Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B31/00—Compressor arrangements
  • F25B31/002—Lubrication
  • F25B31/004—Lubrication oil recirculating arrangements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B1/00—Compression machines, plants or systems with non-reversible cycle
  • F25B1/10—Compression machines, plants or systems with non-reversible cycle with multi-stage compression
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B47/00—Arrangements for preventing or removing deposits or corrosion, not provided for in another subclass
  • F25B47/02—Defrosting cycles
  • F25B47/022—Defrosting cycles hot gas defrosting
  • F25B47/025—Defrosting cycles hot gas defrosting by reversing the cycle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2313/00—Compression machines, plants or systems with reversible cycle not otherwise provided for
  • F25B2313/027—Compression machines, plants or systems with reversible cycle not otherwise provided for characterised by the reversing means
  • F25B2313/02741—Compression machines, plants or systems with reversible cycle not otherwise provided for characterised by the reversing means using one four-way valve
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/06—Several compression cycles arranged in parallel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/07—Details of compressors or related parts
  • F25B2400/075—Details of compressors or related parts with parallel compressors
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2500/00—Problems to be solved
  • F25B2500/16—Lubrication

Definitions

• the invention relates to a method for balancing the levels of lubricant in a multi-stage compression unit of a heat exchange system and a heat exchange system implementing such a method.
• lubricant in a multi-stage compression unit of a heat exchange system and a heat exchange system implementing such a method lubricant in a multi-stage compression unit of a heat exchange system and a heat exchange system implementing such a method.
• 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 interior medium, said first and second heat exchangers each having an inlet and an outlet and forming one an evaporator and the other an condenser,
• a coolant circuit adapted to circulate a coolant 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 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 (low pressure) and at least a second compressor (high pressure) 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
• control unit connected to the heat transfer fluid circuit and to the balancing line, said control unit being adapted to determine whether there is a need for heating of the interior medium and whether the need for heating of the interior medium 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.
• the lubricant usually mineral or synthetic oil
• the lubricant is generally not miscible in the coolant but it can be driven and transported in the form of droplets by the coolant. 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.
• the balancing of the lubricant level between the compressors is an important problem.
• 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.
• 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 compressor from low pressure 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.
• the invention improves the situation.
• the invention proposes better management of the balancing of the lubricant levels in a multi-stage compression unit.
• 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 casing 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:
• 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.
• 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.
• 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.
• 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 interior medium, said first and second heat exchangers each having an inlet and an outlet and forming one an evaporator and the other an condenser,
• a coolant circuit adapted to circulate a coolant 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 an expansion unit placed between the condenser outlet 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 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 first and second valves arranged in parallel, 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 casing of the first compressor to the casing of the second compressor, and a blocking direction from the casing of the second compressor to the casing of the first compressor,
• control unit connected to the heat transfer fluid circuit and to the balancing line, said control unit being adapted to determine whether there is a need for heating of the interior medium and whether the need for heating of the interior medium 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
• 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,
• 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.
• FIG. 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 according to a air conditioner mode,
• FIG. 2 is a schematic representation of the heat exchange system of FIG. 1 operating in a heat pump mode
• FIG. 3 is a schematic representation of the multi-stage compression unit of the heat exchange system of FIG. 1, illustrating a line for balancing the lubricant levels between first and second compression stages of the unit. of compression, the balancing line comprising two separate valves to ensure transfers of excess lubricant between the first and second compression stages,
• FIG. 3b is a variant of the multi-stage compression unit of Figure 3 by the elements constituting the balancing line.
• FIG. 4 is a diagram illustrating steps of the method for balancing the lubricant levels in the multi-stage compression unit of the heat exchange system of FIG. 2;
• FIG. 5 is a diagrammatic representation of a valve of the balancing line of a variant of the heat exchange system of FIG. 1, the valve alone ensuring transfers of excess lubricant between first and second compression stages,
• FIG. 6 is a diagram illustrating steps of the method of balancing the lubricant levels in the multi-stage compression unit in another variant of the heat exchange system of FIG. 1, in which a single solenoid valve provides the transfers of excess oil between first and second stages of compression.
• FIGS. 1 and 2 show a heat exchange system 1 respectively for cooling and heating an internal medium, for example water, circulating in a space 2, such as a part of a dwelling, a technical room or other.
• an internal medium for example water, circulating in a space 2, such as a part of a dwelling, a technical room or other.
• 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) heat taken (Figure 2), either to cool the water by taking heat (cold source) and transferring to the outside air (hot source) heat taken (Figure 1).
• the heat exchange system 1 comprises:
• first heat exchanger 5 selectively forming an evaporator or a condenser, intended to perform heat exchanges with the outside air, the first heat exchanger having a first end 6 and a second end which form one input 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 having a first end and a second end forming an inlet; E and the other an output S,
• heat transfer fluid includes a multi-stage compression unit
