JP3890870B2 - Air conditioner - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air conditioner.
[0002]
[Prior art]
In Japanese Patent Laid-Open No. 10-185343 (reference), in a refrigeration cycle in which injection is performed, an intermediate pressure, which is a pressure in a gas-liquid separator, is measured by some means, so that the measured pressure becomes a target pressure. Among the expansion valves provided before and after the pipe of the liquid separator, the opening degree of the expansion valve on the downstream side is controlled. In addition, there is an example in which the downstream side expansion valve of the main refrigerant circuit is controlled so that the intermediate pressure or the intermediate temperature corresponding to the maximum flow rate of the intermediate gas refrigerant flowing through the injection circuit is obtained. Furthermore, in order to calculate the intermediate pressure, it is described that the outlet temperature of the gas-liquid separator is detected and the intermediate pressure is calculated based on this and the rotational speed of the compressor.
[0003]
[Problems to be solved by the invention]
In the above prior art, it is necessary to provide a temperature sensor or the like in the gas-liquid separator in order to control the downstream expansion valve. When the intermediate pressure is controlled by the gas-liquid separator temperature, if the gas-liquid separator temperature can be detected accurately, the downstream expansion valve can be properly controlled. Therefore, the accuracy and resolution of the absolute value of the temperature sensor are determined by the control amount. When the gas-liquid separator temperature is different by 1 ° C., the performance is changed by several percent. Therefore, an expensive temperature sensor with high accuracy is required. In practice, it is difficult to detect the gas-liquid separator temperature with such high accuracy, and there is a problem that the downstream side expansion valve cannot be controlled properly.
[0004]
An object of the present invention is to maximize the performance improvement effect by injection by appropriately controlling the downstream side expansion valve.
[0005]
Another object of the present invention is to prevent performance degradation caused by the occurrence of liquid injection by stopping the injection under conditions where liquid injection is likely to occur.
[0006]
[Means for Solving the Problems]
The objective compressor, the outdoor heat exchanger, the first throttle device capable of adjusting the opening degree, the gas-liquid separator, the second throttle device capable of adjusting the opening degree, and the indoor heat exchanger In the air conditioner having an injection pipe for supplying refrigerant from the gas-liquid separator to the compressor, and detecting the outside air temperature. Means for controlling the throttle amount of the downstream throttling device of the two throttling devices according to the detected compressor speed and the outside air temperature, and the same compressor speed during cooling operation When the outside air temperature is lower, the downstream side of the two expansion devices is opened. During heating operation, at the same compressor speed, the higher the outside air temperature, By providing a function to control the opening on the downstream side It is made.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to embodiments shown in the drawings. The configuration of an air conditioner according to an embodiment (first embodiment) of the present invention is shown in FIG.
[0024]
Compressor 1, four-way valve 2, outdoor heat exchanger 3, first expansion device 4 that can change the amount of expansion such as an electric expansion valve, gas-liquid separator 5, electric expansion valve and the like that can change the amount of expansion The expansion device 6 and the indoor heat exchanger 7 of 2 are sequentially connected by a refrigerant pipe to constitute a main refrigeration cycle. During the cooling operation, the four-way valve 2 is switched as shown by the solid line in FIG. 1, and the refrigerant flows in the direction indicated by the solid line in FIG. During the cooling operation, the refrigerant compressed by the compressor condenses in the outdoor heat exchanger 3 and dissipates heat to the air, and then is decompressed by the first electric expansion valve 4 to become an intermediate pressure between the condensation pressure and the evaporation pressure, The gas-liquid separator 5 separates the refrigerant into a gas refrigerant and a liquid refrigerant. The liquid refrigerant is further depressurized by the second electric expansion valve 6, absorbs heat from the air in the indoor heat exchanger 7, and returns to the compressor 1. On the other hand, the gas refrigerant separated by the gas-liquid separator is injected into the compressor 1 through the injection pipe 8. The injection pipe 8 is provided with a two-way valve 9, and the injection can be stopped by closing the two-way valve 9 as necessary.
