Compression mechanism oil equalizing circuit, refrigeration system heat source unit, and refrigeration system provided with the same

The present invention provides an oil equalizing circuit that can improve the reliability of the oil supply to the compression mechanisms in a refrigeration system provided with a plurality of compression mechanisms. The compressor group of the air conditioning system is equipped chiefly with first, second, and third compressors and an oil equalizing circuit. The oil equalizing circuit is equipped with the first, second and third oil separators provided on the discharge sides of the compressors; first, second, and third oil return pipes connecting the oil separators to the intake sides of the compressors; a communication pipe for allowing the oil return pipes to communicate with one another; first, second, and third oil ON-OFF switching mechanisms provided downstream of the parts where the oil return pipes connect to the communication pipe; and first, second, and third pressure reducing mechanisms provided upstream of the parts where the oil return pipes connect to the communication pipe.

TECHNICAL FIELD

The present invention relates to an equalizing circuit for a compression mechanism, a heat source unit for a refrigeration system, and a refrigeration system equipped with the same. More specifically, the present invention relates to a vapor compression refrigeration system provided with a plurality of compression mechanisms for compressing the refrigerant, the refrigeration system being further provided with an equalizing circuit for equalizing the distribution of oil among the compression mechanisms and a refrigeration system heat source unit.

BACKGROUND ART

One example of conventional vapor compression refrigeration systems provided with a plurality of compression mechanisms are air conditioning systems used to air-condition buildings. This kind of air conditioning system is provided with a plurality of user units and a heat source unit capable of accommodating the heating and cooling loads of the user units. In order to enable the system to be operated in a partial load mode, the heat source unit is provided with a circuit configuration made up of a plurality of comparatively small-capacity compression mechanisms connected in parallel. The compression mechanisms are provided with an oil equalizing circuit including oil separators connected to the discharge sides of the compression mechanisms, oil return pipes for returning the oil separated by the oil separators to the compression mechanisms, and oil equalizing pipes connected between the compression mechanisms for reducing imbalances in the amount of oil in the compression mechanisms.

In the conventional oil equalizing circuit just described, the amount of oil in each compression mechanism is ensured by providing oil return pipes and oil equalizing pipes. However, there are times when air conditioning systems provided with a plurality of compression mechanisms are run in a partial load mode in which some compression mechanisms are running and some are stopped and times when such systems are run in a partial load mode in which some compression mechanisms are operated with a reduced operating load using inverter control or the like. During these various operating patterns, it is sometimes difficult to supply oil sufficiently to the compression mechanisms that are running. Thus, the reliability of the oil supply achieved with conventional oil equalizing circuits is insufficient.

DISCLOSURE OF THE INVENTION

The object of this invention is to provide an oil equalizing circuit that can improve the reliability of the oil supply to the compression mechanisms.

In a first embodiment of the present invention, a compression mechanism oil equalizing circuit is provided for equalizing the distribution of oil among the compression mechanisms in a vapor compression refrigeration system provided with a plurality of compression mechanisms for compressing the refrigerant. The oil equalizing circuit is provided with oil separators, oil return pipes, a communication pipe, oil ON-OFF switching means, and pressure reducing means. The oil separators are provided on the discharge side of the compression mechanisms and function to separate the oil from the gaseous refrigerant. The oil return pipes connect each oil separator to the intake side of its respective compression mechanism and allow the oil separated by the oil separators to be delivered to the intake sides of the compression mechanisms. The communication pipe is connected to the oil return pipes so that the oil return pipes can communicate with each other. Oil ON-OFF switching means are provided in each oil return pipe. The oil ON-OFF switching means serve both to ensure the flow of oil to the communication pipe from the oil separators and to turn on and shut off—by being opened and closed—the delivery of oil from each oil separator to the intake side of the respective compression mechanism. The pressure reducing means are provided in each oil return pipe or the communication pipe and serve to reduce the pressure of the oil sent from the oil separators to the communication pipe and the intake sides of the compressor mechanisms.

This compression mechanism oil equalizing circuit can supply the oil separated by the oil separators to the intake sides of the compression mechanisms by opening the oil ON-OFF switching means provided in the oil return pipes. Meanwhile, the supply of oil can be shut off by closing the oil ON-OFF switching means. As a result, the supply of oil to compression mechanisms that are stopped can be cut off and a sufficient amount of oil can be supplied to the compression mechanisms that are running, thereby improving the reliability of the oil supply to the compression mechanisms.

In a second embodiment of the present invention, a compression mechanism oil equalizing circuit is provided in accordance with the first aspect, wherein the oil separators are provided so as to correspond to each of the compression mechanisms.

In a third aspect of the present invention, a compression mechanism oil equalizing circuit is provided in accordance with the first aspect or the second aspect, wherein the oil separators each include a first stage oil separator that is connected to the dischar side of the compression mechanism and configured to separate oil from the gaseous rigerant and a second stage oil separator that is connected to the first stage oil separator and configured to collect the oil separated by the first stage oil separator. The oil return pipes are connected to the second stage oil separators.

With this compression mechanism oil equalizing circuit, the oil separated from the gaseous refrigerant in the first stage oil separator can be immediately sent to the second stage oil separator, thereby reducing the amount of oil mixing with the gaseous refrigerant flowing out of the first stage oil separator.

In a fourth aspect of the present invention, a compression mechanism oil equalizing circuit is provided in accordance with the third aspect and further provided with gas return pipes connecting the gas phase sections of the second stage oil separators to the intake sides of the compression mechanisms.

With this compression mechanism oil equalizing circuit, the gaseous refrigerant and other gaseous components mixed with the oil sent from the first stage oil separator and collected in the second stage oil separator can be returned to the intake side of the compression mechanism, thereby increasing the separating capacity of the oil separator as a whole.

In a fifth aspect of the present invention, a compression mechanism oil equalizing circuit is provided in accordance with the first to fourth aspects, wherein the oil ON-OFF switching means are provided downstream of the arts where the oil return pipes connect to the communication pipe.

With this compression mechanism oil equalizing circuit, the oil ON-OFF switching means are provide downstream of the parts where the oil return pipes connect to the communication pipe. As a result, both the function of turning on and shutting off the delivery of oil to the intake side of the compression mechanism and the function of ensuring the flow of oil to the communication pipe from the oil separator can be accomplished with a single oil ON-OFF switching means, thereby reducing the number of parts making up the oil equalizing circuit.

In a sixth aspect of the present invention, a compression mechanism oil equalizing circuit is provided in accordance with any one of the first to fifth aspects, wherein the pressure reducing means are provided upstream of the parts where the oil return pipes connect to the communication pipe.

With this compression mechanism oil equalizing circuit, the pressure reducing means are provided upstream of the parts where the oil return pipes connect to the communication pipe. As a result, both the function of reducing the pressure of the oil flowing to the intake side of the compression mechanism and the function of reducing the pressure of the oil flowing toward the communication pipe can be accomplished with a single pressure reducing means, thereby reducing the number of parts making up the oil equalizing circuit.

In a seventh aspect of the present invention, a compression mechanism oil equalizing circuit is provided in accordance with any one of the first to sixth aspects, wherein the pressure reducing means are capillary tubes.

With this compression mechanism oil equalizing circuit, the structure is simplified because capillary tubes are used as the pressure reducing means.

In the eighth aspect of the present invention, a refrigeration system is provided with a plurality of compression mechanisms for compressing the refrigerant, an oil equalizing circuit in accordance with any one of the first to seventh aspects for equalizing the distribution of oil among the compression mechanisms, and an oil equalization control means. The oil equalization control means detects if the compression mechanisms are running or stopped, executes control to close the oil ON-OFF switching means corresponding to the stopped compression mechanisms so that oil does not flow to the intake sides of the stopped compression mechanisms, and executes control to open the oil ON-OFF switching means corresponding to running compression mechanisms so that oil is supplied to the intake side of the running compression mechanisms.

Since this refrigeration system is provided with an oil equalization control means for controlling the oil equalizing circuit, oil can be supplied exclusively to the compression mechanisms that are running by opening and closing the oil ON-OFF switching means of the compression mechanisms in accordance with whether or not each compression mechanism is running. Thus, the reliability of the oil supply to the compression mechanisms can be improved.

