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.

 CE-RM-93-801 COMMENT OR7

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 lIofficialll 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

 CE-RM-93-801 COMMENT OR7

.' 

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. Merr iam', ADL 

Michael McCabe, DOE 

Jim McMahon, LBL 

Sincerely, 

Jea~ 

~~~\ M. Lup1nabc1 '7! ~' I7S ;L1A! L 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 .

alitBoIlanl_

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 01alara.. err"" by oI>c Tult _10qUllllify 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 of oI>c.-1 uled by DoE In tenlI1. ollc 1993 _ (AD!.,

1912) .Tho improve......d.all mainly wioh .... u.... lnlaface. ond oI>c addilioo ofmol..........

excbanJU1.lhcmaavc rtfriaaanu and new compressor modds lhat do noc rcqWre e&IorimrrAer IUlin,

wi&b I panicular new rdriJUllM. AHAM wk (on:e members. CIIlpnecn U'OIII &be ...

_ ....""Ifreearmanulac:IUrin._ies. used .... ERA modd 10 perf""" ........._ reponed

bore ond povidcd all .... neceutI}' InPUI dilL

Purpose and itOpt

For man)' Ofthe 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 ofCIlCrIl' ..vi.... podiacd by oI>c ERA modd. Howevcr _ ... Iial. or no

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 10 rei)' I1most w:lul1vc1)' on mcdd·bua:I csDlJVI'':I fOllhc:le CDnlelVaDon

InCISura. 'Thisreport presenllresults of an 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) __DAInOdd 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.ll •

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.

 CE-RM-93-801 COMMENT OR7

Accuracy Analysis or Ihe !ADLIERA Model 

Prepat<d fa< 

Backcround . 

Association of Home Appliance Manu{acQ,lrus 

NAECA 1 .... Fon:e 

Preporod by 

aut Bullard A"o";'",, 

$09 Wea WuhinilOft S ... 

UrI>ona OIinoiJ 61101 

nu. ....... wu IIRporod u .... ""1 .... oClhc NAECA Tult Fon:eoClhc ".eoci· .... OC_ 

Applilnoe ~.r_ h is ..... of llar,et c(f"" by Ihc Tult Fon:e 10 qlllAdIy .... -wnry 

woc:iucd with ulima ... oC.....,. lI"'p oWlDcd 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-*ular new 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 of the 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 10 rei), aJmost e.u:lusivd)' on modd·buod csci",, ~ f« &hare conlaVuion 

measwu. 'nul repan pRsentlfelUlli 01 an dfon 10 cllimaae Ihe uncertaintiCl UIONt.cd with such 

model·based estirna~ 

6c 

I To 

ERA 

... 

P'CII*" 

iII .. 

Iftd 

c"'''oI_ 

input flictMiDd 

EAA.add, ift., USUA', ADL 

Dt.Ii 

ptO¥ided 

Mv.k

u.AHANTut 

ip&o ..... )'1 bpon. 

Fore. 

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-sweat 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 basis 

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 Vera ion 1.0 User'Q Manual, 
• tllm ovemcnts

· acuumitls...... · ......'" ....... ......... ·

· on. • """ · llCOC n

· .., ... Table 1. meaana !, uS

A1imI>k wiD_............-of'l"""lifJlol..__............ wiIh 11\

ERA_ot &7 .... Far.buccuenofri_._dlal....-*I..-• ...,·

weot2.00k_y•..a I.lOk_y aftctlhc:dcsipbu_~..~.

............................ .-01.._..,.1IIIIJ1la,_ ~<Cllldudodlalu"", 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 -*IjaY"&" ' 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 01irrq IC)'

..._:\}.-...In Ihc:.........- opcciIIod U .............ERAlIllldd; 2)

• • DaNCeL11 1iaERA'.eq...aoa.;ud3)lCnaIiudvc:N:lMlyClDiald~ERA"'"

.._c:uea...... otlyp<l n ....'3 _ 110 qllllllif'lOd IIdlia..,..........1acI: 01daIa, 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'•

 CE-RM-93-801 COMMENT OR7

Table I. O' ...... 'ioa InCIU'II I . cd 

A ........... wiU ................ ........-~~ ... _·nocI· ... wiIh .. 

ERA_otaICrQ .... For. _cut 1Ofri_. __ ........ _ 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 . ................. ....., IIWop AI! 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)' ... y odd ... _~ 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"cn iD 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 it WII 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 a rt_ 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 equationsikscribin. the s)'llem) and klfcclS the nlw;s 0(Ihc OUrpUI variables

(in our case 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

Oftaumuous 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 olon!)' 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 if onl)' • 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(12»)

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

 CE-RM-93-801 COMMENT OR7

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 of B liu wilhin Ihc ranp B: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. It iJ 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 ol the 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 of onalysis I, ealled "sin&le.sampit u~ll .. y analysi'" __ .dc/iaa dle ..... wi .... 

