US2401827A

US2401827A - Refrigerating apparatus

Info

Publication number: US2401827A
Application number: US501384A
Authority: US
Inventors: Regis D Heitchue
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1943-09-06
Filing date: 1943-09-06
Publication date: 1946-06-11
Anticipated expiration: 1963-06-11

Description

June 11, 1946.

WITNESSES:

COMPRESSOR R. D. HEITCHUE REFRIGERAIING APPARATUS Filed Sept. 6, 1943 CONDENSER Fig.1.

2 Sheets-Sheet l 1 LP! lvLa 5'7 INVENTOR' REQIS D. HElTCHUE.

TTORNEY June 11, 1946. R HEITCHUE 2,4o1,827 v REFRIGERATING APPARATUS I Filed Sept. 6, .1943 2 Sheets-Sheet 2 DISCHHRG E PRESS URE WITNESSES: 3s INVENTCR RE l5 D.HEITCHUE. )J W Pic, 4-. q

A ORNEY Patented June 11, 1946 UNITED STATES PATENT OFFIC nEFniGEaA'rmo APPARATUS Regis n. Heitchue, Springfield, Mass, assignor' to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application September 6, 1943, Serial No. 501,384

8 Claims. 1 My invention relates to refrigerating apparatus, and more particularly to a motor-compressor unit therefor, and it has for an object to provide improved apparatus of the character set forth.

In selecting a motor to drive the compressor of a refrigerating system, consideration must be given to the torque required to drive the compressor during what is commonly termed the pulldown period. That is, after the refrigerating systern has been shut down for some time, the sac-- tion pressure is much higher than during normal operation. The torque requiredto drive the compressor while the suction pressure is above normal, which is the pull-down period, is-usually considerably in excess of the normal torque requlred, particularly when the refrigerating system normally operates at a relatively low suction pressure or temperature. This is due to the f ct that at higher suction pressure, the density of the gas is higher so that more power is required to compress the greater mass of the refrigerant gas. In one compressor, for example, which normally operates at a suction pressure corresponding to 5 R, the motor input is increased more than 50% when the suction temperature is 50 F.

It is an object of my invention to eliminate the necessity for such a high torque during the pulldown period so that asmailer motor may be used and the cost of the apparatus thereby reduced.

In accordance with my invention, I provide one or more cylinders of the compressor with an unloader mechanism and I also provide a control for unloading one or more but not all of the cylinders of the compressor in response to high suction pressure, so that during the pulledown period, the load on the motor is held down to a value within the capacity oi the motor. while another cylinder or cylinders are operated to reduce the suction pressure. When the suction pressure has been reduced to substantially its normal value, then the remaining cylinders may be loaded.

Compressors for refrigerating systems are irequently provided with unloader mechanisms to re. duce the capacity or output of the compressor in medians compressor in accordance with variations in load and also for w one or more cyiinrs to reduce the load 'durms the pull-d wn in I :4,

These and other objects are effected by my invention as will be apparent from the following description and claims taken'in accordance with the accompanying drawings, forming a partcf this application, in which:

Fig. 1 is a diagrammatic view of 'one embodiinentof my invention utilizing a pull-down con-' trol and temperature control for operating the unloader mechanisms; 5

Fig. 2 is a sectional view of one of the unloader mechanisms shown in Fig. 1;

' Fig. 3 is a sectional view of the solenoid-operated pilot valve employed in Fig. 1; and,

Fig. 4 is a diagrammatic view of a second em-- hodiment of my invention utilizing a pull-down control and a suction pressure control for operating the unloader mechanism.