In the ninth aspect of the present invention, a refrigeration system is provided with a plurality of compression mechanisms for compressing the refrigerant, an oil equalizing circuit in accordance with any one of the first to seventh aspects for equalizing the distribution of oil among the compression mechanisms, and an oil equalization control means. The oil equalization control means detects if the compression mechanisms are running or stopped, executes control to close the oil ON-OFF switching means corresponding to the stopped compression mechanisms so that oil does not flow to the intake sides of the stopped compression mechanisms, and, when one compression mechanism is running, executes control to open the oil ON-OFF switching means corresponding to the running compression mechanism so that oil is supplied to the intake side of the running compression mechanism. When there are two or more compression mechanisms that are running, oil is supplied to the intake side of all of the compression mechanisms that are running by opening the oil ON-OFF switching means corresponding to the running compression mechanism one at a time for a prescribed period of time each in a periodic manner, keeping the other oil ON-OFF switching means closed while one is open.

With this refrigeration mechanism, the oil equalization control means for controlling the oil equalizing circuit can achieve the following oil equalization operating modes. When one compression mechanism is running, the oil equalization control means supplies oil by opening only the oil ON-OFF switching means corresponding to the compression mechanism that is running. When two or more compression mechanisms are running, the oil equalization control means supplies oil to the compression mechanisms that are running by supplying oil to one running compression mechanism at a time for a prescribed period of time each in a periodic manner. When two or more compression mechanisms are running, oil is supplied intermittently to only one compression mechanism at a time through the oil return pipes and, as a result, oil is supplied to all of the running compression mechanisms with certainty. Thus, the reliability of the oil supply to the compression mechanisms can be improved.

In a tenth aspect of the present invention, a refrigeration system is provided in accordance with the ninth aspect, wherein the oil equalization control means controls the oil ON-OFF switching means corresponding to the compression mechanisms that are running in such a manner that when one oil ON-OFF switching means is switched from the closed state to the open state, there is a transitional period which both oil ON-OFF switching means are in the open state simultaneously.

With this refrigeration system, the oil equalization control means for controlling the oil equalizing circuit controls the oil ON-OFF switching means in such a manner that when one oil ON-OFF switching means is switched from the open state to the closed state and another oil ON-OFF switching means is switched from the closed state to the open state, there is a transitional period during which both oil ON-OFF switching means are in the open state simultaneously. Consequently, such undesirable situations as all of the oil ON-OFF switching means being closed such that the discharge of oil from the oil separators is obstructed can be prevented. As a result, the flow of oil through the oil equalizing circuit can be switched in a reliable manner.

In an eleventh aspect of the present invention, a refrigeration system heat source unit is a heat source unit for a refrigeration system provided with a compression mechanism for compressing the refrigerant, the heat source unit being provided with an oil separator, an oil return pipe, and a connection pipe. The oil separator is provided on the discharge side of the compression mechanism and serves to separate oil from the gaseous refrigerant. The oil return pipe is provided with an oil ON-OFF switching means that can turn on and shut off the supply of oil from the oil separator to the intake side of the compression mechanism. The connection pipe is connected to the oil return pipe between the oil separator and the oil ON-OFF switching means and makes it possible to connect to the oil return pipes of the compressor mechanisms of other heat source units.

With this refrigeration system heat source unit, when a plurality of heat source units are connected together in parallel and the oil ON-OFF switching means of the oil return pipes of the heat source units are opened, oil separated by the oil separators can be supplied to the intake side of the compression mechanisms of the heat source units. Meanwhile, the supply of oil to the intake sides of the compression mechanisms of the heat source units can be shut off by closing the oil ON-OFF switching means provided in the oil return pipes of the heat source units. As a result, the supply of oil to compression mechanisms that are stopped can be cut off and oil can be supplied exclusively to the compression mechanisms that are running, thereby improving the reliability of the oil supply to the compression mechanisms.

In a twelfth aspect of the present invention, a refrigeration unit heat source unit is provided in accordance with the eleventh aspect, wherein the oil separator includes a first stage oil separator that is connected to the discharge side of the compression mechanism and configured to separate oil from the gaseous refrigerant and a second stage oil separator that is connected to the first stage oil separator and configured to collect the oil separated by the first stage oil separator. The oil return pipe is connected to the second stage oil separator.

With this refrigeration system heat source unit, the oil separated from the gaseous refrigerant in the first stage oil separator can be immediately sent to the second stage oil separator, thereby reducing the amount of oil mixing with the gaseous refrigerant flowing out of the first stage oil separator.

In a thirteenth aspect of the present invention, a refrigeration system heat source is provided in accordance with the twelfth aspect, and further provided with a gas return pipe connecting the gas phase section of the second stage oil separator to the intake side of the compression mechanism.

With this refrigeration system heat source unit, the gaseous refrigerant and other gaseous components mixed with the oil sent from the first stage oil separator and collected in the second stage oil separator can be returned to the intake side of the compression mechanism, thereby increasing the separating capacity of the oil separator as a whole.

In a fourteenth aspect of the present invention, a refrigeration system is provided with a plurality of refrigeration system heat source units in accordance with any one of the eleventh to thirteenth aspects and a communication pipe connecting the connection pipes of the heat source units together.

With this refrigeration system, oil can be equalized among the heat source units because the oil return pipes of the oil separators of the heat source units are connected together.

PREFERRED EMBODIMENTS OF THE INVENTION

Embodiments of compression mechanism oil equalizing circuits and refrigeration systems equipped therewith will now be described with reference to the drawings.

(1) Constituent Features of the Refrigerant Circuit and Oil Equalizing Circuit of an Air Conditioning System

FIG. 1is a schematic view of the refrigerant circuit of an air conditioning system1serving as a first embodiment of a compression mechanism oil equalizing circuit in accordance with the present invention and a refrigeration system provided with the same.

The air conditioning system1is provided with one heat source unit2and a plurality of user units5(two in this embodiment) connected in parallel thereto. It is used, for example, to air-condition an office building or the like. The heat source unit2is equipped chiefly with first, second, and third compressors21ato21c,a four-way selector valve12, and heat-source-side heat exchanger13. In this embodiment, the heat-source-side heat exchanger13serves to exchange heat between the refrigerant and air or water serving as a heat source. The user units5are each equipped chiefly with an expansion valve14and a user side heat exchanger15. These devices12to15and21ato21care connected together in sequence by refrigerant piping to form the refrigerant circuit of the air conditioning system1.

The first, second, and third compressors21ato21care compression mechanisms for compressing the gaseous refrigerant that returns to the heat source unit2after passing through the user-side heat exchanger15of the user unit5and are connected in parallel to form a compressor group11. In this embodiment, the first compressor21ahas a built-in inverter so that its operating capacity can be varied by controlling the rotational speed and the second and third compressors21b,21care fixed-capacity compressors not provided with inverters.

The compressor group11is equipped with the following: first, second, and third compressors21ato21c;refrigerant intake main pipe22, first, second, and third intake branch pipes23ato23c;an oil equalizing circuit42; and a discharge merge pipe31.

The refrigerant intake main pipe22connects to the outlet of the four-way selector valve12. The discharge merge pipe31connects to the inlet of the four-way selector valve12. The first, second, and third intake branch pipes23ato23cbranch in a parallel manner from the refrigerant intake main pipe22and connect to the intake sides of the first, second, and third compressors21ato21c,respectively. The discharge sides of the first, second, and third compressors21ato21care connected to the discharge merge pipe31through first, second, and third oil separators24ato24c(discussed later). The check valves29and30are provided downstream of the second and third oil separators24b,24c,respectively.

