FR2557962A1 - TWO-STAGE, FLEXIBLE OPERATION AND HIGH EFFICIENCY REFRIGERATION DEVICE - Google Patents

Abstract

A REFRIGERATION DEVICE CHARACTERIZED BY A FIRST STAGE SUPERCOMPRESSOR 12 SUPPLYING MULTIPLE COMPRESSORS IN PARALLEL OF A SECOND STAGE 14, 16 IN A CONVENTIONAL CLOSED-LOOP REFRIGERATION DEVICE USED BY A CONDENSER 22 AND 18 'EVAPORATOR 24 AND RETURNS THE STEAM FROM THE ECONOMIZER TO AN INTER-STAGE PRESSURE POINT LOCATED BETWEEN THE FIRST STAGE AND THE SECOND STAGE, OPERATES A VERY FLEXIBLE AND EFFICIENT MANNER BY DRIVING THE SUPERCOMPRESSOR AT A VARIABLE SPEED AND THE COMPRESSORS SECOND STAGE AT CONSTANT SPEED, MAXIMUM CAPACITY, THESE MACHINES CANNOT BE UNLOADED. THE CONTROL DEVICE USING A SENSOR 64 OF THE EVAPORATOR PRESSURE, ITS TEMPERATURE OR SUCTION PRESSURE VARIES THE SPEED OF THE SUPERCOMPRESSOR DRIVING MOTOR M TO INITIALLY SLOW DOWN, THEN CONNECT OR DISCONNECT THE COMPRESSORS SECOND FLOOR. THE SUPERCOMPRESSOR IS STILL OPERATING AND THE ECONOMIZER IS STILL OPERATIONAL. AS THE HIGH-SPEED STAGE MACHINES DO NOT DISCHARGE, THEY ALWAYS RUN AT THEIR MAXIMUM EFFICIENCY.

Description

1. The present invention relates to devices

  refrigeration and air conditioning systems, employing

  multi-stage pressers and, more particularly, a provision

  sitif using an economizer to sub-cool the cooling

  refrigerant condensed before its vaporization in the evaporator, and an arrangement giving great flexibility to

  multiple compressor operations, while maintaining

  keeping the efficiency of the refrigeration device

  carrying the compressors of the first and second stages.

  Supermarkets currently use typical-

  three-stage compressors connected in parallel which are switched on and off by pressure to

  aspiration. Such devices typically do not include-

  no economizer and therefore the efficiency j5 is low because the compression ratios are high, and

  there is an important cyclic functioning of the compress-

  sisters and the suction pressure range

  remains fairly large. These factors translate into poor

  will yield and by a lack of reliability.

  Therefore, the present invention has 2.

  main object a perfect refrigeration device

  multi-compressor in which the device

  base still uses three compressors, one compressor

  supercompression and two high stage compressors

  vé, o the device employs an economizer which is constantly active inside the device and which does not

  requires only two basic transducers for control

of the entire system.

  The present invention relates to a refrigeration circuit which comprises at least one compressor

  on one stage, two compressors on a second stage, one

  densifier, an economizer, an evaporator and a conduit containing a compressible refrigerant working fluid in connection with the compressor of the first

  second stage, the compressors on the second stage as a group

  eg the condenser, the economizer, the evaporator, in se-

  in this order in a closed loop and with the

  second stage compressors in parallel with one

  be. The conduit means further comprises means for extracting part of the condensed refrigerant from the

  closed loop downstream of the condenser and relax it inside

  inside the economizer to subcool the refrigerant

  liquid rant inside the closed loop which is

  introduced into the evaporator and to return the refrigerant

  manager relaxing in the form of refrigeration vapor

  rant at relatively high pressure to a point near

  intermediate channel inside the closed loop in

  be the output of the first stage compressor and the input of the second stage compressors. Means are provided

  to relax the liquid refrigerant to. high pressure, over-

  cooled, downstream of the economizer at. the evaporator. Motors are provided to drive the compressors, and the device comprises means for controlling the operation of the compressors of the first and second stages, comprising means for selectively driving 3.

