulations. ' : Serious en"ClrS apparently exist in the: pan of ERA that simuilles 1...cnlIz. cycles. Repeated**att~~** by in experienood refrigerator dw,nc:r failed 10 produce • result ahowin,. 

### u:mpc:ruure 

### &Iide of the magnitude predicted by the NlST propeny data.**AJ~** ERA', usc of. constant spccUlC heat 10 approximate the behavior of uoaopes Cluses the spoc:ific heat 

### noo 10 be in 

### error by 

### as much 

### as a factor of 7 as mixture composition chMIel 

### thtoulh the evlpcnaor. This can lead to serious errors in high-effectiveness heat exehanFfS, For dual-evaporltor systems IS well 1$ Lorenz-cyele 1yltemJ. ERA'l inlbility 10 model cabinet lemperiture control sJratepes and orr«.sicn**perl'onnar.~** incrodooea IfUl unc:crtainty into any estimateS ofenergy iavin,s, A syStem optimlu:d for opcraIion in I 9O"F environment is almost ceruin to experience contrOl problems It lower ambients and in ruponsc to reallstic:'cSc:J«.opening schedules, and the energy cost ofeUmlnatin. these problems is noI included in the model. ERA's ability to predict the, effects ofalternative rem.ennts or uotrOplc blends is further compromised by ERA's compressor rating point model because it contains empirical relations that are speciflc 10 R-12 and leading 10 errors**ofS-8~** in prt.diCM, eneraY use for R-I34L Li.kewiie the compressor physical model is deficient because it demands that the user specify parameters WI are unfamiliar to compressor designers., thereby IClCUnglO input 

### e:rron. A simple model requirina the user to specify a conStant isentrOpic efficiency might be more ac:cUl'lte. Ie is rccomrnended that 

### oe;ther the physical model 

### nor the nrin, point model be used; 

### oompres.sor calorimelCrdatfsh9Vld be obtained (or analysis ofany**~ation** opcions involvin, allemative rem,CrlnlS, mixtures or variable-speed compressors. . the cyctin,loss**~ec:don** in the ERA model should be mnovcd, and rdriccnton compared on the basis of steadY:Stlle petfonnanoe. The !=yclin,loss cotreCCion in**~e** model extrapolalCS results obtained &om a sinale tCSt refrigerllor, fails 10 ac:oount properly for significant variables (e.g. remaer1nf/oil solubility; runtime), and yields results that differ patly from teSl data obtained by m&llufacturen:. Th. vulput format should be c:han,cd to display**daiJ~** enerJ)' use 10 more signi(ant eliCits. This**~Ir'** :acilit,lte analyses o( parameDic unceru.inty, and would help designeR evalUiIt more lClCUr1tely Ihe derivalive ofenergy use with respect to inpot variables, The user input menu should be changed 10 ICCCpl at IWllhree sicnific:anl di,its for the value of foam conductivity. The t'NO digits cumntly ac:cepted are l.nadcqUiIe 10 suppon even the thrce-diCit results calculated for daily enerlY use, which is extremely sensitive 10 (aun conductivity. The pm:cding sUlicstions are necessarily oonservative and neplive because they are based on very limited dalL Only (ew data points are needed 10 reject a hypothesis. while many are requiRd co confinn it 1be ERA model re, :esenlS a sienifiant improvement over its predece.s.sor, and mighl only 16 The NlST lhennodynamk: property**rouli~** used by ERA may ICoId to cm:n in energy 

### we exeecding I*' 

### for R · I34a. More 

### aa:unlC roubllCS Itt**a~lablc** from 

### N1ST: in IdendcaJ 

### formal and should be wed 

### for all R·I34a simulations. . Serious errors applttntly

## em. in the pan ofERA lhu simwucs Lorenzeyclc.t. Rcpwcd**~** by incxpericnc:c:d mngenlOrdcliJDCl' flliled 10 

### JrOducc arault ahowinl'**~** &lick of the mapiludc predicted by the NISTpope:rty dIlL**AI~** BRA', 

### u.se ofa constllu IpCCiIic be&! to approximate the behavior ofuotropcs causes the ipCCific heal ralio to be. in 

### c:rror by u mlK:h IS' ftc1oroC7 IS mixru.rc composition chanctJ 

### Ihrou&h the evapcnlOf . This can kid IOICrious errors in**hiCh~ft'ectivcncss** helle.xchanJCt1. Fordual·cvapcntor syslems IS wclll$**~nz.qelc** I)'IIICmS. ERA's 

### inabUity to model cabinet cemperilurc control sjrllelic.s and off«sicn**prer1c:rmar. e**  lncroduca IJ'W uncerWncy intoany csbmateS 0(mercy iavinp. A I)'SlCm opdmiud far opaadon in a 9()-F environment iI aJ.most cenain 10 

### experience eontrol problems 

### at lower ambienu and in 

### raponse to ruUltie door-openlna schedules, and Ihe enerlY eost 

### ofeliminadnc thele 

### problems iI not 1nc:ludcd in the 

### model. ERA's 

### ability 10 predict the,

### e«cclS ofalternative 

### refri,c:ranu or t.CIOlrOplc blends Is 

### funher compromjsed by ERA'scompressor mina poinl 

### model because it 

### contains empirical relations thaI 

### are specifIC to R·121nd leading 10 errors ofS.8.. in prr.dictin, 

### enero use for R-l34L Likewiit the compressor physical model is dd'lCienl because it demand,1hII the user specify pwarneaa1 &bat ft

### unfamiliar 10**eompr~5S0t desiane~,**  

### thereby leadinllO inPUI 

### ann. A strople model requirin, the user 10 specify a eonsulu iscruropicemcienc:y miahl bemoreac:curue. llls ,ccu"mClldcd lhll**~therthe** physiea1 modd nor lheflrin,point model be used; compres.sorcalorimeterdal4**~Id** be obWned 

### for analysis ofany 

### conservltion options involvin, allCmltive 

### refriaeranu. mixtures or variable-speed compressors. 

### The cycling los. oarcc.ion in .he ERA model sIIoIIld be rancJV<4.lIId refri,........_putd

### on the t.sis ofsteady:stlle 

### pc.dormance. The cyelln, loss c:om.ction in the model 

### unpolilc.S results obtained &om a sinllc tesl refriaetltor. 

### fails to ac:cot.Im properly for sienifiCltlt 

### variables (c... refriaenntloil solubility. runtime). and y;eJds rcsulls that differ JRltly from IeSI data obtained by tna.IUflCturer1 . n •

.; VUIpUI format should be chan,ed to displl)'**daiJ~** eneraY use 10 more: si,nifaeanc di,ilS. This**~1" ~aeilit** **ate** anal)'scs ofparameDic 

### unc:enainty. and 

### would help 

### dcslanen evaluace 

### more IlXUralel), the derivative ofenerlY use 

### whh respect 10 input variables. 'The user inpul menu should be chan,ed 10 accept It IWI three ticnifieant diailS for the value of foam conductivilY. The IWO dlJ.iu cumntly accepted are lnadequ,ce II) support even Ihe**thtee~j,it** results calcullted 

### for daily entrey use, which isextremtl), sensitive 

### 10 foam conductivicy. The pn:a:dinl sullestions**~** necessarily eonscrvative and neptive becluse they are bued on very limited 

### dll&. Only 

### fewdall points an: nccdcd to 

### reject I hypothesis. while many ft required fO ccnfinn iL The ERA model n:, .'escnIS a sicnificanl improvement over its Fedccessor, and miahl only 16 

### - ERA calculation. show the ettect ot errors on energy conau.ption ot**le8. than**  0.5'. - A 

### mistyped eSD coetticient wa. tound and corrected tor R-141b. The



### corrected »Odel predict. the expected glide. The reviewer .eriou.ly ai.interpret. the approach u.ed in 

### ERA.**~he** 

### -adel allow. the vapor, liquid, and two-phaa. regi... in the 

### heat

exchangers, and 

### the refrigerant required properties, to be 

### .adeled in as aany •• gaents a. the u.er d••

### ir... Dl.agree e.ployed syate •• strongly. 

### ERA allow•• everal control .trategies to be 

### to control cabinet temperature. tor a dual-loop It will al.o show the re.ult. it no atrategy i. used. The ettects of environ.ent and door opening. on cabinet load. are explicitly modeled. Data is not pre.ented by the reviewer to 8upport this ciaill.

- !\gree. The map lIIodel is preterable. In case. where data is 

### not

available, however, the other _ode18 allow a tirat-cut analysis to be 

### perfona.d .

- The aDdel should be strengthened, revi.ed or abandoned; ba.ed on

in-depth review of . additional data.

- This 8uggestion wae already incorporated into Vereion 1.0.

- This suggestion wae already incorporated into veraion 1 . 0 .

# .. ftlqUirc mocSeIC impIovcmenu in order 10 bec:omt • usc(",11OOI for anU)'linllmpItU of IhtIc cntIJY

### CCXlJCI"iin. deaips. However 11 wlD like 

### considcnbk: time and d'f(W11O amass 

## me dua ftecdcd 10 iI:npo¥c: and validale many 01 &he (wum cvahaaccd here. Dau oa .his .. 01 CONCn'abon options:_ WS'f**~Il** d\i$ lime. and.c &herdcn hddu proprie&uy iDIormuion by**Ihc~** Ihat ._. dc>eJopod it. U.al man: espericncc i. willldlt............... 1Dd y '-10 dlt pul>I.,_dlt ..... .,_ 01 .... EllA

__ 110 10

__ willi pal ..... A fiDII Cllloionuy _Is IlOCWIr)' 

### u ............... EllA

_ II. daIp llIlldoI, .

___ E_iCaU 10.... IDdoqualiooa

__ wlIapaf .......,. _

_ ooIy 110 capabIc oI.....-lin, pafORlllllCO ...........P 

# 1,_ _oIf-

... ppaf_(.... dltetr ... oIdIan .... __ cft... oIaddiIiooaI_

...... due .. door

### opcnil>js.) The u...

### ·lflCCiI"ood input wi ... fill'

_ aupaboallDd

__

.._,,,,, in_to ooml"''''''

## rO(**ERA~** lock 01 

### oquadooadacribioi ......... 

# flow-Po-

........_ f.. dlt .. pillary 1lI 1Dd 

### oq_aIiona ... WOIIId 

# ""'* 01 refri_ c:Illqe. 1lladore whal diCf ..... kilchal_ bCllllllplc, EIlA

__

....... refri has ......,pd and fiood willi.

_ <apiIlary IlIbo pod .. pn>duoe ....



### ....·lflCCiI"ood .upa!leat ..-lin'

_ ambi ... _ Therefore. refri - desip M:IOd by EllA '" paf .... well dai,n 

### pol.' (9O'F

__ $OF freeoer; 

# lin !JaIl food) wlU """";Iy keep food from .poIl1n, u .... 

### ainbico'

__ dian .... ":0 prodict oIfdesip performance characl:cris6cs such as &hi, rcquws. tnIC simulation modd chit models expUcidy

..........vior 01 .... C'lpillary milo and .... 

### '!iarae"","""Y. RererenctJ Anhllr D. lillie Inc.. "EPA ..

## rn''''...... alysis""' """'_•• DRAFT. 

## Nay 1992 AnhurD. 

### Lilll.. Inc••

### Rqrlt",,,,,rtwlF"'"r C rlIode'**Uur~** 

# a .... u.s. Depo ....., 01 Enerll'. Wuhi_ 

### D.C.. 19'2- 8ou&blon. 8. E.• T. A. HeweD. A; M. aausinJ. A"**,,,~ti,adolt.O/** ItDfudold

### rl/rl,tTlIJOTCdbiMI /4Qds. ACRC-TR·21. Air Condicionina and RcfriJefllion center, UDivenil)' ollUinois II UrbMaC!wnpai,•• M.y 1992.135 

### pp. Conklin. J. C and F. •• Vineyard. -Heat CXtNnlU lhermaI pafOl'1DMCC for two nonucocropic



## ..rn.....' .........·.l'rc><. XVIII 1.,1. C..,rru o/Rr,frf,,_. -. A_,I99I. Flynn. S.• K. Rouch and H. A. Fine. ·Finile ekmenl analysis of bell crulla' Ihroulh lhe luket "aion ofrefril""Of/frec....•• £I'AHJOiR·92If11)9. U.iIOd SIIIa 

### £0."""-"'1-"" 

# A.....,.. Wuhinl'on DC OclOborl992 <la11a.,....l.. NalionaIlnotiI... 01 SlIlldanh and Te<hnoIoaY. -icalion.l..lIIIY 1993. . Janssen. M. J. P .• J. A. de Wil. L J. M. Kuijpen. ·Cyc1inl ktsIa in domcJtic: appliances: an uptrimentaJ and IhcoreIicaJ analysis·, 

### ',«.UR 

### 'wtlM CDI(",,,", Wea l.aflyeaC, Indiana. AulUSl 

### 1990. 11 n:quirc InOdeIl impro.u,....u,J iA order 10 bc:comc I u.scfullOOl for analyzia. impICU oflhae: enctIY• 

### ....-ta,dtlips. H-..rll wiU "'"_ .... 1nII dTc;n 10 ..........ella i-.s '"**~** Md validl&e man)' 01 &he rwuru cvalUiICd here. DIuoa &his ..01 00Na'Y1Ilon opcions are WI)'**~** .. Ih.is bmt.. and ft.thcrd'OR held ..proprietary WarmMion by &he cc:.npuiCa &hal ••• dtwIopod .. UDliI ...... pcrieoce is _ .... willi ......

# --...s.... ella -..widely a..u.bIe ...... pullli<:-...., .... p<Odic:....01 .... EllA _ .....bo ........... willi .......... A finoI Clllionary _ II...,....,.

### u._ ........ EllA

### _Ia.daip

### -*I.

### om.

__ E_ ifaU Iopuu and oquadou __..... porf"" oenaioIy. ...._ -"IooIybocopobleol_lin, porf_ .... 

### p .... ppoial. Itcould ...........oIfdaip pafarIDIDCC (c... _ ctrca 01

### chMaina embiallllAapalWa.ft. me 

### ctrer:t 01 +tided cabiDtt _due

# "'doot-">is-) The ..... -spccifood '- VII ...

# for_aupaIIcaI and_



# ..bcooIin, ... 1n1Cftdod .,

# _sa.. (Of ERA**~** lack 01 oquadaoa

### _bioi.........

# fIow-p.....,. cbop ..1ation (or .... <apillaly Nbo.1nII "'I...........

# would.., no\: 01 .... mri..... ' dIarp. 

## n.e..r"", w..........specif ....dllf ..... ldochal_....

## rc. ............... EllA_ ......

.... .... mri_has bccnlOClwpd and fioood willi. new CIpiIIary .. bo ......... "'..- .... _-tpeciIiod superIIea, ....

