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Патент USA US3098373

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July 23, 1963
R. M. SHRADER
3,098,363
REFRIGERATION SYSTEM DEFROSTING BY CONTROLLED
mow OF‘ GASEOUS REFRIGERANT
Filed Feb. 24, 1961
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ATTORNEYS
United States Patent Office
1
3,098,363
REFRKGERATION SYSTEM DEFROSTING BY CON
TRQLLED FLGW 0F GASEOUS REFRIGERANT
Raymond M. Shrader, Decatur, Ga., assignor to Larki-n
Coils, inc, Atlanta, Ga, a corporation of Georgia
Filed Feb. 24, 1961, Ser. No. 91,528
6 Claims. (Cl. 62-151)
3,098,363
Patented July 23, 1963
2
Another di?iculty has been brought about by the re
cent introduction of several grades of compressors in
tended for use in various applications. Each grade of
compressor is designed to pump a speci?c ?ow of refri
gerant at speci?c pressure differential. That is, each
grade of compressor is designed with a certain maximum
suction pressure. Any deviation above this suction pres
sure will create an over-loaded condition leading to com
The present invention relates to mechanical refrigera
pressor stoppage. This condition is in no way related
tion systems of the type is which defrosting of the evapora 10 to the hazard of liquid carry-over into the compressor.
tor is accomplished by the periodic replacement of total
refrigerant in the evaporator by hot refrigerant gas from
the compression side of the compressor. This hot refrig
erant is generally supplied to the evaporator by way
An object of the present invention, therefore, is the
provision of a novel refrigeration system having hot gas
defrosting means, wherein means are provided to main
tain .a pressure within the evaporator which has a
of a branch conduit which taps the line from the high pres 15 corresponding condensing temperature below the tem
sure side of the compressor to the condenser.
perature of the refrigerant gas leaving the coils, thereby
There are several drawbacks to this method of de
preventing the condensation of any amount of refrigerant
frosting. The hot refrigerant gas, upon contacting the
in the evaporator.
Another object of the present invention is the provision
cold surface of the evaporator coil, may condense. As
the condensate builds up in the form of liquid refrigerant, 20 of a novel refrigeration system having hot gas defrosting
it may carry over into the suction line and thence into the
means, wherein means are provided to automatically and
compressor. As the liquid is incompressible, breakage of
to constantly maintain the compressor suction pressure
the compressor parts may result. This hazard is particu
below the overload point for the various grades of ma
larly great in systems in which the evaporator operates
chines upon which the evaporator coil and defrosting
at temperatures below freezing, becoming greater as the 25 equipment may be operated.
temperature of the refrigerated space decreases. To pro
Another object of the present invention is the provision
of a novel refrigeration system having hot gas defrosting
vide for a su?icient amount of refrigerant gas in the
means, wherein means are provided to permit only a
compressor-evaporator defrosting circuit, the condenser
and receiver section of the refrigerating equipment must
gradual build-up of ?ow of hot refrigerant gas into the
evaporator at the begining of the defrost cycle;
be open to the evaporator at the start of the defrost cycle.
The pressure in the condenser and receiver is considerably
Another object of the present invention is the provision
greater than the pressure in the evaporator section of the
system. This results in a ?ow, from the condenser sec
of a novel refrigeration system having hot gas defrost
ing means, wherein means are provided to achieve maxi
tion into the evaporator, of refrigerant which, because it
mum defrosting ef?ciency by operating the defrosting
is more highly saturated, is at a greater density than 35 system at the highest evaporator pressure commensurate
with pressure safety during the changing weight-?ow rate
the refrigerant in the evaporator and suction side of the
through the defrost cycle.
system. The in?ux of more highly saturated gas into
The provision for a valve so placed that it automatically
the system, couplied with the ?xed cubic volume pump
regulates the evaporator pressure and compressor suc
ing rate of the compressor, results in a relatively high
tion pressure to a predetermined point during defrosting,
weight per unit time pumping rate. As the defrost cycle
and which permits a gradual build up of pressure within
continues, pressure equilibrium is rapidly reached as the
the system at onset of defrosting will be carried forth
compressor discharge pressure and the pressure in the
in this invention. Other objects of the invention will
condenser and receiver section equalize. When the
appear as the following description of a preferred and
branch conduit supplying hot gaseous refrigerant to the
evaporator during the defrost cycle connects with the line 45 practical embodiment thereof proceed.
