US3599440A

US3599440A - Controllable compressor cooling installation

Info

Publication number: US3599440A
Application number: US860309A
Authority: US
Inventors: Ludwig Melion
Original assignee: Luwa Ltd
Current assignee: Luwa Ltd
Priority date: 1968-09-26
Filing date: 1969-09-23
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17
Also published as: DE1948127A1; FR2018930A1; GB1271119A; AT297068B; CH496931A

Abstract

A novel controllable compressor cooling installation is disclosed, the installation being provided with a primary coolant circulation path from a compressor, through a condenser, a shutoff valve, in expansion valve, an evaporator, and then back to the compressor. An auxiliary or secondary coolant circulation path is provided from the outlet of the compressor to the inlet of the evaporator, this secondary or auxiliary coolant path containing a second shutoff valve. In the preferred inventive embodiment, a check or relief valve is provided in the primary coolant circulation path between the branchoff of the auxiliary path and the condenser. Importantly, both shutoff valves in the primary and in the auxiliary coolant paths can be controlled in a time-delayed fashion with respect to one another by means of a two-stage control process. The control is such that, in each instance, the shutoff valve in the primary coolant circulation path closes first and, thereafter, the shutoff valve in the auxiliary or secondary coolant circulation path opens.

Description

United States Patent [72] Inventor Ludwig Melion Buchrain, Oberrohrdorf, Switzerland [21 Appl. No. 860,309

[22] Filed Sept. 23, 1969 [45] Patented Aug. 17, 1971 [73] Assignee Luwa AG Zurich, Switzerland [32] Priority Sept. 26, 1968 [3 3] Switzerland [54] CONTROLLABLE COMPRESSOR COOLING INSTALLATION 5 Claims, 1 Drawing Fig.

[52] US. Cl 62/158, 62/196, 62/278 [51] Int. Cl F25b 29/00 [50] Field of Search 62/196,

[56] References Cited UNITED STATES PATENTS 2,344,215 3/1944 Soling 62/196 3,332,251 7/1967 Watkins Primary Examiner-Meyer Perlin At!0rneyWerner W. Kleeman ABSTRACT: A novel controllable compressor cooling installation is disclosed, the installation being provided with a primary coolant circulation path from a compressor, through a condenser, a shutoff valve, in expansion valve, an evaporator, and then back to the compressor. An auxiliary or secondary coolant circulation path is provided from the outlet of the compressor to the inlet of the evaporator, this secondary or auxiliary coolant path containing a second shutoff valve. In the preferred inventive embodiment, a check or reliefvalve is provided in the primary coolant circulation path between the branchoff of the auxiliary path and the condenser. Importantly, both shutoff valves in the primary and in the auxiliary coolant paths can be controlled in a time-delayed fashion with respect to one another by means of a two-stage control process. The control is such that, in each] instance, the shutoff valve in the primary coolant circulation path closes first and, thereafter, the shutoff valve in the auxiliary or secondary coolant circulation path opens.

PATENTED mm mm 35:99AM) LUDW/G MEL lO/l/ INVEN 1 OR ATTORNEYS CONTROLLABLE COMPRESSOR COOLING INSTALLATION BACKGROUND OF THE INVENTION This invention generally relates to cooling installations and particularly concerns a controllable compressor cooling installation of the type which is provided with a primary coolant circulation path from a compressor, through a condenser, a shutoff valve, an expansion valve, an evaporator, and then back to the compressor as well as a secondary or auxiliary coolant circulation path extending from the outlet of the compressor to the evaporator inlet.

In some cooling installations, it is necessary to effect operational control over the cooling output thereof. A typical example of an installation wherein such control is necessary, is the so-called climatic control installation wherein the cooling requirements thereof are highly variable in dependence upon both the month and the time of day and wherein the full capacity of such installation is demanded only during relatively short portions of the total operational period. Accordingly, in this instance, as well as in many other applications, economic and operational considerations dictate only a partial output or load operation of the installation.

