EP2729744B1 - Method for balancing lubricant levels in a multi-stage compression unit of a heat exchange system, and heat exchange system implementing such a method - Google Patents

Description

The invention relates to a method for balancing the lubricant levels in a multi-stage compression unit of a heat exchange system and to a heat exchange system implementing such a method.

• des premier et deuxième échangeurs de chaleur pour échanger de la chaleur respectivement avec l'air extérieur et le milieu intérieur, lesdits premier et deuxième échangeurs de chaleur présentant chacun une entrée et une sortie et formant l'un un évaporateur et l'autre un condenseur,
• un circuit de fluide caloporteur adapté pour faire circuler un fluide caloporteur entre l'évaporateur et le condenseur, ledit circuit de fluide caloporteur comprenant une unité de compression multi-étagée placée entre la sortie de l'évaporateur et l'entrée du condenseur, et une unité de détente placée entre la sortie du condenseur et l'entrée de l'évaporateur, ladite unité de compression comprenant au moins un premier compresseur (basse pression) et au moins un deuxième compresseur (haute pression) agencés en série, le premier compresseur refoulant le fluide caloporteur dans le deuxième compresseur, les premier et deuxième compresseurs comportant chacun un carter recevant du lubrifiant,
• une ligne d'équilibrage adaptée pour faire passer du lubrifiant entre les carters des premier et deuxième compresseurs, la ligne d'équilibrage comprenant une première vanne présentant un sens passant depuis le carter du deuxième compresseur vers le carter du premier compresseur,
• une unité de commande connectée au circuit de fluide caloporteur et à la ligne d'équilibrage, ladite unité de commande étant adaptée pour déterminer s'il existe un besoin de chauffage du milieu intérieur et si le besoin de chauffage du milieu intérieur est important ou modéré et pour, lorsqu'il existe un besoin de chauffage du milieu intérieur important :
  • commander un fonctionnement multi-étagé en connectant l'unité de compression entre la sortie du premier échangeur de chaleur et l'entrée du deuxième échangeur de chaleur, en connectant l'unité de détente entre la sortie du deuxième échangeur de chaleur et l'entrée du premier échangeur de chaleur, et en faisant fonctionner en série les premier et deuxième compresseurs, et
  • périodiquement, commander un dégivrage du premier échangeur de chaleur en connectant l'unité de compression entre la sortie du deuxième échangeur de chaleur et l'entrée du premier échangeur de chaleur, en connectant l'unité de détente entre la sortie du premier échangeur de chaleur et l'entrée du deuxième échangeur de chaleur, en arrêtant le premier compresseur et en faisant fonctionner le deuxième compresseur.

In particular, the invention applies to a heat exchange system adapted to perform heat exchange between outside air located outside a space and an inner medium flowing inside the space. , said heat exchange system comprising:

• first and second heat exchangers for exchanging heat respectively with the outside air and the indoor medium, said first and second heat exchangers each having an inlet and an outlet and forming one an evaporator and the other a condenser ,
• a coolant circuit adapted to circulate a heat transfer fluid between the evaporator and the condenser, said coolant circuit comprising a multi-stage compression unit placed between the outlet of the evaporator and the inlet of the condenser, and a expansion unit placed between the condenser outlet and the inlet of the evaporator, said compression unit comprising at least a first compressor (low pressure) and at least a second compressor (high pressure) arranged in series, the first compressor repressing the coolant in the second compressor, the first and second compressors each having a housing receiving lubricant,
• a balancing line adapted to pass lubricant between the casings of the first and second compressors, the balancing line comprising a first valve having a direction passing from the casing of the second compressor to the casing of the first compressor,
• a control unit connected to the heat transfer fluid circuit and the balancing line, said control unit being adapted to determine whether there is a need for heating of the indoor environment and whether the need for heating of the indoor environment is important or moderate and for when there is a need for significant indoor heating:
  • control multi-stage operation by connecting the compression unit between the outlet of the first heat exchanger and the inlet of the second heat exchanger, connecting the expansion unit between the outlet of the second heat exchanger and the inlet the first heat exchanger, and operating in series the first and second compressors, and
  • periodically, control defrosting of the first heat exchanger by connecting the compression unit between the outlet of the second heat exchanger and the inlet of the first heat exchanger, connecting the expansion unit between the outlet of the first heat exchanger and the inlet of the second heat exchanger, stopping the first compressor and operating the second compressor.

To lubricate the components of the heat transfer fluid circuit, particularly the first and second compressors, the lubricant, usually mineral or synthetic oil, is mixed with the coolant. The lubricant is generally not miscible in the heat transfer fluid but it can be driven and transported in the form of droplets by the heat transfer fluid. The risk is then to accumulate the lubricant in a part of the circuit until one and / or the other of the first and second compressors no longer contains enough lubricant and deteriorates rapidly. In a circuit comprising several compressors, the balancing of the lubricant level between the compressors is an important problem.

In a single-stage heat transfer fluid circuit comprising a plurality of compressors in parallel, a known way to achieve lubricant balancing is to accumulate the lubricant in the high pressure part of the circuit, usually by installing a lubricant separator coupled to a reservoir. of lubricant on a common discharge line of the compressors. Each compressor is equipped with a lubricant level detection means and a lubricant injection means connected to the lubricant reservoir via a pilot valve. It is thus possible to regulate the level of lubricant in each compressor.

In a multi-stage circuit comprising a plurality of series compression stages, for example a low pressure compression stage comprising the first compressor (s) and a high pressure compression stage comprising the second compressor (s), the risk is to accumulate lubricant. in the compressors of one of the compression stages at the expense of the compressors of the other stages of compression. While it is relatively easy to transport the lubricant from the high pressure compression stage to the low pressure compression stage by using the pressure difference, the reverse poses more difficulties.

The document EP 2,221,559 describes a heat exchange system of the type defined above in which the balancing of the low pressure compressor to the compressor high pressure occurs at the start of the heat exchange system and the balancing of the high pressure compressor to the low pressure compressor is effected at the start of the heat exchange system.

In addition, the document US 2008/098760 discloses a heat exchange system implementing a balancing method according to the preamble of claim 1.

The invention improves the situation.

In particular, it proposes better management of the balancing of the lubricant levels in a multi-stage compression unit.

