JPH09229494A - Air conditioner - Google Patents

Abstract

(57) Abstract: By appropriately controlling the expansion device 4 of the main circuit, the liquid injection circuit can be effectively used, and it is possible to prevent deterioration of the heat pump capacity when the outside air temperature is low, and to provide air with excellent comfort. Get a harmony machine. A compressor, a four-way valve, an indoor heat exchanger,
In a refrigeration cycle including an expansion valve, an outdoor heat exchanger, a gas-liquid separator, and a liquid injection circuit, the expansion valve is controlled so that the compressor inlet has a target superheat degree.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a refrigeration cycle having a liquid injection circuit, and is particularly suitable for an air conditioner capable of both cooling operation and heating operation.

[0002]

2. Description of the Related Art As a conventional technique, JP-A-6-32364
No. 0, Japanese Patent Application No. 7-16670, a refrigeration cycle with a liquid injection circuit often uses a compressor with a fixed operating frequency, and a throttle tube uses a capillary tube to fix the refrigerant flow rate. Although it was suitable for the refrigeration cycle, there was no statement about means for appropriately controlling the expansion device when the operating frequency of the compressor changed or when the refrigeration cycle changed for cooling and heating.

Further, JP-A-6-272978 and JP-A-6-272978.
In an air conditioner using a refrigeration cycle with a liquid injection circuit as disclosed in Japanese Patent Publication No. 180153, the structure is such that the liquid injection circuit is used regardless of cooling operation or heating operation, and operation is possible by using injection. There were cases where the environmental range was limited.

In addition, the operation means is different from that of an air conditioner using a refrigeration cycle without a liquid injection circuit,
It required special knowledge when inspecting the equipment. ◆ Furthermore, it is necessary to assist the decrease in heat pump capacity when the outside air temperature is low with combustion energy such as kerosene or gas, exhaust gas is generated, refueling is required, and knowledge about combustion equipment is required. was there.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to properly control the expansion device of the main circuit so that the liquid injection circuit can be effectively used and the heat pump capacity can be prevented from being lowered when the outside air temperature is low. To obtain an air conditioner with excellent performance. Furthermore, the purpose of the present invention is to use the liquid injection circuit only for heating operation, thereby standardizing the refrigeration cycle operation method during cooling operation as with the refrigeration cycle operation method without the liquid injection circuit, which facilitates facility inspectors. To obtain an air conditioner capable of diagnosing a refrigeration cycle.

[0006]

An air conditioner according to the present invention comprises a compressor, a four-way valve, an indoor heat exchanger, an expansion valve,
In a refrigeration cycle having an outdoor heat exchanger, a gas-liquid separator, and a liquid injection circuit, the expansion valve is controlled so that the compressor inlet has a target superheat degree.

[0007]

Embodiments of the present invention will be described below.

FIG. 1 shows a refrigerating cycle with a liquid injection circuit of an air conditioner, and the two-dot chain lines represent an indoor unit and an outdoor unit, respectively. ◆ The refrigeration cycle is composed of a compressor 1, a four-way valve 2, an outdoor heat exchanger 3, an outdoor expansion valve 4, an indoor expansion valve 5, an indoor heat exchanger 6, a gas-liquid separator 7, and an expansion valve 8 for liquid injection. , Are connected by respective pipes. Further, the indoor and outdoor heat exchangers are provided with a blower 9, and the heat is exchanged between the refrigerant and the air by blowing air to the heat exchanger.

Further, the air conditioner is operated by the refrigeration cycle operating means 13 by taking in the detected values obtained from the pressure detecting means 10 and the temperature detecting means 11 by the detected value inputting means 12.

Temperature detectors are attached to the compressor 1, the outdoor heat exchanger 3, and the indoor heat exchanger 7, and the compressor discharge refrigerant temperature Td, the compressor intake refrigerant temperature Ts, the outdoor air temperature Tao, and the outdoor are respectively The heat exchanger inlet refrigerant temperature Te1, the outdoor heat exchanger outlet refrigerant temperature Te2, the indoor air intake temperature Ta1, the indoor air blowing temperature Ta2, the indoor heat exchanger inlet refrigerant temperature Tr1, and the indoor heat exchanger outlet refrigerant temperature Tr2 are detected. Further, the compressor 1 is provided with a pressure detecting means, and the compressor suction pressure is
Detect Ps and compressor discharge pressure Pd. (Explained by symbols below) ◆ Here, the flow of the refrigerant when the refrigeration cycle is operated in the cooling operation state is as follows: compressor 1, four-way valve 2, outdoor heat exchanger 3, outdoor expansion valve 4, indoor expansion The valve 5, the indoor heat exchanger 6, the gas-liquid separator 7, and the compressor 1 are arranged in this order.