In the drawing:
from the high pressure side of the compressor to the
FIGURE 1 is a diagrammatic lay-out of a refrigera
condenser by a T or valve in an arrangement of con
tion system embodying the principle of the invention;
duits similar to that illustrated in the accompanying
FIGURE 2 is a cross-section through the T-?tting 25.
drawing, the more highly saturated or heavier gas particles
Referring now in detail to the drawing, the rectangle
tend to follow a straight path through the connection '
1, designated by the broken lines, represents the refrig
into the condenser while the lighter, less saturated gas
particles more readily change course and ?ow through
erated chamber in which the temperature is maintained
the branch conduit. Consequently, the density or weight
below 32° F. Within that chamber is the evaporator 2,
per unit volume of the hot refrigerant gas circulating
below which is a pan 3 for catching the water resulting
in the compressor-evaporator defrosting circuit gradually 55 from the defrosting, said pan discharging through drain
decreases. This gas, when pumped at a constant volume
pipe 4 which extends to the point 5 outside the refrigerated
per unit of time, then exhibits a decreasing weight per
chamber. Said pan is heated during defrosting by an
unit time pumping rate. A ?xed restriction in the form
electrical means to prevent the formation of ice within.
of a non-regulating valve or restricting device located in
A fan '7 driven by the motor 8, circulates air through the
the defrosting circuit, therefore, cannot maintain a con
evaporator and throughout the refrigerated chamber.
stant evaporator and compressor suction pressure in the
Outside of the refrigerated chamber is a compressor 9 con
face of the varying weight .per unit time gas ?ow, as
nected to the upper part of the evaporator by the suction
the pressure differential across such a device is a func
line 14} and to the condenser 11 by the hot compressed
tion of the weight-?ow through it.
gasous refrigerant pipe 12. The condenser is connected
A second point which must be considered in the pre
‘at its lower end to the receiver 13, the receiver being con
vention of liquid carry over into the compressor is that
nected by the liquid refrigerant pipe 14- thr-ongh a nor
an accumulation of liquid refrigerant and oil or a com
mally open solenoid valve 20’ the expansion valve 15’ to
bination of both may be lying in the evaporator coil
the lower part of the evaporator. The compressor is
at the start of the defrost cycle. A sudden, high velocity
driven by the motor 16. In the system as illustrated, the
in-rush of hot refrigerant gas would cause the pick-up 70 liquid refrigerant line 14 passes in heat exchanging rela
of this liquid and oil in the form of a slug which would
tionship to the suction pipe 10' in the heat exchanger de
then be carried over into the compressor.
vice 17, where the liquid is cooled by the gas in the suc
3,098,363
3
tion line, whereby its refrigerating efficiency is enhanced.
For the purpose of defrosting, branch conduit 18 leads
from the hot gaseous refrigerant pipe 12 at a point be
tween the compressor and condenser, through a regulating
valve 26 and thence through the solenoid valve 20 into
the pipe 15 adjacent the evaporator, bypassing the expan
sion valve 15'. For convenience there is a cutoff valve
119 at the lower end of the branch conduit 18 which is nor
4
structed to respond to the weight per unit volume gas flow
of the gaseous refrigerant into the evaporator during the
defrost cycle and adjusted to automatically regulate evapo
rator pressure and compressor suction pressure to a pre
determined point during defrosting and to permit only a
gradual build up of How of hot refrigerant gas into the
evaporator at the beginning of the defrost cycle.
2. In a refrigeration system, a compressor, condenser,
mally left open. Since the pan 3 and discharge pipe 4
receiver, evaporator, expansion valve, and the usual suc
mostatic bulb 22 against the suction line adjacent to the
outlet end of the evaporator.
normally closed when said system is in its freezing cycle,
means for opening said defrosting valve periodically to
within the refrigerated chamber are constantly within a 10 tion line from the evaporator to the low side of the com
pressor, the hot gas line from the high side of the com
freezing atmosphere, they are heated to keep the defrost
pressor to the condenser, the liquid line from the receiver
water liquid until it reaches the outside of the refrigerated
to the expansion valve, and the connection from the ex
chamber. For heating the discharge pipe 4, the branch
pansion valve to the evaporator, means for defrosting the
conduit 18 is substantially in heat exchanging relation
ship to the discharge pipe throughout the part of its ex 15 evaporator comprising a branch conduit from said hot
gas line to the connection between said expansion valve
tent which is within the refrigerated chamber.
and evaporator, a defrosting valve in said branch conduit
The expansion valve 15’ operates in response to a ther
Defrosting is automatically accomplished by means of
defrost control 23, the operation of which is outlined in
United States Patent No. 2,688,850 assigned to Larkin
Coils, Inc., Atlanta, Georgia, and will not be discussed in
greater detail than is necessary to outline the salient fea
tures of this invention.
