JP5871723B2 - Air conditioner and control method thereof - Google Patents

Description

  The present invention relates to an air conditioner having a refrigeration cycle operation function based on natural circulation and a control method thereof, and more particularly to an air conditioner capable of switching between a refrigeration cycle operation based on natural circulation and a refrigeration cycle operation based on forced circulation.

  As a conventional air conditioner capable of switching operation between refrigeration cycle operation (natural circulation operation) by natural circulation and refrigeration cycle operation (forced circulation operation) by forced circulation, it is described in JP-A-11-182895 (Patent Document 1). There is something that was done. In such an air conditioner, a natural circulation operation is performed by circulating a refrigerant by connecting an evaporator and a condenser installed at a higher position than the evaporator with a refrigerant pipe. . This natural circulation operation is used when the outside air is lower than room temperature, and the refrigerant is circulated only by the refrigerant head difference (the difference between the evaporator and the condenser head) without operating the compressor. Is possible.

  In the air conditioner described in Patent Document 1, a compressor, a condenser, an expansion valve, an evaporator disposed below the condenser, a circuit connection connected to the evaporator and the compressor and the condenser Means (four-way valve), an expansion valve bypass circuit for bypassing the expansion valve, a condenser fan and an evaporator fan. In the natural circulation operation, the expansion valve bypass circuit is used, and the evaporator and the condenser are connected by the circuit connecting means to constitute a refrigerant circuit for natural circulation operation. Further, during the forced circulation operation, the expansion valve bypass circuit is closed so that the refrigerant flows into the expansion valve, and the evaporator and the compressor are connected by the circuit connecting means, and the forced circulation operation is performed. The refrigerant circuit is configured. This enables both natural circulation operation and forced circulation operation.

  Also, in this Patent Document 1, during the natural circulation operation, the fan power is reduced by detecting the room temperature and controlling the air volume of at least one of the condenser fan and the evaporator fan. At the same time, an excessive decrease in the room temperature is prevented.

Japanese Patent Laid-Open No. 11-182895

  In the thing of the said patent document 1, although it is trying to control power saving and room temperature appropriately by performing fan control, indoor temperature (room temperature) is not only outside temperature but internal load generated indoors. Therefore, when fan control is performed only for capacity control, the operation state of the refrigeration cycle may become unstable and natural circulation operation may not be continued.

  For example, when the outside air temperature is high and the internal load is small, when the condenser fan is controlled at a low speed to reduce the capacity, the refrigerant state at the outlet of the condenser becomes a gas-liquid two-phase state, and the outdoor unit When a large amount of gas refrigerant is mixed in the liquid connection pipe (liquid pipe) that connects the indoor unit and the indoor unit, a stable liquid head difference cannot be generated, and natural circulation operation (natural circulation cooling operation) stops. There is.

  On the other hand, when the outside air temperature is low and the internal load is small, the capacity reduction is not sufficient just by controlling the condenser fan at low speed, and the evaporator fan may be controlled at low speed. is there. In this case, the refrigerant state at the evaporator outlet becomes a wet state, and the head difference in the direction that cancels the liquid head difference in the liquid connection pipe acts on the gas connection pipe (gas pipe) that connects the indoor unit and the outdoor unit. Therefore, the stable natural circulation cannot be performed, and in this case, the possibility that the natural circulation operation stops is further increased.

  An object of the present invention is to obtain an air conditioner that can be restarted to a stable natural circulation operation and a control method thereof when the natural circulation operation is stopped.

The present invention for achieving the above object includes an evaporator, a condenser installed at a position higher than the evaporator, a liquid side connection pipe and a gas side connection pipe connecting the evaporator and the condenser, A refrigeration cycle operation by natural circulation, comprising a valve device provided on the upstream side of the evaporator, an evaporator fan for sending air to the evaporator, and a condenser fan for sending air to the condenser An air conditioner for performing a natural circulation operation stop determination device that detects cooling capability during cooling operation by natural circulation and determines whether natural circulation operation is stopped, and the stop determination device includes at least the evaporator inlet air temperature and based on the difference between the outlet air temperature is determined to stop the presence or absence of natural circulation operation, if you stop the natural circulation operation to the cooling operation by natural circulation, the evaporator upstream valve device provided in the Fully closed, the evaporator fan and the condenser fan are accelerated to increase the liquid refrigerant in the liquid side connection pipe, and the gas side connection pipe is controlled to increase the gas refrigerant. A control device is provided that controls to open the valve device on the upstream side of the evaporator so as to restart the natural circulation operation.