which &he result willlic, even if only 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 dill on Ihccaa'JYcooservin,desians 10 pc:rmiIICCURee cuimarion oIlhc mean valuuollhe ~tcn dacribinalhc 

improved systc.nu; Ind 2) I MonIC Cuk» anaI)'Iis in which hunchds of h)'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 Ei 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'OeI of 

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, 

3 
AppllCl.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

.caneyof!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 01uperience and CIlWIIi........,01olIi.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 oftesM' and an&Iysis. unoauindc:s remain due1O~,

limiWions and &he lid; of S&&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 ftK aU 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 forsevaal

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 of chc ,asku and

4

 CE-RM-93-801 COMMENT OR7

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 of oho 1)'_ dw ... "'" -,cd. For 

cumpIe in die.,.,. of -... Vl<Wm panels, only put of oho 10111\ is ",pIIocd. WIw is n:leYll!'.!" die 

ocancy of die model is how wdllht ....... volues of Iht ",pIoood loom IOd die v_ """" ... 

bowl>. ladle.,.,. of RII 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.-1Od WCNi .. 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 

of portmtlCtl dclCribln, die buc.,.,. dc'i&n. EwI1>Ica ioclude bctl exdIanccr __ ond 

pskCl bctt 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 utcr of .... ERA -*I; 2) ""IfI!Pdon! ph 1+c' in ERA'I cqu.aDonS; and 3) ICmlS inadYcnc.ndy omiad from ERA Iqutions. T)'pe I cmn 

IfC quantified 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 Mille ERA-caScuIucd heal nnsfcr 

is doni ...... I»' .... r .... ,""....".. tnd Iht,!he """ .... etr"" of til 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 

Heasure.ante pertoraed at The Univeraity of Maryland for a series 

of 9asket .odification_ co.~r.d f.vor.bly with 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 this docu~ent agree with the general finding. of the ~ccuracy Analysis in thia 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 ofcncto 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 iudf wiD 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 orthe 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.lICQbincu; it c:ouad be p«lpOl'UonItely1lrJa'for 1993 or vltr.Nn't-plnCl

cabinetsin Ihe (UUlR.) Ac:rudc: wlylo .e:tOUnl for.it infilnlion usina the ERA model would be 10

5

 CE-RM-93-801 COMMENT OR7

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) confinnod 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 of Ryn . . ... 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. If os .... E!\A ...................... dIe ....... hea,IcaIt .............. .,. I. raa yIdd ............. 1 .. fordle_cue. 

~"no I"uanuc lhM caJcu.l.donI of CftCtp savin,s d&ae 10 ftIdcIip will be c:aftICt, For caunpk if 

die ..... fIan,. poaud<. pall lilt ...... ' . ... 11 or lilt heal 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 of die psIIo, wUlbe ....... _ . MIl die ..... nnsfcr dvouIh Iht 

pskt:1 i&self wiD be much tar,er. The enu,y uvu.as due 10 chanpn, ~ pstet maICriIl, 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 mainly Oft Ihc ClIe'" 10 whk h 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:r c:q1oWionl in ERA 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&ti 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 

of die ............. wilL 

_ puhwo, for ..... pin IIuouIh lilt ........ , ........ airWU ........ Is .... i&1IOftd1a lilt ERA 

model. ManuflCtUftt'S 1'tpcr1 d\II dds (1C1Of' is hi,hly varilble.1nd conaibuca Iip~lCMdy CO the lOW 

...... , ............. pi. or 20 "' 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 

s 
specify 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 _liltranaindtr '" 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 andS_ . (FuUy modclod) :Whldau \ •

Vacuum p8AC'1 la.sulaUon

A quMDlltive anaI)"is w.inl ERA was conduacd by one manufacc.ntfot a pan:icu....c:onfieuratioa of

'¥acu~ panelsin a refri&enaor hlvinll baseline enerl)'conaumptian of 616 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.

 CE-RM-93-801 COMMENT OR7

5pCCify IOITIC "equivalent numbcroC door-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 INe for 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 

foa b 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. ise tha t good 

de a lgn practice 1. tollowed. It i •••• u.ad that a aanu f ac ture r would 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 account . Hence, the coa.ent would appear t o app ly 

t o • product that would never be .anufac tured . 
Comparison ofthese results illustrates another polemialsource 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 of k·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" of a vacuum panel in I door may cause $OIT)C warping of the,door

and lead to increased airinfiltration. Data from-one manufaetura' indicates the existence ofsuch 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 psketregion.

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. Howeverifthis 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 of the 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 of three-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

of the 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.

 CE-RM-93-801 COMMENT OR7

Comparison or these results illustrates another pc)(cmial source of 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 proceu of't'*1ling arouhd 

vacuum panels. the lCmpenture dependence or k-vaJues •• nd otl:Iei characteristics of foams made.with 

non-CFC blowing agents. Untillhese unccnainties are resolved. the uncenainty analysis muSt address 

all thIce parameters (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" of I vacuum panel u:.. door may cause $OITlC warping of thejljoor 

and lead to increased air ihfila-ation. Data from-one manuflCtUR:r indic.llts (he existence of such an 

effect. but much more data would be requimS to quantify iL The ERA model would then need to be 

modified to account for the resulting infilD'ltion through the psket re&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 if this 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 of increased wall insulation) would increase the temperature of the sheet metal to a level 

Ipproaching approaching that of the 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 of three-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 

of the 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 ot vacuum panels 10 maximize 3-

D eneJ"1Y $lviniS Ind minirNzt 3-0 energy 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-oF/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 equationsrequiring 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 of R-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 arorlends 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 of the latent enthalpy dill for R·l34a will propapte through the ERA model k) affect

its estimates of annual energy use almoSt proponionately. 1bat is. a 1., errorin latent enthalpy 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 forsuch 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: of stile. At an ev.pomin'lempclSUlR: of -2O"F the em;If isIbo

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.

