U.S. patent number 3,905,202 [Application Number 05/431,757] was granted by the patent office on 1975-09-16 for refrigeration system.
This patent grant is currently assigned to Emhart Corporation. Invention is credited to Neal P. Schumacher, Victor W. Smith, Donald L. Taft.
United States Patent |
3,905,202 |
Taft , et al. |
September 16, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Refrigeration system
Abstract
A closed cycle refrigeration system comprising one or more
compressors, a condenser exposed to ambient temperatures and of
sufficient capacity to condense all of the gaseous refrigerant
discharged from the compressors, a surge type receiver and one or
more evaporators, is arranged so as to assure at least partial
flooding of the condenser under normal ambient temperature
conditions whereby the liquid refrigerant leaving the condenser is
cooled to approximately ambient temperature prior to passage
thereof to the evaporators. As a result, a sub-cooler using
expanded refrigerant is not generally required and a substantial
saving in the power requirements for operating the system is
effected. Furthermore, the pressures to which the gaseous and
liquid refrigerant are subjected throughout the system are
maintained within optimum limits for more efficient and economical
operation of the compressors and evaporators. In preferred
embodiments of the invention an additional condenser is provided
for use in reclaiming heat from the compressed refrigerant in which
event the other condenser may function primarily to sub-cool the
liquid refrigerant. Hot refrigerant gas from the compressor may
also be used for defrosting the evaporators without adversely
reducing the pressure at which liquid refrigerant is supplied to
those evaporators operating on a refrigerating cycle.
Inventors: |
Taft; Donald L. (Glendale,
CA), Smith; Victor W. (Trenton, NJ), Schumacher; Neal
P. (Trenton, NJ) |
Assignee: |
Emhart Corporation (Hartford,
CT)
|
Family
ID: |
23713292 |
Appl.
No.: |
05/431,757 |
Filed: |
January 8, 1974 |
Current U.S.
Class: |
62/152; 62/196.4;
62/510 |
Current CPC
Class: |
F25B
1/00 (20130101); F25B 47/022 (20130101); F25B
5/00 (20130101); F25B 2400/075 (20130101); F25B
2400/22 (20130101) |
Current International
Class: |
F25B
1/00 (20060101); F25B 47/02 (20060101); F25B
5/00 (20060101); F25D 021/00 () |
Field of
Search: |
;62/196,197,198,510,278,183,228,152 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wayner; William E.
Attorney, Agent or Firm: Sperry and Zoda
Claims
We claim:
1. A refrigerating system comprising a compressor having a
discharge line and an intake line, a condenser connected to the
discharge line of said compressor, a receiver for receiving
condensed refrigerant from said condenser, a plurality of
evaporators each provided with an expansion valve, a liquid line
extending from said receiver to each of said expansion valves and
evaporators, a return line extending from said evaporators to the
intake line of the compressor, means for selectively defrosting
said evaporators by the use of hot refrigerant gas from the
discharge line of the compressor, a line extending from the
discharge line of the compressor to said receiver and having a
pressure reducing valve therein operable to maintain the pressure
in said receiver and liquid line lower than the pressure in the
discharge line of the compressor, and means operable during defrost
and responsive to a reduction in pressure in the receiver
forincreasing the pressure in the discharge line of the
compressor.
2. A refrigerating system as defined in claim 1 wherein said means
for maintaining liquid refrigerant in the receiver and liquid line
under substantially constant pressure includes a line extending
from said compressor discharge line to said receiver and has a
valve therein responsive to a pressure below that which will
actuate said pressure responsive valve in said liquid line.
3. A refrigerating system as defined in claim 1 wherein a heat
reclaiming coil is provided together with means for selectively
connecting said heat reclaiming coil in series with said
condenser.
4. A refrigeration system as defined in claim 1 wherein means are
provided for delivering gaseous refrigerant to each of said
evaporators at a pressure exceeding the liquid line pressure for
defrosting said evaporator.
5. A refrigerating system as defined in claim 1 wherein there are a
plurality of compressors and a plurality of evaporators, the
compressor capacity being in excess of that required to satisfy the
refrigerant load of said evaporators under low ambient temperature
conditions and means are provided for rendering at least one of
said compressors inoperative under low ambient temperature
conditions.