# _n'...... new

# _tIM_ Thcn{"",. __ - dcsip prodic:ood by EllA 10 perf ....well ......de&i", 

### pol" (9O'F__S"F -.

### «1'F"'" rood) wiU "'" """";Iy kcq> (ood (lOtII.poiUn, u .... ambicn' __chan ...**~o** pndico oIf

## usnpcrfarTi\lftCle chuaacrisdcslUCh as this rt:quircs 'INC aimulalion modd Ih.tl Jmdeb c:apUeitJ)'

.... _vi«01 ....<>pill.ry Nbo and ....CMtc< ..... noory. Rererenttl Anhur D _ Liulclnc.. "EPA ..m, ....... analysis ""''''''' ...............DRAFT. Nay 1992 Anh... D . Lialc. Inc.• 

### Rqr!luouxONlFmur C...,..,.,""IUw's G_. U.s. Dtpo&_,01 EocrU. W",""",," 

## lie. 1_ Boultllon. 8 . E. .T. A. Hewd. A: M. Claus",,,**.A""II~Il,"rIM** 

### tI/IttHudtDId rt/rl,trtIIM c:GIHM. 1oGds. ACRe
-TR-ll.AI< Condioiooin, and R.rri..,..;on Ccow.lJoi-ucy 0I1UinoiJ .. UtbonaOwnpai,.. M.y 1991. 135 pp. ConIdin.I. C and F. .. Vincyaod. 'Hea, .. chan,er ohcnnaI perf .........

## rc. ....**~** mri""", miallU'Cl·.l'roc. XVIII 1.11. C..,,,u

### ofRtfrt,_,.... MoNreal,

# A., 1991 . flynn. S., K. Rouch and H. A. Fint, "Finile cklnenl anllysiJ ofheal nnwdarou.h the lukel 

### RIlon 

## or rcfriletllot/frencn-. 

### UAHJOIR·91IOO9, Uftili.d SClIa EnyiroNncn&aJ 

### Prow.aioft Ap:nq. WulIln_DC Ocoobor 1992 Galla"",.

### I• •Nooionallnsoiouoc 015_. and 

### Tcchnc>lc>D•....-._Wi ..

### ;c......Janouy 1993. I....... M . I. P.•I. A. de WIo. L-I. M . K. l jpers. ·C\'<lin' ...... 1n domcsIic oppWa_: an uperime:nw and**~** lMIysb", "ot. UR PwJM**Cotf~.ItC.t .**  Wca LUlyea., Indiana. AUJUSl 1990. 17Morrison.O.•ndM.O.McUndcn,AppJi(QlioltofIIItord4pMrt4quG1io"of10re/,I"rQlluGIld,qri,c'4IffmUfwU,NBSTechnicalNoce1226.NI'ionaIBureauofSundudJ.OahhenburlMD,1986•Poncr.K.J..andC.W.Bullard.M«kNltfONJStltSj,iv/ry(JNJ/ysJI0/"rqrlpratorl/rttursyIUm.ACRe-TR-ll.AirCondifioninlandReinaeraQonCenter,UniwnicyoI1Uinoi,IIUrbM,a·._.Ownpai,n,December1992,.7pp.UnilCldStileSEnvitonmenlllProcectionAacncy.-Mr.aluplepch....ys10supererrw:ie,urcfri,auan-.om",olAunosplIcricand1ndoo<AirPropuns.DRAfT,"'1Inwy1992OWENUORNING GRANVILLE TECHNICAL CENTER 2790 COLUMBUS ROAD, ROUTE 16 GRANVILLE, OHIO 43023.1200 614,587.0610



## November 9, 1993 

## H. Alan Flne, So.D. Global Change Division 

# u.s. 'E.P.A. (6202J) 401 M 

# st., sw Washington, DC 20460 

## 202-233-9094 FAX:3-9579 

## Dear Alan·: I wanted to personally thank you for all.of your efforts in getting the ERA program effort going. This software has been extremely

. helpful- in 

## convincing both ourselves and our customers of the

potential of AURA technology in refrigerators. As we both know vacuum panel technology is no longer a question of "it" but rather "when" it will be embraced by the industry. In fact, it appears that this is already happening. The ERA code has certainly helped speed up our product development efforts, and as you know speed to**~arket** 

## can make the**differen~~** 

## between success and failure. ERA puts forth all of the complexities that we face daily' into a format'that is both user friendly and accurate. Dick Godfrey in 

## our Product Technology group has just run ERA up against some**d~tailed** 

## finite element work on ANSYS**a~d** 

## has found very good agreement. I believe we could share the results of this work with you if you wish. What I personally like about ERA is that we can now talk intelligently to**cus~omers** 

## about their applications. Even if customers qon1t always agree with the exact details or outputs we have a common starting point from which to dialogue. In summary, I applaud your efforts in this very important effort. Updated versions of ERA will no doubt appear from time to time. I would like you' to add Owens-Corning to the distribution list for the new versions. For**exa~ple,** 

## I heard that version 1.2 

## may now be available with the internal freezer door. Can you send me this now or is there still a wait?

OWENs-<:ORNING FIBERGLAS CORPORATION oWENt.CORNING GRANVILLE T ECH N ICAL CENTER 279 0 COLUMBUS ROAD, ROUTE 16 GRANVILLE, OHIO 43023.1200 6\01.587 .06\0



## November 9, 1993 

## H. Alan Fi"ne, Sc.D. Global Change Division 

# u.s . E.P . A. (6202J) 401 M 

## st., SW Washington, DC 20460



## .. 202-233-9094 FAX:3-9579 

## Dear Alan · : I wanted to personally thank you for all . of your efforts in getting the ERA program effort going . This software has been extremely

. helpful' in convincing both ourselves and our customers of the

potential of AURA technology in refrigerators. As we both know vacuum panel technology is no longer a question of 

# "it" but rather "when" it will be embraced by the industry. In fact , it appears that this is already happening. The ERA code has certainly helped speed up our product development efforts, and as you know speed to**~arket** 

## can make the**differen9~** 

## between success and failure. ERA puts forth all of the complexities that we face daily · into a format that is both user friendly and accurate. Dick Godfrey in our Product Technology group has just run ERA up against some**d~tailed** 

## finite element work on ANSYS**a~d** 

## has found very good agreement. I believe we could share the results of this work with you if you wish. What I personally like about ERA is that we can now talk intelligently to**cus~omers** 

## about their applications. Even if customers qon1t always agree with the exact details or outputs we have a common starting point from which to dialogue. In summary, I applaud your efforts in this very important effort. Updated versions of ERA will no doubt appear from time to time. I would like you to add. Owens-Corning to . the distribution list for the new versions. For**exa~ple,** 

## I heard that version 1.2 

## may now be available with the internal freezer door . Can you send me this now or is there still a wait? .

OWENHORNING FIBE R GLAS CORPORATION

## H. Alan Fine November 9, 1993 

## Page 2 Lastly, we have some mirior ideas that could .make ERA even more**ver~atile** 

## than**i~** 

## already is. Can you evaluate our. ideas within your organization for possible inclusion in future versions? For example, two**ar~** 

## quite ·:simple--allowing foil thicknesses below "O.lmm to be" run with resistivities above 3.5. The third is a

little more**c6mp~ex--allow~ng** 

## the foil. thickness to vary across the panel cross section and allowing for various draft angles on the panel edge. 

## , Thanks again, Alan. Regards,

cc: Patrick Aubourg Barry Arch Ralph McGrath Warren ·"Wolf Merle McBride John Mumaw Dick Godfrey H. Alan Fine November 9, 1993 

## Page 2 

## Lastly, w e have some mirior i deas that could . make ERA 

## even more**ver~atile** 

## than**i~** 

## already is . Can you evaluate our . ideas within your organization for possible inclusion in future versions? For example, two**ar~** 

## quite · :simple--allowing foil thicknesses below

· O.lmm 

## to be· run with resistivities above 3.5. 

## The third is · a

little more**c6mp lex--allow~ng**  

## the foil .thickness to vary across the panel cross section and allowing for various draft angles on the panel edge. 

## , Thanks again, Alan. Regards,

. 

## cc: Patrick Aubourg Barry Arch Ralph McGrath Warren ·'Wolf Merle McBride John Mumaw Dick Godfrey.EONARD J. SWATKOWSK/, JR. WFlECl'OR, ENGINEERING $E.IlVICES ASSOCIATION OF HOMEAPPLIANCE MANUFACTURERS 20 NORTH WACKER DRIVE. CHICAGO,ILLINOIS 60606 3J2984"5800 EXT" 328 FAX: 3J2 98'f.!;(J23 

## September 23, 1993 Mr. H. Alan Fine Environmental Protection Agency 401 M Street, sw Washington, DC 20460 SUBJECT: Final Report from University of Illinois, Air" Conditioning arid Refrigeration Center (ACRC) Titled "Accuracy Analysis of the ADLIERA Model" Dear Alan: Attached is the final 'report of Dr. Clark Bullard's analysis of the accuracy inherent in the ERA model. "The scope**of'Dr~** 

## Bullard's analysis was limited to

non-conventional refrigerator-freezer technologies "not currently being used in mass production. An 

## initial analysis of**t~e** 

## ERA model using files from one hundred current production units showed an uncertainty 

# (± two sigma) of 

# ± 23.07%. The majority of those modesl (60 

## of the initial 100) were 'reassessed by Lawrence Berkeley Laboratory due to

mis"interpretation of ERA input protocols. The**uncert~inty** 

## on those "files changed from 

# ± 19.04' 

## (oriqinal AMAH data) to + 

## 19.10' (reassessed by LBL). While the current version of the ERA model is a vast improvement over the preceding version used in the**~993** 

## NAECA Rulemakinq,**~here ~re**  

## specific areas within the model that need considerable improvement. For**ins~~nce, serio~s**  

## errors were found**~n** 

## attempts to**simu~ate** 

## Lorenz"**Cy~le refr~geration,**  

## as well as**convent~onal** 

## refrigeration using zeotropic blends. ERA outputs using these technologies were off in some areas by as much as a factor of seven and should only be**simulat~d** 

## in the future" using compressor calorimeter outputs. Additionally, cycling losses simulated in the mode! are projected from a single bench test and differ qreatly from actual data obtained by 

## manufacturers. .EONARD J . SWATKOWSKI, JR. WAECTOR, ENGINEERING S£.IiVICES ASSOCIATION O F HOMEAPPLIANCE MANUFACTURERS 20 NORT H WACKER DRIVE. CHICAGO,ILLINOIS 60606 3J2 984-5800 EXT. 328 FAX: 3J2 984-5823 

## September 23, 1993 Mr. 8-. 

## Alan Fine Environmental Protection Agency 401 M Street, SW Washington, DC 20460 SUBJECT: Final Report from University of Illinois, Air· Conditioning arid Refrigeration Center (ACRe) Titled "Accuracy Analysis of the ADLIERA Model" Dear Alan: Attached is the final report of Dr. Clark Bullard's analysis of the accuracy iJ;'lherent in the ERA model •

. The scope of· Dr: Bullard's analysis was limited to

non-conventional refrigerator-freezer technologies

-not currently being used in mass production.

An 

## initial analysis of**t~e** 

## ERA model using files from one hundred current production units showed an uncertainty 

# (± two sigma) of 

# ± 23.07%. The majority of those modesl (60 

## of the initial 100) were

. reassessed by**L~wrence** 

## Berkeley Laboratory due to

misinterpretation of ERA input protocols. The**uncert~inty** 

## on those · files changed from 

# ± 19 . 04\ (original AMAH data) to + 

## 19.10% (reassessed by LBL). While the current version · of the ERA model is a vast improvement over the preceding version used in the**~993** 

## NAECA Rulemaking,**~here ~re**  

## specific areas . within the model that need considerable improvement. For**ins~~nce, serio~s**  

## errors .were found**~n** 

## attempts to**simu~ate** 

## Lorenz cy

_ cle**refr~geration,** 

## as well as conventi. onal refrigeration using zeotropic blends. ERA outputs using these technologies were off in some**~reas** 

## by as much as a factor of seven and should only be**simulat~d** 

## in the future . using compressor calorimeter outputs. Additionally, cycling losses simUlated in the model are projected from a single bench test: and differ greatly from actual data obtained by 

## manufacturers.ASSOCIA nON OF HOMEAPPLIANCE MANUFACTURERS 

## Mr. 

## H. Alan Fine September 22, 1993 -2- It should be noted that the ERA" model is a design --model and not a simulation model. A successful

simulation run is no**qu~rantee** 

## that a model built to that configuration would be capable of preserving food. The accuracy of the output of the ERA model, of course, is dependent upon the qualifications of "the personnel using**it~** 

## However, :the flexibility of the _model allows the simulation of aOrefrigerator-freezer

design with advanced options and has the capability

. of providing information not available from any

currently available public domain computer program. We will continue our assessment of ERA model (Version 1)**utiliz~ng·i~puts** 

## from freezer manufacturers (the**d~aft** 

## version didn't**all~w** 

## for this type of simulation). Also, wbrk being done at Arthur D. -Little (AOL) under. 

# a. DOE 

## ·contract will provide an·· updated version of. the model capable of . simulating single door refrigerators and freezers. Si;cerep<_===:h

# ,(pl'-,~~ Leonard J. 

## Swatkowski Director Engineering Services·

lJS:dmn ASSOCIA nON OF HOMEAPPLIANCE MANUFACTURERS 

## Mr . 

## H. Alan Fine September 22, 1993 -2- It should be noted that the ERA model is a design ""model and not a simulation model. A successful

simulation run is no qua:rantee that a model built to t hat confi gurat ion**ld** 

## be capable of preserving food. The accuracy of the output of the ERA model, of course, is dependent upon the qualifications of " the personnel using it;: . 

## However, :the flexibility of the "model allows the simulation of a "refrigerator-freezer

des I gn with advanced options and has the capability "of providing information not available from any

currently available public domain computer program . We will continue our assessment of ERA model (Version 1)**utiliz~ng i~puts**  

## from freezer manufacturers (toe**d~aft** 

# version didn't allow for this type of**~** 

## simulation). Also, wbrk being done at Arthur D. " Little (AOL) under "

# a. DOE 'contract will provide an' " updated version Of. the**~** 

## model capable of . simulating single door refrigerators and freezers .

IJS:dmn 

## Leonard J. 

## Swatkowski Director Engineering Services '

# Accuracy Analysis of the ADLIERA Model Prepared for Association ofHome Appliance Manufacturers NAECA Task Force Prepared 

## by Clark Bullard Associates 509 West Washington Street Urbana Illinois 61801 

## Background This report was prepared at the request ofthe NAECA Task Force of the Association ofHorne 

### Applianco Manufacturers. It 

### is part of a larger effon 

## by the 

## rask Force to quantify**t~e** 

### uncertainty associated with estimates (. energy savings obtained using the USEPA's refrigerator analysis program 

# ,

. (the ERA program). The program was developed 

## by ArthurD. Little Inc. (1992)**a~d** 

### will 

## be used 

## by'

DoE in**th~e** 

### 1998 standard-setting process. 1 

### The ERA model is an improved version of the model used 

### by DoE in setting the 1993 standards (ADL, 

### 1982). the improvements 

### dealt mainly with the user interface. and the addition ofmultizone heat exchangers, alternative refrigerants and new compressor models that do not require calorimeter . sting with a particular new refrigerant. AHAM task force members, engineers from the major refrigerator/freezer manufacruring companies, used the ERA model to petfonn the anaJyses reported here and provided all the necessary input data. 

