Patent Description:
In the related art, when cooling operation is performed in an air conditioner where a plurality of indoor units are connected to at least one outdoor unit by a liquid pipe and a gas pipe, a degree of opening of an expansion valve corresponding to each indoor unit is adjusted such that a refrigerant superheating degree on a refrigerant exit side of the indoor heat exchanger of each indoor unit functioning as an evaporator becomes a predetermined reference value (for example, <NUM> deg. ) (for example, see Patent Literature <NUM>).

Specifically, for each indoor unit, a refrigerant temperature (hereinafter, described as a heat exchange entrance temperature) at a refrigerant entrance side of the indoor heat exchanger and a refrigerant temperature (hereinafter, described as a heat exchange exit temperature) at the refrigerant exit side of the indoor heat exchanger are detected, and the heat exchange entrance temperature is subtracted from the heat exchange exit temperature to determine refrigerant superheating degrees of the indoor units (for example, see Patent Literature <NUM> or <NUM>). Patent Literature <NUM> falls under Article <NUM>(<NUM>) EPC.

Then, the degrees of opening of the expansion valves corresponding to the indoor units are adjusted such that the obtained refrigerant superheating degrees of the indoor units become the above-described reference value. Specifically, when the refrigerant superheating degree obtained at a certain indoor unit is greater than the reference value, the degree of opening of the expansion valve corresponding to the indoor unit is increased. By increasing the degree of opening of the expansion valve, the amount of refrigerant flowing into the indoor heat exchanger of the indoor unit increases and the refrigerant superheating degree decreases. On the other hand, when the refrigerant superheating degree obtained at a certain indoor unit is smaller than the reference value, the degree of opening of the expansion valve corresponding to the indoor unit is decreased. By decreasing the degree of opening of the expansion valve, the amount of refrigerant flowing into the indoor heat exchanger of the indoor unit decreases and the refrigerant superheating degree increases.

Patent Literature <NUM>: <CIT>, Patent Literature <NUM>: <CIT>, Patent Literature <NUM>: <CIT>.

When cooling operation is performed by the above-mentioned air conditioner, the amount of refrigerant flowing into a specific indoor unit may be reduced depending on an installation state of the outdoor unit and each indoor unit. For example, if installation locations of the indoor units are higher than an installation location of the outdoor unit, and there is a height difference between the installation positions of the indoor units, since the refrigerant is less likely to flow into the indoor unit installed above, the amount of refrigerant flowing into the indoor unit is smaller than the amounts of refrigerant flowing into the other indoor units. At the time of cooling operation, the refrigerant flowing from the outdoor unit toward each indoor unit is condensed by the outdoor heat exchanger of the outdoor unit to become liquid refrigerant, and this is because the liquid refrigerant must flow to the indoor unit installed above the outdoor unit against gravity.

Further, even if the installation location of each indoor unit and the installation locations of the outdoor units are approximately the same height, if a distance between an indoor unit and the outdoor unit is different, the amount of refrigerant flowing into the indoor unit disposed at a location far from the outdoor unit is smaller than the amount of refrigerant flowing into the indoor unit disposed at a location near the outdoor unit. For the indoor unit installed at a location far from the outdoor unit, since the pressure loss due to the refrigerant pipe is greater than that of other indoor units, the length of the refrigerant pipe connecting the indoor unit to the outdoor unit is longer than that of each refrigerant pipe connecting the other indoor unit to the outdoor unit.

As described above, when the indoor units are installed in such a manner that the amount of refrigerant flowing into a specific indoor unit decreases, in a case where a distance between the indoor unit installed at the highest when the height difference between the indoor units is large (for example, <NUM> or more) and the outdoor unit or between an indoor unit installed farthest from the outdoor unit and the outdoor unit is large (for example, <NUM> or more), the amount of refrigerant flowing into the indoor unit is significantly decreased, resulting in a shortage of refrigerant, and there is a possibility that the cooling ability required by the user cannot be displayed.

On the other hand, at the time of cooling operation, even when the indoor units are not installed in such a manner that the amount of refrigerant flowing into a specific indoor unit decreases, in a case where the number of indoor units connected to the outdoor unit is large and the sum of rated capacities of the indoor units is greater than the a capacity of the outdoor units, the amount of refrigerant flowing into each indoor unit is small compared with when the total value of the rated capacities of the indoor units is equal to or smaller than the rated capacity of the outdoor unit.

As described above, when the number of indoor units connected to the outdoor unit is large and the total value of the capacities of the indoor units is greater than the capacity of the outdoor unit, in the indoor unit with a large air conditioning load (for example, the room temperature of the room where the indoor unit is installed is a high temperature close to <NUM>), the amount of refrigerant currently flowing in may be insufficient for the amount of refrigerant required to display the cooling capacity required by the user.

When there is an indoor unit where the amount of refrigerant flowing in is insufficient due to the above-described reason at the time of cooling operation and the cooling ability cannot be displayed, the refrigerant superheating degree in the indoor unit is a high value (for example, <NUM> deg. At this time, as described in Patent Literature <NUM>, even if the degree of opening of the corresponding expansion valve is increased in order to set the refrigerant superheating degree to the reference value in the indoor unit, because the amount of refrigerant flowing into the indoor unit is insufficient in the first place, the refrigerant superheating degree does not decrease. That is, even if the degree of opening of the expansion valve is increased to set the refrigerant superheating degree to the reference value in the indoor unit, the state in which the cooling ability cannot be displayed cannot be eliminated.

The present invention solves the above-mentioned problem, and an object thereof is to provide an air conditioner capable of displaying sufficient cooling ability at each indoor unit by allowing a sufficient amount of refrigerant to flow into indoor units where cooling ability cannot be displayed.

Patent Literature <NUM> discloses an air conditioner according to the preamble of claim <NUM>.

To solve the above-mentioned problem, an air conditioner of the present invention is provided having the features of claim <NUM>.

According to the air conditioner of the present invention configured as described above, by executing the refrigerant amount balance control at the time of cooling operation, since refrigerant is distributed from the indoor units having the sufficient amount of refrigerant to the indoor units having the insufficient amount of refrigerant, it is possible to display sufficient cooling ability in each indoor unit during the cooling operation.