6. A refrigerating system as defined in claim 4 wherein there are a
plurality of evaporators which may be defrosted by the delivery of
gaseous refrigerant thereto, means for sensing the pressure of the
refrigerant in the receiver, and valve means responsive to the
operation of said sensing means operable to maintain the pressure
at which refrigerant is discharged from the compressor above the
pressure applied to liquid refrigerant in said liquid line.
7. A refrigerating system as defined in claim 5 wherein said means
for rendering at least one of said compressors inoperative is
responsive to the pressure of refrigerant gas in a suction line
leading from said evaporators to said compressors.
8. A refrigerating system as defined in claim 7 wherein said
sensing means is operable to control the pressure at which gaseous
refrigerant is discharged from said compressor and a pressure
sensing line extends from said receiver to said sensing means to
actuate the same.
Description
FIELD OF INVENTION
It has been common practice heretofore to provide refrigeration
systems embodying a compressor, a condenser, a receiver and an
evaporator, with means for utilizing a part of the heat developed
in compressing refrigerant gas to heat areas within the store or
enclosure in which the refrigerated equipment is located. In some
installations a portion of such heat is also used for defrosting
evaporators in the system. Typical constructions of this type are
disclosed in U.S. Pat. Nos. 2,555,161; 3,150,498; 3,180,109;
3,358,469; and 3,427,319.
While such systems are generally effective for their intended
purposes the power requirements for operating the equipment are
relatively high and the over-all efficiency of the systems is
correspondingly low. This is particularly true in large
installations such as supermarkets wherein there may be a large
number of refrigerated fixtures containing evaporators several of
which may be operating at the same time and one or more of which
may require defrosting while others are operating on a
refrigerating cycle. In such systems several compressors may be
required for meeting a heavy refrigeration load under some
conditions whereas a lesser number of compressors would be adequate
at other times. When air cooled condensers are employed in such
systems there may be wide variations in the condensing capacity of
the condenser with changes in the ambient temperature with
resulting variations in the condensing pressure and in the
temperature and pressure of the liquid refrigerant supplied to the
evaporators. Thus for example, the temperature of the liquid
refrigerant leaving the condenser heretofore has generally been in
the neighborhood of 80.degree.F to 100.degree.F. It is then
necessary for a portion of the liquid to be vaporized in the
evaporator as "flash gas" in order to reduce its temperature to the
operating temperature of the evaporator before any refrigeration
effect can be attained by further evaporation thereof. In some
cases an evaporative type sub-cooler is provided for reducing the
temperature of the liquid refrigerant before it enters the
evaporator but such sub-cooling equipment requires the expansion of
refrigerant which must be made up by further operation of the
compressor and the expenditure of considerable energy.
In those systems of the prior art wherein hot or saturated
refrigerant gas is circulated through the evaporators to defrost
the same, the pressure at which liquid refrigerant is supplied to
those evaporators then operating on a refrigerating cycle is often
reduced or fluctuates in a manner which seriously reduces the
operating efficiency of the evaporators and their associated
expansion valves.
In accordance with the present invention, these and other
difficulties and objections are overcome and a system provided
whereby the energy required for operation thereof is substantially
reduced and the refrigeration efficiency is increased.
These results are preferably attained by providing a condenser
which is cooled by ambient air and has sufficient capacity to
condense the entire refrigerant output of the compressors under
normal temperature conditions and by further varying the effective
capacity of the condenser by controlled flooding thereof. At least
a portion of the condenser then functions as a sub-cooler to reduce
the temperature of the liquid leaving the condenser to
approximately the temperature of the ambient atmosphere. When the
ambient temperatures are relatively low, say 30.degree.F or
40.degree.F, a very substantial saving in power is effected and the
need for the sub-coolers heretofore employed is eliminated whereas
a substantial but lesser economy is effected at all ambient
temperatures below that for which the condensing system is designed
for effective operation.