## Purposetand scope For.many ofthe conservation measures likely to be 

### considered by USDoE when setting the 1998 NAECA energy efficiency standards, adequate test data exist and enable manufacturers to guage the credibility and certainty ofenergy savings predicted by the ERA model. However there are little or no test data available for the measures listed in Table I. Therefore DoE and other parties to the NAECA rulemaking may 

## be forced to rely almost exclusively on model-based estimates for these conservation measures. This report presents results of an effort to estimate the uncertainties associated with such model-based estimates.

1 To assist in this evaluation of the ERA model, ADL provided the AHAM Task Force members with disks containing the ERA program and input files used in the U5EPA's Draft Multiple Pathways Repon in 1992. Shortly after completion of the analysis reponed here, AHAM.'yas informed that USEPA was about to 

### release an updated version (1.0) ofthe ERA model and user's manual. Thm version was said to contain a number ofimproveme, its 

### over the version reviewed herein, but none 

### !hal would subsl..1ntially aller the conclusions and recommendations contained in this report. 

## I 

# Accuracy Analysis of the ADLIERA Model

Background Prepared for Association ofHome Appliance Manufacturers NAECA Task Force Prepared by Clark Bullard Associates 509 West Washington Street Urbana lIlinois 61801

This report was prepared at the request ofthe NAECA Task Force ofthe A ssociation ofHome 

### Applianco Manufacturers. It 

### is part of a larger effon by the rask Force to quantify the uncertainty associated with estimates f 

### energy savings obtained using the USEPA's refrigerator analysis program 

# ,

. (the ERA program). .The program was developed by ArthurD. Little Inc. (1992)**a~d** 

### will 

## he used by '

DoE in**th~e** 

### 1998 standard-setting process.! The ERA model is an improved version of the model used 

### by DoE in setting the 1993 standards (ADL. 1982). 

## the improvements dealt mainly with the user interface. and the addition of multizone heat exchangers, alternative 

### refrigerants and new compressor models that do not require caJorimetc;' . sting with a particular new refrigerant. AHAM task force members, engineers from the major refrigerator/freezer manufacruring companies, used the ERA model to perf onn the analyses reported here and provided all the necessary input data. Purpose t and scope For.many ofthe conservation measures likely to be considered by USDoE when setting the 1998 NAECA energy efficiency standards, adequate test data exist and enable manufacturers to guage the credibility and certainty ofenergy savings predicted 

## by the ERA model. However there are little or no test data available for the measures listed in Table 

## 1. Therefore DoE and other parties to the NAECA rulemaking may be 

### forced to rely almost exc1usivelY 'on model-based estimates for these conservation measures. This report presents results of an effort to estimate the uncertainties associated 

### with such model-based estimates.

1 To assist in this evaluation of the ERA model, ADL provided the AHAM Task Force members with disks containing the ERA program and input files used in the USEPA's Drnfl Multiple Pathways Report in 1992. Shortly after completion of the analysis reported here, AHAM.'yas informed that USEPA was about to 

### release an updated version (1.0) ofthe ERA model and user's manual. Thm version was said to contain a number ofimprovem eIllS over the version rev i ewed herein. but none that would substantially aller lhe conclusions and recommendations contained in this report 

## I

### • 

### Gasket im rovements 

# · Vacuum insulation • Alternative refrigerants & 

### mixtures • 

### Lorenz cycle • 

### Variable speed compressors • 

### Reduce cvcling losses 

## • Dual evaporator 

## Table 1. 

## Conservation measures considered A simple example will demonstrate the importance of quantifying the uncenainties associated with an 

## ERA 

## estimate ofenergy use. For a base case refrigerator, suppose that the model predicts' an' energy use of2.oo kWh/day, and 1.80 kWh/day after the design bas been modified to 

### incorporate a 

### conservation measure. In the absence of an uncertainty analysis, one would conclude that savings of 0.20 kWh/day could be 

### achieved. However ifthe uncertainties on both the badeline and altered 

### results" 

### are about 5%, 

### say ±G.lO 

### kWh/day, then Ihe estimated energy savings aE 

### could be 

### said to lie in 

### the interval: 

### 0 

## < till 

## < 0.4 kWh/day.2 The error. 

## ± 0.2 kWh/day, is as large as**th~** 

### original**esti~at~** 

### (nominal value) for energy savings that was obtained initially by running the model twice. This is a common problem encountered when subtracting two large numbers. especially when the large numbers are only known to three significant figures, as the ERA model is programmed to display its calculated energy use prediction.**~is** 

### example illustrates the imponance ofknowing what the uncenainties are, and how they propagate through the model to influence the results. In nonlinear models. input uncenainties and errors may 

## be !Dagnified or shrunk. and they may add

# in a worst-case fashion or cancel one another (Porter and 

### Bullard, 1992). The paucity ofdata on the effecliveness of these conservation options has another important implication. It 

### means that some of [he equations used to quantify the energy savings may not yet have been subjected to 

### rigorous validation. Therefore in the' following analysis three sources ofinaccuracy are considered: 1) uncertainties in the parameters specified as inputs to the ERA model; 2) 

### assumptions embedded in ERA's equations; and 3) terms inadvertently omitted from ERA equations. In most cases errors oftypes 

### #2 and #3 cannot 

## be quantified in this report due to lack ofdata, but in some cases it was possible to use limited proprietary data from manufacturers to lest for the presence of these types of errors. 

## Overview of methodology The general approach is straightforward. It 

### is based on the concept that one can identify independent sources oferror. Each of these errors propagates through the system (or in our case the set of 2 The maximum savings could be 

### 2.1
- 1.7 = 

### 0.4 kWh/d and lhe minimum could be 

### 1.9
- 1.9 = 

### 0 kWh/d. 

### 2 • 

### Gasket im rovements 

## • 

## Vacuum insulation • Alternative refrigerants 

### & mixtures • 

### Lorenz cycle • 

### Variable speed compressors • 

### Reduce cycling losses 

## • Dual evaporator Table 1. Conservation measures considered A simple example will demonstrate the importance of quantifying the uncenainties associated wilh an 

## ERA 

## estimate ofenergy use. For a base case refrigerator, suppose that the model predicts'an' energy use of 

## 2.00 kWh/day, and 1.80 kWh/day after the design has been modified to 

### incorporate a 

### conservation measure. In the absence of an uncertainty analysis, one would conclude that savings of 0.20 kWh/day could be 

### achieved. However ifthe uncertainties on bOlh the badeline and altered 

## results" are about 

## 5%, say 

## ±G.IO kWh/day, then the estimated energy savings 6E could be 

### said to lie in 

### the interval: 

### 0 

## <**~** 

## < 0.4 kWh/day.2 The error. 

## ± 0.2 kWh/day, is as large as**th~** 

### original**es~~at~** 

### (nominal value) for energy savings mat was obtained initially by running me model 

## twice. This is a common problem encountered when subtracting two large numbers. especially when the large numbers 

### are only known to 

### three significant figures, as the 

### ERA model is programmed to display its calculated energy use prediction.**~is** 

### example illustrates the irnponance ofknowing what the uncenainties are, and how they propogate through the model to influence the results. In nonlinear models.input uncertainties and errors may 

## be !Dagnified or shrunk. and they may add in a worst-case fashion or cancel one another (Porter and 

### Bullard. 1992). Thepaucity ofdata on 

## the effectiveness of these conservation options has another important implication. 

## It means that some of the equations used to 

### quantify the energy savings may not yet have been subjected to 

### rigorous validation. Therefore in the·following analysis three sources ofinaccuracy are considered: 1) 

### uncertainties in the parameters specified as inputs to the 

### ERA model; 2) assumptions embedded in 

### ERA's equations; and 

### 3) terms inadvertently omitted from 

### ERA equations. In most cases errors oftypes 

### #2 and 

### #3 cannot 

## be quantified in this 

### report due to lack ofdata, but in some cases 

### it was possible to use limited proprietary data from 

### manufacturers to test for the presence ofthese types of errors. Overview of methodology The general approach is straightforward. It is based on the concept that one can identify independent sources oferror. Each of these errors propagates through the system (or in our case the set of 2 The maximum savings could be 

### 2.1
- 1.7 = 

### 0.4 IcWh/d and lhe minimum could be 

### 1.9
- 1.9 = 

### 0 kWh/d. 

### 2

### nonlinear simultaneous equations describing the system) and affects the values ofthe oUiput variables (in our case we are primarily interested in the effect on only one of them, the energy use E). Since these input errors are independent, their effects can be 

### added: "the resultant uncertainty is given by a root-sum-squared equation. Given that 

## E = 

## E(XI. X2•... xn) and given the uncertainties**~X:l, ~X2,**  

### ...**~xn** 

### on each of the independent variables. then the uncertainty in E is given by 

## 6E ([(aE/aXI)i\xl12 

## + [(aWx2)i\x212 

## + ... + [(aE/axn)i\xn12j}0.S (I) 

## In our case we will define 

## I1x such that we are 95% certain that the true value ofx lies within the range x 

## ± 6.x. Then there is a 95% chance that the actual value ofE lies within the range E 

## ± dE. 

## If "these uncertainties are normally distributed, the upper and lower limits ofx may be considered to be 

### spooified at the 

# ± 2cr level. Note from 

## eq. (1) that the result will be 

### dominated by the largest term inside the [ ] because each is squared. It is therefore possible to limit the analysis to the relatively few large tenns, and to ignore the more numerous smaller ones. For example the sum of a 10% error due to one of the inputs plus twenty-one 1% errors will result in only an 11 % 

### error on E, the annual energy use.3 Therefore attention was" focused on obtaining accurate estimates of only the largest tenns contributing to the total uncertainty. This kind of analysis is called "single-sample uncertainty analysis" because it defines the range within which:"the result will lie, even if only a few measurements and variables Xi 

### are involved.4 

### The result is therefore very conservative, mainly because not enough data exist for mean values to be 

### known.5 To

.**de~ne** 

### a more realistic range on E would require two things: "1) 

### more extensive data on the energyconserving designs to 

### permit accurate estimation of the mean values of the parameters describing the improved systems; and 2) a Monte Carlo analysis in which hundreds ofhypothetical refrigerators were "constructed" from inputs Xi 

### randomly selected from "bins" containing values in the range Xi 

## ± Mi. The resulting Ei would lie within a much narrower range than E 

## ± if the errors combined so as to

. cancel one another. We will. take the simpler raot·sum-squared approach outlined above. It is

generally not advisable to start with a Monte Carlo analysis; it is better to learn first which' sources or" uncertainty are the most important to model.

3 The combined error is given by (102 

### + 11 (12)J 4 For a detailed explanation oflhis kind of unccrtainty analysis see R. 

### 1. Moffat, HDescribing uncenainties in experimental results", 

### Experimental Thermal and Fluid Science 1988: 1:3-17; or S. 

### J. Kline and F. A. McClintock, "Describing uncenainties in single-sample experiments", 

### Mech. Eng.. 3-8, January 1953. 5 It 

### is not**~s** conservative as a worst case analysis in which all inputs x were set at lh("r '.:xlreme values in such a manner that all the errors added. The appro<lch used here accounts for the fact that the ,es of uncertainty are indepcndentand are therefore unlikely LO add in a worst-case manner. 

## 3 nonlinear simultaneous equations describing the system) and affects the values of the output variables (in our case we are primarily interested in the effect on only one of them, the energy use E). Since these input errors are independent, their effects can be 

### added: " the resultant uncertainty is given by a root-sum-squared equation. Given that 

## E = 

## E(x,. X2•... 

## xn) and given the uncertainties 6Xl, Lh2, .. ' 

### AXn on each of the independent variables, then the uncertainty in E is given by 

## 6E = 

## ([(aE/ax,)t.x,12 + (aE/ax2)t.x212 + ... + (aE/axn)t.xn12]} o.S (\) In our case we will define 

## I1x such that we are 95% certain that the true value ofx lies within the range x 

## ± Ax. Then there is a 95% chance that the actual value ofE lies within the range E 

## ± AE. 

## If these uncertainties are nonnally distributed, the upper and lower limits ofx may be considered to be spooified at the

# ±**~(J** 

### level. Note from eq. (1) that the result will be 

### dominated by the largest term inside the [ ] because each is squared. It is therefore possible to 

### limit the analysis to the relatively few large tenns, and to ignore the more numerou s smaller ones. For example the sum of a 10% error due to one of the inp. uts plus twenty-one 1% errors will result in only an 11 % error on E, the annual energy use.3 Theref ore attention waS focused on obtaining accurate estimates of only the largest tenns contributing to the total uncertainty. This kind of analysis is called "single-sample uncertainty analysis" because it defines the range within

## which**the** result will lie. even ifonly a few measurements and variables Xi 

### are involved.4 

### The result is therefore very conservative, mainly because not enough data exist for mean values to 

### be known.5 To .

.**de~ne** 

### a more realistic range on E would require two things:

-1) 

### more extensive data on the energyconserving designs to 

### pennit accurate estimation of the mean values of the parameters describing the improved systems; and 2) a Monte Carlo analysis in which hundreds ofhypothetical refrigerators were "constructed" from inputs X i 

### randomly selected from "bins" containing values in the range Xi 

## ± Mi. The resulting Ej would lie within a much narrower range than E 

## ± Lffi 

## if the errors combined so as to cancel one another. We will. take the simplerroot·sum-squared approach outlined above. 

## It is generally not advisable to start with a Monte Carlo analysis; it is better to learn first which·sources o( uncertainty are the most important to model.