In this respect, a number of control possibilities are known to the art wherein the cooling output of a compressor cooling installation is controlled or alternatively temporarily reduced. However, the prior art solutions, as will be discussed hereinbelow, are either uneconomical, or are unsatisfactory in other respects.

Perhaps the simplest technique wherein control over the cooling output of a compressor cooling installation can be effected is to switch the compressor motor on and off as required. However, when so doing, substantial variations in temperature can occur, and even more importantly, an undesirable peak demand is placed upon the electrical feed system upon each successive startup of the electric drive motor. If a high switching frequency is desired such as for obtaining a quasi-steady cooling control, the danger of overheating the electric motor exists due to the repetitive high startup current flows, this danger being particularly great when one is utilizing single-phase drive motors. Larger cooling installations can be provided with a plurality of parallely working though separately driven compressors which are individually switched on and off so as to effect control over the cumulative cooling output. In this instance, as was the case in the example discussed above, each and every switching operation creates a peak load in the system. Furthermore, the application range as well as the gradation of the cooling control are fixed by the number of compressors provided, which number normally is relatively low.' As another alternative, control over the rotational speeds of the compressor drive motor may be effected to achieve gradation of the cooling output. Yet, in this instance, the low end range of control is severely limited in practice due to the speed characteristics of the electric motor as well as to the characteristics and properties of the control or governor therefor.

A further known means to effect control over the cooling output of compressor cooling installations involves constructional modification of the reciprocating compressor so as to reduce the circulation of the coolant. Such techniques comprise lifting of a control valve, opening a bypass valve at individual cylinders of the compressor or changing the dead space or volume therein. By such techniques, the power input requirements of the drive motor for the compressor admittedly are correspondingly reduced. Yet, when compared and contrasted with operation of the compressor at full load, the proportional or relative motor losses actually increase, and the friction losses as well as the compression losses of the unloaded portions of the compressor remain practically the same. So as to remove the relatively increased heat losses generated at the compressor after the condenser, only the reduced flow of coolant is available. Accordingly, the danger of overheating on the pressure side of the compressor is prevalent. Yet, the coolant which is mixed with lubricating oil cannot exceed a certain maximum temperature at any point of its circulation as otherwise the chemical stability of the coolant mixture is endangered. Thus, a sufficient quantity of coolant must continuously be kept in circulation. In other words, the cooling output must not be allowed to decrease below a more or less significant fraction of the full cooling output.

For the purpose of partial cooling load operation, it is also known in the art to provide a regulating valve or the like in the suction conduit of the compressor so as to reduce the quantity of coolant which is suctioned in from the evaporator. For similar reasons, as discussed in the above prior art examples, the danger of overheating the compressed coolant-oil-mixture is highly prevalent.

In other known arrangements and with other known techniques for reducing the cooling output, a gas bypass conduit is provided between the high pressure side and the low pressure side of the coolant circulation path. A regulating valve such as a so-called output regulator or governor operated by a governor or other control is disposed in the gas bypass conduit. In dependence upon the amount of opening of the regulating valve, a portion of the coolant flow is diverted through the bypass conduit whereas the remaining portion of the coolant flow circulates in the normal or primary circulation path. However, such arrangements operate very uneconomically at reduced output, since even when operating at such reduced output, the entire quantity of coolant is always conducted through the compressor or is otherwise compressed. Furthermore, if the high pressure side of the compressor is directly connected with its low pressure side, a great danger of overheating exists since a portion of the compressed heating gas is not allowed to cool off in the condenser but again directly reaches the suction side of the compressor.

SUMMARY OF THE INVENTION Thus, a need exists in the art for a. controllable compressor cooling installation wherein the cooling output thereof can be controlled in a fashion eliminating the drawbacks of the above-described prior art. It is the primary object of the in stant invention to provide such a cooling installation. Additionally though equally important objects of the instant invention, are:

The provision of a controllable compressor cooling installation which operates economically even when under only a partial load;

The provision of a controllable compressor cooling installation by which control over the cooling load can be effected to a great extent and throughout a relatively large range, even down to zero output without the danger of overheating the coolant; and,

The provision of a controllable compressor cooling installation which does not create deleterious electrical load peaks in the electrical feed system of the compressor motor.