• au cours du fonctionnement multi-étagé, de transférer l'excédent de lubrifiant du carter du deuxième compresseur au carter du premier compresseur par la première vanne de la ligne d'équilibrage,
• au cours du dégivrage du premier échangeur de chaleur, de transférer un excédent de lubrifiant du carter du premier compresseur au carter du deuxième compresseur par la deuxième vanne de la ligne d'équilibrage.

The invention proposes in particular a method for balancing the lubricant levels in a multi-stage compression unit of a heat exchange system of the aforementioned type. The balancing method uses first and second valves arranged in parallel in the balancing line of the heat exchange system, the first valve having a direction passing from the housing of the second compressor to the casing of the first compressor, the second valve having a direction passing from the crankcase of the first compressor to the crankcase of the second compressor, and a blocking direction from the crankcase of the second compressor to the crankcase of the first compressor. The balancing process further provides:

• during multi-stage operation, transferring the excess lubricant from the casing of the second compressor to the casing of the first compressor by the first valve of the balancing line,
• during defrosting of the first heat exchanger, transferring excess lubricant from the casing of the first compressor to the casing of the second compressor by the second valve of the balancing line.

Thus, the invention takes advantage of the fact that when there is a large heating requirement, determined for example directly or indirectly from an outside temperature of the outside air, a compression ratio of the unit of compression or any other quantity, where appropriate with respect to a threshold value, the heat exchange system, acting as a heat pump for taking heat from the outside air and transferring it to the internal environment, passes necessarily by deicing cycles.

In addition, transfers of excess lubricant are performed automatically by the effect of only pressure differences between the first and second compressors. The balancing process thus offers a management of lubricant levels which is simple, safe and relatively inexpensive. The balancing is furthermore carried out regularly during the use of the heat exchange system.

The heat exchange system may further comprise a single lubricant separator placed at the discharge of the second compressor and a lubricant return line between the lubricant separator and the casing of the second compressor. The balancing method can then provide for separating the lubricant from the heat transfer fluid, collecting the lubricant in the lubricant separator and returning the collected lubricant to the casing of the second compressor.

The single lubricant separator placed at the discharge of the second compressor, high pressure, slows the accumulation of lubricant that may occur in multi-stage operation in the casing of the first compressor, low pressure. The balancing process can then take advantage of the defrost cycles, even several hours apart, to bring the lubricant from the low pressure compressor back to the high pressure compressor.

The control unit can be adapted to, when there is a need for moderate indoor heating, to control a single-stage operation by connecting the compression unit between the outlet of the first heat exchanger and the inlet of the second heat exchanger, connecting the expansion unit between the outlet of the second heat exchanger and the inlet of the first heat exchanger, stopping the first compressor and operating the second compressor. The balancing method can then provide, during the single-stage operation, to transfer excess lubricant from the casing of the first compressor to the casing of the second compressor by the balancing line.

Lubricant balancing management is further improved by taking advantage of the fact that, when there is a need for moderate heating, determined in particular in the same way as the need for substantial heating, the heat exchange system acting as a heat pump operates in single-stage. This method of balancing oil is particularly suitable for a heat pump for the building, which can operate alternately multi-stage and single-stage depending on the outside temperature and heating requirements.

For example, the heat exchange system may comprise at least two first fixed capacity compressors connected in parallel, and a second compressor with variable capacity, the first compressors having different capacities, the balancing line comprising a pipe connecting the casings of the first compressors. The balancing method can then provide to transfer the excess lubricant from the casing of the first compressor of lower capacity to the casing of the other first compressor.

• des premier et deuxième échangeurs de chaleur pour échanger de la chaleur respectivement avec l'air extérieur et le milieu intérieur, lesdits premier et deuxième échangeurs de chaleur présentant chacun une entrée et une sortie et formant l'un un évaporateur et l'autre un condenseur,
• un circuit de fluide caloporteur adapté pour faire circuler un fluide caloporteur entre l'évaporateur et le condenseur, ledit circuit de fluide caloporteur comprenant une unité de compression multi-étagée placée entre la sortie de l'évaporateur et l'entrée du condenseur, et une unité de détente placée entre la sortie du condenseur et l'entrée de l'évaporateur, ladite unité de compression comprenant au moins un premier compresseur et au moins un deuxième compresseur agencés en série, le premier compresseur refoulant le fluide caloporteur dans le deuxième compresseur, les premier et deuxième compresseurs comportant chacun un carter recevant du lubrifiant,
• une ligne d'équilibrage adaptée pour faire passer du lubrifiant entre les carters des premier et deuxième compresseurs, la ligne d'équilibrage comprenant des première et deuxième vannes agencées en parallèle, la première vanne présentant un sens passant depuis le carter du deuxième compresseur vers le carter du premier compresseur, la deuxième vanne présentant un sens passant depuis le carter du premier compresseur vers le carter du deuxième compresseur, et un sens bloquant depuis le carter du deuxième compresseur vers le carter du premier compresseur,
• une unité de commande connectée au circuit de fluide caloporteur et à la ligne d'équilibrage, ladite unité de commande étant adaptée pour déterminer s'il existe un besoin de chauffage du milieu intérieur et si le besoin de chauffage du milieu intérieur est important ou modéré et pour, lorsqu'il existe un besoin de chauffage du milieu intérieur important :
  • commander un fonctionnement multi-étagé en connectant l'unité de compression entre la sortie du premier échangeur de chaleur et l'entrée du deuxième échangeur de chaleur, en connectant l'unité de détente entre la sortie du deuxième échangeur de chaleur et l'entrée du premier échangeur de chaleur, et en faisant fonctionner en série les premier et deuxième compresseurs, et
  • périodiquement, commander un dégivrage du premier échangeur de chaleur en connectant l'unité de compression entre la sortie du deuxième échangeur de chaleur et l'entrée du premier échangeur de chaleur, en connectant l'unité de détente entre la sortie du premier échangeur de chaleur et l'entrée du deuxième échangeur de chaleur, en arrêtant le premier compresseur et en faisant fonctionner le deuxième compresseur,
  ladite unité de commande étant en outre adaptée pour mettre en oeuvre le procédé d'équilibrage tel que défini précédemment.