The liquid injection circuit in the heating operation makes it possible to operate the refrigeration cycle even when the evaporation pressure is low when the evaporator capacity is so low that heat cannot be pumped up from the evaporator. It has the function of suppressing the decrease in the refrigerant circulation amount and the abnormal overheating of the compressor. ◆ In addition, the liquid injection circuit during cooling operation allows the outdoor unit to adjust the outlet refrigerant superheat degree (hereinafter referred to as TdSH) independently of the operating state of the indoor unit.

FIG. 2 shows a general Mollier diagram.

In a normal refrigeration cycle, the evaporator outlet refrigerant is compressed without being overheated to keep TdSH constant. However, when the evaporator outlet refrigerant is compressed by being superheated, it is excessive.
It becomes TdSH, and abnormal temperature rise of the compressor may cause deterioration of the compressor motor coil and deterioration of the refrigerating machine oil.

Here, in order to use the liquid injection circuit, it is necessary to secure the superheat degree of the refrigerant at the outlet of the evaporator shown in FIG. This is because if a liquid injection circuit is used in a normal refrigeration cycle where TdSH does not rise, TdSH will drop and the refrigerant will melt into the refrigeration oil, reducing the lubrication performance of the refrigeration oil and causing the compressor to slide. This is because there is a possibility that the surface will be worn away, and this will be avoided.

FIG. 3 shows a means for ensuring the degree of superheat of the refrigerant at the outlet of the evaporator.
This will be described with reference to FIG. ◆ First, start operation of the air conditioner. (Step 100) ◆ Next, suction pressure Ps and suction temperature Ts
Is detected. (Step 101) ◆ Obtain the refrigerant saturation temperature Tc at the compressor suction pressure Ps. (Step 102) ◆
As for the refrigerant saturation temperature, there are methods such as having a table in which the refrigerant saturation temperature for each pressure is described in the refrigeration cycle operating means 13, and a method of expressing the relationship between the pressure and the saturation temperature in the form of an approximate expression. Was used.

The difference Δt between the compressor suction refrigerant temperatures Ts and Tc is determined (step 103), and the target superheat degree (TsSH) is compared with Δt. (Step 104) ◆ If TsSH> Δt, it is determined that the refrigerant flow rate is large, and the expansion valve opening is reduced. (Step 105) ◆ When TsSH = Δt, the refrigerant flow rate is judged to be appropriate and the expansion valve opening is not operated. (Step 10
6) ◆ When TsSH <Δt, determine that the refrigerant flow rate is low and increase the expansion valve opening. (Step 107) ◆ After completion of the operation of the opening degree of the expansion valve, the process returns to Step 101 again. ◆ The target TsSH can be secured by the above operation.

Next, another embodiment will be described with reference to FIGS. ◆ Figure 4 shows changes in pressure and temperature at the inlet and outlet of the evaporator. ◆ It is generally known that the pressure at the outlet of the evaporator is lower than the pressure at the inlet due to the pressure loss due to the piping of the evaporator. Further, even when the refrigerant flow rate is small and the pressure loss is small, it is physically impossible that the outlet pressure becomes higher than the inlet pressure. This is because the refrigerant flowing through the evaporator is in a gas-liquid two-phase state at the inlet, and when the refrigerant flow rate is larger than the capacity of the evaporator, it is also gas-liquid two-phase at the evaporator outlet side, but the evaporator capacity is reduced. When the flow rate of the refrigerant is appropriate or when the flow rate of the refrigerant is equal to or less than the capacity of the evaporator, the vaporized refrigerant has a single-phase state at the evaporator outlet side. Therefore, by keeping the difference between the refrigerant temperature at the inlet and the refrigerant at the outlet constant, the refrigerant at the outlet of the evaporator can have a superheat degree.

Further, an example of ensuring the superheat degree of the refrigerant at the outlet of the evaporator in another embodiment will be described step by step with reference to FIG. ◆ Start operation of the air conditioner. (Step 20
0) ◆ Detect evaporator inlet temperature Tr1 and evaporator outlet temperature Tr2. (Step 201) ◆ Here, evaporator inlet temperature
The difference Δt between Tr1 and the evaporator outlet temperature Tr2 is determined (step 102), and the target superheat (TsSH) is compared with Δt. (Step 203) ◆ When TsSH> Δt, it is determined that the refrigerant flow rate is large, and the expansion valve opening degree is reduced. (Step 204)
◆ When TsSH = Δt, judge that the refrigerant flow rate is appropriate and do not operate the expansion valve opening. (Step 205) ◆ TsSH <△ t
In this case, it is determined that the refrigerant flow rate is small and the expansion valve opening degree is increased. (Step 206) After the expansion valve opening operation is completed, the process returns to Step 201 again. From the above, the target TsSH can be secured.