<FIG> and <FIG> are explanatory diagrams of an air conditioner in an embodiment of the present invention; <FIG> is a refrigerant circuit diagram; and <FIG> is a block diagram of an outdoor unit controller and an indoor unit controller.

Hereinafter, embodiments of the present invention will be described in detail based on the attached drawings. The embodiments will be described by using as an example an air conditioner where to one outdoor unit installed on the ground, three indoor units installed on the floors of the building, respectively, are connected in parallel and cooling operation or heating operation can be simultaneously performed by all the indoor units in an installation state where the amount of refrigerant flowing into a specific indoor unit during the cooling operation is insufficient. The present invention is not limited to the second embodiment and may be variously modified without departing from the scope of the claim.

As shown in <FIG> and <FIG>, an air conditioner <NUM> of the present embodiment includes one outdoor unit <NUM> installed on the ground and three indoor units 5a to 5c installed on the floors of a building <NUM>, respectively, and connected in parallel to the outdoor unit <NUM> by a liquid pipe <NUM> and a gas pipe <NUM>. Specifically, the liquid pipe <NUM> has its one end connected to a closing valve <NUM> of the outdoor unit <NUM> and has its other end branched to be connected to liquid pipe connection portions 53a to 53c of the indoor units 5a to 5c. The gas pipe <NUM> has its one end connected to a closing valve <NUM> of the outdoor unit <NUM> and has its other end branched to be connected to gas pipe connection portions 54a to 54c of the indoor units 5a to 5c. This constitutes a refrigerant circuit <NUM> of the air conditioner <NUM>.

First, the outdoor unit <NUM> will be described. The outdoor unit <NUM> includes a compressor <NUM>, a four-way valve <NUM>, an outdoor heat exchanger <NUM>, an outdoor expansion valve <NUM>, the closing valve <NUM> to which one end of the liquid pipe <NUM> is connected, the closing valve <NUM> to which one end of the gas pipe <NUM> is connected, an accumulator <NUM> and an outdoor fan <NUM>. These devices except the outdoor fan <NUM> are interconnected by refrigerant pipes described below in detail, thereby constituting an outdoor unit refrigerant circuit <NUM> forming part of the refrigerant circuit <NUM>.

The compressor <NUM> is a variable ability compressor the operation capacity of which is variable by being driven by a non-illustrated motor the rpm of which is controlled by an inverter. A refrigerant discharge side of the compressor <NUM> is connected to a port a of the four-way valve <NUM> described later by a discharge pipe <NUM>, and a refrigerant suction side of the compressor <NUM> is connected to a refrigerant outflow side of the accumulator <NUM> by a suction pipe <NUM>.

The four-way valve <NUM> is a valve for switching the direction in which the refrigerant flows, and is provided with four ports a, b, c and d. The port a is connected to the refrigerant discharge side of the compressor <NUM> by the discharge pipe <NUM> as mentioned above. The port b is connected to one refrigerant entrance and exit of the outdoor heat exchanger <NUM> by a refrigerant pipe <NUM>. The port c is connected to a refrigerant inflow side of the accumulator <NUM> by a refrigerant pipe <NUM>. The port d is connected to the closing valve <NUM> by an outdoor unit gas pipe <NUM>.

The outdoor heat exchanger <NUM> performs heat exchange between the refrigerant and the outside air taken into the outdoor unit <NUM> by the rotation of the outdoor fan <NUM> described later. One refrigerant entrance and exit of the outdoor heat exchanger <NUM> is connected to the port b of the four-way valve <NUM> by the refrigerant pipe <NUM> as mentioned above, and the other refrigerant entrance and exit thereof is connected to the closing valve <NUM> by an outdoor unit liquid pipe <NUM>.

The outdoor expansion valve <NUM> is provided on the outdoor unit liquid pipe <NUM>. The outdoor expansion valve <NUM> is an electronic expansion valve, and by the degree of opening thereof being adjusted, the amount of refrigerant flowing into the outdoor heat exchanger <NUM> or the amount of refrigerant flowing out from the outdoor heat exchanger <NUM> is adjusted. The degree of opening of the outdoor expansion valve <NUM> is made full opening when the air conditioner <NUM> is performing cooling operation. When the air conditioner <NUM> is performing heating operation, by controlling the degree of opening thereof according to the discharge temperature of the compressor <NUM> detected by a discharge temperature sensor <NUM> described later, the discharge temperature is prevented from exceeding a performance upper limit value.

The outdoor fan <NUM> is made of a resin material, and disposed in the neighborhood of the outdoor heat exchanger <NUM>. The outdoor fan <NUM> is rotated by a non-illustrated fan motor to thereby take the outside air into the outdoor unit <NUM> from a non-illustrated inlet, and discharges the outside air heat-exchanged with the refrigerant at the outdoor heat exchanger <NUM> from a non-illustrated outlet to the outside of the outdoor unit <NUM>.

The accumulator <NUM>, as mentioned above, has its refrigerant inflow side connected to the port c of the four-way valve <NUM> by the refrigerant pipe <NUM> and has its refrigerant outflow side connected to the refrigerant suction side of the compressor <NUM> by the suction pipe <NUM>. The accumulator <NUM> separates the refrigerant having flown from the refrigerant pipe <NUM> into the accumulator <NUM> into a gas refrigerant and a liquid refrigerant and causes only the gas refrigerant to be sucked into the compressor <NUM>.

In addition to the above-described components, various sensors are provided in the outdoor unit <NUM>. As shown in <FIG>, the discharge pipe <NUM> is provided with a discharge pressure sensor <NUM> that detects the discharge pressure which is the pressure of the refrigerant discharged from the compressor <NUM> and the discharge temperature sensor <NUM> that detects the temperature of the refrigerant discharged from the compressor <NUM>. In the neighborhood of the refrigerant inflow port of the accumulator <NUM> on the refrigerant pipe <NUM>, a suction pressure sensor <NUM> that detects the pressure of the refrigerant sucked into the compressor <NUM> and a suction temperature sensor <NUM> that detects the temperature of the refrigerant sucked into the compressor <NUM> are provided.