 CE-RM-93-801 COMMENT OR7

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 of state 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 of R-l34a predicted by !:he esD 

equarions of Slate 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 aD equations 

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 of uncertainty from lhe model is to Jt:pllce the esD 

equations of state 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 of annual enellY use almost propontofl.l.lely. 'Iblt is. a 1 ~ error in latent enthalpy 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 10 the way in 

wbich ERA handles cYcling losses, bulthese are probably insiinificant compared ro the 1 ~ enor in 

annual cntr'JY use that could result from inlccuracies in lhe popeny data at the evaponlinl 

1CmpCtUUre. Similarly, a 4~ enor in latent enthalpy at thecondensin& temperaNre will alter the 4T al 

the condenser (and thererore the EER) as the medel holds the user-specified values of UA and 

~bcooling COnSWlt. 

Addi~naJ errors will be introduced when ERA is used 10 simuJaIC mixtures of rdrileranu. 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, beause of a lack of data on.Jlte uncenainty of the intcnction oocfflCienlS lhemsdves, and on 

latent enthalpy and Olher key properties of lhe mri&~nts most likd)' 10 be used in mixtures for 

rd"ri&tnlor-freezers. 

, Fer uample 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 of compressor 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 orI Ie.St conducted by one manuracturer usin,l

.mL.rure 0( 6S~ R22 and 3S~ R141 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 oC crounow and counlerflow .eomcrrieslllhe .

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 of counterflow 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 Cor erCectiveness depends ailicall)' on the ratio or

heal capacities (prodUCl of m.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.

 CE-RM-93-801 COMMENT OR7

l"he ERA moders ability It) ticAl willllllteltuU;ve rcrri,C.rIIlLJ Mel ..,i.lt!u,e,t; is runha limited 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 or the Lorenz. cycle rCll\u'e or the ERA model beaan with a 

limple. anempt 10 compve mockIltSults &0 the ltSuhs O'r a lest eond...acd by one manllrKtlftl' IIsin& a 

.mixture oI65~ 1U2 and 3S~ R 141 b. The ene:rIY uvin,s estlnwed by ERA ~ discarded U nGI 

credible because the proJBfTI predk:ted temper1.ture Iii des of O'nly o,rc and I.rc (or the: condenser 

and evaporator, respectively. Thesc differed &Tully rrom.the l!ides or 30°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' of hea' 

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.of achicYin& thi.s ,Oil in pncticc &iYen the 

pacb&in& conscralnll in rt.lriacrltor/rruz.crs. an IlIcmpl was made. to' comparc ERA', estimates or the 

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: or ener.,. Ute was 

_bc:II. 

Both of these findln&! Indlcate.lhc presence orll leasl one: seriOIlJ cnor In the ERA prop am, 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 propvn ml&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 or cl'Ounow.nd countc.rllow ,eomctrie.S lllhe 

specified desia" condition (minim.1 supelMII or subtoolinl). 

Bec.use or lhese problems with ERA'J .bililY 10' properly modellhe behavtoror milillUteS 1M lhe 

dTcct of counterflow hell exchancu ,eomttries,lhe IInctnainlY tnllY1ls was laminlled II this point. 

1'1lere Is also cause (ot concem aboU1 .ppro~lmllions ~ by ADL In Clkilialin, the effectiveness of 

heat exchineen in the l.ortn~ (),de. Tbe equalion for effeccivc:ocst depends citially on Ihe rlrio or 

heal apacilies (product or mass now .nd specific heat) of thc..'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 III chlev. 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 of the heat c:xchanacr is amaIl, this error in Ihe rMio 01 hell c:apKWe& wiU hive oN)' I

_ eIf""",,1hc ~1Oll _aossIlowIIId _taflow daips. On ....__it....

elfc<O...... is 1-.1lIbstonliIIann may be inlrOll_ ....--.or.....nowIIId

_,.....,nes.

OIhcr~yin,,,,u"'9'ionsmade 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 (orRfriJUMI

mixuu bc:cIUIC they ue known lObc:havc VU"J dilferuaJ)'.

FiNIIy Ihc ERA pro...... Ulna ....,..prdeli..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 Kdcvdopin. benet WI),S of mcdclina coo.+ Sian is 10 be able 10 pndiet I!iWA

coo.+UiC.I"s pa10rmancc with alurnative rclrilcnntl. Sinoc canpraIOtmap equatigu are boch

COli4Awoc, and rdripanl·SpcciftC.1he ERA model indudc:I rwoCMher~lOI"moddL 80ch

RIQUiR; Ihe YSCI' 10 inpulsuch 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

 CE-RM-93-801 COMMENT OR7

calculaaes W5 faOo usin, an lIlIU4It. 5pCdrw: hw which it ~5 from rdri~ Wd and OIoIdec 

ctaCbaJpie:s and &cmpUI1W'CS. However lhe KCUII value 01 dliI1pcc: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 ... Iio 01 heal. c:apKilia by 1M same Caca. 1(Jhc: 

dfcaivcness of the hw cuNnI" 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 ... ......... 