According to a second aspect, the invention relates to a heat exchange system adapted to perform heat exchanges between outside air located outside a space and an internal medium flowing inside the space, said heat exchange system comprising:

• first and second heat exchangers for exchanging heat respectively with the outside air and the indoor medium, said first and second heat exchangers each having an inlet and an outlet and forming one an evaporator and the other a condenser ,
• a coolant circuit adapted to circulate a heat transfer fluid between the evaporator and the condenser, said coolant circuit comprising a multi-stage compression unit placed between the outlet of the evaporator and the inlet of the condenser, and a an expansion unit placed between the outlet of the condenser and the inlet of the evaporator, said compression unit comprising at least a first compressor and at least a second compressor arranged in series, the first compressor discharging the coolant in the second compressor, the first and second compressors each comprising a housing receiving lubricant,
• a balancing line adapted to pass lubricant between the casings of the first and second compressors, the balancing line comprising first and second valves arranged in parallel, the first valve having a direction passing from the casing of the second compressor to the crankcase of the first compressor, the second valve having a direction passing from the crankcase of the first compressor to the crankcase of the second compressor, and a blocking direction from the crankcase of the second compressor to the crankcase of the first compressor,
• a control unit connected to the heat transfer fluid circuit and the balancing line, said control unit being adapted to determine whether there is a need for heating of the indoor environment and whether the need for heating of the indoor environment is important or moderate and for when there is a need for significant indoor heating:
  • control multi-stage operation by connecting the compression unit between the outlet of the first heat exchanger and the inlet of the second heat exchanger, connecting the expansion unit between the outlet of the second heat exchanger and the inlet of the first heat exchanger, and operating in series the first and second compressors, and
  • periodically, control defrosting of the first heat exchanger by connecting the compression unit between the outlet of the second heat exchanger and the inlet of the first heat exchanger, connecting the expansion unit between the outlet of the first heat exchanger and the inlet of the second heat exchanger, stopping the first compressor and operating the second compressor,
  said control unit being further adapted to implement the balancing method as defined above.

The first valve may be a float valve and the second valve may be a valve.

• la figure 1 est une représentation schématique d'un système d'échange thermique selon un mode de réalisation de l'invention, le système d'échange thermique comprenant une unité de compression multi-étagée, le système d'échange thermique fonctionnant selon un mode climatiseur,
• la figure 2 est une représentation schématique du système d'échange thermique de la figure 1 fonctionnant selon un mode pompe à chaleur,
• la figure 3 est une représentation schématique de l'unité de compression multi-étagée du système d'échange thermique de la figure 1, illustrant une ligne d'équilibrage des niveaux de lubrifiant entre des premier et deuxième étages de compression de l'unité de compression, la ligne d'équilibrage comprenant deux vannes distinctes pour assurer les transferts d'excédant de lubrifiant entre les premier et deuxième étages de compression,
• La figure 3b est une variante de l'unité de compression multi-étagé de la figure 3 par les éléments constituant la ligne d'équilibrage.
• la figure 4 est un diagramme illustrant des étapes du procédé d'équilibrage des niveaux de lubrifiant dans l'unité de compression multi-étagée du système d'échange thermique de la figure 2,
• la figure 5 est une représentation schématique d'une vanne de la ligne d'équilibrage d'une variante du système d'échange thermique de la figure 1, la vanne assurant à elle seule les transferts d'excédant de lubrifiant entre des premier et deuxième étages de compression,
• la figure 6 est un diagramme illustrant des étapes du procédé d'équilibrage des niveaux de lubrifiant dans l'unité de compression multi-étagée dans une autre variante du système d'échange thermique de la figure 1, dans laquelle une seule électrovanne assure les transferts d'excédant d'huile entre des premier et deuxième étages de compression.

Other objects and advantages of the invention will appear on reading the following description of a particular embodiment of the invention given by way of non-limiting example, the description being made with reference to the appended drawings in which :

• the figure 1 is a schematic representation of a heat exchange system according to one embodiment of the invention, the heat exchange system comprising a multi-stage compression unit, the heat exchange system operating in an air conditioner mode,
• the figure 2 is a schematic representation of the heat exchange system of the figure 1 operating in a heat pump mode,
• the figure 3 is a schematic representation of the multi-stage compression unit of the heat exchange system of the figure 1 , illustrating a line for balancing lubricant levels between first and second compression stages of the compression unit, the balancing line comprising two separate valves for providing lubricant excess transfers between the first and second stages compression,
• The figure 3b is a variant of the multi-stage compression unit of the figure 3 by the elements constituting the balancing line.
• the figure 4 is a diagram illustrating steps of the method of balancing lubricant levels in the multi-stage compression unit of the heat exchange system of the figure 2 ,
• the figure 5 is a schematic representation of a valve of the balancing line of a variant of the heat exchange system of the figure 1 , valve alone ensuring transfers of excess lubricant between first and second compression stages,
• the figure 6 is a diagram illustrating steps of the method of balancing the lubricant levels in the multi-stage compression unit in another variation of the heat exchange system of the figure 1 , in which a single solenoid valve transfers the excess oil between first and second compression stages.

In the figures, the same references designate identical or similar elements.

The figures 1 and 2 represent a heat exchange system 1 respectively for cooling and heating an indoor environment, for example water, flowing in a space 2, such as a room of a dwelling, a technical room or other. Alternatively, the internal environment could be other than water, including air. The heat exchange system 1 allows either to heat the water by drawing heat from outside air located outside the space 2 (cold source) and transferring to the water (hot source) the heat taken ( figure 2 ), or to cool the water by taking heat (cold source) and transferring to the outside air (hot source) the heat taken ( figure 1 ).

• un premier échangeur de chaleur 5, formant sélectivement un évaporateur ou un condenseur, destiné à réaliser des échanges thermiques avec l'air extérieur, le premier échangeur de chaleur 5 présentant une première extrémité 6 et une deuxième extrémité 7 qui forment l'une une entrée E et l'autre une sortie S,
• un deuxième échangeur de chaleur 15, formant sélectivement un évaporateur ou un condenseur, destiné à réaliser des échanges thermiques avec l'eau, le deuxième échangeur de chaleur 15 présentant une première extrémité 16 et une deuxième extrémité 17 qui forment l'une une entrée E et l'autre une sortie S,
• un circuit de fluide caloporteur connecté aux premier 5 et deuxième 15 échangeurs de chaleur et adapté pour faire circuler un fluide caloporteur, tel qu'un fluide frigorigène, entre le premier échangeur de chaleur 5 et le deuxième échangeur de chaleur 15.