3 The combined error is given by (102 

### + 11(12)] 4 For a detailed explanation oflhis kind of uncertainty analysis see R. 

### 1. Moffat,**~Describing** 

### uncenainties in experimental results", Experimental Thermal and Fluid Science 1988: 1:3-17; or S. 

### J. Kline and F. 

### A. McClintOCk, "Describing uncenainties in si ngl e-sample experiments", Mech. Eng., 3-8, January 1953. 5 It 

### is not**~s** 

### conservative as a worst case analysis in which aU inputs x were set at**lh <··~**  

### '! xlreme values in such a manner that all the errors added. The appro<lch used here accounts for the facttha! the , es of uncertainly are independent and are therefore unlikely to 

### add in a worst-case manner. 

## 3

## Application to conservation options To estimate the uncertainty relating to 

### a particular conservation option, we will ignore for the moment the effect ofuncertainties on parameters describing parts ofthe system that are not changed. For example in the case of adding vacuum panels, only part of the foam is replaced. What is**releva~t** 

### ..**~o.** 

### the accuracy ofthe model is how well the mean values of the replaced foam and the vacuum panel are known. In 

### the case ofRII foam it might be 

### argued that the thermal conductivity k and the resulting Rvalue for the wall panel known, due to years of experience and extensive testing ofthis material. In fact it might 

## be reasonable to assume that .the 

## mean value is known with perfect accuracy. In 

### that case the only uncertainty introduced by the replacement offoam by vacuum panels would be 

### those associated with the thermal conductivity and thickness of the vacuum panels. Because ofthe lack of extensive testing and data, such uncertainties are analyzed using the single-sample methods described above.

. 

### For other conservation measures, however, there exists substantial uncertainty about the mean values ofparameters describing the base case design. Examples include heat exchanger conductances and gasket heat leaks. Despite years oftesting and analysis, uncertainties remain due to measurement limitations and the lack of standardized tests. For conservation measures involving these components, uncertainties 

## in the base case estimates are considered explicitly. In 

### the following subsections the conservation measures are analyzed individually for all three types of error sources: I) uncertainties in the inputs specified by the user ofthe ERA model; 2) assumptions .' 

### ..

# _. embedded in ERA's equations; and 3) tenns inadvertently omitted from ERA equations. Type I errors are quantified where possible, while the others are discussed in qualitative tenns. 

## Gasket heat leak The ERA I1'l;odel allows the user to 

### input a gasket heat leak, and it includes a calculational assist feature to calculate that figure from infonnation about the gasket material and geometry. Typical values for the main parameters affecting this calculation are shown below: Internal exposed width Internal heat transfer coefficient Cabinet skin thickness Gasket thickness 0.95 

## ± 0.25 

## em 5.0 

## ± 1.0 W/m20C 1.30 

## ± 0.38 

## mm 0.43 

## ± 0.13 mm An ERA simulation was conducted using these values. It showed that the ERA-calculated heat transfer is dominated by the first two tenns, and that the aggregate effect of all the uncertainties is about 2.6%, or about 15 kWh/y for a baseline 18 cubic foot model. These results are highly suspect for several reasons. First, conduction through the cabinet flange is**~odeled** 

### in ERA, while conduction through the door flange is apparently ignored. Second, the ERA model does not allow the user to specify the most important factors affecting gasket region heat leak, namely the relative positions of the gasket and 4 

## Application to conservation options To estimate the uncertainty relating to 

## a particular conservation option, we will ignore for the moment the effect ofuncertainties on parameters describing parts of the system that are not changed. For example in the case of adding vacuum panels, only part of the foam is replaced. What is**releva~t**

## ..**~o .**  

## the accuracy ofthe model is how well the mean values of the replaced foam and the vacuum panel are known. In 

## the case ofRli foam it might be 

## argued that the thermal conductivity k and the resulting Rvalue for the wall panel known, due to years of experience and extensive testing ofthis material. In fact it might 

## be reasonable to assume that . the 

## mean value is known with perfect accuracy. In 

## that case the only uncertainty introduced by the replacement offoam by vacuum panels would be 

## those associated with the thermal conductivity and thickness of the vacuum panels. Because ofthe lack of extensive testing and data, such uncertainties are analyzed using the single-sample methcxls described above.

. 

## For other conservation measures, however, there exists substantial uncertainty about the mean values ofparameters describing the base case design. Examples include heat exchanger conductances and gasket heat leaks. Despite years oftesting and analysis, uncertainties remain due to measurement limitations and the lack of standardized tests. For conservation measures involving these components, uncertainties in the base case estimates are considered explicitly. In 

## the following subsections the conservation measures are analyzed individually for all three types of error sources: 1) uncertainties in the inputs specified by the user ofthe ERA model; 2) assumptions .' 

### . .

# _ . embedded in ERA's equations; and 3) terms inadvertently omitted from ERA equations. Type 1 errors are quantified where possible, while the others are discussed in qualitative terms. 

## Gasket heat leak The ERA model allows the user to 

## input a gasket heat leak, and 

## it includes a calculational assist feature to calculate that figure from infonnation about the gasket material and geometry. Typical values for the main parameters affecting this calculation are shown below: Internal exposed width Internal heat transfer coefficient Cabinet skin thickness Gasket thickness 

## 0.95 

## ± 0.25 em 5.0 

## ± 1.0 W/m20C 1.30 

## ± 0.38 mm 0.43 

## ± 0.13 mm An ERA simulation was conducted using these values. It showed that the ERA-calculated heat transfer is dominated by the first two terms, and that the aggregate effect of all the uncertainties is about 2.6%, or about 15 kWh/y for a baseline 18 cubic foot model. These results are highly suspect for several reasons. First, conduction through the cabinet flange is I,llodeled in ERA, while conduction through the door flange is apparently ignored. Second, the ERA model does not allow the user to specify the most important factors affecting gasket region heat l eak, namely the relative positions ofthe gasket and 4

### flanges. 

### It appears that ERA attempts to account for most of the heat gain through the door edge 

### region as direct heat transfer through the gasket, while in fact conduction through the sheet metal flanges is the critical factor. Aynn, et al. (1992) confinned this fact by demonstrating through finite element modeling that it is the interaction between the flanges and the gasket, rather than the dimensions ofeither, that detennine the heat transfer through the door edge region. ERA only allows the user to 

### change the dimensions of the flanges and gasket, not to change their interactions in the ways demonstrated by Flynn, et. a1.. The work ofBoughton et. 

## aI. (1992) and that ofFlynn, et. al. (1992) indicate that simply changing gasket

. dinlension.s.could yield savings greater or less than the magnitude predicted by ERA, depending on the

extent to which the flanges protrude past the edge ofthe gasket into the refrigerator. 

## If as the ERA users manual states, the gasket heat leak calculations do in fact yield accurate results for the base case, there is no gUarantee that calculations ofenergy saVings due ·to redesign will be correct For example if the steel flange protrudes past the gasket, most of the heat will travel through the flange and warm the internal eXflOsed surface ofthe gasket. On the other hand if the flange tenninates halfway through the gasket the internal exposed surface of the gasket will be 

### much colder, and the heat transfer through the gasket itself will be much larger. The energy savings due to changing**th~** 

### gasket material, its internal exposed width, or the flange thickness will differ greatly among these cases, which cannot 

## be distinguished by ERA. ERA users must also be 

### aware of other interactions besides those addressed by Flynn, el. aL{l992), who concentrated mainly on the extent to which the gasket overlapped the ends of the metal flanges. Heat leaks through the gasket and the sheet meta} flanges may 

## be exacerbated by the presence of mulli.on heaters and anti-sweat heaters, which are modeled independently in ERA. Also, threedimensional heat transfer occurs wherever the sheet metal door or cabinet skin protrudes imo the cold interior to provide for the magnetic door seal. The wall heat transfer equations in ERA do not account for this 3-D effect, which will lower the temperature of the outer skin and thereby reduce 2-D heat transfer through the wall. Since ERA apparently ignores conduction throul!h the door flange, a crude approach to modeling ihis effect using ERA would be 

### to add this value to I 

### user-specified gasket heat leak, and use that instead of the calculational assist. Another pathway for heat gain through**the~sket** 

### region, air infiltration, is also ignored in the ERA model. Manufacturers report that this factor is highly variable, and contributes significantly to the total gasket-region heat gain of 20 to 25% of total cabinet heat load. (Note that this percentage was applicable to 1990-vintage cabinets; it could be proportionately larger for 1993 or vacuum-panel cabinets in the futurt.) A crude way to account for air infiltration USing the ERA model would be 

### to 

## 5 flanges. It 

### appears that ERA attempts to account for most of the heat gain through the door edge region as direct heat transfer through the gasket, while in fact conduction through the sheet metal flanges is the critical factor. Aynn. et al. (1992) continued this fact by demonstrating through finite element modeling that 

### it is the interaction between the flanges and the gasket, rather than the dimensions ofeither. that detennine the heat transfer through the door edge region . ERA only allows the user to 

### change the dimensions of the flanges and gasket, not to change their interactions in the ways demonstrated by Flynn. et. a1.. The work ofBoughton et. 

## aI. (1992) and that ofAynn, et. al. ( 1992) indicate that simply changing gasket

. dimension. s.could yield savings greater or less than the magnitude predicted by ERA. depending on the extent to which the flanges protrude past the edge ofthe gasket into the refrigerator. 

## If as the ERA users manual states. the gasket heat leak calculations do in fact yield accurate results for the base case. there is no guarantee that calculations ofenergy saVings due·to redesign will be correct For example if the steel flange protrudes past the gasket, most of the heat will travel through the flange and warm the internal eXJ'Osed surface ofthe gasket. On the other hand if the flange terminates halfway through the gasket the internal exposed surface ofthe gasket will be 

### much colder, and the heat transfer through the gasket itself will be much larger. The energy savings due to changing thl? gasket material. its internal exposed width. or the flange thickness will differ greatly among these cases, which cannot 

## be distinguished by ERA. ERA users must also be 

### aware of other interactions besides those addressed by Flynn, et. al.-{l992), who concentrated mainly on the extent to which the gasket overlapped the ends of the metal flanges. 

# . Heat leaks through the gasket and the sheet metal flanges may 

## be exacerbated by the presence of

. mulli.on heaters and anti-sweat heaters, which are modeled independently in ERA. Also, threedimensional heat transfer occurs wherever the sheet metal door orcabinet skin protrudes into the cold interior 10 provide for the magnetic door seal. The wall heat transfer equations in ERA do not account for this 3-D effect, which will lower the temperature of the outer skin and thereby reduce 2
-D heat transfer through the walL Since ERA apparently ignores conduction throllQ"h the door flange, a crude approach 10 modeling ihis effect using ERA would be 

### to add this value to , user-specified gasket heat leak, and use that instead of the calculational assist. Another pathway for heat gain through**the~sket** 

### region. air infiltration, is also ignored in the ERA model. Manufacturers report that this factor is highly variable, and contributes significantly to the total gasket-region heat gain of 20 to 25% of total cabinet heat load. (Note that this percentage was applicable to 1990-vintage cabinets; it could 

## be proportionately larger for 1993 or vacuum-panel cabinets in the future.) A crude way to account for air infiltration using the ERA model would be 

### to 

## 5

### specify some "equivalent number ofdoor-openings." Note also that heat leaks occuring on the DoE test involve relatively dry 90°F air, while in actual refrigerators the infiltrating air will be somewhat cooler but weuer thereby increasing defrost energy. The reports by Flynn, et. al. and Boughton et al. were based on laboratory studies aimed at isolating gasket-region heat leaks from the remainder ofthe c.abinet loads. The more typical situation, however, is that a manufacturer will test an entire cabinet and compare the result to the ERA prediction. One manufacturer did this, using the ERA calculational assist to quantify the gasket-region contribution, and compared the totals. The results are shown in the Table below. Model Cabinet Heat Leak Type (w/o 

### Fans, Defrost, Door Energy Usage ofCabinet and System And Size Openings, Etc.) (Fully modeled) (Watts) (kWh/dav) (Actual
- Predicted)/ Actual Predicted Actual % Error 

## (%) Top' Mount 

## 21.2 1.71 

## 2.37 27.8 15 Cu. Ft. Side-By-Side 

## 24.4 2.37 3.11 23.8 20 Cu. Ft. Side-By-Side 

## 25.3 2.57 3.39 24.2 24 Cu. Ft.



## Vacuum panel insulation A quantitative analysis using ERA was conducted by one manufacturer for a particular configuration of vac_uum panels in a refrigerator having a baseline energy consumption of 686 kWh/yo**E~ergy** 

### savings. of 106 kWh/y due to 

### the vacuum panels were estimaled by the model. UnceI1ainries about the enclosure thickness (± 

### 18%) and panel reSistivity (± 

### 10%) combined to place the result in the 

## following range: 97 

## < 106 

## < 115 kWh/yo This preliminary result was based on the assumption that the mean value of the foam resistivity (R = 

### '0.58 m2_oC/W-cm) was known with perfect certainty. 'While this may arguably be 

### true for Rll foam (individual panels may vary due 10 

### manufacturing tolerances etc. but the mean is by now well known) the same may not be 

### true for non-CFC foams. IfDoE were 10 

### simply use a laboratory teSI result for a new (R141 b) foam 10 

### calculate energy savings, Ihe input value ofk might be in error by as much as 

## ± 10% because ofyet-unknown differences between laboratory specimens and actual blowing around vacuum panels; the difference between laboratory test temperatures (75°F) and actual temperatures of foam in a refrigerator operating in a 90°F test chamber, elc. Factoring this unceI1ainty into 

## both the base-case and vacuum·panel refrigerator changes the result dramatically to 75 

## < 106 

## < 137 kWh/yo


## 6 specify some "equivalent number ofdoor-openings." Note also that heat leaks occuring on the DoE test involve relatively dry 90°F air, while in actual refrigerators the infiltrating air will 

## be somewhat cooler but wetter thereby increasing defrost energy. The reports by Flynn, et. al. and Boughton et al. were based on laborat ory studies aimed at isolating gasket-region heat leaks from the remainder ofthe c, abinet loads. The more typical situation, however, is that a manufacturer will test an entire cabinet and compare the result to th
- e ERA prediction. One manufacturer did this, using the ERA calculational assist t o quantify the gasket-region contribution, and compared the totals. The results are shown in the Table below. Model Cabinet Heat Leak Type (w/o 

### Fans, Defrost, Door Energy Usage ofCabinet and System And Size Openings, Et c.) (Fully modeled) (Watts) (kWh/day) (Actual
- Predicted)/ Actual Predicted Actual % 

### Error 

## (%) Top' Mount 

## 21.2 1.71 2.37 27.8 IS Cu. Ft. Side-By-Side 

## 24.4 2.37 3.1 1 23.8 20 Cu. Ft. Side-By-Side 

## 25.3 2.57 3.39 24.2 24 Cu. Ft.



## Vacuum panel insul ation A quantitative analysis using ERA was conducted by one manufacturer for a particular configuration of vac.uum panels in a refrigerator having a baseline energy consumption of 686 kWh/yo**E~ergy** 

### savings . of 106 kWh/y due to 

### the vacuum panels were estimat ed by the model. UnceI1ainries about the enclosure**t~ickness** 

### (± 

### 18%) and panel reSistivity (± 

### 10%) combined to place the result in the 

## following range: 97 < 106 < liS kWh/yo This preliminary result was based on the assumption that the mean value of the foam resistivity (R =



### · 0.58 m2-oC/W-cm) was known with perfect certainty.
- While this may arguably be 

### true for Ril foam (individual panels may vary due to manufacturing tolerances etc. but the mean is by now well known) the same may nor be true for non-CFC foams. IfDoE were to simply use a laboratory test result for a new (R 141 b) foam to calculate energy savings, the input value ofk might be in error by as much as 

## ± 10% because ofyet-unknown differences between laboratory specimens and actual blowing around vacuum panels; the difference between laboratory test temperatures (.75°F) and actual temperatures of foam in a refrigerator operating in a 90°F test chamber; etc. Factoring this unceI1ainty into 

## both the base-case and vacuum·panel refrigerator changes the result dramatically to 75 

## < 106 

## < 137 kWh/yo


## 6

### Comparison of these results illustrates another potential source oferror: careless extrapolation of limited test data by the analyst running the ERA model. The 

## ± 10% uncertainty On foam conductivity may be 

### reduced considerably over time as more is learned about the process of foaming around vacuum panels, the temperature dependence of k-values, and other characteristics of foams made.with non-CFC blowing agents. Until these unce11ainties are resolved, the uncertainty analysis must address all three parameters (panel resistivity; enclosure thickness; foam resistivity); the lauer cannot 

## be neglected as in the case of Rll-blown foam. Other uncertainties unique to vacuum panels cannot be 

### analyzed quantitatively using the ERA model. For example the "bimetallic effect" of a vacuum panel in a door may cause some warping of the door and lead to increased air infiltration. Data from one manufacturer indicates the existence of such an effect, but much more data would be required t.o quantify it. The ERA model would then need to be 

### modified to account for the resulting infiltration through the gasket region. Heat leaks through the gasket region are also underestimated by the ERA model, as described in the previous section. 