Between the outdoor heat exchanger <NUM> and the outdoor expansion valve <NUM> on the outdoor unit liquid pipe <NUM>, a outdoor heat exchange temperature sensor <NUM> for detecting the temperature of the refrigerant flowing into the outdoor heat exchanger <NUM> or the temperature of the refrigerant flowing out from the outdoor heat exchanger <NUM> is provided. In the neighborhood of a non-illustrated inlet of the outdoor unit <NUM>, an outside air temperature sensor <NUM> that detects the temperature of the outside air flowing into the outdoor unit <NUM>, that is, the outside air temperature is provided.

The outdoor unit <NUM> is provided with an outdoor unit controller <NUM>. The outdoor unit controller <NUM> is mounted on a control board housed in a non-illustrated electric component box of the outdoor unit <NUM>. As shown in <FIG>, the outdoor unit controller <NUM> includes a CPU <NUM>, a storage unit <NUM>, a communication unit <NUM> and a sensor input unit <NUM>.

The storage unit <NUM> is formed of a ROM and a RAM, and stores a control program of the outdoor unit <NUM>, detection values corresponding to detection signals from various sensors, control states of the compressor <NUM> and the outdoor fan <NUM>, and the like. The communication unit <NUM> is an interface that performs communication with the indoor units 5a to 5c. The sensor input unit <NUM> receives the results of the detections at the sensors of the outdoor unit <NUM> and outputs them to the CPU <NUM>.

The CPU <NUM> receives the above-mentioned results of the detections at the sensors of the outdoor unit <NUM> through the sensor input unit <NUM>. Moreover, the CPU <NUM> receives the control signals transmitted from the indoor units 5a to 5c through the communication unit <NUM>. The CPU <NUM> controls driving of the compressor <NUM> and the outdoor fan <NUM> based on the received detection results and control signals. Moreover, the CPU <NUM> controls switching of the four-way valve <NUM> based on the received detection results and control signals. Further, the CPU <NUM> adjusts the degree of opening of the outdoor expansion valve <NUM> based on the received detection results and control signals.

Next, the three indoor units 5a to 5c will be described. The three indoor units 5a to 5c includes indoor heat exchangers 51a to 51c, indoor expansion valves 52a to 52c, the liquid pipe connection portions 53a to 53c to which the other ends of the branched liquid pipe <NUM> are connected, the gas pipe connection portions 54a to 54c to which the other ends of the branched gas pipe <NUM> are connected, and indoor fans 55a to 55c, respectively. These devices except the indoor fans 55a to 55c are interconnected by refrigerant pipes described below in detail, thereby constituting indoor unit refrigerant circuits 50a to 50c forming part of the refrigerant circuit <NUM>. The three indoor units 5a to 5c all have the same ability, and if refrigerant superheating degree on a refrigerant exit side of the indoor heat exchangers 51a to 51c at the time of cooling operation can be made not more than a predetermined value (for example, <NUM> deg. ), sufficient cooling ability can be displayed at each indoor unit.

Since the components of the indoor units 5a to 5c are the same, in the following description, only the components of the indoor unit 5a are described, and description of the other indoor units 5b, 5c is omitted. Moreover, in <FIG>, the component devices of the indoor units 5b, 5c corresponding to the component devices of the indoor unit 5a are denoted by reference designations where the last letters of the numbers assigned to the component devices of the indoor unit 5a are changed from a to b or c, respectively.

The indoor heat exchanger 51a performs heat exchange between the refrigerant and the indoor air taken into the indoor unit 5a from a non-illustrated inlet by the rotation of the indoor fan 55a described later, one refrigerant entrance and exit thereof is connected to the liquid pipe connection portion 53a by an indoor unit liquid pipe 71a, and the other refrigerant entrance and exit thereof is connected to the gas pipe connection portion 54a by an indoor unit gas pipe 72a. The indoor heat exchanger 51a functions as an evaporator when the indoor unit 5a performs cooling operation, and functions as a condenser when the indoor unit 5a performs heating operation.

The refrigerant pipes are connected to the liquid pipe connection portion 53a and the gas pipe connection portion 54a by welding, flare nuts or the like.

The indoor expansion valve 52a is provided on the indoor unit liquid pipe 71a. The indoor expansion valve 52a is an electronic expansion valve, and when the indoor heat exchanger 51a functions as an evaporator, that is, that is, when the indoor unit 5a performs heating operation, the degree of opening thereof is adjusted such that the refrigerant supercooling degree at the refrigerant exit (the side of the liquid pipe connection portion 53a) of the indoor heat exchanger 51a is a target refrigerant supercooling degree. Here, the target refrigerant supercooling degree is a refrigerant supercooling degree for sufficient heating ability to be displayed at the indoor unit 5a. When the indoor heat exchanger 51a functions as a evaporator, that is, when the indoor unit 5a performs cooling operation, the degree of opening of the indoor expansion valve 52a is adjusted such that the refrigerant superheating degree at the refrigerant exit (the side of the gas pipe connection portion 54a) of the indoor heat exchanger 51a is an average refrigerant supercooling degree described later.

The indoor fan 55a is made of a resin material, and disposed in the neighborhood of the indoor heat exchanger 51a. The indoor fan 55a is rotated by a non-illustrated fan motor to thereby take the indoor air into the indoor unit 5a from a non-illustrated inlet, and supplies the indoor air heat-exchanged with the refrigerant at the indoor heat exchanger 51a from a non-illustrated outlet into the room.

In addition to the above-described components, various sensors are provided in the indoor unit 5a. Between the indoor heat exchanger 51a and the indoor expansion valve 52a on the indoor unit liquid pipe 71a, a liquid side temperature sensor 61a that detects the temperature of the refrigerant flowing into the indoor heat exchanger 51a or flowing out from the indoor heat exchanger 51a is provided. The indoor unit gas pipe 72a is provided with a gas side temperature sensor 62a that detects the temperature of the refrigerant flowing out from the indoor heat exchanger 51a or flowing into the indoor heat exchanger 51a. In the neighborhood of a non-illustrated inlet of the indoor unit 5a, an inflow temperature sensor 63a that detects the temperature of the indoor air flowing into the indoor unit 5a, that is, the inflow temperature is provided.

The indoor unit 5a is provided with an indoor unit controller 500a. The indoor unit controller 500a is mounted on a control board housed in a non-illustrated electric component box of the indoor unit 5a, and as shown in <FIG>, is provided with a CPU <NUM>10a, a storage unit 520a, a communication unit 530a and a sensor input unit 540a.