The heat exchange system 1 comprises:

• a first heat exchanger 5, selectively forming an evaporator or a condenser, intended to perform heat exchanges with the outside air, the first heat exchanger 5 having a first end 6 and a second end 7 which form an inlet E and the other an output S,
• a second heat exchanger 15, selectively forming an evaporator or a condenser, intended to perform heat exchanges with water, the second heat exchanger 15 having a first end 16 and a second end 17 which form an E inlet and the other an output S,
• a heat transfer fluid circuit connected to the first and second heat exchangers 15 and adapted to circulate a coolant, such as a refrigerant, between the first heat exchanger 5 and the second heat exchanger 15.

The heat transfer fluid circuit comprises a multi-stage compression unit 20 and an expansion unit 10.

On the figures 1 , 2 and 3 the compression unit 20 is bi-stepped and comprises a first compression stage 21 and a second compression stage 22 arranged in series. Alternatively, the compression unit 20 could comprise more than two compression stages arranged in series.

The first compression stage or low pressure compression stage 21 comprises two first compressors or low-pressure compressors 23a, 23b connected in parallel. Each of the low-pressure compressors 23a, 23b is, for example, with a fixed capacity, and in particular at a fixed speed. In addition, in the embodiment shown, the low-pressure compressors 23a, 23b respectively have different displacements. In particular, the low-pressure compressor 23b, identified BP2 on the figure 3 , has a higher capacity than that of the low pressure compressor 23a, identified BP1 on the figure 3 . Alternatively, the low pressure compression stage 21 could comprise one or more two low pressure compressors 23 in parallel.

The second compression stage or high pressure compression stage 22 comprises a second compressor or high pressure compressor 24, identified HP on the figure 3 . The high-pressure compressor 24 is, for example, variable capacity, including variable speed. Alternatively, the high pressure compression stage 22 could comprise a plurality of high pressure compressors 24 in parallel.

Each of the low pressure compressors 23a, 23b and high pressure 24 has a suction inlet 25 and a discharge outlet 26. In the embodiment shown, the suction inlets 25 of the low pressure compressors 23a, 23b are connected to a same suction line 27 and the discharge outlets 26 of the low pressure compressors 23a, 23b are connected to the same discharge line 28. The low pressure compressors 23a, 23b and high pressure 24 are arranged in series, that is to say that is, the delivery line 28 of the low-pressure compressors 23a, 23b is connected to the suction inlet 25 of the high-pressure compressor 24. Furthermore, as will be apparent from the following description, the suction line 27 low pressure compressors 23a, 23b are connected to the output S of the first and second heat exchangers 15 which form the evaporator, and the discharge outlet 26 of the high pressure compressor 24 e It is connected to the inlet E of the first 5 and second 15 heat exchangers which forms the condenser.

The low pressure compressors 23a, 23b and high pressure 24 each comprise a housing 30 receiving lubricant, and in particular mineral or synthetic oil, which can be driven by the coolant to lubricate the low pressure compressors 23a, 23b and high pressure 24 and the other components of the coolant circuit. In this regard, the low pressure compressors 23a, 23b and high pressure 24 may be hermetic type, in which the oil is accumulated in the housing 30 at the suction pressure (typically scroll compressors or piston). The housings 30 are provided with respective taps 31 located on their nominal oil levels.

To allow a single-stage operation in addition to a two-stage operation which will be described below, according to conditions which will also be described in the following description, the compression unit 20 comprises a branch line 11 provided a valve 12 connected in parallel with the low pressure compression stage 21, with an upstream end connected upstream of the suction line 27 and a downstream end connected downstream of the discharge line 28 of the low pressure compressors 23a , 23b. The bypass line 11 bypasses the low pressure compression stage 21 to use only the high pressure compression stage 22 in the single-stage operation.

As shown, a bypass line 3 provided with a valve 4 may also be provided in parallel with the high pressure compression stage 22, with an upstream end connected upstream of the suction inlet 25 and a connected downstream end. downstream of the discharge outlet 26 of the high-pressure compressor 24. This bypass line 3 has a role of protection against possible high pressures in the event of failure of the high-pressure compressor 24 while the low-pressure compressors 23a, 23b are in walk.

In the embodiment shown, the heat exchange system, used in a heat pump mode described below and according to the two-stage operation, operates according to an injection cycle with a subcooling exchanger 45 or economizer.

For this purpose, the subcooling exchanger 45 is connected to the first end 6 of the first heat exchanger 5 and to the second end 17 of the second heat exchanger 15. The heat exchange system 1 further comprises a heat pipe. injection 46 connecting the second end 17 of the second heat exchanger at the suction inlet 25 of the high-pressure compressor 24 through the subcooling exchanger 45. An expander 47 is placed in the injection line 46 between the second heat exchanger 15 and the subcooling exchanger. In this embodiment, a liquid reservoir 48 may be provided. It is thus possible to cool the heat transfer fluid between the low pressure compression stage 21 and the high pressure compression stage 22 to limit the temperature at the discharge outlet 26 of the high pressure compression stage 22 and thereby achieve a higher condensing pressure. The cooling is carried out here by taking condensed heat transfer fluid at the outlet of the condenser and re-injecting it between the delivery line 28 of the low pressure compression stage 21 and the suction inlet 25 of the compression stage. high pressure 22.

The invention is however not limited to a heat exchange system implementing an injection cycle with a subcooling exchanger and applies to a heat exchange system using for example an injection cycle total or a partial injection cycle, the heat exchange system being adapted accordingly.

As it appears on figures 1 and 2 , the heat transfer fluid circuit also comprises a distribution circuit 40 for circulating the coolant from the compression unit 20 to the first heat exchanger 5 or from the compression unit 20 to the second heat exchanger 15 so to ensure the reversibility, or invertibility, of the heat exchange system 1.

In particular, the distribution circuit 40 comprises a compression loop 41 in which the low-pressure compressors 23a, 23b and high-pressure 24 are placed, and a four-way valve 42 connecting the compression loop 41 to the first 5 and second 15 heat exchangers. heat. The four-way valve 42 is adapted to circulate the heat transfer fluid from one of the first 5 and second 15 heat exchangers and entering the compression loop 41 to the suction line 27 of the low-pressure compressors 23a, 23b, and for distributing the heat transfer fluid from the discharge outlet 26 of the high pressure compressor 24 to the other heat exchanger 5, 15.

The expansion unit 10 comprises an expansion valve connecting, via one or more pipes, the outlet S of that of the first 5 and second 15 heat exchangers. heat which forms the condenser and the inlet E of that of the first 5 and second 15 heat exchangers which forms the evaporator.