Referring specifically to Figs. 1, 2 and 3 of the. drawings for a detailed description of the first embodiment of my invention,.I show a six-cylinder compressor Ill driven by an electric motor I i. In accordance with the present invention, the motor ii need only be of sumcient capacity to drive the compressor when the suction pressure is down substantially to its normal value. It need not be of sumcient capacity to -drive the compressor fully loaded during the pull-down period, when the higher density of the suction gas inn poses greater load, per cylinder. The compressor and motor are preferably enclosed in a fluidtight casing l2. Compressed refrigerant is conveyed through a conduit is to a condenser diagram= matically shown at it, Irom which condensed retrigerant is conveyed through a conduit l5 and an expansion valve It to an evaporator ll. The

evaporator it is disposed in an enclosure wherein the air is to be cooled or conditioned. The vapor.

pressor unit. The expansion valve it may heof any suitable type. for example, it may be a thermostatic eion valve having a thermostatic bulb is subjected to the temperature of the sucdegree of superheat of the vaporised refrigerant J tion conduit is and regulating the flow of acids-- erant to the evaporator to maintain a constant leaving the evaporator.

The six cylinders are (imam into three psirs of cylinders, each pair being provided with a common cylinder head II. and a pair of unloeder mechanisms 22. Referring to Fig. 2, the cylinder head in a formed with an inlet chamber as and v a discharge chamber 2d. The inlet chambers as of several cylinders communicate with the suction conduit 18 through the motor-contain- I discharge chambers 24 communicate with the discharge conduit l3 through other suitable passages (not shown) formed in the casing I2. A valve cage 25 is clamped between each cylinder and the cylinder head associated therewith, and contains the suction and discharge valves for controlling flow of refrigerant gas between the cylinder and the suction and

discharge chambers

23 and 24,.

respectively. The suction valves are pressure operated, suction valve 26 in Fig. 2 being of the reed type. By holding the reeds of the valve 26 down, the cylinder is unloaded, since refrigerant gas may return to the suction chamber 23 upon upward movement of the piston in the cylinder.

The unloader mechanism 22 for each cylinder, shown in Fig. 2, is operated in the unloading directionby the discharge pressure of the compressor. The unloading mechanism 22 comprises a bar 21 which may be, as shown, attached to a v rod 28 that extendsthrough the cylinder head 2| The bar 21 carries fingers 29 adapted to engage the several reeds of the valve 26. A bellows 30 contained in a sealed casing 3| actuates the rod 28 and may be directly connected to it.

The bellows 30 for the first, second and third sets of cylinders are controlled by solenoid-operated

pilot valves

32, 33 and 34, respectively, con structed as shown in Fig. 3. Each pilot valve is connected to a conduit 35 which communicates with the two bellows 30 of the associated pair of cylinders, a conduit 36 which communicates with the compressor discharge through the conduit l3, and a conduit 31 which communicates with the crankcase of the compressor, which is at suction pressure by reason of communication with the suction passages within the casing l2 of the motor-compressor unit. When the solenoid is deenergized, as shown in Fig, 3, the pilot valve places the

conduits

35 and 35 in communication, thereby applying compressor discharge pressure to the unloaders and unloading the associated pair of cylinders by depressing the fingers 29 to hold the valve reeds open. When the sole noid is energized, the pilot valve places conduits 35 and 31 in communication, thereby applying suction pressure to the unloaders, so that the bellows 3|! expands and loads the associated pair of cylinders by retracting the fingers 29.

Referring again to Fig. 1, I show an unloader control system'which maintains the compressor l0 completely unloaded during starting after an inactive period, partially unloads the compressor v during pull-down, and serves to control the temperature of the media to be refrigerated bypartially unloading or fully loading the compressor.

In order to accomplish these functions, I provide a control 38 having an element 39 responsive to the temperature of the media to be refrigerated, that is, the air in the enclosure cooled by the evaporator l1, and having fixed contacts 40, 4| and 42 connected to the solenoid-operated

pilot valves

32, 33 and 34, respectively, and a movable contact 43 which is capable of engaging one, two or all three of said fixed contacts, or of being completely disengaged therefrom. I also provide a starting relay 44 and an electricallyoperated time delay relay 45. I furthermore provide a pull-down control device 46 which is responsive to suction pressure by communication of a bellows 41 with the interior or suction pressure zone of the sealed casing l2 through a conduit 48. The bellows operates a pivoted lever 43 The

contacts

54 and 52 are connected to the solenoid-operated

pilot valves

33 and 34, respectively, in series with the contacts 4| and 42, respectively. Accordingly, each of these valves is deenergized to unload the associated cylinders whenever the circuit therethrough is opened at either of its contacts.