The storage portion 520a is formed of a ROM and a RAM, and stores a control program of the indoor unit 5a, detection values corresponding to detection signals from various sensors, setting information related to an air-conditioning operation by the user, and the like. The communication portion 530a is an interface that performs communication with the outdoor unit <NUM> and the other indoor units 5b, 5c. The sensor input portion 540a receives the results of the detections at the sensors of the indoor unit 5a and outputs them to the CPU 510a.

The CPU 510a receives the above-mentioned results of the detections at the sensors of the indoor unit 5a through the sensor input unit 540a. Moreover, the CPU 510a receives, through a non-illustrated remote control light receiving portion, a signal containing operation information, timer operation setting and the like set by the user operating a non-illustrated remote control unit. Moreover, the CPU 510a transmits an operation start/stop signal and a control signal containing operation information (the set temperature, the room temperature, etc.) to the outdoor unit <NUM> through the communication portion 530a, and receives a signal containing information such as a temperature of the outside air detected by the outdoor unit <NUM> from the outdoor unit <NUM> through the communication portion 530a. The CPU 510a adjusts the degree of opening of the indoor expansion valve 52a and controls driving of the indoor fan 55a based on the received detection results and the signals transmitted from the remote control unit and the outdoor unit <NUM>.

The above-described outdoor unit controller <NUM> and the indoor unit controllers 500a to 500c constitute the controller of the present invention.

The above-described air conditioner <NUM> is installed in a building <NUM> shown in <FIG>. Specifically, the outdoor unit <NUM> is disposed on the ground; the indoor unit 5a, on the first floor; the indoor unit 5b, on the second floor; and the indoor unit 5c, on the third floor. The outdoor unit <NUM> and the indoor units 5a to 5c are interconnected by the above-described liquid pipe <NUM> and gas pipe <NUM>, and these liquid pipe <NUM> and gas pipe <NUM> are buried in a non-illustrated wall or ceiling of the building <NUM>. In <FIG>, the difference in height between the indoor unit 5c installed on the highest floor (the third floor) and the indoor unit 5a installed on the lowest floor (the first floor) is represented as H.

Next, the flow of the refrigerant at the refrigerant circuit <NUM> and the operations of components at the time of the air-conditioning operation of the air conditioner <NUM> of the present embodiment will be described by using <FIG>. In the following description, a case where the indoor units 5a to 5c perform cooling operation will be described, and detailed description of a case where they perform heating operation is omitted. The arrows in <FIG> indicate the flow of the refrigerant at the time of cooling operation.

As shown in <FIG>, when the indoor units 5a to 5c perform cooling operation, the CPU <NUM> of the outdoor unit controller <NUM> switches the four-way valve <NUM> to the state shown by solid lines, that is, such that the port a and the port b of the four-way valve <NUM> communicate with each other and the port c and the port d communicate with each other. This brings the refrigerant circuit <NUM> into a heating cycle where the outdoor heat exchanger <NUM> functions as an condenser and the indoor heat exchangers 51a to 51c function as evaporators.

The high-pressure refrigerant discharged from the compressor <NUM> flows through the discharge pipe <NUM> into the four-way valve <NUM>, and flows from the four-way valve <NUM> through the refrigerant pipe <NUM> into the outdoor heat exchanger <NUM>. The refrigerant having flown into the outdoor heat exchanger <NUM> exchanges heat with the outside air taken into the outdoor unit <NUM> by the rotation of the outdoor fan <NUM> and is condensed. The refrigerant having flown out from the outdoor heat exchanger <NUM> flows from the outdoor unit liquid pipe <NUM>, the outdoor expansion valve <NUM> the degree of opening of which is fully opened, and the closing valve <NUM> into the liquid pipe <NUM>.

The refrigerant flowing through the liquid pipe <NUM> flows into the indoor unit 5a to 5c through the liquid pipe connection portions 53a to 53c. The refrigerant having flown into the indoor units 5a to 5c flows through the indoor unit liquid pipes 71a to 71c, is decompressed by the indoor expansion valves 52a to 52c, and flows into the indoor heat exchangers 51a to 51c. The refrigerant having flown into the indoor heat exchangers 51a to 51c exchanges heat with the indoor air taken into the indoor units 5a to 5c by the rotation of the indoor fans 55a to 55c, and is evaporated. As described above, the indoor heat exchangers 51a to 51c function as evaporators and the cooled indoor air heat-exchanged with the refrigerant at the indoor heat exchangers 51a to 51c is flown out form a non-illustrated outlet into the rooms, thereby performing cooling in the rooms where the indoor units 5a to 5c are installed.

The refrigerant having flown out from the indoor heat exchangers 51a to 51c flows through the indoor unit gas pipes 72a to 72c, and flows into the gas pipe <NUM> through the gas pipe connection portions 54a to 54c. The refrigerant flowing through the gas pipe <NUM> flows into the outdoor unit <NUM> through the closing valve <NUM>. The refrigerant having flown into the outdoor unit <NUM> flows through the outdoor unit gas pipe <NUM>, the four-way valve <NUM>, the refrigerant pipe <NUM>, the accumulator <NUM> and the suction pipe <NUM> in this order, is sucked by the compressor <NUM> and compressed again.

When the indoor units 5a to 5c perform heating operation, the CPU <NUM> switches the four-way valve <NUM> to the state shown by the broken line, that is, such that the port a and the port b of the four-way valve <NUM> communicate with each other and the port b and the port c communicate with each other. This brings the refrigerant circuit <NUM> into a heating cycle where the outdoor heat exchanger <NUM> functions as a evaporator and the indoor heat exchangers 51a to 51c function as condensers.

Next, the operation, workings and effects of the refrigerant circuit in the air conditioner <NUM> of the first embodiment will be described by using <FIG>. When the indoor heat exchangers 51a to 51c function as evaporators, liquid side temperature sensors 61a to 61c that detect the heat exchange entrance temperature, which is the temperature of the refrigerant flowing into the indoor heat exchangers 51a to 51c, and gas side temperature sensors 62a to 62c that detect the heat exchange exit temperature, which is the temperature of the refrigerant flowing out from the indoor heat exchangers 51a to 51c, the outdoor unit controller <NUM>, the indoor unit controllers 500a to 500c are superheating degree detectors.

