FR2593897A1 - METHOD AND SYSTEM FOR CONTROLLING A REFRIGERATING INSTALLATION COMPRISING A CAPACITY CONTROL DEVICE, AUTOMATICALLY REAJUSTMENT OF THE TEMPERATURE OF THE REFRIGERATED WATER ADJUSTMENT POINT - Google Patents

Abstract

The present invention relates to a control system for controlling the readjustment of a temperature set point of a refrigerated fluid exiting in a refrigeration installation of the type comprising a microprocessor system and an evaporator. This system is characterized in that it comprises means 18 for entering at least two pairs of data into the microcomputer 17, means 15 for producing a first control signal which is a function of the temperature of the incoming heat transfer fluid. in the evaporator 5, means 13 for producing a second control signal which is a function of the temperature of the heat transfer fluid leaving the evaporator 5, and a processor 17. (CF DRAWING IN BOPI)

Description

The present invention relates to methods and systems

  control systems for the operation of

  gories and more particularly processes and systems

  controlling the operation of capacitance adjusters

  such as guide vanes of a compressor, in centrifugal vapor compression refrigeration plants so that the temperature

  chilled water leaving the cooler is automatically

  when the cold load or demand decreases

naked.

  In general, refrigeration installations

  carry an evaporator, a cooler, a compressor and

  a condenser. Usually a heat transfer fluid

  is circulated through a tube in the evapo-

  a heat transfer coil for transferring heat from the heat transfer fluid through the tube to the refrigerant in the evaporator. The heat transfer fluid, refrigerated in the tube in the evaporator, is normally water or glycol that is circulated to a remote location to meet a cold demand. The refrigerant in the evaporator evaporates as it absorbs heat from the water flowing through the tube into the evaporator and the compressor operates to extract this refrigerant vapor from the evaporator. evaporator, to compress this refrigerant vapor and to repress the compressed vapor towards the condenser. In this condenser the refrigerant vapor is condensed and is returned to the evaporator where the

refrigeration cycle starts again.

  In order to maximize the efficiency of the operation, it is desirable to adapt the amount of work supplied by the compressor to the work required to meet the demand.

  of cold to which the refrigeration system is subjected.

  Usually this is done by a communication device

  capacity that adjusts the amount of friable vapor

  gorigen flowing through the compressor. The capacity control device may be constituted by vanes

  which are arranged between the compressor and the

  vaporizer and which can move between a fully open position and a fully closed position in response to the temperature of the chilled water leaving the chilled water coil in the evaporator. When the temperature of the refrigerated water in the evaporator drops, which indicates a reduction in the cold demand to which the refrigeration system is subjected, the guide vanes move towards their position of

  total closure, which leads to a reduction in the

  Refrigerant vapor flow flowing through the compressor. This decreases the amount of work that must

  be supplied by the compressor, resulting in a reduction

  the amount of energy needed to operate

  set up the refrigeration plant. At the same time this has the effect of increasing the temperature of the chilled water

  leaving the evaporator. On the contrary, when the temperature

  refrigerated water leaving the evaporator rises

  which indicates an increase in demand for cold

  what is the cooling installation, the blades

  guidelines are moving towards their position of

  full height. This increases the amount of steam

  Through the compressor, this compressor works further, which consequently results in a decrease in the temperature of the refrigerated water leaving the evaporator and which allows the refrigeration plant to respond to the increased demand for cold. In this way the compressor operates to maintain the temperature of the chilled water leaving the evaporator at a set point temperature or within a certain range of such temperatures. The temperature setting point of the outgoing chilled water can be adjusted routinely on the operator's desk and after this adjustment is made, the temperature of the chilled water leaving the evaporator is maintained at the selected set point, and whatever the cold demand to which the machine is subjected.

  There are several systems for ordering

  different cities to order a refrigeration plant

  than in the manner indicated above. For example, such a system

  control system, namely a cooling control model

  electronic valve CP-8142-024 manufactured by the Company

  Rarber-Colman Company of Rockford, Illinois allows for

  _er a capacity control device in a plant

  Refrigeration according to the difference in the temperature of the chilled water leaving the evaporator compared to a

  temperature of a desired set point. When the temperature

  of the outgoing chilled water deviates from the temperature

  the selected control point of a prede-

  completed, the capacity control device is adjusted

  continuously by an actuator which is excited continuously] .-

  by a train of electrical impulses provided to

  the actuator. The predetermined magnitude of the temperature difference

  before the actuator is continuously excited.

