NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT NBS REPORT

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U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, repr part, Is prohibited Approved for public release by the

unless permission is ol . . idards, Washington n „ c . Director ot the National Institute ot

25.D.C. Such perml >rt has been specificany prepared if tha Standards and Technology (NIST) ort for , ts own use , on October 9, 2015.

S£L?

Defrosting Character! sfcl es of the Theroe-Kiag l-fen are

house &eflftgerating Unit, l£edel l 51, 1th Gasoline and

Electrics .Drives

l. ii -T£ ouseriof

The potential UMhlMM of full reverse cycle operation

of the gaeellne engine driven, refrigerating mite for heating

mxt defrosting was invest* mted by Msec -juarttfrsp , >, «d

in thf* coimeetlon the Heating and Air Conditioning lection

was requested to melee a study of the defrosting characterise

tics of the I-ton mit , being manufactured by II* >. Theno

Control Company at that time, and identified m There# f ing

iisHiel E:$l* A development contract for an improved defrostlag system had hem awarded fey Headquarter®, , Ei.'B and it

was desired to know the details of the present system to per- it an evaluation of any modification*

Accordingly, tests of the defrosting ehartketerlstles of

t .=i© unit were conducted, and have been completed, Coafeitlcrr>£

studied were?

a. ith automatic control of d«fro«ti *uj? cycle*

b* .1th nenaal control of defrostin':-; cycle*

c* At 35i refrigerator tent-erature*

4* At OF refrigerator temperature*

.‘.iter invest! mtiag the variables Hated above with the

unit refrigerating an empty 600 cubic foot warehouse, ether

teste were made with the warehouse loaded with **c* r*Attons to

sionl&te a -refrlgemter in service, and tests were al**o run

of the defrosting performance of this unit with the electric

meter conversion drive apparatus*

s. Ti.f moeirimg

the teste with the mmr-ty warehouse Mere ©ensile *«d as

the firs* so* Th# has* transmission factor ©f the deBmmtahXe prefabricated ware* ©use uas determined by operating

at a constant internal temperature for several days, and uai?

the average outdoor teeperetvre for the period involved* Thi

method| while not as precise as similar tests cor. ducted in a

controlled temperature nee*, was considered suf iciently ace - nte for th® purposes of these tests* In order to avoid the

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direct effect of solar i Ml the warehouse, it was shielded

*l%h coat a Mounted a foot ox* acre about the roof*

Fhe unit was Installed in the isonsal panel y rovlderf at

©«e end of the warehouse* *• easut'esents of aabient t^apereture,

refrigerator temperature, teepeircture of the stored roduct

,

and cany temperatures, pressures, etc*, pertaining to the

operation of the refri&erAtiug unit itself were observed during the testa* Hot all of the data recorded In these tests

are reported !:*:rc but if additional iufomatior is desired it

can be suMMurlsed or request*

The : ©del b 51 Ther-ia-ling unit was provided with a. tiding device, operated frost the engine crankshaft, uhldfc at constant speed of 2400 rpa provided an automatis defrosting approximately every 4*1/2 hours. The length of the defrost cycle was

controlled by & licit thermostat which restored the unit to

refrigerating service. It should be- noted that the Medal h . 51

was not a reverse cycle unit 1st that it did not rofri /crate

the tondatteer during the heating operation* The hot discharge

.«:• was introduced Into the evaporator and the heating was

limited to the work r*srf©n»®d or. the -.as by the cm rar^or, ••••it,h the refrli .--rant condensing in the evaporator* All tests were

aade with the refrigerator teaper&fcure at approximately 0* F

and a relative humidity of 6<K* faring extended operation at

OP, *cne • if flenity was experienced with tVe hu In^ficr freezing up , but . is old bot occur '.o frequently ss to dlstrub t>*e

results significantly* during the tests that were terminated

ten a taii.para.ture of OF could no longer be tsaintai nad betau e

of the frost as cumulated on the evaporator soil, the refrigerator

te- -iperature would mmtimes rise above OF before the defrost

operations were began*

During the tests with the refrigerator leaded, the com*

paresnor (1 - lui ©del 4»*S) failed and was replaced with

another of the same model borrowed from another 1 251 unit on

hand, Tests ©f the unit with the electric conversion drivo

apparatus were made with this second compressor and no eonparisen tests were jand# to determine the relative capacity of the

two compressors.

