EP0080916A1 - Efficient multi-compressor refrigeration installation - Google Patents

Abstract

The improved installation comprises at least one refrigerating set having, in parallel between a suction manifold (5) and a delivery pipe (6), a number of motor-compressor sets (1, 2, 3, 4) of different powers, the values of which are chosen with a view to obtaining, for a given total power, a larger number of combinations of these motor- compressor sets representing a maximum number of fractional values of this total power at all levels of the latter, making it possible for the installation to respond as closely as possible to the particular refrigeration requirements. <IMAGE>

Description

The present invention relates to a refrigeration installation with improved efficiency with multi-compressors.

The known refrigeration installations with multi-compressors are usually installations comprising several motor-compressors of identical powers, mounted in parallel.

In an installation with four identical compressor units, for example, if all the four compressor units operate at the same time, a power of 100% of that of the installation is obtained. If only three of these four compressors are operating, 75% of the power of this installation is produced, and so on. It follows that in such an installation, can only be obtained a staggering of 0, 25, 50, 75 and 100% of the total power of the latter respectively with a number of 0, 1, 2, 3, and 4 motor-compressors set working. However, in an example where a refrigeration requirement corresponding to 55% of the power of the installation is requested, we are obliged to commission at least three motor compressors which represent 75% of the total power, 20% of this total power being this fact brought into play unnecessarily. Furthermore, in an installation comprising only three compressors, for a refrigeration demand requested corresponding to 40% of the power of the installation, the incidence is even more unfavorable than the previous example because two compressors, that is to say 66 , 6% of the total power must be put into service, 26, 6% of the total power then being put into use unnecessarily.

The present invention, having the aim of avoiding these drawbacks or wasting energy, makes it possible to produce an economic refrigeration installation with multimotocompressors, capable in its operation to get as close as possible to the refrigeration needs requested, and therefore to achieve appreciable energy savings and excellent efficiency.

According to the invention, the refrigeration installation with improved efficiency, with multi-compressors comprises at least one refrigeration unit having, between a common suction manifold and a common discharge line, several motor-compressors of different powers mounted in parallel.

• - la figure 1 représente une vue schématique d'une installation frigorifique à multimotocompresseurs selon un premier exemple de réalisation de l'invention,
• - la figure 2 représente une vue schématique d'une installation frigorifique à multimotocompresseurs, selon un deuxième exemple de réalisation de l'invention,
• - la figure 3 représente un diagramme montrant des valeurs en pourcentage de la puissance totale de l'installation pouvant être obtenues dans une installation frigorifique connue (ligne A) et une installation frigorifique de l'invention (ligne B), comportant chacune quatre motocompresseurs en réalisant des combinaisons de ces motocompresseurs dans leur mise en marche,
• - la figure 4 représente un graphique de fonctionnement de l'installation frigorifique connue de la figure 3, pour répondre à une courbe de besoins frigorifiques demandés et,
• - la figure 5 représente un graphique de fonctionnement de l'installation frigorifique de l'invention de la figure 3, pour répondre à une courbe de besoins frigorifiques demandés, identique à celle indiquée dans la figure 4.

To better understand the invention, a number of embodiments are illustrated below, illustrated by the appended drawings, including:

• FIG. 1 represents a schematic view of a refrigeration installation with multi-compressors according to a first embodiment of the invention,
• FIG. 2 represents a schematic view of a refrigeration installation with multi-compressor, according to a second embodiment of the invention,
• FIG. 3 represents a diagram showing values in percentage of the total power of the installation which can be obtained in a known refrigeration installation (line A) and a refrigeration installation of the invention (line B), each comprising four motor-compressors in making combinations of these motor compressors in their start-up,
• FIG. 4 represents a graph of operation of the refrigeration installation known from FIG. 3, in order to respond to a curve of requested refrigeration needs and,
• FIG. 5 represents a graph of operation of the refrigeration installation of the invention of FIG. 3, in order to respond to a curve of requested refrigeration needs, identical to that indicated in FIG. 4.

A refrigeration installation produced according to the invention comprises at least one group having several motor compressors of different powers, the values of which are chosen so as to obtain, for a given power, a greater number of combi of these motor compressors, reflecting a maximum number of fractional values of this total power and at all levels of the latter allowing the installation to respond as closely as possible to the refrigeration needs requested. This number of combinations of motor compressors of different powers is, at least greater than that obtained in a known refrigeration installation having the same number of motor compressors whose powers are identical.

In the examples of FIGS. 1 and 2, a refrigeration installation having a refrigeration group of four motor-compressors, produced according to the invention is shown.