These objects as well as other objects which will become apparent as the description proceeds, are implemented by the novel compressor cooling installation which, in accordance with the invention, is characterized by the provision, in a compressor cooling installation as discussed at the outset of the specification, of a relief or check valve in the primary circulation path between the condenser and the branchoff of the auxiliary or secondary circulation path, and the provision of a second shutoff valve in the auxiliary path. Each of the shutoff valves, in the primary and in the secondary or auxiliary circulation paths, can be controlled in a time-delayed fashion with respect to one another by means of a two-stage control process in such a manner that, in every instance, the shutoff valve in the primary circulation. path closes first and,

thereafter, the shutoff valve in the auxiliary or secondary circulation path opens.

The time-delayed control of the shutoff valves can advantageously be effected by connecting the shutoff valves via control circuits and the like to a governor or like regulating device in which a valve control command time delay is preselected. However, according to an alternative inventive embodiment, a governor or like regulating device operating with a time delay can be eliminated and the primary circulation path shutoff valve can be directly controlled by a governor whereas the shutoff valve in the auxiliary or secondary circulation path can be connected via a conductor to a pressure sensor responding to reduced coolant pressure in the evaporator whereby an opening command for the second shutoff valve is generated. In this manner, the time-delayed switching of the shutoff valves as discussed can occur in direct dependency upon the pressure in the coolant circulation path so as to determine the point and switching time without necessitating the preselection and determination of approximate constant time delays. In each, instance, the novel invention in the preferred embodiment thereof, contemplates the utilization of magnetic valves for the shutoff valves of the system.

Q 7 BRIEF DESCRIPTION OF THE DRAWING I The invention itself will be better understood and features and advantages thereof not previously discussed will become apparent from the following detailed description of a preferred inventive embodiment, such description referring to the appended single sheet of drawing wherein the sole FIGURE thereon depicts an exemplary embodiment, in schematic illustration, of the novel inventive controllable compressor cooling installation or system.

DETAILED DESCRIPTION OF A PREFERRED INVENTIVE EMBODIMENT Referring now to the drawing, the main or primary circulation path of the coolant can be traced in the manner discussed hereinbelow. A compressor'l driven by an electric motor 2 suctions or draws in coolant via a conduit 18 running from an evaporator 8. The gaslike compressed chemical coolant leaves the compressor 1 via a hot gas conduit 10 from where such gas passes through a relief or check valve 24 into a conduit 12 and subsequently reaches a condenser'4 whereat the gas is cooled and liquified by cooling water circulation 5. As illustrated, a collector 6 for the liquified coolant can be provided after the condenser 4 or, if desired, the condenser itself can be constructed so as to include a collector. Thereafter, the liquified coolant passes in known manner through an aftercooler (not illustrated) at the condenser 4 or the collector 6, respectively.

The liquid coolant then passes through conduit 14 in which a controllable shutoff valve such as a magnetic valve, and an expansion valve 7 are successively provided. Thereafter, the coolant flows through conduit 16 into an evaporator 8 whereat the coolant absorbs heat from the environment by evaporation and thus, the surrounding environment is cooled.

The coolant, which is now in vapor or gas form, then passes into compressor 1 and the continuous cycle repeats.

As will be noted, an auxiliary or secondary conduit 19 branches off from the hot gas conduit 10. Conduit 19 is provided with a second shutoff valve 22 which may likewise be constructed as a magnetic valve, the auxiliary or secondary conduit leading to conduit 16 which feeds the input to evaporator 8. The operation of the shutoff valves 20 and 22 will be discussed hereinbelow.

When it is desired to operate the cooling installation at full cooling output, shutoff valve 20 is opened and shutoff valve 22 is closed. Now, the entire quantity of coolant circulates in known manner in the above-described primary circulation path. Compressor 1 serves to compress the entire flow of coolant and raise the pressure thereof to that required to maintain the circulation, the primary pressurereduction of the coolant occurring at the expansion valve 7.