At the beginning of the defrost cycle, solenoid valve 2%’
is closed, preventing the admission of liquid refrigerant
to the evaporator, and solenoid valve 20 is opened, admit
ting hot gas to the evaporator for defrosting. The regu
lating valve 26, which is essentially connected in the
branch conduit 18, is preferably an outlet pressure sensi
tive modulating valve, of known construction, which is
responsive to downstream pressure to regulate ?ow there
through. The valve 26 is so set at the initial adjustment
of the system as to automatically regulate the pressure
within the evaporator and the suction pressure of the com—
pressor at a point below the overload pressure of the com
effect ‘defrosting, and ‘an automatic downstream pressure
responsive modulating valve in said branch conduit con
structed to respond to the weight per unit volume gas
?ow of the gaseous refrigerant into the evaporator during
the defrost cycle and maintain a pressure within the evap
orator which has a corresponding condensing temperature
below the temperature of the refrigerant gas leaving the
evaporator to prevent condensation of refrigerant in the
evaporator.
3. In a refrigeration system, a compressor, condenser,
receiver, evaporator, expansion valve, and the usual suc
tion line from the evaporator to the low side of the corn
pressor, the hot gas line from the high side of the com
pressor to the condenser, the liquid line from the receiver
to the expansion valve, and the connection from the ex
pansion valve to the evaporator, means for defrosting
the evaporator comprising a branch conduit from said hot
gas line to the connection between said expansion valve
and evaporator, a defrosting valve in said branch conduit
pressor. The condensing temperature corresponding to
normally closed when said system is in its freezing cycle,
this pressure will, in all cases, be below the temperature
40
means
for opening said defrosting valve periodically to
of the refrigerant gas leaving the evaporator, thus prevent
effect defrosting, and ‘an automatic downstream pressure
ing any condensation of hot refrigerant gas within the
responsive modulating valve in said branch conduit con
evaporator. In the T connection 25, an ori?ce is placed
at the termination of branch line 18, as detailed in FIG
URE 2, so sized as to prevent damaging overloading of
the compressor in the event of total failure of the regulat
structed to respond to the weight per unit volume gas ?ow
of the gaseous refrigerant into the evaporator during the
ing valve 26 in the open position.
It may therefore be seen that the physical relationship
predetermined point during defrosting and to permit
of any of the components within the system, one with the
other, have no bearing upon the proper functioning of this
invention, but that ef?cient defrosting of the evaporator
with the protection for the compressor ‘depends only upon
operating conditions within the system itself.
While but one preferred embodiment of the present
invention has been particularly shown and described, it is
apparent that various modi?cations may be made therein
within the spirit and scope of the invention, and it is
desired, therefore, that only such limitations be placed on
the invention as are imposed by the prior art ‘and set forth
in the appended claims.
defrost cycle and ‘adjusted to automatically regulate evap
orator pressure and compressor suction pressure to a
only a gradual build up of flow of hot refrigerant gas
into the evaporator at the beginning of the defrost cycle,
and means providing ‘an ori?ce of ?xed size within said
branch conduit between said evaporator and said defrost
ing valve permanently determining a constant maximum
rate of flow through said branch conduit, so calibrated
with respect to the capacity of the system with which it is
employed as to limit the rate of flow of hot gaseous
refrigerant to said evaporator to the extent that it can
not condense in sufficient quantity to slug over into said
suction line.