[0025]
During the heating operation, the four-way valve 2 is switched as indicated by the broken line in FIG. 1 and the refrigerant flows in the direction of the broken arrow. During the heating operation, the refrigerant compressed by the compressor condenses in the indoor heat exchanger 7 and dissipates heat to the air, and then is depressurized by the second electric expansion valve 6 to become an intermediate pressure between the condensation pressure and the evaporation pressure. The gas-liquid separator 5 separates the refrigerant into a gas refrigerant and a liquid refrigerant. The liquid refrigerant is further depressurized by the first electric expansion valve 4, evaporated by the outdoor heat exchanger 3, absorbs heat from the air, and returns to the compressor 1. On the other hand, the gas refrigerant separated by the gas-liquid separator is injected into the compressor through the injection pipe 8.
[0026]
A compressor chamber surface temperature sensor 10 is provided in the compressor chamber to detect the chamber temperature of the compressor head. Instead of the compressor chamber temperature sensor, a compressor discharge refrigerant pipe temperature sensor may be provided in the refrigerant discharge pipe. In the following description, the compressor discharge refrigerant pipe temperature or the compressor head chamber surface temperature is referred to as a compressor discharge refrigerant temperature. A compressor suction refrigerant pipe temperature sensor 11 is provided in the refrigerant suction pipe of the compressor to detect the suction refrigerant temperature. Instead of providing a sensor in the compressor suction pipe, a sensor may be attached to a liquid reservoir (accumulator) or the like provided in the compressor suction portion. The outdoor unit is provided with an outdoor air temperature sensor 12 and an outdoor heat exchanger sensor 13 to detect the outdoor air temperature and the outdoor heat exchanger temperature.
[0027]
Control of the compressor 1, the first electric expansion valve 4, the second electric expansion valve 6, etc., and the acquisition of signals from sensors are performed by the control device 14. The control device 14 includes a microcomputer 15 and its peripheral devices. The rotation speed of the compressor 1 is controlled by the control device 14 and the inverter circuit 16. The rotation speed of the compressor is sensed and taken into the microcomputer 15. The compressor rotational speed is sensed by a method such as feeding back the output current to the motor. A rotation speed sensor may be attached to the compressor.
[0028]
Next, the operation of the injection cycle and the improvement of the cycle efficiency will be described with reference to FIG. The Mollier diagram shown in FIG. 2 represents the characteristics of the refrigeration cycle with the horizontal axis representing enthalpy and the vertical axis representing pressure. A broken line represents a conventional cycle, and a solid line represents a gas injection cycle. In the conventional cycle, the refrigerant is compressed by the compressor from the point A to the point D ′, and the refrigerant is condensed in the condenser from the point D ′ to the point E to dissipate heat to the outside air. From the point E to the point H ′, the refrigerant is expanded by the expansion valve, and from the point H ′ to the point A, the refrigerant evaporates in the evaporator and absorbs the heat of the indoor air. In the injection cycle, the refrigerant is first compressed from the point A to the point B by the compressor, where the gas refrigerant separated in the gas-liquid separator is injected to reach the point C, and further from the point C to the point D in the compressor. Until compressed. From point D to point E, the refrigerant condenses in the condenser, from point E to point F, the refrigerant expands at the first electric expansion valve, and the gas-liquid separator at point F, which is an intermediate pressure between the evaporation pressure and the condensation pressure. The refrigerant is separated into gas and liquid. The gas is injected into the compressor from point F to point C, the liquid is depressurized by the second electric expansion valve from point G to point H, and evaporated from the point H to point A by the evaporator. In the case of cooling operation, the evaporation capacity of the conventional cycle, that is, the cooling capacity, is expressed by the difference between the enthalpies at point A and H ′, and the evaporation capacity at the injection cycle is expressed by the difference between the enthalpies at point A and H. Since the enthalpy at the H point is smaller than the enthalpy at the H 'point, the cooling capacity increases in the injection cycle. In the case of heating operation, if the refrigerant flow rate of the condenser in the conventional cycle is G and the refrigerant flow rate injected in the gas injection cycle is G1, the refrigerant flow rate flowing through the condenser in the injection cycle is G + G1, and the enthalpy of the condenser inlet / outlet The heating capacity, which is the product of the difference and the refrigerant flow rate, increases.
