Note: Descriptions are shown in the official language in which they were submitted.
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; BACKGROUND OF THE INVENTION
1. Field of the Invention
; The invent~onrelates to refrigeration systems,
' particularly those of the type used in refrigerated display
;; cases installed in food supermarkets. In a more particular
sense the invention may be classified as a defrosting system r,
of the type in which the fluid refrigerant normally used for -
refrigeration purposes is utilized, in a gaseous state, for `-
defrost purposes.
In yet a more particular sense, the invention can be
~, appropriately classified with those in which the defrost by
the gaseous refrigerant utilizes, as a primary source of the ` -
.:.;,, , ' ' '.
`r~ defrost fluld, saturated gaseous refrlgerant ("cool gas")
flowing from a receiver through the evaporators being defrosted,
'' reversely to the direction in which the fluid refrigerant
normally flows during a refrigerating cycle~
~ 2. Description of the Prior_~rt
;`l The prior art is known to include refrigeration
;~' systems, utilizing the same basic relative arrangement as the
~ 20 present invention, in respect ta the location and operating
. .
characteristics, within the system, of condensers, compressors,
~-` receivers, and evaporators. Typical of systems of this type
.,~. ~ . .
is that disclosed in United States Patent 3,905,202 issued
`;~ September 16, 1975. By way of example, a defrost arrangement
is incorporated in the disclosed, patented system that utilizes
~; hot gas flowing from the discharge line of the compressor or
series of compressors, for defrosting the evaporators conven-
tionally incorporated in the refrigeration system.
~ It is also known to provide, in a refrigerating
`~ 30 system of the general category described previously herein,
an arrangement in which saturated gaseous refrigerant ("cool
~; gas") flows from the top of a liquid receiver, to the
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evaporators for defrost purposes. Such an arrangement is found
in United States Patent 3,427,819 issued February 18, 1969.
The use of a hot gas defrosting system is widespread.
Such systems are highly efficient. It is thought by some of
the industry, however, that hot gas defrost systems may
possess some disadvantages. For example, it has been contended
,! that hot gas defrost systems will at times cause breakage and
leaks in refrigerant lines due to excessively rapid, thermal
expansion of tubing embodied in the system. And, it has also
been contended that the evaporator coils are subjected, in hot
; gas defrost systems, to excessive defrosting temperatures, and
have as a result produced visual fog or steam.
Accordingly, as an alternate to hot gas defrost, for
use by those who have some objections to a hot gas defrost
. system, it has been heretofore proposed, as for example in the
`!~` above-mentioned patent no. 3,427,819, to use, instead of hot
gas, desuperheated or "saturated gas". This is known also in
the industry as "cool gas", a term which will be used for pur-
poses of convenience hereinafter, and which will be understood
as meaning desuperheated or saturated gaseous refrigerant
occurring in a refrigeration system of the type here under
consideration. ~
SUMMARY OF THE INVENTION `--
The invention provides, in one aspect, a refrigera-
tion system including compressor means having low and high `~
~, pressure sides, a plurality of evaporators each of which has
'i, one end connected to the low side of the compressor means, a
refrigerant liquid supply line having an inlet end, said line
having a discharge end connected to the other ends of the
evaporators, condenser means having an input side~connectedto the high side of the compressor means and an output side
connected to the inlet end of the liquid line, a surge-type - :
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receiver, a connecting line extending between the receiver and
the liquid line, and a defrost line extending from the receiver
to said one end of the evaporators for supplying saturated
` gaseous refrigerant to the evaporators for defrosting the same,
the improvement that comprises defrost control means for per-
mitting flow in both directions through said connecting line
in the presence of a predetermined pressure balance as between
the receiver and liquid line, and for preventing flow at least
~ in a direction from the liquid line to the receiver, responsive
; 10 to the appearance therebetween of a pressure imbalance in which
7,`
the liquid line exceeds, by a predetermined differential value,
the pressure within the receiver.