The oil equalizing circuit42serves to equalize the oil distribution among the first, second, and third compressors21ato21cand is provided with the following: first, second, and third oil separators24ato24c;first, second, and third oil return pipes25ato25c;a communication pipe26; first, second, and third oil ON-OFF switching means27ato27c;and first, second, and third pressure reducing means28ato28c.The first, second, and third oil separators24ato24care connected to the discharge sides of the first, second, and third compressors21ato21cand serve to separate oil from the gaseous refrigerant. The first, second, and third oil return pipes25ato25cconnect first, second, and third oil separators24ato24cto the intake sides of the compressors21ato21c(more specifically, to the first, second, and third intake branch pipes23ato23c), respectively, and serve to deliver the oil separated by the first, second, and third oil separators24ato24cto the intake sides of the compressors21ato21c.The communication pipe26is connected to the oil return pipes25ato25cso that the oil return pipes25ato25ccan communicate with each other. The first, second, and third oil ON-OFF switching means27ato27care provided in the oil return pipes25ato25c,respectively, and serve both to ensure the flow of oil to the communication pipe26from the oil separators24ato24cand to turn on and shut off the delivery of oil from the first, second, and third oil separators24ato24cto the intake sides of the compressors21ato21c.More specifically, the first, second, and third oil ON-OFF switching means27ato27care solenoid valves provided downstream of the parts where the oil return pipes25ato25cconnect to the communication pipe26. The first, second, and third pressure reducing means28ato28care provided in the oil return pipes25ato25cor in the communication pipe26and serve to reduce the pressure of the oil that flows from the first, second, and third oil separators24ato24cto the intake sides of the compressors21ato21cand the communication pipe26. More specifically, the first, second, and third pressure reducing means28ato28care capillary tubes provided upstream of the parts where the oil return pipes25ato25cconnect to the communication pipe26.

The air conditioning system1is further provided with an oil equalization control means41that detects if the first, second, and third compressors21ato21care running or stopped and opens and closes the first, second, and third oil ON-OFF switching means27ato27caccordingly. More specifically, the oil equalization control means41detects if the compressors21ato21care running or stopped, executes control to close the oil ON-OFF switching means corresponding to the stopped compressors so that oil does not flow to the intake sides of the stopped compressors, and executes control to open the oil ON-OFF switching means corresponding to running compressors so that oil is supplied to the intake sides of the running compressors. In this embodiment, the oil equalization control means41is installed inside the heat source unit2.

(2) Operation of the Air Conditioning System and the Oil Equalizing Circuit

The operation of the air conditioning system1and oil equalizing circuit42of this embodiment will now be described usingFIGS. 1to2.FIG. 2illustrates the control states of the oil ON-OFF switching means27ato27cin the oil equalizing circuit42according to the operating pattern of the compressors21ato21c.

When the air conditioning system1is run, first the inverter-controllable first compressor21ais started. As a result, oil together with gaseous refrigerant flows from the refrigerant intake main pipe22into the first compressor21athrough the first intake branch pipe23a.The gaseous refrigerant drawn into the first compressor21ais then compressed and discharged, after which it flows into the first oil separator24a.Since the gaseous refrigerant discharged from the first compressor21acontains excess oil, the excess oil is separated from the gaseous refrigerant by vapor-liquid separation in the first oil separator24a.Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the first oil separator24a,flows into the discharge merge pipe31, and circulates through the refrigerant circuit of the air conditioning system1.

Meanwhile, the oil equalization control means41detects that the first compressor21ais running and the second and third compressors21b,21care stopped and issues an open command to the first oil ON-OFF switching means27aand a close command to the second and third oil ON-OFF switching means27band27ccorresponding to the second and third compressors21b,21c,which are stopped. (See {circle around (1)} ofFIG. 2.) As a result of this control, oil separated by the first oil separator24ais returned to the first intake branch pipe23athrough the first oil return pipe25aand is drawn again into the first compressor21aalong with gaseous refrigerant. Since the second and third compressors21b,21care stopped, the oil pressure at the parts where the second and third oil return pipes25b,25cconnect to the communication pipe26is held higher than the oil pressure at the part where the first oil return pipe25aconnects to the communication pipe26and oil that has collected in the second and third oil separators24b,24cand the second and third oil return pipes25b,25cflows into the first oil return pipe25athrough the communication pipe26. In this way, when only the first compressor21ais run, oil inside the refrigerant circuit is supplied only to the first compressor21a.

[2] Partial Load Operation (First and Second Compressors Running)

If, after the first compressor21ais started, the second compressor21bis started in order to increase the operating load, gaseous refrigerant flowing through the refrigerant intake main pipe22will be drawn into both the first compressor21aand the second compressor21b.Similarly to the gaseous refrigerant drawn into the first compressor21a,the gaseous refrigerant drawn into the second compressor21bis then compressed and discharged, after which it flows into the second oil separator24bwhere the gaseous refrigerant and oil are separated by vapor-liquid separation. Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the second oil separator24b,flows into the discharge merge pipe31, merges with the gaseous refrigerant discharged from the first compressor21a,and circulates through the refrigerant circuit of the air conditioning system1.

Meanwhile, the oil equalization control means41detects that the first and second compressors21a,21bare running and the third compressor21cis stopped and issues an open command to the first and second oil ON-OFF switching means27a,27band a close command to the third oil ON-OFF switching means27c.Then, the oil equalization control means41controls the first and second oil ON-OFF switching means27a,27bcorresponding to the first and second compressors21a,21b(which are running) such that they are repeatedly opened and closed alternately (periodically) for a prescribed time t1each, i.e., first the first oil ON-OFF switching means27ais opened for a prescribed time t1while the second oil ON-OFF switching means27bis closed and next the second oil ON-OFF switching means27bis opened for a prescribed time t1while the first oil ON-OFF switching means27ais closed, and so on. Thus, oil is supplied to the intake sides of the two compressors that are running, i.e., the first and second compressors21a,21b(see ({circle around (2)} of FIG.2). As a result, oil is delivered to the first and second compressors21a,21bwith certainty, although intermittently. The prescribed time t1is set to an amount of time that takes into account such factors as the time that oil resides inside the running compressors21a,21bso that oil deficiencies do not occur at the compressors21a,21bduring the periods when oil is not supplied to them. Furthermore, the oil equalization control means41opens and closes the first and second oil ON-OFF switching means27a,27bin such a manner that when one oil ON-OFF switching means (27a,for example) is switched from the open state to the closed state and the other oil ON-OFF switching means (27b,for example) is switched from the closed state to the open state, there is a transitional period Δt1during which both oil ON-OFF switching means27a,27bare in the open state simultaneously (see {circle around (2)} of FIG.2). More specifically, when the oil equalization control means41switches from a state in which one of the first and second oil ON-OFF switching means (27aor27b) is open and the other of the first and second oil ON-OFF switching means (27bor27a) is closed to the opposite state in which the open and closed oil ON-OFF switching means are reversed, it first opens the first or second oil ON-OFF switching means (27bor27a) that was closed while keeping the first or second oil ON-OFF switching means (27aor27b) that was open in the open state. It then closes the first or second oil ON-OFF switching means (27aor27b) that was open after the period Δt1has elapsed (see {circle around (2)} of FIG.2).

[3] Full Load Operation (First, Second, and Third Compressors Running)

If, after the second compressor21bis started, the third compressor21cis started in order to achieve full-load operation, gaseous refrigerant flowing through the refrigerant intake main pipe22will be drawn into the first, second, and third compressors21ato21c.Similarly to the gaseous refrigerant drawn into the first and second compressors21a,21b,the gaseous refrigerant drawn into the third compressor21cis compressed and discharged, after which it flows into the third oil separator24cwhere the gaseous refrigerant and excess oil are separated by vapor-liquid separation. Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the third oil separator24c,flows into the discharge merge pipe31, merges with the gaseous refrigerant discharged from the first and second compressors21a,21b,and circulates through the refrigerant circuit of the air conditioning system1.

Meanwhile, the oil equalization control means41detects that the first, second, and third compressors21ato21care running and issues open commands to the first, second, and third oil ON-OFF switching means27ato27c.Then, similarly to when two compressors, i.e., the first and second compressors21aand21b,are run, the oil equalization control means41controls the first, second and third oil ON-OFF switching means27ato27csuch that they are repeatedly opened and closed alternately (periodically) for a prescribed time t2each, i.e., first the first oil ON-OFF switching means27ais opened for a prescribed time t2while the second and third oil ON-OFF switching means27b,27care closed, next the second oil ON-OFF switching means27bis opened for a prescribed time t2while the first and third oil ON-OFF switching means27a,27care closed, then the third oil ON-OFF switching means27cis opened for a prescribed time t2while the first and second oil ON-OFF switching means27a,27bare closed, and so on. As a result, oil is supplied to the intake sides of the compressors that are running, i.e., the first, second, and third compressors21ato21c(see {circle around (3)} of FIG.2). As a result, oil is delivered to the first, second, and third compressors21ato21cwith certainty, although intermittently. Similarly to the previously described time period t1, the prescribed time t2is set to an amount of time that takes into account such factors as the time that oil resides inside the running compressors21ato21cso that oil deficiencies do not occur at the compressors21ato21cduring the periods when oil is not supplied to them.