As described above, the superheat degree of the refrigerant at the outlet of the evaporator is ensured. However, in the operating state of the compressor, especially in the variable operating frequency type compressor, when the operating frequency is low, the calorific value of the compressor is small. In some cases, TdSH may not be secured. For this, it is preferable to switch the use of the liquid injection circuit according to the operating state of the refrigeration cycle, as described below.

As the condition for switching the use, the outside air temperature Ta of the capacity of the evaporator can be used, which will be described step by step with reference to the flowchart of FIG. ◆ First, start operation of the air conditioner. (Step 300) ◆ Next, the outdoor atmosphere temperature Tao is detected. (Step 301) ◆
Here, the operation switching temperature (5 ° C. in the present embodiment, but determination may be made at a temperature other than 5 ° C.) and the outdoor atmosphere temperature Tao are compared. (Step 302) If Tao> 5 ° C., it is judged that the evaporator capacity is sufficient, and the liquid injection circuit is not required and the operation is performed. (Expansion valve opening is 0 pulse: fully closed. Step 303) Tao = 5
In the case of ° C, the current operating condition is maintained and the operation is not switched. (Step 304) ◆ If Tao <5 ° C., it is determined that the evaporator capacity is insufficient, and the liquid injection circuit is used to operate. (Step 305) ◆ After the operation switching is completed, the process returns to Step 301. As described above, an appropriate operating state can be secured.

As the condition for switching the use, the compressor discharge refrigerant temperature Td may be used, which will be described below with reference to the flowchart of FIG.

The operation of the air conditioner is started. (Step 400) ◆ The compressor discharge refrigerant temperature Td is detected. (Step 401) ◆ The operation switching temperature (70 ° C. in the present embodiment, but determination may be made at a temperature other than 70 ° C.) and the compressor discharge refrigerant temperature Td are compared. (Step 402) ◆ If Td <70 ° C., it is judged that TdSH is about to decrease, and the liquid injection circuit is not required and operation is started. (The expansion valve opening is 0 pulse:
Fully closed. (Step 403) ◆ If 70 ° C. ≦ Td ≦ 80 ° C., the current operating state is maintained and the operation switching is not performed. (Step 404) ◆ If Td> 80 ° C., it is determined that TdSH is about to rise, and operation is performed using the liquid injection circuit. (Step 405) ◆ Return to Step 401 again after the operation switching is completed. As described above, an appropriate operating state can be secured.

Further, as the condition for switching the use, it is preferable to use the compressor suction refrigerant pressure Ps, which will be described with reference to the flowchart of FIG.

The operation of the air conditioner is started. (Step 500) ◆ The compressor suction refrigerant pressure Ps is detected. (Step 501) ◆ Here, the operation switching pressure (0.4M in this example)
However, it may be judged with a value other than 0.4 Mpa) and the compressor suction refrigerant pressure Ps. (Step 502) ◆ Ps> 0.5M
In the case of pa, it is judged that the evaporator capacity is sufficient, and the liquid injection circuit is not required for operation. (Expansion valve opening is 0 pulse: fully closed. Step 503) If 0.4Mpa ≦ Ps ≦ 0.5Mpa, the current operating state is maintained and operation switching is not performed. (Step 504) ◆ Ps>
In the case of 0.4Mpa, it is judged that the evaporator capacity is insufficient, and the liquid injection circuit is used for operation. (Step 50
5) ◆ After the operation switching is completed, the process returns to step 501 again.
As described above, an appropriate operating state can be secured.

In the case of a refrigeration cycle with a liquid injection circuit, the role of this liquid injection circuit lies in the adjustment of TdSH. Therefore, the liquid injection expansion valve 8 is moved here to control Td to the target temperature.

Further, since the effect of liquid injection on the refrigeration cycle appears as an increase in the refrigerant circulation amount to the condenser side, the condensation pressure must be raised in the defrosting operation when frost is formed on the evaporator side heat exchanger. It becomes easier to rub and the defrosting performance can be improved.

In the cooling operation of a general refrigeration cycle without a liquid injection circuit, the indoor expansion valve 5 is used to control Td, and when equipment is installed at the same location as the refrigeration cycle with a liquid injection circuit. However, there is a risk of confusion due to different refrigeration cycles when performing facility inspections.