Other features of the present invention include an evaporator, a condenser installed at a higher position than the evaporator, a liquid side connection pipe and a gas side connection pipe connecting the evaporator and the condenser, and the evaporation. An air conditioner comprising a valve device provided upstream of the condenser, an evaporator fan for sending air to the evaporator, and a condenser fan for sending air to the condenser, and performing a refrigeration cycle operation by natural circulation And determining whether or not the natural circulation operation is stopped based on at least the difference between the intake air temperature and the blown air temperature of the evaporator, and when the natural circulation operation is stopped, on the upstream side of the evaporator The provided valve device is fully closed, the evaporator fan and the condenser fan are accelerated to increase the liquid refrigerant in the liquid side connection pipe, and the gas refrigerant is increased in the gas side connection pipe Control so that Opens the valve device of the rear said evaporator upstream in carrying out the restart of natural circulation operation by.

  ADVANTAGE OF THE INVENTION According to this invention, when a natural circulation driving | operation stops, there exists an effect which can obtain the air conditioner which can be restarted to the stable natural circulation driving | operation, and its control method.

The refrigeration cycle block diagram which shows Example 1 of the air conditioner of this invention. The Mollier diagram which shows the ideal state at the time of the natural circulation driving | operation in the air conditioner of FIG. The Mollier diagram which shows the driving | running state which the refrigerant | coolant circulation at the time of the natural circulation driving | operation of the air conditioner of FIG. 1 tends to stagnate.

  Hereinafter, specific embodiments of the air conditioner and the control method thereof according to the present invention will be described with reference to the drawings.

A first embodiment of an air conditioner and a control method thereof according to the present invention will be described with reference to FIGS.
FIG. 1 is a configuration diagram of a refrigeration cycle of an air conditioner in the present embodiment. In the figure, 100 is an outdoor unit, and 200 is an indoor unit. The outdoor unit 100 is installed at a position higher than the indoor unit 200 by H1 (m).

The outdoor unit 100 includes a compressor 1, a four-way valve 2, an outdoor heat exchanger 3 that becomes a condenser during cooling operation, a subcooler 34, an outdoor expansion valve 4, a liquid blocking valve 60, a gas blocking valve 61, an accumulator 9, and the like. Is provided. The outdoor heat exchanger 3 is provided with a distributor 33 on the liquid side and a gas side header 36 on the gas side.
The indoor unit 200 is provided with an indoor expansion valve (valve device) 6 and an indoor heat exchanger 7 that serves as an evaporator during cooling operation.

5 is a liquid side connection pipe connecting the liquid blocking valve 60 side of the outdoor unit 100 and the indoor expansion valve 6 side of the indoor unit 200, and 8 is a gas blocking valve 61 side of the outdoor unit 100 and the indoor unit. 200 is a gas side connection pipe connecting the 200 indoor heat exchanger 7 side.
Further, in the present embodiment, as shown in FIG. 1, the liquid side connection pipe 5 and the indoor unit 200 have a height dimension Hhex of the indoor heat exchanger 7 1 / Connected at up to 4 height dimension range positions. Further, the gas side connection pipe 8 and the indoor unit 200 are connected to the height dimension Hhex of the indoor heat exchanger 7 at a height dimension range position up to 1/4 from the upper part to the lower side. Yes. In this way, by connecting the liquid side connection pipe 5 and the gas side connection pipe 8 to the indoor unit 200, the indoor heat is transmitted from the outdoor heat exchanger 3 through the liquid side connection pipe 5. The liquid refrigerant easily flows to the exchanger 7 side, and the gas refrigerant easily flows from the indoor heat exchanger 7 to the outdoor heat exchanger 3 side via the gas side connection pipe 8.

  And the said compressor 1, the four-way valve 2, the outdoor heat exchanger 3, the subcooler 34, the outdoor expansion valve 4, the liquid blocking valve 60, the liquid side connection piping 5, the indoor expansion valve 6, the indoor heat exchanger 7, the gas side connection These devices are connected to the compressor 1 via the piping 8, the gas blocking valve 61, the four-way valve 2, and the accumulator 9 again so that they are connected in a ring shape with refrigerant piping, and the refrigeration cycle operation by forced circulation ( Forced circulation operation).

  In this embodiment, a bypass pipe (first bypass pipe) 20 that connects the gas blocking valve 61 and the gas side of the outdoor heat exchanger 3 is provided, and the bypass pipe 20 includes a first pipe. On-off valve 21 and bypass check valve 25 are provided. Furthermore, a second on-off valve 22 is provided in the middle of the refrigerant pipe connecting the gas side of the outdoor heat exchanger 3 and the four-way valve 2, and the refrigerant connecting the gas blocking valve 61 and the four-way valve 2. A third on-off valve 23 is provided in the middle of the piping. One end of the bypass pipe 20 is connected between the third on-off valve 23 and the gas blocking valve 61, and the other end of the bypass pipe 20 is connected to the gas of the second on-off valve 22 and the outdoor heat exchanger 3. The refrigerant pipe 35 is connected to the side header 36.