As described above using <FIG>, in the air conditioner <NUM> of the present embodiment, the outdoor unit <NUM> is installed on the ground of the building <NUM> and the indoor units 5a to 5c are installed on the floors, respectively. That is, the outdoor unit <NUM> is installed in a lower position than the indoor units 5a to 5c, and there is a height difference H between the installation locations of the indoor unit 5a and the indoor unit 5c. In this case, the following problem arises when cooling operation is performed by the air conditioner <NUM>.

In cooling operation, the gas refrigerant discharged from the compressor <NUM> flows from the discharge pipe <NUM> into the outdoor heat exchanger <NUM> through the four-way valve <NUM> and the refrigerant pipe <NUM>, exchanges heat with the outside air in the outdoor heat exchanger <NUM>, is condensed, and becomes the liquid refrigerant. At this time, since the outdoor unit <NUM> is installed in the lower position than the indoor units 5a to 5c, the liquid refrigerant condensed at the outdoor heat exchanger <NUM> and having flown out into the liquid pipe <NUM> flows through the liquid pipe <NUM> against gravity toward the indoor units 5a to 5c.

Therefore, it becomes more difficult for the liquid refrigerant having flown out into the liquid pipe <NUM> to flow toward the indoor units 5a to 5c as the installation positions of the indoor units 5a to 5c become high compared with that of the outdoor unit <NUM>. When there is a height difference H in the installation positions of indoor units 5a to 5c, the pressure of the refrigerant on the upstream side (the side of the outdoor unit <NUM>) of the indoor expansion valve 52c of the indoor unit 5c installed on the third floor is lower than the pressure of the refrigerant on the upstream side of the indoor expansion valves 52a, 52b of the indoor units 5a, 5b installed on the other floors. For this reason, a difference between the refrigerant pressure on the upstream side of the indoor expansion valve 52c of the indoor unit 5c and the refrigerant pressure on the downstream side thereof (the side of the indoor heat exchanger 51c) is small compared with a difference between the refrigerant pressure on the upstream side of the indoor expansion valves 52a, 52b of the indoor units 5a, 5b and the refrigerant pressure on the downstream side thereof.

In the state of the refrigerant circuit <NUM> as described above, the smaller the difference between the refrigerant pressure on the upstream side of the indoor expansion valves 52a to 52c and the refrigerant pressure on the downstream side thereof, the smaller the amounts of refrigerant passing through the indoor expansion valves 52a to 52c. Therefore, the amount of refrigerant flowing through the indoor unit 5c installed on the third floor is small compared with the amounts of refrigerant flowing in the other indoor units 5a, 5b. This becomes more conspicuous as the height difference H between the indoor unit 5a installed on the first floor (the lowest position) and the indoor unit 5c installed on the third floor (the highest position) increases. That is, as the height difference becomes larger, the liquid refrigerant flowing out from the outdoor unit <NUM> into the liquid pipe <NUM> becomes harder to flow toward the indoor unit 5c, and the amount of refrigerant flowing into the indoor unit 5c is smaller compared with the amounts of refrigerant flowing into the indoor units 5a, 5b.

If the height difference between the indoor unit 5a and the indoor unit 5c is equal to or greater than a certain value (for example, <NUM>), the amount of refrigerant flowing into the indoor unit 5c may be insufficient for the amount of refrigerant required to display the required cooling ability. At this time, even if the degree of opening of the indoor expansion valve 52c is increased in order to increase the amount of refrigerant flowing into the indoor unit 5c, since the amount of refrigerant flowing from the outdoor unit <NUM> toward the indoor unit 5c is insufficient in the first place, the amount of refrigerant flowing into the indoor unit 5c does not increase, and there is a problem that a state in which the cooling ability cannot be exhibited cannot be eliminated.

Accordingly, in the first embodiment, when the air conditioner <NUM> performs cooling operation, the refrigerant superheating degree on the refrigerant exit side of the indoor heat exchangers 51a to 51c of the indoor units 5a to 5c (the side of gas side closing valves 54a to 54c) is calculated periodically (for example, every thirty seconds), the maximum value and the minimum value of the calculated refrigerant superheating degrees are extracted, and an average refrigerant superheating degree which is the average value of these is obtained. Then, a refrigerant amount balance control is executed in which the degrees of opening of the indoor expansion valves 52a to 52c of the indoor units 5a to 5c are adjusted so that the refrigerant superheating degree on the refrigerant exit side of the indoor heat exchangers 51a to 51c becomes the obtained average refrigerant superheating degree.

As described above, even if the indoor expansion valve 5c is enlarged, when the refrigerant does not flow to the indoor unit 5c and the amount of refrigerant is insufficient and no cooling ability is not displayed at the indoor unit 5c, the refrigerant superheating degrees of the indoor units 5a to 5c increase as the installation positions thereof become higher from the outdoor unit <NUM> such as <NUM> deg. in the indoor unit 5a, <NUM> deg. in the indoor unit 5b and <NUM> deg. , in the indoor unit 5c. While the refrigerant superheating degree has a large value due to the insufficient amount of refrigerant in the indoor unit 5c, in the indoor units 5a and 5b, the amounts of refrigerant are larger than that of the indoor unit 5c, which indicates that the refrigerant superheating degree is a small value. That is, it indicates that the refrigerant distribution in each of the indoor units 5a to 5c is biased in the refrigerant circuit <NUM> during cooling operation.

If the refrigerant amount balance control is executed when the refrigerant distribution in each of the indoor units 5a to 5c is biased during the cooling operation, in the indoor units 5a, 5b whose refrigerant superheating degrees are smaller than the average refrigerant superheating degree (in the case of the above example, <NUM> deg. which is an average value of the maximum value: <NUM> deg. and the minimum value: <NUM> deg. ), the degrees of opening of the indoor expansion valves 52a, 52b are narrowed in order to raise the refrigerant superheating degree to the average refrigerant superheating degree. Accordingly, the amounts of refrigerant flowing into the indoor units 5a, 5b are reduced, and the refrigerant pressure on the downstream side (sides of indoor heat exchangers 51a, 51b) of the indoor expansion valves 52a, 52b is reduced.

