Purdue University
Purdue e-Pubs
International Refrigeration and Air Conditioning
Conference
School of Mechanical Engineering
1988
An Evaluation of Two Refrigerant Mixtures in a
Breadboard Air Conditioner
W. Mulroy
National Bureau of Standards
M. Kauffeld
National Bureau of Standards
M. McLinden
National Bureau of Standards
D. Didion
National Bureau of Standards
Follow this and additional works at: http://docs.lib.purdue.edu/iracc
Mulroy, W.; Kauffeld, M.; McLinden, M.; and Didion, D., "An Evaluation of Two Refrigerant Mixtures in a Breadboard Air
Conditioner" (1988). International Refrigeration and Air Conditioning Conference. Paper 34.
http://docs.lib.purdue.edu/iracc/34
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AN EVALUATION OF TWO REFRIGERANT MIXTURES
IN A BREADBOARD AIR CONDITIONER
William Mulroy
Michael Kauffel d
Mark McLinde n
David Didion
Nationa l Bureau of Standar ds
Gaither sburg, Marylan d 20899
Abstrac t
that is
An experim ental, water-to -water, breadbo ard heat pump,
for
one which could easily be reconfig ured, was constru cted
4 ahd
compari son of pure R22 to the refrige rant mixture s R22/R11
.
Three evapora tor configu rations were extensi vely studiedcy
R13/Rl2 .
best efficien
In all cases the best mixture outperfo rmed R22. The higher than
with R22/Rl1 4 was 32% higher and with R13/Rl2 was 16%
other obserya tions were,
the best e~ficiency measure d with R22.
er efficien cy
first, that mixture s can take advanta ge of heat exch~ng
rant is
that, ih a gliding tempera ture applica tion; a pure refrige
e between the
incapab le of utilizin g. Secondl y, that heat exchang
to some mixed
condens ed and evapora ting refrige rant is benefic ial
of enthalpy
refrige rants . . Finally , mixture s exhibit nonline arity
signific ant
versus tempera ture in the two phase region which has
impact on both heat exchang er and cycle design.
EVALUAT~ON DE DEUX MELANGES
D'AIR EXPERIMENTAL
DE
FRIGORIGENES DANS UN CONDITlONNEUR
d~re
Une pompe a chaleur eau-eau , exper~mentale, c'est-aRESUME
ration, a ete
une pompe dont on peut facilem ent modifie r la configu
s de
cbnstru ite en vue de la compara ison du R22 pur aux melange ete etuont
R22-Ril4 et Rl3-Rl2 . Tro~s configu rations d'evapo rateur melange avait
r
diees de fa~on poussee . Dans tous les cas, le meilleu
nt du melange
une meilleu te perform ance que le R22, le meilleu r rendeme
de Rl3-Rl2
melange
du
de R22-Rll4 etait superieu r de 32 % et celui
On a observe
superieu r de 16 % au meilleu r rendeme nt mesure du R22.
ben~fice du
de plus, d'abord que les melange s pouvaie nt tirer un
applica tion de
rendeme nt de l'echang eur de chaleur pur que, dans une
le d'utilis er ;
tempera ture glissan te, un frigorig ene pur est incapab
condens e et le
ensuite que l'echang e de chaleur entre l.e frigorig enes
melange s de
frigorig ene en evaporat~on etait favorab le a certains
non-lin earite de
frigorig enes. Enfin que les melange s present ent une
diphasiq ue,
l'entha lpie en fonction de la tempera ture dans la region de chaleur et
eur
ce qui a un impact net sur la concept ion de l'echang
du cycle.
2
I ,
An Evaluatio n of Two Refrigera nt
MiXtl.il"es
in a Breadboar d Air Condition er
by
W. Mulroy, M. Kauffeld, M. McLinden and D. Didion
INl'RODUCTION
The National Bureau o£ Standa-:cds has evaluated two nonazeotr
opic refrigera nt
mixtures, R22/R114 and R13/R12, in a water-to- water
breadboar d heat pumping
apparatus at temperatu res typical of air condition ing applicati
ons. As is sh01m i_n
figure 1, the best perfo1:min g test series with the mixture
R22/R114 resulted i.n a
coefficie nt of performan ce of 6.9 (EER = 23.6), 32% higher
than the best efficienc y
obcained with pure R22.