By comprising in this way, it becomes the structure which can also perform the refrigerating cycle driving | operation (natural circulation driving | operation) by natural circulation. That is, by opening the first on-off valve 21 and closing the second and third on-off valves 22, 23, the gas refrigerant from the evaporator (indoor heat exchanger 7) is supplied to the compressor 1. The natural circulation cooling operation can be performed by flowing to the condenser (outdoor heat exchanger 3) through the bypass pipe 20 without flowing. Accordingly, each of the first to third on-off valves 21 to 23 constitutes a switching circuit that switches between forced circulation operation and natural circulation operation.

Further, in this embodiment, a refrigerant pipe (gas side connection pipe) between the third on-off valve 23 and the gas blocking valve 61 and a refrigerant pipe between the outdoor expansion valve 4 and the liquid blocking valve 60 are provided. A bypass pipe (second bypass pipe) 30 for connecting (liquid side connection pipe) is provided, and the bypass pipe 30 is provided with a refrigerant reservoir 10 for storing surplus refrigerant. The bypass pipe 30 on both sides of the refrigerant reservoir 10 is provided with a gas side on / off valve 26 and a liquid side on / off valve 27 for opening and closing the bypass pipe 30.
The bypass pipe 30 may be provided so as to connect the outdoor heat exchanger 3, the liquid side connection pipe 5 connecting the indoor heat exchanger 7, and the gas side connection pipe 8. Preferably, as shown in FIG. 1, the vicinity of the gas side connection pipe 8 in the outdoor unit 100 (near the gas blocking valve 61) is connected to the vicinity of the liquid side connecting pipe 5 (near the liquid blocking valve). And good.

  In FIG. 1, reference numeral 24 denotes a discharge check valve for preventing the refrigerant from flowing backward to the compressor 1. 40 is a discharge temperature sensor for detecting the discharge side temperature of the compressor 1, 41 is a liquid temperature sensor for the outdoor heat exchanger 3, and 42 is a sub cooler outlet for detecting the temperature of the liquid refrigerant at the outlet of the sub cooler 34. The temperature sensor 43 is a liquid temperature sensor of the indoor heat exchanger 7, 44 is a gas temperature sensor of the indoor heat exchanger 7, and 45 is an indoor suction temperature for detecting the temperature of the indoor air sucked into the indoor heat exchanger 7. A sensor 46 detects the temperature of the air blown into the room after heat is exchanged by the indoor heat exchanger 7, and 47 detects the temperature of the outdoor air sucked into the outdoor heat exchanger 3. The outdoor suction temperature sensor 48 is a discharge pressure sensor for detecting the pressure of the refrigerant discharged from the compressor 1.

  Detection data from each of these sensors 40 to 48 is sent to the control unit 70 provided in the outdoor unit 100, the indoor unit 200, or a remote controller or a remote monitoring device (not shown). Based on information from the sensors, the compressor 1, a four-way valve (switching circuit) 2, an outdoor expansion valve 4, an indoor expansion valve 6, the on-off valves 21 to 23, 26, 27, the outdoor fan 50, The indoor fan 51 is controlled.

  Further, the control device 70 is constituted by a microcomputer or the like, and information inputted from the sensors 40 to 48 or the control objects 1, 2, 4, 6, 21 to 23, 26, 27, 50, 51. The control information is stored.

  Further, the control device 70 is provided with a stop determination device 71 for determining that the natural circulation operation is stopped during the natural circulation operation. The stop determination device 71 determines whether or not the natural circulation operation is stopped, for example, by detecting the cooling capacity during the natural circulation cooling operation. In this embodiment, the stop determination device obtains the difference between the intake air temperature detected by the indoor intake temperature sensor 45 of the evaporator and the blown air temperature detected by the indoor blowout temperature sensor 46, and the difference If is below a predetermined value, it is determined that the natural circulation operation is stopped. The stop determination device 71 includes a rotation speed of the condenser fan (outdoor fan 50), a rotation speed of the evaporator fan (indoor fan 51), an opening degree of the indoor expansion valve (valve device) 6, and the outdoor suction temperature. In addition to at least one of each information such as the outdoor air temperature detected by the sensor 47 (the intake air temperature of the condenser) and the indoor air temperature detected by the indoor intake temperature sensor 45 (the intake air temperature of the evaporator) Further, it is more preferable to determine whether to stop the natural circulation operation.

  A predetermined amount of refrigerant is enclosed in the refrigeration cycle, for example, refrigerants such as R410A, R407C, R404A, R134a, R32, R1234yf, R1234ze, R152a, R744, R717, R290, R600a, or a mixture thereof. It is used. In selecting the refrigerant, it is desirable that the pressure loss is low and the latent heat of vaporization is large because the efficiency of forced circulation operation and natural circulation operation can be increased.