Furthermore, the system includes a surge type receiver together
with means for maintaining a controlled pressure in the receiver
and in the liquid lines within limits which assure effective and
efficient operation of the expansion valves and evaporators to
which the refrigerant is supplied. At the same time such pressure
is maintained below that at which gaseous refrigerant is supplied
to the evaporators during defrosting operations. In this way liquid
refrigerant discharged from the evaporators during defrost is
readily returned to the liquid line without adverse reduction in
the pressure of the refrigerant being supplied to those evaporators
operating on a refrigerating cycle.
The system thus provided normally is operated with substantial
saving in its energy requirements and is adapted for use in large
installations and when the reclaiming of heat for use in a building
or enclosure is desired.
THE DRAWINGS
FIG. 1 is a diagrammatic illustration of a simplified refrigeration
system embodying the present invention; and
FIG. 2 is a diagrammatic illustration of a more complete
refrigeration system embodying the present invention.
In the simplified embodiment of the invention chosen for purposes
of illustration in FIG. 1 the refrigeration system comprises a
compressor 2, a condenser 4, a surge type receiver 6 and an
evaporator 8. Refrigerant gas compressed in the compressor 2 is
passed through a discharge line 10 to a condenser 4 exposed to
ambient temperature as by being located on the roof of a market or
other building in which refrigerated fixtures are used. The
condenser 4 is of a size type and design rating such that it has a
condensing capacity sufficient to assure condensation of all of the
compressed refrigerant gas supplied thereto by the compressor 2
during normal temperature conditions to which it will be subjected.
Thus the condenser may be designed to have a higher rated
condensing capacity for use in southern latitudes where the average
ambient temperatures may be relatively higher than the design
rating of the condenser used in systems employed in northern
climates where the normal ambient temperature will be substantially
lower.
The liquid refrigerant leaving the condenser 4 flows through a
drain line 12 to a liquid line 14 by which liquid refrigerant is
supplied to one or more evaporators 8. The liquified refrigerant
then passes through an expansion valve 16 for vaporization in the
evaporator to refrigerate a fixture of any suitable or preferred
type. The expanded and vaporized refrigerant gas leaving the
evaporator 8 is returned to the compressor 2 through a return line
18. The liquid refrigerant receiver 6 communicates with the liquid
line 14 by means of a connection 20 whereby a suitable amount of
refrigerant may be stored and maintained in the system to assure
continued operation thereof.
A modulating pressure responsive valve 22 is located in the drain
line 12 leading from the condenser 4 to liquid line 14 and is
adjusted to respond to a predetermined pressure so as to maintain
the head pressure of the compressor 2 at a desired operating level
and sufficiently high to assure at least partial flooding of the
condenser at all or at least most ambient temperatures to which the
condenser will be subjected.
In accordance with the present invention the pressure to which
liquid refrigerant in the receiver 6 and liquid line 14 is
subjected is maintained relatively constant and sufficiently high
to assure satisfactory and efficient operation of the expansion
valve 16 associated with the evaporator 8. For this purpose a
pressure control line 26 extends from the discharge line 10 of the
compressor 2 to the receiver 6 and is provided with a pressure
responsive valve 28 adjusted to respond to a pressure below that
which will actuate valve 22 in drain line 12 extending from the
condenser to liquid line 14 but high enough to assure effective
operation of the expansion valve 16 and evaporator 8.
The system thus provided assures complete condensation of the
gaseous refrigerant passing from the compressor 2 to the condenser
4 with at least partial flooding of the condenser at all, or at
least most, ambient temperature conditions so that the liquid
refrigerant passing from the condenser through drain line 12 to
liquid line 14 will be reduced in temperature to approximately
ambient temperature. Thus in a typical operation wherein the
temperature of the ambient air passed over the condenser is
40.degree.F the liquid refrigerant passing to liquid line 14 will
be about 40.degree.F. Under such conditions when using R502
refrigerant, for example, the pressure responsive valve 22 between
drain line 12 and liquid line 14 may be adjusted to respond to a
pressure of, say, 160 pounds per square inch. This valve will then
remain closed until enough liquid refrigerant has backed up in the
condenser so as to reduce its effective condensing capacity and
increase its condensing pressure and the compressor discharge
pressure to about 160 p.s.i. Thereafter, valve 22 will modulate to
maintain a constant pressure in the condenser.