On the other hand, in the indoor unit 5c where the refrigerant superheating degree is higher than the average refrigerant superheating degree, since the refrigerant pressure on the downstream side of the indoor expansion valves 52a, 52b decreases and this decreases the refrigerant pressure on the downstream side of the indoor expansion valve 52c, the difference in pressure between the upstream side and the downstream side of the indoor expansion valve 52c increases. Accordingly, in order to reduce the refrigerant superheating degree of the indoor unit 5c to the average refrigerant superheating degree in the refrigerant amount balance control, when the degree of opening of the indoor expansion valve 52c is increased, the amount of refrigerant passing through the indoor expansion valve <NUM> increases, that is, the amount of refrigerant flowing into the indoor unit 5c increases, so that the cooling ability of the indoor unit 5c increases.

Next, the control at the time of cooling operation in the air conditioner <NUM> of the present embodiment will be described by using <FIG> shows the flow of the processing related to the control performed by the CPU <NUM> of the outdoor unit controller <NUM> when the air conditioner <NUM> performs cooling operation. In <FIG>, ST represents a step, and the number following this represents a step number. In <FIG>, the processing related to the first embodiment is mainly described, and description of processing other than this, for example, general processing related to the air conditioner <NUM> such as control of the refrigerant circuit <NUM> corresponding to the operation conditions such as the set temperature and air volume specified by the user is omitted. In the following description, a case where all the indoor units 5a to 5c are performing cooling operation will be described as an example.

In the following description, the heat exchange entrance temperatures, which are the refrigerant temperature at the refrigerant entrance side of the indoor heat exchangers 51a to <NUM>1c detected by the liquid side temperature sensors 61a to 61c of the indoor units 5a to 5c, are set as Ti (unit: °C. When referring to the indoor units 5a to 5c individually, Tia to Tic), the heat exchange exit temperatures, which are the refrigerant temperature at the refrigerant exit side of the indoor heat exchangers 51a to 51c detected by the gas side temperature sensors 62a to 62c of the indoor units 5a to 5c, are set as To (unit: °C. When referring to the indoor units 5a to 5c individually, Toa to Toc), the refrigerant superheating degrees in the indoor units 5a to 5c obtained by subtracting the heat exchange entrance temperatures Ti from the heat exchange exit temperatures To are set as SH (unit: deg. When referring to the indoor units 5a to 5c individually, SHa to SHc), a maximum refrigerant superheating degree which is the maximum value among the refrigerant superheating degrees SH of the indoor units 5a to 5c is set as SHmax, and a minimum refrigerant superheating degree which is the minimum value of the refrigerant superheating degrees SH of the indoor units 5a to 5c is set as SHmin, and an average refrigerant superheating degree obtained by averaging the maximum refrigerant superheating degree SHmax and the minimum refrigerant superheating degree SHmin is set as SHv.

First, the CPU <NUM> determines whether the user's operation instruction is a cooling operation instruction or not (ST1).

When it is not a cooling operation instruction (ST1-No), the CPU <NUM> executes heating operation start processing which is the processing to start heating operation (ST11). Here, the heating operation start processing is that the CPU <NUM> operates the four-way valve <NUM> to bring the refrigerant circuit <NUM> into the heating cycle, and is the processing performed when the heating operation is started from the state where the air conditioner <NUM> is stopped, or when the cooling operation is switched from the cooling operation to the heating operation.

Then, the CPU <NUM> starts the compressor <NUM> and the outdoor fan <NUM> at predetermined rpm, instructs the indoor units 5a to 5c, through the communication unit <NUM>, to control driving of the indoor fans 55a to 55c and adjust the degrees of opening of the indoor expansion valves 52a to 52c to thereby start control of heating operation (ST12), and advances the process to ST8.

At ST1, when it is a cooling operation instruction (ST1-Yes), the CPU <NUM> executes cooling operation start processing (ST2). Here, the cooling operation start processing is that the CPU <NUM> operates the four-way valve <NUM> to bring the refrigerant circuit <NUM> into the state shown in <FIG>, that is, bring the refrigerant circuit <NUM> into the cooling cycle, and is the processing performed when the cooling operation is started from the state where the air conditioner <NUM> is stopped, or when the cooling operation is switched from the heating operation to the cooling operation.

Then, the CPU <NUM> performs control of the cooling operation (ST3). In the cooling operation start processing, the CPU <NUM> starts the compressor <NUM> and the outdoor fan <NUM> at rpm corresponding to the ability required from the indoor units 5a to 5c. The CPU <NUM> fully opens the opening of the outdoor expansion valve <NUM>. Further, the CPU <NUM> transmits an operation start signal indicating the start of cooling operation to the indoor units 5a to 5c through the communication unit <NUM>.

The CPUs 510a to 510c of the indoor unit controllers 500a to 500c of the indoor units 5a to 5c having received the operation start signal through the communication units 530a to 530c start the indoor fans 55a to 55c at rpm corresponding to the user's air volume instruction. Further, the CPUs 510a to 510c subtracts the heat exchange entrance temperatures Tia to Tic detected by the liquid side temperature sensors 61a to 61c from the heat exchange exit temperatures Toa to Toc detected by the gas side temperature sensors 62a to 62c to obtain the refrigerant superheating degrees SHa to SHc at the refrigerant exit side of the exchangers 51a to 51c (the side of the gas pipe connection portions 54a to 54c. The opening degrees of the indoor expansion valves 52a to 52c are adjusted such that the obtained refrigerant superheating degrees SHa to SHc become the target refrigerant superheating degree (for example, <NUM> deg. ) at the start of operation.

Here, the target refrigerant superheating degree is a value previously obtained by performing a test or the like and stored in the storage units 520a to 520c, and is a value where it has been confirmed that cooling ability is sufficiently displayed at each indoor unit. During the time from the start of cooling operation to when the state of the refrigerant circuit <NUM> is stabilized (for example, three minutes from the start of operation), the CPUs 510a to 510c adjust the degrees of opening of the indoor expansion valves 52a to 52c such that the refrigerant supercooling degrees become the above-mentioned target refrigerant superheating degree at the time of start of operation.

