Energy conservation system having improved means for controlling receiver pressure

Disclosed is a means for preventing "logging" of receivers, that is, the excess filling of a receiver with liquid in a refrigeration system of the type in which a compressor, a condenser, and one or more evaporators are connected in a closed cycle in association with a surge receiver. Communication between the discharge side of the compressor and the receiver incorporates a valve of the differential pressure regulating type, having means sensitive to the relationship of pressures established and maintained in a liquid line extending from the condenser to the evaporator and in the compressor discharge line extending from the compressor to the condenser, respectively. The valve responds to the pressure differential between these lines to maintain pressure in the receiver at a value slightly less than the maintained condensing pressure existing in the liquid line, to prevent excess liquid from accumulating in the receiver and in this way eliminate "starving" of the expansion valves associated with the evaporators. The disclosed means for establishing and maintaining receiver pressure in a preferred embodiment utilizes a capillary sensing element in association with the differential pressure regulating valve. The element senses pressure in the liquid line upstream from an inlet pressure regulating valve. The inlet pressure regulating valve establishes and maintains an optimum condensing pressure and as a consequence thereof establishes the desired optimum differential between the pressures at the inlet and outlet sides of the condenser.

BACKGROUND OF THE INVENTION 
1. Field Of The Invention 
The present invention relates to those refrigeration systems that are 
especially suitable for use in refrigerating food products displayed in 
refrigerated display cases, especially though not necessarily those of the 
open front type, installed in food supermarkets. In a more particular 
sense the invention may be classified as an improvement in refrigeration 
systems of the type that utilize the concept of effecting power savings 
through sub-cooling of a refrigerant within a condenser exposed to outside 
ambient air temperatures. In systems of this type, natural sub-cooling is 
controlled in a manner to reduce compressor operation with resultant power 
savings. This is done by varying the effective capacity of the condenser 
through controlled flooding thereof. 
In yet a more particular sense the improvement comprising the present 
invention can be appropriately classified as an automatic control in 
refrigeration systems of the category described in which pressures within 
a surge receiver are automatically regulated to closely follow an 
automatic condensing and compressor discharge pressure regulating 
function. 
2. Description Of The Prior Art 
A refrigeration system in which the present improvement is especially 
suited for use is exemplified by U.S. Pat. Nos.3,905,202 to Taft et al; 
and 4,012,921 to Willitts et al. 
A system of the type disclosed by these patents works admirably, in 
effecting power savings under a wide variety of differing outside ambient 
air temperatures. However, under certain circumstances it becomes 
desirable to incorporate additional, improved features in such systems, as 
regards establishing and maintaining pressures in the surge receiver 
characteristically employed in such a system. 
At present, there is provided, in the patented systems referred to, means 
in the form of an outlet pressure regulating valve, connected between the 
compressor discharge and the receiver. This valve has been sensitive to 
existing receiver pressures. The valve has a fixed setting, and whenever 
the receiver pressure drops below this setting, the valve opens to 
communicate the compressor discharge with the receiver, to raise the 
receiver pressure to the fixed setting. 
Keeping in mind that the receiver pressure must at all times be lower than 
the head pressure of the system (that is to say, the pressure in the 
discharge line extending from the compressor to the condenser), a problem 
has been produced in that one cannot operate the system at head pressures 
lower than the fixed receiver pressure control valve setting. This has 
reduced the versatility of the system and the capability thereof as 
regards saving energy. 
A problem of at least equal or perhaps even greater significance, in the 
prior art, results from the fact that utilizing a fixed setting in the 
receiver pressure control valve arrangement, sensitive only to existing 
receiver pressure, has produced "logging" of liquid within the receiver, 
under certain circumstances. This is a condition in which the receiver 
tends to fill with an excessive amount of liquid, and as a consequence 
tends to deprive or "starve" the expansion valves associated with the 
several evaporators. Starving of the expansion valves means that the 
valves are not supplied with sufficient liquid condensate to efficiently 
discharge their function. 