Control over the cooling output in the illustrated inventive embodiment is achieved by means of a two-stage control process wherein the system is repeatedly and reversibly switched between two different operational conditions which,

for convenience, will be referred to hereinbelow as work interval and rest interval" respectively. The change or control in the cooling output is achieved by varying the time relationship between the work interval and the rest interval, and, as such, it is possible to achieve a quasi-steady control over the cooling output with due consideration being given of a switching frequency sufficient for the thermal time constant of the embodiment. The range of cooling control will be seen to be disposed between the extreme and opposite conditions of permanent work condition" representing full output and permanent rest condition representing zero output.

Control over the cooling output is exclusively achieved by means of an open-close control of both of the shutoff valves 20 and 22 while the compressor 1 continuously operates. The work condition or work interval" corresponds to the abovedescribed normal operation in which shutoff valve 20 is open and shutoff valve 22 is closed. The transition from the work interval" to the rest interval takes place in every instance in a two-stage process and is initiated by closing valve 20. Subsequently, while valve 22 is still in its previously closed condition, compressor 1 suctions the coolant vapor from the evaporator 8 and feeds such vapor via conduit 10 and relief'or check valve 24 to the condenser 4 where such coolant is liquified and stored in collector 6. Since an afterflow of coolant to evaporator 8 is impossible with valve 20 being closed, the coolant pressure in the evaporator 8 quickly drops during this intermediate control phase. Thereafter, shutoff valve 22 in the auxiliary or secondary conduit 19 is opened and this constitutes the second state, thereby achieving a rest condition or rest interval." Accordingly, during the rest interval," a circulation path of low flow resistance via the auxiliary or secondary conduit 19, shutoff valve 22, and evaporator 8, exists between the suction conduit 18 and the pressure conduit 10 of the compressor 1. Accordingly, a relatively low-residual quantity of the coolant circulates in the above-mentioned lowpressure circulation path while the major portion of the coolant on the condenser side is maintained between the relief or check valve 24 and the shut-off valve 20. Through suitable dimensioning of the auxiliary conduit 19 and of the valve 22, the coolant flow resistances in the low pressure circulation path are maintained low such that compressor 1 is only slightly loaded with the circulation quantity of coolant during the rest interval, such circulation quantity furthermore being strongly reduced. The power draw of the drive motor 2 is thus correspondingly low.

The rest interval is terminated and the work interval initiated by opening valve 20 and closing valve 22, In the work interval," the entire quantity of coolant is again circulated via the condenser 4, and the evaporator 8, with the compressor 1 being fully loaded and the installation operating at its full cooling capacity.

The residual quantity of the coolant which circulates during the rest interval through the auxiliary or secondary conduit 19, open valve 22,and evaporator 8, functions to conduct away the slight heat loss occurring in the strongly unloaded compressor 1 as the .drive motor 2 therefor continues to run. This heat loss is discharged to the surrounding environment upon passage of the coolant through the evaporator 8. Throughout this circulation path, the residual quantity of coolant permanently remains in a gaslike condition contrary to the normal or primary circulation through condenser 4 with a full output operation. Accordingly, the coolant enters evaporator 8 already in the form of a gas and is not evaporated therein. Thus, during the rest interval" a zero cooling output of the installation is easily obtained. In fact, the cooling output is even' somewhat negative due to the above-mentioned discharge into the environment of the residual heat loss.

The pressure differential which must be produced by com- 1 pressor 1 during the rest interval is determined only by the flow resistances prevalent in the auxiliary or secondary circulation path through valve 22 and evaporator 8. So as to keep these resistances and thus the compression work during the rest interval" to a minimum, the auxiliary or secondary conduit 19 as well as the valve 22 are suitably constructed so as to exhibit large passage cross sections to the extent possible. The residual quantity of coolant which remains in circulation during the rest interval" is dependent and interrelated with its above-described function of removing the slight heat loss from compressor 1. In any given cooling installation, the vapor pressure in the auxiliary or suction-in conduit 19 or in evaporator 8, respectively, is a partial measure of this quantity. In a given installation, it is exemplary stated that the pressure in the evaporator during the rest interval" is suitably reduced to about 1 ata. as compared to 5 ata. during the work interval" or full cooling output operation. This corresponds to a flow of coolant through the compressor which has been reduced to about 20 percent of its full operational value. The power input to the motor 2 is likewise accordingly reduced by about 80 percent during the rest interval.