4. In a refrigeration system, a compressor, condenser,
60 receiver, evaporator, expansion valve, ‘and the usual suc
What is claimed is:
tion line from the evaporator to the low side of the com
1. In a refrigeration system, Ia compressor, condenser,
pressor, the hot gas line from the high side of the com
receiver, evaporator, expansion valve, and the usual suc
pressor to the condenser, the liquid line from the receiver
tion line from the evaporator to the low side of the com
to the expansion valve, and the connection from the
pressor, the hot gas line from the high side of the com
expansion valve to the evaporator, means for defrost
pressor to the condenser, the liquid line from the receiver
ing the evaporator comprising a branch conduit from said
to the expansion valve, and the connection from the expan
hot gas line to the connection between said expansion
sion valve to the evaporator, means for defrosting the
valve and evaporator, a defrosting valve in said branch
evaporator comprising a branch conduit from said hot gas
conduit normally closed when said system is in its freez
line to the connection between said expansion valve and 70 ting cycle, means for opening said defrosting valve period
evaporator, a defrosting valve in said branch conduit nor
cially to effect defrosting, and an automatic downstream
mally closed when said system is in its freezing cycle,
pressure responsive modulating valve in said branch
means for opening said defrosting valve periodically to
conduit constructed to respond to the weight per unit
effect defrosting, and an automatic downstream pressure
volume gas flow of the gaseous refrigerant into the eva
responsive modulating valve in said branch conduit con 75 porator during the defrost cycle and maintain a pressure
3,098,363
6
Within the evaporator which has a corresponding con
pansion valve positioned in operative relationship to the
densing temperature below the temperature of the refrig
evaporator inlet, conduit means connecting the condenser
erant gas leaving the evaporator to prevent ‘condensation
outlet to the expansion valve for supplying refrigerant to
of refrigerant in the evaporator, and means providing an
the evaporator during the freezing cycle of the system, a
ori?ce of ?xed size Within said branch conduit between
suction conduit from the evaporator outlet to the suction
said evaporator and said defrosting valve permanently de
side of the compressor, a hot gas conduit connecting the
termining a constant maximum rate of ?ow through said
compressor discharge with the condenser inlet, means for
branch conduit, so calibrated with respect to the capacity
defrosting the evaporator comprising a branch conduit
of the system with which it is employed as to limit the
from said hot gas conduit to the evaporator inlet between
rate of flow of hot igaseous refrigerant to said evaporator 10 the evaporator inlet and said expansion valve, a defrost
to the extent that it cannot condense in su?icient quantity
ing valve in said branch conduit normally closed to pre
to slug over into said suction line.
vent ?oW of hot gaseous refrigerant through said branch
conduit when the system is in its freezing cycle, means
5. In a refrigeration system including an intercon
for opening said defrosting valve periodically to admit
expansion valve positioned in operative relationship to the 15 hot gaseous refrigerant through said branch conduit to
nected compressor, a condenser, an evaporator, and an
said evaporator inlet to elfect defrosting and outlet
pressure responsive modulating valve means in said branch
conduit operatively subject to pressure in said branch
conduit between said modulating valve and the evapora
suction conduit from the evaporator outlet to the suction
side of the compressor, a hot gas conduit connecting the 20 tor inlet for responding to the weight per unit time gas
?ow through said modulating valve to automatically regu
compressor discharge with the condenser inlet, means for
late evaporator pressure and compressor suction pressure
defrosting the evaporator comprising a branch conduit
at a selected level during defrosting and respond to vol
from said hot gas conduit to the evaporator inlet between
ume density as Well as ?ow rate of gaseous refrigerant
the evaporator inlet and said expansion valve, a defrosting
valve in said branch conduit normally closed to prevent 25 through the branch conduit into the evaporator to permit
flow of hot gaseous refrigerant through said branch con
only a gradual build up of flow of refrigerant into the
duit when the system is in its freezing cycle, means for
evaporator at the beginning of the defrosting cycle.
opening said defrosting valve periodically to admit hot
gaseous refrigerant through said branch conduit to said
References Cited in the ?le of this patent
evaporator inlet to effect defrosting, and outlet pressure 30
UNITED STATES PATENTS
responsive modulating valve means in said branch con
2,688,8501
White _______________ __ Sept. 14, 1954
duit operatively subject to pressure in said branch conduit
2,934,911
Micai ________________ _.. May 3, 1960'
between said modulating valve and the evaporator inlet
2,944,411
McGrath ____________ __ July 12, 1960
for responding to the weight per unit time gas ?ow through
Buchanan ____________ __ Oct. 25, 1960
said modulating valve to automatically and constantly 35 2,957,316»
evaporator inlet, conduit means connecting the condenser
outlet to the expansion valve for supplying refrigerant to
the evaporator during the freezing cycle of the system, a
maintain a pressure within the evaporator which has a
corresponding condensing temperature below the tempera
OTHER REFERENCES
Anderson, S. A.: Automatic Refrigeration, MacLaren
ture of the refrigerant gas leaving the evaporator.
6. In a refrigeration system including an intercon
and Sons, Limited, for Danfoss, Nordberg, Denmark,
nected compressor, a condenser, an evaporator, and an ex 40
1959, pages 183-186 and 210-212, TP49'2-A56.
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