cl aaJ)' 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 not be 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 tempcnNft conaol. If CYlporMOr 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 cl ERA", 'conllOl' o9Iioos. iovoMna Ihe diJdoItp cl,.,...,. W 10 

&be fRsb fco1 c:ompuuntnl 01 bypusin, pan cllbc Cyapcrum-lIP. would Willi. --0 rdMive 10 

_ QOftnaI condidon .. which aM CVlpotllOn ~ de5i"" to opcrI& 

Variable-lIMed comprHlOrt 

RCCCDl cia dopmcMS 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 a vllrilWc·spc:ed dri .... or wilt. 1ft 

ahcmaIivc rdriaawn hiyin,a diffCftNI 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 Accuracy 

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 the 
CompressorraJing poitll mot: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 of the"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.

En...•v RunJime .. vpmu:I.~'ly 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.

ICompressor 1.0 '9.' oz. ,.u,

maD melhod :Rattng potnt 0.9Z0 '1.0 77. '>.43·,

model

Comprusor physical model ADL's documentation ofthe t::ompR.SSOr physical model was ~viewed

by Task Force memberS who design compressors. in anticipation of c: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 of the 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 or enor into the ERA simulation. They SUUested that a D'I(R accurate . - . approach would be 10 simply specify the standard "isentropic compres$Of efficiency" 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.

 CE-RM-93-801 COMMENT OR7

Compressor raJing poilll mot: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 ssures. However these c:a1culations are baSed on cmpiric:aI com:lations 

obWned for c:ompressors usine R· I2. Since the slopes of the' c:ompre.ssor performance maps vl!Y. 

significantly for different reirigtl arus. one would not expca the ERA raona poinl model 10 yield 

accurate results for anything but R·l2. One Task Force member simulalCd IWO refrlcc:rators using an 

acN&l compn:ssor mapobWned with R·l34l. and rqaled the simulations usinalhe ERA rating point 

model. The energy requirements 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 &.encraliud c::oodusion from this 

limited information, However it is clear that this dlla. shown in the table below, pvvides no evidence 

that me min, point mode~ is as ICalrate IS ~ min, widely KCCpICd map-t.sed models. 

Compressor physical model ADL's documentalion of the ~ physical model was ~vlewed 

by Task Fon::e memberS who design compressors, in anticipation of c:ondlKtin, a dc:LaiIcd accurac:y 

analysis, The E.RA model requires the user to specify. amonl other parameters. an "isernropic 

compression efficiency" 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 of power; 

clischarJ;e line loss), Because of the ioousuy's unfamiliarity wilh the$C parltnQcn and rtsulWIIlKk 

of rtllable data. Task Force mcmben concluded that the uncauimy on these input panmetets would 

inaoo.uoe an inlOleRbIe amoum of erTOI' into the 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 minimum 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 exist for a refrigerant blend, and the analyst wishes to explore whether the blend .ight 

have soae promise , then some means must be available to estimate 

how the compressor will behave with the blend . 

Althouqh ~orrelations are an important part of the rating-point 

.odel, various thermodynamic relationshivs also form part of the 

algoritn.s used. for example, the effect on the net pumpinq rate 

of ~efrigerant gas density 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~pressor 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 example , 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 diuvllidWt, eiohcr....jI/lyIil:aI_o.......... paio, _.I.......pIe by.ilemptin' ....prod "".... _ _ til...

C<lI"oditillllS. ThisIs tIte mlnimalllllOWltofnlidalioll_i1oc1 bcf<n sud>..;.w.eoUId be substit.....

for mIpI for c:onswu·speed opuarion with alternadve refriaennq, IfIUCh _ wen avaiJablc, il ali'" be .......bI.....pea tIte ""ysica! and ....., poin'nakIs ......_y-"

_opcratico II oondilions u'niflcandydilf....'flom .... lIO'Fambient .......__

inIec laaperacurcs on which Ihc pcrfcnnancc maps buod. Jiowcva'. before uain. JUdt IIIOdcq, io

JII<dics dI. cfI«U til v_.·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.

11tcERA 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

 CE-RM-93-801 COMMENT OR7

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 of the C)'1Utdcr luclt (I ...... procodn, II ~ ~ EllA 

model doa not cllim 10 be able 10 limulaae lOW)' vane CIDIIIp'eIIG'I. 

Neither ADL 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_ _opention II 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 of vlriobl,·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'Ieihr IDDIkl 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"t aimed 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). If the 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 _ode I 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 wi 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 analysis 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 state 
of rnodd 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~twi... 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

elfoctorrdri,,,,,,, mi by_In, COP by 1.I1i orqoela ............ 1, u

oppIiod 10 a11 ..m' dial do ...-.In. _ val Tho or ollis aroruobvioosly

'i 1 ' ...oil< q""" orrdria<nnt chup dialml_itwiIl_ ...,tipiIl<udy_,

__I ADL_idelllOjoali_ for opplJiollhi. v oD ..mea-"~ or

chup. Moroo.er, ......unojllSlifo<alioo lor oppIyio, r_.. refriacnat equlJlPOd 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 or NllIime 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 allrdri_ 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 __.Iec~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••

 CE-RM-93-801 COMMENT OR7

0( modeJ ruullS 10 uncenainry in &he input ... ariabks rdadnllO &he conecUon fKIGn. nb t)'pC of 

analysis cannot be done in !his cue bcceuse &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.aor ls cw...,...s 011_ puu. The rnt .. iaceIldod to ~ 1M 

dTa:lorldria""'" mipdoa by_1II1 cor by 1.1._ dIc_ofqoeleo ..... IIour.· hil 

applied '" all rem_1hoI do ... -.In I _ valve. The ___ of dIU_ 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 110 jUIIiIIcaIioo for 1ppIP,1 die _ r_ .. ~ oqllipped willi 

.....,. .... n:cipnulinl c6mFrcu .... _ hi .. I hlah·aide...,., UId III111aIaap blhe 

Itfri ...... (whidl diuol_1o Ihe 011 durina die a/r-qclo) 10 VIpClria UId ...... drculadna duria& die 

on-cyclc (il ftI.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, of NO iaa (...y 

q<1o) <&/I be mdible. On dIoortcicaI--" aIone.lhe pea ......... due .. __ ......... 