For the reasons given above, the prior art devices have failed to operate 
with as much efficiency, in all types of outside ambient air temperature 
conditions, as would be desirable. This undesirable condition, it is 
believed, derives from an inherent lack of flexibility in the means for 
controlling receiver pressures. This lack of flexibility in respect to the 
control of receiver pressures has in turn produced a corresponding, 
undesirable limitation of the range of condensing and head pressures 
considered desirable to make optimum usage of the widely varying ambient 
temperatures found in the various seasons of the year. Thus, while 
atmospherically responsive refrigerating systems of the type disclosed in 
the above-mentioned patents represent an important advance in the art, it 
has been found desirable to increase the general capability thereof for 
making the most efficient use possible of varying climatic conditions. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a refrigeration system of the 
type shown, for example, in U.S. Pat. No. 3,905,202 utilizes a pressure 
differential control valve in place of the outlet pressure regulating 
valve presently incorporated in a line connected between the compressor 
discharge line and the receiver. The valve installed pursuant to the 
present invention is sensitive to pressures developed within the liquid 
line extending from the condenser, upstream from a modulating pressure 
responsive valve now installed in the liquid line as an automatic control 
of condensing and head pressures. The mentioned modulating pressure 
responsive valve is in and of itself part of the systems disclosed in the 
named patents, and is effective to establish and maintain, automatically, 
pressures in the liquid line from the condenser and in the compressor 
discharge line at pre-selected operating levels with a continuously 
existing pressure differential therebetween. In accordance with the 
invention, it is proposed to control receiver pressure by causing the 
receiver pressure to be established and maintained at all times at values 
that are a function of the condensing and head pressures, and the 
differential therebetween, effected by the modulating pressure responsive 
valve means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the single FIGURE of the drawing, there is illustrated a refrigeration 
system which is like that disclosed both in U.S. Pat. No. 3,905,202 issued 
to Taft et al and U.S. Pat. No. 4,012,921 issued to Willitts et al, so far 
as the basic essentials of such a system are concerned. Accordingly, the 
present invention has been illustrated as applied to a system like that in 
FIG. 2 of U.S. Pat. No. 3,905,202, in which by way of example three 
compressors 40, 42, 44 are connected in parallel with a common gas 
discharge manifold 46 from which compressed gaseous refrigerant is forced 
under pressure through a compressor discharge line 48 to condenser 50 
positioned to be cooled by ambient air and having a capacity sufficient to 
condense the entire refrigerant discharged from all three compressors. 
Condensed liquid refrigerant is forced under pressure from condenser 50 
through a liquid line 52 extended at 54 through a modulating pressure 
responsive valve 56. Not illustrated in the mentioned U.S. patents, but 
found desirable in practice, is a check valve 57 mounted in liquid line 54 
downstream from valve 56. 
A surge receiver 58 is connected at its bottom to a connecting line 60 
extending downwardly to a juncture with liquid line 54. Line 54 continues 
past receiver 58, and is connected to evaporators 62, 64 through lines 66, 
68 respectively. Refrigerant from the evaporators is returned to the 
compressors through return lines 70, 72, connected to a return manifold 73 
extending into communication with the common return header 74 of the 
several compressors. Not essential to the present invention, but desirable 
in a typical commercial installation, is a heat reclaim means illustrated 
herein and in U.S. Pat. No. 3,905,202 as including a heat reclaim coil 76, 
connected to discharge line 48 through a bypass line 78 and a 
thermostatically controlled solenoid valve 80. A condenser inlet pressure 
regulating valve 82 is connected in a line 84 extending from 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 section 92 
of the compressor discharge line 48 between bypass line 78 and condenser 
50. Valve 88 closes when valve 80 is opened, to assure flow of hot gas in 
series through coil 76 and condenser 50 when the heat reclaim coil is in 
use. 
Valve 56 is adjusted to respond to a predetermined pressure so as to assure 
the desired condensing pressure in condenser 50 and produce at least 
partial flooding thereof under outdoor temperature conditions requiring 
throttling of the valve. This in turn maintains the head pressure of the 
compressors 40, 42, 44 at a desired operating level, sufficiently high to 
assure said partial flooding of the condenser at any ambient temperatures 
below the temperature valve to which the valve is pre-set. 
The refrigerating system disclosed may utilize hot gas as a means for 
defrosting the evaporators. However, although a hot gas defrost means is 
illustrated, it is not critical to operation of the improvement comprising 
the present invention, and is illustrated purely as typical of one type of 
defrost which can be advantageously utilized with said improvement. 
Thus, in the disclosed system, by way of example of a typical defrost 
means, hot gas from the compressors may be delivered through a hot gas 
header 46 and branch hot gas line 100 to any evaporators that 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, while 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. As a result, 
the temperature of the coils and fins of the evaporator is elevated, to 
defrost the evaporator. In the process of defrosting the evaporator, the 
hot gas is cooled and is at least partially condensed to a liquid. The 
resulting condensate then flows through bypass line 106 and check valve 
107 about the expansion valve 94, and returns through line 66 to the 
liquid line 54. 