Furthermore, similarly to when two compressors, i.e., the first and second compressors21aand21b,are run, the oil equalization control means41opens and closes the first, second, and third oil ON-OFF switching means27ato27cin such a manner that when one oil ON-OFF switching means (27a,27b,or27c) is switched from the open state to the closed state and another oil ON-OFF switching means (27a,27b,or27c) is switched from the closed state to the open state, there is a transitional period Δt2during which both oil ON-OFF switching means are in the open state simultaneously (see {circle around (3)} of FIG.2).

(3) Characteristic Features of the Air Conditioning System and the Oil Equalizing Circuit

The oil equalizing circuit42of this embodiment has the following characteristic features.

[1] Improved Reliability of the Oil Supply to the Compressors

With the oil equalizing circuit42of this embodiment, oil separated by the first, second, and third oil separators24ato24ccan be delivered to the intake sides of the compressors21ato21cby opening the first, second, and third oil ON-OFF switching means27ato27cprovided in the first, second, and third oil return pipes25ato25c.The delivery of oil to the compressors21ato21ccan also be shut off by closing the first, second, and third oil ON-OFF switching means27ato27c.Furthermore, since the oil return pipes25ato25care connected together by the communication pipe26, the oil in the oil return pipes whose oil ON-OFF switching means are closed flows through communication pipe26into the oil return pipes whose oil ON-OFF switching means are open. As a result, the supply of oil to compressors that are stopped can be cut off and a sufficient amount of oil can be supplied to the compressors that are running, thereby improving the reliability of the oil supply to the first, second, and third compressors21ato21c.

Also, since the oil return pipes25ato25care connected to the communication pipe26at a position downstream of the pressure reducing means28ato28c,the oil pressure in oil return pipes whose oil ON-OFF switching means are closed is higher than the oil pressure in the oil return pipes whose oil ON-OFF switching means are open. As a result, oil that has collected in oil separators and oil return pipes whose oil ON-OFF switching means27ato27care closed flows into the oil return pipes whose oil ON-OFF switching means are open through the communication pipe26. As a result, oil is reliably delivered to the compressors that are running.

[2] Simply Constructed Oil Equalizing Circuit

In the oil equalizing circuit42of this embodiment, the first, second, and third oil ON-OFF switching means27ato27care provided downstream of the parts where the oil return pipes25ato25cconnect to the communication pipe26. As a result, both the function of turning on and cutting off the delivery of oil to the intake side of the compressors21ato21cand the function of ensuring the flow of oil to the communication pipe26from the oil separators24ato24ccan be accomplished, thereby reducing the number of parts making up the oil equalizing circuit42.

Furthermore, with this oil equalizing circuit42, the first, second, and third pressure reducing means28ato28care provided upstream of the parts where the oil return pipes25ato25cconnect to the communication pipe26. As a result, both the function of reducing the pressure of the oil flowing to the intake side of the compressors21ato21cand the function of reducing the pressure of the oil flowing toward the communication pipe26can be accomplished, thereby reducing the number of parts making up the oil equalizing circuit42. Also, the construction is simple because capillary tubes are used for the first, second, and third pressure reducing means28ato28c.

[3] Periodic Open/Close Control of the Oil ON-OFF Switching Means Corresponding to Compressors that are Running

With the air conditioning system1of this embodiment, the oil equalization control means41can accomplish the following oil equalization operating modes. For example, when the first compressor21ais running and the second and third compressors21b,21care stopped (i.e., when the number of running compressors is one), oil can be supplied to the first compressor21aalone by opening only the first oil ON-OFF switching means27a(see {circle around (1)} of FIG.2). When the first and second compressors21a,21bare run and the third compressor21cis stopped, oil is supplied to both of the running compressors21a,21bby periodically supplying oil to one or the other of the running first and second compressors21a,21bfor a prescribed time t1each. Similarly, when the first, second, and third compressors21ato21care all run, oil is supplied to all of the running compressors21ato21cby periodically supplying oil to one or the other of the first, second, and third compressors21ato21cfor a prescribed time t2each. Thus, when two or more compressors are running, oil is supplied intermittently to only one compressor at a time through the oil return pipes and, as a result, oil is supplied reliably to all of the running compressors. Thus, the reliability of the oil supply to the compressors can be improved.

Additionally, the oil equalization control means41controls the oil ON-OFF switching means in such a manner that when one oil ON-OFF switching means is switched from the open state to the closed state and another oil ON-OFF switching means is switched from the closed state to the open state, there is a transitional period during which both oil ON-OFF switching means are in the open state simultaneously. Consequently, such undesirable situations as all of the oil ON-OFF switching means being closed such that the discharge of oil from the oil separators is obstructed can be prevented. As a result, the flow of oil through the oil equalizing circuit42can be switched in a reliable manner.

Moreover, since the oil equalization control means41operates the oil ON-OFF switching means27ato27cby detecting which of the first, second, and third compressors21ato21care running, the same control can be accomplished regardless of which compressors among the first, second, and third compressors21ato21care running. Thus, oil can be delivered reliably to two running compressors not only when it is the first and second compressors21a,21bthat are running, but also when, for example, it is the first and third compressors21a,21cthat are running. As a result, the service life of the compressors can be extended.

(1) Constituent Features of the Refrigerant Circuit and Oil Equalizing Circuit of the Air Conditioning System

FIG. 3is a schematic view of the refrigerant circuit of an air conditioning system101serving as a second embodiment of a compression mechanism oil equalizing circuit in accordance with the present invention and a refrigeration system provided with the same. The air conditioning system101is provided with a plurality of heat source units (three in this embodiment), i.e., first, second, and third heat source units102ato102c,and a plurality of user units (not shown in the figure) connected in parallel to the heat source units. The air conditioning system101is a large-capacity air conditioning system in which the first, second, and third heat source units102ato102care connected in parallel and each is provided with a plurality of compressors.

The first, second, and third heat source units102ato102cwill now be described. Since the second and third heat source units102b,102care constructed in the same manner as the first heat source unit102a,the first heat source unit102awill be described in detail while omitting similar descriptions of the second and third heat source units102b,102c.

The first heat source unit102ais equipped chiefly with a compression mechanism111a,a four-way selector valve112, and heat-source-side heat exchanger113. These devices111a,112,113are connected together along with the user units (not shown) with refrigerant piping to form the refrigerant circuit of the air conditioning system101.

The first compression mechanism111aserves to compress the gaseous refrigerant that returns to the heat source unit102afrom the user unit (not shown) and is provided with the following: first, second, and third compressors121a,122,123; a refrigerant intake main pipe124; first, second, and third intake branch pipes125,126,127; first, second, and third oil separators128a,129,130; and first, second, and third oil return pipes131a,132,133. The refrigerant intake main pipe124connects to the outlet of the four-way selector valve112. The refrigerant pipes at the outlets of the first, second, and third oil separators128a,129,130merge with the discharge merge pipe139. The discharge merge pipe139connects to the inlet of the four-way selector valve112.

Among the first, second, and third compressors121a,122,123, the first compressor121aruns constantly when the heat source unit102ais running and the second and third compressors122,123are started and stopped depending on the operating load of the first heat source unit102a.

The second intake branch pipe126branches from the refrigerant intake main pipe124and is connected such that it corresponds to the intake side of the second compressor122. The third intake branch pipe127branches from the refrigerant intake main pipe124at a position downstream of the second intake branch pipe126and is connected such that it corresponds to the intake side of the third compressor123. The first intake branch pipe125branches from the refrigerant intake main pipe124at a position downstream of the third intake branch pipe127and is connected to the intake side of the first compressor121a.The refrigerant intake main pipe124is arranged such that it slopes downward from the part where it connects to the second and third intake branch pipes126,127toward the part where it connects to the first intake branch pipe125.

The first, second, and third separators128a,129,130are connected to the discharge sides of the respective first, second, and third compressors121a,122,123in order to separate the oil from the gaseous refrigerant compressed by the first, second, and third compressors121a,122,123.