Then, the CPU <NUM> receives the heat exchange entrance temperatures Ti (Tia to Tic) and the heat exchange exit temperatures To (Toa to Toc) from the indoor units 5a to 5c through the communication unit <NUM> (ST4). The heat exchange entrance temperatures Ti and the heat exchange exit temperatures To are the detection values at the liquid side temperature sensors 61a to 61c and the gas side temperature sensors 62a to 6sc that the CPUs 510a to 510c receive at the indoor units 5a to 5c and transmit to the outdoor unit <NUM> through the communication units 530a to 530c. The above-mentioned detection values are received by the CPU <NUM> and the CPUs 510a to S 10c every predetermined time (for example, every <NUM> seconds) and stored in the storage unit <NUM> and the storage units 520a to 520c.

Next, the CPU <NUM> subtracts the heat exchange entrance temperature Ti from the heat exchange exit temperature To of each of the indoor units 5a to 5c received at ST4, and obtains the refrigerant superheating degrees SH of the indoor units 5a to 5c (ST5). Specifically, the CPU <NUM> subtracts the heat exchange entrance temperature Tia from the heat exchange exit temperature Toa of the indoor unit 5a to obtain the refrigerant superheating degree SHa, associates this with the indoor unit 5a, and stores it in the storage unit <NUM>. Similarly, the CPU <NUM> obtains the refrigerant superheating degrees SHb, SHc for the indoor unit 5b and the indoor unit 5c, associates these with the indoor units 5b or 5c, and stores them in the storage unit <NUM>.

Next, the CPU <NUM> sets the maximum value of the refrigerant superheat degrees SHa to SHc of the indoor units 5a to 5c obtained in ST5 as the maximum refrigerant superheating degree SHmax and the minimum value as the minimum refrigerant superheating degree SHmin, and the maximum refrigerant superheating degree SHmax and the minimum refrigerant superheating degree SHmin are averaged to obtain the average refrigerant superheating degree SHv (ST6). The average refrigerant superheating degree SHv is an arithmetic average value of the maximum refrigerant superheating degree SHmax and the minimum refrigerant superheating degree SHmin: [maximum refrigerant superheating degree SHmax + minimum refrigerant superheating degree SHmin] / <NUM>.

Then, the CPU <NUM> transmits the average refrigerant superheating degree SHv obtained at ST6 to the indoor units 5a to 5c through the communication unit <NUM> (ST7). The CPUs 510a to 510c of the indoor units 5a to 5c having received the average refrigerant superheating degree SHv through the communication units 530a to 530c obtain the refrigerant superheating degrees SHa to SHc by subtracting the heat exchange entrance temperatures Tia to Tic detected by the liquid side temperature sensors 61a to 61c from the heat exchange exit temperature Toa to Toc detected by the gas side temperature sensors 62a to 62c, and adjust the degrees of opening of the indoor expansion valves 52a to 52c such that the obtained refrigerant superheating degrees SHa to SHc become the average refrigerant superheating degree SHv received from the outdoor unit <NUM>.

The above-described processing from ST4 to ST7 is the processing related to the refrigerant amount balance control.

The CPU <NUM> having finished the processing of ST7 determines whether there is an operation mode switching instruction by the user or not (ST8). Here, the operation mode instruction is an instruction to switch from the current operation (in this description, cooling operation) to another operation (heating operation). When there is an operation mode switching instruction (ST8-Yes), the CPU <NUM> returns the process to ST1. When there is no operation mode switching instruction (ST8-No), the CPU <NUM> determines whether there is an operation stop instruction by the user or not (ST9). The operation stop instruction is an instruction to stop the operation of all the indoor units 5a to 5c.

When there is an operation stop instruction (ST9-Yes), the CPU <NUM> executes operation stop processing (ST10), and ends the process. In the operation stop processing, the CPU <NUM> stops the compressor <NUM> and the outdoor fan <NUM> and fully closes the outdoor expansion valve <NUM>. Moreover, the CPU <NUM> transmits an operation stop signal indicative of the stop of operation to the indoor units 5a to 5c through the communication unit <NUM>. The CPUs 510a to 510c of the indoor units 5a to 5c having received the operation stop signal through the communication units 530a to 530c stop the indoor fans 55a to 55c and fully close the indoor expansion valves 52a to 52c.

When there is no operation stop instruction at ST9 (ST9-No), the CPU <NUM> determines whether the current operation is cooling operation or not (ST13). When the current operation is heating operation (ST13-Yes), the CPU <NUM> returns the process to ST3. When the current operation is not heating operation (ST13-No), that is, when the current operation is heating operation, the CPU <NUM> returns the process to ST12.

Next, a second embodiment which is part of the present invention will be described by using mainly <FIG>. What is different from the first embodiment is that in the second embodiment, the refrigerant amount balance control is started from the point of time when it is determined that there is an indoor unit where cooling ability required by the user cannot displayed, whereas in the first embodiment, the refrigerant amount balance control is executed from the time of start of cooling operation (precisely, from when the refrigerant circuit <NUM> is stabilized). Detailed description of points other than this, that is, the components of the air conditioner <NUM> and the state of the refrigerant circuit <NUM> at the time of cooling operation is omitted since it is the same as that of the first embodiment.

As described in the first embodiment, if the refrigerant amount balance control is executed, in the indoor unit where the refrigerant superheating degree is higher than the average refrigerant superheating degree of the indoor units 5a to 5c (in the first embodiment, the indoor unit 5c), the amount of refrigerant flowing into the indoor unit increases and cooling ability increases. On the other hand, in the indoor unit where the refrigerant superheating degree is lower than the average refrigerant superheating degree (in the first embodiment, the indoor units 5a, 5b), the amount of the refrigerant flowing into the indoor unit decreases compared with when the refrigerant amount balance control is not performed, and cooling ability decreases. That is, in order that cooling ability is displayed in the indoor unit 5c installed above where the required cooling ability cannot be displayed, cooling ability is decreased in the indoor units 5a, 5b installed below the indoor unit 5c.

In the first embodiment, the refrigerant amount balance control is executed from the time of start of cooling operation. Consequently, the refrigerant amount balance control is executed irrespective of whether there is an indoor unit where the required cooling ability cannot be displayed or not. If the refrigerant amount balance control is executed when there is no indoor unit where the required cooling ability cannot be displayed, cooling ability is unnecessarily decreased in the indoor unit where cooling ability is displayed.