R410A, which is currently widely used in packaged air conditioners (commercial air conditioners) and room air conditioners, can reduce power consumption and reduce indirect effects on global warming.
In addition, if R32 with large latent heat of vaporization is used, the amount of refrigerant circulating when operating with the same capacity can be reduced, resulting in lower pressure loss than R410A and improved operating efficiency. Carbon dioxide can be reduced. In addition, since R32 has a small GWP (global warming potential) of the refrigerant, it is possible to reduce the direct influence of global warming that occurs when the refrigerant leaks into the atmosphere. The low pressure loss characteristic when using R32 is natural circulation because it is easy to maintain stable circulation even when the differential pressure for driving the refrigeration cycle is very small as in natural circulation operation. It is particularly effective as a refrigerant for a type of air conditioner that is used by switching between operation and forced circulation operation. In addition, you may use the refrigerant | coolant which made not only R32 but the ratio of R32 50% or more (-less than 100%) as said refrigerant | coolant.

  During the forced circulation operation for driving the compressor 1, the first on-off valve 21 is closed in both the cooling operation and the heating operation, and the second on-off valve 22 and the third on-off valve 23 are controlled to be opened. The In the forced circulation cooling operation, the four-way valve 2 is switched so that the discharge side of the compressor 1 and the gas side of the outdoor heat exchanger 3 are connected, and the accumulator 9 and the gas blocking valve 61 side are connected. As a result, the refrigerant which has been compressed by the compressor 1 and becomes high temperature and high pressure is led to the outdoor heat exchanger 3 through the four-way valve 2 and cooled by the outdoor air blown from the outdoor blower (condenser fan) 50. It is condensed and becomes a liquid refrigerant. Thereafter, the liquid refrigerant passes through the outdoor expansion valve 4 that is controlled to be fully opened, passes through the liquid blocking valve 60 and the liquid side connection pipe 5, and is sent to the indoor unit 200.

  The liquid refrigerant sent to the indoor unit 200 is depressurized by a predetermined amount by the indoor expansion valve (valve device) 6, becomes a low-pressure gas-liquid two-phase flow, and flows into the indoor heat exchanger (evaporator) 7. Here, the low-pressure refrigerant in the gas-liquid two-phase flow is evaporated by exchanging heat with the indoor air from the indoor blower (evaporator fan) 51 to become a low-pressure gas refrigerant, and the indoor air is cooled, thereby cooling. The action is made.

  Thereafter, the low-pressure gas refrigerant returns to the outdoor unit 100 through the gas side connection pipe 8, passes through the gas blocking valve 61, flows from the four-way valve 2 to the accumulator 9, and is sucked into the compressor 1.

  As described above, in the forced circulation cooling operation in the air conditioner, the refrigerant is compressed by the compressor 1, condensed by the outdoor heat exchanger 3, decompressed by the indoor expansion valve 6, and evaporated by the indoor heat exchanger 7. It constitutes a series of refrigeration cycles.

  During the forced circulation heating operation, the four-way valve 2 is switched so that the discharge side of the compressor 1 and the gas blocking valve 61 side are connected, and the accumulator 9 and the gas side of the outdoor heat exchanger 3 are connected. In the operation of the refrigeration cycle, the indoor heat exchanger 7 acts as a condenser and the outdoor heat exchanger 3 acts as an evaporator, compared with the case of forced circulation cooling operation. Heating action will be done. That is, the operation of the refrigeration cycle is reversed, and the states of the indoor heat exchanger 7 and the outdoor heat exchanger 3 are reversed. However, since the principle of the refrigeration cycle is the same, other detailed description is omitted.

  Next, the operation during natural circulation cooling operation (natural circulation operation) will be described with reference to the refrigeration cycle configuration diagram of FIG. 1 and the Mollier diagram of FIG. When switching from forced circulation cooling operation to natural circulation cooling operation, the control device 70 first stops the operation of the compressor 1 and then operates the first to third on-off valves 21 to 23 constituting the switching circuit. And do it. That is, the first on-off valve 21 is opened, and the second on-off valve 22 and the third on-off valve 23 are controlled to close.

  Thereby, since the refrigerant circulation to the compressor 1, the four-way valve 2 and the accumulator 9 is interrupted, unnecessary refrigerant accumulation is prevented, and the amount of refrigerant during natural circulation operation is easily secured. Further, liquid compression due to liquid return when the compressor 1 is restarted can be prevented, and it is possible to prevent a problem that leads to a decrease in reliability.

