US3371500A

US3371500A - Refrigeration system starting

Info

Publication number: US3371500A
Application number: US549839A
Authority: US
Inventors: Jr Roy F Marcus
Original assignee: Trane Co
Current assignee: Trane US Inc
Priority date: 1966-05-13
Filing date: 1966-05-13
Publication date: 1968-03-05
Anticipated expiration: 1985-03-05
Also published as: DE1551329A1; NL6706654A; FR1522893A; BE698412A; GB1123887A

Description

March 5, 1968 R. F. MARCUS. JR 3,371,500

REFRIGERATION SYSTEM STARTING Filed May 13, 1966 2 Sheets-Sheet 1 NVEN'TOR.

ATTORNEYS ROY F. MARCUS,JR.

. March 5; 1968 v R. F. MARCUS. J 3,371,500

REFRIGERATION SYSTEM STARTING Filed May 15, 1966 2 SheetsSheet 2 FIG. 4

JNVENTOR. ROY F. MARCUS, JR.

ATTORNEYS Patented Mar. 5, 1968 3,371,560 REFRIGERATION SYSTEM STARTING Roy F. Marcus, .Iru, Onalaska, Wis., assignor to The Trane Company, La Crosse, Wis., a corporation of Wisconsin Filed May 13, 1966, Ser. No. 549,839 17 Claims. (Cl. 62117) This invention relates to vapor compression refrigeration systems and particularly the means and manner of starting such refrigeration systems when environmental conditions are such that the pressure with the system is insufficient to permit the compressor to start.

Refrigeration systems are often provided with a low pressure cut-out switch which prevents the compressor from operating when the system pressure falls below a predetermined minimum pressure. Such switches serve to shut the system off in case of loss of charge, possible freeze-up of the evaporator, and possible compressor motor burnout due to insuflicient refrigerant flow to cool the compressor motor. Such switches are also used to terminate a pumpdown cycle often used at the end of the compressor run cycle to remove refrigerant from the evaporator prior to the compressor off period thereby avoiding possible slugging at startup, The system herein described is one of the latter type in which the inventor has chosen to illustrate his invention.

Conventionally refrigeration systems were not installed in environments wherein the temperature might fall below that required to maintain within the system sufficient pressure to permit the low pressure cutout to operate the compressor at least during the seasonal periods while the system was in use. However of recent years refrigeration, especially for air conditioning, has been used during very low outdoor temperatures. Further, to aggravate the situation, it has been an increasing practice to install the entire refrigeration system outdoors such as on rooftops and the like wherein merely the evaporator is insulated and kept relatively warm by a secondary refrigerant. In such recent installations, the refrigeration system may be called upon to start when the outdoor temperature is F. or below. Under such circumstances there is insufficient pressure in the condenser and receiver to cause liquid refrigerant to flow to the relatively warm evaporator. Because no refrigerant flows to the evaporator, no refrigerant is vaporized to raise the refrigerant pressure sufficiently above the setting of the low pressure cutout switch, and the compressor will not start.

The instant invention serves to overcome these difficulties and enables a refrigeration system to start despite low environmental temperatures. Briefly the instant invention pertains to refrigeration apparatus comprising a closed refrigerant circuit including a compressor means, condenser means, receiver means, throttling means, and evaporator means connected respectively in series; means for discontinuing operation of said compressor means in response to a predetermined minimum pressure in a portion of said refrigerant circuit; and means for starting said compressor means when the pressure in said condenser means is insulficient to raise the pressure in said portion of said refrigerant circuit to said predetermined minimum pressure including flow interrupting means for temporarily interrupting fluid communication between said condenser means and receiver means, support means supporting said receiver means above said evaporator means, and equalizer means for substantially equalizing the pressure between said evaporator means and receiver means whereby liquid refrigerant may flow by gravity through said refrigerant circuit from said receiver means into said evaporator means to vaporize and raise the pressure'in said portion of said refrigerant circuit above said predetermined minimum pressure thereby permitting said compressor means to start.