In figure 2, the best efficienc y with the mixture R13/R
I2
was 16% better than R22.
7r-----~-=~,-----,-----,
-----.
R22/R114
~
ci 5
ci
44%
4
• WHh liquid IinS neat exchang~;~r
• Without liquid line heat exchanger
3 ~-----L------L-----~------~----_J
100
80
60
40
20
0
WEIGHT% R22
figure 1:
Performan ce of the mixture R22/R114 fo1: evaporate !: configura
tion No
4.
7r---- -,----- .------ .-----. -----.
R13/A12
6
~
ci
0
C.O.P for R22
• With liquid lino heat exchanger
• Without liquid line Mat exchanger
4
100
80
60
40
20
0
WEIGHT %A13
Figure 2:
Performan ce of the mixture R13/R12 for evaporato r configura
tion No. ''.
TEST CONDITIONS
The -cwo primary criteria used to define comparab le condition
s for evaluatin g
the tested refrigera nts were fixed water temperatu res and
constant capacity. Tl1e
fixed wate,; temperatu res chosen as typical of air condition
ing were 80°F (26.7°C)
inlet and 55°F (12.8°C) outlet for the evaporato r, and
82"F (27.8°C) inlet and
l17°F (11? .2°C) outlet for the cond~nser.
Because water temperatu res were fcxecl,
refrigera nt tempe~atures and pressures were dependen t on
refrigera nt propertie s_
Since the evaporato r area was to be kept constant
for each test series
constant heat flux criteria requil:ed constant capacity.
For this r-eason,
refrigera nt propertie s chang~d it was necessary to change
compresso r speed.
1
3
~:ho
t-~s
itions were the evapora tor
The test vari.abl es other than refrige rant compos
(UA) and the use of intracy cle heat
overall heat transfe r coeffic ient cimes area
s as sho~n in figure 3.
The evapora tor heat exchang er had three passage
e~change.
through passage s of differe nt cross
By routing water or evapora ting refrige rant
drops and water·t o·refrig erant heae
section or surface area, differe nt pressur e
rations were. examine d for a full
exchang e coeffic ients were obt.aine d. Three configu
The third evapora tor passage was
range. of refrige rant mixture cornpos lt.ions.
ed liquid refrige rant and the
availab le for heat exchang e between the condens
out the length of the evapora tor.
evapora ting refrige rant in counter flow through
ized in table 1.
The te.sted evapora tor configu rations are summar
Configu ration
4
Table 1:
Evapora ting Refrige rant
c
B
A
Liquid Refrige rant
B
c
B
Water
A
A
c
A
B
to Figure 3).
Tested evapora tor configu rations (letter s refer
Cross Sect1onal
Area
227 mm'
A
122 mm2
B
mm 2
c
Figure 3:
310
~
100 mm
120 mm
BO mm
Evapora tor cross section (not to scale).
APPARATUS
The
pump is shown in figure 4.
A schema tic diagram of the breadbo ard heat
A shaft. dynamom eter
e speed motor.
open compres sor is belt dr ive.n by a variabl
tachome ter) mounted between the
(strain gage torquem eter plus magneti c pickup
primary cycle power input measuremG!nt.
compres sor pulley and flywhee l was used as the
through an oil eeparat. or and then enters
From the compres sor the refrige rant pas~es
Condens er
count.er flow water loop.
the condens er which ;LejeC1;:S i"T;;:S heat: to a
ent: and by compari son of the water
capacit y was measure d by a wate:L side measurem
manual
The
clec"T;;:r.ic trimmin g heater.