In a typical embodiment of the present invention, a
refrigeration system of the type disclosed in the above-
mentioned patents, embodying a compressor or compressor series,
a condenser, a receiver, and one or more evaporators or sets
.
thereof, has tubing components arranged to permit flow of cool
gas directly from the receiver to an evaporator that is to be
defrosted, reversely to the normal flow of liquid refrigerant
through said evaporator. Such embodiment of the invention
incorporates a pressure--responsive control val-ve in a connec- `~
tion conventionally provided between the system's liquid
refrigerant supply line and the receiver. This valve is basic
to a number of different embodiments of the invention. In each
embodiment, it acts to temporarily-prevent flow from the
liquid line to the receiver, so that the liquid within the ,;
:, ;.
receiver may be fully evaporated in providing cool gas for
defrost purposes. In these circumstances, hot gas flows from
the compressor discharge line and through the receiver, which
in these circumstances becomes primarily a conduit for the
hot gas. The hot gas flows out of the receiver into the line -~
connecting the receiver to the evaporators for defrost purposes.
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; Advantages from the automatic switching from cool to
hot gas defrost operation are found in the elimination of the `
possibility of liquid refrigerant being "stolen" from the
liquid supply line that extends to the evaporators, a condi- ;
;~ tion known to cause flash gas and starving of the evaporators. ;
: ., .:
; Figure 1 is a diagrammatic illustration of a typical
refrigeration system embodying one form of the invention;
Figure 2 is a fragmentary, diagrammatic illustration ~ ~
of the same system, showing a modified form; ;
Figure 3 is a fragmentary, diagrammatic illustration i`~
of the system showing a third form of the invention; and `` ~-
Figure 4 is a fragmentary, diagrammatic illustration ~ `
i of the system showing a fourth form of the invention. -
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
i~ Basic to all forms of the invention is a compressor ~
;~ means comprising compressors 10, 12, 14. The compressors are ~ `
~ provided with a suction or low pressure side operating at a ~`
i`~!'~ predetermined suction pressure. A suction header or intake
``~ line 16 is connected to the suction of the compressors.
20 Vaporous refrigerant from the evaporators is returned to the ;~
; compressors through the suction header. The compressors have ~;
a high side, to which is connected a discharge manifold 17, ~ -
through which hot gaseous refrigerant is discharged, to flow
through a discharge conduit or line 18 to condenser 20. The ~ ;
hot compressed gaseous refrigerant (hereinafter "hot gas")
is reduced by condenser 20 to its condensing temperatur and - ~;
pressure, flowing from the condenser through condenser output
,~ line 22 to a joint or connecting fitting 23 that connects ;
'~, receiver liquid line 24 in communication with line 22. `;
~; 30 Intermediate its ends, the condenser discharge con~
~` duit 22 is provided with a modulating pressure responsive
valve 26, which is responsive to the pressure in the condenser
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and in the conduit 22 at the discharge side of the condenser, .to modulate flow to evaporator liquid supply line 28 extending
from joint 23 and disposed in constant communication with the
conduit 22, thus in effect constituting an extension of the ~:
condenser discharge conduit.
Flow to line 28 is thus modulated in such fashion
as to control the pressure within the condenser to provide
partial or full flooding thereof.
A surge-type receiver 30 is connected at its bottom
in communication with line 24 whereby to maintain a liquid
refrigerant source for normal operation of the system.
Branch liquid lines or conduits 32 extend from a
liquid header 34 constituting an extension of line 28, for .~ : .
supplying pressurized liquid refrigerant to expansion valves
36, 38 that control the supply of refrigerant to evaporators ~ ,;
40, 42. Refrigerant leaves the evaporators, during the refri- .
gerating cycles thereof, through evaporator output branch
lines 44, 46 respectivèly, extending into communication with ` .
return or suction line 16.
A pressure control means generally designated 48, ~-
positioned in header 34, maintains the pressure of refrigerant
in the input branch lines 32, 34 at a value less than the .
refrigerant in the liquid line 28. This pressure differential `-
assures against reverse flow during defrost. During defrost,
gaseous refrigerant is directed to the evaporator or evapora-
tors undergoing defrost through a main defrost line or header ~.