aast iaaease as nan time: dec::IuIea. To ilNMnle this dYea OM lInIftulaawu provWcd 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 """"""'" _1hoI r ...... _Ibao n:fri_ mipuioo ... y .... _ 

dYoc:u on c)'Clil'lossc:s. 

1bc aocond pan or !he q<11II1_apptia only 10 _ havIolI _vol ... IIIC1U111y 

_Ihe COP 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 ICfriaaucn wI.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 .i9nificant experi .. nta l data baa. ia reported to have been ~eveloped by ... nutacturer in an atteapt to evaluate the cycle 

0111 .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)' nyulwu 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 10 remove 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 airfrom 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: airflow rue CNtr me 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

IWO eVaporalors 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 evaponlOf caklrinMIlu 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~yWo the COlI

1\rcnrquircd Ift:II miJht be IUbufMiaIIJ -auor 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•

 CE-RM-93-801 COMMENT OR7

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 lime mri,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 .... -.Jd be .... dimlnadoa or Ihe CVIjlOIVOfr .. ,.,...... • 

·..-Ilhe compttuor ena'J)' 10 rtrnOYe dw heal from lbt c: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 

_I ochuduol<:vapO .. "Of c:onfi' ........ ilia, mlllU "ploil 0Iher 'yp<S 0( CIICIJl' cooscrvllion 

opportunities. 

1be buc case rcf'ripalOl' for chis e.xpcrimenI was usumed 10 haw. unak evap: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 evaponlOf ran power whhin 5t.. The comIJincd ell' ... 01_ cv_ .... spoci/ie 

"""",,",lies propaplCd ,,,",,,'" 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 tamS oIlhcir conduccancu 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., 

ne 

10 na.~ 

....... lfta rN ... 

_Ie-bc~l, -CMtI'1 ponioA .. Ff 01" 

• ...rtct 

MIl,... ... ... 

"-,,, ~.,......w., ......... ., EaA. 11 ...... 

-.0 lheODll 

10 

~ 

....... ItIIIIyUt "1IIe ~ctjffCIUCC 

IOpnIC*Id -S 

between 

'1tdd tome '1inJIc. -iaN ,,,,,, Wo .1aUiIiYil,oI.add1Caka 

..... ~...,.IY*IN 

10 will,.,.. ad..,...,

deWW 

. Hawrnct 

a. .. 

k ~ 

,.. .. ,...... 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 this 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 of the 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 of the 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 of the 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 oferroneous assumptions and omi.ss:i&lfIs in the ERA model itself. The findings

tq)Of1CIoo .hove ltad to the following conClusions and recommendations:

Estimatcs of energy 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 of eneTlY 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.

 CE-RM-93-801 COMMENT OR7

because of the relative dlrficuhy of the calorimetry p·roble.m. This produced. ± 1.S'II uncenaioty in 

energy use. 

The energy savines 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 of the platCostyle swic eviporltors are.Duch JrC&'Cf &han the aru of the sinllc 

forced4Bft evapontor. If the 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 of refrigerant switching valves, sensOrs and CO'Ib'OUen to me eXIrII COSt of' evapontor 

swface IJUS.. It may 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 of Ihe accww::y analysis ~uct.ci\ 

for the conservation options listed in Table 1. The options were selected bc:cau.se lhere is inadequate 

lest dallavailable 10 validate the pans of the ERA model used to calculate enerzy savingS. For a few 

of these conservation· options. limited amounts of lest 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 of the 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 of the analysis could not be 

completed bectuse of erroneous assumptions and ~ in the ERA model itself. The findlnls 

~ .bove ltad to the following conClusions and recorrvncndations: 

Estimatcs of enefgy 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 of SOtI or mea .• 

ERA's estimates of cnerlY 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 _isinterprets 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 inexperienood 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 uoaopesCluses 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-evaporltorsystems 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 of alternative rem.ennts or uotrOplc blends is further

compromised by ERA's compressorrating 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 userspecify 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 calorimelCr datfsh9Vld

be obtained (or analysis of any ~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 designeRevalUiIt more

lClCUr1tely Ihe derivalive of energy 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

 CE-RM-93-801 COMMENT OR7

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 of ERA lhu simwucs Lorenzeyclc.t. Rcpwcd ~ 

by in cxpericnc:c:d mngenlOr dcliJDCl' flliled 10 JrOducc a rault ahowinl' ~ &lick of 

the mapiludc predicted by the NIST pope:rty dIlL AI~ BRA', u.se of a constllu IpCCiIic be&! to 

approximate the behavior of uotropcs 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 hell e.xchanJCt1. 