3. TF3T BLK30LTJ

At 35? refrigerator temperature, in the first phase of

the tests, i . e* , with the empty warehouse , the Afrost cycle©

occurred at intervals of approximately 4-1/2 hctire, under

automatic control., lasted from 14 to 16 minutes and the amount
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36 -’{>?.;i . and

the refrtgwretnr te? rertturf* rose or the average jfrer

35'' to 59*1 during tfcr* defrost period* v — rint 5r r ;fri~

gerater temperature should be considered is the light of the

s»anr:*r of testing* To lead the refri -e rating uni*' c fall

capacity, 1sternal heat was ap-liod electrically with the

i ,r/f nt arounttwn: lied in the c^ae of the tests un. er auto*. Stic

cc-rtrel of defrosting* ' v ea the refrigerator ter;.-«nture rr- s*

above the control pel q, in t 1® ease 3$f, the crntrol'U ; turfred

©IT thf’rri cl pal ir.tcreel hg.fr. The r*’ :>e in reffire ; -,toi t : - pare sure wss then caused fey other internal heat sr 1 (.f t; ,

?• txJrfif >r, §ie.) } heat gain tl rough the walla, *tr;d he xt 4>.lv :.. of- t • th^ ; T^.;'©r - tor unit. In the Ohse of the teste ••.-•- A. tf e defrosting w*e under saansal control, all of tht Intern 1 heat

w 1 ©. f hurit-.r the defrost, end t

: * rise 1» refri afcor te^

©e raters was dee to heat ain through the trails ar.d * eat ; 5 *ee

©!'i" by the evaporator unit fly* In both e* ses defrost - < .ts

Iffei - course, affected the amount of V-. ?t entering through the wareh wall# 6’ ring the various de£roe beets* Ike eayeheaje

used for th«*t tests had a tran a.- 1 scion factor of approx!-

ft&trly 56 Btu/hr,/*P, so that 3- varying tnfeient tenperatiiree,

the > *v '“.tin through the walls night rmm fro® 2260 yui/h* at

a 40 do ree 1 diffe. once to 3040 Btu/rr at a 90 degree i fi .- orence* Tree f 3 slier con flit iov e would occur it service l

1- w a these vari ations redoc

observations but trust fee considered ir. cvaln-itlng the r-sul . ?.

Under manual control at 35r refrigerator to»*>*ratur. t @

time required for the cell to acoumsl&te sufficient fr© #t or

ice to reduce the refri derating capacity to approximately

6C 30 Btu/hr was 36 h urs, .and the anoust of * iter obi 1- f.f, /rr,:,

tfe:; z defrost was nearly 49 pq :ni for the same refrigerator

teapereburv* Fifty J&.i»tties were requ 4 rco to 1 afro at aid lue

warehouse t-r- .*r .are rase to 60 T Tjrlnr tfros t.

At W rtfHgssrat-or temperature, the frequency of tfefror

eytlee under automatic control v/as once every 6-1/2 turnra, the

rest 'wig varied frees. 14 to 1? minutes, and the vat

’ tained fren the defrost r n ec frc,. ": to 3-3 A pound-.., : ?.- refri ;te rater air tea^er^tere rose fm® 0*h to p*F duri..; . efrostirg, Bader Kaaeal control at the sane refrigerator u.r - trr&ture, r/N-. tirtc- red t© nc urul- to r-nr-ah ice 0 .•- jes

the eapaeity to a- troxinately 7200 Bt-u/hr w a* in ^xc^j?3 of '-'5 hours, and the WM»unt of water obtained during defrost was

23-3/4 round a. The r«-fri aerator tes- ^errture ro--e to $?'.)!• ; ur !?»•»•
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the defrost period, which lasted about 2$ micutes* Under

r<.arv’-a the refrigeration ©yel* was started after

defrost by the a&sie temperature-limit thermostat on the

evaporator coil as n.^od under automatic control*

Milder the ihm4 obese, with the warehouse loaded,

test# wore made with the unit operated both with the gasoline engine drive and with the- electric motor eonversion