The heat exchange system 1 also comprises an air circuit 35 associated with the first heat exchanger 5 to achieve a heat exchange between the coolant and the outside air, and a water circuit 36 associated with the second heat exchanger 15 to achieve a heat exchange between the coolant and the water circulating inside the space 2. In particular, the air circuit 35 may comprise pipes, not shown, connected to an air intake and an air outlet, and a fan 39 adapted to circulate the air between the air inlet and the air outlet through the first heat exchanger 5. The water circuit 36, for example d a sanitary heating or floor heating installation may include pipes connected to a pumping system ensuring the circulation of water in the pipes.

Depending on the direction of circulation of the coolant, the heat exchange system 1 can operate in an air conditioner mode ( figure 1 ) or in a heat pump mode ( figure 2 ). A control of the heat exchange system 1 between the different modes is provided by a control unit connected to the coolant circuit. The control unit comprises for example an electronic microprocessor to which a temperature sensor adapted to measure an outside temperature of the outside air is connected. Other sensors or measuring instruments of the control unit can be connected to the electronic microprocessor. The control unit may also include a memory in which different data, and in particular a threshold temperature for the outside temperature, are stored.

The control of the heat exchange system 1 according to the air conditioner mode, the heat pump mode and the various operations described in the following description in connection with the heat pump mode can be performed depending on the need for cooling or heating of the inner environment. The need for cooling or heating can be determined in any suitable manner. For example, an operator can choose the mode and operation by acting directly on an input interface of the control unit. Alternatively, the control unit can determine the mode and operation of the heat exchange system 1 directly or indirectly from a measured quantity and a corresponding corresponding threshold value. The control unit may for example comprise a thermostat measuring a temperature of the internal environment and determining the mode and operation of the heat exchange system 1 from a set temperature for the indoor environment. The control unit can further determine the mode and operation of the heat exchange system 1 from the outside temperature, in particular by means of a water law stored in the memory of the control unit. . It can also be provided that the mode and operation of the heat exchange system is determined by a compression ratio obtained by making a ratio between a suction pressure of the compression unit 20 and a discharge pressure of the compressor. compression unit 20. The compression ratio is high when the outside temperature is low and, conversely, it is low when the outside temperature is high. The control unit can also qualify, or even quantify, the need for cooling or heating, to thus determine in particular if this need is important or moderate.

• depuis l'unité de compression 20 vers la deuxième extrémité 7, formant l'entrée E, du premier échangeur de chaleur 5, puis
• depuis la première extrémité 6, formant la sortie S, du premier échangeur de chaleur 5 vers la deuxième extrémité 17, formant l'entrée E, du deuxième échangeur de chaleur 15 au travers de l'unité de détente 10 et de l'échangeur de sous-refroidissement 45, puis
• depuis la première extrémité 16, formant la sortie S, du deuxième échangeur de chaleur 15 vers l'unité de compression 20.

Thus, when there is a need for cooling of the internal environment, the heat exchange system 1 is in air conditioner mode, represented on the figure 1 . The coolant circulates in a closed loop:

• from the compression unit 20 towards the second end 7, forming the inlet E, of the first heat exchanger 5, and then
• from the first end 6, forming the output S, of the first heat exchanger 5 to the second end 17, forming the inlet E, of the second heat exchanger 15 through the expansion unit 10 and the heat exchanger subcooling 45 and then
• from the first end 16, forming the output S, of the second heat exchanger 15 to the compression unit 20.

The second heat exchanger 15 forms the evaporator collecting heat from the interior and the first heat exchanger 5 forms the condenser transferring the heat to the outside air, so as to cool the internal environment.

• depuis l'unité de compression 20 vers la première extrémité 16, formant l'entrée E, du deuxième échangeur de chaleur 15, puis
• depuis la deuxième extrémité 17, formant la sortie S, du deuxième échangeur de chaleur 15 vers la première extrémité 6, formant l'entrée E, du premier échangeur de chaleur 5 au travers de l'unité de détente 10 et de l'échangeur de sous-refroidissement 45, puis
• depuis la deuxième extrémité 7, formant la sortie S, du premier échangeur de chaleur 5 vers l'unité de compression 20.

When there is a need for heating the indoor environment, the heat exchange system 1 is in heat pump mode, shown in FIG. figure 2 . The coolant circulates in a closed loop:

• from the compression unit 20 towards the first end 16, forming the inlet E, of the second heat exchanger 15, and then
• from the second end 17, forming the output S, of the second heat exchanger 15 towards the first end 6, forming the inlet E, of the first heat exchanger heat 5 through the expansion unit 10 and the subcooling exchanger 45, and then
• from the second end 7, forming the output S, of the first heat exchanger 5 to the compression unit 20.

The first heat exchanger 5 forms the evaporator which draws heat from the outside air and the second heat exchanger 15 forms the heat transfer condenser, thereby heating the interior medium.

For example, the control unit determines the existence of a heating requirement from the outside temperature and a threshold temperature.

In particular, when the outside temperature is above the threshold temperature, for example between 2 ° C and 8 ° C, the heating requirement is moderate and the compression ratio is compatible with a single-stage operation. The control unit then commands the start of the high-pressure compressor 24 and the stopping of the low-pressure compressors 23a, 23b which are bypassed via the pipe 11, an opening of the valve 12 being controlled by the unit control.

When the outside temperature is below the threshold temperature, the heating requirement is high and the required compression ratio requires multi-stage operation, and in particular in the embodiment shown a two-stage operation. The control unit then controls the start-up of the low-pressure compressors 23a, 23b in series with the high-pressure compressor 24.

In the two-stage operation, to improve the efficiency and the capacity of the heat pump, the control unit acts on the heat transfer fluid circuit so that a first portion of the coolant flows from the second end 17 (outlet) the second heat exchanger 15 (condenser) to the suction inlet 25 of the high pressure compressor 24 through the injection pipe 46, and a second portion of the heat transfer fluid from the second end 17 (outlet) of the second heat exchanger 15 (condenser) to the first end 6 (inlet) of the first heat exchanger 5 (evaporator).