Further, in the circuit with liquid injection, the effect of increasing the cooling capacity cannot be expected in the cooling operation in which the refrigerant circulation amount of the evaporator is required. Therefore, liquid injection should be used only during heating operation, while the refrigeration cycle during cooling operation is standardized regardless of the presence or absence of liquid injection. This example will be described with reference to the flowchart of FIG.

The operation of the air conditioner is started. (Step 600) ◆ Detect an operation command. (Step 601) ◆
Here, it is determined whether the operation command is cooling or heating. (Step 602) ◆ In the case of cooling, the liquid injection circuit is unnecessary and the operation is performed. (Expansion valve opening is 0 pulse: fully closed. Step 603) ◆ In the case of heating, the liquid injection circuit is used for operation. (Step 604) After the operation switching is completed, the process returns to step 601 again. ◆ This makes it possible to use the liquid injection circuit only during heating operation. However, this judgment can be put to practical use only when the operation is started.

[0030]

According to the present invention, by properly controlling the expansion device of the main circuit and effectively using the liquid injection circuit, it is possible to prevent the heat pump capacity from deteriorating when the outside air temperature is low, and the comfort is excellent. An air conditioner can be provided.

Further, according to the present invention, by using the liquid injection circuit only for the heating operation, it is possible to provide the air conditioner in which the facility inspector can easily diagnose the refrigeration cycle.

Further, according to the present invention, it is not necessary to supplement the capacity with auxiliary energy such as kerosene or gas, and the trouble of exhaust gas generation and refueling is eliminated, and facility inspection can be performed without knowledge of combustion equipment. Therefore, it is possible to provide an air conditioner in consideration of safety and environment.

Furthermore, the liquid injection circuit can be selectively used according to the operating state of the refrigeration cycle, and an air conditioner with improved reliability can be provided by appropriately maintaining the superheat degree of refrigerant discharged from the compressor.

[0034]

[Brief description of drawings]

FIG. 1 is a block diagram (refrigeration cycle system diagram) illustrating a refrigeration cycle.

FIG. 2 is a Mollier diagram illustrating a refrigeration cycle.

FIG. 3 is a flow chart for explaining how to secure the superheat degree at the compressor inlet to a target value.

FIG. 4 is a graph diagram illustrating refrigerant pressure and temperature changes in an evaporator.

FIG. 5 is a flow chart for explaining ensuring the superheat degree at the evaporator outlet at a target value.

FIG. 6 is a flow chart for explaining determining whether or not the liquid injection circuit can be used.

FIG. 7 is a flowchart for explaining determining whether or not the liquid injection circuit can be used.

FIG. 8 is a flowchart for explaining determining whether or not the liquid injection circuit can be used.

FIG. 9 is a flowchart for explaining determining whether or not the liquid injection circuit can be used.

[Explanation of symbols]

1 ... Compressor, 2 ... Four-way valve, 3 ... Outdoor heat exchanger, 4 ... Outdoor expansion valve, 5 ... Indoor expansion valve, 6 ... Indoor heat exchanger, 7 ... Gas-liquid separator, 8 ... Expansion valve for liquid injection , 9 ... Blower, 10 ... Pressure detecting means, 11 ... Temperature detecting means, 12 ... Detected value input means, 13 ... Refrigeration cycle operating means.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaharu Imagawa 390 Muramatsu, Shimizu City, Shizuoka Prefecture, Hitachi Shimizu Engineering Co., Ltd. Within the business unit

Claims (8)

[Claims] 1. A compressor, a four-way valve, an indoor heat exchanger,
In an air conditioner having an expansion valve, an outdoor heat exchanger, a gas-liquid separator, and a liquid injection circuit, the expansion valve is controlled so that the compressor inlet has a target superheat degree. Harmony machine. 2. The air conditioner according to claim 1, wherein the expansion valve is controlled to maintain a constant refrigerant temperature difference between the inlet and outlet of the heat exchanger. 3. The air conditioner according to claim 1, wherein whether or not the liquid injection circuit can be used is determined according to the state of the refrigeration cycle. 4. The air conditioner according to claim 3, wherein the use of the liquid injection circuit is determined by the outdoor temperature. 5. The air conditioner according to claim 3, wherein the use of the liquid injection circuit is determined by the compressor temperature. 6. The air conditioner according to claim 3, wherein the use of the liquid injection circuit is determined by the refrigerant pressure at the inlet of the compressor. 7. The air conditioner according to claim 1, wherein the liquid injection circuit is used during a defrosting operation of an indoor heat exchanger or an outdoor heat exchanger as an evaporator. 8. The air conditioner according to claim 1, wherein the liquid injection circuit is used during heating operation.