Compressor system with demand cooling

A refrigeration system is disclosed which incorporates apparatus for preventing overheating of the compressor by selectively feeding liquid refrigerant from the outlet of the condenser to the compressor. In one embodiment the refrigerant fluid from the compressor is injected into the suction manifold of the compressor. In another embodiment this fluid is injected directly into the compression chamber or chambers. Control means are provided which include a temperature sensor located within the compressor discharge chamber and valve means responsive thereto to control the flow of liquid refrigerant to the suction manifold or compression chamber.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates generally to refrigeration systems and more 
particularly to refrigeration systems incorporating means to prevent 
overheating of the compressor by selectively injecting liquid refrigerant 
into the suction manifold. 
In response to recent concerns over depletion of the ozone layer due to 
release of various types of refrigerants such as R12, the government has 
imposed increasingly stricter limitations on the use of these 
refrigerants. These limitations will require refrigeration systems of the 
future to utilize substitute refrigerants. Presently, the available 
substitutes for commonly used refrigerants such as R-12 and R-502 are not 
well suited for low temperature applications because they result in high 
discharge temperatures which may damage or shorten the life expectancy of 
the compressor particularly under high load situations and high 
compression ratios. 
Liquid injection systems have long been used in refrigeration systems in an 
effort to limit or control excessive discharge gas temperatures which 
cause overheating of the compressor and may result in breakdown of the 
compressor lubricant. Typically, these prior systems utilized capillary 
tubes or thermal expansion valves to control the fluid injection. However, 
such systems have been very inefficient and the capillary tubes and 
thermal expansion valves were prone to leaking during periods when such 
injection cooling was not needed. This leakage could result in flooding of 
the compressor. Additionally, when the compressor was shut down, the high 
pressure liquid could migrate from the receiver to the low pressure 
suction side through these capillary tubes or expansion valves thereby 
resulting in slugging of the compressor upon startup. Also, the thermal 
sensors utilized by these prior systems were typically located in the 
discharge line between the compressor and condenser. This positioning of 
the sensor often resulted in inadequate cooling as the sensed temperature 
could vary greatly from the actual temperature of the discharge gas 
exiting the compression chamber due to a variety of factors such as the 
ambient temperature around the discharge line and the mass flow rate of 
discharge gas. Thus overheating of the compressor could occur due to an 
erroneous sensed temperature of the discharge gas. 
The present invention, however, overcomes these problems by providing a 
liquid injection system which utilizes a temperature sensor positioned 
within the discharge chamber of the compressor in close proximity to and 
in direct contact with the compressed gas exiting the compression chamber. 
Thus a more accurate indication of the compressor heating is achieved 
which is not subject to error due to external variables. Further, the 
present invention employs in a presently preferred embodiment a positive 
acting solenoid actuated on/off valve coupled with a preselected orifice 
which prevents leakage of high pressure liquid during periods when cooling 
is not required. Additionally, the orifice is sized for a maximum flow 
rate such that it will be able to accommodate the cooling requirements 
while still avoiding flooding of the compressor. The term "liquid 
injection" is used herein to denote that it is liquid refrigerant which is 
taken from the condenser in such systems but in reality a portion of this 
liquid will be vaporized as it passes through the capillary tube, 
expansion valve or other orifice thus providing a two phase (liquid and 
vapor) fluid which is injected into the compressor. The present invention 
also injects the fluid (i.e. 2 phase fluid) directly into the suction 
chamber at a location selected to assure even flow of the injected fluid 
to each compression chamber so as to thereby maximize compressor 
efficiency as well as to insure a maximum and even cooling effect. 
In another embodiment of the present invention the refrigerant fluid is 
injected directly into the compression chamber preferably immediately 
after the suction ports or valve has been closed off thus acting to cool 
both the compression chamber and suction gas contained therein. While this 
arrangement offers greater efficiency in operation, it tends to be more 
costly as additional controls and other hardware are required for its 
implementation. 
Additional advantages and features of the present invention will become 
apparent from the subsequent description and the appended claims taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings and more particularly to FIG. 1, there is 
shown a typical refrigeration circuit including a compressor 10 having a 
suction line 12 and discharge line 14 connected thereto. Discharge line 14 
extends to a condenser 16 the output of which is supplied to an evaporator 
18 via lines 20, receiver 22 and line 24. The output of evaporator 18 is 
thence fed to an accumulator 26 via line 28 the output of which is 
connected to suction line 12. As thus described, this refrigeration 
circuit is typical of such systems employed in both building air 
conditioning or other refrigerating systems. 