On the contrary, in the second embodiment, whether there is an indoor unit where the required cooling ability cannot be displayed or not is determined by a method described below, and the refrigerant amount balance control is executed only when there is an indoor unit. Accordingly, while the cooling ability of the indoor unit where the required cooling ability cannot be displayed is prevented from being decreased unnecessarily at the time of cooling operation, when there is an indoor unit where the required heating ability cannot be displayed, the cooling ability of the indoor unit can be increased.

The determination as to the presence or absence of an indoor unit where the required cooling ability cannot be displayed is performed as follows. First, the CPU <NUM> of the outdoor unit <NUM> obtains the maximum refrigerant superheating degree SHmax and the minimum refrigerant superheating degree SHmin in the same manner as the method described in the first embodiment. If a refrigerant superheating degree difference (hereinafter, described as refrigerant superheating degree difference SHd (unit: deg. )) which is the difference between the maximum refrigerant superheating degree SHmax and the minimum refrigerant superheating degree SHmin is equal to or greater than a predetermined threshold superheating degree difference (for example, <NUM> deg. , hereafter, described as threshold superheating degree difference SHTs (unit: deg. )), it is determined that the cooling ability required by the indoor unit having the maximum refrigerant superheating degree SHmax cannot be displayed.

Here, the threshold superheating degree difference SHTs is previously tested or the like and stored in the storage unit <NUM> of the outdoor unit controller <NUM>, and if the refrigerant superheating degree difference SHd is equal to or greater than the threshold superheating degree difference SHTs, it is a value which determines that the cooling capacity required by the indoor unit having the maximum refrigerant superheating degree SHmax cannot be exhibited, and the amount of refrigerant flowing into the indoor unit is insufficient.

Next, the control at the time of cooling operation in the air conditioner <NUM> of the present embodiment will be described by using <FIG> shows the flow of the processing related to the control performed by the CPU <NUM> of the outdoor unit controller <NUM> when the air conditioner <NUM> performs cooling operation. In <FIG>, ST represents a step, and the number following this represents the step number. In <FIG>, the processing related to the present invention is mainly described, and description of processing other than this, for example, general processing related to the air conditioner <NUM> such as control of the refrigerant circuit <NUM> corresponding to the operation conditions such as the set temperature and air volume specified by the user is omitted. In the following description, a case where all the indoor units 5a to 5c are performing cooling operation will be described as an example as in the first embodiment.

Since the flowchart shown in <FIG> is the same processing as the flowchart shown in <FIG> described in the first embodiment except the processing of ST36, detailed description thereof is omitted, and only the processing of ST36 will be described here.

The CPU <NUM> that has finished the processing of ST34 (corresponding to ST4 in the first embodiment) and ST35 (corresponding to ST5 in the first embodiment) sets the maximum value as the maximum refrigerant superheating degree SHmax and the minimum value as the minimum refrigerant superheating degree SHmin among the refrigerant superheating degrees SHa to SHc of the indoor units 5a to 5c obtained in ST35, and determines whether the refrigerant superheating degree difference SHd obtained by subtracting the minimum refrigerant superheating degree SHmin from the maximum refrigerant superheating degree SHmax is equal to or greater than the threshold superheating degree difference SHTs (ST36).

If the refrigerant superheating degree difference SHd is not equal to or greater than the threshold superheating degree difference SHTs (ST36-No), the CPU <NUM> determines that it is not necessary to execute the refrigerant amount balance control, and advances the process to ST39. On the other hand, if the refrigerant superheating degree difference SHd is equal to or greater than the threshold superheating degree difference SHTs (ST36-Yes), the CPU <NUM> determines that it is necessary to execute the refrigerant amount balance control, executes the processing of ST37 (corresponding to ST6 in the first embodiment) and ST38 (corresponding to ST7 in the first embodiment), and advances the process to ST39.

The above-described processing from ST34 to ST38 is the processing related to the refrigerant amount balance control in the second embodiment of the present invention.

As described above, the air conditioner <NUM> of the present invention executes the refrigerant amount balance control to adjust the degrees of opening of the indoor expansion valves 52a to 52c such that the refrigerant superheating degrees SHa to SHc in the indoor units 5a to 5c at the time of cooling operation become an average refrigerant superheating degree SHv obtained by averaging the maximum refrigerant superheating degree SHmax and the minimum refrigerant superheating degree SHmin among them. Accordingly, since the amount of refrigerant flowing into the indoor unit where the cooling ability cannot be displayed due to the shortage of the amount of refrigerant flowing thereinto, the cooling ability of the indoor unit is increased.

Claim 1:
An air conditioner comprising:
an outdoor unit (<NUM>);
a plurality of indoor units (5a, 5b, 5c) each of which includes an indoor heat exchanger (51a, 51b, 51c) and an indoor expansion valve (52a, 52b, 52c);
an superheating degree detector which detects a refrigerant superheating degree which is a superheating degree of a refrigerant flowing out from each indoor heat exchanger (51a, 51b, 51c) when each indoor heat exchanger (51a, 51b, 51c) is functioning as an evaporator; and
a controller (<NUM>, 500a, 500b, 500c) which is configured to adjust degrees of opening of the plurality of indoor expansion valves (52a, 52b, 52c),
wherein the controller (<NUM>, 500a, 500b, 500c) is configured to execute a refrigerant amount balance control to adjust the degree of opening of each indoor expansion valve (52a, 52b, 52c) such that an average refrigerant superheating degree (SHv) is obtained by averaging a maximum value (SHmax) and a minimum value (SHmin) of the refrigerant superheating degrees detected by the superheating degree detector, and the refrigerant superheating degree of each indoor unit (5a, 5b, 5c) becomes the average refrigerant superheating degree (SHv),
characterized in that the controller (<NUM>, 500a, 500b, 500c) is configured to obtain a refrigerant superheating degree difference (SHd) which is a difference between the maximum value (SHmax) and the minimum value (SHmin) of the refrigerant superheating degrees of the indoor units (5a, 5b, 5c), if the obtained refrigerant superheating degree difference (SHd) is greater than a predetermined threshold superheating degree difference (SHTs), the controller is configured to determine whether there is an indoor unit (5a, 5b, 5c) where cooling ability required by the plurality of indoor units (5a, 5b, 5c) is displayed or not, and when there is an indoor unit (5a, 5b, 5c) where the required cooling ability cannot be displayed, the controller (<NUM>, 500a, 500b, 500c) is configured to execute the refrigerant amount balance control.