  This provides a "dead" temperature band in which the capacitance controller is not set. The pulse frequency of the electrical pulse train supplied to the actuator determines the speed of adjustment

  overall capacity control device. This frequency

  impulses can be established at a minimum value

  male, medium or maximum, thereby providing a

  limited ability to adapt the operation of the capacity control system in order to meet

  particular operating conditions of a particular application

  of the refrigeration plant. However, as this

  This is the case with most control systems

  once the temperature set point

  outgoing chilled water was selected, the temperature

  refrigerated water is maintained at

  ture of the selected setpoint when the load or cooling demand varies from a load or zero demand to a total load or demand, while the temperature of the incoming chilled water deviates from the

  temperature of the outgoing refrigerant water from the linear

  re from scratch lAT, for a load or request null] e,

  up to an expected value T at full load or demand.

  However the operating mode of a capacity control system with a fixed set point for the outgoing chilled water is not very efficient from the point of view of energy consumption, at low loads, because

  that the refrigeration plant still maintains a temperature

  erosion of the outgoing refrigerated water which is lower than that which is actually needed to ensure comfort in the volume that is cooled. There is thus a

  need for the development of capac-

  cited for chillers that reduce energy consumption at low loads, by raising the temperature of chilled water leaving the chiller

  when the demand for cold decreases.

  It is therefore an object of the present invention to provide a simple microcomputer system with good

  performance and efficiency in order to control the capacity of a

refrigeration plant.

  Another object of the present invention is to provide

  an easily programmable microcomputer system to control the set point of chilled water leaving the cooler, directly in response to variations in

the demand for cold.

  These and other objects of the present invention are attained by a capacity control system for a refrigeration plant comprising a capacity control device for controlling

  the flow of a refrigerant into the refrigerating plant

  a microcomputer to readjust

  setting of the temperature of the outgoing refrigerated water according to selected parameters, and means for

  producing first and second signals respectively representing

  a detected temperature of the transfer fluid

  heat entering the cooler and a temperature

  the detected heat transfer medium

  cooler. These first and second signals are app i

  to the microcomputer that determines the outgoing chilled water temperature set point readjustment program based on two pairs of data

  programmed by the system operator in the micro-computer.

  tor. Each pair of data consists of a temperature difference and a desired readjustment value for that temperature difference. Thus the set point of the temperature of the outgoing chilled water can vary with the load or demand of cold, either from a minimum load to a maximum load or between two

  any values of intermediate charges. The provision

  capacity control is adjusted to control

  the flow of the refrigerant into the refrigerating

  in response to the control signal provided by the

  cro-computer. By selecting different pairs of

  The operation of the capacitance controller can be easily, effectively and efficiently adapted to meet operational requirements.

  particular application for the

  refrigeration plant, by establishing a program of

  precisely for the temperature set point. outgoing chilled water, program that is based on the load. An embodiment of the present invention will be described hereinafter by way of nonlimiting example, with reference to the appended drawing in which:

  FIG. 1 is a schematic diagram of a plant

  centrifugal vapor compression refrigeration

  equipped with a control system to vary the capacity of the refrigeration plant

according to the invention.

  Figure 2 is a diagram illustrating the variation

  the temperature of the chilled water as a function of

load.

  If we refer to Figure 1, we see that this

  figure represents a cooling system i with compres-

  steam reactor, which comprises a centrifugal compressor 2 with a control system 3 for varying the capacity of the refrigeration plant 1 according to the principles of the present invention. As can be seen in FIG. 1, the refrigerating plant I comprises

  a condenser 4, an evaporator 5 and a stem valve 6.

  In operation a compressed gaseous refrigerant is discharged

  from the compressor 2, through a conduit 7 of refoul-

  from the compressor to the condenser 4 o the refrigeration

  gaseous gene is condensed by condensation water

  cold condensate flowing through a tube 8 into the condenser 4. The condensed liquid refrigerant from the condenser 4 passes through the stem valve 6, in a

  refrigerant duct 9 leading to the evaporator 5. The refrigerant

  liquid rig is evaporated in this evaporator 5 to cool a heat transfer fluid, such as water or glycol, which flows through a tube 10 in the evaporator 5. This refrigerated heat transfer fluid is used to cool a building or it can be used for other purposes. The gaseous refrigerant from the evaporator 5 flows through the conduit

  11 compressor suction, to return to this compres-

  2 under the control of the inlet guide vanes 12 of the

  compressor. The gaseous friqorigen entering the com-

  pressing 2 through the guide vanes 12 is compressed by the compressor 2 and discharged from the compressor 2, through the discharge pipe 7 of the compressor, to complete the refrigeration cycle. This refrigeration cycle is repeated continuously during normal operation

of the refrigerating plant.