t-empera ture rise to there over the metered
ing as observe d at the
subcool
slight
n
maintai
to
d
adjuste
was
expansi on valve
condens ar exit slghtgl ass.
y which was use:d to calcula te cycle
The primary meas~~e of evapora tor capacit
heat input (electr ic heaters , water
total
the
ng
measuri
by
d
provide
was
cy
efficien
l heat gain) to the calorim eter box
the·wal
·
through
eter
calorim
pump,
cing
circula
loop. Seconda ry 1neasure s of evapora toi"
-which surroun ded the evapora tor and its water
son of the water tempera ture drop
compari
and
tion
calcula
side
water
a
-were.
y
capacit
turc rise through the metered heaters
through the evapora tor to the water tempet'a
used to match the cvapoxa tor capacit y.
return hole was used at "Che evapora tor
A special accumu lator which l.:3cked an oil
only saturat ed vapor returnin g 'o che
outlet to allow flooded coil operatio n with
se refrige rant-si de heat transfe r
compres sor so that t.he evapora tor area in two-pha
insensi tive. Mixed refrige rant
would stay constan t and the system be charge
sor dischar ge gas samples using a
compos ition was determi ned by analysi s of compres
ograph.
chromat
gas
Figure. 5 shows variatio n of system effici<!-n cy with
compress or speed for pure R2'2
whlle holding suction and discharg e pressure s constant
.
Efficien cy ~as felt co be
sufficie ntly constant to allow mixture testing without
correcti on for this variable .
Because of vibratio ns in the compress or mounting m.1.d
drive systems (resultin g in n
market decrease in measured system efficien cy) tests
were not run near the speed of
750 rpm.
Figure 4:
Schemati c of breadboa rd heat pump.
-------·-~--
-
0.:
0
c.i
-----
4
3L--------h~~------~--------~
500
Figure 5:
750
1000
COMPRESSOR SPEED, rpm
i250
System efficien cy as a function of compress or speed
for pure R22.
DISCUSSION AND RESULTS
Water and refriger ant temperat ure profiles through
the evaporat ors for pure
R22 are shown in figure 6.
The four parts of this figure are for four differen
t
evaporat or configur ations (i.e. flow routed through
differen t passages ) which
resulted in differen t: overall heat t:ransfer coeffici
ent times area (UA) values. rn
the best configur ation (figure 6d-confi guration
4) the water t.ernperat .ure has
reached that of the refriger ant in a quarter of the
length of the evapora tor. "I he
remainde r of the evaporat or is ineffect ive.
This "pinch point 11 resultin g frorn a
mismatch of the refriger ant and water temperat ure
glides limi t:s the efficien cy
attainab le with a pure refriger ant to that resultin
g from its thermody namic
properti es and the LMTD (log mean temperat ure differen
ce) when pinching first occun.
As can be seen in figure 7 (for the mixture R22/Rll4
) properly chosen miXLurcs
do not have a pinch point.
Unlike a pure refriger ant, their LMTD continuo usly
decreas~s and cycle efficien cy continuo
usly increase s with increasi ng heat exchange r
size.
It should be noted that :mixtures always have: a th~rmody
namic advantag e ovet"
pure refriger ants because of Carnot versus Lorenz
cycle consider ations and this
advantag e is greatest when temperat ure lifts are low
and pinch points approach ed.
Whct:her this theoreti cal advantag e results in better
efficien cy relacive to a given
pure refriger ant depends on the respectl ve performa nce
of the refriger ants in question .
Figures 7c and d are temperat ure profiles for a heat
exchange r configuJ: "ation
(configu ration 3 is shown, configur ation 1 would be
similar) in which pure R22 has
5
mixtur e
efficie ncy (Figur e 7c) occurs with a
The best
than that result ing in the temper ature
contai ning consid erably more R22 (75% R22)
(Figur e 7d, 57% R22). In figure 1
ature
temper
water
the
ng
matchi
glide most nearly
higher cycle efficie ncy in the
much
a
in
ed
result
R22
pure
that
seen
lt could be
this case where the mixtur e and the
in
Hence,
R114.
pure
did
than
tus
test appara
LMTD' s, best perform ance occurs in a
pure refrig erant can operat e at compa rable
ent. Howeve r as can be seen in figure
compon
ming
perfor
better
the
in
mi~ture rich
cycle efficie ncy compar ed to pure R22.