In order to assure proper operation of the expansion valves at times when 
several evaporators are being defrosted at the same time (a situation in 
which the demand for hot gas from the compressor is so great as to reduce 
the pressure thereof in line 100), a receiver pressure sensing line 110 is 
connected to receiver 58 and extends to a regulating valve 112 located in 
compressor discharge line 48 downstream from the juncture of lines 48 and 
100. Valve 112 is normally open but operates to restrict the flow of gas 
from the compressor through discharge line 48 in the event that the 
pressure in the discharge line should fall below the desired liquid line 
pressure. In this event valve 112 tends to close and modulate to increase 
the compressor head pressure and the pressure applied to the liquid 
refrigerant within the receiver through pressure control line 98, which in 
the disclosed embodiment extends from the top of the receiver to a 
juncture with line 48 downstream from valve 112. An adequate and 
pre-determined difference in pressure between the hot gas used for defrost 
purposes and the liquid refrigerant supplied to the evaporators is thus 
assured under all operating conditions. 
Depending upon the ambient temperature to which the condenser 50 is 
subjected, elements 116, 118 responsive to compressor suction pressures 
are provided to cycle off one, and sometimes two, of the several 
compressors. 
When automatically high ambient temperature conditions are encountered, it 
may sometimes be necessary to resort to the use of an evaporative type 
sub-cooling device 120. This is only illustrated, however, because of its 
inclusion in the basic system disclosed in U.S. Pat. No. 3,905,202. It may 
be found unessential to successful operation of the system as improved by 
the present invention but is nevertheless disclosed as an optional device 
usable in the system. 
All the above has been illustrated and described in U.S. Pat. No. 3,905,202 
with the exception of the check valve 57, a check valve 122 in line 98 
upstream from valve 96, and the extension of line 98 to discharge line 48. 
The check valves, and the extension of line 98 to a juncture with line 48 
at the location disclosed, have been found desirable in a commercial 
embodiment but like the rest of the basic system do not comprise part of 
the present invention. 
In accordance with the present invention, valve 96 is a differential 
pressure regulating valve, and utilizes a pressure sensing means 
preferably in the form of a capillary tube 124 extending into 
pressure-sensory relationship to liquid line 52, between valve 56 and the 
outlet of the condenser 50. 
This concept becomes of importance in changing the operating 
characteristics of the entire system during the refrigeration cycle 
thereof. 
In considering examples of the operation, it should first be noted that 
discharge line pressure in line 48 is normally higher, in a typical 
working system, than the pressure existing in line 52 between condenser 50 
and valve 56 (the "condensing pressure"). The condensing pressure is 
always lower than the compressor discharge pressure, but stays at a value 
very close to that of the compressor discharge pressure, normally on the 
order of four or five p.s.i. lower. 
As a result, if for example valve 56 is set at 175 p.s.i., it begins to 
close and modulate whenever the condensing pressure drops below that 
value. The condensing pressure would drop, it may be noted, responsive to 
a drop in the head pressure of the compressor means 40, 42, 44, because 
any drop in pressure in the compressor discharge line 48 (that is, any 
drop in head pressure) is reflected as a corresponding drop in the 
condensing pressure existing in line 52 between valve 56 and condenser 50. 
The differential, as previously noted, is a constant, that is, a pressure 
of 175 p.s.i. in line 48 means that there is a pressure in line 52 
upstream from valve 56 of approximately 170 p.s.i. 
If valve 56 is set, by way of example, at 175 p.s.i., then the appearance 
of 170 p.s.i. in line 52 at the inlet side of valve 56 causes the valve to 
tend to close and modulate, to elevate the pressure at its inlet to its 
setting of 175 p.s.i. This in turn would produce a corresponding increase 
in compressor discharge line 48, elevating the pressure there to 180 
p.s.i. There is, thus, an established, automatically maintained pressure 
differential between the head pressure represented by the pressure in the 
compressor discharge line 48, and the condensing pressure represented by 
the pressure in line 52 between the inlet of valve 56 and the outlet of 
condenser 50. 
In the prior art devices as disclosed in the abovementioned patents, the 
receiver pressure control valve (valve 96 of U.S. Pat. No. 3,905,202 and 
valve 46 of U.S. Pat. No. 4,012,921) had a fixed setting which might, for 
example, be 175 p.s.i. As a result, the receiver pressure control valves 
of the prior art systems disclosed in these patents opened, should the 
pressure within the receiver drop below the setting of the valve, so as to 
elevate the receiver pressure to the fixed setting. Said valves, however, 
remained closed no matter how high the pressure within the receiver should 
go above the fixed setting. 