[0029]
Next, the operation of the refrigeration cycle control in the present embodiment will be described with reference to the flowchart of FIG. In the following description, the two electric expansion valves are referred to as an upstream expansion valve and a downstream expansion valve, respectively. Of the two electric expansion valves, the first electric expansion valve 4 in FIG. 1 serves as an upstream expansion valve and the second electric expansion valve 6 serves as a downstream expansion valve during cooling operation, and the electric expansion valve during heating operation. 6 is an upstream expansion valve, and the electric expansion valve 4 is a downstream expansion valve. The numerical value of the expansion valve opening is defined as the direction in which the expansion valve opens as the numerical value increases.
[0030]
FIG. 3 shows a flow in the case of cooling, but the same is basically the case in the case of heating. When the calculation formulas differ between heating and cooling, each will be described in the text.
[0031]
In step 101 of FIG. 3, initialization processing such as variable initialization is performed, and in step 102, an initial operation timer is started. In the initial operation, the two-way valve 9 shown in FIG. 1 is closed to operate for a predetermined time without performing gas injection, and this timer gives the time. In step 103, initial values of upstream and downstream expansion valve openings are set. The downstream side expansion valve is normally fully opened, but may be set to an opening degree corresponding to the compressor speed. In the next step 104, a timer for giving a sampling time is started. This timer gives an interval (sampling time) for sensing the compressor discharge refrigerant temperature and the like and controlling two expansion valves. In step 105, the compressor discharge refrigerant temperature Td, the compressor suction refrigerant temperature Ts, the outside air temperature To, the outdoor heat exchanger temperature Teo, and the compressor rotation speed N are read. In step 106, the opening degree change amount of the upstream side expansion valve is calculated. The upstream expansion valve is controlled according to the compressor discharge refrigerant temperature and the amount of change. Next, in step 107, it is determined whether or not the initial operation time has elapsed. If the initial operation time has not been reached, the two-way valve is kept closed in step 108, and in step 109, the downstream side expansion valve is Keep it fully open. After the initial operation time has elapsed, in step 110, it is determined whether or not to perform gas injection based on the compressor speed and the outside air temperature. In the cooling operation, when the compressor rotation speed is equal to or lower than the predetermined value or the outside air temperature is equal to or lower than the predetermined value, that is, when any of the following formulas (1) and (2) is satisfied, gas injection is not performed.
[0032]
N ≤ Nc0 (1)
To ≤ Toc0 (2)
Here, N is the compressor speed, To is the outside air temperature, and Nc0 and Toc0 are constants. That is, when the compressor speed is low, it is determined that the operation is low-capacity, and when the outside air temperature is low, the indoor temperature is not so high and the operation is low.
[0033]
In the heating operation, gas injection is not performed when the compressor rotation speed is equal to or lower than a predetermined value or when the outside air temperature is equal to or higher than a predetermined value, that is, when either of the expressions (3) and (4) is satisfied.
[0034]
N ≤ Nh0 (3)
To ≧ Toh0 (4)
Here, Nh0 and Toh0 are constants. As with cooling, when the compressor speed is low, it is determined that the operation is low-capacity, and when the outside air temperature is high, the indoor temperature is not so low and the operation is low.
[0035]
The reason why gas injection is not performed under these conditions is that the evaporation pressure is high under such conditions, so even if gas injection is performed, the amount of injection is very small and not very effective, and liquid injection tends to occur. This is because there is a risk of decline.
[0036]
When the gas injection is not performed, the two-way valve is closed at step 108 and the downstream side expansion valve is fully opened at step 109. When the downstream valve is fully opened from the throttled state, it may be gradually opened until it is fully opened instead of being fully opened at once. Alternatively, the two-way valve may be closed when the downstream side expansion valve is gradually opened and fully opened. By gradually opening the downstream side expansion valve, it is possible to avoid a sudden drop in the compressor discharge refrigerant temperature or the compressor suction superheat.