For dual·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 into any 

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 of eliminadnc thele problems iI not 1nc:ludcd in the model. 

ERA's ability 10 predict the, e«cclS of alternative refri,c:ranu or t.CIOlrOplc blends Is funher 

compromjsed by ERA's compressor 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 of any 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 of steady: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" ~aeilitate anal)'scs of parameDic unc:enainty. and would help dcslanen evaluace more 

IlXUralel), the derivative of enerlY 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 cia ill. 

- !\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 cntIJYCCXlJCI"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

'-10dlt pul>I.,_dlt ......,_01 .... EllA __110 10__willi pal.....

A fiDII Cllloionuy _IsIlOCWIr)' u ...............EllA _ II.daIpllIlldoI, .

___ 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_toooml"'''''' rO( ERA~ lock 01oquadooadacribioi .........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,tTlIJOT CdbiMI

/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..,rruo/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

 CE-RM-93-801 COMMENT OR7

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. DIu oa &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_ if aU Iopuu and oquadou __ ..... porf"" oenaioIy . .... _ 

-"I ooIybocopobleol_lin, porf_ .... p .... ppoial. It could ........... 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 oIfusn pcrfarTi\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. 

mri""", 

ConIdin.I. 

miallU'Cl·.l'roc. 

C and F. .. Vincyaod. XVIII 1.11

'Hea, . C..,,,u .. chan,er of Rtfrt,_,.... ohcnnaI perf ......... 

MoNreal, 

rc. .... A., ~ 

1991. 

flynn. S., K. Rouch and H. A. Fint, "Finile cklnenl anllysiJ of heal nnw darou.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.ljpers. ·C\'<lin' ...... 1n domcsIic oppWa_: an uperime:nw and ~ lMIysb", "ot.UR PwJM Cotf~.ItC.t. Wca LUlyea., Indiana. AUJUSl 

1990. 

17 
 CE-RM-93-801 COMMENT OR7 Morrison. O . • nd 

M. O. McUndcn, AppJi(Qliolt of II Itord 4pMrt4quG1io" of 10 re/,I"rQllu GIld 

,qri,c'4Iff mUfwU, NBS Technical Noce 1226. NI'ionaI Bureau of SundudJ. Oahhenburl MD, 

1986 • 

Poncr. K. J .. and 

C. W. Bullard. M«kNltf ONJ StltSj,iv/ry (JNJ/ysJI 0/" rqrlpratorl/rttur syIUm. 

ACRe-TR-ll. Air Condifioninl and ReinaeraQon Center, Uniwnicy oI1Uinoi, II UrbM,a· ._. 

Ownpai,n, December 1992, .7 pp. 

UnilCld StileS Envitonmenlll Procection Aacncy. -Mr.aluple pch .... ys 10 super errw:ie,u rcfri,auan-. om", ol AunosplIcric and 1ndoo< Air Propuns. DRAfT, "'1Inwy 1992 
OWENUORNING 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

 CE-RM-93-801 COMMENT OR7

oWENt.CORNING GRANVILLE TECHNICAL CENTER 

2790 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 FIBERGLAS 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~ngthe 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

 CE-RM-93-801 COMMENT OR7

H. Alan Fine 

November 9, 1993 

Page 2 

Lastly, we 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 HOME APPLIANCE 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.

 CE-RM-93-801 COMMENT OR7

.EONARD J. SWATKOWSKI, JR. 

WAECTOR, ENGINEERING S£.IiVICES 

ASSOCIATION OF HOME APPLIANCE MANUFACTURERS 

20 NORTH 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. 
ASSOCIAnON OF HOME APPLIANCE 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

 CE-RM-93-801 COMMENT OR7

ASSOCIA nON OF HOME APPLIANCE 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 ha t confi gura t 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 desI 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 of Home 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 of the NAECA Task Force of the Association of Horne

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 of multizone 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 of the 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 of energy 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

 CE-RM-93-801 COMMENT OR7

Accuracy Analysis of the ADLIERA Model 

Background 

Prepared for 

Association of Home Appliance Manufacturers 

NAECA Task Force 

Prepared by 

Clark Bullard Associates 

509 West Washington Street 

Urbana lIlinois 61801 

This report was prepared at the request of the NAECA Task Force of the Association of Home 

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 US EPA'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 perfonn the analyses reported 

here and provided all the necessary input data. 

Purpose t and scope 

For.many of the 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 of energy 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) 

of the ERA model and user's manual. Thm version was said to contain a number of improve me IllS over the version 

rev iewed 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 of energy 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 if the 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 of knowing 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 of data 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 of types #2 and #3 cannot be quantified in this report due to lack of data, 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 of error. 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

 CE-RM-93-801 COMMENT OR7

• 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 of energy 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 if the 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 of knowing 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). 