  the motors of the second stage compressors to activate

  selectively see the compressor motors of the second

  stage and to control the refrigerant flow of a ma-

  selectively to the second stage compressors. Improvement includes driving the first stage compressor-blower at a variable speed of

  so as to obtain a large variation in the flow of the

  refrigerant through, and o the compressors of the se-

  cond stage include compressors operating in a fixed manner at the maximum load and thus operating at their peak efficiency, so that the inter-stage pressure is kept reasonable, and o the control means

  includes a first transducer to detect any one

  has the following parameters: evaporation pressure, evaporation temperature or suction pressure, and a

  second transducer to detect the interstage pressure

  ge of the refrigerant circulating in the closed loop in order to control the speed of the first stage compressor-supercharger in such a way that at the start the control

  is obtained by slowing down the booster and, in

  cond place, when the inter-stage pressure reaches a minimum

  predetermined mum, one of the second stage compressors

  stopped; from which it follows that the inter-state pressure

  ge automatically grows and increases the burden of the

top floor presser remaining.

  Any or all of the compressors

  can be reciprocating compressors,

  rotary screw helical sisters, rotary compressors

  sliding fins, or spi- compressors

  rale. The compressor supercharger drive motor

  of the first stage can consist of an internal

  duction using a speed control inverter

  reliable, with the frequency varying between 20 and 100 Hertz.

  The present invention will be well understood when

  of the following description made in conjunction with

  4. attached drawings in which: Figure 1 is a schematic representation of a closed loop refrigeration circuit according to a preferred embodiment of the present invention; Figure 2 is a graph of the inter-stage pressure for the device of Figure 1 as a function

  of the load / capacity of the device, illustrating the com-

  simplified control and flexibility of this device

  refrigeration. In connection with Figure 1, there is shown a closed loop refrigeration device according to a preferred embodiment of the present invention, shown at 10. The closed loop device comprises a booster 12 forming the first stage, a pair of second compressors or high-stage compressors 14, 16, an air-cooled condenser 18, a receiver 20, an economizer 22, and one or more evaporators 24, which are basic components of the refrigeration device 10 to

  closed loop. A driving means is used to connect the elements

  in series with the two high stage compressors

  14, 16 in parallel as a group within the circuit

  cooked in series with the closed loop. As such, circuit 26

  containing an appropriate refrigerant working fluid,

  me the product R-502, form in point 27 two pipes in

  parallel 28 and 30 so as to provide the output of the sur-

  compressor 12 of the first stage at an intermediate pressure

  diary to the suction block, or inlet, of the compressors 14, 16 of the second stage. The outputs of the compressors 14, 16 are connected, via lines 32 and 34, to a junction point 33 where the vapor of the refrigerant compressed at high pressure is applied to the inlet of the condenser 18 via a

  line 36. The condenser outlet allows the refrigerant to

  rant condensed to flow to the receiver 20 via a line 38. As indicated, the refrigerant R in liquid form located inside the receiver 20 flows via 5. a line 40 to the economizer 22. Au point 41, a draw-off or bypass line 42 allows part of the liquid refrigerant R to be extracted from the primary closed-loop circuit and to relax via an expansion valve 44 inside the economizer 22

  operating in such a way as to sub-cool the main part

  liquid refrigerant blade which passes directly to the

  or the evaporators 24 via a line 46. The refrigerant

  The sub-cooled liquid expands via an ex-

  expansion 48 to enter the evaporator (s) 24

  in order to perform a useful function inside the device

  positive refrigeration. The refrigerant vapor returns

  from the evaporator (s) 24 crosses a pipe 50 to the suction side, or low pressure side, of the supercharger 12 of the first stage, thus completing the

closed loop circulation.

  Furthermore, the refrigerant drawn off via the

  line 42 which vaporizes inside the economy

  in order to perform subcooling, crosses

  a pipe 52 to reach an inter-pressure point

  medial, such as 54, inside the device and

  plug in line 26 connecting the compressor outlet

  sor of the first stage at the inlet of one or the other or of the two compressors 14, 16 of the second stage. Note that while only two compressors 14, 16 have been shown, there could be three or more, all of these compressors being mounted in parallel and controlled appropriately. The device illustrated is deliberately limited to the two compressors 14, 16 at the top

3rd floor.