  The inlet guide vanes 12 of the compressor are opened and closed by an actuator 14 of the guide vanes which is controlled by the capacity control system 3 which comprises a system interface card.

  16, a processor card 17, a set point card,

  and display 18 and an analog / digital converter

  19. Also a temperature sensor 13 which is provided

  to detect the temperature of the heat transfer fluid

  Fig. 5 is shown in FIG. 5, in which the temperature sensor of the evaporator 5 passes through the tube 10, and a temperature sensor 15 which detects the temperature of the heat transfer fluid entering the evaporator through the tube 10, is connected by electrical lines.

  20 and 22, directly to the analog converter

that / digital 19.

  Preferably the temperature sensors 13 and

  are temperature-sensitive resistance devices

  such as thermistors having their sensitive parts housed in the heat transfer fluid in the tube 10 in the evaporator 5, their

  resistances being monitored by the analog converter

  loqic / digital 19 as shown in the figure

  1. Naturally, as the specialists will understand

  of the technique to which the present

  vention, the temperature sensors 13 and 15 can be

  any of a large number of temperature sensors

  ture to produce a signal representing the temperature of the heat transfer fluid in the tube in the evaporator 5, and to provide the

  signals thus produced to the analogue / digital converter

that 19.

  The processor card 17 may be a single device or a combination of devices capable of receiving a plurality of input signals, processing the

  input signals thus received following pre-pro-

  grammed, and to produce desired output control signals in response to the received and processed input signals, in accordance with the principles of the present invention. By

  example the processor card 17 may comprise a micro-processor

  computer such as a type 8031 microprocessor manufactured

  by the Intel Corporation of Santa Clara Califor-

  denies. Preferably the analog to digital converter 19 is a double slope converter which processes all the analog input signals to digital output signals and is suitable for use with the processor board 17. It should also be noted that , although the analog / digital converter 19 is shown as a separate module in the figure

  1, this analogical converter! Nu; 19 years: do phy-

  only part of the processor card 17 in a system

  real capacity control system 3.

  Further preferably the set-point and display board 18 comprises a visual display including, for example, light-emitting diodes (LEDs) or a liquid crystal display (LCD) forming a multi-digit display which is under control. of the processor board 17. Similarly, the set point and display board 18 includes a device such as a keyboard which serves as a data input device as well as

  programming tool, in order to enter the pairs of

  to establish a readjustment program for the chilled water leaving the evaporator 5 through the tube 10

  refrigerated water from the evaporator.

  In addition, the interface card of the system 16 preferably comprises at least one switch device, such as a triac of the SC-140 type manufactured by General Electric, Corp. Auburn New York, which is used as a switching element for controlling a power supply (not shown), through power lines 21, of the actuator 14 of the guide vanes. The triac switches on the system interface board 16 are controlled

  in response to control signals received by these inter-

  In this way the electrical energy is supplied, through the power line 21, to the actuator 14 of the guide vanes under the control of the processor card 17, so as to operate the actuator 14 of the guide vanes of a

  corresponding to the principles of the present invention.

  as will be described later with more

  details. Naturally, as will be clearly understood by

  specialists in the technique to which the pre-

  In this invention, switching devices other than triacs may be used to control the passage of electrical energy from the power source (not shown) through the power line 21 to the power supply.

  the actuator of the guide vanes in response to

  Exit command numbers from the process map

17.

  The guide vane actuator 14 may be any device suitable for driving the guide vanes 12 towards their open or closed position, in response to electrical supply signals received via the power lines 21. example the actuator 14 of the guide vanes can be

  an electric motor, such as a motor of the type MC-351

  Barber-Colman Company of Rockford, Ill.

  nois, to drive the guide vanes 12 either towards

  their open position towards their closed position, followed

  1, which is excited in response to the control signals received by the triac switches from the processor card 17. The aetizer 14 of the guide vanes is driven by the two switches tri triae on the system interface board 16. these guide vanes 12 towards either their fully open position or their fully closed position, with a constant and fixed speed, only during the portion of a selected base time interval during which the appropriate triae switch, on the system interface board 16,

is excited.