During this operation, taking into account the external temperature, frost is formed on the first heat exchanger 5 acting as an evaporator. The control unit then periodically controls a defrost of the first heat exchanger 5. To do this the four-way valve 42 is controlled to reverse the cycle and connect the compression unit 20 between the outlet S, formed by the first end 16 of the second heat exchanger 15 and the inlet E formed by the second end 7 of the first heat exchanger 7, and by connecting the expansion unit 10 between the outlet S formed by the first end 6 of the first heat exchanger 5 and the inlet E formed by the second end 17 of the second heat exchanger 15. The control unit controls the shutdown of the low pressure compressors 23a, 23b and the start of the high pressure compressor 24.

To ensure the balancing of the oil levels in the crankcases 30 of the low-pressure compressors 23a, 23b and high-pressure 24, the heat exchange system 1 also comprises an oil balancing line 50 which connects the crankcases 30 of the crankcases. low pressure compressors 23a, 23b and high pressure 24 by connecting them at their connections 31 on their respective nominal oil levels. The balancing line 50 is controlled by the control unit to allow the implementation of a balancing process described below in connection with the figure 4 .

• des première 51 et deuxième 52 vannes agencées en parallèle entre le compresseur haute pression 24 et le compresseur basse pression BP1 23a de plus faible capacité pour réguler le transfert d'huile d'un étage de compression vers l'autre, et
• une conduite 53 reliant les carters 30 des compresseurs basse pression 23a, 23b entre leurs piquages 31 à leur niveau d'huile nominaux respectifs.

In the embodiment shown, the balancing line 50 comprises:

• first 51 and second 52 valves arranged in parallel between the high-pressure compressor 24 and the lower-pressure compressor BP1 23a of lower capacity for regulating the transfer of oil from one compression stage to the other, and
• a line 53 connecting the housings 30 of the low pressure compressors 23a, 23b between their connections 31 at their respective nominal oil level.

The first valve 51 makes it possible to transfer the oil during two-stage operation of the casing 30 of the high-pressure compressor 24 to the casing 30 of the low-pressure compressor BP1 23a of smaller capacity. The first valve 51 then has a direction passing from the housing 30 of the high pressure compressor 24 to the housing 30 of the low pressure compressor BP1 23a. The first valve 51 is preferably a float type valve which maintains the nominal oil level in the casing 30 of the high pressure compressor 24 and transfers the excess oil to the low pressure compressor BP1 23a thanks to the pressure difference between housings 30.

The second valve 52 makes it possible to transfer the oil from the casing 30 of the low-pressure compressor BP1 23a of smaller capacity to the casing 30 of the high-pressure compressor 24 when only the high-pressure compressor 24 is running (in two-stage operation this second valve remains closed). The second valve 52 then has a direction passing from the casing 30 of the LP1 low pressure compressor 23a to the casing 30 of the high pressure compressor 24, and a blocking direction from the casing 30 of the high pressure compressor 24 to the casing 30 of the LP1 low pressure compressor 23a. The second valve 52 is preferably a valve type valve, allowing the passage of oil only in the direction of the housing 30 of the LP1 low pressure compressor 23a to the housing of the high pressure compressor 24. In fact, when only the high pressure compressor 24 is in operation, the pressure drop created on the suction line causes the casing 30 of the high pressure compressor 24 is at a pressure slightly lower than that of the casing 30 of the LP1 low pressure compressor 23a.

A single oil separator 54, provided for example with a float valve, is connected to the discharge outlet 26 of the high pressure compressor 24. An oil return line 55 extends between the float valve of the oil separator 54 and a tapping on the housing 30 of the high-pressure compressor 24 located above the nominal oil level, to be able to return the oil collected in the oil separator 54 in the housing 30 of the high-pressure compressor 24 .

The figure 4 represents the main steps of the method of balancing the oil levels in the compression unit 20. The balancing method described in relation to the two-stage compression unit of the heat exchange system 1 described above applies to any invertible heat pump in which the coolant circuit comprises at least two separate compressors in series which can operate alternately in multi-stage, and in particular two-stage, and in single-stage, and in which the defrosting of the evaporator is done by cycle inversion.

To ensure the proper functioning of the heat exchange system 1, a maximum period T1 of two-stage operation before performing a defrost for the purposes of the oil balance is stored in the memory of the control unit. The control unit then comprises a counter C1 which increments the time during two-stage operation. In addition, a minimum defrost duration T2 or single-stage operation for the purposes of the oil balance is also stored in the memory of the control unit. The control unit then comprises a counter C2 which increments the time during defrosting or single-stage operation. For example, the maximum period T1 of two-stage operation is between three hours and 10 hours and the minimum duration T2 defrosting or single-stage operation is between one minute and 20 minutes.

When there is a heating requirement (S1) detected by the control unit, the heat exchange system 1 is in heat pump mode. The control unit then determines whether the heating requirement is large or moderate (S2), for example from the outside temperature. To do this, the control unit compares the outside temperature with the threshold temperature.

If the outdoor temperature is above the threshold temperature, there is a need for moderate heating and the heat pump is in single-stage operation (S3). During this operation, there is no risk of accumulation of oil in one of the housings 30. All the excess oil of the housings 30 of the low-pressure compressors 23a, 23b can be brought back to the crankcase 30 of the high pressure compressor 24 by the equalization line 50 through the second valve 52 (valve). The low pressure compressors 23a, 23b being stopped, there is no risk that their oil levels fall below their nominal levels. All the oil collected at the oil separator 54 can also be returned to the casing 30 of the high-pressure compressor 24. At the passage in single-stage operation, the counter C2 is started to count the one-stage operating time whereas counter C1 is reset (reset). It can be expected that when the counter C2 exceeds the minimum duration T2 of single-stage operation, the control unit checks whether there is a need for heating and whether the need is large or moderate.

If, however, the outside temperature is below the threshold temperature, there is a significant heating requirement and the heat pump is in two-stage operation (S4). During this operation, the excess oil of the casing 30 of the high-pressure compressor 24 can be transferred to the casings 30 of the low-pressure compressors 23a, 23b by the first valve 51 (float). When switching to two-stage operation, the counter C1 is started to count the two-stage operation time while the counter C2 is reset (reset).

There is, however, in this two-stage operation, a risk of accumulating the oil transported in the rest of the coolant circuit in the casings 30 of the low-pressure compressors 23a, 23b.

The oil separator 54 limits the amount of oil transported by the coolant. The accumulation of oil that may occur in the crankcase 30 low-pressure compressors 23a, 23b is thus very slowed down by the presence of the oil separator 54.