The natural circulation operation can be performed when the outdoor air temperature To detected by the outdoor suction temperature sensor 47 is lower than the indoor air temperature Ti detected by the indoor suction temperature sensor 45. For example, If the equation is true, the natural circulation cooling operation is performed.
To <Ti-10 (K)
The driving force of the refrigerant by the natural circulation operation is the head difference ΔP generated from the density difference between the liquid refrigerant and the gas refrigerant and the installation height difference H1 between the outdoor unit and the indoor unit. This head difference ΔP is obtained by the following equation. Can do.
ΔP = (ρ _L −ρ _g ) · g · H1
Here, ρ _L is the refrigerant liquid density (kg / m ³ ), ρ _g is the refrigerant gas density (kg / m ³ ), g is the gravitational acceleration (m / s ² ), and H1 is the height between the outdoor unit and the indoor unit. Difference (m).

  That is, in the refrigeration cycle configuration diagram shown in FIG. 1, the refrigerant in the outdoor heat exchanger (condenser) 3 is cooled by outdoor air (lower temperature than indoor air) blown by the outdoor blower (condenser fan) 50. Then, it is condensed and becomes a liquid refrigerant, and circulation is started by the head difference ΔP.

  In this natural circulation operation, the outdoor expansion valve 4 is controlled to be fully opened, so that the liquid refrigerant from the outdoor heat exchanger 3 passes through the outdoor expansion valve 4 as it is, and further passes through the liquid blocking valve 60, It is guided to the indoor unit 200 through the side connection pipe 5.

  In this indoor unit 200, it passes through a substantially fully opened indoor expansion valve (valve device) 6 provided on the upstream side of the indoor heat exchanger 7 as the evaporator, and the indoor heat exchanger (evaporator) 7. To be introduced. When the installation height difference H1 between the outdoor unit 100 and the indoor unit 200 is large, the flow rate is controlled by adjusting the opening degree of the indoor expansion valve 6, thereby performing the capacity control for controlling the cooling capacity. There is also.

  In this capacity control, based on the difference between the intake air temperature of the evaporator detected by the indoor intake temperature sensor 45 and the set air temperature in the air-conditioning target room, the condenser fan (outdoor blower) 50 is first turned on. Control and do. If the capacity control is insufficient only by controlling the condenser fan 50, the evaporator fan (indoor fan) 51 is controlled next. If capacity control is still insufficient, capacity control is performed by controlling the opening degree of the valve device 6 on the upstream side of the evaporator. In this order, if necessary, for example, by controlling the fans 50 and 51 to the low speed side and the valve device 6 to the low opening side in order, capacity control to the low capacity side is possible. Become.

  In this embodiment, the example in which the valve device 6 provided upstream of the evaporator (indoor heat exchanger 7) is configured by only an indoor expansion valve has been described. However, the valve device 6 is an expansion valve. In the natural circulation cooling operation, the expansion valve is fully closed and the on-off valve is opened so that the refrigerant passes through the bypass circuit. You may comprise.

  The liquid refrigerant that has flowed into the indoor heat exchanger 7 is heated by exchanging heat with the indoor air blown by the indoor blower (evaporator fan) 51 and evaporated to become a gas refrigerant. At this time, the room air is cooled to cool the room.

  The gas refrigerant in the indoor heat exchanger 7 rises through the gas side connection pipe 8, flows into the outdoor unit 100 installed above, passes through the gas blocking valve 61, and then passes through the first on-off valve. 21, a series of refrigeration cycles in which the air passes through the bypass check valve 25 and returns to the outdoor heat exchanger (condenser) 3 again.

Here, when the operation state at the time of natural circulation operation is shown on the Mollier diagram of FIG. 2, a → b represents the condensation action in the outdoor heat exchanger (condenser) 3, and b → c represents the outdoor unit 100 to the indoor unit. The liquid head difference ΔPL is increased by the descending liquid refrigerant to the machine 200, and the pressure is increased. The liquid head difference ΔPL is:
ΔPL = ρ _L · g · H1
Can be obtained. Note that b → c in FIG. 2 also takes into account the pressure loss ΔPLpipe of the liquid side connection pipe 5. Δh is a specific enthalpy difference between the evaporator and the condenser, Gr is a refrigerant circulation amount during normal natural circulation operation, SCco is a condenser outlet supercooling degree, and SHeo is an evaporator outlet superheat degree.

Next, c → d is the evaporation effect in the indoor heat exchanger (evaporator) 7, and d → a is the pressure loss ΔPgpipe in the gas side connection pipe 8 due to the rise of the gas refrigerant from the indoor unit 200 to the outdoor unit 100. And a pressure drop due to the gas head difference ΔPg (= ρ _g · g · H1). In this way, the refrigerant naturally circulates from a → b → c → d → a to constitute a refrigeration cycle for natural circulation operation.