50 extending from the top of receiver 30.
~ . .
Connected between discharge manifold 17 and the top
of receiver 30 is a receiver pressure control line 52, in
which is installed a pressure reducing valve 54 arranged and
` functioning similarly to a corresponding line and valve dis-
closed in Patent 3,905,202.
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Also incorporated in the system is a heat reclaim
means located and functioning similarly to a corresponding means
disclosed in Patent 3,905,202. It includes a heat reclaim coil
56 connected to discharge line 18 through a bypass line 57 in
which is mounted a thermostatically controlled solenoid valve ;~
60. A condenser inlet pressure regulating valve 64 is con- ;
nected in line 62 extending from reclaim coil 56 to condenser
20 through a check valve 66, and serves to maintain the desired
head pressure in the compressor when the heat reclaim coil 56
is in use. A solenoid valve 58 and check valve 63 are located
in line 18 between the bypass line 57 and the condenser 20. ~
Valve 58 closes when valve 60 is opened, so as to assure flow `
of hot gas in series through heat reclaim coils 56 and conden~
ser 20 when the heat reclaim coil is in use
The disclosure of Patent 3,905,202 is further incor-
porated in the present application by reference, in respect to
means for terminating operation of one or more of the compres- ,
sors, responsive to reduction in the compressor suction pres-
` sures, said means being illustrated at 70, 72.
Also desirable in the system is a sub-cooler 74,
mounted as illustrated in association with line 28 to assure
the supply of refrigerant to the evaporators when, for example,
abnormally high ambient temperature conditions are encountered. ,!~
When a particular evaporator, as for example evapora-
tor 40 is undergoing defrost, the gaseous refrigerant used for
i~ defrost purposes will flow through the evaporator in a reverse
direction as compared to the flow therethrough during a
refrigerating cycle. If it may be assumed that evaporator 40
is in a defrost cycle while evaporator 42 is in a refrigerating
;30 cycle, it is important that the pressure of the gaseous refri-
` gerant used for defrosting evaporator 40 and flowing in a
reverse direction therethrough as compared to flow during a
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refrigerating cycle thereof, be greater than the pressure of
refrigerant directed through evaporator 42, which in the
example described is in a refrigerating cycle.
If a pressure differential did not exist under these
circumstances~ the desired reverse Elow of the defrosting fluid
through evaporator 40 would be prevented due to the pressure
existing on the input side of evaporator 42. To achieve this
desired pressure differential, the pressure control means 48 -
hereinbefore referred to, is placed at the inlet of the :~
refrigerant supply header 34. By creating the pressure differ-
ential, reverse flow in a given evaporator or set thereof,
required for defrost, is assured.
Means 48 includes solenoid actuated valve 86 in
header 34, mounted in parallel with check valve 88 located in
bypass line 90. Valve 86 is normally open to allow full flow
into the header 34 from line 28. Valve 86 is responsive to
any evaporator or set of evaporators that are to undergo de-
frost, and in these circumstances closes to force refrigerant `~`
passing through the line 28 to flow through the bypass line -
20 90. Valve 88 is set for any desired value such that the pres- ``
sure of the refrigerant on the upstream side of the valve 88
will be greater, by a predetermined value, than the pressure
~t .
on the downstream side of the check valve. By presetting of
the pressure differential, full reverse flow through any
evaporator or set thereof undergoing defrost is assured.