• the compression unit 20 is bi-staged and comprises a first compression stage 21 and a second compression stage 22 arranged in series.
• 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.
• the low-pressure compressors 23a, 23b respectively have different displacements.
• the low-pressure compressor 23b, identified BP2 in FIG. 3 has a higher capacity than that of the low-pressure compressor 23a, identified BP1 in FIG. 3.
• the low-pressure compression stage 21 could comprise a or more than 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 as HP in FIG. 3.
• the high-pressure compressor 24 is, for example, of variable capacity, and especially of variable speed.
• 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.
• 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.
• 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.
• 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.
• the compression unit 20 comprises a branch line 1 1 provided with 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 1 1 bypasses the low pressure compression stage 21 to use only the high pressure compression stage 22 in the single-stage operation.
• 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.
• 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.
• 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.
• 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.
• the heat transfer fluid circuit also comprises a distribution circuit 40 making it possible to circulate the heat transfer fluid from the compression unit 20 to the first heat exchanger 5 or from the compression unit To the second heat exchanger 15 to ensure the reversibility, or invertibility, of the heat exchange system 1.
• 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 output 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.
• 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.
• 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.
• an operator can choose the mode and operation by acting directly on an input interface of the control unit.
• 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.
• the heat exchange system 1 when there is a need for cooling of the internal environment, the heat exchange system 1 is in air conditioner mode, shown in FIG. 1.
• the heat transfer fluid then circulates in a closed loop:
• 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.
• the heat exchange system 1 is in heat pump mode, shown in Figure 2.
• the heat transfer fluid then circulates in a closed loop:
• 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.
• the control unit determines the existence of a heating requirement from the outside temperature and a threshold temperature.
• the control unit controls the start-up 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 control unit.
• the outside temperature is below the threshold temperature, the heating requirement is large 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.
• 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).
• 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.
• 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.
• the heat exchange system 1 also comprises an oil balancing line 50 which connects the casings 30 of the low pressure compressors 23a, 23b and high pressure 24 by connecting them at their taps 31 to their respective nominal oil levels.
• the balancing line 50 is controlled by the control unit to allow the implementation of a balancing method described below in relation to FIG. 4.
• the balancing line 50 comprises:
• first 51 and second 52 valves arranged in parallel between the high-pressure compressor 24 and the low-pressure compressor BP1 23a of smaller capacity for regulating the transfer of oil from one compression stage to the other, and
• 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 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 .
• FIG. 4 represents the main steps of the method of balancing the oil levels in the compression unit 20.
• the balancing method described in relation with the two-stage compression unit of the heat exchange system 1 describes 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 by cycle inversion.
• 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.
• 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.
• 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.
• the control unit 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.
• S1 heating requirement
• S2 moderate
• 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.
• 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.
• 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).
• the counter C1 is started to count the two-stage operation time while the counter C2 is reset (reset).
• 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 may be different from the defrost condition due to the need for oil balance.
• 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.
• oil return is similar to oil return in single-stage operation.
• a defrost termination condition due to defrosted evaporator may be different from the defrost end condition due to the end of oil balance.
• the end of defrosting due to defrosted evaporator can be detected from a measurement of the condensation pressure.
• the heat pump can return to two-stage operation, checking continuously or periodically whether the heating requirement still exists.
• 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.
• 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 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.
• the float valve 51 is replaced by a solenoid valve 51 1.
• a flow reduction device 512 preferably of the capillary tube type, is optionally placed in series with the solenoid valve 51 1.
• the method of balancing the oil levels in this variant is similar to that described above in relation to FIG. 4, with the particularity of the control of the solenoid valve 51 1: when the heat exchange system operates in a two-stage mode, stage (S4), the solenoid valve 51 1 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 51 1 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.
• FIG. 6 illustrates the method of balancing oil levels in such a variation. The balancing method is similar to that described above in connection with Figure 4 and will not be repeated in detail.
• the steps S1 ', S2', S3 ', S4' and S5 ' respectively correspond to the steps S1, S2, S3, S4 and S5 of FIG. 4 and reference will be made to the description which has been made these steps for more detail.
• FIG. 5 illustrates a single valve 56 combining the functions of the float valve and the valve described above.
• 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.
• valve or valves described above could be placed inside the housing 30 of the high-pressure compressor 24.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Compression-Type Refrigeration Machines With Reversible Cycles (AREA)

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• 2011
  • 2011-07-06 FR FR1156120A patent/FR2977657B1/fr not_active Expired - Fee Related
• 2012
  • 2012-07-04 WO PCT/FR2012/051564 patent/WO2013004974A1/fr active Application Filing
  • 2012-07-04 EP EP12738564.9A patent/EP2729744B1/de not_active Not-in-force

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