The liquid refrigerant accumulated in the flooded portion of the
condenser will be cooled during its retention therein to
approximately ambient temperature (40.degree.F) and thereafter will
pass through the valve 22 from drain line 12 to liquid line 14 at a
relatively low temperature. The excess of liquid refrigerant over
that immediately required for use in the evaporator or evaporators
8 will pass from the liquid line 14 through connection 20 to the
receiver 6 so as to be stored therein for use as required.
In the event the receiver 6 should be so located as to attain the
ambient temperature (40.degree.F), the vapor therein, when using
R502 refrigerant, will reach saturation at a pressure of about 80
p.s.i. and the pressure of the liquid refrigerant being supplied to
the evaporator 8 would only be 80 p.s.i. which is insufficient to
assure effective and efficient operation of a typical expansion
valve 16 associated therewith. However, in accordance with the
present invention the pressure of the liquid refrigerant in
receiver 6 and liquid line 14 is maintained and controlled
independently of the temperature of the receiver and the
refrigerant therein. For this purpose the pressure responsive valve
28 in pressure control line 26 extending from the compressor
discharge line 10 to receiver 6 is adjusted to respond to a
predetermined pressure, (say 150 p.s.i.) which is somewhat below
that which will actuate valve 22 at the condenser outlet. As a
result the pressure applied to the liquid refrigerant in the
receiver and liquid line 14 will be maintained constant and will
not be significantly influenced by the temperature of the
refrigerant entering and leaving the receiver. It can instead be
maintained sufficiently high to insure efficient operation of the
expansion valves and evaporators under all conditions of operation.
Moreover, the maintaining of proper and substantially constant
pressure on the liquid refrigerant passing to the evaporator will
be assured no matter where the receiver may be located and whether
it is subjected to low ambient temperature or is positioned in a
machine room with compressors and the like where its temperature
may be relatively high.
In the example cited above wherein the ambient temperature to which
the condenser is subjected is 40.degree.F the condensing pressure
and the compressor output pressure will be relatively low and the
power expended in operating the system is materially reduced
representing a substantial saving in the cost of operation.
However, even when the ambient temperature is relatively high, say
90.degree.F, some power savings may be effected. Thus if the
ambient temperature is 90.degree.F the condensing temperature will
be about 105.degree.F and the condensing pressure and the
compressor output pressure will be about 232 p.s.i. when using R502
refrigerant. The liquid refrigerant leaving the condenser will then
be about 90.degree.F and be under a pressure above the 160 p.s.i.
setting of the pressure responsive valve 22 between drain line 13
and the liquid line 14. The valve 22 will then assume a fully open
condition so that liquid refrigerant will pass directly from the
condenser to the liquid line without restriction and little or no
sub-cooling of the liquid refrigerant will take place. However, the
liquid refrigerant in receiver 6 and liquid line 14 will then be
under sufficient pressure to assure effective and efficient
operation of the evaporator and its expansion valve throughout the
refrigeration cycle. The pressure control line 26 and its valve 28
will then be unnecessary and will not function due to the adequate
pressure developed in the receiver.
It will thus be apparent that sub-cooling of the refrigerant in the
flooded condenser will take place at all times when the ambient
temperature is below the temperature for which the system is
designed, say 90.degree.F, and at all times when the condensing
pressure is below the setting at which the pressure responsive
valve 22 will modulate to pass liquid refrigerant from the
condenser drain line 12 to the liquid line 14. Accordingly,
significant savings in the power expended will be effected during
all ambient temperature conditions below that for which the system
is designed. Nevertheless, if desired an evaporative sub-cooling
element indicated in dotted lines at 30 in FIG. 1 can be provided
for use under abnormally high ambient temperature conditions.