In addition, as explained above, to overcome the phenomenon of icing of the evaporator, the heat pump regularly performs the defrost (S5), especially when the counter C1 exceeds the maximum period T1. If necessary, to limit ice accumulation on the evaporator, it is possible to defrost with a shorter period. A defrost condition due to ice accumulation, based on excessive evaporator icing detection, may be different from the defrost condition due to the need for oil balance. In particular, a defrosting requirement due to ice accumulation can be detected from the difference between the outdoor temperature and the evaporation temperature or through pressure drop sensors on the air passing through the evaporator.

During defrost, oil return is similar to oil return in single-stage operation. At each defrost, the excess in the casings 30 of the low-pressure compressors 23a, 23b is thus brought back to the casing 30 of the high-pressure compressor 24 by the second valve 52 (valve). When switching to defrosting, the counter C2 is again started to count the operating time in defrost and the counter C1 is reset. A defrost termination condition due to defrosted evaporator, based on defrost detection of the evaporator, may be different from the defrost end condition due to the end of oil balance. In particular, the end of defrosting due to defrosted evaporator can be detected from a measurement of the condensation pressure.

When the counter C2 exceeds the minimum defrost duration T2 and the evaporator is defrosted, the heat pump can return to two-stage operation, checking continuously or periodically whether the heating requirement still exists.

For the oil balancing between the housings 30 of the low-pressure compressors 23a, 23b, the lower-pressure compressor BP2 23b of higher capacity having a higher suction mass flow rate than the low-pressure compressor BP1 23a of lower capacity, its pressure Carter 30 will tend to be lower. The excess oil from the casing 30 of the low pressure compressor BP1 23a can therefore be transported to the casing 30 of the low pressure compressor BP2 23b by pressure difference.

Moreover, at the level of the oil separator 54, the oil is separated from the coolant and collected. All collected oil is then returned to the housing 30 of the high pressure compressor 24 which is the oil reservoir of the coolant circuit.

The description has been made with a heat exchange system 1 in which the balancing line 50 comprises a float valve 51 and a flapper valve 52 arranged between the housings 30 of the low pressure compressor BP1 23a and the high pressure compressor 24. The invention is however not limited to this type of valve or this arrangement.

In particular, the use of one or more solenoid valves is provided.

In particular, on the figure 3b the float valve 51 is replaced by a solenoid valve 511. A flow reduction device 512, preferably of the capillary tube type, is optionally placed in series with the solenoid valve 511. The method of balancing the oil levels in this variant is similar to that described above in relation to the figure 4 , with particularity the control of the solenoid valve 511: when the heat exchange system operates in two-stage mode (S4), the solenoid valve 511 is open for a few seconds or fractions of seconds at a determined time interval. When the heat exchange system operates in defrost mode (S5) or single-stage mode (S3), the solenoid valve 511 is preferably open. Alternatively, when the heat exchange system operates in two-stage mode, the solenoid valve could be controlled by an oil level sensor in the housing 30 of the high pressure compressor 24.

Alternatively, the two valves 51, 52 could be replaced by a single solenoid valve. The figure 6 illustrates the process of balancing the oil levels in such a variant. The balancing process is similar to that previously described in relation to the figure 4 and will not be repeated in detail. On the figure 6 , the steps S1 ', S2', S3 ', S4' and S5 'respectively correspond to the steps S1, S2, S3, S4 and S5 of the figure 4 and reference is made to the description that has been made of these steps for more detail. In the case of a single solenoid valve, in two-stage operation (S4 '), the solenoid valve is open for a time T3, generally of a few seconds, for example between a half second and three seconds, at a determined time interval T4 for example between ten minutes and two hours. In single-stage operation (S3 '), the solenoid valve is always open.

In another variant, the figure 5 illustrates a single valve 56 combining the functions of the float valve and the valve described above. In particular, in the same housing 57, a closure element 58, for example in the form of a ball movable relative to a seat 59 formed at one end of a pipe connecting the valve 56 to the housing 30 of the low compressor pressure 23a, is connected to a float 60. The assembly thus formed by the ball 58 and the float 60 is guided in translation relative to the housing 57. An excess of oil in the housing 30 of the high pressure compressor 24 opens the valve by means of the float 60 and an excess of oil in the casing 30 of the low-pressure compressor 23a opens the valve by acting directly on the ball 58 when the difference in pressure allows it.

Moreover, the valve or valves described above could be placed inside the housing 30 of the high-pressure compressor 24.

Claims (10)

1. Method for balancing levels of lubricant in a multilevel compression unit (20) of a heat exchange system (1) adapted for creating heat exchanges between the outside air located outside of a space (2) and an internal environment circulating inside the space (2), said heat exchange system (1) comprising:

   - first (5) and second (15) heat exchangers to exchange the heat respectively with the outside air and internal environment, said first (5) and second (15) heat exchangers each having an inlet (E) and an outlet (S) and forming an evaporator on one and a condenser on the other,

   - a heat transfer fluid circuit adapted for making a heat transfer fluid circulate between the evaporator and the condenser, said heat transfer fluid circuit comprising the multilevel compression unit (20) positioned between the outlet (S) of the evaporator and the inlet (E) of the condenser, and a damper unit (10) positioned between the outlet (S) of the condenser and the inlet (E) of the evaporator, said compression unit (20) comprising at least one first compressor (23) compressing the heat transfer fluid in the second compressor (24), the first (23) and second (24) compressors each comprising a crankcase (30) receiving the lubricant,

   - a balancing line (50) adapted for making the lubricant pass between the crankcases (30) of the first (23) and second (24) compressors, the balancing line (50) comprising a first valve (51) having a direction passing from the crankcase (30) of the second compressor (24) towards the crankcase (30) of the first compressor (23),

   - a control unit connected to the heat transfer fluid circuit and to the balancing line (50), said control unit being adapted for determining if there is a need to heat the internal environment and if the need for heating the internal environment is significant or softened, and for when there is a significant need to heat the internal environment:

   to control a multilevel functioning, by connecting the compression unit (20) between the outlet (7, S) of the first heat exchanger (5) and the inlet (16, E) of the second heat exchanger (15), by connecting the damper unit (10) between the outlet (17, S) of the second heat exchanger (15) and the inlet (6, E) of the first heat exchanger (5), and by making the first (23) and second (24) compressors function in series, and

   periodically, to control a defrosting of the first heat exchanger (5) by connecting the compression unit (20) between the outlet (16, S) of the second heat exchanger (15) and the inlet (7, E) of the first heat exchanger (5), by connecting the damper unit (10) between the outlet (6, S) of the first heat exchanger (5) and the inlet (17, E) of the second heat exchanger (15), by stopping the first compressor (23) and by making the second compressor (24) function,

   said balancing method being characterised in that it implements a second valve (52) arranged in parallel from the first valve (51) in the balancing line (50) of the heat exchange system (1), the second valve (52) having a direction passing from the crankcase (30) of the first compressor (23) towards the crankcase (30) of the second compressor (24), and a blocking direction from the crankcase (30) of the second compressor (24) towards the crankcase (30) of the first compressor (23),

   and in that it provides:

   - during the multilevel functioning, to transfer the surplus lubricant from the crankcase (30) of the second compressor (24) to the crankcase (30) of the first compressor (23) by the first valve (51) of the balancing line (50),

   - during the defrosting of the first heat exchanger (5), to transfer the surplus lubricant from the crankcase (30) of the first compressor (23) to the crankcase (30) of the second compressor (24) by the second valve (52) of the balancing line (50).
2. Balancing method according to claim 1, wherein the heat exchange system further comprises one single lubricant separator (54) positioned at the backflow of the second compressor (24) and a lubricant return pipe (55) between the lubricant separator (54) and the crankcase (30) of the second compressor (24),
   the balancing method providing to separate the lubricant from the heat transfer fluid, to collect the lubricant in the lubricant separator (54) and to return the lubricant collected towards the crankcase (30) of the second compressor (24).
3. Balancing method according to any one of the claims 1 and 2, wherein the control unit is adapted for when there is a need to heat the softened internal environment, to control a single-level functioning by connecting the compression unit (20) between the outlet (7, S) of the first heat exchanger (5) and the inlet (16, E) of the second heat exchanger (15), by connecting the damper unit (10) between the outlet (17, S) of the second heat exchanger (15) and the inlet (6, E) of the first heat exchanger (5), by stopping the first compressor (23) and by making the second compressor (24) function,
   the balancing method providing, during the single-level functioning, to transfer the surplus lubricant from the crankcase (30) of the first compressor (23) to the crankcase (30) of the second compressor (24) by the balancing line (50).
4. Balancing method according to any one of the claims 1 to 3, wherein the heat exchange system (1) comprises at least two first compressors (23a, 23b) with a set capacity, connected in parallel, and a second compressor (24) with a variable capacity, the first compressors (23a, 23b) having different capacities, the balancing line (50) comprising a pipe (53) connecting the crankcases (30) of the first compressors (23a, 23b),
   the balancing method providing to transfer the surplus lubricant from the crankcase (30) of the first compressor (23b) of a lower capacity towards the crankcase (30) of the other first compressor (23a).
5. Heat exchange system (1) adapted for creating heat exchanges between the outside air located outside a space (2) and an internal environment circulating inside the space (2), said heat exchange system (1) comprising:

   - first (5) and second (15) heat exchangers to exchange heat respectively with the outside air and the internal environment, said first (5) and second (15) heat exchangers each having an inlet (E) and an outlet (S) and forming an evaporator on one and a condenser on the other,

   - a heat transfer fluid circuit adapted for making a heat transfer fluid circulate between the evaporator and the condenser, said heat transfer fluid circuit comprising the multilevel compression unit (20) positioned between the outlet (S) of the evaporator and the inlet (E) of the condenser, and a damper unit (10) positioned between the outlet (S) of the condenser and the inlet (E) of the evaporator, said compression unit comprising at least one first compressor (23) and at least one second compressor (24) arranged in series, the first compressor (23) compressing the heat transfer fluid in the second compressor (24), the first (23) and second (24) compressors each comprising a crankcase (30) receiving the lubricant,

   - a balancing line (50) adapted for making the lubricant pass between the crankcases (30) of the first (23) and second (24) compressors, the balancing line (50) comprising a first valve (51) having a direction passing from the crankcase (30) of the second compressor (24) towards the crankcase (30) of the first compressor (23),

   - a control unit connected to the heat transfer fluid circuit and to the balancing line (50), said control unit being adapted for determining if there is a need to heat the internal environment and if the need for heating the internal environment is significant or softened, and for when there is a significant need to heat the internal environment:

   to control a multilevel functioning, by connecting the compression unit (20) between the outlet (7, S) of the first heat exchanger (5) and the inlet (16, E) of the second heat exchanger (15), by connecting the damper unit (10) between the outlet (17, S) of the second heat exchanger (15) and the inlet (6, E) of the first heat exchanger (5), and by making the first (23) and second (24) compressors function in series, and

   periodically, to control a defrosting of the first heat exchanger (5) by connecting the compression unit (20) between the outlet (16, S) of the second heat exchanger (15) and the inlet (7, E) of the first heat exchanger (5), by connecting the damper unit (10) between the outlet (6, S) of the first heat exchanger (5) and the inlet (17, E) of the second heat exchanger (15), by stopping the first compressor (23) and by making the second compressor (24) function,

   the heat exchange system being characterised in that the balancing line (50) comprises a second valve (52) arranged in parallel from the first valve (51), the second valve (52) having a direction passing from the crankcase (30) of the first compressor (23) towards the crankcase (30) of the second compressor (24) and a blocking direction from the crankcase (30) of the second compressor (24) towards the crankcase (30) of the first compressor (23),

   and in that said control unit is further adapted for implementing the balancing method according to any one of the claims 1 to 4.
6. Heat exchange system (1) according to claim 5, wherein the first valve (51) is a float valve and the second valve (52) is a damper.
7. Heat exchange system (1) according to claim 5, wherein the first valve (51) is a solenoid valve and the second valve (52) is a damper.
8. Heat exchange system (1) according to claim 7, wherein the solenoid valve, is assembled in series with a capillary tube-type flow reduction body.
9. Heat exchange system (1) according to any one of the claims 5 to 8, further comprising one single lubricant separator (54) positioned at the backflow of the second compressor (24) and a lubricant return pipe (55) between the lubricant separator (54) and the crankcase (30) of the second compressor (24).
10. Heat exchange system (1) according to any one of the claims 5 to 9, comprising at least two first compressors (23a, 23b) with a set capacity, connected in parallel, and a second compressor (24) with a variable capacity, the first compressors (23a, 23b) having different capacities, the balancing line (50) comprising a pipe (53) connecting the crankcases (30) of the first compressors (23a, 23b).

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