It is thus a prime object of this invention to provide a refrigeration system which may be started despite installation in very low ambient temperature.

It is a further object to provide a method of starting a refrigeration system installed in very low ambient temperature.

It is still another object of the instant invention to provide a refrigeration system which may be started under low ambient conditions without excessive compressor cycling and without the danger of evaporator freeze-up.

Other objects and advantages will become apparent as this specification proceeds to describe the invention with reference to the accompanying drawing in which like numerals have been used to identify like elements wherein:

FIGURE 1 is a schematic of a refrigeration system embodying a form of my invention;

FIGURE 2 is a fragment of FIGURE 1 showing a second position for the three-way valve thereof;

FIGURE 3 is a line diagram of the electrical circuit for control of the refrigeration system shown in FIGURE 1; and

FIGURE 4 is a schematic of a refrigeration system embodying a second form of my invention.

Turning now to FIGURES 1-2 of the drawings, the system comprises a closed refrigerant circuit 10 including a refrigerant compressor means such as reciprocating compressor 12., a refrigerant condenser means such as air cooled condenser 14, a refrigerant receiver means such as liquid receiver 16, refrigerant throttling means such as expansion valve 18, and a refrigerant evaporator means such as water chiller 20 respectively serially connected in a closed refrigerant loop.

Compressor 12 has a normally closed spring biased suction valve 22 and a normally closed spring biased dis charge valve 24. Such valves, in addition to their normal function of imparting direction to the refrigerant while the compressor is operating, will serve to limit the migration of refrigerant gas through the compressor from the suction side to the discharge side when the compressor is not operating and when the suction side pressure exceeds the discharge side pressure as will be discussed hereinafter.

Condenser 14 may be of the conventional fin and tube type having a fan 26 for passing cooling air over the fins to condense refrigerant hot gas from compressor 12 within the tubes.

Receiver 16 is provided with a support means 28 locat ing the receiver above the evaporator 2d to enable liquid refrigerant collected therein from condenser 14 to flow by gravity to evaporator 20.

Expansion valve 18 may have the conventional temperature sensing bulb and external equalizer line connected at the evaporator outlet if desired.

Evaporator 20 has a thermostatic switch 30 disposed in heat exchange relation therewith which is arranged to close upon an increase in temperature and to open upon a decrease in temperature thereby sensing the load on the evaporator.

The refrigeration system illustrated in FIGURE 1 has a condenser bypass conduit 32 and a head pressure control valve means 34 for maintaining sufficient pressure at the inlet of expansion valve 18 during periods of compressor operation under low condenser ambient conditions. Valve 34 may be of the type disclosed in US. Patent 2,986,899 and has the effect of restricting the condenser outlet and opening the condenser bypass conduit upon a fall in head pressure in the bypass conduit causing the condenser to fill with liquid and reduce the heat transferring capacity of the condenser. Upon a rise in head pressure, valve 34 restricts the bypass conduit and opens the condenser outlet thereby increasing the heat transferring capacity of the condenser.

For purposes of control a low pressure cutout switch 36 is connected to the circuit between evaporator and compressor 12 and arranged to open upon a decrease in pressure below a predetermined minimum pressure and a high pressure cutout switch 38 is connected to the circuit 16 between compressor 12 and condenser 14 and arranged to open upon an increase in pressure above a predetermined maximum pressure.

The Circuit 10 also has a normally closed solenoid operated shutoff valve 41) disposed between receiver 16 and expansion valve 18 for automatically shutting off the liquid refrigerant flow to the evaporator upon a decrease in load at the evaporator as sensed by thermostatic switch 31).

The system herein disclosed is intended for outdoor installation subject to temperatures sufficiently low to cause, during the idle periods of the compressor, the pressure within the condenser and other portions of the circuit to fall below minimum pressure at which switch 36 will permit compressor 12 to operate. in order to permit the system to start under these conditions, the system is provided with a pressure equalizer conduit 42 extending from a point in circuit 10 between evaporator 20 and compressor 12 to a point in circuit 10 between valve 34 and receiver 16. The purpose of conduit 42 is to permit refrigerant gas from evaporator 21 to pass to receiver 16 thereby equalizing the pressure between the receiver and the evaporator to permit liquid in the receiver to flow by gravity to the evaporator which upon being vaporized in the evaporator raises the pressure suiliciently to cause pressure switch 36 to close and permit the compressor to start.