drive* To sirfsmlet© a produet lead the warehouse was leaded

with 154 cartons of Army W C* Rations, the case# being 1*1 cubic

feet in v and weighing ? • nee# fbSSO S were

arranged in four eolw»ns two cases wide, two cases rise? arc

stacked snyroxlBately 9 cas*i« high, with ventil ting aisles

or spaees between cel asms* Tfceroocmirles were pieced at

marrows point® in and ors these columns? on the exterior

carton surfaces fneisr the carnors of the refrigerator, be*

tween two esrteits and about 3 s in fro*:, the cut side of the

colu- » (referred to as "ireide turfaee* ) and in the center

of the as.tin.'' surfaces between two c Art*;- ns, ( referred to as

"center* ) • The t o»j-*ro.turt ot&erv tion# of the carton starfade? r. •*?• ed were 'J 1 bade fro® t’her"*oeouplo*

approxi&atatiLy midway fro® floor to ceiling#

The primary ywryose of re pettier these defrosting tests

with the loaded warehouse whs to detorikiM the effect on genera! storage teaser*turf- when there wee produce in the varo*

house, that would absorb heat as seepsrod with our previous

testa with the empty warehouse* Tests were made only at 0

re fr5. =- er.-> tor te^yeratur# * The test with the gasoline mg ino drive wee terminated

sooner than desired because of failure of the e-rpre? sor*

This failure did not prevent the compressor fro® Handling refrirerbnt, but it would not ratain sufficient oil for adequate

lubri.es. ti*- a* Frost, was eseumlstod for five days, at refri -e.. . t r emd.it. lone of approadsmtely OF and 60$ r*b. , with varying

ten* wraturee fro® 4& to 52f * The defrost required 50 minutes, t e amount ©f water obtained waa 37-1/2 pounds, and the a v rage refrigerator air temperature .rose from approximately 6F to 20F

»

the temyereturen of the cases of rations rose as follows: outside surfaces * 16 degrees {fro® 6 to >21'}; Inside surfaces,

h *<?froes (from 4 to *f ) 5 and center, none (stayed at IF)
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Following this test the e .cpres#or wa® reeved and

smother in trialled* The replacement so^pre .or was borrowed

fro® another f 51 on hand, and had been operated during; tests

of that unit. It retH'ineti iu» oil charge and trap ed out

the additional oil which had been. added to keep the defective

compressor operating* The unit was then placed in the test

calorimeter in the c ontrol1 ed-1e mparature test .room and coroarative capacity teate were made with the geeoline on ;ine

drive versus the elr-etri« motor conversion drive# These tests

were made with a rei- /iterator temperature of OF and in an ambient temperature of HOF. Under these conditions the net

refri seating capacity with, the gasoline drive was approx! ..ately

97$0 Btu/hr and with the electric motor drive eras Apyroxii. vtcly

5970 Btu/hr# The results of these comparison tests will be

covered in acre detail in another report, but are significant

in connection with the defrost in.-’ tests In that one .such test

wee made with tfc<r electric «mt or drive# It should fee noted ti-at

the operating speed of the eorapressor was different for the z.m

methods of drive, 24CM1 rpm with the gasoline engine and 1750 rpm

with che electric ester# The fans, Seth evaporator end ear- denser,

were operated at the cane speed for the two cases, however, by

means > m-; It h I

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:

3 ©y si ? ... After placing the unit beck in the loaded warehouse, a defrosting test was made with the electric motor drive, frost

was ttsd for about 35 days, whs* the unit was unable t©

hoi the refrigerator tsunueratur* below 12F in an ambient erature of 75b, corresponding to a refrigerating capacity of -a? • roximatsly 3500 Btu/fer. The defrost required 1 hour $0 i&itratos and

the water obtained was 69 pounds# The refri -orator air tempera*

ur# roes fro* Iff to 32?, and the stored produce rose in testersu- ture as follows s outbids surfaces, IS degrees (from 12 to 30F)$

inside surfaces, 7 degrees (from 10 to T?P); and the center, none

' stayed at !0F)# The temperature rise of the Individual pi-skaesa

of *G* mtlons was undoubtedly less than that of the exterior

surfaces of the cartons because of the insulating value of the

cardborad carton*

5i'o tests wore made in the loaded refrigerator with the

automatic defrosting control since it was clear that the in c cruel temperature ri with the leaded refrigerator was materially

less than, with the empty warehouse, and suitable ce r arise*

data had already b#o* •stained with the estpty warehouse under

'•ut ii ,1 control*.
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