The first and second oil return pipes131a,132connect from the oil outlets of the first and second oil separators128a,129to the intake sides of the second and third compressors122,123, respectively. The third oil return pipe133is connected from the third oil separator130to the intake side of the first compressor121a.More specifically, the first and second oil return pipes131a,132are connected to the second and third intake branch pipes126,127, respectively, and the third oil return pipe133is connected to the refrigerant intake main pipe124at a position downstream of the second intake branch pipe126.

The first oil return pipe131ais connected to the intake side of the second compressor122such that oil is delivered to the refrigerant intake main pipe124due to gravity when the first compressor121ais running and the second and third compressors122,123are stopped. The second oil return pipe132is connected to the intake side of the third compressor123such that oil is delivered to the refrigerant intake main pipe124due to gravity when the first and second compressors121a,122are running and the third compressor123is stopped. More specifically, the second and third intake branch pipes126,127are arranged such that they slope downward from the part where they connect to the first and second oil return pipes131a,132, respectively, toward the part where they connect to the refrigerant intake main pipe124.

The second heat source unit102bhas a second compressor mechanism111b,a first compressor121b,a first oil separator128b,and a first oil return pipe131b,similarly to the first heat source unit102awhich has a first compressor mechanism111a,a first compressor121a,a first oil separator128a,and a first oil return pipe131a.Likewise, the third heat source unit102chas a third compressor mechanism111c,a first compressor121c,a first oil separator128c,and a first oil return pipe131c.

The air conditioning system101is further provided with an oil equalizing circuit142for equalizing the distribution of oil among the compressor mechanisms111ato111cof the heat source units102ato102c.The oil equalizing circuit142is made up of the following: the first oil separator128aand first return pipe131aof the first heat source unit102a;the first oil separator128band first oil return pipe131bof the second heat source unit102b;the first oil separator128cand first oil return pipe131cof the third heat source unit102c;a communication pipe134; first, second, and third oil ON-OFF switching means135ato135c;and first, second, and third pressure reducing means136ato136c.

The oil separators128ato128care connected to the discharge sides of the first, second, and third compressors121ato121cof the first, second, and third compression mechanisms111ato111c,respectively, and serve to separate oil from the gaseous refrigerant. As described previously, the oil return pipes131ato131cconnect the first oil separators128ato128cof the heat source units102ato102cto the intake sides of the compressors121ato121c,respectively, and serve to deliver oil separated by the oil separators128ato128cto the intake sides of the compressors121ato121c.The communication pipe134is connected to the oil return pipes131ato131cso that the oil return pipes131ato131ccan communicate with each other. More specifically, connection pipes137ato137cfor connecting to the communication pipe134are connected to the oil return pipes131ato131cbetween the oil separators128ato128cand the first, second, and third oil ON-OFF switching means135ato135c.The oil return pipes131ato131cof the heat source units102ato102care connected together through these connection pipes137ato137c.

The first, second, and third oil ON-OFF switching means135ato135care provided in the oil return pipes131ato131c,respectively, and serve both to ensure the flow of oil to the communication pipe134from the oil separators128ato128cand to turn on and shut off the delivery of oil from the oil separators128ato128cto the intake sides of the compressors121ato121c.More specifically, the first, second, and third oil ON-OFF switching means135ato135care solenoid valves provided downstream of the parts where the oil return pipes131ato131cconnect to the communication pipe134.

The first, second, and third pressure reducing means136ato136care provided in the oil return pipes131ato131cor in the communication pipe134and serve to reduce the pressure of the oil that flows from the oil separators128ato128cto the intake sides of the compressors121ato121cand the communication pipe134. More specifically, the first, second, and third pressure reducing means136ato136care capillary tubes provided upstream of the parts where the oil return pipes131ato131cconnect to the communication pipe134.

The air conditioning system101is further provided with an oil equalization control means141that detects if the compression mechanisms111ato111c(more specifically, first compressor121aof the first compression mechanism111a,the first compressor121bof the second compression mechanism111b,and the first compressor121cof the third compression mechanism111c) are running or stopped and opens and closes the first, second, and third oil ON-OFF switching means135ato135caccordingly. More specifically, the oil equalization control means141detects if each of the first, second, and third compressors111ato111cis running or stopped and executes control to close the oil ON-OFF switching means corresponding to the stopped compressors so that oil does not flow to the intake sides of the stopped compressors and control to open the oil ON-OFF switching means corresponding to running compressors so that oil is supplied to the intake sides of the running compressors. In this embodiment, the oil equalization control means141is built into the oil equalizing unit140along with the communication pipe134of the oil equalizing circuit142.

(2) Operation of the Air Conditioning System and the Oil Equalizing Circuit

The operation of the air conditioning system101and oil equalizing circuit142of this embodiment will now be described usingFIGS. 3to5.FIG. 4illustrates the refrigerant circuit and oil circuit of the compression mechanism111ainside the first heat source unit102a.FIG. 5is a simplified view showing only the compression mechanism and oil equalizing circuit portions of FIG.3and illustrating the connections between the compression mechanisms111ato111cof the heat source units102ato102cand the oil equalizing circuit142.

[1] Partial Load Operation (First Heat Source Unit Running)

When only the first heat source unit102aof the air conditioning system101is run, the first compressor121aof the first the compression mechanism111ais started and oil together with gaseous refrigerant flows from the refrigerant intake main pipe124into the first compressor121athrough the first intake branch pipe125. The gaseous refrigerant drawn into the first compressor121ais then compressed and discharged, after which it flows into the first oil separator128a.Since the gaseous refrigerant discharged from the first compressor121acontains excess oil, the excess oil is separated from the gaseous refrigerant by vapor-liquid separation in the first oil separator128a.Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the first oil separator128aand flows into the discharge merge pipe139.

Meanwhile, the oil equalization control means141detects that the first compression mechanism111aof the first heat source unit102a(more specifically, the first compressor121a) is running and that the second compression mechanism111bof the second heat source unit102band the third compression mechanism111cof the third heat source unit102care stopped and issues an open command to the first oil ON-OFF switching means135aand a close command to the second and third oil ON-OFF switching means135b,135c.As a result of this control, similarly to the first embodiment, oil separated by the first oil separator128ais returned to the first intake branch pipe125through the first oil return pipe131aand drawn again into the first compression mechanism111a(more specifically, the first compressor121a) along with gaseous refrigerant. In this way, when only the first compression mechanism111ais run, oil is supplied to the first compression mechanism111aand not to the other compression mechanisms111b,111c.

In the heat source unit102a,the oil separated in the first oil separator128aleaves the oil outlet of the first oil separator128a,passes through the first oil return pipe131a,and flows into the second intake branch pipe126. Then, since the second intake branch pipe126is configured so as to slope downward from the part where it connects to the first return pipe131ato the part where it connects to the refrigerant intake main pipe124, the oil that flows into the second intake branch pipe126from the first oil return pipe131aflows down the second intake branch pipe126due to the action of gravity and into the refrigerant intake main pipe124. After it flows into the refrigerant intake main pipe124, the oil is drawn into the first compressor121aagain along with gaseous refrigerant flowing through the refrigerant intake main pipe124. Since the refrigerant intake main pipe124slopes downward toward the first intake branch pipe125, the oil flowing into the refrigerant intake main pipe124flows readily toward the first intake branch pipe125. In this way, an oil supply circuit is formed in which oil is supplied to the first compressor121aonly.

If, after the first compressor121ais started, the second compressor122is started in order to increase the operating load of the first heat source unit102a,a portion of the gaseous refrigerant flowing through the refrigerant intake main pipe124will be drawn into the second compressor122through the second intake branch pipe126. Meanwhile, the oil that flows into the second intake branch pipe126from the first oil return pipe131ais drawn into the second compressor122along with the gaseous refrigerant flowing through the second intake branch pipe126. Similarly to the gaseous refrigerant drawn into the first compressor121a,the gaseous refrigerant drawn into the second compressor122is then compressed and discharged, after which it flows into the second oil separator129where the gaseous refrigerant and oil are separated by vapor-liquid separation. Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the second oil separator129and flows into the discharge merge pipe139.