## It was suggested that an estimate of heat conduction through the sheet metal door flange could be 

### included in the user-specified gasket heat leak. However if this were done, 

## and the model were then used to estimate energy savings due to vacuum panels, the energy savings would be overestimated because heat flux through the flange would increase. The vacuum panels (or any other kind ofincreased wall insulation) would increase the tempcrarure ofthe sheet metal to 

### a level approaching approaching that ofthe test chamber, whHe the temperature inside the refrigerator remai.ned constant. The higher temperature differential would cause more heat to be 

### transferred through the flange than in the base case without vacuum panels. Preliminary tests conducted by this manufacturer for fou·r configurations showed that ERA-predicted energy savings exceeded measured. energy savings by 18%,20%,47% and 60%, respectively. Part of these differences may 

## be attributable to 3-D effects such as flange heat leaks not modelled by ERA, while the rest is probably attributable to the factors quantified above. This kind ofthree-dimensional effect, ignored in ERA, can be 

### analyzed using a much more complex finite-difference'model. One manufacturer did so for two configurations and found that ERA under: predicted energy savings by 73% and 74%, respectively. A laboratory test was then conducted for one ofthe refrigerators, and the actual savings were actually 60% greater than predicted by ERA. The lesson here is that more accurate 3-D models can guide the placement ofvacuum panels to maximize 3- D energy savings and minimize 3-D energy losses. The fact remains, however, that the crude assumptions in the ERA model may combine with uncertain input parameters to greatly overestimate or underestimate the energy savings achievable with vacuum panels.



## 7 Comparison of these results illustrates another potenrial source oferror: careless extrapolation of limited 

## test dam by the analyst running the ERA model. The 

## ± 10% uncertainty on foam conductivity may be 

## reduced considerably over time as more is learned about the process of foaming around vacuum panels, the temperature dependence ofk-values, and other characteristics of foams made.with non-CFC blowing agents. Until these unce11ainties are resolved, the uncertainty analysis must address all three parameters (panel resistivity; enclosure thickness; foam resistivity); the latter cannot 

## be neglected as in the case of Rll-blown foam. Other uncertainties unique to vacuum panels cannot be 

## analyzed quantitatively using the ERA model. Forexample the "bimetallic effect" of a vacuum panel in a door may cause some warping of the door and lead to increased air infiltration. Data from one manufacturer indicates the existence of such an effect, but much more data would be required t.o quantify it. 

## The ERA model would then need to be 

## modified to account for the resulting infiltration through the gasket region. Heat leaks through the gasket region are also underestimated by the ERA model, as described in the previous section. 

## It was suggested that an estimate of heat conduction through the sheet metal door flange could be 

## included in the user-specified gasket heat leak. However if this were done, and 

## the model were then used to estimate energy savings due to vacuum panels, the energy savings would be overestimated because heat flux through the flange would increase. The vacuum panels (or any other kind ofincreased wall insulation) would increase the tempcrurure ofthe sheet metal to 

## a level approaching approaching that ofthe test chamber, while the temperature inside the refrigerator remai,ned constant. The higher temperature differential would cause more heat to be 

## transferred through the flange than in the base case without vacuum panels. Preliminary tests conducted by this manufacturer for fou' r configurations showed that ERA-predicted energy savings exceeded measured. energy savings by 

## 18%,20%,47% and 

## 60%, respectively. Part of these differences may 

## be attributable to 3-D effects such as flange heat leaks not modelled by ERA, while the rest is probably attributable to the factors quantified above. This kind of three-dimensional effect, ignored in ERA, can 

## be analyzed using a much more complex finite-difference'model. One manufacturer did so for two configurations and found that ERA under: predicted energy savings by 73% and 74%, respectively. A laboratory test was then conducted for one ofthe refrigerators, and the actual savings were actually 60% greater than predicted by ERA. The lesson here is that more accurate 3
-D models can guide the placement ofvacuum panels to maximize 3- D energy savings and minimize**3~D** 

## energy losses. The fact remains, however, that the crude assumptions in the ERA model may combine with uncenain input parameters to greatly overestimate or underestimate the energy savings achievable with vacuum panels.



## 7

### Alternative refrigerants and mixtures The thennooynamic property data used by ERA are the CSD equations of state obtained from NIST REFPROP 3 program (Morrison and McLinden, 1986). They could be a significant source of uncertainty because they are relatively crude equations requiring only minimal experimental data..., . They were used in ERA because unlike other more accurate equations of state they can be easily combined to 

### approximate the propenies of mixtures. However ERA uses them for pure fluids as well. Preliminary comparisons have shown that the latent enthalpy ofR-134a predicted by the CSD equations of state to contain to 

### vary by about 1 to 4% from the Martin-Hou and Benedict-Webb-Rubin (BWR) equarions. 6 

### Similar discrepancies are found in the near-superheat regime. The magnitude of' these errors were confirmed by NIST (Gallagher, 1993) who estimated that: the CSD equations estimate the vapor pressure curve quite accurately (±O.2%); for latent enthalpy errors 

## in the 3-5% range are.entirely possible; and that the NIST BWR equations are the most**accurat~** 

### for R-134a. Therefore the only way to 

### remove this source of uncenainty from the model is to replace the CSD 

# , equations of state by the NlST BWR equations when simulating systems using R- t]4a. Similar errors may exist for other pure refrigerants. Note that this error tends not to 

### be randomly distributed about a mean. but introouces a clear bias in the positive direction. The direction may be differen! for other refrigerants. The inaccuracy of the latent enthalpy data for R-134a will propagate through the ERA model to 

### affect its estimates of annual energy use almost proportionately. That is, a 1% error in latent enthalpy at the evaporator temperature will cause ERA to alter the run time and hence the energy use by an equal amount.· There·will be some second-order effects in the compressor model and due to the way**l~** 

### which ERA handles cycling losses, but these are probably"insignificant compared to the 1% error in annual energy use that could result from inaccuracies in the property data at the evaporating temperature. Similarly, R 

### 4% error in latent enthaJpy at die condensing temperature will alter the.6.T R! 

### the condenser (and therefore the EER) as the model holds (he user-specified values ofUA and subcooling constant. Additional errors will be introduced when ERA is used to simulate mixtures ofrefrigerants. The interaction coefficients in the NIST propeny routines are intended to account for such factors as zeotropic behavior. No quantitative analysis ofthe associated uncertainty could be conducted, however, because of a lack of data on .the uncenainty ofthe interaction coefficients themselves, and on**-~** 

### latent enthalpy and other key properties ofthe refrigerants most likely to be used in mixtures for refrigerator-freezers. 6 For example at a condensing temperaLure of**~30°F** the CSD equations' value for latent enthalpy is about 4% larger than the value given by the MarLin-Hau equaLions of state. At an evaporating temperature of _20°F the error is about 1

### %. 

## 8 Alternative refrigerants and mixtures The thennooynamic property data used by ERA are the CSD equations of state obtained from NIST REFPROP 3 program (Morrison and McLinden, 1986). They could be a significant source of uncenainty because they are relatively crude equations requiring only minimal experimental data.. ... They were used in ERA because unlike other more accurate equations of state they can be easily combined [0 

### approximate the properties of mixtures. However ERA uses them for pure fluids as well. Preliminary comparisons have shown that the latent enthalpy ofR-134a predicted by the CSD equations of state to contain to vary by about 1 to 4% from the Martin-Hou and Benedict-Webb-Rubin (BWR) equations. 6 

### Similar discrepancies are found in the near-superheat regime. The magnitude of · these errors were confumed by NIST (Gallagher, 1993) who estimated that: the CSD equations estimate the vapor pressure curve quite accurately (iO.2%); for latent enthalpy errors 

## in the 3-5% range are. entirely possible; and that the NIST BWR equations are the most accurate: for R-134a. Therefore the only way to 

### remove this source of uncertainty from the model is to replace the CSD 

# , equations of state by' the NIST BWR equations when simulating systems using R- t34a. Similar errors may exist for omer pure refrigerants. Note mat this error tends not to 

### be randomly distributed about a mean , but introduces a clear bias in the positive direction. The direction may be differen! for other refrigerants. The inaccuracy of the latent enthalpy data for R·134a will propagate through the ERA model to 

### affect its estimates of annual energy use almost proportionately. That is, a 1% error in latent enthalpy at the evaporator temperature will cause ERA to alter the run time and hence the energy use by an equal amount. · There ·will be some second-order effects in the compressor model and due to the way

## l~ which ERA handles cycling losses, but mese are probably"insignificant compared to the 1% error in annual energy use that could result from inaccuracies in the property data at the evaporating temperature. Similarly, a 4% error in latent enth"aJpy at die condensing temperature will alter the.aT a! the condenser (and therefore the EER) as the model holds the user-specified values ofUA and subcooling constant. Additional errors will be introduced when ERA is used to simulate mixtures ofrefrigerants. The interaction coefficients in the NIST property routines are intended to account for such factors as zeotropic behavior. No quantitative analysis of me associated**un~ertainty** 

### could 

## be conducted, however, because of a lack of data on .the uncertainty ofthe interaction coefficients themselves, and on**-~** 

### latent enthalpy and other key properties ofthe refrigerants most likely to be used in mixtures for refrigerator-freezers. 6 Forexample at a condensing temperaLure of !30°F the CSD equations' value for latent enthalpy is about 4% larger than the vaJue given by the Martin-Hou equations of slate. At an evaporating temperature of _20°F the error is about 1

### %. 

## 8

## The ERA model's ability to deal with alternative refrigerants and mixtures is further limited by inadequacies in the compressor models (see below). Reliable results can probably only be based on maps ofcompressor calorimeter data obtained with the refrigerant or blend in question. 

## Lorenz cycle Efforts to conduct an uncertainty analysis of the Lorenz cycle feature of the ERA model began with a simple" attempt to compare mooel results to the results of a test conducted by one manufacturer using a mixture of 65% R22 and 35% R141b. The energy savings estimated by ERA were discarded as not credible because the program predicted temperature glides of only O.2°e and 1.2°e for the condenser' and evaporator, respectively. These differed greatly from the glides of30°C and 37°C predicted by the REFPROP program from NIST. The Task Force member conducting the analysis reported that the resubs did not change when the interaction coefficient from REFPROP was entered into the ERA program. A second apparent error in the ERA program was discovered when examining the effect of heat exchanger geometry. To fully exploit the thennodynamic benefits of the Lorenz cycle a counterflow heat exchanger is required. However due to the difficulty of achieving this goal 

## in practice given the packaging constraints in refrigerator/freezers, an attempt was made to compare ERA's estimates of the perfonnance ofcrosstlow and counterflow designs. The starting point was input file B6_05LRZ.ERA which was used by USEPA (1992) in its "multiple pathways" repon on super efficient refrigerators: Strangely, that input file specified crosstlow rather than counterflow heat exchangers. When the inputs were changed to counterflow and the program re-run, the resulting estimate ofenergy use was identical. Both of these findings indicate the presence of at least one serious error in the ERA program, or at a minimum a serious problem with the user interface that would allow experienced designer to make data input errors that would lead to such erroneous results. The error(s) in the program might conceivably have a common cause, because in the absence of a temperature glide one would expect to 

## see no significant difference between the perfonnance ofcrossflow and counterflow geometries at the

. specified design condition (minimal superheat or subcooling).

Because ofthese problems with ERA's ability to properly mooel the behavior ofmixtures and the effect ofcounterflow heat exchanger geometries, the uncenainty analysis was tenninated at this point. There is also cause for concern about approximations made by ADL in calculating the effectiveness of heat exchangers in the Lorenz cycle. The equation for effectiveness depends critically on the ratio of heat capacities (product ofmass flow and specific heat) ofthe refrigerant and air streams. ERA 

## 9 TheERA model's ability to deal with alternative refrigerants and mixtures is further limited by inadequacies in the compressor models (see below). Reliable results can probably only be based on maps ofcompressor calorimeter data obtained with the refrigerant or blend in question. Lorenz cycle Efforts to conduct an**unc~rtainty** 

### analysis ofthe Lorenz cycle feature of the ERA model began with a simple'attempt to 

### compare model results to the results of a test conducted by one manufacturer using a mixture of 65% R22 and 35% 

## RI4Ib. The energy savings estimated by ERA were discarded as not credible because the program predicted temperature glides of only 

## O.2°e and 

## I .2°e for the condenser and evaporator, respectively. These differed gready from the glides of 30°C and 37°C predicted by the REFPROP program from NIST. The TaskForce member conducting the analysis reported that the resuhs did not change when the interaction coefficient from REFPROP was entered into the ERA program. A second apparent error in the ERA program was discovered when examining the effect of heat exchanger geometry. To fully exploit the thennodynamic benefits ofthe Lorenz cycle a counterflow heat exchanger is required. However due to the difficulty of achieving this goal 

## in practice given the packaging constraints in refrigerator/freezers, an auempt was made to compare ERA's estimates ofthe performance ofcrossflow and counterflow designs. The starting point was input file B6_0SLRZ.ERA which was used by USEPA (1992) in its "multiple pathways" report on super efficient refrigerators, Strangely, that input file specified crossflow rather than counterflow heat exchangers. When the inputs were changed to counterflow and the program re-run, the resulting estimate ofenergy use was identical. Both of these findings indicate the presence of at least one serious errorin the ERA program, or at a minimum a serious problem with the user interface that would allow experienced designer to make data input errors that would lead to such erroneous results. The error(s) in the program might conceivably have a common cause, because in the absence of a temperature glide one would expect to 

### see no significant difference between the performance of crossflow and counterflow geometries at the

. specified design condition (minimal superheat or subcooling).

