US2400335A

US2400335A - Refrigerating system

Info

Publication number: US2400335A
Application number: US542782A
Authority: US
Inventors: Wayne E Dodson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1944-06-29
Filing date: 1944-06-29
Publication date: 1946-05-14
Anticipated expiration: 1963-05-14

Description

May 14, 1946. w. E DODSON 2,400,335

REF RIGERATING SYSTEM I Filed June 29, 1944 v FigJ.

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Inventor-z Wa ne E. Dodson,

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Patented May 14, 1946 REFRIGERATING SYSTEM Wayne E. Dodson, Caldwell, N. J., assignor to General Electric Company, a corporation of i New York Application June 29, 1944, Serial No. 542,782

6 Claims.

My invention relates to refrigerating systems employing compressors driven by electric motors or other prime movers which tend to overheat under excessive loads and particularly to control arrangements for such systems.

Most refrigerating machines employed in low temperature cooling systems, air conditioning systems, and the like and which are designed for predetermined normal loads encounter excessive loads during certain periods of operation. For example, when an air conditioning system is started at the beginning [of the cooling season, or when a low temperature refrigeration system is started at ambient temperature, the operation of the motor compressor unit in establishing normal operating pressures of the system may result in excessive loads, and also, during the operation of the system, when there is an abnormal increase in the temperature of the condenser coolin fluid, excessive loads may be met. Heretofore automatic control devices have been provided which stop the operation of the system when there is an overload on the prime mover as indicated, for example, by excessive current drawn by an electric motor or by excessive motor winding temperature. The operation of the safety devices results in interruption of the service for a considerable period of time which is required for the motor temperature to fall to a sufficiently low value. In an effort to overcome these disadvantages oversize motors have been employed; however, it is obviously undesirable to provide a motor much larger than necessary to meet normal load requirements. When the larger motor is not provided the normal size motor runs for short periods, its operation being interrupted by the protective devices. Accordingly, it is an object of my invention to provide a refrigerating system including a compressor driven by a prime mover subject to overheating under excessive loads and including an improved arrangement for controlling the system so that the prime mover may be operated continuously under conditions otherwise tending to produce excessive loads.

It is another object of my invention to provide a refrigerating system includin an electric motor driven compressor and an improved arrangement for modifying the operation of the system to prevent overheatlng of the motor while continuing the operation of the motor under conditions which otherwise tend to produce excessive motor temperatures.

Further objects and advantages of my invention will become apparent as the following descrlption proceeds. and the features of novelty appreciable refrigerating capacity. I

One of the frequent causes of overload of elecwhich characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of my invention reference may be had to the accompanying drawing in which Fig, 1 illustrates diagrammatically an air conditioner provided with a refrigerating system embodying my invention; Figs. 2 and 3 illustrate diagrammatically portions of an air conditioner similar to that of Fig. 1 illustrating further embodiments of my invention; and Fig. 4 is, a diagrammatic view of an air conditioner pro vided with a refrigerating machine including a further embodiment of my invention.

Briefly, the air conditioners illustrated in the drawing include compression type refrigerating machines having compressors driven by electric motors, refrigerant being circulated by operation of the compressor in the usual manner. The flow of refrigerant from the condenser to the evaporator is controlled by a suitable expansion device to maintain predetermined normal operating conditions. An additional control device is provided which is responsive to an abnormal condition of operation of the electric motor such that when the operation of the system tends to produce an overload 0n the motor the mass flow of refrigerant through the system is reduced thereby preventing overloading of the motor and allowing the motor to continue in operation and to maintain tric motors driving refrigerant compressors in air conditioning systems is excessive temperature of the air or other cooling medium employed to cool the condenser. It has been found, for'example, that the temperature of the motor rises at a substantially greater rate than the rise in temperature of the cooling fluid which causes the increase of motor temperature. In other words, the ratio of losses in the motor t the power output increases. I have found that by providing a control embodying my invention a moderate reduction of motor load ma be effective to keep the motor temperature within permissible limits without reducing too greatly the refrigeration output. This arrangement insures continued operation of he air conditioning system to cause some degree of cooling even though the air or other fluid employed for cooling the condenser should reach abnormally high temperatures,

Referring now to the drawing, the air conditioner in Fig. 1 includes a duct I through which air is circulated by a suitable blower (not shown) and passes over a cooling unit 2 arranged in the duct. The cooling unit 2 i the evaporator of a refrigerating machine including a compressor 3 driven by a motor 4 and supplying compressed refrigerant gas to a condenser where the gas is cooled and liquefied and collects in a liquid receiver 6. The cooling medium for the condenser 5 may be the ambient air or any other suitable medium such as well water or river water. The liquid refrigerant flows from the receiver 6 through a liquid line 1 to the evaporator 2 under control of a suitable expansion device which has been illustrated as a thermostatic expansion valve 8 having its temperature feeler bulb or superheat control element 9 connected to be responsive to the temperature of the refrig erant vapor withdrawn from the evaporator 2 through a suction line ID. The operation of the systemis' controlled by a thermostat ll arranged in the duct I on the intake side of the evaporator 2 so that it is responsive to the temperature of the air to be cooled. l'he thermostat ll includes a bimetallic element l2 and a permanent magnet l3 which renders the bimetallic element snap acting in a manner known to the art. Closing of the contacts of thermostat Ii connects the motor 4 across suitable electric supply lines H.