  On the other hand, what is shown on the Mollier diagram of FIG. 3 is an operating state of natural circulation cooling when the rotational speeds of the condenser fan (outdoor fan 50) and the evaporator fan (indoor fan 51) are suppressed. . When the rotational speed of the condenser fan is controlled to be low, the refrigerant state in the condenser (outdoor heat exchanger 3) decreases from a ′ → b ′ and the specific enthalpy difference Δh ′, and the condenser outlet state becomes liquid refrigerant. It becomes a gas-liquid two-phase state mixed with gas refrigerant. Further, when the evaporator fan is controlled at a low speed, the refrigerant state in the evaporator is c ′ → d ′, and at the outlet of the evaporator, a gas-liquid two-phase state in which the liquid refrigerant is mixed into the gas refrigerant is obtained.

When the outlet state of the condenser (outdoor heat exchanger 3) is in a gas-liquid two-phase state, the liquid-side connection pipe in which the refrigerant descends from the condenser to the evaporator (indoor heat exchanger 7) is also in the gas-liquid two-phase state. The liquid head difference ΔPL ′ of the liquid side refrigerant is
ΔPL ′ = ρ _L ′ · g · H1
It becomes. Here, the average refrigerant density ρ _L ′ (kg / m ³ ) in the liquid side connection pipe 5 is smaller than that in the liquid side connection pipe 5 due to the mixing of the gas refrigerant. The head is reduced.

When the evaporator outlet state becomes a gas-liquid two-phase state, the gas-side connection pipe 8 in which the refrigerant rises from the evaporator to the condenser also becomes a gas-liquid two-phase state, and the gas head difference ΔPg ′ of the gas-side refrigerant. Is
ΔPg ′ = ρ _g ′ · g · H1
It becomes. Since the average refrigerant density ρ _L ′ (kg / m ³ ) of the refrigerant in the gas side connection pipe 8 becomes larger than that in the case of operating with only gas due to the mixture of liquid refrigerant, the head in the gas side connection pipe 8 is The force increases in the direction that hinders refrigerant circulation.

Further, the pressure loss in each of the connection pipes when the refrigerant flows in a gas-liquid two-phase state increases as compared with the case where only the liquid refrigerant or only the gas refrigerant circulates in each of the connection pipes 5 and 8. . Accordingly, the refrigerant circulation amount Gr ′ during the natural circulation cooling operation shown in FIG. 3 is smaller than the refrigerant circulation amount Gr during the normal natural circulation operation shown in FIG. 2, and the specific enthalpy in the evaporator and the condenser is reduced. Since the difference also decreases as Δh ′ shown in FIG. 3, the cooling capacity Q ′ is
Q ′ = Gr ′ · Δh ′
It decreases to. Thereby, it is possible to adjust the cooling capacity according to the cooling load in the room.

However, when control is performed to reduce the rotational speed of the condenser fan and the evaporator fan in order to adjust the temperature of the air-conditioned room, as described above, the gas refrigerant to the liquid side connection pipe 5 Due to mixing or mixing of the liquid refrigerant into the gas side connection pipe 8, the downward flow in the liquid side connection pipe 5 and the upward flow in the gas side connection pipe 8 may be hindered.
For example, when the refrigerant circulation amount Gr ′ decreases, the gas refrigerant in the liquid side connection pipe 5 cannot fall to the evaporator side, or the liquid refrigerant in the gas side connection pipe 8 rises to the condenser side. You may not be able to. For this reason, refrigerant circulation may stop unintentionally and natural circulation operation may not be possible.

  When the natural circulation cooling operation stops, the cooling capacity cannot be exhibited, the temperature inside the air-conditioned room rises, and if it is used for interpersonal air conditioning, the comfort for residents is impaired, such as a computer When used as an air conditioner, there arises a problem that the stable operation of the device is impaired.

  Therefore, in the air conditioner of this embodiment, during the natural circulation operation, if the temperature difference between the intake air temperature and the blown air temperature in the evaporator is zero for a predetermined time or more, natural circulation is performed. It is determined that the operation has stopped, and the process proceeds to the natural circulation restart control described below.

  In the natural circulation restart control, first, the indoor expansion valve (valve device) 6 installed on the upstream side (upstream side during natural circulation operation) of the evaporator (indoor heat exchanger 7) is closed and the condensation is performed. The fan (outdoor fan 50) and the evaporator fan (indoor fan 51) are operated at an increased speed. As a result, liquid refrigerant is stored in the condenser (outdoor heat exchanger 3), and the refrigerant is gasified and gas refrigerant increases in the evaporator, so the liquid refrigerant decreases.