Because ofthese problems with ERA's ability to properly mooel the behavior ofmixtures and the effect ofcounterflow heat exchanger geometries, the uncenainty analysis was tenninated at this point. There is also cause for concern about approximations made by ADL in calculating the effectiveness of heat exchangers in the Lorenz cycle. The equation for effectiveness depends critically on the ratio of heat capacities (product ofmass flow and specific heat) ofthe refrigerant and air streams. ERA 

## 9

## calculates this ratio using an average specific heat which it determines from refrigerant inlet and outlet enthalpies and temperatures. However the actual value ofthis specific heat can vary by as much as a factor of seven or more through the heat exchanger (Conklin" and Vineyard, 1992), depending on the refrigerant mixture selected. This in turn 

## affects the ratio of heat capacities by the same factor. !f.Jhe effectiveness ofthe heat exchanger is small, this error in the ratio of heat capacities will have only a small effect on the comparison between crossflow and counterflow designs. On the other hand if the effectiveness is large, substantial errors may be introduced into comparisons ofcrossflow and counterflow geometries. Other simplifying assumptions made in the 

## ERA model will also introduce uncertainties into estimates ofenergy savings achievable through the Lorenz cycle.**~ey** 

## were id.entified in the User's Manual" (ADL, 1992); they are not addressed in detail here because the accuracy analysis was terminated at an earlier stage for the reasons stated above. For example, the heat transfer correlations used to calculate conductance were originally determined for pure fluids, and**s~ould** 

## not be used for refrigerant mixtures because they are known to behave very differently. Finally the ERA program skirts the major design problem associated with Lorenz cycle refrigerators-- cabinet temperature control. If evaporator areas are optimized for a particular design operating condition, compartment temperatures could float to (cold) levels that would waste energy or (wann) levels that would spoil food, depending on climate and door-opening conditions experienced under actual operating conditions. Both of ERA's "control" options, involving the discharge offree.zer to the fresh food compartment or bypassing pan of the evaporator 

## area, would waste energy relative'to the nominal condition at which the evaporators were designed to operate. 

## Variable-s pee d comp 

## resso rs Recent developments in electric motor technology have created the opponunity for using variablespeed drives on compressors as well as the fans that move air over heat exchangers. A variable-speed compressor could eliminate cycling losses, track loads induced by usage patterns and climate, and increase operating efficiency by reducing condensing temperatures and increasing evaporating temperatures, That is one reason for developing [he capability for modeling such equipment. A second reason for developing better ways ofmodeling compressors is to 

## be able to predict a given compressor's perfonnance with alternative refrigerants. Since compressor map equations are both compressor- and refrigerant-specific, the ERA model includes two other compressor models. Both require the user to input such physical parameters as displacement volume and speed (rpm), which are needed [0 

## predict how a particular compressor will perfornl with a**variable~speed** 

## drive, or with an alternative refrigerant having a different specific volume and other thennodynamic properties. 

## 10 calculates this ratio using an 

## average specific heat which it determines from refrigerant inlet and outlet 

## enthalpies and temperatures. However the actual value ofthis specific heat can vary by as much as a factor of seven or more through the heat exchanger (Conklin·and Vineyard, 1992), depending on the refrigerant mixture selected. This in tum affects the ratio of heat capacities by the same factor. tUlle effectiveness ofthe heat exchanger is small, this error in the ratio of heat capacities will have only a small effect on the comparison between crossflow and counterflow designs. On the other hand if the effectiveness is large, substantial errors may 

## be introduced into comparisons ofcrossflow and counterflow geometries. Other simplifying assumptions made in the ERA model will also introduce uncertainties into estimates ofenergy savings achievable through the Lorenz cycle.**~ey** 

## were id. entified in the User's Manual . (ADL, 1992); they are not addressed in detail here because the accuracy analysis was terminated at an earlier stage for the reasons stated above. For example, the heat transfer correlations used to calculate conductance were originally detenruned for pure fluids, and**s~ould** 

## not be used for refrigerant mixtures because they are known to behave very differently. Finally the ERA program skirts the major design problem associated with Lorenz cycle refrigeratorscabinet temperature control. Ifevaporator areas are optimized for a particular design operating condition, companment temperatures could float to (cold) levels that would waste energy or (wann) levels that would spoil food, depending on climate and door-opening conditions experienced under actual operating conditions. Both of ERA's "control" options, involving the discharge offree. zer**~U::** 

## to the fresh food companment or bypassing pan of the evaporator area, would waste energy relative'to the nominal condition at which the evaporators were designed to operate. Variable-sJ5eed compressors Recent developments in electric motor technology have created the opportunity for using variablespeed drives on compressors as well as the fans that move air over heat exchangers. A variable-speed compressor could eliminate cycling losses, track loads induced by usage patterns and climate, and increase operating efficiency by reducing condensing temperatures and increasing evaporating temperatures. That is one reason for developing [he capability for modeling such equipment. A second reason for developing better ways ofmodeling compressors is to be 

## able to predict a given compressor's perfonnance with alternative refrigerants. Since compressor map equations are both compressor- and refrigerant-specific, the ERA model includes two other compressor models. Both require the user to input such physical parameters as displacement volume and speed (rpm), which are needed to predict how a particular compressor will perfornl with a variable-speed drive, or with an alternative refrigerant having a different specific volume and other thennooynamic properties. 10

## Compressor rating poine model The rating point model requires the user to input the EER only at a single rating point, and then proceeds to calculate its perfonnance lhroughoUl the 'map' range of evaporating and condensing pressures. However these calculatio.ns are based on empirical correlations obtained for compressors using R-12. Since the slopes of the compressor perfonnance maps v3!Y. . significantly for different refrigerants, one would not expect the ERA rating point madelto yield accurate results for anything but R-12. One Task Force member simulated two refrigerators using an actual compressor map obtained with R-134a, and repeated the simulations using lhe ERA rating point model. The energy requirements predicted by the rating point model were 5% and 8% lower than those predicted using the map-based model. It is difficult to draw a generalized conclusion from this limited infonnation. However it is clear that this data, shown in the table below, provides no evidence·· . that the rating point model is as accurate as the more widely accepted map-based models.

. . 

# . NonnaJized RunTime Operating Capacity Operating EER Energy % 

## Btu/h Btu/hIW Top Mount 19 Cu. Ft. Compressor 1.0 48.U 667 4.75 map method Rating point 0.948 5U 613 5.12 model**~lde.bY~lde** 

## 22 Cu. Flo Compressor 1.0 4'.4 82<> 5.u5 mao method Rating pOlnt 0.'20 51.0 77<> 5.43 model



## _ Compressorphysical model ADL's documentation of the compressor physical model was reviewed

by Task Force members who design compressors, in anticipation ofconducting a detailed accuracy analysis. The ERA model requires the user to specify, among other parameters, an "isentropic compression efficiency" which appears to 

## refer to 

## a parameter known in lhe industry as "piston work isentropic compression efficiency". This parameter equals the standard "isentropic compressor efficiency" defined in thennodynamics texts, modified for motor losses and friction and windage losses. In addition, the ERA model demands that the user specify input parameters that differ from the standard parameters familiar to designers (e.g. motor-pump efficiency; can loss as percent ofpower; discharge line loss). Because ofthe industry's unfamiliarity with these parameters and resultant lack ofreliable data, Task Force members concluded that the uncertainty on these input parameters would introduce an intolerable amount oferror into the ERA simulation. They suggested that a more accurate 

# .;;., approach would be 

## to simply specify the standard "isentropic compressor efficiency" as the input parameter that would be 

## used to calculate the power required.

II 

## Compressor rating poine model The rating point model requires the user to input the EER only at a single rating point, and then proceeds to calculate its performance throughout th e 'map' range of evaporating and condensing pressures. However these calculatio. ns are based on empirical correlations obtained for compressors using R-12. Since the slopes of the compressor performance maps v3!Y.. . significantly for different refrigerants, one would not expect the ERA rating point model to yield accurate results for anything but R- 12. One Task Force member simulated two refrigerators using an actual compressor map obtained with R-134a, and repeated the simulations using the ERA rating point model. The energy requirements predicted by the rating point model were 5% and 8% lower than those predicted using the map-based model. It is difficult to draw a generalized conclusion from this limited infonnation. However 

## it is clear that [his data, shown in the table below, provides no evidence·· . that the rating point model is as accurate as the more widely accepted map-based models.

. . 

# . Normalized RunTime Operating Capacity Operating EER Energy _ % 

## Btulh Btu/hIW 

# '!:op Mount 19 Cu. Ft. Compressor 1.0 48.U 667 4.75 map method Rating pomt 0.948 5U 613 5 .12 model**~!de-bY~lde** 

## 22 Cu. Ft. Compressor 1.0 4,.4 82<> 5 .u5 map method Rating pmot 0.,20 51.0 77<> 5.43 model**~** 

## Compressorphysical model ADL's documentation of the compressor physical model was reviewed by Task Force members who design compressors, in anticipation ofconducting a detailed accuracy analysis. The ERA model requires the user to specify, among other parameters, an "isentropic compression efficiency" which appears to 

## refer to 

## a paramet er known in the indusoy as "piston work isentropic compression efficiency". This parameter equals the standard "isentropic compressor efficiency" defined in thermodynamics texts, modified for motor l osses and friction and windage losses. In addition, the ERA model demands that the user specify input parameters that differ from the standard parameters familiar to designers (e.g. motor-pump efficiency; can loss as percent ofpower, discharge line loss). Because ofthe indusoy's unfamiliarity with these parameters and resultant lack ofreliable data, Task Force members concluded that the uncenainty on these input parameters would introduce an intolerable amount oferror into the ERA simulation. They suggested that a more accurate 

## ..;;..

, . approach would be 

## to simply specify th e standard "isentropic compressor efficiency" as the input parameter that would be 

## used to calculate the power required.

II

### In 

### contrast to power inpUl, the compressor mass flow rate is**compute~** 

### in-ERA's "compressor physical model" in a much more srraightforward manner. 

### It follows directly from the user-specified values of displacement, clearance volume, rpm and a relation between volumetric effi.ciency and pressure ratio that is hard-wired into the program. This type of model places most ofthe burden on the user tQ.

__. _ supply the correct inputs, but there are still uncertainties about the accuracy of the volumetric efficiency formula and its applicability to alternative refrigerants. The greatest uncertainty, however, is tied into the extremely complex heat transfer phenomena that occur inside the compressor shell between the exit ofthe suction line and the suction port of the cy1inder itself (in a reciprocating compressor). The ERA model does not claim to be able to simulate rotary vane compressors. Neither ADL nor EPA have published data validating either the physical model or the rating point model, for example by attempting to reproduce compressor maps for the standard matrix oftest conditions. -This is the minimal amount of validation required before such models could be substituted 

## , for maps for constant-speed operation with alternative refrigerants. If such data were available, it might be reasonable to expect the physical and rating point models to more accurately simulate compressor operation at conditions significantly different from the 90°F ambient air and refrigerant inlet temperatures on which the perfonnance maps are based. However, before using such models to predict the effects of variable-speed operation, there should be some validation done under those conditions because the compressor can heat rransfer (and the closely-related heat loss from the motor windings and friction losses) may differ greatly from the full-load case. Because ofthese deficiencies in the rating point and physical models, the Task Force members have no confidence in them. In the absence of validating data it is recorrunended that neither model 

## be used to 

### predict- the power, mass flow or can heat loss as a function ofrefrigerant properties or**compres~or_** 

### speed. In the meantime simulations involving alternative refrigerants or variable-speed compressors ought to 

### be based on the map-based model using data obtained for the specific refrigerant (or blend) at the particular rotational speed being simu1ared. 

## Reducing ·cycling losses Cycling losses are estimated by the ERA model as a part ofeach simulation. However the model is set up to analyze only one conservation measure aimed at reducing such losses: a check valve that would prevent the refrigeram from migrating to the evaporator during the off-cycle.? Other approaches to dealing with cycling losses (e.g. reducing the refrigerant charge) cannot be simulated by ERA. The ERA model simulates steady-state operation at standard design conditions. 

## It then deals with cycling losses by applying a correction factor taken by ADL (1992) from a report by Janssen et. al. (1990). If the correclion factor formulae were credible, i[ would make sense to examine the sensitivity 7 One or two valves would be required, depending on whether Lhe compressor is a rotary or reciprocating lype. 

### 12 In 

### contrast to power input, the compressor mass flow rate is**compute~** 

### in ·ERA's "compressorphysical model" in a much more srraightforward manner. It 

### follows directly from the user-specified values of displacement, clearance volume, Ipm and a relation between volumetric effi. ciency and pressure ratio that is hard-wired into the program. This type of model places most ofthe burden on the user tQ .. ._. 

### supply the correct inputs, but there are still uncertainties about the accuracy of the volumetric efficiency formula and its applicability [0 

### alternative refrigerants. The greatest uncertainty . however. is tied into the extremely complex heat transfer phenomena that occur inside the compressor shell between the exit ofthe suction line and the suction port of the cylinder itself (in a reciprocating compressor). TheERA model does not claim to be 

### able to simulate rotary vane compressors. Neither 

## ADL nor EPA have published data validating either the physical model or the rating point model, for example by attempting to reproduce compressor maps for the standard matrix oftest conditions. 'This is the minimal amount of validation required before such models could be substituted 

## , for maps for constant-speed operation with alternative refrigerants. If such data were available. it might be reasonable to expect the physical and rating point models to more accurately simulate compressor operation at conditions significantly differem from the 90°F ambient air and refrigerant inlet temperatures on which the perfonnance maps are based. However, before using such models to predict the effects of variable-speed operation, there should be 

### some validation done under those conditions because the compressor can heat rransfer (and the closely-related heat loss from the motor windings and friction losses) may differ greatly from the full-load case. Because ofthese deficiencies in the rating point and physical models, the Task Force members have no confidence in them. 

## In the absence of validating data it 

### is reconunended that neither model 

## be used to 

### predict the**pow~r.** 

### mass flow or can heat loss as a function ofrefrigerant properties or**compres~of. .**  

### . speed. In the meantime simulations involving alternative refrigerants 

## or variable-speed compressors ought to 

### be based on the map·based model using data obtained for the specific refrigerant (or blend) at the particular rotational speed being simu1ated. 