[0037]
If the conditions of the expressions (1), (2) or (3), (4) are not satisfied in step 110, the two-way valve is opened in step 111 to perform gas injection. If the two-way valve is already open, it remains open.
[0038]
Next, at step 112, the target value Tds of the compressor discharge refrigerant temperature Td is calculated by equation (5).
[0039]
Tds = a1 ・ N + b1 ・ To + c1 (5)
Here, N is the compressor speed (sensed value), To is the outside air temperature, and a1, b1, and c1 are constants.
[0040]
In the next step 113, the reference value Tss of the compressor suction temperature Ts is calculated by the equation (6).
[0041]
Tss = a2 ・ N + b2 ・ To + c2 (6)
Here, a2, b2, and c2 are constants.
[0042]
The reference value Tss of the compressor suction temperature may be obtained by Equation (7) using the outdoor heat exchanger temperature Teo in consideration of the case where frost forms on the outdoor heat exchanger in the case of heating.
[0043]
Tss = a2 ・ N + b2 ・ Teo + c2 (7)
In the next step 114, it is determined whether or not the liquid is mixed with the refrigerant to be injected. In the determination, it is determined that liquid injection is occurring when Expression (8) and Expression (9) are satisfied simultaneously.
[0044]
Td ≤ Tds − α (8)
Ts ≧ Tss + β (9)
Here, Tds is the target value of the compressor discharge refrigerant temperature calculated in step 112, Tss is the reference value of the compressor intake refrigerant temperature calculated in step 113, and α and β are constants. The reason why the liquid injection can be determined under such conditions is that when the liquid injection occurs, the refrigerant in the compression chamber is cooled by the liquid, the refrigerant discharge refrigerant temperature decreases, and the refrigerant accumulates in the gas-liquid separator. This is because the refrigerant becomes insufficient and the compressor suction refrigerant temperature rises.
[0045]
If the condition is satisfied in step 114, it is considered that liquid injection has occurred, and in step 115, a predetermined amount dP2a is added to the correction value SP (n) of the downstream side expansion valve opening as shown in equation (10).
[0046]
SP (n) = SP (n−1) + dP2a (10)
The value of dP2a is positive (value in the direction in which the expansion valve opens). Here, n is a sampling number. Since the refrigerant pressure in the gas-liquid separator decreases by opening the downstream valve, the liquid injection can be terminated. SP (n−1) is the previous value of the opening correction value. Here, the description will be made assuming that liquid injection is determined when this value is zero. If it is determined that the injection is liquid injection, the current correction amount is set to dp2a. When it is determined that the liquid injection is still continued next time, the correction amount is 2dp2a, and the process is repeated until the liquid injection is settled. That is, the correction amount is integrated. There is also a method in which the injection is stopped by closing the two-way valve instead of opening the downstream valve.
[0047]
In the next step 116, the reference value P2s of the downstream side expansion valve opening is calculated by equation (11).
[0048]
P2s = a3 ・ N + b3 ・ To + c3 + SP (n) (11)
Here, N is the compressor speed, To is the outside air temperature, SP (n) is the correction amount for the downstream side expansion valve opening, and a3, b3, and c3 are constants. In the cooling operation, a3 is positive and b3 is negative. In the heating operation, a3 is positive and b3 is also positive. Therefore, in the cooling operation, the downstream expansion valve is throttled as the outside air temperature is high, and in the heating operation, the downstream expansion valve is opened as the outside air temperature is high.
[0049]
The reason will be explained. The reason for adjusting the opening degree in proportion to the compressor rotational speed is that if the rotational speed is high, the amount of refrigerant circulation increases and the liquid refrigerant in the gas-liquid separator increases, which is likely to result in liquid injection. This is to prevent liquid injection by opening the valve.