During the operation of the refrigerating systern, if the temperature of the air circulated through the condenser 5 is increased, the load on the compressor 3 and on the motor 4 is increased accordingly and the motor draws more current from the lines H. The increased current produces greater heating of the motor and when the load becomes excessive it is necessary to stop the operation of the motor in order to prevent undue heating and damage to the windings. In air conditioning systems having air cooled condensers, an increase in the temperature of the outdoor air whichv cools the condenser represents an increase in the demand for cooling and the stopping of the motor due to excessive temperatures results in discomfort and failure of the operation of the air conditioning system at the time when cooling is most necessary. In order to maintain operation of the motor 4 during operating conditions tending to pro? duce excessive heating of the motor, I provide a throttle valve for decreasing the mass how of refrigerant in response to such operating conditions. By reducing the flow of refrigerant the load on the motor is reduced and the system may continue in operation at the reduced capacity. Even though the cooling of the air in the duct 1 is not suiiicient to lower the temperatures to the normal operating temperature maintained by the system, nevertheless substantial cooling is effected and the electricmotor may be maintained in operation without danger of damage due to overheating. The valve 15 obviously may be located at any suitable position between the receiver 6 and the compressor intake to control the mass flow of refrigerant from the receiver 6 through the evaporator and back to the comprcssor, and, in Fig. l, I have illustrated the valve I5. as located on the high pressure side of the thermostatic expansion valve 8. The valve i5 includes a movable valve element l8 which may be actuated by an expansible bellows H, the valve normally being held open by a spring i8 arranged in the bellows. A second spring [9 and an adjusting stem are provided to adjust the normal position of the valve element IS. The space between the bellows l1 and the casing of the valve I5 is sealed. and a thermal bulb .2! arranged to be responsive to the temperature or the motor 4 is connected with the bellows chamber through a capillary tube 22. The bulb is partially filled with a volatile liquid and maintains the bellows at a pressure dependent upon the temperature of the motor; when the motor temperature exceeds a predetermined value determined by the setting of the spring 18 and IS, the valve element I5 is moved towards its closed position to decrease the rate of flow of refrigerant through the evaporator 2. This decrease lii mass flow modifies the effect oi the operation of the thermostatic expansion valve 8.

The motor 4 will continue to drive the compres sor 3 with a reduced rate of refrigerant flow in the system and will continue in operation until stopped byopening of the thermostatic switch ii. The air passing through the duct I is thus cooled to as great an extent as possible without raising the temperature of the motor 5 above its permissible value for continuous running.

In Fig. 2 there is illustrated a portion oi an air conditioning system similar to that of Fig. l and corresponding parts have been designated by the same numerals, certain parts of the mechanism being omitted as they are not necessary to an understanding of the invention. In Fig. 2 o. throttling valve 23 is connected in the suction line l0 between the compressor and the point to which the ieeler bulb 9 is connected. The valve 23 operates in a manner similar to the valve it of Fig. l but is actuated in accordance with the

energization oi solenoids

24 and 25 responsive to the voltage and current, respectively, at the terminals of the motor l. When both coils are connected to be energized, the valve 23 is actuated in accordance with the power supplied to the motor a. In some systems it may be desirable to employ only the current responsive coil 25, the voltage coil 24 being omitted or disconnected. The arrangement of Fig. 2 permits the system to operate with reduced flow of refrigerant during abnormal conditions in the same manner as explained in connection with Fig. 1 above. The valve 23 may, of course, be connected elsewhere in the liquid line or suction line just as can the valve l5, that location being selected which is most desirable for the particular installation under consideration.

In Fig. 3 I have illustrated the application of my invention to a system provided with a flooded type evaporator. Unly the evaporator and control valve have been shown as the remaining parts of the system are essentially the same as those illustrated in Fig. 1 and corresponding parts have been designated by the same numerals. The evaporator 2 employed in Fig. 3 is provided with a liquid recirculatin passage or conduit 26 connected between a top header 2'! and a bottom header 28 so that any liquid refrigerant reaching the top header may be returned to be recirculated through the evaporator. Liquid refrigerant is supplied from the liquid line 1 through a float valve 29 connected through a conduit 30 to the lower header 28. During normal operation of the system liquid refrigerant accumulates in a chamber 3! of the valve 29 to a level determined by operation of a float 32 which on rising opens a valve 33 to allow the liquid refrigerant to pass the evaporator. Durin abnormal operating conditions the operation of the float valve is modified by a device responsive to the abnormal condition. and in the arrangement illustrated the modification under abnormal conditions is effected by a solenoid 36 connected to be energized in accordance with the current supplied to the motor 4.