In refrigeration systems employed in supermarkets for example, it
is advantageous to connect several evaporators or groups of
evaporators to a condensing unit. When this is done it is desirable
to have some means for controlling the capacity of the condensing
unit as the evaporator loads vary due to changing store conditions
and variation in the portions of the load on defrost take place. In
particular the required capacity of the compressor and condensing
unit is reduced when low ambient temperatures increase the liquid
sub-cooling which takes place in the condenser thus decreasing the
required refrigeration load reflected to the compressors.
Under such conditions a more complete system may be employed as
illustrated in FIG. 2. As there shown three compressors 40, 42 and
44 are connected in parallel with a common gas discharge header 46
from which compressed gaseous refrigerant is delivered through
discharge line 48 to a condenser 50 positioned to be cooled by
ambient air and of sufficient capacity to condense the entire
refrigerant discharged from all three compressors. The condenser 50
delivers liquid refrigerant to a drain line 52 and liquid line 54
through pressure responsive valve 56. The liquid line 54 is
connected to a surge type receiver 58 through connection 60 and is
connected to the evaporators 62 and 64 through lines 66 and 68
respectively. Refrigerant from the evaporators is returned to the
compressors through return lines 70 and 72 and a common return
header 74.
As shown in FIG. 2 at least a portion of the heat produced in
compressing the refrigerant may be reclaimed and used to heat an
area of the supermarket and for this purpose a heat reclaim coil 76
is connected to the discharge line 48 through a bi-pass line 78 and
a thermostatically controlled solenoid valve 80. A condenser inlet
pressure regulating valve 82 is connected in a line 84 extending
from reclaim coil 76 to the condenser 50 through a check valve 86
and serves to maintain the desired head pressure in the compressor
when the heat reclaim coil 76 is in use. A solenoid valve 88 and
check valve 90 are located in the section 92 of the compressor
discharge line 48 between the bi-pass line 78 and the condenser 50.
The valve 88 closes when valve 80 is opened so as to assure flow of
hot gas in series through heat reclaim coil 76 and condenser 50
when the heat reclaim coil is in use.
As in the form of the invention shown in FIG. 1 the valve 56 is
adjusted to assure the desired condensing pressure in condenser 50
and assure at least partial flooding thereof under normal ambient
temperature conditions. At the same time a pressure control line 98
having a pressure responsive valve 96 therein extends from
discharge header 46 to receiver 58 and establishes the pressure at
which the liquid refrigerant in receiver 58 and liquid line 54 will
be maintained for delivery to the evaporators 62 and 64. The
adjustment of valve 96 preferably is such that the pressure applied
to the receiver and liquid line from gas discharge header 46 will
be lower than the discharge pressure of the compressed refrigerant
gas delivered to discharge line 48 and condenser 50 so that there
will be no danger of reverse flow of refrigerant from the receiver
to the condenser.
In using the system illustrated in FIG. 2 it will, of course, be
apparent that any number of evaporators required for use in the
system may be connected in this manner to the liquid line 54 and
sufficient liquid refrigerant should be contained in the receiver
58 to assure delivery of liquid refrigerant to the liquid line 54
through connection 60 when the demands of the evaporator exceeds
the supply of liquid refrigerant received from the condenser 50 at
any period of operation.
In order to defrost the evaporators when ice or frost has
accumulated thereon, hot gas from the compressors may be delivered
through the hot gas header 46 and branch hot gas line 100 to
whichever evaporators require defrosting. Thus when evaporator 62
is to be defrosted solenoid valve 102 in branch 103 of hot gas line
100 is opened to deliver hot refrigerant gas to the line 70 whereas
valve 105 in return line 73 is closed. The hot gas then flows
through evaporator 62 in a direction reverse to that in which the
expanding gas flows during the refrigerating operation whereby the
temperature of the coils and fins of the evaporator is raised to
defrost the same whereas the hot gas is cooled and at least
partially condensed to a liquid. The resulting condensate then
flows through bi-pass line 106 and check valve 107 about the
expansion valve 94 and returns through line 66 to the liquid line
54.