## Reducing ·cycling losses Cycling losses are estimated by the ERA model as a part ofeach simulation. However the modei is set up to analyze only one conservation measure aimed at reducing such losses: a check valve that would prevent the refrigerant from migrating to the evaporator during the off-cycle. 7 

### Other approaches to dealing with cycling losses (e.g. reducing the refrigerant charge) cannot be 

### simulated by ERA. The ERA model simulates steady-state operation at standard design conditions. 

## It then deals with cycling losses by applying a correction factor taken by ADL (1992) from 

## a report by Janssen et. al. (1990). Ifthe correction factor formulae were credible, it would make sense to examine the sensitivity 7 

### One or two valves would 

### be required, depending on whether Lhe compressor is a rotary or reciprocating type. 

### 12

### ofmodel results to uncertainty in the input variables relating to the correction factors. TIlis type of analysis cannot be done in this case because the correction factor is not credible. Ils estimates of cycling losses are grossly inconsistent with data provided by refrigerator manufacturers. ERA's cycling loss correction factor is composed of two parts. The first is intended to capture the effect ofrefrigerant migration by decreasing COP by 1.1 % times the number of cycles per hour.s It is applied to all refrigerators that do not contain a shutoff valve. The magnitude ofthis error is obviously dependent on the quantity ofrefrigerant charge that migrates, it will therefore vary significantly among refrigerators. ADL provides nojustification for applying this value to all refrigerd!ors, regardiess of charge. Moreover, there is nojustification for applying the same factor to refrigerators equipped with rotary vs.-reciprocating compressors. Rotaries have a high-side sump and it take.s longer for the refrigerant (which dissolves in the oil during the off-cycle) to vaporize and begin circulating during the on-cycle 

# (i! must wait for the can to heat up). Sinrc ERA ignores such factors as compressor tJ:tennal mass 

## it cannot model this difference, al1d the correCil·:m factor cannot 

## be altered by the user to 

### account 

# ,

. for the presence of a rotary compressor.

AHAM Task Force members indicated that no correction factor that is independent ofrun time (duty cycle) can 

# hi credible. On theoretical grounds alone., the percentage error due to refrigerant migration must**inc~ease** 

### as run time decreases. To illustrate this effect one manufacturC?r provided experimental data showing meastl!ed COP for twO refrigerators at 

## 40% 

## < runtime 

## < 60%**an~** 

## 45 min 

## < cycle length 

## < 75 min. These results showed that runtime affected the "cycling loss correction factor" under**t4~e** 

### condi?ons by 10% for reciprocating compressors and by as much as 100% for rotaries. Clearly the effect"ofruntime cannot be ignored as in the ERA model. Moreover the variation between rotary and reciprocating compressors demonstrates that factors other than refrigerant migration may have greater effects on :Cycling losses. The second part ofthe cycling correction applies.only to systems having a shutoff valve. It actually increases the COP as a function ofduty cycle to approach 3$ymptotically the hypothetical case in which the increase in cycling frequency combines with the thennal mass of the heat exchangers to hold evaporating and condensing temperatllres at levels corresponding to the case of a variable-speed compressor operating continuously with no cycling loss. ADL uses a ratio of Carnal COP's to adjust the actual COP for the change in ev...porating and condensing temperawr**~.** 

### Again, ADL offers no justification for applying to all refrigerators the quantitative correction ob!o,erved by Janssen et. al. (1990) in a single experimental apparatus containing heat exchangers of unknown thermal mass. To test the efficacy of the ERA correclion factor for systems equipped with a shUloff valve, the tests described above were expanded by adding a shutoff valve to the refrigeratOrs with rotary compressors. 8 This value is taken directly from the reference lO the single experiment reported by Janssen et. al. (1990). 

## 13 of

### model resulls to uncertainly in lhe input variables relating to the correction factors. TIlis type of analysis cannot be done in this case because the correction factor is not credible. Its estimates of cycling losses are grossly inconsistent with data provided by refrigerator manufacturers. ERA's cycling loss correction factor is composed of two parts. The first is intended to capture the effect ofrefrigerant migration by decreasing COP by 1.1 % times the number ofcycles per hour.8 It is applied to all refrigerators that do not contain a shutoff valve. The magnitude ofthis error is obviously dependent on the quantity ofrefrigerant charge that migrates, it will therefore vary significantly among refrigerators. ADL provides nojustification for applying this value to all refrigenltors, regardless of charge. Moreover, there is nojustification for applying the same factor to refrigerators equipped with rotary vs.- reciprocaring compressors. Rotaries have a high-side sump and 

### it takes longer for the refrigerant (which dissolves in the oil during the off-cycle) to vaporize and begin circulating during the on-cycle**(i ~**  

### must wait for the can to heat up) . Sinrc ERA ignores such factors as compressor tJ:tennal mass 

## it cannot model this difference, Md the correctIOn factor cannot 

## be altered by the user to 

### account 

# , for the presence of a rotary compressor. AHAM Task Force members indicated that no correction factor that is independent ofrun time (duty cycle) can 

# hicredible. On theoretical grounds alone , the percentage error due to refrigerant migration must**inc~ea se**  

### as run time decreases . To illustrate thi s effect one**manufac tu** **r~r** 

### provided experimental data showing**measu~ed** 

### COP for tWi) refrigerators at 40% 

## < runtime 

## < 60%**an~** 

### 45 min 

## < cycle iength 

## < 75 min. These results showed that runtime affected the "cycling loss correction factor" under**t~cse** 

### condi?ons by 10% for reciprocating compressors and by as much as 100% for rotaries. Clearly the effect'ofruntime cannot be ignored as in the ERA model. Moreover the variation between romry and reciprocating compressors demonstrates that factors other than refrigerant migration may have greater effects on**~ycling** 

### losses . The second part of the cycling correction applies . only to systems having a shutoff valve. It actually increases the COP as a function ofduty cycle to approach 8$ymptotically the hypothetical case in which the increase in cycling frequency combines with the thermal mass of the heat exchangers to hold evaporating and condensing temperatures at levels corresponding to the case of a variable-speed compressor operating continuously v: ith no cycling loss. ADL uses a ratio of Carnot COP's to adjust the actual COP for the change in ev::porating and condensing remperatu 1 ..... Again, ADL offers no justification for applying to all refrigerators the quantitative correction ob:-.erved by Janssen et. al. (1990) in a single experimental apparatus containing heat exchangers of unknown thermal mass. To test the efficacy of the ERA correction factor for systems equipped with a shutoff valve, the tests described above were expanded by adding a shutoff valve to the refrigeralOrs with rotary compressors. 8 This value is laken di rccl.ly from the reference lO Lhe single experim ent reported by Janssen el. al. (1990) . 

## 13

### Subsmntial energy savings were achieved, but cycling performance was still worse than steady-state. In 

### contrast the ERA correction factors, computed for these same refrigerators, predicted a 1-3% 

## increase in 

## COP over the**s[eady~state** 

### value. Because of these obvious defects in the structure of the equations dealing with cycling losses, the accuracy analysis was terminated at this point. 

## Dual 

## evaporator ERA represents the dual evaporator system as a special case of the Lorenz cycle, keeping both evaporators in series and simply eliminating one ofthe intercoolers. The particular configura"rion considered in this analysis has no air exchange between the two compartments, and assumes The primary mode ofenergy conservation in this case would be the elimination of the evaporator fan power ·and 

### the compressor energy to remove that heat from the cabinet. The only other potential for conserving energy would seem to be 

### savings in defrost energy, since no humid air from the fresh food comparnnent would contact the freezer evaporator. However such savings would not 

## be observed on the DoE test, or in simulations of closed-door operation. 

## It appears that ERA is unable to model other dual-evaporator configurations that might exploit other types ofenergy conservation opportunities. The base case refrigerator for this experiment was assumed to have a single evaporator, and subject to the following uncenainties. The conductance, or V-value for**two-pha~e** 

### operation was assl,1rn.ro**t~~1?e** 

### known within 

## ± 10%.9 The volumetric air flow rate over the**e~aporator** 

### is also known within 10%, and the evaporator fan power within 

## 5%. The combined effect of these evaporator-specific uncertainties propagated through the model to produce a 

## ± 0.73% uncertainty in ERA's·estimate of energy use. The dual evaporator system contains none of the aforementioned compone.nts, which were replaced by two static evaporators defined in terms of their conductances and their areas. To ensure that the cabinet temperatures were comparable between the single- and**dual~evaporator** 

### simulations, the areas ofthe two evaporators were defined to achieve the proper temperatures in each compartment under

## closed~ .. door conditions in a 

## 90°F env.ironment. 10 

### ERA's calculational assist menus were used to calculate the conductances ofthese natural-draft evaporators, which 

## are assumed to 

## be known only within ±15%

9 Actually a typical evaporator calorimeLCr is able to compare evaporatm's wilhin 

### ± 5%. but the absolute value is more difficult to determine. Since a dIfferent type ofcalorimeter would have to be 

### used for static evaporators, it is appropriate to compare the absolute values. 10 This assumption helps the energy portion of the analysis. but introduces great uncertainty into the COSt analysis. The required area might 

### be substantially larger or smaller than the value predicted by ERA. It is made here to 

### enable lhe analysis to proceed and yield some insight into lhe sensitivity of model resullS 

### to this parameter. However 

### it recognizes that the cost difference between a single-ev3ponlLOr and dual-evapornlor systems will require a detailed cOSt analysis anyway. 

### 14 Subsmntial energy savings were achieved, but 

### cycling performance was still worse than steady-state. In 

## contrast the ERA correction factors, computed for these same refrigerators, predicted a 1-3% 

## increase in COP over the steady-state value. Because of these obvious defects in the structure of the equations dealing with cycling losses . the accuracy analysis was terminated at this point. 

## Dual evaporator ERA represents the dual evaporator system as a special case of the Lorenz cycle, keeping both evaporators in series and simply eliminating one ofthe intercoolers. The particular configura ' tion considered in this analysis has no air exchange between the two compartments, and assumes The 

## primary mode ofenergy conservation in this case would be the elimination of the evaporator fan power 'and the compressor energy to remove that heat from the cabinet. The only other potential for conserving energy would seem [0 

### be 

## savings in defrost energy, since no humid air from the fresh food comparnnent would contact the freezer evaporator. However such savings would not 

## be observed on the DoE test, or in simulations ofclosed
-door operation. 

## It appears that ERA is unable to model other dual-evaporator configurations that might exploit other types ofenergy conservation opportunities. The base case refrigerator for this experiment was assumed to have a single evaporator, and subject to the following uncertainties. The conductance, or V-value for**two-pha ~e**  

## operation was assl,lrn.ed-**t~~1?e** 

## known within 

## ± 10%.9 The volumetric air flow rate over the**e~aporator** 

## is also known within 10%, and the evaporator fan power within 5%. The combined effect of these evaporator-specific uncertainties propagated through the model to produce a 

## ± 0 .73% uncertainty in ERA's'estimate of energy use. The dual evaporator system contains none of the aforementioned compone. nts, which were replaced by two static evaporators defined in t erms of their conductances and their areas. To ensure that the cabinet temperatures were comparable between the single- and dual-evaporator simulations , the areas ofthe two evaporators were defined to achieve the proper temperatures in each compartment under

## closed**~** " door conditions in a 

## 90°F env. ironment. 10 

## ERA's calculational assist menus were used to calculate the conductances ofthese natural-draft evaporators, which are assumed to 

## be known only within ±15%

9 Actually a typical evaporator calorimet er is able to compare evaporaters wilhin 

### ± 5%, but the absolute value is more difficult to determine. Since a dirr erent type orcalorimeter would have to be 

### used for Static evaporators, it is appropriate to compare the absolute values. 10 This assumption helps the energy portion of the analysis. but introduces great uncertainty imo the cost analysis. The required area might 

### be substantially larger or smaller lhan the value predicted by ERA. It is made here to enable lhe analysis to proceed and yield some insight into lhe sensitivity of model results to this parameter. However it T ecognizes that the cost diff erence between a single-evapor.lLOr and dual-evapornlor systems will require a detailed cost analysis anyway. 

### 14

### because of the relative difficulty of the calorimetry problem. This produced a 

## ± 1.5% uncertainty in energy use. The energy savings associated with eliminating the fan were approximately 13%. Considering**th~~** 

### . uncertainties, the savings are estimated in this quantitative analysis to lie within the 11-15% range. However, this quantitative analysis may' not address the most important sources ofuncertainty. For example the areas of the plate-style static evaporators are much greater than the area ofthe single forced-draft evaporator. 

## If the resuhing charge requirements are also proportionately larger, cycling losses due to refrigerant migration will also increase.**Th~** 

### greatest uncertainty, however, is associated with the teinperature Control problem, which the ERA model ignores. Overcoming this problem will certainly make the system more .costly, for example by adding the cost ofrefrigerant switching valves, sensors and controllers to the extra cost ofevaporator surface areas. 

## It may also increase energy requirements, depending on the control option chosen. For example exchanging air between the compartments may erode defrosting savings, fans might be 

### needed to prevent stratification, and pulldown requirements might demand a larger compressor thereby shortening the duty cycle. 

## Conclusions and 

## recommendations

-- This report described both the qualitative and quantitative aspects ofthe accuracy analysis cprv;luct<:9 for the conservation options listed in Table 

## 1. The options were selected because there is inadequate test data available to validate the parts of the ERA model used to calculate energy savings. For a few

. ofthese conservation options, limited amounts oftest data were provided by manufacturers on a

confidential bJisis. In some cases it was possible to conclude, based on this admittedly sparse and confidential data, that certain parts of the ERA program must 

## be improved before they can be used to accurately predict energy savings associated with certain conservation options. Except for the gasket heat leak and vacuum panel insulation analysis, the quantitative part of the analysis could not be 

### completed because oferroneous assumptions and omissions in the ERA model itself. The findings reported above lead to the following conclusions and recommendations:
• Estimates ofenergy savings oblainable from gasket improvements should be detennined directly by experiment. ERA's calculational assist yields results that fail to agree with published data and experiments conducted by manufacturers, and may lead to errors of50% or more. • ERA's estimates of energy savings due to vacuum panel insulation may be 

### in error by 

## ± 10% due to 

# -. uncertainties aboUl enclosure thickness and and panel resistivity alone. Careless use of laboratoryreported**k~values** 

### for non-CFC foam can increase these errors to 

## ± 50%. ERA's failure to deal with 3-D effects apparently led to even larger errors in tests conducted by one manufacturer. 15 

## because of the relative difficulty of the calorimetry problem. This produced a 

## ± 1.5% uncertainty in energy use. The energy savings associated with eliminating the fan were approximately l3%. Considering**th~ ~**  

## . uncertainties, the savings are estimated in this quantitative analysis to lie within the 11-15% range. However, this quantitative analysis may' not address the most important sources ofuncertainty. Forexample the areas of me plate-style static evaporators are much greater than the area ofthe single forced-draft evaporator. 