In order that gas passing in the equalizer conduit is not dissipated by passage to the condenser, the system is provided with means for temporarily interrupting the fluid communication between the receiver and condenser. In the system illustrated in FIGURE 1, this means includes a three way solenoid actuated valve 44 having a deenergized position connecting the condenser 14 to receiver 16 as shown in FIGURE 1 and an energized position connecting the equalizer conduit 42 to receiver 16 as shown in FIGURE 2. When valve 44 is in the last mentioned position, refrigerant gas from evaporator 20 is precluded from passing to the condenser via compressor 12 by the spring bias of

valve

22 and 24. In order to facilitate the passage of liquid refrigerant from receiver 16 to evaporator 20 expansion valve 18 may have a bypass passageway 46. This is particularly desirable when the sensing elements of expansion valve 18 are located at the outlet of the evaporator partially subjected to the cold outdoor arnbient. In such case, the expansion valve 18 senses the cold outdoor ambient until refrigerant gas flow from the evaporator is established. However, without passageway 46, how may not be established and expansion valve 18 may remain closed for the reason that it is sensing the cold ambient. Passageway 46 thus may be desired to establish initial flow which in turn will permit the expansion valve to control. Bypass passageway 46 may have a normally closed bypass passageway solenoid valve 48 which is actuated to an open position during startup.

To control the operation of

valves

40, 44 and 48 and compressor 12, an electrical control system 50 is provided as illustrated in FIGURE 3. It will be noted that previously mentioned

elements

12, 30, 36, 38, 4t), 44 and 48 of FIGURE 1 have been identified in FIGURE 3. In addition to these elements the system 50 includes a starting relay 52 having a normally open switch 54 and a compressor control relay 56 having a normally closed switch 58 and normally open

switches

55 and 60. Control system 50 is best understood in conjunction with the operation of the refrigeration system.

4 OPERATION Assume that valve 40 is closed because the load on the evaporator has been met and that the segment of the refrigerant circuit between valve 40 and compressor 12 has been pumped down by action of the compressor and that operation of the compressor has been discontinued by the opening of minimum pressure switch 36. Also assume that the pressure in the condenser and receiver, due to low ambient conditions, is below the pressure in the evaporator.

Upon sensing a load at the evaporator, switch 30 closes, establishing a circuit to energize valve 40 to the open position. Upon the mere opening of the valve 40, liquid refrigerant will not flow from the receiver to the evaporator because the pressure in the receiver and condenser is lower than in the evaporator. Since no liquid refrigerant reaches the evaporator, none can be vaporized in the evaporator to raise the pressure at switch 36 and start the compressor. However in the instant invention, switch 30 also establishes a circuit through relay 52 to close switch 54. The closure of switch 54 establishes a

circuit including switches

54, 38, 58 and three way solenoid valve 44 to energize valve 44 to a position connecting equalizer conduit 42 and receiver 16 as shown in FIGURE 2. Also valve 48 which is electrically in parallel with valve 44 may be energized to an open position. This equalizes the pressure in the receiver with that in the evaporator and permits the liquid refrigerant to flow by gravity from the receiver to the evaporator. Bypass passageway 46 facilitates this flow particularly when expansion valve 1 8 is closed initially because of low ambient conditions. Liquid refrigerant entering the evaporator is vaporized to raise the pressure at switch 36 which then closes establing a

circuit including switches

54, 38, 36 and relay 56. Upon energization of relay 56, switch 58 is opened and switches 55 and 69 are closed. The closure of switch 60 establishes a circuit to operate compressor 12 while the opening of switch 58

de-energizes valves

44 and 48 thereby causing valve 48 to close and valve 44 to move to the position shown in FIGURE 1. The compressor 12 is thus started despite the low ambient condition.