  The refrigeration device as illustrated allows highly efficient refrigeration which uses

  one or more evaporators 24 in all conditions

  load thanks to the constant use of a cy-

  3 economizer key, i.e. the booster 12 6.

  of the first floor still works but that the economy-

  sor 22 is still active. Voluntarily, we use the two compressors 14,16 of the high stage so that

  inter-stage pressure variations remain under control.

  In addition, high-floor machines, which can be reciprocating compressors without load capacity, are not

  not discharge and therefore always work at their

  dementally maximum. The first stage booster 12 can be a variable speed reciprocating compressor, but could be a variable speed screw compressor, a rotary compressor with variable speed sliding vanes, etc. It is also possible to use a variable speed turbo-compressor, i.e. a

centrifugal compressor.

  The purpose of the device is to obtain the return

  as high as possible, and the device basically employs a booster 12 operating at a

  variable speed, combined with two or more machines

  high floor, of fixed capacity, so that the

  inter-stage pressure is maintained at a reasonable value

  nable. In the illustrated system, a motor M1, for example at 56, is connected as indicated by the dotted line

  58 to blower 12 on the first floor, so that

  drag at variable speed and provide for refrigeration-

  rant R which crosses the compressor preferably a flow range from five to one or better. In turn, the compressor 16 of the second stage is directly driven by a second motor M2, for example at 72,

  whereas an M3 engine, for example in 74, drives di-

  the other compressor 14 of the second stage.

  The control device is simple and inherently stable. The device illustrated employs a control panel, for example at 62, which is connected to a

  source S via wires 76. The motor 58 is therefore supplied

  tee via the control panel 62 via 7. an electrical line 60. The device uses two

  transducers. The first transducer 64 is a transducer

  pressure regulator as shown, which detects the pressure at the suction of the supercharger 12 and is shown as being mounted in a line 50 supplying refrigerant between the evaporator (s) 24

  and the super-coepressor 12 at the inlet, or suction side-

  tion, of the supercharger 12. As a variant, the transducer 64 could be a transducer detecting the evaporation pressure or the evaporation temperature for the or

  the evaporators 24. The signal from the transducer 64 is ap-

  folded to the control panel 62 via a line 66. The second transducer 73 detects the inter-stage pressure,

  and is in this case plugged into line 26 which provides

  nit the discharge fluid from the supercharger of the first

  stage at the inlet of the compressors 14, 16 of the second stage

  ge. A pressure transducer 73 provides a signal via

  a line 75 at the control panel 62. In addition to the line

  gene 60, which leaves the control panel 62 and whose function is to vary the speed of the motor 56 directly driving the supercharger 12, a certain number of other lines leave the control panel 62 and join various components of the device. In this regard, a control line 70 connects the control panel 62 to a solenoid-actuated valve 68, which is placed inside the pipe 28 opening into the inlet of the compressor 14 of the second stage and operates from

  so as to selectively disconnect the device from the

  presser 14 under certain conditions which will be explained later. A command line 67 leaves the panel

  62 and supplies current to the motor 72 drive

  directly to compressor 16 of the second stage. A li-

  power supply 78 extends from the control panel 62 to the motor 74 so as to directly drive the

spring 14 from the second floor.

second stage compressor 14.

8.

  On the march, while there is a drop in needs

  care in the refrigerant or evaporators 24, the suction pressure at the inlet of the supercharger 12

  drop and transducer 64 provides a command signal

  from via line 66 to the control panel bringing out the drop in suction pressure. In turn,

  the control panel 62 varies the current cross-

  the drive motor 56 so as to slow the booster and therefore reduce the flow of refrigerant passing through the supercharger 12 of the first stage. The motor 56 can be an induction motor using a variable speed inverter control, in which case the control panel 62 operates to vary the

  frequency of current supplied to motor 56 via line 60.