The four motor compressors in this group respectively have powers corresponding to 15%, 20%, 30% and 35% of the total power. In such an installation, twelve combinations of motor compressors indicated in the area below the line B in FIG. 3, make it possible to obtain powers corresponding to 15%, 20%, 30%, 35%, 45%, 50%, 55%, 65%, 70%, 80%, 85%, 100% of the total power of the installation. On the other hand, in a known refrigeration installation which also comprises four motor-compressors but of identical powers and each representing 25% of the total power, only four combinations of these motor-compressors are obtained and indicated in the zone below line A of FIG. 3 and provide four powers corresponding to 25%, 50%, 75%, 100% of the total power of the installation.

For a given total power, the greater the number of combinations of motor compressors to start translating fractional values of this total power and at all levels, the more the installation is able to respond as closely as possible to various refrigeration requirements requested. In other words, the power used unnecessarily by the installation is low and the efficiency of the installation is better.

Figures 4 and 5 show the adaptability of the known refrigeration plant and that of the invention, indicated in Figure 3 to the same requested refrigeration requirements represented by identical CDEF ... OPQR curves.

In the known refrigeration installation, to satisfy the refrigeration needs of the sections CD and EF of the representative curve (FIG. 4), corresponding respectively to 10% and 15% of the total power of the installation during the times tl - t2 and t2 - t3, a motor-compressor, representing 25% of the total power, must be started, the hatched surface CDEFF'C 'then representing the work brought into play unnecessarily during the time tl = t3 by the installation; then to satisfy the refrigeration needs of the GH and IJ sections of the representative curve corresponding respectively to 27% and 40% of the total power of the installation during times t3-t4 and t4-t5 two motor compressors, representing 50% of the power total, must be started, the hatched area GHIJJ'G 'then representing the work brought into play unnecessarily during the time t3-t5 by the installation; then to satisfy the cooling requirements of the sections KL, MN, OP of the representative curve corresponding respectively to 32%, 57%, 62% of the total power of the installation during times t5-t6, t6-t7, and t7 -t8, three motor compressors representing 75% of the total power must be started, the hatched surface KLMNOPP'K 'then representing the work brought into play unnecessarily during the time t5-t8 by the installation; finally to satisfy the cooling requirements of the QR section of the representative curve corresponding to 80% of the total power of the installation during the time t8-t9, four motor-compressors, representing 100% of the total power, must be started, the hatched surface QRR'Q 'then representing the work brought into play unnecessarily during the time t8-t9 by the known installation.

On the other hand, in the refrigeration installation produced according to the invention, to meet the cold requirements of the sections CD and EF of an identical representative curve (FIG. 5), corresponding respectively to 10% and 15% of the total power during the times tl-t2 and t2-t3 a motor compressor representing 15% of the total power must be switched on, a small hatched area CD EC 'then representing the work brought into play unnecessarily during the time tl-t3 by the installation; then to meet the cooling requirements of the GH section of the representative curve, corresponding to 27% of the total power during time t3-t4, a motor compressor representing 30% of the total power must be started, a small hatched area GHH 'G' then representing the work brought into play unnecessarily during the time t3-t4 by the installation; then to satisfy the cooling requirements of the IJ section of the representative curve corresponding to 40% of the total power of the installation during the time t4-t5, two motor compressors representing respectively 15% and 30% of the total power walks a small hatched area IJJ'I 'then representing the work brought into play unnecessarily during the time t4-t5 by the installation; then to meet the cooling requirements of the KL section of the representative curve corresponding to 52% of the total power of the installation during the time t5-t6, two motor compressors representing 20% and 35% of the total power respectively walking, a small cross-hatched area KLL'K 'then representing the work brought into play unnecessarily during the time t5-t6 by the installation, then to satisfy the cold requirements of the sections MN and OP of the representative curve, corresponding respectively to 57 % and 62% of the total power of the installation during times t6-t7 and t7-t8, two motor compressors representing respectively 30% and 35% of the total power must be started, a small hatched area MNOPP'M ' representing then the work put in needlessly during time t6-t8 by the installation, finally to satisfy the requirements in cold of the section QR of the representative curve corresponding to 80% of the power to tale of the installation during time t8-t9 three motor compressors representing respectively 15%, 30%, 35% of the total power must be started, no work being put into play unnecessarily during time t8-t9 per l 'installation.

The amount of work represented by the hatched areas in FIG. 5 brought into play unnecessarily by the installation of the invention during the response to the requested cold requirements indicated by the curve CDEF ... OPQR, is clearly lower than that represented by the hatched surfaces in FIG. 4 concerning the known installation.

The installation produced according to the invention is thus capable of meeting the refrigeration needs requested in a more suitable manner than that of the known installation. Better efficiency is obtained and an appreciable energy saving is achieved.