The electrical connections are clearly shown in Fig. l and further description is not thought necessary.

Operation Assume the system has been shut down for some time by the opening of the line switch 51. The control system will be in the position shown in Fig. 1 and the control 38 will be in such position that the movable contact 43 will be in engagement with all three of the fixed contacts 43, 4| and 42. This is because the temperature in the enclosure to be cooled has increased and the temperature-responsive element 39 has moved the movable contact 43 into the position shown. The pull-down control 46 will be in the position shown in Fig. 1 with all contacts open because the suction pressure will be relatively high. When the line switch 51 is closed to connect the electrical control circuit to line L1, L2, the starting relay 44 is closed and motor H is energized. However,

as the

contacts

58 and 59 are open, all the cylin-' ders are unloaded at this time so that the motor reaches its normal operating speed in a few seconds. The time delay relay 45 is also energized and after a few seconds a movable contact 5t associated therewith bridges contacts 59, thereby energizing the first pilot valve 32 and loading its associated pair of cylinders. Due to the high suction pressure and density of the gas tobe compressed, the load on a loaded cylinder is now greater than normal. third of the cylinders are loaded, the total load on'the motor is not greater than normal.

Operation continues with one pair of cylinders loaded, and assuming that the control 381 still calls for refrigeration, the suction pressure in the refrigerating system decreases until it reaches a value of, for example, 60 pounds per square inch gauge, when dichlorodifluoromethane is the refrigerant used. The bellows 4'! of the control 56 then contracts .and

contacts

53 and 55 are closed. Pilot valve 33 is thereby energized and the second pair of cylinders is loaded. The density of the refrigerant gas is now sufliciently low that four cylinders may be operated without overloading the motor.

As the'suction pressure decreases to a lower value, for example, 50 pounds per square inch gauge, the bellows 4T contracts still further and contacts 5| and 52 are closed, thereby energizing pilot valve 35 and loading the third pair thetemperature drops below F. A further drop in temperature to below, for example, '79 F. moves contact 43 out of engagement with contact 4|, thus deenergizing-pilot valve 33 and un However. since only one accuser loading its associated pair of cylinders. When the demand for refrigeration is completely satis-- fled, for example, when the temperature drops before the suction pressure rises above 50 pounds per square inch gauge, the control 38 loads either one, two or three pairs of cylinders, depending on the demand, and the suction pressure control 46 does notfunction to effect unloading. If, however, refrigeration has not been required for some time, the suction pressure may rise sufficiently to open

contacts

53 and 54 or to open both

contacts

53, 54 and 5|, 52, thereby unloading one or two pairs of cylinders depending on which contacts are opened, until the suction pressure reaches its normal operating value.

Since the contacts of the control 38 are in a utilize the same set of unloader mechanisms both series with the respective contacts of the control 46, the contacts of either control are adapted to effect unloading of the associated cylinders, regardless of the action of the other control.

Figure 4 Fig. 4 shows exactly the same unloader and control system as shown in Fig, 1, for use with the same refrigerating system, except that the control 38' is provided with a bellows 56 which is responsive to the suction pressure in the refrigerating system, instead of the temperatureresponsive element 39 of the first embodiment. Accordingly, the operation of the motor-compressor unit is controlled to maintain the suction pressure substantially constant, The control 38' may be so arranged that the movable contact 43 engages the fixed contacts 40, H and 42 as the suction pressure increases to 33, 35 and 31 pounds per square inch, respectively.

The operation is generally the same as that of the first embodiment. The pull-down control 48 operates in exactly the same way during the pull-down period to limit the load on the motor. After the pull-down, the control 38' controls the operation of the compressor to maintain the suction pressure substantially constant. As the suction pressure decreases to 37 pounds and to 35 pounds per square inch, respectively, the movable contact disengages the contacts 42 and 4| to unload first one and then a second pair ofcylinders. Upon a further decrease to 33 pounds per square inch the contact 43 disengages the contact 40 to shut down the compressor unit. Conversely,- upon increase in pressure, the contact 43 engages to contact 40 to start operation and the contacts 4i and 42 to load additional pairs of cylinders.