When the load at the evaporator 20 has been met, switch 30 opens which opens the circuit to relay 52 and valve 40, causing switch 54 to open and valve 40 to close. The opening of switch 54 has no immediate effect as switch 55, which shunts switch 54, is now closed. Compressor 12 continues to operate until the pressure at switch 36 falls below the predetermined minimum pressure causing switch 36 to open which opens the circuit to relay 56. De-energization of relay 56 causes switches 55 and 60 to open and switch 58 to close. Opening of switch 60 opens the circuit to compressor 12 and discontinues operation thereof. The system is now ready for another start.

If bypass passageway 46 is sized small enough, valve 48 may be eliminated with some increase in time preparatory to compressor startup. Bypass passageway 46 may be entirely eliminated if valve 18 and the sensing bulb thereto are insulated from the cold outdoor ambient such as by installation within an insulating enclosure for the evaporator water chiller 20.

Now referring to FIGURE 4 it will be seen that a modified form of the invention is therein illustrated. The refrigeration system 62 shown in FIGURE 4 may be identical to the system 10 shown in FIGURE 1 except that three way solenoid valve 44 has been eliminated and

check valves

64 and 66 have been inserted in

conduits

42 and 32 respectively to function as the fiow interrupting means. During startup conditions of condenser pressure lower than evaporator pressure,

valves

34 and 66 serve to interrupt the fluid communication between receiver and condenser while check valve 64 permits flow in the equalizer conduit 42 only during such conditions. Valve 66 may serve the same function if placed at the outlet of valve 34, however in such case the valve must be of larger size. The operation of the system 64 is otherwise similar to that of system 10.

Having thus described in detail several preferred embodiments of my invention. I contemplate that many changes may be made without departing from the scope or spirit of my invention and I desire to be limited only by the claims.

I claim:

1. A refrigeration apparatus comprising a closed refrigerant circuit including a compressor means, condenser means, receiver means, throttling means, and evaporator means connected respectively in series; means for discontinuing operation of said compressor means in response to a predetermined minimum pressure in a portion of said refrigerant circuit; and means for starting said compressor means when the pressure in said condenser is insuflicient to raise the pressure in said portion of said refrigerant circuit to said predetermined minimum pressure including flow interrupting means for temporarily interrupting fluid communication between said condenser means and receiver means, support means supporting said receiver means above said evaporator means, and equalizer means for substantially equalizing the pressure between said evaporator means and said receiver means whereby liquid refrigerant may flow by gravity from said receiver means into said evaporator means to vaporize and raise the pressure in said portion of said refrigerant circuit above said predetermined minimum pressure thereby permitting said compressor means to start.

2. The refrigeration apparatus as defined by claim 1 further including a shutoff valve disposed in said refrigerant circuit between said receiver means and said evaporator means; means for'actuating said shutoff valve to an open position in response to an increase in load on said evaporator means and to a closed position in response to a decrease in load on said evaporator means; and said portion of said refrigerant circuit being disposed downstream of said shutoff valve and upstream of said compressor means.

3. The refrigeration apparatus defined by claim 2 including a bypass passageway extending from a point in said refrigerant circuit between said receiver means and throttling means, bypassing said throttling means, to a point in said refrigerant circuit between said throttling means and evaporator means.

4. The refrigeration apparatus defined by claim 3 including a bypass passageway valve disposed in said passageway; and control means for actuating said bypass passageway valve normally to a closed position and temporarily to an open position during the period when a load is placed upon said evaporator means prior to starting of said compressor means.

5. The refrigeration apparatus as defined by claim 2 wherein said portion of said refrigerant circuit is disposed downstream of said shutoff valve and upstream of said compressor means.

6. The refrigeration apparatus as defined by claim 1 wherein said portion of said refrigerant circuit is disposed downstream of said throttling means and upstream of said compressor means.

7. The refrigeration apparatus as defined by claim 1 wherein said portion of said refrigerant circuit is disposed downstream of said evaporator means and upstream of said compressor means.