Furthermore, the fact of putting into operation motor compressors which have a total generated volume greater than that of the demand, causes a lower evaporation temperature than that which is necessary, and an irregular low evaporation temperature in the evaporators causes '' disadvantage of low and uncontrolled humidity in cold rooms or cold use points. This drawback can be avoided by the costly use of constant pressure control valves on each evaporator. However, if these valves improve the operation of these cold rooms or cold use points, they do not change the poor performance of the compressors. In fact, a lowering of the evaporation temperature without being accompanied by a change in power of the motor of the motor-compressor results in a lowering of the refrigeration production per unit of energy consumed.

On the other hand, a large number of combinations of different power compressors allow the refrigeration installation of the invention to respond as closely as possible to the refrigeration needs requested, and to improve, by increasing the suction pressure, the efficiency at the unit of energy consumed.

In the refrigeration installations illustrated in FIGS. 1 and 2, only one group of motor compressors of different powers 1, 2, 3 and 4 is represented. These compressors are mounted in parallel between a common suction manifold 5 and a pipe discharge common 6. During their operation the motor compressors 1 to 4 respectively suck through the manifold 5 of the refrigerant gas coming from the points of use 7 and discharge it through the line 6, the oil separator 8 and the condenser 9 , in a common tank 10 which supplies liquid refrigerant to the points of use 7.

According to the first exemplary embodiment (FIG. 1) each of these motor compressors comprises a low pressure pressure switch 11, 12, 13, 14 and a high pressure pressure switch 15, 16, 17, 18. The starting and stopping of the motor compressors 1 to 4 are provided by low pressure pressure switches 11 to 14 which have an offset setting for example with respect to each other. The high pressure pressure switches 15 to 18 protect the installation by stopping their corresponding motor-compressors as soon as the high pressure exceeds a predetermined level, deemed inadmissible. Motor compressors 1 to 4 are each fitted with a differential oil safety pressure switch 19, 20, 21, 22. The refrigeration system can also be fitted with a low pressure pressure switch 23 which triggers an audible and / or light alarm in the case of a too low pressure detected at the suction manifold 5, and a high pressure pressostat 24 which triggers an audible and / or light alarm before the high pressure safety pressure switches 15 to 18 stop the motor compressors 1 to 4. High pressure switches 25, 26, 27 can be fitted to control the starting of the cooling fans 28, 29, 30 of the condenser 9.

According to a second exemplary embodiment, an electronic system 31 automatically ensures the selection of the combinations of motor-compressors, the operating control in order to achieve an optimal efficiency of the installation in satisfying the refrigeration needs requested. This electronic system 31 comprises a single low pressure tap by a low pressure sensor 32 in which a pressure variation in the suction manifold 5 generates an electrical signal intended to be interpreted by a electronic regulator 33 and an electronic unit of the microprocessor type 34 which give a combination of motor-compressor, the best suited to meet the demand for cold demand and act on control devices 35 to start these motor-compressors. This system 31 also includes a high pressure outlet by a high pressure sensor 36 in which a pressure variation in the discharge line 6 produces an electrical signal intended to be interpreted by an electronic regulator 37 and the electronic unit 34 which react on control devices 35 to ensure the operational safety of the installation. The other functions such as those of control, regulation, operation, signaling, defrosting are also performed in a known manner by the electronic system 31.

Claims (4)

1. Refrigeration installation with multi-compressors, characterized in that it comprises at least one refrigeration unit having, between a common suction manifold (5) and a common discharge line (6), several motor-compressors (1, 2, 3, 4 ) of different powers, mounted in parallel. 2. Installation according to claim 1, characterized in that in this refrigeration unit, the different power values of the motor compressors (1, 2, 3, 4) are chosen so as to obtain for a given total power, a greater number of combinations of these compressors, translating a maximum number of fractional values of this total power and at all levels of this latter. 3. Installation according to one of claims 1 and 2, characterized in that, in this refrigeration unit, the motor compressors (1, 2, 3, 4) are four in number, and respectively have powers corresponding to 15%, 20%, 30% and 35% of the total power of this group. 4. Installation according to one of claims 1 to 3, having an electronic system (31) automatically ensuring at least the selection of combinations of motor-compressors, the operating command, control, regulation, security, signaling, defrosting. , characterized in that it comprises in this electronic system (31) for the determination of the best combinations of the motor compressors (1, 2, 3, 4) to be started according to the refrigeration needs requested a single low pressure outlet in the suction manifold (5) of the refrigeration unit carried out by a sensor (32) which transforms a variation in pressure into an electrical signal intended to be interpreted by other members (33, 34) of this system (31).

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