Assume that the refrigerating system has been shutdown for a time sumcient to permit the suction pressure to increase to 60 pounds per square inch and that the load when operating is relatively light. Upon closing. the line switch 51, all cylinders are unloaded until the motor-compressor unit comes up to speed, after which the pilot valve 32 will load two of the cylinders, As

the suction pressure drops to 60 and 50 pounds per square inch, respectively, additional pairs of cylinders will be loaded. The motor-compressor unit .will then continue to operate until the suction pressure drops down to 37 pounds 'per'square.

inch, whereupon the control 38 will again unload one pair of cylinders and as the suction pressure 6 drops to 35 pounds per square inch, another of cylinders will be unloaded.

pair

It may be noted that in this embodiment the" controls 38' and 4.6 will never, assuming the apparatus to be in proper working condition, effect unloading at the same time. The control 46 will efiect unloading only above 50 pounds per square inch and the control 38' will effect unloading only below 37 pounds per square inch.

It is, therefore, clear that I have provided an improved control system for unloaders in a refrigerating system which completely unloads the compressor for starting, partially unloads the compressor during pull-down, and controls the temperature or suction pressure of the system during normal operation.

From the above description, it will be seen that, by combining the two controls, I am able to factory operation.

While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What I claim is:

1. In a refrigerating system having a highpressure side including a refrigerant con-' denser and a low-pressure side including a refrigerant evaporator for cooling 2!. media, the combination of a refrigerant comp.essor for withdrawing refrigerant from the low-pressure for driving the compressor, said refrigerating system having active and inactive periods and having a high pressure prevailing in the lowpres'sure side of the system after an inactive period of such duration that the evaporator approaches ambient temperature, means for partially unloading the compressor during the first part of the active period of the system following I said last-mentioned inactive period after said prime mover has reached its normal operating speed and for maintaining said compressor partially unloaded until the pressure in the lowpressure side of the system approaches the value normally prevailing therein during an active period, and means for controlling the pressure in the low-pressure side of the system to maintain the same at a substantially constant average value during said active periods, said last means comprising unloading means for fully loading the compressor at one pressure prevailing in the low-- pressure side of the system and for partially unloading the compressor at lower pressures in the low-pressure side of the system.

2. In a refrigerating System-having a high= pressure side including a refrigerant condenser anda low-pressure side including a refrigerant evaporator for cooling a media, the combination of a refrigerant compressor for withdrawing refrigerant from the low-pressure side of the system' and compressing it into the high-pressure side of thesystem, a prime mover for driving the compressor, said refrigerating system having active and inactive periods and" having a high pressure prevailing in the low-pressure side of the system after an inactive period of such duration that the evaporator approaches ambient temperature, means for partially unloading the compressor during the first part of the active period of the system following said last-men- I tioned inactive period after said prime mover has reached its normal operating speed and for maintaining said compressor partially unloaded until the pressure in the low-pressure side of the system approaches the value normally prevailing therein during an active period, and means for controlling the temperature of said media to maintain the same at a substantially constant average value during active periods of the system, 7

tive and inactive periods and having a high pressure prevailing in the low-pressure side of the system after an inactive period of suchduration that the evaporator approaches ambient temperature, means for partially unloading the compressor during the first part of the active period of the system following said last-mentioned inactive period after said prime mover has reached its normal operating speed and for maintaining and a low-pressure side including a refrigerant evaporator for cooling a media, the combination of a refrigerant compressor for withdrawing refrigerant from the low-pressure side of the system and compressing it into the high-pressure side of the system, a prime mover for driving the compressor, said refrigerating system having active and inactive periods and having a high pressure prevailing in the low pressure side of the system after an inactive period of such duration that the evaporator approaches ambient temperature, an unloading mechanism for said compressor, means for actuating said unloading mechanism to partially unload the compressor during the first part of an active period following said lastmentioned inactive period after said prime mover has reached its normal operating speed and for maintaining said compressor unloaded until the pressure in the low-pressure side of the system approaches the valu normally prevailing therein during an active period and for them fully loading the compressor, and means for thereafter actuating said unloading mechanism to partially unload the compressor as the refrigerating load on said evaporator decreases.