Alternatively, means 48 could be a pressure modula-
ting valve, allowing variable and close control of the pressure
differential. This is thought sufficiently obvious as not to
require special illustration, it being mainly important to
provide means at the location illustrated, that will assure an
adjusted, regulated pressure upstream from the evaporators, in
the liquid supply line through which refrigerant is supplied
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to the evaporators for refrigerating purposes. `~
Also incorporated in the illustrated s~stem are
solenoid valves 76, 78 controlling flow of the defrosting fluid
from defrost header 50 to defrost branch lines 79, 80 that `
extend into communication with lines 44, 46. Solenoid valves
76, 78 are normally closed, but open to deliver the gaseous
defrost fluid to their associated evaporators 40, 42. Normally
open valves 92, 82, through which refrigerant returns to the `
compressors through suction line 16 during refrigerating cycles
of the compressors, close simultaneously with opening of their
respective, associated valves 76, 78, that is to say, if for
example valve 76 opens, its associated valve 92 closes to
terminate a refrigerating cycle in evaporator 40 and initiate
a defrost cycle thereof.
During defrost, the gaseous defrost fluid directed
through the evaporators undergoing defrost is cooled and is at
least partially condensed to a liquid. The liquid condensate ;
flows out of the evaporator through by-pass lines 96, 98 and
check valves 94, 84 past the valves 36, 38. Each of these is
open during the refrigerating cycle of its associated evapora-
tor. During the defrost cycle valves 36, 38 close to an extent
that would retard the flow of condensate out of the coil being
defrosted, hence requiring the use of the by-pass lines. ~ -
It will be noted at this point that everything that
has been so far described and illustrated, with the exception
of the connection of the defrost header 50 to the top of
receiver 30, and the pressure differential control means 48,
,i . .
is disclosed in U.S. Patent 3,905,202 and is recognized as ;-~
part of the prior art. Further, connection of a defrost `
header to the top of a surge-type receiver, in and of itself,
is disclosed in U.S. Patent 3,427,819 and does not per se con~
! stitute part of the present invention. The pressure diffër~
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ential control means 48 is also known, per se, being disclosed
in Patent 3,427,819.
The present invention is directed to an improved
defrosting control for refrigeration systems of the type des~
cribed previously herein, and relates to defrosting arrange-
ments oE the type primarily relying upon cool gas for defrost
purposes. "
In accordance with the present invention, control
valve means generally designated 100 in the form of the inven-
10 tion shown in Figure 1, is mounted in the connecting line 24 ;;
extending between the refrigerant liquid supply conduit 22 -~
and the bottom of the receiver 30. In the form of the inven-
tion shown in Figure 1, valve 100 is a solenoid valve, mounted
in parallel with a check valve 103 mounted in bv-pass 104 to
permit flow past valve 100 in a direction from the receiver
to the conduit 22 whenever the valve is closed. Valve 100 is
normally open to permit flow in either direction within line
# ,. ;.
24 when normal operating conditions exist, that is, when the
pressures in receiver 30 and line 22 are in a predetermined
balanced state.
Extending from a source of electrical power are leads
106, 108 respectively connected to the terminals of the sole-
noid valve 100. Electrical power from said source is normally
prevented from flowing through the normally open and de-,
energized valve, by reason of a differential pressure control
switch 110, which is normally open and which may be mounted,
as illustrated, in lead 106. Switch 110 is, per se, conven-
tional. It may, for example, be of the diaphragm type, ;~
wherein a diaphragm deflects under predetermined, adjusted
differences in pressure at opposite sides of the switch, toactuate a bridging element 112 into a contact closing position,
thus to close the switch and permit flow of the electrical
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current to the solenoid valve lO0.
The opposite, pressure-responsive sides of the
switch are connected by tubular elements 114, 116 to the de-
frost header 50 and refrigerant liquid supply conduit 22 -
respectively. Element 114 is connected to header 50 between
the receiver 30 and the connection of the header 50 to the
defrost branch lines 79, 80. The tubular element 116 is con-
nected to the conduit 22 at a location downstream from con-
denser 20, valve 26, and a check valve 102, and upstream from - ~ -
the connection 23 that connects conduit 22 in communication
with the receiver connecting line 24.
