JP3864519B2 - Air conditioner - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air conditioner including a compressor controlled to have variable compression capacity.
[0002]
[Prior art]
2. Description of the Related Art An air conditioner that includes an inverter and that variably controls the operation frequency of a compressor according to a user's remote control operation or the like has been conventionally used. In such an air conditioner, the operation of the compressor is shown on a graph as shown in FIG. 6 with the condensing pressure and the operating frequency as two axes in relation to the operating frequency of the compressor and the torque of the compressor driving motor. A possible area is formed. The one-dot chain line in the figure shows the operable area.
[0003]
Here, the operating frequency of the compressor is changed from f1 ′ to f2 ′ shown in FIG. 6 by changing the set temperature by the user's remote control operation, for example, in the cooling operation when the outdoor temperature is high, for example, under operating conditions with high condensation pressure. Consider the case of changing to Since the condensation pressure is high when the operating frequency is f1, the operating point of the refrigerant circuit at that time is located at A1 ′. However, while the operation frequency of the compressor is rapidly changed from f1 ′ to f2 ′ by the control of the microcomputer or the like via the inverter, the condensation pressure is delayed with respect to the change of the operation frequency as shown by the broken line in FIG. However, it changes from p1 'to p2'. Therefore, before the operating point of the refrigerant circuit reaches A2 ′, the operating point exceeds the operable area indicated by the one-dot chain line when the operating frequency becomes Fstop. If the operation is continued beyond the operable area, an unreasonable load is applied to the compressor, and the compressor cannot be operated and may be abnormally stopped. Therefore, in the conventional air conditioner, the outdoor temperature is detected by an outdoor temperature sensor provided in the outdoor unit, and the operation frequency of the compressor is controlled based on the outdoor temperature.
[0004]
FIG. 5 is a flowchart showing control of the compressor in the conventional air conditioner performed based on the outdoor temperature. First, in step S11, the outdoor temperature DOA is measured by the outdoor temperature sensor. Next, in step S12, the measured outdoor temperature DOA is compared with a predetermined reference temperature DOAMN. When the outdoor temperature DOA is higher than the reference temperature DOAMN, the process proceeds to step S13, and the lower limit operating frequency is set to F1 (see FIG. 6) higher than the Fstop, while the outdoor temperature DOA is lower than the reference temperature DOAMN. If so, the process proceeds from step S12 to step S14, and the lower limit operating frequency is set to F0 (see FIG. 6). By limiting the lowering of the operating frequency of the compressor by the lower limit operating frequency, the operating point of the refrigerant circuit is prevented from deviating from the operable area of the compressor, and the reduction of the condensing pressure is reduced. Even if it occurs later than the operating frequency, the compressor does not stop abnormally.
[0005]
[Problems to be solved by the invention]
The condensing pressure is certainly greatly influenced by the outdoor temperature. Therefore, as in the conventional air conditioner described above, the operation temperature is controlled by indirectly considering the outdoor temperature as the load of the compressor, so that the abnormal stop of the compressor can be avoided by simple control. However, the condensing pressure fluctuates not only according to the outdoor temperature but also depending on the indoor temperature, the temperature set by a remote controller or the like, the air volume set, and the like. Therefore, for example, when the indoor set temperature by the user is relatively high, the compressor load may not be very heavy even if the outdoor temperature is high. Therefore, in such a case, even if the outdoor temperature DOA is higher than the reference temperature DOAMN, the operation frequency of the compressor can be made lower than the lower limit operation frequency F1 without causing an abnormal stop.
[0006]
However, in the conventional air conditioner, since the lower limit operation frequency of the compressor is determined based on the outdoor temperature, the operation is higher than necessary because the outdoor temperature is high even though the load on the compressor is not so heavy. The compressor was sometimes operated at a frequency. And by operating the compressor at an operation frequency higher than necessary in this way, the supply of air conditioning capacity to the indoor unit becomes excessive, and the compressor starts and stops repeatedly, which makes the vertical movement of the room temperature intense. There was a problem that air conditioning comfort was impaired. There is also a problem that excessive supply of air conditioning capability to the indoor unit as described above causes waste of electric power, which contributes to an increase in running cost. Furthermore, since the compressor is operated at an operation frequency higher than necessary, there is a problem that the operation noise increases and air conditioning comfort is impaired.
[0007]
The present invention has been made to solve the above-mentioned conventional drawbacks, and its object is to reliably avoid an abnormal stop of the compressor and to appropriately set the operating frequency according to the load of the compressor. An object of the present invention is to provide an air conditioner capable of performing control.