When the current in the solenoid reaches a predetermined value, an armature 35 is pulled downwardly, and, since the armature is linkedt the lever of the float 32 by a connection 36 the operation of the float is modified so that a greater quantity of liquid refrigerant is required to lift the float and more liquid is collected in the chamher 35. The total refrigerant circulated in the system is thereby reduced and the motor may then operate at reduced load in the same manner as in the systems of Figs. 1 and 2.

The system shown in Fig. I} is similar to that shown in Fig. l and corresponding parts have been designated by the same numerals. In this system the operation of the thermostatic expansion valve ll is modified in accordance with changes in motor temperature by energization of an electric heater 3? concocted to supply heat to the ieeler bulb 9 whenever the motor is in operation. The bulb and heater are preferably surrounded by insulation as indicated at '33 so that they are relatively unaffected by changes in ambient temperature. The heater til is normally energized from the line it through a variable resistance illustrated as a carbon pile 39 which is compressed to a value determined by the setting oia stop do at one end of a compressor lever M which is pivoted to a stationary support at $2. During operation of the motor i at normal temperatures, the energization of the heater 3'! is substantially constant; however, when a predetermined high temperature is reached in the motor i as determined by a feeler bulb 43 responsive to motor temperature, a bellows at connected to the bulb d3 expands in opposition to the force of a spring 45 and decreases the pressure on the carbon pile 39 thereby reducing the energization of the heater 37. The thermal bulb 9 then re quires a greater amount of heat to be supplied from the gas flowing through the suction line it! and the thermostatic expansion valve 8 operates to decrease the rate of flow of refrigerant through the system. It will thus be apparent that the operation of the thermostatic expansion valve has been modified to decrease the mass flow of refrigerant through the system and to permit continued operation of the motor A to supply a substantial amount of refrigeration under the abnormal operating conditions.

The specific details of the system of Fig. 4 are described and claimed in a copendin application of Robert U. Berry, Serial No. 542,747, filed con-= currently herewith and assigned to the same assignee as the present invention.

Frointhe foregoing it i readily apparent that I have provided a simple and efiective control arrangement for maintaining in operation under abnormal operating conditions a refrigerating system having a compressor driven by a prime mover which tends to overheat under such conditions. This arrangement makes it. unnecessary to interrupt the operation of the system due to high ambient temperature, for example, and prevents short cycling of the prime mover by operation of the overload protection device.

While I have described specific systems em booying my invention in connection with air conditioners driven by electric motors other applications will readily be apparent to those skilled in the art. I do not, therefore, desire my invention to be limited to the particular arrangements shown and described and I intend in the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:'

1. A refrigerating system comprising a compressor and a condenser and an evaporator, a prime mover for driving said compressor, a thermostatic expansion valve for controlling the flow of refrigerant from said condenser to said evaporator, and means dependent upon a predetermined abnormal operating condition of said prime mover for modifying the operation of said expansion valve to decrease the mass flow of refrigerant through said evaporator without interrupting the operation of said prime mover.

2. A refrigerating system comprising a compressor and a condenser and an evaporator, an electric motor for driving said compressor, an expansion device for controlling the flow of refrigerant from said condenser to said evaporator, and means operative to restrict the flow of refrigerant to said device and responsive to a predetermined increased electrical operating condition of said motor produced by an abnormal load on said motor for decreasingthe mass how of refrigerant through said evaporator without interrupting the operation of said motor.

3. A refrigerating system comprising a compressor and a condenser and an evaporator, an electric motor includinga stator having windings thereon and a rotor for driving said compressor, an expansion device for controlling the flow of refrigerant from said condenser to said evaporator, and means operative to restrict the how of refrigerant to said device and dependent upon a predetermined rise in temperature of the Windings of said motor for decreasing the mass flow of refrigerant through said evaporator without interrupting the operation of aid motor.

4. A refrigerating system comprising a corn pressor and a condenser and an evaporator, a prime mover for driving said compressor, an expansion device for controlling the flow of refrigerant from said condenser to said evaporator, a flow controlling device arranged in series with said expansion device in the path of flow of refrigerant from said condenser to said evaporator, and means dependent upon a predetermined abnormal operating condition oi said prime mover for actuating said flow controlling device to decrease the mass flow of reirigeratn through said evaporator Without interrupting the operation of said prime mover.

5. A refrigerating system comprising a com pressor and, a condenser and an evaporator, a prime mover for driving said compressor, a float actuated valve for controlling the how of refrigerant from said condenser to said evaporator, and means dependent upon a predetermined abnormal operating condition of said prime mover and arranged to modify the action of the float of said valve to decrease the flow of refrigerant through said valve without interrupting the operation of said prime mover.

6. A refrigerating system comprising a compressor and a, condenser and an evaporator, an

electric motor for driving said compressor, a

thermostatic expansion valve for controlling the flow of refrigerant from said condenser to said evaporator, and means responsive to a predetermined increase in the current supplied to said motor for modifying the operation of said valve to decrease the mass of flow of refrigerant j) l through said evaporator without interrupting the operation of said motor.

WAYNE E. DODSON.