In the first heat source unit102a,the oil separated in the second oil separator129leaves the oil outlet of the second oil separator129, passes through the second oil return pipe132, and flows into the third intake branch pipe127. Then, since the third intake branch pipe127, similarly to the second intake branch pipe126, is configured so as to slope downward from the part where it connects to the second return pipe132to the part where it connects to the refrigerant intake main pipe124, the oil that flows into the third intake branch pipe127from the second oil return pipe132flows into the refrigerant intake main pipe124due to the action of gravity. The third intake branch pipe127connects?? at a position closer to the first intake branch pipe125than the second intake branch pipe126does, i.e., at a position further downstream relative to the flow of the gaseous refrigerant. Consequently, the oil that flows into the refrigerant intake main pipe124from the third intake branch pipe127is drawn into the first compressor121aagain along with the gaseous refrigerant flowing through the refrigerant intake main pipe124and does not flow into the second compressor122. In this way, an oil supply circuit is formed inside the first compression mechanism111asuch that oil is supplied in turn to the first and second compressors121a,122only.

If, after the second compressor122is started, the third compressor123is started in order to raise the first heat source unit102ato full-load operation, a portion of the gaseous refrigerant flowing through the refrigerant intake main pipe124will be drawn into the third compressor123through the third intake branch pipe127. Meanwhile, the oil that flows into the third intake branch pipe127from the second oil return pipe132is drawn into the third compressor123along with the gaseous refrigerant flowing through the third intake branch pipe127. Similarly to the gaseous refrigerant drawn into the first and second compressors121aand122, the gaseous refrigerant drawn into the third compressor123is compressed and discharged, after which it is separated from the oil by vapor-liquid separation in the third oil separator130. Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the third oil separator130and flows into the discharge merge pipe139.

Meanwhile, inside the first heat source unit102a,the oil separated in the third oil separator130leaves the oil outlet of the third oil separator130, passes through the third oil return pipe133, and flows into refrigerant intake main pipe124at a position between where the first intake branch pipe125connects and where the third intake branch pipe127connects. In this way, an oil supply circuit is formed in which oil is supplied in turn to all of the compressors, i.e., the first, second, and third compressors121a,122,123, of the first compression mechanism111a.

[2] Partial Load Operation (First and Second Heat Source Units Running)

Now a situation in which, after the first heat source unit102ais started, the second compression mechanism111bof the second heat source unit102bis started in order to further increase the operating load will be described. The operation of the compressors that make up the second compression mechanism111bis not described here because it is the same as the operation of the first compression mechanism111a.

When the first and second compression mechanisms111a,111bare run, the oil equalization control means141detects that the first and second compression mechanisms111a,111bare running and the third compression mechanism111cis stopped and issues an open command to the first and second oil ON-OFF switching means135a,135band a close command to the third oil ON-OFF switching means135c.As a result of this control, the distribution of oil between the first and second compression mechanisms111a,111bis equalized similarly to the oil equalization control executed between the compressors21aand21bof the first embodiment and, thus, oil is supplied to the compression mechanisms that are running, i.e., the first and second compression mechanisms111a,111b.

[3] Partial Load Operation (First, Second, and Third Heat Source Units102ato102cRunning)

Now a situation in which, after the second compression mechanism111bis started, the third compression mechanism111cof the third heat source unit102cis started in order to achieve full-load operation will be described. The operation of the compressors that make up the third compression mechanism111cis not described here because it is the same as the operation of the first and second compression mechanisms111a,111b.

When the compression mechanisms111ato111care run, the oil equalization control means141detects that the compression mechanisms111ato111care running and issues an open command to the first, second, and third oil ON-OFF switching means135ato135c.As a result of this control, the distribution of oil between the compression mechanisms111ato111cis equalized similarly to the oil equalization control executed between the compressors21ato21cof the first embodiment and, thus, oil is supplied to the compression mechanisms that are running, i.e., the compression mechanisms111ato111c.

(3) Characteristic Features of the Air Conditioning System and the Oil Equalizing Circuit

With the oil equalizing circuit142of this embodiment, the same oil equalization control as is executed by the oil equalizing circuit42of the first embodiment is executed among the heat source units102ato102c.

Thus, the reliability of the oil equalization control in a large-capacity air conditioning system provided with a plurality of heat source units can be improved by executing oil equalization control among the heat source units102ato102c.

Also, while in the past it has been necessary to produce a variety of heat source units range from small capacity to large capacity in order to meet the demands of users, a large-capacity air conditioning system having highly reliable oil equalization control can be achieved by connecting a plurality of small-capacity heat source units together with the previously described oil equalizing circuit. Thus, the need to produce heat source units of various capacities is eliminated and manufacturing costs can be reduced.

Also, since the heat source units102ato102care each provided with connection pipes137ato137cserving as a pipe nozzle for connecting to the communication pipe134, when the heat source units102ato102care connected in parallel, the oil equalizing circuit142can be established with ease by merely connecting the communication pipe134to the connection pipes137ato137c.

Furthermore, onsite installation can be made easier by producing an oil equalizing unit140as a product that comprises an oil equalization control means141and a portion of an oil equalizing circuit142(i.e., communication pipe134, etc.) like those previously described.

(1) Constituent Features of the Refrigerant Circuit and Oil Equalizing Circuit of the Air Conditioning System

FIG. 6is a schematic view of the refrigerant circuit of an air conditioning system201serving as a third embodiment of a compression mechanism oil equalizing circuit in accordance with the present invention and a refrigeration system provided with the same. The air conditioning system201is provided with a plurality of heat source units (three in this embodiment), i.e., first, second, and third heat source units202ato202c,and a plurality of user units (not shown in the figure) connected in parallel to the heat source units. The air conditioning system201is a large-capacity air conditioning system in which, similarly to the air conditioning system101of the second embodiment, the first, second, and third heat source units202ato202care connected in parallel and each is provided with a plurality of compressors.

The first, second, and third heat source units202ato202cwill now be described. Since the second and third heat source units202b,202care constructed in the same manner as the first heat source unit202a,the first heat source unit202awill be described in detail while omitting similar descriptions of the second and third heat source units202b,202c(portions of the compression mechanisms of the second and third heat source units202b,202chave also been simplified in FIG.6).

The first heat source unit202ais equipped chiefly with a first compression mechanism211a,a four-way selector valve212, and heat-source-side heat exchanger213. These devices211a,212,213are connected together along with the user units (not shown) by refrigerant piping to form the refrigerant circuit of the air conditioning system201.

As shown inFIGS. 6 and 7, the first compression mechanism211aserves to compress the gaseous refrigerant that returns to the heat source unit202afrom the user units (not shown) and is provided with the following: first, second, and third compressors221a,222,223; a refrigerant intake main pipe224; first, second, and third intake branch pipes225,226,227; first, second, and third oil separators228a,229,230; and first, second, and third separator-side oil return pipes231a,232,233. The refrigerant intake main pipe224connects to the outlet of the four-way selector valve212. The refrigerant pipes at the outlets of the first, second, and third oil separators228a,229,230merge with the discharge merge pipe239. The discharge merge pipe239connects to the inlet of the four-way selector valve212.

Among the first, second, and third compressors221a,222,223, the first compressor221aruns constantly when the heat source unit202ais running and the second and third compressors222,223are started and stopped depending on the operating load of the first heat source unit202a.

The second intake branch pipe226branches from the refrigerant intake main pipe224and is connected such that it corresponds to the intake side of the second compressor222. The first intake branch pipe225and the third intake branch pipe227branch from the refrigerant intake main pipe224at positions farther downstream than the position where the second intake branch pipe226branches from the same and connect so as to correspond to the intake sides of the first compressor221aand third compressor223, respectively. The first, second, and third intake branch pipes225,226,227are configured such that they slope downward toward the parts where they connect to the refrigerant intake main pipe224.

The first, second, and third oil separators228a,229,230are connected to the discharge sides of the respective first, second, and third compressors221a,222,223in order to separate the oil from the gaseous refrigerant compressed by the first, second, and third compressors221a,222,223. The oil separator228ais designed to separate oil in two stages and has a first stage oil separator251athat is connected to the discharge side of the first compressor221aand configured to separate oil from the gaseous refrigerant and a second stage oil separator252athat is connected to the first stage oil separator251aand configured to collect the oil separated by the first stage oil separator251a.With this first oil separator228a,the oil separated from the gaseous refrigerant in the first stage oil separator251acan be immediately sent to the second stage oil separator252a,thereby reducing the amount of oil mixing with the gaseous refrigerant flowing out of the first stage oil separator251a.