8. The refrigeration apparatus as defined by claim 1 wherein said equalizer means includes an equalizer conduit extending from a first point in said refrigerant circuit between said evaporator means and compressor means, bypassing said compressor means and condenser means, to a second point in said refrigerant circuit between said condenser means and said receiver means.

9. The refrigeration apparatus as defined by claim 8 wherein said flow interrupting means includes valve means; and actuating means for actuating said valve means normally to a first position communicating said receiver means and condenser means and temporarily to a second position communicating said receiver means and equalizer conduit during the period when a load is placed upon said evaporator means prior to starting of said compressor means.

19. The refrigeration apparatus as defined by claim 9 wherein said flow interrupting means includes a check valve.

11. The refrigeration apparatus as defined by claim 9 wherein said How interrupting means includes an electrically actuated valve.

12. The refrigeration apparatus as defined by claim 11 wherein said electrically actuated valve is a three way valve disposed at said second point and said actuating means is responsive to the temperature at said evaporator means.

13. The refrigeration apparatus as defined by claim 8 further including a condenser bypass conduit extending from a third point in said refrigerant circuit between said compressor means and condenser means to a fourth point in said refrigerant circuit between said condenser means and said second point; and head pressure control valve means disposed at said fourth point for increasing communication betwen said second point and said condenser means in response to an increase in pressure at said third point and for increasing communication between said second point and said condenser bypass conduit in response to a decrease in pressure at said third point thereby controlling the pressure in said receiver during operation of said compressor means.

14. The refrigeration apparatus as defined by claim 8 wherein said flow interrupting means includes a valve means; a first electric control circuit including in series a first switch actuated in response to the load on said evaporator, a second switch actuated in response to a pred-etenmined maximum pressure in said refrigerant circuit, a third switch actuated in response to a predetermined m-inimum pressure in said portion of said refrigerant circuit and a relay for controlling the operation of said compress-or means; and a second electric control circuit including in series said first and said second switches, a fourth switch actuated in response to said relay, and electromagnetic means for controlling said valve means; said fourth switch being in parallel relation with said third switch and said relay.

15. In a refrigeration system having a closed refrigerant circuit including a compressor means, condenser means, receiver means, throttling means, and evaporator means connected respectively in series and means for discontinuing operation of said compressor means in response to a predetermined minimum pressure in a portion of the refrigerant circuit, the method of starting said compressor means when the pressure in the condenser means is insufficient to raise the pressure in said portion of said refrigerant circuit to said predetermined minimum pressure including the steps of: interrupting fluid communication between said condenser means and receiver means; passing refrigerant gas from aid evaporator means to said receive-r means via a route bypassing said compressor means and condenser means; passing liquid refrigerant in said receiver means to said evaporator means by gravity flow; vaporizing said liquid refrigerant in said evaporator means for passage back to said receiver mean and for raising the pressure in said portion of said circuit to said predetermined minimum pressure; activating said compressor means in response to said rise in pressure in said portion of said refrigerant circuit to said predetermined minimum pressure; and terminating said interrupting step.

16. In 'a refrigeration system having a closed refrigerant circuit including a compressor means, condenser means, receiver means, shutoff valve means, throttling means, and evaporator means connected respectively in series and a low pressure cutout means for discontinuing operation of said compressor means in response to a predetermined minimum pressure in a portion of the refrigeration circuit, the method of operating said refrigeration system including the steps of: sensing the load on said evaporator means; opening said shutoff valve means in response to a sensed increase in load on said evaporator means; interrupting the fluid communication between said condenser means and receiver means; passing refrigerant gas from said evaporator means to said receiver means via a route bypassing said compressor means and condenser means; passing liquid refrigerant in said receiver means to said evaporator means by gravity flow; vaporizing said liquid refrigerant in said evaporator for passage back to said receiver means and for raising the pressure in said portion of said circuit to said predetermined minimum pressure; activating said compressor means in response to said low pressure cutout means sensing a rise in pressure in said portion of said refrigerant circuit to said predetermined minimum pressure; terminating said interrupting step in response to a rise in pressure to said predetermined minimum pressure; permitting said cornpressor means to operate until the load at said evaporator means is substantially met; closing said hutoff valve means in response to a sensed decrease in load at said evaporator means; and terminating operation of said compressor means in response to said low pressure cutout means sensing a fall in pressure in said portion of said circuit below said predetermined minimum pressure.