  For a range of one to five of the supercharger 12, the value

  riance of the frequency of the control signal applied to the

  motor 56 can be between 20 and 100 Hertz.

  When the inter-stage pressure reaches a minimum

  predetermined mum, one of the two compressors of the second

  floor will be stopped, and the inter-floor pressure will automatically increase

  matically and will increase the load of the remaining compressor (s) of the high speed stage. In the device

  illustrated, the second transducer 73 detecting the pressure

  Inter-stage sion will provide a signal representative of the new inter-stage pressure reduction, via the line, to control panel 62. Control panel 62

  will then stop the compressor, for example the one shown

  felt in 14 by stopping the excitation of the drive motor

  74 via line 78. Simultaneously, if necessary, the control valve 68 actuated by solenoid will change state so as to cut off the circulation of refrigerant in the pipe 28 opening into the compressor 14 of the

second floor, via line 70.

  The operation of the device is shown graphically in FIG. 2, which is a pressure curve 9.

  inter-floor depending on the load / capacity of the device

  tif. The two parallel lines in solid lines P and P '

  are the inter-stage pressure curves depending on whether

  operate one or two high-floor machines. The curve P relates to a single compressor of the second stage, while the curve P 'relates to a higher load / capacity operation of the device of between 40 and%. If it is assumed, for example, that the device operates at low load with a single compressor operating in the second stage, ie compressor 16, and remembering that the supercharger of the first stage

  always works and therefore economizer 22 is always

  operational days, when the operation of the device

  tif is such that the inter-stage pressure reaches a point

  high of line P, for example a point chosen B corresponds to

  laying at 0.4 MPa, the compressor 14 of the second stage comes into action, the pressure between stages drops to approximately O026 MPa,

  at point 3 'of the second curve P' for operation

  ment of the two high stage compressors. As we can

  2 <notice, as the charge believes, the pressure between

  stage at which the compressor 14 of the second stage is restarted is set to a value greater than the rebalanced inter-stage pressure at which the second compressor is stopped, the breakpoint on the line Pl being

  in A which corresponds to a pressure of approximately 0.14 MPa com-

illustrated me for the device.

  It should be remembered that the curve shown relates to an efficient and reliable refrigeration device for supermarket, involving one or more evaporators 24, and constitutes the basis of a generic control philosophy or logic diagram where the refrigerant can be

  type R-502 and the device has an evapo-

  ration of -300C. In the system shown, an excess of cycling of the compressors 14, 16 is avoided, which would have the effect of having a serious effect on the yield of the device since the economizer is always kept in the active state. When the inter-stage pressure falls along the line P 'to 0.1 MPa and reaches point A, the

  device moves aside the compressor 14 maintaining the com-

  presser 16 of the second stage, and the interstate pressure

  ge immediately increases (for the same load) to around 0.32 MPa. The single compressor 16 of the second stage maintains the operation of the device while

  the base charge continues to decrease and the

  compressor 12 is further slowed down by a command

  propriée coming from the control panel 62 and applied

  to motor 56 driving the supercharger via the line

  gene 60. As indicated previously, if the load increases after transfer from the device to the only compressor 16 of the second stage, the speed of the motor 56 increases by one

  appropriately, providing increased de-

  bit of refrigerant passing through compressor 12 of the first

  1st stage until, naturally, the inter-stage pressure reaches a value of 0.42 MPa (point B, curve P), where the compressor 14 of the second stage starts up and compresses the refrigerant in parallel with

  the refrigerant passing through the other compressor 16 of the se-

cond floor.

  In the device illustrated, the load of the system

  falling, the transducer 64 of the suction pressure

  tion causes the speed of the supercharging to decrease

  sor 12. When the inter-stage pressure reaches A (curve P '), a second stage compressor is switched off and the inter-stage pressure rebalances (point A', curve P). The increase in the load causes the supercharger 12 to accelerate and the second compressor or the next compressor of the second stage to start operating,

at B (curve P).