This produced certain undesirable results, in that there was no maintenance 
of a prescribed relationship between the receiver pressure on the one hand 
and the condensing and head pressures (or more specifically the 
differential therebetween) on the other hand. 
The failure to establish and maintain such a relationship, in the prior art 
devices as represented by the above-mentioned patents, under certain 
circumstances resulted in, for example, filling of the receiver with 
liquid with resulting starving of the expansion valves. For instance, the 
receiver pressure control valve simply remained closed, and non-operating, 
whenever the receiver pressure should go above the fixed setting, for 
example, 175 p.s.i. Should the receiver pressure drop too far below the 
discharge or head pressure, during this mode then the relatively high 
pressure resulting in line 52 (4-5 p.s.i. less than the head pressure) in 
respect to the low pressure within the receiver would be translated into 
the filling of the receiver with liquid. 
In accordance with the invention, receiver pressure is controlled in a 
wholly new manner, by means of a valve in a line extending from the 
receiver to the compressor discharge line, the valve being set to open and 
modulate to permit one-way flow from the compressor discharge line to the 
receiver, for the purpose of establishing and maintaining a receiver 
pressure which is at a prescribed value in respect to the pressure 
differential between the condensing and head pressures as established and 
maintained by operation of the valve 56. In a typical working embodiment, 
as noted above the condensing pressure is approximately four or five 
p.s.i. less than the head pressure. Therefore, whenever valve 56 operates 
to establish the condensing pressure at a desirable, predetermined 
operating level, this is translated automatically into a head pressure 
approximately four or five p.s.i. above that established in line 52 by 
modulation of valve 56. In turn, the receiver pressure is automatically 
adjusted to a value which is a function of this pressure differential. In 
a working embodiment, it is proposed, desirably, to establish the receiver 
pressure at a level approximately five to ten p.s.i. less than the 
condensing pressure in line 52. 
In these circumstances, it has been found that the tendency toward 
"logging" of the receiver is eliminated, thus in turn eliminating 
resultant starving of the expansion valves. 
Of great importance, further, is the fact that establishing and maintaining 
a receiver pressure so that it will closely follow the condensing 
pressure, increases the versatility of the refrigeration systems shown in 
U.S. Pat. Nos. 4,012,921 and 3,905,202. Heretofore, the range of settings 
that could be utilized in valve 56 was limited by the requirement for a 
fixed setting of the receiver pressure control valve 96 of U.S. Pat. No. 
3,905,202 of 46 of U.S. Pat. No. 4,012,921. Settings for valve 56 would 
have to fall in a range the lower limit of which would be above the fixed 
setting of the receiver pressure control valve. That fixed setting could 
not be selected to fall below, for example, about 175 p.s.i. in actual 
practice. This, in turn, prevented the system from making maximum use of 
outdoor ambient air temperatures for energy saving purposes. The reason is 
that the receiver pressure must be lower than the head pressure, and by 
having an arrangement in which the receiver pressure in effect follows the 
condensing pressure, and is a function of the pressure differential 
between the condensing and head pressures, one can set valve 56 at any 
pressure desirable to make optimum use of the expected outside ambient 
temperatures. One might, for example, set valve 56 at 140 p.s.i. rather 
than at a normal 185 p.s.i. In accordance with the invention the receiver 
pressure would automatically be controlled as a function of the 
differential between the condensing and head pressures of 140 and 145 
p.s.i. respectively that would be established as desirable operating 
levels under these particular circumstances. This would be desirable in 
high outside temperature conditions. The converse is true when the outside 
ambient air temperature is low. Under these latter conditions, it may be 
desired to establish, through appropriate setting of valve 56, a 
condensing pressure of 175 p.s.i., resulting in a head pressure of 
approximately 180 p.s.i. This, in accordance with the present invention, 
would automatically maintain the receiver pressure at about 165-170 p.s.i. 
In all settings of the valve 56, an optimum relationship is established 
and maintained between the receiver pressure, the condensing pressure, and 
the head pressure, such as to prevent binding of liquid within the 
receiver, filling of the receiver with liquid, and other undesirable 
operating characteristics. 
While particular embodiments of this invention have been shown in the 
drawings and described above, it will be apparent, that many changes may 
be made in the form, arrangement and positioning of the various elements 
of the combination. In consideration thereof it should be understood that 
preferred embodiments of this invention disclosed herein are intended to 
be illustrative only and not intended to limit the scope of the invention.