8, the mixtur e still result s in improv ed
not reache d a pinch point.
1
90
90
~
~
.. ... . .
75
~
"'
<
ffi
""
~
30
30
60
~
..
?
20
10
"'
ai
a:
~
t-
45
C.O P,- _.
~
;;>
~ 75
u.i
"'~"'
60
~
~
111
.~
Re!ri~Qrllrlt
......
?
20 ui
~0:"'
10
C.O f' • S
~
~
45 •
,!:i
~13
30
30
OISTANCe THROUGH EVAPORATOR
DISTANCE THROUGH EVAPORATOR
a)
b)
Config uratio n 1
Config uration 2
90
90
:;'-
75
g!
"'~
60
~
"'....'"
30
30
~
'
45
c
0 p . 4.85
?
20 u.i
0:
"'~
0:
10
~
"~
t
75
L
• W.,_l!!l
• Rc!rlgertlnl
w
0:
;;>
60 •
\<
0:
~
~
?
20
10
45
C O.P • 5 ,II
uf
a:
;;>
~
"''"
t-
30
DISTANc,; THROUGH EVAPORATOR
30
DISTANCE THROUGH EVAPOR ...TOR
c)
d)
Config uratio n 3
Figure 6:
WaLer and
~efrigerant
Config uratio n 4
R22.
evapor ator temper ature profil es using pure
there is a high evapor ator UA and a
Figure 7a and b are for a case in which
Becaus e of the tenden cy for.
2)"
on
gurati
(confi
dt'op
Both
high refrig erant pressu re
much of the glide is lost.
re
pressu
W:i.th
drop
t.o
ature
satura tion temper
re drop case has only
for a 5n R22 mixure , but the high pressu
1
fisure 7b and 7d are
case has a 25°F glide. A second liabil ity
a l6°F glide where the low pressu re dr.op
n result s from the consta nt heat
in the hie;h pressu re drou co!lfig uratio
for mixture~
tration s
ty is reduce d with increa sed Rll4 concen
flux 1;:e.st criter ion. Refrig erant. capaci
gas
sed compr essor speed result ing in highe-c
which was compen sated for by increa
For this case in which
increa sed pressu re drop.
veloc ities and, conseq uently
nance
a signif icant effact on system perforr
pressu re drop was high enough to have
1
1
than expect ed conce ntratio n of R22.
thi& result ed in best efficie ncy with a higher
" which had low pressu re drop and the
Figure 7e and 7f are for config uratio n
an R22 concen tration which
ncy occurs at
best overa ll UA. In thi5 case best efficie
glide
glide closer to the water temper ature
result s in a refrig erant temper ature
efficie ncy measur ed in t.his
cycle
best
t.he
in
and
s
uration
than in the other confl"g
Simple
ement over pure R22 is shown.
Referr ing to figure 1, a 32% improv
study.
using pure R22 and pure R1 J 4.
cycles
for
ency
effici.
equal
t
predic
eye le simula tions
being
t.o be caused by the compre ssor design
Greatl y reduce d efficie ncy believ ed
If compr essor
ed with pure R114.
observ
was
res,
pressu
ing
operat
the
unsuit ed to
ated,
s mixtur e requir ements it is then est:.im
design s were availa ble t.o suit the variou
may be possib le.