The present invention, however, provides a unique demand cooling fluid 
injection system indicated generally at 30 which operates to prevent 
potential overheating of the compressor. Fluid injection system 
incorporates a temperature sensor 32 positioned within the compressor 10 
which operates to provide a signal to an electronic controller 34 which 
signal is indicative of the temperature of the compressed gas being 
discharged from the compressor 10. A fluid line 36 is also provided having 
one end connected to line 20 at or near the output of condenser 16. The 
other end of fluid line 36 is connected to a solenoid actuated valve 38 
which is operatively controlled by controller 34. The output from solenoid 
valve 38 is fed through a restricted orifice 40 to an injection port 
provided on compressor 10 via line 42. 
As best seen with reference to FIGS. 2 through 4, compressor 10 is of the 
semi-hermetic reciprocating piston type and includes a housing 44 having a 
pair of compression cylinders 46, 48 disposed in longitudinally aligned 
side-by-side relationship. Housing 44 has a suction inlet 50 disposed at 
one end thereof through which suction gas is admitted. Suction gas then 
flows through a motor chamber provided in the housing and upwardly to a 
suction manifold 52 (indicated by the dotted lines in FIG. 4) which 
extends forwardly and in generally surrounding relationship to cylinders 
46, 48. A plurality of passages 54 serve to conduct the suction gas 
upwardly through a valve plate assembly 56 whereupon it is drawn into the 
respective cylinders 46, 48 for compression. Once the suction gas has been 
compressed within cylinders 46, 48, it is discharged through valve plate 
assembly 56 into a discharge chamber 58 defined by overlying head 60. 
As best seen with reference to FIGS. 3 and 4, line 42 is connected to an 
injection port 62 provided in the sidewall of housing 44 and opening into 
suction manifold 52 at a location substantially centered between cylinders 
46, 48 and directly below passage 54. The location of this injection port 
was determined experimentally to optimize efficiency and to insure even 
cooling of each of the two cylinders. Preferably this location will be 
selected for a given compressor model such that the compressed gas exiting 
from each of the respective compression chambers will be within a 
predetermined range relative to each other (i.e. from hottest to coolest) 
and more preferably these temperatures will be approximately equal. It 
should be noted that it is desirable to inject the liquid as close to the 
cylinders as possible to optimize operational efficiency. 
Also as best seen with reference to FIGS. 2 and 3, temperature sensor 32 is 
fitted within an opening 64 provided in head 60 and extends into discharge 
chamber 58 so as to be in direct contact with the discharge gas entering 
from respective cylinders 46, 48. Preferably sensor 32 will be positioned 
at a location approximately centered between the two cylinders 46, 48 and 
as close to the discharge valve means 66 as possible so as to insure an 
accurate temperature is sensed for each of the respective cylinders. It is 
believed that this location will place the temperature sensor closest to 
the hottest compressed gas exiting from the compression chambers. 
Solenoid actuated valve 38 will preferably be an on/off type valve having a 
capability for a very high number of duty cycles while also assuring a 
leak resistant off position so as to avoid the possibility of compressor 
flooding or slugging. Alternatively, solenoid valve could be replaced by a 
valve having the capability to modulate the flow of liquid into suction 
manifold 52 in response to the sensed temperature of the discharge gas. 
For example, a stepping motor driven valve could be utilized which would 
open progressively greater amounts in response to increasing discharge 
temperature. Another alternative would be to employ a pulse width 
modulated valve which would allow modulation of the injection fluid flow 
by controlling the pulse duration or frequency in response to the 
discharge temperature. 
In order to limit the maximum flow of fluid into suction manifold 52 via 
injection port 62 as well as to reduce the pressure of the fluid to 
approximately that of the suction gas flowing from the evaporator, an 
orifice 40 is provided downstream of valve 38. Preferably orifice 40 will 
be sized to provide a maximum fluid flow therethrough at a pressure 
differential of about 300 psi which corresponds to an evaporator 
temperature of about -40.degree. F. and a condenser temperature of about 
130.degree. F. so as to assure adequate cooling liquid is provided to 
compressor 10 to prevent overheating thereof. Evaporator temperature 
refers to the saturation temperature of the refrigerant as it enters the 
evaporator and has passed through the expansion valve. Condenser 
temperature refers to the saturation temperature of the refrigerant as it 
leaves the condenser. This represents a worst case design criteria. The 
maximum flow will vary between different compressors and will be 
sufficient to prevent the discharge temperature of the compressor from 
becoming excessively high yet not so high as to cause flooding or slugging 
of the compressor. It should be noted that it is important that orifice 40 
be sized to create a pressure drop thereacross which is substantially 
equal to the pressure drop occurring between the condenser outlet and the 
compressor suction inlet across the evaporator so as to prevent subjecting 
the evaporator to a back pressure which may result in excessive system 
efficiency loss. 