In accordance with the invention, whenever the pres-
sure in conduit 22 exceeds the pressure within the receiver 30
by a predetermined amount, switch 110 reacts, causing valve
100 to close. This prevents the flow of the refrigerant liquid
from conduit 22 upwardly through connecting line 24 into the
receiver 30. ~
~ormally, the pressure in line 22 is similar to the ~ ;
receiver pressure. Any increase in pressure in line 22 above
that in the receiver would result from elevation or lowering
of ambient temperature surrounding the condenser, resulting
from cycling of the condenser fan between on and off conditions
thereof. ;;
` Normally, thus, 205 p.s.i.g. would be normal in a
typical installation, in line 22 and within the receiver. -~
An increase in the pressure in line 22, relative to ~ ; -
; the pressure in the receiver, results in flow, under normal
conditions, through connecting line 24 upwardly into the
receiver. In some instances, this causes the receiver to
collect refrigerant to such an extent as produces starving of
the liquid supply line extending to the evaporators for the
purpose of supplying refrigerant thereto for use in the
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refrigerating cycles of the evaporators. The receiver, at
times, may flll completely with the liquid refrigerant, in
these circumstances.
Check valve 102 is provided, because whenever pres-
sure upstream from the check valve is lower than in the ^~
receiver, a reverse flow can occur, within conduit 22, through
the inlet pressure regulating valve 26, which controls the ~ i
compressor head pressure, as a result of which damage may
result, and liquid needed for refrigeration may be temporarily
lost to the condenser.
The arrangement has been found to be highly bene-
ficial in cool gas defrosting systems, and incorporates an
automatic defrost fluid switching function in a defrost system
of this type.
This results from the fact that during use of satu- `
rated gaseous refrigerant, that is, "cool gas", taken from
receiver 30, above the liquid level in the receiver for defrost
purposes, the liquid within the receiver tends to evaporate
for the purpose of providing the cool gas. Should the liquid
become fully evaporated, and with the receiver pressure held
in the manner described to a value less than that in line 22,
hot gas will begin to flow from compressor discharge header 17,
through line 52 to the receiver. The hot gas will flow through ;`
the receiver which becomes under these circumstances no more
than a conduit for the hot gas, said hot gas flowing out of
the receiver into the defrost header 50 and thence to the
' particular evaporator or evaporators that are undergoing a ,
defrost cycle.
In this way, there is automatic switching from cool
to hot gas for defrost purposes, responsive to depletion of
the supply of cool gas within the receiver.
This avoids difficulties noted in the prior art,
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wherein in the circumstances there would be flow into the
receiver from liquid line 22 to replace the evaporated liquid,
thus in effect stealing liquid from the liquid supply line 22
as a result of which the possibility of flash gas is raised, j.
together with starving of the evaporators during their refri-
gerating cycles.
The invention, thus, proùides a carefully regulated
control of the pressure within line 22 relative to the pres-
sure within receiver 30, operable automatically whenever the -
pressure in the line 22 exceeds that of the receiver by a
predetermined value, and adapted in these circumstances to
stop what would be the normal result of such pressure differ- ` :
ential, that is, flow from conduit 22 of refrigerant liquid
into the receiver 30. At the same time, means is provided to
prevent damage to the head pressure control system and its
associated tubing, plus loss of control of the liquid refri-
gerant, through the provision of the check valve 102 located
between the head pressure control valve 26 and the connection
23 of line 22 to the receiver.
--It is appropriate to note why a pressure differen- i
tial may develop between line 22 and receiver 30, considering
; the fact that valve 100 is normally open. It is true, as ;~
previously noted, that normally these pressures are similar. ~-
However, it may be recalled that during a defrost cycle, cool `
gas is taken from the receiver above the liquid level for
,. . .
defrost purposes, as a result of which the liquid within the
`~ receiver tends to evaporate for the specific purpose of pro-
viding the cool gas needed for defrost. This removal of cool
gas, and the consequent evaporation of receiver liquid, has
; 30 the effect of lowering the receiver pressure. As a result, a
pressure differential between the receiver and the pressure .