[0008]
[Means for Solving the Problems]
Accordingly, the air conditioner according to the first aspect includes the compressor 1 that is controlled so that the compression capacity is variable, and is provided with a predetermined lower limit operating frequency so that the lowering of the operating frequency of the compressor 1 is limited by the lower limit operating frequency. In the air conditioner, the condensing temperature detector 13 is provided, and the lower limit operating frequency is a predetermined first reference frequency F0 when the condensing temperature DC detected by the condensing temperature detector 13 is equal to or lower than a predetermined reference temperature. On the other hand, when the condensation temperature DC is higher than the reference temperature, the second reference frequency FTR is higher than the first reference frequency F0, and the reference temperature is higher than when the condensation temperature DC is lowered. It is characterized by being set so as to be higher when doing.
[0009]
In the air conditioner of the first aspect, the lower limit operating frequency is set based on the condensation temperature. Since there is a direct correlation between the condensing temperature and the load of the compressor 1, the air conditioner operates according to the load of the compressor 1 while reliably avoiding the abnormal stop of the compressor 1. Appropriate control of the frequency can be performed.
[0011]
In the above air conditioner, when the load is light, the lower limit operating frequency is set low, thereby avoiding operating the compressor at an operating frequency higher than necessary while reliably avoiding abnormal stop of the compressor 1. It becomes possible.
[0013]
Further, in the above air conditioner, the control of the compressor 1 can be made simple by using two reference frequencies to facilitate the implementation thereof.
[0015]
In the air conditioner, it is possible to further improve air conditioning comfort by preventing hunting.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Next, specific embodiments of the air conditioner of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 4 is a diagram showing a refrigerant circuit of the air conditioner. As shown in the figure, in this air conditioner, a discharge pipe 1a and a suction pipe 1b of the compressor 1 are connected to a four-way switching valve 10, and the four-way switching valve 10 includes an outdoor heat exchanger 2, a capillary. The tube 3 and the indoor heat exchanger 4 are sequentially connected in an annular shape by a first gas pipe 19a, a first liquid pipe 19b, a second liquid pipe 19c, and a second gas pipe 19d. A part of the second liquid pipe 19c becomes the liquid pipe 17 of the communication pipe, and a part of the second gas pipe 19d becomes the gas pipe 16 of the communication pipe. The compressor 1 is controlled by the control unit 12 through the inverter 11 so that the compression capacity can be varied. The control unit 12 is configured using a microcomputer or the like. Furthermore, an outdoor heat exchanger thermistor 13 is attached to the outdoor heat exchanger 2. The outdoor heat exchange thermistor 13 functions as a condensation temperature detector during the cooling operation, and the detected condensation temperature is input to the control unit 12.
[0018]
The air conditioner can perform a cooling operation or a heating operation based on a command from a remote controller or the like. When performing the cooling operation, the four-way switching valve 10 is switched in the direction of the solid line shown in the figure, and the refrigerant is sequentially supplied from the compressor 1 to the outdoor heat exchanger 2, the capillary tube 3 (or motor-operated valve), and the indoor heat exchanger. 4, the outdoor heat exchanger 2 functions as a condenser, and the indoor unit 4 functions as an evaporator. Then, the amount of heat absorbed in the room is released to the outside of the room through the refrigerant, thereby cooling the room at a lower temperature. On the other hand, when performing the heating operation, the four-way switching valve 10 is switched in the direction of the broken line shown in the figure to circulate the refrigerant in the direction opposite to that during the cooling operation, and the outdoor heat exchanger 2 functions as an evaporator. In addition, the indoor heat exchanger 4 is caused to function as a condenser, and the amount of heat absorbed by the outdoor heat exchanger 2 is released into the room through the refrigerant, thereby heating the room by raising the temperature in the room.
[0019]
Moreover, in the said air conditioner, the compressor 1 is controlled by variable compression capability so that air-conditioning capability can be exhibited appropriately according to a user's remote control setting or the like. This control is performed by the control unit 12 changing the operating frequency of the compressor 1 via the inverter 11. However, in the air conditioner as well, as in the case of the conventional air conditioner, a graph with the condensing pressure and the operating frequency as two axes in the relationship between the operating frequency of the compressor 1 and the torque of the motor that drives the compressor 1. The compressor 1 cannot be operated beyond the operable area formed above. If such operation is continued, an unreasonable load is applied to the compressor 1, and the compressor 1 may become inoperable and abnormally stop. Such a situation may occur under an overload condition in which the compressor 1 is driven at a low operating frequency when the outdoor temperature is high and the cooling operation is performed. Therefore, in the above air conditioner, the outdoor heat exchange thermistor 13 is provided in the outdoor unit, and the decrease in the operation frequency of the compressor 1 is limited by using the condensation temperature detected by the outdoor heat exchange thermistor 13 during the cooling operation. Next, this will be described.