The paucity of data 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 of inaccuracy 

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 of types #2 and #3 cannot be quantified in this report due to lack of data, but in 

some cases it was possible to use limited proprietary data from manufacturers to test 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 of error. 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 of the 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 of x lies within the range

x ± 6.x. Then there is a 95% chance that the actual value of E lies within the range E ± dE. If "these

uncertainties are normally distributed, the upper and lower limits of x 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 of hypothetical 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

 CE-RM-93-801 COMMENT OR7

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 of x lies within the range 

x ± Ax. Then there is a 95% chance that the actual value of E lies within the range E ± AE. If these 

uncertainties are nonnally distributed, the upper and lower limits of x 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 numerous 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 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 pennit accurate estimation of the mean values of the parameters describing the 

improved systems; and 2) a Monte Carlo analysis in which hundreds of hypothetical refrigerators were 

"constructed" from inputs Xi 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 simpler root· 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 ngle-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 of uncertainties 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 of the model is how well the mean values of the replaced foam and the vacuum panel are

known. In the case of RII 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 of this 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 of foam by vacuum panels would be those

associated with the thermal conductivity and thickness of the vacuum panels. Because of the 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

of parameters describing the base case design. Examples include heat exchanger conductances and

gasket heat leaks. Despite years of testing and analysis, uncertainties remain due to measurement

limitations and the lack ofstandardized 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 of the 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

 CE-RM-93-801 COMMENT OR7

Application to conservation options 

To estimate the uncertainty relating to a particular conservation option, we will ignore for the moment 

the effect of uncertainties 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 of the model is how well the mean values of the replaced foam and the vacuum panel are 

known. In the case of Rli 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 of this 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 of foam by vacuum panels would be those 

associated with the thermal conductivity and thickness of the vacuum panels. Because of the 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 

of parameters describing the base case design. Examples include heat exchanger conductances and 

gasket heat leaks. Despite years of testing 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 of the 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 leak, namely the relative positions of the 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 of either, 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 of Boughton et. aI. (1992) and that of Flynn, 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 of the 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 of energy 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 of the 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

 CE-RM-93-801 COMMENT OR7

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 of either. 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 of Boughton 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 of the 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 of energy 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 of the gasket. On the other hand if the flange terminates 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 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 or cabinet 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 throll Q"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 of door-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 of the 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 of Cabinet 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. If DoE were 10 simply use a laboratory teSI result for a

new (R141 b) foam 10 calculate energy savings, Ihe input value of k might be in error by as much as ±

10% because of yet-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

 CE-RM-93-801 COMMENT OR7

specify some "equivalent number of door-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 laboratory studies aimed at isolating 

gasket-region heat leaks from the remainder of the 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 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 of Cabinet and System 

And Size Openings, Etc.) (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 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 estimated 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. If DoE were to simply use a laboratory test result for a 

new (R141 b) foam to calculate energy savings, the input value of k might be in error by as much as ± 

10% because of yet-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 of error: 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 ofsuch 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 of increased wall insulation) would increase the tempcrarure of the sheet metal to a level

approaching approaching that of the 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 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

of the 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 of vacuum 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

 CE-RM-93-801 COMMENT OR7

Comparison of these results illustrates another potenrial source of error: 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 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 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. 

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 th e 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 of increased wall insulation) would increase the tempcru rure of the sheet metal to a level 

approaching approaching that of the 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 

of the 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 of vacuum 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 ofstate 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 ofstate 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 of R-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 ofstate 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 of UA 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 of the associated uncertainty could be conducted,

however, because of a lack of data on .the uncenainty of the interaction coefficients themselves, and on -~

latent enthalpy and other key properties of the 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

 CE-RM-93-801 COMMENT OR7

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 of R-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 of UA and 

subcooling constant. 

Additional errors will be introduced when ERA is used to simulate mixtures of refrigerants. 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 of the interaction coefficients themselves, and on -~ 

latent enthalpy and other key properties of the 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 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 of compressor 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 of crosstlow 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 of energy 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 of crossflow and counterflow geometries at the

. specified design condition (minimal superheat or subcooling).

Because of these problems with ERA's ability to properly mooel the behavior of mixtures and the

effect of counterflow 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 of mass flow and specific heat) of the refrigerant and air streams. ERA

9

 CE-RM-93-801 COMMENT OR7

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 of compressor calorimeter data obtained with the refrigerant or blend in question. 

Lorenz cycle 

Efforts to conduct an unc~rtainty analysis of the 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 Task Force 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 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 auempt was made to compare ERA's estimates of the 

performance of crossflow 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 of energy 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 performance of crossflow and counterflow geometries at the 

. specified design condition (minimal superheat or subcooling). 

Because of these problems with ERA's ability to properly mooel the behavior of mixtures and the 

effect of counterflow 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 of mass flow and specific heat) of the 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 of this specific heat can vary by as much as a

factor ofseven 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 of the 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 of crossflow and

counterflow geometries.

Other simplifying assumptions made in the ERA model will also introduce uncertainties into estimates

of energy 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 of free.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.

Va ria ble-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 of modeling 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

 CE-RM-93-801 COMMENT OR7

calculates this ratio using an average specific heat which it determines from refrigerant inlet and outlet 

enthalpies and temperatures. However the actual value of this 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 of the 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 of crossflow and 

counterflow geometries. 