in line 22 is produced, tending to cause flow into the
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receiver from the liquid line 22 to replace the evaporated
liquid. This in effect "steals" liquid from the line 22. This `~
only happens in the defrost cycle, and the basic concern is
that when the pressure differential is in the wrong direction,
so to speak (that is, when the receiver pressure goes lower
than the pressure in the line 22) it becomes important to shut
the valve 100 and thus prevent the refrigerant liquid in line
22 from flowing into the receiver 30. By closing the valve
100 in these circumstances, I permit the liquid in the receiver -`
to continue evaporating to supply cool gas for the purpose
of accomplishing the defrost function without the mentioned
stealing of liquid from the liquid supply line to replace that
which evaporates and flows out of the receiver through line
50.--
In Figure 2, there is illustrated an arrangementidentical to that shown in Figure 1, except that instead of
valve 54 in line 52, there is provided a valve 54a arranged -
as a differential pressure regulating valve, which at the
high side of the compressor means may be set to maintain a
pressure of 210 p.s.i.g., and which at its other side is
adapted to maintain a pressure of 205 p.s.i.g. within the
receiver.
This pressure differential is merely typical, and
can of course be adjusted as desired. It is mainly important
to note that a predetermined difference is established, and
is maintained in line 52 between the compressor discharge
header and the top of the receiver. ~`
Thus, if the condenser pressure at the discharge
` side of the condenser should go to 230 p.s.i.g., the pressure
; 30 in the receiver would automatically be reset to 225 p.s.i.g. ~
The receiver pressure thus follows that in line 22 upwardly ,
or downwardly, normally, but will never go below the pressure
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within the liquid line 22, thus assuring proper operation of ~. .
the system during the defrost cycle hereinbefore mentioned. .::
In Figure 3, the switch 110 is eliminated. In
these circumstances there is provided a differential pressure
regulating valve 100a, sensitive to pressures at opposite sides
thereof, that is, adapted to maintain a predetermined differ~
ential between the pressure at the side of valve l00a con~
nected to line 22, and the side thereof connected to the bottom ,.
of receiver 30. The pressures would be selected to assure
10 that at all times, the valve will remain open as long as the :
pressure in the line 22 does not exceed that in the receiver .....
by a predetermined value. Once that value is reached, however, ;
valve 100a closes thus to again prevent undesired flow of
refrigerant liquid upwardly into the receiver, under circum- ..
stances that would cause starving of the evaporators and im- .
proper defrost operation resulting from filling of the receiver
,~
with refrigerant liquid. .~
. Finally, in Figure 4 there is illustrated an arrange- .
ment similar to that shown in Figure 3, except that an associa- ;~
20 tion with valve 100a, there is used:the valve 54a shown in
. Figure 2. This provides a regulation of the pressure in the .
receiver relative to that in the line 22 maintained with even
more accuracy than may be possible with the construction shown .:
in Figure 2. -~ :
In every form of the invention, as will be noted, .
;. there is the common characteristic wherein the pressure within
! the receiver relative to that in the line 22 is controlled in
; such fashion as to prevent flow of liquid from line 22 into
the receiver whenever the line 22 pressure exceeds that in the
30 receiver by a predetermined value. In this way, the liquid .
.~ level in the receiver is accurately controlled during defrost- .
ing operation, permitting maximum utilization of the cool gas
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supplied from the receiver. Further, the arrangement results
in the automatic switching from cool gas to hot gas for defrost
purposes whenever the liquid within the receiver is fully
vaporized, since there is no replenishment of the receiver
liquid in these circumstances, no starving of the evaporators
that may at the same time be in refrigerating cycles, and no
damage to the system resulting from loss of full compressor
head pressure control.
It will be understood that although valve 100 is ~;
illustrated as normally open when deenergized, the circuitry
could be arranged such as to use a valve that is normally closed `
with the circuit open. In these circumstances, switch 110
would be closed when the receiver and liquid line pressures
are in balance, to energize the valve and hold it open. When
the pressures go out of balance, switch 110 would open, opening
the circuit to the valve and allowing the now deenergized valve
to operate to a closed position.
As used in this application, "evaporator" means
either a single refrigerating coil, or a set of refrigerating
coils connected for joint refrigeration or defrost thereof.
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