6. In a refrigerating system having a highpressure side including a refrigerant condenser and a low-pressure side including a refrigerant j evaporator for cooling a media, the combination said compressor partially unloaded until the pressure in the low-pressure side of the system approaches the value normally prevailing therein during an active period, said means also completely loading the compressor at one pressure prevailing in said low-pressure side of the system during an active period and partially unloading said compressor at lower pressures prevailing in said low-pressure side of the system, to maintain a substantially constant average pressure therein. '4. In a refrigerating system having a highpressure side including a refrigerant condenser and a low-pressure side including a refrigerant evaporator for cooling 9. media, thecombination of a refrigerant compressor for withdrawing re.-

frigerant from the low-pressure side of the system and compressing it into the high-pressure side of the system, a prime mover for driving the compressor, said refrigerating systemhaving active and inactive periods and having a high pressure prevailing in the low-pressure side of the system after an inactive period of'such duration that the evaporator approaches ambient temperature, and means for partially unloading the compressor during the first part of the active period of the system following said last-mentioned inactive periodafter said prime mover has reached its normal operating speed and for maintaining said compressor partially unloaded until the pressure in the'low-pressure side of the system approaches the value normally prevailing therein during an active period, said means also completely loading the compressor at-one temperature of the media during an active period and partially unloading said compressor-at lower temperatures of said media, to maintain a sub- 5. In a refrigerating system having a highof a multi-cylinder refrigerant compressor for withdrawing refrigerant from said low-pressure side and compressing it into the high-pressure side, a motor for driving the compressor, said refrigerating system having active and inactive periods and having a high pressure in said lowpressure side after an inactive period of such duration that said evaporator approaches ambient temperature, and means adapted to .unload at least one of said-cylinders and to load at least one of said cylinders during the first part of'the active period of the system following said inactive period after the motor has reached its operating speed and for maintaining at least said one cylinder unloaded until the pressure in the low-pressure side of the system approaches the value normally prevailing therein during an active cycle of said system. I

'7. In a refrigerating system having a highpre'ssure side including a refrigerant condenser and a low-pressure side including a refrigerant evaporator for cooling a media, the combination of a multi-cylinder refrigerant compressor for withdrawing refrigerant from said low-pressure side and. compressing it int the high-pressure side, a motor for driving the compressor, said refrigerating system having active and inactive periods and having a high pressure in said lowpressure side after an inactive period of such duing the first part of an active period following said last-mentioned inactive period after the motor has reached its operating speed and for maintaming at least said one cylinder unloaded until stantially constant average temperature the pressure in the low-pressure side of th system approaches the value normally prevailing therein during an active period and for then fully loading the compressor, and means for thereafter unloading at least one of said cylinders in repouse to a decrease in refrigerating load on said evaporator.

pressure side including a refrigerant condenser 8. A control-for a refrigerating system havin a low-pressure side and a high-pressure side including a multi-cylinder compressor and driving means for the compressor, said control comprisin: means for energizing said compressor driving means in response to a predetermined demand upon said refrigerating system, an unloader mechanism for unloading and loading one or more but not all the cylinders of said compressor, means controlling said unloader mechanism to load the associated cylinder or cylinders in response to increase in saiddemand to a second and higher predetermined value-and to unload the associated cylinder or cylinder upon decrease in said demand below said second predetermined value. and means responsive to increase in the pressure in the low-pressure side of the refrigerating system to a predetermined value above the normal pressure for controlling said unloader mechanism to unload the associated cylinder or cylinders independently of the action of said 10 means responsive to demand upon the system.

REGIS D. HEITCHUE.