1
over pure R22
as shown in figure 1, that a 44% improv ement
n which result ed in the greate st
It should again be noced that chis config uratio heat heat exchan ger area that
the
times
four
ed
employ
R22
pure
improv ement over
(see figure 6d). The pure R22 experi ences
would be reason able for a pure R22 system
utiliz e large heat. exchan gers
y to effect ively
a "pinch point" which limits its abilit
riate te.rnperatur12 glides
- a limit.a tion that mixtur es with approp
do not experience.
operating with
If the heat eo<changer were s tlll larger,
the mixture,
"\ton
the system,
still better effie l~':.IIC)'
would be expected to have a
wh:i.c.h would not occur with pure R22.
sor-------------------~
?S
30
~•W1Ii>t
R22/R11417312-----71
1
.
~
~
20
~~
~
~
Aatr.gnr~nt gt.~ll
45
coP
.J
§
10
r~
~
P.~lfiOillrAnl
!-
c0
p •
gild!! • 16 ;)"F
50~
3QL_______________________
~·
0
00~----------------------~
DISTANCE THROUGH EVAPORATOR
DISTANCE THROUGH EVAPORATOR
a)
b) Configuration 2, best t:lide _
Configuration 2, best COP.
90
30
30c_________________________ ,
30~----------------------~
DISTANCE THP.QUGH EVAPORATOR
c)
DISTANCE THROUGH EVAPORATOR
Configuration 3 1 best COP_
d) Configuration 3, bcs t glide
sor-------------------------,,0
so.-------------------------._,0
I W<'ltM
~
"'''"''""
~
~
45
10
~
R~lrtgcrJnt
gtldo
e se
~
OOL------------------------~
DISTANCE THROUGH EVAPORATOR
DISTANCE THROUGH EVAPORATOfl.
Configuration 4, best COP"
Figure 7;
~
~
coP
L __ _ _ _ _ _ _ _ _ ____
e)
20
GO
i
30
R2:?1R114 l6014QJ _______.
~?
75
f) Configuration 4, best glicle _
Evaporator temperature profiles for mixtures of R22/R114 which resulted
in the highest COP and in a refrigerant glide most n<?:arly matching t:hat
of the water (25'F, 3.9'C).
7
R22/R114
o W /0 liquid Ime H~
Conf1gurat1on 2
W /0 liquid line HX
Configuration :3
c W/0 liquid line HX
• W1th liquid line HX
• With liquid line HX
* With liquid l1nc HX
r:.
4
100
so
Conflguratlon
Configuration
Conf1gurC!.t1on
Conf1gurat1on
60
4
2
S
4
40
WEIGHT %R22
Figure 8: Performance of the mixture R22/R114 for evaporator configurations 2,
3 ancl 4_
tion two! ~hree,
9 summarize s the test results for evaporato r configura
Figure
compositi ons of R13
and four for the mixture R13/R12. Tests were not run at high
because of high discharge pressures .
differenc e
ng
the
between
system
performan ce
for
the
mixture
An outstandi
in figure 8, is th~
R13/R12, as shown in figure 9, and that with R22jR114, as shown
between the evaporati ng refrigera nt. and subcooled liquid
effect of heat exchange
refrigera nt leaving the
This
condenser .
heat
exchange
dramatic ally
improved
the mixture R22/R114.
efficienc y for the mixture R13/R12 but has lictle effect for
R13/R12
v W/0 liquid line HX
Conf1gurat1on 2
1J. W/0 l1quid l1ne HX
Configuration 4
c With liquid line HX
Configuration 2
4
o With l1q11id l1ne HX
Configuration 3
<:1 W1th llqu1d line HX
Configuration 4
100
80
20
40
60
WEIGHT % R13
Figure 9:
2,
Performan ce of the mixture R13/Rl2 for evaporato r configura tion
3 and 4.
'"!kJ/I<gl
Eml1a1py
Figure 10:
ng
Effect of heat exchange betw,en subcooled liquid and evaporati
refrigera nt for a 40tj60% mixture of R13/R12.