  With reference to FIG. 2, it can be seen that this figure represents a straight line curve in dashes A which gives the temperature of the outgoing refrigerated water that

  is obtained with a prior known control system-

  without readjustment. This figure also shows a slope curve B, in full line, which represents the set point of the temperature of the outgoing chilled water obtained according to the invention with a readjustment. These set points are arbitrary. The readjustment value to be applied is calculated by the microcomputer after two pairs of data have been introduced by

  the operator in the set point and display card

  age, using the keyboard. Because the microprocessor

  automatically adjusts the temperature setpoint

  of the outgoing refrigerated water according to the

  age, the operator can reduce energy consumption

  under certain load conditions. The temperature of the incoming chilled water corresponding to the curve A without readjustment, is represented by the curve C in sloping slope, while the curve D represents the temperature of

  incoming chilled water during any

  The ordinate is plotted with the desired readjustment of the curve B. The ordinate is plotted the temperature of the chilled water entering and leaving the evaporator. On the abscissa is the load or demand of cold to which is

  subjected the refrigeration system. On the abscissa is also

  It represents a typical set of L \ T values. the

  value of 5.60C, chosen for the value A T of the evapora-

  fully loaded, is an arbitrary choice.

  In the example given in FIG. 2, the curve A illustrates an arbitrary point of adjustment for the temperature.

  outgoing chilled water while curve B illus-

  the corresponding temperature of the refrigerated water

  aunt with the desired value of the readjustment applied. Thus in this example, assuming a value selected for AT of 60 ° C for a 100% load, the operator desires the refrigeration plant to maintain the temperature of the outgoing chilled water at 7.20 ° C. when the load is of

  100% and at 100C when the load is 0%. Thus the opera-

  to introduce two pairs of data into the micro-

  computer, the first pair of data being a readjustment

  of 2.80C forT = OOC while the second pair of

  The data is a readjustment of Ooc for 4T = 5.6C.

  the pairs of data in this example introduce

  In the set point and display board 18, the microprocessor calculates, when the load or cooling demand varies, a new set point of the temperature of the outgoing chilled water to ensure that the set point the temperature of the outgoing refrigerated water

  is the correct value for the load conditions

  aunts. If, for example, the load decreases from 100% to 20%, with the above-mentioned data pairs introduced, the temperature control point of the outgoing refrigerated water increases from 7.2 ° C to 9.4 ° C while this readjustment of the set point did not exist, the set point of the temperature of the outgoing chilled water would have remained 7.2 C. Thus the energy consumption is reduced by

  the temperature of the chilled water leaving the refrigerator

  stripper rises when the demand for cold decreases.

  Any number of data pairs can

  be entered in the set point and display card

  ge, following the desired set point.

P rEVIEr: l I iPNS

  1.- System of command, to order the readjustment

  temperature setpoint of a refrigerated fluid exiting in a refrigeration system of

  type comprising a microprocessor system and an evaporator

  in which a refrigerant absorbs heat from a heat transfer fluid passing therethrough, characterized in that it comprises means (18) for introducing at least two pairs of data into

  the microcomputer (17) and to produce a corresponding signal

  for each of the data pairs thus introduced, the first data pair corresponding to the magnitude of the readjustment from a fixed setpoint of the temperature of the outgoing refrigerant, for a first load, while the second pair of data corresponds to the magnitude of readjustment from this fixed set point of the temperature of the refrigerated fluid exiting for a second charge, means (15) for producing a first control signal which is a function of the temperature of the heat transfer fluid entering in the evaporator

  (5), means (13) for producing a second

  which is a function of the temperature of the heat transfer fluid leaving the evaporator (5), and a processor (17) receiving a signal corresponding to each of the introduced data pairs, as well as the first and second control signals, so as to processing the received signals according to preprogrammed procedures to determine a set point temperature for the heat transfer fluid leaving the evaporator, for the actual load to which the refrigeration system is subjected. 2. Control system according to claim 1 characterized in that the processor (17) determines the temperature of the set point in proportion to the data pairs introduced and the difference between the

  temperatures of the heat transfer fluid to the

  in the evaporator and on its exit.

  3.- Method of readjustment of a set point

  the temperature of a refrigerated liquid coming out of a

  refrigeration system with a micro-computer system

  and an evaporator in which a refrigerant absorbs heat from the refrigerated liquid passing therethrough, characterized in that a first set point signal corresponding to a first data point introduced into the microprocessor is produced, a second set point corresponding to a second data point introduced into the microprocessor is generated, a first temperature signal corresponding to the actual temperature of the incoming refrigerant is produced, and a

  output signal proportionally to a predefined relationship

  terminated between the first and second point signals of

  setting and the first and second temperature signals.

  4. A process according to claim 3 characterized in that the first data point introduced-corresponds to

  a pair of data corresponding to the size of the readjustment

  from a fixed set point of the temperature.

  re of refrigerated liquid exiting in a first load condition and the second data point introduced corresponds

  to a pair of data corresponding to the size of the

  precisely from this set point of temperature

  of the refrigerated liquid leaving in a second

charge edition.

  5. A process according to claim 4 characterized

  in that the output signal is produced proportionally-

  the sum of the set point signal and the difference

  between the first and second temperature signals.