  Further, in this embodiment, as described with reference to FIG. 1, the liquid side connection pipe connecting the condenser and the evaporator is connected to the height dimension Hhex of the evaporator (indoor heat exchanger 7). Connected to the evaporator at a height dimension range up to 1/4 from the lower part of the evaporator, and the gas side connection pipe 8 is connected to the upper part of the evaporator with respect to the height dimension Hhex of the evaporator. From the condenser to the liquid side connection pipe 5 side, and as a result, the liquid refrigerant can easily flow from the condenser to the liquid side connection pipe 5 side. The side connection pipe 5 is filled with the liquid refrigerant. On the other hand, the state of the gas side connection pipe 8 changes so as to be filled with the gas refrigerant.

  Thus, by changing the state so that the liquid side connection pipe 5 is filled with liquid refrigerant and the gas side connection pipe 8 is filled with gas refrigerant, a sufficient head difference for restarting the natural circulation operation is obtained. Comes to work. The natural circulation operation can be restarted by opening the indoor expansion valve (valve) 6 after holding the control state as described above for a certain period of time.

  Furthermore, in order to facilitate the restart of the natural circulation operation, the liquid side connection pipe 5 is configured only by descending the path from the condenser 3 to the evaporator 7, and a part having a reverse gradient in the middle ( By preventing the occurrence of a trap portion), it is possible to prevent the gas refrigerant from accumulating in the liquid side connection pipe 5, and the effect of facilitating restart can be obtained. Preferably, the path of the gas side connection pipe 8 from the evaporator 7 to the condenser 3 is configured only by ascending so that a portion having a reverse gradient (a portion serving as a trap) does not occur in the middle. The liquid refrigerant can be prevented from accumulating in the middle of the gas side connection pipe 8 and can be easily restarted.

  After the above-described natural circulation restart control is performed, if the generation of the cooling capacity cannot be detected again, that is, the temperature of the air blown from the evaporator 7 detected by the indoor air temperature sensor 46 is the indoor air intake temperature. When the state in which the temperature does not become lower than the intake air temperature to the evaporator 7 detected by the sensor 45 continues for a certain time or longer, the control device 70 performs control to switch to the forced circulation cooling operation. That is, the control device 70 switches the first to third on-off valves 21 to 23 constituting the switching circuit to enable the forced circulation cooling operation, and controls the compressor 1 to start.

  More specifically, the first on-off valve 21 is closed, and the second on-off valve 22 and the third on-off valve 23 are controlled to be opened. Thereafter, the compressor 1 is started, and the refrigerant that has been compressed by the compressor 1 to high temperature and high pressure is led to the outdoor heat exchanger 3 through the four-way valve 2 and is blown from the outdoor blower 50. It is cooled and condensed by the above, and becomes a liquid refrigerant. Thereafter, the liquid refrigerant passes through the outdoor expansion valve 4 that is controlled to be fully opened, and is further sent to the indoor unit 200 through the liquid blocking valve 60 and the liquid side connection pipe 5.

  The liquid refrigerant sent to the indoor unit 200 is decompressed by a predetermined amount by the indoor expansion valve 6, becomes a low-pressure gas-liquid two-phase flow, and flows into the indoor heat exchanger 7. Here, the gas-liquid two-phase low-pressure refrigerant evaporates by exchanging heat with the room air from the indoor blower 51, and becomes a low-pressure gas refrigerant and cools the room air, thereby performing a cooling operation.

  Thereafter, the low-pressure gas refrigerant returns to the outdoor unit 100 through the gas-side connection pipe 8, passes through the gas blocking valve 61, flows from the four-way valve 2 to the accumulator 9, and is sucked into the compressor 1 again. Forced circulation cooling operation is performed.

  In this way, by performing the forced circulation cooling operation for a certain time, the liquid side connection pipe 5 is filled with the liquid refrigerant, and the gas side connection pipe 8 is filled with the gas refrigerant. For this reason, switching to the subsequent natural circulation operation can be performed reliably.

According to the present embodiment, in natural circulation operation, the refrigerant state in the liquid side connection pipe 5 and the gas side connection pipe 8 is not ideal, and even if natural circulation operation is stopped, stable natural An air conditioner capable of promptly restarting the circulation operation can be obtained.
Further, according to the present embodiment, when the natural circulation operation is stopped unexpectedly, the stop state can be determined promptly and accurately, and the system can be promptly restarted to a stable natural circulation operation, so that unnecessary power consumption is suppressed. In addition, it is possible to reduce adverse effects on comfort due to an increase in the temperature of the air-conditioned room.

DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Four-way valve, 3 ... Outdoor heat exchanger (condenser), 4 ... Outdoor expansion valve,
5 ... Liquid side connection piping, 6 ... Indoor expansion valve (valve device), 7 ... Indoor heat exchanger (evaporator),
8 ... Gas side connection piping, 9 ... Accumulator, 10 ... Refrigerant reservoir,
20: Bypass piping (first bypass piping),
21-23 ... switching circuit (21 ... 1st on-off valve, 22 ... 2nd on-off valve,
23 ... Third on-off valve)
24 ... discharge check valve, 25 ... bypass check valve,
26 ... Gas side on / off valve, 27 ... Liquid side on / off valve,
30: Bypass piping (second bypass piping),
33 ... Distributor, 34 ... Subcooler,
36 ... Gas side header, 40 ... Discharge temperature sensor,
41, 43 ... liquid temperature sensor, 42 ... subcooler outlet temperature sensor,
44 ... gas temperature sensor,
45 ... Indoor suction temperature sensor, 46 ... Indoor discharge temperature sensor,
47 ... outdoor suction temperature sensor, 48 ... discharge pressure detection means,
50 ... Outdoor fan (condenser fan), 51 ... Indoor fan (evaporator fan),
60 ... Liquid blocking valve, 61 ... Gas blocking valve,
70 ... Control device, 71 ... Stop determination device,
100: outdoor unit, 200: indoor unit.

Claims (9)

An evaporator, a condenser installed at a position higher than the evaporator, a liquid side connection pipe and a gas side connection pipe connecting the evaporator and the condenser, and an upstream side of the evaporator. An air conditioner comprising a valve device, an evaporator fan for blowing air to the evaporator, and a condenser fan for blowing air to the condenser, and performing a refrigeration cycle operation by natural circulation,
A natural circulation operation stop determination device that detects whether or not the natural circulation operation is stopped by detecting the cooling capacity during the cooling operation by natural circulation is provided, and the stop determination device includes at least the intake air temperature and the blown air temperature of the evaporator Based on the difference with
When the natural circulation operation is stopped during the cooling operation by natural circulation, the valve device provided on the upstream side of the evaporator is fully closed, and the evaporator fan and the condenser fan are accelerated, and the liquid side connection is performed. Control is performed to increase the liquid refrigerant in the pipe and to increase the gas refrigerant in the gas side connection pipe, and then open the valve device on the upstream side of the evaporator to restart the natural circulation operation. An air conditioner comprising a control device. 2. The air conditioner according to claim 1 , wherein the stop determination device further includes a rotation speed of the condenser fan, a rotation speed of the evaporator fan, an opening degree of the valve device, and an intake air temperature of the condenser. The air conditioner is characterized by determining whether or not the natural circulation operation is stopped by adding at least one piece of information on the intake air temperature of the evaporator. The air conditioner according to claim 1 or 2 , wherein the condenser fan and the evaporator are based on a difference between an intake air temperature of the evaporator and a set air temperature in an air-conditioning target room during natural circulation operation. An air conditioner that performs capacity control by sequentially controlling a fan and a valve device on the upstream side of the evaporator in order toward a low speed side or a low opening side as necessary. 3. The air conditioner according to claim 1, wherein the liquid side connection pipe is configured such that a portion having a reverse gradient does not occur in the middle thereof. 4. It is an air conditioner of Claim 4 , Comprising: The said gas side connection piping is comprised so that the part which becomes a reverse gradient may not arise in the middle. It is an air conditioner of Claim 1 or 2 , Comprising: The said liquid side connection piping is a height dimension range up to 1/4 with respect to the height dimension of the said evaporator toward the upper direction from this evaporator lower part. The gas side connection pipe is connected to the evaporator at a position at a height dimension range position up to ¼ from the upper part of the evaporator toward the lower side with respect to the height dimension of the evaporator. An air conditioner characterized by being connected to. The air conditioner according to claim 1, comprising a compressor for forced circulation operation, and a switching circuit for switching between forced circulation operation and natural circulation operation,
After the natural circulation operation is stopped, if the control device cannot be restarted even if control is performed to restart the natural circulation operation, the control device switches the switching circuit and the compressor. An air conditioner characterized by being controlled to start up and perform forced circulation operation. The air conditioner according to claim 1 or 7 , wherein a refrigerant containing 50% or more of R32 or R32 is used as the refrigerant. An evaporator, a condenser installed at a position higher than the evaporator, a liquid side connection pipe and a gas side connection pipe connecting the evaporator and the condenser, and an upstream side of the evaporator. A control method for an air conditioner comprising a valve device, an evaporator fan for blowing air to the evaporator, and a condenser fan for blowing air to the condenser, and performing a refrigeration cycle operation by natural circulation,
Determining whether or not to stop the natural circulation operation based on at least the difference between the intake air temperature and the blown air temperature of the evaporator,
When the natural circulation operation stops, the valve device provided upstream of the evaporator is fully closed, and the evaporator fan and the condenser fan are accelerated to increase the liquid refrigerant in the liquid side connection pipe. The gas-side connection pipe is controlled to increase the gas refrigerant, and then the valve device on the upstream side of the evaporator is opened to restart the natural circulation operation. Method.

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