In operation, upon initial startup from a "cold" condition, valve 38 will 
be in a closed condition as the temperature of compressor 10 as sensed by 
sensor 32 will be low enough not to require any additional cooling. Thus, 
the refrigeration circuit will function in the normal manner with 
refrigerant being circulated through condenser 16, receiver 22, evaporator 
18, accumulator 26 and compressor 10. However, as the load upon the 
refrigeration system increases, the temperature of the discharge gas will 
increase. When the temperature of the discharge gas exiting the 
compression chambers of compressor 10 as sensed by sensor 32 reaches a 
first predetermined temperature as shown by the spikes in the graph of 
FIG. 5, controller 34 will actuate valve 38 to an open position thereby 
allowing high pressure liquid refrigerant exiting condenser 16 to flow 
through line 36, valve 38, orifice 40, line 42 and be injected into the 
suction manifold 52 of compressor 10 via port 62. It should be noted that 
the liquid refrigerant will normally be partially vaporized as it passes 
through orifice 40 and hence the fluid entering through port 62 will 
typically be two phase (part gas, part liquid). This cool liquid 
refrigerant will mix with the relatively warm suction gas flowing through 
manifold 52 and be drawn into the respective cylinders 46, 48. The 
vaporization of this liquid refrigerant will cool both the suction gas and 
the compressor itself thereby resulting in a lowering of the temperature 
of the discharge gas as sensed by sensor 32 and as shown in the graph of 
FIG. 5. Once the discharge temperature sensed by sensor 32 drops below a 
second predetermined temperature, controller 34 will operate to close 
valve 38 thereby shutting off the flow of liquid refrigerant until such 
time as the temperature of the discharge gas sensed by sensor 32 again 
reaches the first predetermined temperature. Preferably, the first 
predetermined temperature at which valve 38 will be opened will be below 
the temperature at which any degradation of the compressor operation or 
life expectancy will occur and in particular below the temperature at 
which any degradation of the lubricant utilized within compressor 10 
occurs. The second predetermined temperature will preferably be set 
sufficiently below the first predetermined temperature so as to avoid 
excessive rapid cycling of valve 38 yet high enough to insure against 
possible flooding of the compressor. In a preferred embodiment of the 
present invention, the first predetermined temperature was set at about 
290.degree. F. and the second predetermined temperature was set at about 
280.degree. F. The graph of FIG. 5 shows the resulting discharge 
temperature variation as a function of time for these predetermined 
temperatures at -25.degree. F. evaporating temperature, 110.degree. F. 
condensing temperature and 65.degree. F. return temperatures. Return 
temperature refers to the temperature of the refrigerant returning from 
the evaporator as it enters the compressor. 
As noted above, positioning of the sensor 32 and the injection port 62 is 
very important for insuring proper even cooling of the compressor and for 
maximizing operating efficiency of the system. FIG. 6 shows the position 
of injection port 68 and discharge gas sensor 70 in a semi-hermetic 
compressor 72 having three compression cylinders 74, 76, 78. Port 68 opens 
into suction manifold 80 (outlined by dotted lines and extending along 
both sides of the two rearmost cylinders) provided within the compressor 
housing and is preferably centered on the middle cylinder 76. Similarly, 
sensor 70 extends inwardly through the head (not shown) and is positioned 
in closely overlying relationship to the center cylinder 76 so as to be 
exposed to direct contact with the compressed discharge gas exiting from 
each of the three cylinders. Again, it is believed that this location will 
place the sensor closest to the hottest compressed gas exiting from the 
respective compression chambers as is believed preferable. The operation 
of this embodiment will be substantially identical to that described 
above. 
Referring now to FIG. 7, there is shown a refrigeration system similar to 
that shown in FIG. 1 incorporating the same components indicated by like 
reference numbers primed. However, this refrigeration system incorporates 
an alternative embodiment of the present invention wherein the refrigerant 
fluid is injected directly into each of the respective cylinders as soon 
as the piston has completed its suction stroke (i.e. just as the piston 
passes its bottom dead center position). This embodiment offers even 
greater improvements in system operating efficiency in that the fluid 
being injected does not displace any of the suction gas being drawn into 
the compressor but rather adds to the fluid being compressed thus 
resulting in greater mass flow for each stroke of the piston. 