The separator-side oil return pipe231ais connected from the oil outlet of the first oil separator228ato the intake side of the second compressor222. More specifically, the separator-side oil return pipe231ais connected to the second stage oil separator252aof the first oil separator228a.More specifically, the separator-side oil return pipe231ahas a separator-side oil ON-OFF switching means253a,a separator-side non-return means254a,and a separator-side pressure reducing means255a.The separator-side oil ON-OFF switching means253ais a solenoid valve for turning on and shutting off the supply of oil from the first oil separator228ato the intake side of the compressor222. The separator-side non-return means254ais a check valve that only allows oil to flow from the first oil separator228ato the intake side of the compressor222. The separator-side pressure reducing means255ais a capillary tube for reducing the pressure of the oil flowing from the first oil separator228ato the intake side of the second compressor222.

The second stage oil separator252aof the first oil separator228ais provided with a gas return pipe259athat connects the gas phase section inside the second stage oil separator252ato the intake side of the second compressor222. As a result, gaseous refrigerant and other gaseous components mixed with the oil sent from the first stage oil separator251aand collected in the second stage oil separator252acan be returned to the intake side of the second compressor222. The gas return pipe259ahas a pressure reducing means260acomprising a capillary tube for reducing the pressure of the oil flowing from the second stage oil separator252ato the intake side of the second compressor222.

The separator-side oil return pipe232is connected from the oil outlet of the second oil separator229to the intake side of the third compressor223. The separator-side oil return pipe232has a separator-side pressure reducing means237comprising a capillary tube for reducing the pressure of the oil flowing from the second oil separator229to the intake side of the third compressor223.

The separator-side oil return pipe233is connected from the third oil separator230to the intake side of the first compressor221a.The separator-side oil return pipe233has a separator-side pressure reducing means238comprising a capillary tube for reducing the pressure of the oil flowing from the third oil separator230to the intake side of the first compressor221a.

The separator-side oil return pipe231ais connected to the intake side of the second compressor222such that oil is delivered to the refrigerant intake main pipe224by gravity when the first compressor221ais running and the second and third compressors222,223are stopped. The separator-side oil return pipe232is connected to the intake side of the third compressor223such that oil is delivered to the refrigerant intake main pipe224by gravity when the first and second compressors221a,222are running and the third compressor223is stopped. More specifically, the second and third intake branch pipes226,227are arranged such that they slope downward from the parts where they connect to the separator-side oil return pipes231a,232, respectively, toward the parts where they connect to the refrigerant intake main pipe224.

Similarly to the first heat source unit202a,which is provided with a first compression mechanism211aincluding a first compressor221a,a first oil separator228acomprising a first stage oil separator251aand a second stage oil separator252a,and a separator-side oil return pipe231ahaving a gas return pipe259aand a separator side oil ON-OFF switching means253a,the second heat source unit202bis provided with a second compression mechanism211bincluding a first compressor221b,a first oil separator228bcomprising a first stage oil separator251band a second stage oil separator252b,and a separator-side oil return pipe231bhaving a gas return pipe259band a separator side oil ON-OFF switching means253b.Likewise, the third heat source unit202cis provided with a third compression mechanism211cincluding a first compressor221c,a first oil separator228ccomprising a first stage oil separator251cand a second stage oil separator252c,and a separator-side oil return pipe231chaving a gas return pipe259cand a separator side oil ON-OFF switching means253c.

The air conditioning system201is further provided with an oil equalizing circuit242for equalizing the distribution of oil among the heat source units202ato202c.The oil equalizing circuit242is made up of the following: a communication pipe234; the first oil separator228a,oil-equalization-side oil return pipe235a,and connection pipe236aof the first heat source unit202a;the first oil separator228b,oil-equalization-side oil return pipe235b,and connection pipe236bof the second heat source unit202b;the first oil separator228c,oil-equalization-side oil return pipe235c,and connection pipe236cof the third heat source unit202c.

The oil-equalization-side oil return pipes235ato235care provided in the heat source units202ato202c,respectively, and serve to connect the second stage oil separators252ato252cof the heat source units202ato202cto the intake sides of the first compressors221ato221c,respectively, so that oil separated by the first oil separators228ato228cis delivered to the intake sides of the compression mechanisms211ato211c(more specifically, the refrigerant intake main pipe). More specifically, the oil-equalization-side oil return pipes235ato235care connected the second stage oil separators252ato252cof the first oil separators228ato228cof the heat source units202ato202cand include the following: oil-equalization-side pressure reducing means256ato256c;first, second and third oil-equalization-side oil ON-OFF switching means257ato257c;and oil-equalization-side non-return means258ato258c.

The communication pipe234is connected to the oil-equalization-side oil return pipes235ato235cso that the oil-equalization-side oil return pipes235ato235ccan communicate with each other. More specifically, connection pipes236ato236care connected to the oil-equalization-purpose oil return pipes235ato235cbetween the first oil separators228ato228cand the oil-equalization-side oil ON-OFF switching means257ato257c,respectively. By connecting the connection pipes236ato236cto the communication pipe234, the oil-equalization-side oil return pipes235ato235cof the heat source units202ato202care allowed to communicate with each other.

The oil-equalization-side pressure reducing means256ato256care provided in the oil-equalization-side oil return pipes235ato235cand serve to reduce the pressure of the oil that flows from the first oil separators228ato228cto the intake sides of the compression mechanisms211ato211cand the communication pipe234. More specifically, the oil-equalization-side pressure reducing means256ato256care capillary tubes provided between the second stage oil separators252ato252cand the connection pipes236ato236c.

The first, second, and third oil-equalization-side oil ON-OFF switching means257ato257care provided in the oil-equalization-side oil return pipes235ato235c,respectively, and serve both to ensure the flow of oil to the communication pipe234from the first oil separators228ato228cand to turn on and shut off the delivery of oil from the first oil separators228ato228cto the intake sides of the compression mechanisms211ato211c.More specifically, the first, second, and third oil-equalization-side oil ON-OFF switching means257ato257care solenoid valves provided downstream of the parts where the oil-equalization-side oil return pipes235ato235cconnect to the communication pipe234.

The oil-equalization-side non-return means258ato258care check valves that only allow oil to flow from the first oil separators228ato228cto the intake sides of the compression mechanisms211ato211c.

The air conditioning system201is further provided with an oil equalization control means241that detects if the compression mechanisms211ato211c(more specifically, the first compressor221aof the first compression mechanism211a,the first compressor221bof the second compression mechanism211b,and the first compressor221cof the third compression mechanism211c) are running or stopped and opens and closes the first, second, and third oil-equalization-side oil ON-OFF switching means257ato257caccordingly. More specifically, the oil equalization control means241detects if the first, second, and third compression mechanisms211ato211cis running or stopped and executes control to close the oil ON-OFF switching means corresponding to the stopped compressors so that oil does not flow to the intake sides of the stopped compressors and control to open the oil ON-OFF switching means corresponding to running compressors so that oil is supplied to the intake sides of the running compressors.

(2) Operation of the Air Conditioning System and the Oil Equalizing Circuit

The operation of the air conditioning system201and oil equalizing circuit242of this embodiment will now be described usingFIGS. 6to7.

[1] Partial Load Operation (First Heat Source Unit Running)

When only the first heat source unit202aof the air conditioning system201is run, the first compressor221aof the compression mechanism211ais started and oil together with gaseous refrigerant flows from the refrigerant intake main pipe224into the first compressor221athrough the first intake branch pipe225. The gaseous refrigerant drawn into the first compressor221ais then compressed and discharged, after which it flows into the first oil separator228a.Since the gaseous refrigerant discharged from the first compressor221acontains excess oil, the excess oil is separated from the gaseous refrigerant by vapor-liquid separation in the first oil separator228a.Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the first oil separator228aand flows into the discharge merge pipe239. Since the first oil separator228ais made up of a first stage oil separator251aand a second stage oil separator252a,the oil separated from the gaseous refrigerant in the first stage oil separator251acan be immediately sent to the second stage oil separator252a,thereby reducing the amount of oil mixing with the gaseous refrigerant flowing out of the first stage oil separator251a.