[0020]
FIG. 2 is a flowchart illustrating the control performed by the control unit 12 in order to limit the decrease in the operating frequency of the compressor 1. In performing this control, first, the condensation temperature DC is measured by the indoor heat exchanger thermistor 13 in step S1 of the flowchart of FIG. In step S2, the measured condensation temperature DC is compared with predetermined reference temperatures DCTR1 and DCTR4. At this time, if the condensing temperature DC tends to rise, the condensing temperature DC is compared with the temperature rising side reference temperature DCTR1, and if the condensing temperature DC tends to fall, it is set as a temperature lower than the temperature raising side reference temperature DCTR1. Compared with the lowered temperature reference temperature DCTR4. When the condensing temperature DC is higher than the reference temperatures DCTR1 and DCTR4, the process proceeds to step S3, where the lower limit operating frequency of the compressor 1 is set to the first reference frequency F0 which is the lowest limit frequency of the operable area (see FIG. 3)), which is higher than the second reference frequency FTR (see the same figure). On the other hand, when the condensation temperature DC is not more than the reference temperatures DCTR1 and DCTR4, the process proceeds to step S4, and the lower limit operating frequency of the compressor 1 is set to the first reference frequency F0. In other words, as shown in FIG. 1, considering that the condensation temperature DC is once lower than the reference temperature DCTR1 and once exceeds the reference temperature DCTR4 again, until the condensation temperature DC exceeds the temperature increase side reference temperature DCTR1. If the lower limit operating frequency is F0 and the condensation temperature DC exceeds the temperature rising side reference temperature DCTR1, the lower limit operating frequency is set to FTR. On the other hand, the lower limit operating frequency remains FTR until the condensation temperature DC falls below the temperature lowering side reference temperature DCTR4. If the condensation temperature DC falls below the temperature-lowering reference frequency DCTR4, the lower limit operating frequency is returned to F0.
[0021]
FIG. 3 is a diagram showing a lower operation frequency side in the operable area formed on a graph having the condensation pressure and the operation frequency of the compressor 1 as two axes. Here, consider reducing the operating frequency of the compressor 1 from f1 to f2 in FIG. First, when the operating frequency is f1, the operating point of the refrigerant circuit is A1, and the condensation pressure is high. At this time, the condensation temperature DC having a direct correlation with the condensation pressure is higher than both the DCTR1 and the DCTR4. Therefore, regardless of whether the condensation temperature DC tends to increase or decrease, the lower limit operation frequency is set to the second reference frequency FTR. Since the decrease in the condensation pressure is delayed from the decrease in the operating frequency of the compressor 1, the operating frequency of the compressor 1 is limited by the second reference frequency FTR, and the refrigerant circuit is in the state of the operating point A3 in FIG. Become. However, since the operating frequency of the compressor 1 has decreased from f1 to FTR, the condensation pressure generally decreases gradually thereafter. The condensation pressure also decreases when the indoor set temperature is raised by a user's remote control operation or the like. When the condensation pressure is lowered for these reasons, the condensation temperature DC is also lowered because there is a direct correlation between the condensation pressure and the condensation temperature DC. When the condensation temperature DC becomes lower than the temperature decrease side reference temperature DCTR4 in this way, the lower limit operating frequency is set to the first reference frequency F0, so that the operating frequency of the compressor 1 can be lowered to f2. . The operating point of the refrigerant circuit thus reached is indicated by A2 in FIG.
[0022]
On the other hand, even when the operating frequency of the compressor 1 is decreased from f1 to f2 in the same manner, when the condensation pressure is sufficiently low and the condensation temperature DC is lower than any of the reference temperatures DCTR1 and DCTR4, The lower limit operating frequency is set to the first reference frequency F0. Therefore, the operating frequency of the compressor 1 can be lowered from f1 to f2. In FIG. 3, this is shown as a change from the operating point B1 to B2.