As shown in FIG. 7, compressor 10' has a crankshaft 82 operative to 
reciprocate pistons 84, 86 within respective cylinders 88, 90. A plurality 
of indicia 92 equal in number to the number of cylinders provided within 
compressor 10' are provided on a rotating member 94 associated with 
crankshaft 82 which are designed to be moved past and sensed by sensor 96 
as crankshaft 82 rotates. Indicia 92 will be positioned relative to sensor 
96 such that sensor 96 will produce a signal indicating that a 
corresponding piston is moving past bottom dead center. These signals 
generated by sensor 96 will be supplied to controller 98. 
In order to supply refrigerant fluid to each of the respective cylinders 
88, 90, a pair of suitable valves 100, 102 are provided each of which has 
an input side connected to fluid line 36' and is designed to be actuated 
between on/off positions by controller 98 as described in greater detail 
below. An orifice 104, 106 is associated with each of the respective 
valves 100, 102. Orifice 104, 106 perform substantially the same functions 
as orifice 40 described above except that they will be designed to 
maintain the fluid to be injected into the cylinders somewhat above the 
pressure of the suction gas within the cylinders at the time the fluid is 
to be injected which pressure may be above that of the suction gas 
returning from the evaporator. 
The outputs of respective valves 100, 102 and orifices 104, 106 will be 
supplied to respective cylinders 88, 90 via fluid lines 108, 110 
respectively which may communicate with cylinders 88, 90 through any 
suitable porting arrangement such as openings provided in the sidewall of 
the respective cylinders or through a valve plate associated therewith. 
Additionally, suitable check valves may be provided to prevent any 
backflow of refrigerant during the compression stroke if desired. 
A sensor 112 is also provided being disposed within a discharge chamber 114 
defined by head 116 and operative to send a signal indicative of the 
temperature of the compressed gas exiting cylinders 88, 90 to controller 
98. Sensor 112 is substantially identical to sensors 32 and 70 described 
above and will be positioned within discharge chamber 114 in a 
substantially identical manner to and will function in the same manner as 
described with reference to sensors 32 and 70. 
In operation, when sensor 112 indicates to controller 98 that the 
temperature of the compressed gas exiting cylinders 88, 90 exceeds a 
predetermined temperature, controller 98 will begin looking for actuating 
signals from sensor 96. As indicia 92 carried by crankshaft 82 passes 
sensor 96, a signal indicating that one of pistons 84 and 86 is passing 
bottom dead center is provided to controller 98 which in turn will then 
actuate the corresponding one of valves 100 and 102 to an open position 
for a brief predetermined period of time whereby refrigerant fluid will be 
allowed to flow into the corresponding cylinder thus mixing with and 
cooling the suction gas previously drawn into the cylinder for 
compression. This cycle will be repeated for the other of cylinders 88, 90 
as the next indicia 92 moves past sensor 96 carried by crankshaft 82 
thereby providing a supply of cooling refrigerant fluid to that cylinder. 
The actual time periods for which valves 100 and 102 are maintained in an 
open position will be selected so as to provide a sufficient cooling to 
avoid excessive overheating of compressor 10' while avoiding the 
possibility of causing a flooding or slugging of the respective cylinders. 
In some applications it may be desirable to vary the length of time the 
respective valves are maintained in an open condition in response to the 
magnitude by which the temperature of the discharge gas as sensed by 
sensor 112 exceeds a predetermined temperature. In any event, once the 
temperature of the compressed gas sensed by sensor 112 drops below a 
second predetermined temperature, controller 98 will cease actuation of 
respective valves 100 and 102 and the refrigerant system will operate in a 
conventional manner without any fluid injection. 
It should be noted that while the present invention has been described in 
connection with reciprocating piston type compressors, it is also equally 
applicable to other types of compressors such as rotary, screw, scroll or 
any other type thereof. Because the present invention employs a sensor 
exposed directly to the discharge gas as it exits the compression chamber 
or chambers, the possibility of erroneous readings due to external factors 
is substantially eliminated. Further, the use of a positive control valve 
insures that cool liquid will only be supplied at those times that it is 
necessary to effect cooling of the compressor. Also, the provision of a 
properly sized orifice limits maximum liquid flow so as to insure that 
flooding of the compressor will not occur. 
While it will be apparent that the preferred embodiments of the invention 
disclosed are well calculated to provide the advantages and features above 
stated, it will be appreciated that the invention is susceptible to 
modification, variation and change without departing from the proper scope 
or fair meaning of the subjoined claims.