10, a
to be expected from this heat exchange can be seen in figure
The benefits
heat exchange for t:he
pressure enchalpy plot of the cycle with and Wit:hout this
1'
The intracycl e heat exchange results in expansion from point:
mlxt:ure R13/R12.
of the slope of t:he isocherms
to point 2' instead of flashing from 1. to 2 _ Because
1
1
phase region evaporati on from
poin~
2
to point 3
results in the same
in the t~o
resulting in less
average temperatu re as from point 2 to 3 but at: a higher pressure
gj heat exchange must
compresso r ~ork. Note that to achieve the requisite subcoolin
r because of the
take place in counterfl ow throughou t the length of the evaporato
nearly vertical isotherms in the subcooled region.
1l. It can
Similar cycle plot:s for che mixture R22/R114 are shown in figure
t:wo phase region are
be seen that the isothecms in the low quality portion of the
r pressure for che
nearly flat: resulting in no significa nt differenc e in evaporato
pure refrigera nts.
with
case
the
also
is
as
exchange
heat
Without
and
with
cycles
and not the
The reason that intracycl e heat exchange can benefit one mixt:ure
re as is
temperatu
of
function
Unear
a
ily
necessar
not
is
enthalpy
other is chat
nonlinea rity
this
o£
e
importanc
the
o£
ation
demonstr
further
~
generally supposed.
nt. and water temperatu res
is shown in figure 12, comparing plots of refrigera
has been drawn between
line
straight
a
figures
these
In
r.
evaporato
through the
the entering and leaving refrigera nt temperatu res t.o emph.;isizc
t.hat one refrigera nc
ha.s a concave and the other a convex temperatu re profile.
This manifesta tion of
nonlinea rity would interfere with cycle performan ce
predictio n u:.ing simple
computer programs in which only inlet and outlet
temperatu res are specified and
linearity is assumed within the heat exchange rs.
Addi t:ionally, the pinch polnts
whi.ch result: b:om this nonlinea rity reduce cycle efficienc
y.
Figure 11:
Effect of heat exchange bet:ween subcooled liquid and evaporati
ng
refrit;era nt for a 60%/1.<0% mixture of R22/R114.
90
Ll.
•Water
75
R13/R22 132/681
30
• Refrlgorant
\?
ui
ui
20 CL
CL
::>
::>
~ 60
"'w
::;:
~
w
CL
[)._
10
w 45
>-
[)._
::;
w
>-
30
DISTANCE THROUGH EVAPORATOR
90
~
ui
75
• Water
• Refrigerant
R22/R114 166/341
30
\?
::>
20 ui
a:
"'::;
~
c:
w
[)._
CL
::>
~ 60
w
[)._
w
>-
10
45
::;:
w
>-
30L---------------------------~
DISTANCE THROUGH EVAPORATOR
Figure 12:
Compariso n of typical evapor.;to r temperatu re profiles for
che mixtures
R22/Rll4 and R13jR12.
CONCLUSION
2 16%
be 32t bette r, and a mixtu re of R13/R1
A mixtu re of R22jR1 14 was found to
Some system
ation.
applic
g
cionin
condi
air
an
bette r, in effici ency than R22 in
ancia lly
it likely that mixtu res will subst
design chara cteris tics that make
gers~ large heat exchanger5~
exchan
heat
erflow
count
outper form pure refrig erant s are
eranc and
sourc e/sink fluid, match ing of refrig
high tempe rature glide in the heat
lift.
rature
tempe
low
a
and
heat sourc ejsink tempe rature glides
region
on of tempe rature in the two phase
Nonli nearit y of enthal py as a functi
intrac ycle heat
to
ct
respe
with
design
system
on
was observ ed to have an effec t
model s.
exchan ge and cycle simul ation using
ACKNOWLEDGEMENT
nity
of the Office of Build ings and Commu
The autho rs acknow ledge the suppo rt
g chis work throug h the O"k
fundin
for
Energy
of
tment
Depar
System s of the U.S.
Marie cca
ct DE-AC 05-840 R21400 with Martin
Ridge Natio nal Labor atory under contra
Energy System s, Inc.
10