  As can be appreciated, it is only

  necessary to have as an entry, to obtain an order

  of suitable, two basic transducers. One is used to 11. measure the suction pressure or its equivalent, and the other is to measure the inter-stage fluid pressure

  working refrigerant in the closed loop. The logi-

  that generic control is simple and straightforward, and a solid-state control panel can be easy-

  implemented to order the availability of

  sitive with the parameters described. It is believed that the dis-

  positive refrigeration is ideal both for refrigeration-

  industrial ration only for typical heat pumps

  that we use for heating and cooling

  ment of commercial and other buildings. The device

  illustrated only uses three compressors,

  see a supercharger and two compressors on the high speed stage. The device includes suitable redundancy, in that the compressors of the high-speed stage alone can process approximately 50% of the

  maximum load of the device in the absence of the over-command

  presser, and that the supercharger and one of the compressors

  sors of the high speed stage can also handle about 50% of the maximum load of the device, as will be seen from the curves in Figure 2. The power of the supercharger is so low that it may be reasonable to equip it with an inverter or a brushless direct current control to obtain the

  variable speed required by the system.

  The appreciation of some of the measurement values

  res indicated above must take into account that

  come from the conversion of Anglo-Saxon units

in metric units.

  The present invention is not limited to the exemplary embodiments which have just been described, it

  is on the contrary susceptible of variations and modifica-

  that will appear to those skilled in the art.

12.

Claims (8)

  1 - Refrigeration circuit, comprising: a variable capacity compressor means (12) as the first stage; - compressor means (14, 16) as a second stage; - a condenser (18); - an evaporator (24); a conduit means containing a compressible refrigerant which interconnects the compressor means of the first stage, the compressor means of the second stage, the condenser, the evaporator, in series in a closed loop, in the previous order; - motors (M1, M2, M3) to drive the compressor means; - an economizer (22) arranged functionally between the condenser and the evaporator to relax a   part of the condensed refrigerant coming from the iron loop   downstream of the condenser in order to sub-cool the refrig-   manager circulating towards the evaporator;   - a means (52) for introducing the relaxed part   due. refrigerant in an inter-stage point located between the outlet of the compressor means of the first stage and the inlet of the compressor means of the second stage; and   - a control means for controlling the function   operation of the compressor means of the second stage in   response to a certain condition at the inter-floor point.   2 - Refrigeration circuit as claimed   cation l, characterized in that the control means   takes a first detector (6.4) intended to detect a condition on the suction side of the first stage and a second detector (73) intended to detect a condition on the side second floor aspiration.   3 - Refrigeration circuit as claimed   cation 2, characterized in that the second detector (73) 13.   detects the pressure of the inter-stage refrigerant.   4 - Refrigeration circuit as claimed   cation 2, characterized in that the control means   can work to vary the ca-   capacity of the compressor means of the first stage and in   second the capacity of the compressor means of the second stage so that the inter-stage pressure is maintained   within a desired range.   - Refrigeration circuit according to claim 4, characterized in that the capacity of the compressor means of the first stage is controlled in response to a certain condition on the suction side of the first stage, and the capacity of the compressor means of the second stage is ordered in response to a certain condition   on the suction side of the second floor.   6 - Refrigeration circuit according to one which   conch of the preceding claims, characterized in   what the second stage compressor means includes   at least two fixed capacity compressors (14, 16).   7 - Refrigeration circuit as claimed   cation 6, characterized in that the control means   takes a means (68) to selectively close the flow of   inter-stage refrigerant between the first means of com-   presser and at least one of the capacity compressors fixed second floor.   8 - Refrigeration circuit as claimed   cation 6, characterized in that the control means   takes a means to stop the excitation of the drive motor for at least one of the compressors to second floor fixed capacity.   9 - Refrigeration circuit as claimed   cation 6, characterized in that the capacity compressors   fixed tee are mounted in parallel with each other.   - Refrigeration circuit according to one   conch of the preceding claims, characterized in   that the motor (M1) of the first stage compressor is a variable speed motor.