[0023]
In the air conditioner, the lower limit operating frequency is set based on the condensation temperature DC. Since there is a direct correlation between the condensing pressure and the condensing temperature DC, control based on the condensing temperature DC can be performed to directly grasp the load of the compressor 1. In the conventional air conditioner, since the load of the compressor 1 is indirectly grasped based on the outdoor temperature, the compressor may be operated at an operation frequency higher than necessary. However, in the above, since the load of the compressor 1 is directly grasped and control based on this is performed, an abnormal stop occurs in the compressor 1 as in the change from the operating point A3 to A2 in FIG. When the load is light without fear, the operating frequency of the compressor 1 can be reliably reduced. Therefore, it is possible to prevent the compressor 1 from being operated at an operation frequency higher than necessary while avoiding an abnormal stop of the compressor 1. Therefore, the situation where the start and stop of the compressor 1 is repeated due to excessive supply of the air conditioning capability to the indoor unit is avoided, and the air conditioning comfort is improved by suppressing the vertical movement of the room temperature caused by the start and stop of the compressor 1. be able to. Further, by suppressing excessive supply of air conditioning capability to the indoor unit, it is possible to reduce power consumption and reduce running costs. Further, when the load on the compressor 1 is light, the lower limit operating frequency is reliably lowered, so that the operation noise can be suppressed and air conditioning comfort can be further improved. In addition, the temperature decrease side reference temperature DCTR4 to be compared when the condensation temperature DC is decreasing is set lower than the temperature increase side reference temperature DCTR1 to be compared when the condensation temperature DC is increasing. Therefore, it is possible to avoid the hunting phenomenon caused by repeated setting changes of the lower limit operating frequency, thereby further improving the air conditioning comfort. And it can be set as simple control by setting it as control using two lower limit operating frequencies F0 and FTR.
[0024]
Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention. Although the control of the compressor 1 during the cooling operation has been described above, the present invention can also be applied during the heating operation. In this case, an indoor heat exchanger thermistor is attached to the indoor heat exchanger 4, and the condensation temperature detected by the indoor heat exchanger thermistor may be used for comparison with a predetermined reference temperature. In the above, an example in which the lower limit operating frequency is divided into two stages of F0 and FTR has been described. However, by having more reference temperatures DCTR1 and DCTR4, the lower limit operating frequency is increased over three stages and is used as a load. On the other hand, it is possible to set a finer lower limit operating frequency.
[0025]
【The invention's effect】
In the air conditioner according to the first aspect, the lower limit operating frequency of the compressor is set based on the condensing temperature where a direct correlation exists between the condensing temperature and the load of the compressor. Therefore, it is possible to appropriately control the operation frequency according to the load of the compressor while reliably avoiding the abnormal stop of the compressor.
[0026]
Further, by setting the lower limit operating frequency low when the load is light, it is possible to avoid operating the compressor at an operating frequency higher than necessary while reliably avoiding abnormal stop of the compressor.
[0027]
Furthermore, the compressor can be easily controlled by using two reference frequencies.
[0028]
Moreover, it is possible to prevent hunting and further improve air conditioning comfort.
[Brief description of the drawings]
FIG. 1 is a graph for explaining setting of a lower limit operating frequency of a compressor performed in an air conditioner of the present invention.
FIG. 2 is a flowchart for explaining the setting of the lower limit operating frequency.
FIG. 3 is a diagram illustrating compressor operation control performed using the lower limit operation frequency.
FIG. 4 is a refrigerant circuit diagram of the air conditioner.
FIG. 5 is a flowchart for explaining setting of a lower limit operating frequency of a compressor performed in a conventional air conditioner.
FIG. 6 is a diagram illustrating compressor operation control performed in a conventional air conditioner.
[Explanation of symbols]
1 Compressor 13 Outdoor heat exchange thermistor DC Condensing temperature F0 First reference frequency (lower limit operating frequency)
FTR second reference frequency (lower limit operating frequency)

Claims (1)

In an air conditioner provided with a compressor (1) controlled to be variable in compression capacity, provided with a predetermined lower limit motion frequency, and limiting the lowering of the operating frequency of the compressor (1) by this lower limit motion frequency The condensation temperature detector (13) is provided, and the lower limit motion frequency is a predetermined first reference frequency (F0 ) when the condensation temperature (DC) detected by the condensation temperature detector (13) is equal to or lower than a predetermined reference temperature. On the other hand, when the condensation temperature (DC) is higher than the reference temperature, the second reference frequency (FTR) higher than the first reference frequency (F0) is set. An air conditioner characterized in that the air conditioner is set to be higher when it is raised than when it is lowered.

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