From the above considerations, it will be apparent that the novel cooling installation can be economically operated at only a low percentage of its full cooling output capacity even through a long period of time. This is the case since the time average value of the consumed drive power is reduced approximately proportionally to the time average value of the cooling output or load. If the above-mentioned relatively low pressure in the evaporator 8 and in the auxiliary branch stream of the coolant, respectively, is correctly effected, then no danger of coolant overheating results even if the cooling output or load of the installation is completely reduced to zero. 0n the contrary, the gas and motor temperatures drop even below the corresponding values associated with full output operations.

Structurally speaking, it has been found advantageous to keep the volume of the heated gas conduit 10 between the compressor outlet and the relief valve 24 to as small an extent as possible. Likewise, the volume of the auxiliary conduit 19 to valve 22 should be kept at a minimum. This is desirable since, during the transition from work interval to rest interval," when the valve 22 is opened after evaporator 8 has been suctioned off, the coolant gas compressed in the conduit volume discussed above, relaxes or expands itself via valve 22 and again somewhat increases the low pressure produced in the evaporator 8.

As schematically illustrated in the drawing, control over the cooling output of the installation and of the activation of the shutoff valves and 22, which valves preferably are constructed as magnetic valves, is achieved by means of a twostage governor or control apparatus 30 via

control conductors

35 and 36. The nominal or desired value of the cooling output or for the temperature to be maintained by the installation, respectively, is inputted via conductor 32 to the governor or control apparatus 30 whereas the actual value is inputted via conductor 34, such actual value being sensed by a thermal sensing apparatus 33 which determines the cooling temperature as actually obtained in the surrounding environment of evaporator 8. As should be appreciated from the foregoing comments, it is essential that in each instance during the transition from work interval" to rest interval, the shutoff valve 20 is first closed and that thereafter, shutoff valve 22 is only opened after a certain time delay when the required low pressure in the evaporator 8 has been reached. This time delay can be assumed to at least be approximately constant in every given installation and therefore, such time-delay can be predetermined and preselected in the governor or control device 30. Alternatively, instead of controlling the operation of shutoff valve 22 in the auxiliary or secondary conduit 19 by means of the governor or control apparatus 30, such operation can also be controlled as illustrated by the conductor 38 by means of a pressure sensor 37 disposed at the evaporator. This pressure sensor responds when the evaporator 8 is progressively suctioned empty after the closing of valve 20 to thereby reach the desired value of the low pressure which has been preselected or built into sensor 37.

The load changes on the compressor 1 which attend the two-stage control process discussed above become correspondingly noticeable in the input efficiency to the drive motor 2. However, since these load changes occur while the machine group continuously runs, the effect upon the electrical feed system and particularly, the increased current draw during repeated loads, remains quite tolerable. in any event, such are far less than would be the case if the machine group were to start each time from a stopped. or rest position as is the case in the conventional known on-ofl' cooling controls discussed at the outset.

With relatively little additional expenditure and by utilizing a relatively simple governing device or control, control of the cooling output in the above-described novel compressor cooling installation can be effected over the entire range between the full nominal or theoretical output value and a zero value, all without subjecting the machine or the coolant to deleterious overheating. The particular novel control mode also per mits partial cooling outputs during any desired period of time, all with a high efficiency. Furthermore, the novel control process as described effects no undesirable or impermissible peak loads upon the electrical feed system, and, as should be apparent, the novel arrangement and control technique is equally applicable with installations having either a reciprocating compressor or a turbocompressor.