Other simplifying assumptions made in the ERA model will also introduce uncertainties into estimates 

of energy 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. If evaporator 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 of free.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 of modeling 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

_ Compressor physical model ADL's documentation of the compressor physical model was reviewed

by Task Force members who design compressors, in anticipation of conducting 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 of power;

discharge line loss). Because of the 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 of error 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

 CE-RM-93-801 COMMENT OR7

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 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 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 

~ Compressor physical model ADL's documentation of the compressor physical model was reviewed 

by Task Force members who design compressors, in anticipation of conducting 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 the indusoy as "piston work 

isentropic compression efficiency". This parameter equals the standard "isentropic compressor 

efficiency" defined in thermodynamics 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 of power, 

discharge line loss). Because of the 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 of error 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 
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 of the 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 of test

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 of these 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 of refrigerant 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 of each 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

 CE-RM-93-801 COMMENT OR7

In contrast to power input, 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, Ipm and a relation between volumetric effi.ciency and pressure ratio 

that is hard-wired into the program. This type of model places most of the 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 

of the suction line and the suction port of the cylinder 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 of test 

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 of these 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 of refrigerant 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 of each 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). If the 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 
of model 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 of refrigerant 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 of this error is obviously

dependent on the quantity of refrigerant charge that migrates, it will therefore vary significantly among

refrigerators. ADL provides no justification for applying this value to all refrigerd!ors, regardiess of

charge. Moreover, there is no justification 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 of the cycling correction applies.only to systems having a shutoff valve. It actually

increases the COP as a function of duty 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

 CE-RM-93-801 COMMENT OR7

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 of refrigerant migration by decreasing COP by 1.1 % times the number of cycles per hour.8 It is 

applied to all refrigerators that do not contain a shutoff valve. The magnitude of this error is obviously 

dependent on the quantity of refrigerant charge that migrates, it will therefore vary significantly among 

refrigerators. ADL provides no justification for applying this value to all refrigenltors, regardless of 

charge. Moreover, there is no justification 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). Sinr c 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 of run 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 manufactur~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 'of runtime 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 of duty 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 remperatu1 .... . 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 dirccl.ly from the reference lO Lhe single experiment 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 of the intercoolers. The particular configura"rion

considered in this analysis has no air exchange between the two compartments, and assumes The

primary mode of energy 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 of energy 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 of the

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 of these 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 of calorimeter 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

 CE-RM-93-801 COMMENT OR7

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 of the intercoolers. The particular configura'tion 

considered in this analysis has no air exchange between the two compartments, and assumes The 

primary mode of energy 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 of closed-door operation. It appears that ERA is unable to 

model other dual-evaporator configurations that might exploit other types of energy 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 terms of their conductances and their areas. To ensure that the cabinet 

temperatures were comparable between the single- and dual-evaporator simulations, the areas of the 

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 of these natural-draft evaporators, which are assumed to be known only within ±15% 

9 Actually a typical evaporator calorimeter is able to compare evaporaters wilhin ± 5%, but the absolute value is more 

difficult to determine. Since a dirrerent type or calorimeter 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 Tecognizes 

that the cost difference 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 of uncertainty.

For example the areas of the plate-style static evaporators are much greater than the area of the 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 of refrigerant switching valves, sensors and controllers to the extra cost of evaporator

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 of the 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 of test 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 of erroneous assumptions and omissions in the ERA model itself. The findings

reported above lead to the following conclusions and recommendations:

• Estimates of energy 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 of 50% 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

 CE-RM-93-801 COMMENT OR7

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 of uncertainty. 

For example the areas of me plate-style static evaporators are much greater than the area of the single 

forced-draft evaporator. If the 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 of refrigerant switching valves, sensors and controllers to the extra cost of evaporator 

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 of the 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 

. of these conservation options, limited amounts of test 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 of erroneous assumptions and omissions in the ERA model itself. The findings 

. reported above lead to the following conclusions and recommendations: 

• Estimates of energy 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 of 50% or more. 

• ERA's estimates of energy 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 of ERA 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 of 7 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 of energy 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 of eliminating 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 ofsteady-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 of parametric uncertainty, and would help designers evaluate more

accurately the derivative of energy 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

 CE-RM-93-801 COMMENT OR7

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 of ERA 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 of energy 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 of eliminating 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 of parameDic uncertainty, and would help designers evaluate more 

accurately the derivative of energy 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 of conservation 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 of the 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 of equations describing the mass flow-pressure

drop relation for the capillary tube. and equations that would keep track of the 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 ofhouseJwld refrigerator cabinet

loads, ACRC-TR-21, Air Conditioning and Refrigeration Center, University of Illinois 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 ofRefrigeration, Montreal, Aug 1991.

FlYQn, 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 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

 CE-RM-93-801 COMMENT OR7

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 of conselVation 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 of the 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 perfed certainty, the model 

~ould onl~ be capable of representing performance at a sing~e design point ~ 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 ¥C intended to compensate for ERA's lack of equations describing the mass flow-pressure 

drop relation for the capillary tube. and equations that would keep track of the 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 of the 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 of Illinois at UrbanaChampaign, May 1992, 135 pp. 

Conkli!l, J. C. and E. A. Vineyard, "Heat exchanger thermal performance for two nonazeotropic 

refrigerant 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 ofa hard sphere equation ofstate 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 ofa 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 of Atmospheric and Indoor Air Programs, DRAFT, February 1992

18

 CE-RM-93-801 COMMENT OR7

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 of Atmospheric and Indoor Air Programs, DRAFT, February 1992 

18