## Ifthe resuhing charge requirements are also proportionately larger, cycling losses due to refrigerant migration will also increase. The; greatest uncertainty, however, is associated with the teinperature Control problem, which the ERA model ignores. Overcoming this problem will certainly make the system more , costly, for example by adding the cost ofrefrigerant switching valves, sensors and controllers to the extra cost ofevaporator surface areas. It may also increase energy requirements, depending on the control option chosen. For example exchanging air between the compartments may erode defrosting savings, fans might be 

## needed to prevent stratifkation, and pulldown requirements might demand a larger compressor thereby shortening the duty cycle. 

## Conclusions and recommendations

. ' 

## This report described both the qualitative and quantitative aspects ofthe accuracy analysis**cpr\l;luct~9** 

## for the conservation options listed in Table 

## 1. The options were selected because there is inadequate test data available to validate the parts of the ERA model used to calculate energy savings. For a few

. ofthese conservation options, limited amounts oftest data were provided by manufacturers on a

confidential bJisis. In some cases it was possible to conclude, based on this admittedly sparse and confidential data, that certain parts of the ERA program must be improved before they can 

## be used to accurately predict energy savings associated with certain conservation options. Except for the gasket heat leak and vacuum panel insulation analysis, the quantitative part of the analysis could not be 

## completed because oferroneous assumptions and omissions in the ERA model itself. The findings

. reported above lead to the following conclusions and recommendations:

• Estimates ofenergy savings obtainable from gasket improvemems should be detennined directly by experiment ERA's calculational assist yields results that fail to agree with published data and experiments conducted by manufacturers, and may lead to errors of50% or more. • ERA's estimates ofenergy savings due to vacuum panel insulation may be 

## in error by 

## ± 1 0% due to**"7** 

## uncertaimies about enclosure thickness and and panel resistivity alone. Careless use of**laboratory~** 

## reported**k~values** 

## for non-CFC foam can increase these errors to 

## ± 50% . ERA's failure to deal with 3-D effects apparently led to even larger errors in tests conducted by one manufacturer. 15

### The NlST thennodynamic property routines used by ERA may lead 

# to errors in energy use exceeding I

### % for R-134a. More accurate routines are avalIable from NIST in identical fonnat and should 

## be used for all R-134a simulations.

• Serious errors apparently exist in the part ofERA that simulates Lorenz cycles. Repeated**at~f;.tp.pts** 

### by an experienced refrigerator designer failed to produce a result showing a temperature glide of the magnitude predicted by the NlST property data. Also ERA's use of a constant specific heat to approximate the behavior of zeotropes causes the specific heat ratio to be in etror by as much as a factor of7 as mixture composition changes through the evaporator. This can lead to serious errors in high-effectiveness heat exchangers.

• For dual-evaporator systems as well as Lorenz-.cycle systems, ERA's inability to model cabinet temperature"control strategies and off-design performance introduces great uncertainty into any estimates ofenergy savings. A system optimized for operation in a 90°F environment is almost .certain to experience cQntrol problems at lower ambients and in response to realistic door-opening**schedules~** 

### and the energy cost ofeliminating these problems is not included in the model.

• ERA's abiliWto predict the effects of alternative refrigerants or zeotropic blends is further compromised by ERA's compressor rating point model because it contains empirical relations that are specific to R-12 and leading to errors of 5-8% in predicting energy use for R-134a. Likewise the compressor physical model is"deficient because it demands that the user specify parameters that are unfamiliar to compressor designers, thereby leading to input errors. A simple model requiring the user!o specify a constant isentropic efficiency might 

## be more accurate. It is recorrunended that neither the physical model nor the rating point model be used; compressor calorimeter datJ;l sh,?yld be 

### obtained for analysis of any conservation options involving alternative refrigerants, mixtures or variable-speed compressors. • " The cycling loss correction in the ERA model should be removed, and refrigerators compared on the basis of steady-state performance. The cycling loss correction in the model extrapolates results obtained from a single test refrigerator, fails to account properly for significant variables (e.g. refrigerant/oil solubility; runtime), and yields results that differ greatly from test data obtained by manufacturers.
• The output format should be changed to 

### display daily energy use to more significant digits. This would facilitate analyses ofparametric uncertainty, and would help designers evaluate more accurately the derivative ofenergy use with respect to input variables.

• The user input menu should be changed to accept alleast three significant digits for the value of foam conductivity. The two digits currently accepted are inadequate to support even the three-digit results calculated for daily energy use, which is extremely sensitive to foam conductivity. The preceding suggestions are necessarily conservative and negative because they are based on very limited data. Only few data points are needed to reject a"hypothesis, while many are required to confinn it. The ERA model represents a significant improvement over its predecessor, and might only 16 The NlST thennodynamic property routines used by ERA may lead 

## to errors in energy use 

### exceeding 1% for R-134a. More accurate routines are avallable from NIST in identical fonnat and should 

## be used for all R-134a simulations. • Serious errors apparently exist in the part ofERA that simulates Lorenz cycles. Repeated**at~f;Jp.pts**



### . by an experienced refrigerator designer failed to produce a result showing a temperature glide of

the magnitude predicted by the NIST property data. Also ERA's use of a constant specific heat to approximate the behavior of zeotropes causes the specific heat ratio to be in etmr by as much as a factor of7 as mixture composition changes through the evaporator. This can lead to serious errors in high-effectiveness heat exchangers. • For dual-evaporator systems as well as Lorenz-, cycle systems, ERA's inability to model cabinet temperature'control strategies and off-design perfonnance introduces great uncertainty into any estimates ofenergy savings. A system optimized for operation in a gooF environment is almost .certain to experience cQntrol problems at lower ambients and in response to realistic door-opening**schedules~** 

### and the energy cost ofeliminating these problems is not included in the model. • ERA's ability'to predict the effects of alternative refrigerants or zeotTOpic blends is further compromised by ERA's compressor rating point model because it contains empirical relations that are specific to R-12 and leading to 

### errors of 5-8% in predicting energy use for R-134a. Likewise the compressor physical model is
- deficient because it demands that the user specify parameters that are unfamiliar to compressor designers, thereby leading to input errors. A simple model requiring the" user**~o** 

### specify a constant isentropic efficiency might be more accurate. It is recorrunended. that neither the physical model nor the rating point model be used; compressor calorimeter datlol sh9.yld 

## be obtained for analysis of any conservation options involving alternative refrigerants, mixtures or variable-speed compressors. • " The cycling loss correction in the ERA model should be removed, and refrigerators c6mpared on the basis of steady-state performance. The cycling loss correction in the model extrapolates results obtained. from a single test refrigerator, fails to account properly for significant variables (e.g. refrigerant/oil solubility; runtime), and yields results that differ greatly from test data obtained by manufacturers. • The output format should be changed to display daily energy use to more significant digits. This would facilitate analyses ofparameDic uncertainty, and would help designers evaluate more accurately the derivative ofenergy use with respect to input variables. • The user input menu should 

## be changed to accept at least three significant digits for the value of foam conductivity. The two digits currently accepted are inadequate to support even the three-digit results calculated for daily energy use, which is extremely sensitive to foam conductivity. The preceding suggestions are necessarily conservative and negative because they are based on very limited data. Only few data points are needed to reject a " hypothesis, while many are required to confirm it. 

### The ERA model represents a significant improvement over its predecessor, and might only 16

### require modest improvements in order to become a useful tool for**analyzin~** 

### impacts of these energyconserving designs. However it 

### will take considerable time and effort to 

### amass the data needed to 

### improve and validate many of the features evaluated here. Data on this set ofconservation options are very scarce at this time, and are therefore held as proprietary information by the companies that developed it. Until more experience is acquired with these technologies and data become widely available in 

### the public domain, the predictions ofthe 

## ERA model must 

## be interpreted with great care. final cautionary note is necessary as a reminder that the ERA model is a design model, not a simulation model. Even if all inputs and equations were known with perfei.:1 certainty, the model

.**~ould** 

### only be capable ofrepresenting performance at a**sing~e** 

### design point**I~** 

### could not simulate offdesign performance (e.g. the effect of changing ambient temperature, the effect of additional cabinet loads due to door openings.) The user-specified input values for evaporator superheat and condenser subcooling ¥e intended to compensate for ERA's lack ofequations describing the mass flow-pressure drop relation for the capillary tube. 

### and equations that would keep track ofthe refrigerant charge. Therefore when a user specifies 

## a different kitchen**temperat~.** 

### for example, the ERA model assumes that the refrigerator has been recharged and 

## fined with a new capillary tube designed to produce the. user-specified superheat and subcooling at that new ambient temperature. Therefore a refrigerator design predicted by ERA to perfonn well at the design point (90°F ambient; 

## 5°F freezer, 40°F fresh food) will not necessarily keep food from spoiling as the ambient temperature changes. To predict offdesign performance characteristics such as [his requires a true simulation model that models explicitly the behavior of [he capillary tube and the charge inventory. -References

Arthur'D. Little Inc., "EPA refrigerator analysl;} program user's manual", DRAFr, May 1992

, 

### -Anhqr D. Little.- Inc., 

## Refrigerator and Freezer Computer: Model User's Guide, U.S. Department of 'Energy, Washington D.C., 1982. Boughton, B. E., T. A. Newell, A.. M. Clausing, 

## An investigation of houseJwld refrigerator cabinet loads, ACRC-TR-21, Air Conditioning and Refrigeration Center, University ofIllinois at UrbanaChampaign, May 1992, 135 pp. Conklin, 

## J. C. and E. A. Vineyard, "Hea[ exchanger [hennal perfonnance for two nonazeotropic refrigerant mixtures", 

## Proc. XVII/Inri. Congress of Refrigeration, Montreal, Aug 1991. FlYQn, 

## S., K. Rouch and H. A. Fine, "Finite element. analysis of heat transfer through the gasket region ofrefrigerator/freezers", 

## EPAI430IR-921009, United States Environmental Protection Agency, Washington DC, October 1992 Gallagher, 

## 1., National Institute of Standards and Technology, personal communication, January 1993. Janssen, M. J. P., J. A. 

### de Wit, 

## L. J. M. Kuijpers, "Cycling losses in domestic appliances: an experimental and theoretical analysis", 

## Proc.IIR Purdue Conference, West Lafayette, Indiana, August 1990, 17 

### require modest improvements in order to become a useful tool for**analyzin~** 

### impacts of these energyconserving designs. However it will 

### take considerable time and effort to amass the data needed to improve and validate many of the features evaluated here. Data on this set ofconselVation options are very scarce at this time, and are therefore held as proprietary information by the companies that developed it. Until more experience is acquired with these techno logies and data become widely available in the public domain, the predictions ofthe ERA model must be interpreted with great care.**~** 

### final cautionary note is necessary as a reminder 

## that the 

### ERA model is 

## a design model, not a simulation model. Even if all inputs and equations were known with perf ed certainty, the model**~ou ld** **onl~** 

### be capable ofrepresenting performance at a**sing~e** 

### design 

### point**~** 

### could not simulate offdesign performance (e.g. the effect of changing ambient temperature, the ef fect of additional cabinet loads due to door openings.) The user-specified input values for evaporator superheat and condenser subcooling 

## ¥C intended to compensate for ERA's lack ofequations describing 

## the mass flow-pressure drop relation for the capillary 

### tube. and equations that would keep track ofthe refrigerant charge. Therefore when a user specifies 

## a different kitchen**temperat~.** 

### for example, the ERA mooel assumes that the refrigerator has been recharged and 

## fitted with a new capillary tube designed to produce the , user-specified superheat and subcooling at that new ambieO[ temperature. Therefore a refrigerator design predicted by ERA to perform well at the design point (90°F ambient; 5°F freezer; 40°F fresh food) will 

### not necessarily keep food from spoiling as the ambient temperature changes. To predict offdesign performance characteristics such as this requires a true simulation model that models explicitly the behavior ofthe capillary tube and the charge inventory.

-References

Arthur ' D. Little Inc., "EPA refrigerator analysi;') program user's manual", DRAFr, May 1992

-AnhQr D. Little.-Inc., 

## Refrigerator and Freezer Computer: Model User's Guide, U.S. Department of

-Energy, Washington D.C., 1982.

Boughton, B. E., T. A. Newell, A,. M. Clausing. 

## An investigation of household refrigerator cabinet loads. ACRC-TR-21, Air Conditioning and Refrigeration Center, University ofIllinois at Urbana
Champaign, May 1992, 135 pp. Conkli!l, 

## J. C. and E. 

### A. Vineyard, "Heat exchanger thermal performance for two nonazeotropic refri gerant mixtures", 

## Proc. XVIII Inti. Congress of Refrigeration, Montreal, Aug 199 1. Flynn, 

## S., K. Rouch and H. A. Fine, "Finite element,analysis of heat transfer through the gasket region of refrigerator/freezers", 

## EPAI430IR-921009, United States Environmental Protection Agency, Washington DC, October 1992 Gallagher, 

## 1., National Institute of Standards and Technology, personal conununicarion, January 1993 . Janssen, M. J. p" 

### J. A. de Wit, 

## L. J . M. Kuijpers, "Cycling losses in domestic appliances: an experimental and theoretical analysis", 

## Proc,llR Purdue Conference, West Lafayette, Indiana, August 1990. 17

## Monison, G. and M. O. McLinden, Application of a hard sphere equation of state to refrigerants and refrigerant mixtures, NBS Technical Note 1226, National Bureau of Standards, Gaithersburg MD, 1986 Porter. K. 

## J., and C. W. Bullard, Modeling and sensitivity analysis of a refrigeratorlfreezer system, ACRC-TR-31, Air Conditioning and Refrigeration Center, University 

# of Illinois at UrbanaChampaign, December 1992, 87 pp. United States Environmental Protection Agency, "Multiple palhways to 

## superefficient refrigerators", Office ofAtmospheric and Indoor Air 

## Programs, DRAFT, February 1992

18 Monison. G. and M. O. McLinden, 

## Application of a hard sphere equation of state to refrigerants and refrigerant mixtures, NBS Technical Note 1226, National Bureau of Standards, Gaithersburg MD, 1986 Porter, K. 

## J., and C. 

## W. Bullard, 

## Modeling and sensitivity analysis of a re[rigerator!freezer system, ACRC-TR-31, Air Conditioning and Refrigeration Center, University 

# of Illinois at UrbanaChampaign, December 1992, 87 pp. United States Environmental Protection Agency, "Multiple pathways to 

## super efficient refrigerators", Office ofAtmospheric and Indoor Air Programs, DRAFT, February 1992

18