As should now be apparent, the objects initially set forth at the outset of the specification have been successfully achieved. ACCORDINGLY,

What I claim is:

l. A controllable compressor cooling installation, said installation providing a primary coolant circulation path from a compressor, through a condenser, a first shutoff valve, an ex pansion valve, an evaporator, and then back to said compressor; said installation providing a secondary coolant circulation path comprising an auxiliary conduit disposed from the outlet of said compressor to the inlet of said evaporator; check valve means disposed in said primary circulation path between said condenser and the connection branchoff of said auxiliary con duit; a second shutoff valve disposed in said auxiliary conduit; and two-stage time-delay control means for both said first and second shutoff valves, said control means closing said first shutoff valve first and thereafter, opening said second shutoff valve in said auxiliary conduit.

2. A cooling installation as defined in claim ll, wherein said first and second shutoff valves are connected to said control means via control conductors, and wherein said control means comprises a governing device having a preselected time delay between the generation of a control command for said first shutoff valve and a control command for said second shutoff valve.

3. A cooling installation as defined in claim 1, wherein said first and second shutoff valves are magnetic switch valves.

4. A controllable compressor cooling installation, said installation providing a primary coolant circulation path from a compressor, through a condenser, a first shutoff valve, an expansion valve, an evaporator, and then back to said compressor; said installation providing a secondary coolant circulation path comprising an auxiliary conduit disposed from the outlet of said compressor to the inlet of said evaporator; check valve means disposed in said primary circulation path between said condenser and the connection branchoff of said auxiliary conduit; a second shutoff valve disposed in said auxiliary conduit; and two-stage time-delay control means for both said first and second shutoff valves, said control means closing said first shutoff valve first and thereafter, opening said second shutoff valve in said auxiliary conduit, said control means for said first and second shutoff valves comprising a governing device for said first shutoff valve in said primary circulation path, and a pressure sensor means and control conductor therefor for said second shutoff valve, said pressure sensor means responding to a reduced coolant pressure in said evaporator so as to generate an opening command for said second shutoff valve.

5. A controllable compressor cooling installation, said in stallation providing a primary coolant circulation path from a compressor, through a condenser, a first shutoff valve, and expansion valve, an evaporator and then back to said compresshutoff valve first and thereafter, opening said second shutoff valve in said auxiliary conduit, said auxiliary conduitdefining a low pressure circulation path for throughflow of a relatively low residual quantity of the coolant through said secondary coolant circulation path while the major portion of the coolant is maintained between said check valve means and said first shutoff valve of said primary circulation path.

Claims

1. A controllable compressor cooling installation, said installation providing a primary coolant circulation path from a compressor, through a condenser, a first shutoff valve, an expansion valve, an evaporator, and then back to said compressor; said installation providing a secondary coolant circulation path comprising an auxiliary conduit disposed from the outlet of said compressor to the inlet of said evaporator; check valve means disposed in said primary circulation path between said condenser and the connection branchoff of said auxiliary conduit; a second shutoff valve disposed in said auxiliary conduit; and two-stage time-delay control means for both said first and second shutoff valves, said control means closing said first shutoff valve first and thereafter, opening said second shutoff valve in said auxiliary conduit.

2. A cooling installation as defined in claim 1, wherein said first and second shutoff valves are connected to said control means via control conductors, and wherein said control means comprises a governing device having a preselected time delay between the generation of a control command for said first shutoff valve and a control command for said second shutoff valve.

5. A controllable compressor cooling installation, said installation providing a primary coolant circulation path from a compressor, through a condenser, a first shutoff valve, and expansion valve, an evaporator and then back to said compressor; said installation providing a secondary coolant circulation path comprising an auxiliary conduit disposed from the outlet of said compressor to the inlet of said evaporator; check valve means disposed in said primary circulation path between said condenser and the connection branchoff of said auxiliary conduit; a second shutoff valve disposed in said auxiliary conduit; and two-stage time-delay control means for both said first and second shutoff valves, said control means closing said first shutoff valve first and thereafter, opening said second shutoff valve in said auxiliary conduit, said auxiliary conduit defining a low pressure circulation path for throughflow of a relatively low residual quantity of the coolant through said secondary coolant circulation path while the major portion of the coolant is maintained between said check valve means and said first shutoff valve of said primary circulation path.