Meanwhile, the oil equalization control means241detects that the first compression mechanism211aof the first heat source unit202a(more specifically, the first compressor221a) is running and that the second compression mechanism211bof the second heat source unit202band the third compression mechanism211cof the third heat source unit202care stopped and issues an open command to the first oil-equalization-side oil ON-OFF switching means257aand a close command to the second and third oil-equalization-side oil ON-OFF switching means257b,257c.As a result of this control, oil separated by the first oil separator228ais returned to the intake side of the first compression mechanism211athrough the oil-equalization-side oil return pipe235aand is drawn again into the first compression mechanism211a(more specifically, the first compressor221a) along with gaseous refrigerant. In this way, when only the first compression mechanism211ais run, oil is supplied to the first compression mechanism211aand not to the second and third compression mechanisms211b,211c.

In addition to issuing open and close commands to the first, second, and third oil-equalization-side oil ON-OFF switching means257ato257cas just described, the oil equalization control means241issues an open command to the separator-side oil ON-OFF switching means253aof the first heat source unit202a,which is running, and a close command to the separator-side oil ON-OFF switching means253b,253cof second and third heat source units, which are stopped. As a result, oil that has collected inside the oil separators228b,228c(more specifically, the second stage oil separators252b,252c) of the stopped heat source units202b,202cis sent to the oil-equalization-side oil return pipe235aof the first heat source unit202athrough the oil-equalization-side return pipes235b,235cand the communication pipe234and delivered to the intake side of the first compression mechanism211aof the first heat source unit202a.Thus, oil does not collect at the intake side of the compression mechanisms211b,211cof the stopped heat source units202b,202c.

In the heat source unit202a,the oil sent to the second stage oil separator252aof the first oil separator228ais temporarily collected in the second stage oil separator252a.Then, the gaseous refrigerant and other gaseous components mixed with the oil are sent to the intake side of the second compressor222through the gas return pipe259aand the other liquid components are sent to the intake side of the second compressor222through the separator-side oil return pipe231abecause the separator-side oil ON-OFF switching means253ais open. The oil that flows into the second intake branch pipe226from the second stage oil separator252athrough the separator-side oil return pipe231adescends through the second intake branch pipe226due to the action of gravity and is delivered to the refrigerant intake main pipe224. After it flows into the refrigerant intake main pipe224, the oil joins oil delivered from the other compression mechanisms211b,211cthrough the communication pipe234and is drawn into the first compressor221aagain along with gaseous refrigerant flowing through the refrigerant intake main pipe224.

If, after the first compressor221ais started, the second compressor222is started in order to increase the operating load of the first heat source unit202a,a portion of the gaseous refrigerant flowing through the refrigerant intake main pipe224will be drawn into both the second compressor222through the second intake branch pipe226. The oil that flows into the second intake branch pipe226from the gas return pipe259aand the separator-side oil return pipe231ais drawn into the second compressor222along with the gaseous refrigerant flowing through the second intake branch pipe226. Similarly to the gaseous refrigerant drawn into the first compressor221a,the gaseous refrigerant drawn into the second compressor222is then compressed and discharged, after which it is separated from the oil by vapor-liquid separation in the second oil separator229. Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the second oil separator229and flows into the discharge merge pipe239.

In the first heat source unit202a,the oil separated in the second oil separator229leaves the oil outlet of the second oil separator229, passes through the second oil return pipe232, and flows into the third intake branch pipe227. As a result, the oil that flows into the third intake branch pipe227from the separator-side oil return pipe232is delivered to the refrigerant intake main pipe224due to the action of gravity. The oil that flows into the refrigerant intake main pipe224from the third intake branch pipe227is drawn into the first compressor221aagain along with the gaseous refrigerant flowing through the refrigerant intake main pipe224and does not flow into the second compressor222.

If, after the second compressor222is started, the third compressor223is started in order to raise the first heat source unit202ato full-load operation, a portion of the gaseous refrigerant flowing through the refrigerant intake main pipe224will be drawn into the third compressor223through the third intake branch pipe227. The oil that flows into the third intake branch pipe227from the separator-side oil return pipe232is drawn into the third compressor223along with the gaseous refrigerant flowing through the third intake branch pipe227. Similarly to the gaseous refrigerant drawn into the second compressor222, the gaseous refrigerant drawn into the third compressor223is then compressed and discharged, after which it is separated from the oil by vapor-liquid separation in the second oil separator230. Then, the gaseous refrigerant passes through the refrigerant pipe at the outlet of the third oil separator230and flows into the discharge merge pipe239.

In the first heat source unit202a,the oil separated in the third oil separator230leaves the oil outlet of the third oil separator230, passes through the separator-side oil return pipe233, and flows into the first intake branch pipe225. In this way, oil is supplied in turn to all of the first, second, and third compressors221a,222,223of the first compression mechanism211a.

[2] Partial Load Operation (First and Second Heat Source Units Running)

Now a situation in which, after the first heat source unit202ais started, the second compression mechanism211bof the second heat source unit202bis started in order to further increase the operating load will be described. The operation of the compressors that make up the second compression mechanism211bis not described here because it is the same as the operation of the first compression mechanism211a.

When the first and second compression mechanisms211a,211bare run, the oil equalization control means241detects that the first and second compression mechanisms211a,211bare running and the third compression mechanism211cis stopped and issues an open command to the first and second oil-equalization-side oil ON-OFF switching means257a,257band a close command to the third oil-equalization-side oil ON-OFF switching means257c.The oil equalization control means241issues an open command to the separator-side oil ON-OFF switching means253a,253bof the first and second heat source units202a,202b,which are running. As a result of this control, the distribution of oil between the first and second compression mechanisms211a,211bis equalized similarly to the oil equalization control executed between the compressors21aand21bof the first embodiment and, thus, oil is supplied to the compression mechanisms that are running, i.e., the first and second compression mechanisms211a,211b.

[3] Full Load Operation (First, Second, and Third Heat Source Units Running)

Now a situation in which, after the second compression mechanism211bis started, the third compression mechanism211cof the third heat source unit202cis started in order to achieve full-load operation will be described. The operation of the compressors that make up the third compression mechanism211cis not described here because it is the same as the operation of the first and second compression mechanisms211a,211b.

When the compression mechanisms211ato211care run, the oil equalization control means241detects that the compression mechanisms211ato211care running and issues open commands both to the first, second, and third oil-equalization-side oil ON-OFF switching means257ato257cas well as to the separator-side oil ON-OFF switching means253ato253cof the first, second, and third heat source units202ato202c,which are running. As a result of this control, the distribution of oil between the compression mechanisms211ato211cis equalized similarly to the oil equalization control executed between the compressors21ato21cof the first embodiment and, thus, oil is supplied to the compression mechanisms that are running, i.e., the compression mechanisms211ato211c.

(3) Characteristic Features of the Air Conditioning System and the Oil Equalizing Circuit

With the oil equalizing circuit242of this embodiment, the same oil equalization control as is executed by the oil equalizing circuit142of the second embodiment is executed among the heat source units202ato202cand the same effects as the second embodiment are achieved.

Also with the oil equalization circuit of this embodiment, the separating capacity of the oil separator as a whole is improved because the first oil separators228ato228cof the heat source units202ato202care two-stage oil separators comprising a first stage oil separator251ato251cand a second stage oil separator252ato252c.

Although embodiments of the present invention have been described herein with reference to the drawings, the specific constituent features are not limited to those of these embodiments and variations can be made within a scope that does not deviate from the gist of the invention.

(1) It is also acceptable to provide a common oil separator of the kind described in the first embodiment with respect to a plurality of compressors.

(2) The number of compressors and the type of compressor are not limited to the first, second, and third embodiments. Also, the number of heat source units and the operating capacity of the heat source units are not limited to the second and third embodiments.

(3) In the second embodiment, the communication pipe that connects the heat source units together and the oil equalization control means are provided as separate units from the heat source units. It is also acceptable for these items to be built into the heat source units.

Applicability to Industry

By utilizing the present invention, the supply of oil to compression mechanisms that are stopped can be cut off and a sufficient amount of oil can be supplied to the compression mechanisms that are running, thereby improving the reliability of the oil supply to the compression mechanisms.