The liquid refrigerant resulting from the defrosting of the
evaporator 62 is thus made available for use in refrigerating
evaporator 64 and other evaporators employed in the system and to
supplement the supply of liquid refrigerant being passed to such
other evaporators. Such flow of the liquid refrigerant from
defrosting evaporator 62 to liquid line 54 will take place by
reason of the fact that the pressure applied to the liquid
refrigerant in receiver 58 and liquid line 54 by pressure control
line 98 and valve 96 is maintained below the pressure of the hot
refrigerant gas supplied to the defrosting evaporators from branch
hot gas line 100.
There may be some instances, when several evaporators are being
defrosted at the same time, wherein the demand for hot gas from the
compressor will be so great as to reduce the pressure thereof in
the hot gas header 46 and hot gas line 100. In that event the
pressure applied to the liquid refrigerant in the receiver 58 and
liquid line 54 through valve 96 and pressure control line 98 may
fall below that which will assure proper operation of the expansion
valves associated with the evaporators. In order to avoid this
possibility a receiver pressure sensing line 110 is connected to
the receiver 58 and extends to a diaphragm actuated regulating
valve 112 located in the compressor discharge lines 48 at a point
beyond the branch hot gas line 100. The regulating valve 112 is
normally open but is operable to restrict flow of gas from the
compressor through discharge line 48 in the event the pressure in
the discharge line should fall below the desired liquid line
pressure. In that event valve 112 will tend to close and modulate
so as to increase the compressor head pressure and the pressure
applied to the liquid refrigerant in the receiver and liquid lines
through pressure control line 98 and pressure responsive valve 96.
In this way an adequate and predetermined difference in pressure
between the hot gas being used for defrosting purposes and the
liquid refrigerant being supplied to the evaporators is assured
under all conditions of operation of the system.
When the ambient temperature to which the condenser 50 is subjected
is relatively high all three compressors 40, 42 and 44 may be
required to meet the demand for refrigerant by the numerous
evaporators which may be employed in the system. However, when the
ambient temperature adjacent the condenser 50 is moderate or
normal, the temperature of the sub-cooled liquid being supplied to
the liquid line 54 and receiver 58 will be reduced and the
discharge pressure of the condenser will be similarly reduced.
Under such conditions only two of the compressors such as
compressors 40 and 42 may be required to satisfy the refrigerating
load with the result that the third compressor such as compressor
44 can be cycled off. For this purpose an element 116 responsive to
the compressor suction pressure may be provided to terminate
operation of compressor 44 as the refrigeration load is reduced. As
a result the energy input which would otherwise be required to
drive the compressor 44 is saved, and substantial economies
effected in the power demands of the system.
Furthermore, when low ambient temperatures are encountered so that
substantial sub-cooling of the liquid refrigerant is effected, the
defrosting of one or a number of evaporators will further reduce
the demand for liquid refrigerant whereas the hot gas required for
the defrosting operation may be supplied by a single compressor
with the result that the compressors 42 and 44 may both be cycled
off while the single compressor 40 satisfies the refrigerant and
defrosting requirements. For this purpose the element 118 connected
to compressor 42 is provided and designed to respond to a further
reduction in the compressor inlet pressure to terminate operation
of compressor 42. In this way still further reduction in the power
required to operate the refrigerating system is effected.
It will thus be apparent that the system of FIG. 2 can be operated
when employing only a single compressor during those periods when
the condenser 50 is exposed to low ambient temperatures whereas
only two compressors may be required during most normal operation
and the third compressor will only be called into use during such
times as the ambient temperature is abnormally high. The reduction
in the power requirements of the system is thereby accomplished by
utilizing the condenser 50 to effect a sub-cooling of the liquid
refrigerant during all normal periods of operation and significant
reduction in the energy requirements of the system is effected.
Nevertheless, even when abnormally high ambient temperature
conditions are encountered and it is necessary to resort to the use
of an evaporative type sub-cooling device 120, the system will
operate effectively and the advantages afforded by maintaining a
constant liquid line pressure during defrosting operations are
attained.
While typical embodiments of the present invention have been shown
in the drawing and described above it will be apparent that the
invention is capable of many other modifications and changes
without departing from the spirit and principal of the invention.
In view thereof it should be understood that the forms of the
invention specifically disclosed herein are intended to be
illustrative only and are not intended to limit the scope of the
invention.
* * * * *