17. In a refrigeration system having a closed refrigerant circuit including a compressor means, condenser means, receiver means, shutoff valve means, throttling means, and evaporator means connected respectively in series and a low pressure cutout means for discontinuing operation of said compressor means in response to a predetermined minimum pressure in a portion of the refrigeration circuit, the method of operating said refrigeration system including the steps of: sensing the load on said evaporator means; opening said shutoff valve means in response to a sensed increase in load on said evaporator means; interrupting the fluid communication between said condenser means and receiver means; passing refrigerant gas from said evaporator means to said re ceiver means via a route bypassing said compressor means and condenser means; passing liquid refrigerant in said receiver means to said evaporator means by gravity flow via a route bypassing said throttling means; vaporizing said liquid refrigerant in said evaporator for passage back to said receiver means and for raising the pressure in said portion of said circuit to said predetermined minimum pressure; activating said compressor means in response to said low pressure cutout means sensing a rise in pressure in said portion of said refrigerant circuit to said predetermined minimum pressure; terminating said interrupting step in response to a rise in pressure to said predetermined minimum pressure; permitting said compressor means to operate until the load at said evaporator means is substantially met; closing said shutoff valve means in response to a sensed decrease in load at said evaporator means; and terminating operation of said compressor means in response to said low pressure cutout means sensing a fall in pressure in said portion of said circuit below said predetermined minimum pressure.

References Cited UNITED STATES PATENTS MEYER PERLIN, Primary Examiner.

Claims

15. IN A REFRIGERATION SYSTEM HAVING A CLOSED REFRIGERANT CIRCUIT INCLUDING A COMPRESSOR MEANS, CONDENSER MEANS, RECEIVER MEANS, THROTTLING MEANS, AND EVAPORATOR MEANS CONNECTED RESPECTIVELY IN SERIES AND MEANS FOR DISCONTINUING OPERATION OF SAID COMPRESSOR MEANS IN RESPONSE TO A PREDETERMINED MINIMUM PRESSURE IN A PORTION OF THE REFRIGERANT CIRCUIT, THE METHOD OF STARTING SAID COMPRESSOR MEANS WHEN THE PRESSURE IN THE CONDENSER MEANS IS INSUFFICIENT TO RAISE THE PRESSURE IN SAID PORTION OF SAID REFRIGERANT CIRCUIT TO SAID PREDETERMINED MINIMUM PRESSURE INCLUDING THE STEPS OF: INTERRUPTING FLUID COMMUNICATION BETWEEN SAID CONDENSER MEANS AND RECEIVER MEANS; PASSING REFRIGERANT GAS FROM SAID EVAPORATOR MEANS TO SAID RECEIVER MEANS VIA A ROUTE BYPASSING SAID COMPRESSOR MEANS AND CONDENSER MEANS; PASSING LIQUID REFRIGERANT IN SAID RECEIVER MEANS TO SAID EVAPORATOR MEANS BY GRAVITY FLOW; VAPORIZING SAID LIQUID REFRIGERANT IN SAID EVAPORATOR MEANS FOR PASSAGE BACK TO SAID RECEIVER MEANS AND FOR RAISING THE PRESSURE IN SAID PORTION OF SAID CIRCUIT TO SAID PREDETERMINED MINIMUM PRESSURE; ACTIVATING SAID COMPRESSOR MEANS IN RESPONSE TO SAID RISE IN PRESSURE IN SAID PORTION OF SAID REFRIGERANT CIRCUIT TO SAID PREDETERMINED MINIMUM PRESSURE; AND TERMINATING SAID INTERRUPTING STEP.