[0050]
The reason for adjusting the opening of the downstream side expansion valve according to the outside air temperature is that the outdoor heat exchanger acts as a condenser during cooling, and if the outside air temperature rises rapidly, the condenser temperature The proportion of the gas refrigerant increases as the amount of condensation decreases. For this reason, the pressure of the condenser increases. The increase in condenser pressure results in an increase in pressure throughout the cycle. At this time, since the intermediate pressure in the compressor also increases, if the intermediate pressure in the gas-liquid separator is not increased, the amount of gas injection will decrease, leading to COP reduction. This is to make it happen. On the other hand, during heating, the outdoor unit functions as an evaporator. As the outside air temperature increases, the evaporator temperature also increases and the amount of evaporation increases. For this reason, the pressure in an evaporator becomes large and the suction pressure of a compressor becomes large. An increase in the suction pressure means an increase in the density of the gas refrigerant sucked into the compressor, which means that the amount of refrigerant compressed by the compressor has increased, resulting in an increase in the amount of refrigerant circulation. Means. At this time, since the pressure increase in the gas-liquid separator is larger than the pressure increase in the injection port of the compressor, there is a possibility that the amount of liquid in the gas-liquid separator increases and the liquid returns. For this reason, the expansion valve on the downstream side is opened to prevent liquid return.
[0051]
In the next step 117, the downstream expansion valve opening P2 (n−1) at the previous sampling time and the calculation in step 116 are performed in order to limit the throttle amount to be limited to one downstream expansion valve to a predetermined value dP2max or less. If the difference from the determined downstream expansion valve opening P2s is equal to or less than dP2max, in step 118, the downstream expansion valve opening P2 (n) is set to P2s. Otherwise, in step 119, the downstream side expansion valve opening P2 (n) is set to a value obtained by subtracting dP2max from the previous opening. The reason for limiting the throttle amount to be reduced once is that if the downstream expansion valve is suddenly throttled, the intermediate pressure rises and liquid injection is likely to occur. This is because stability is impaired.
[0052]
In the next step 120, the amount of change in the downstream expansion valve opening is obtained, and in step 121, a pulse is output to the expansion valve coil to operate the upstream and downstream expansion valves. In step 122, the sampling time is counted. When the sampling time is reached, the process returns to step 104 and the following series of operations is repeated.
[0053]
According to the present embodiment, the intermediate pressure can be appropriately maintained by controlling the downstream side expansion valve opening degree according to the compressor rotational speed and the outside air temperature, so that the performance improvement by gas injection is great. Moreover, since the liquid injection is determined based on the compressor discharge refrigerant temperature and the compressor suction refrigerant temperature and the downstream side expansion valve opening is adjusted, the performance deterioration due to the liquid injection can be prevented. Moreover, according to this embodiment, since the control which stops a two-way valve by closing a two-way valve according to a compressor rotation speed and external temperature is performed, the performance fall by liquid injection does not occur easily.
[0054]
FIG. 4 shows the configuration of an air conditioner according to another embodiment (second embodiment) of the present invention. The refrigeration cycle configuration in the present embodiment is the same as that in the first embodiment, but the indoor unit is provided with an indoor intake air temperature sensor and an indoor heat exchanger sensor. The operation of the refrigeration cycle control in this embodiment will be described with reference to the flowchart of FIG. Since the basic flow of the control operation is the same as that of the first embodiment, the description related to this embodiment will be made only for parts different from the first embodiment.
[0055]
In step 205, the indoor intake air temperature Ti and the indoor heat exchanger temperature Tei are read in addition to the compressor discharge refrigerant temperature Td, the compressor intake refrigerant temperature Ts, the outdoor air temperature To, and the outdoor heat exchanger temperature Teo. When the indoor intake air temperature and the indoor heat exchanger temperature cannot be directly taken into the control unit of the outdoor unit, they may be taken into the control unit provided in the indoor unit and sent to the control unit of the outdoor unit. .
[0056]
In the determination of whether or not to perform the gas injection in step 210, in the cooling operation, if any of the equations (12) to (14) is established, the gas injection is not performed.
[0057]
N ≤ Nc0 (12)
To ≤ Toc0 (13)
Ti ≧ Tic0 (14)
Here, N is the compressor speed, To is the outside air temperature, Ti is the indoor intake air temperature, and Nc0, Toc0, and Tic0 are constants. Further, an indoor intake air humidity sensor may be provided, and the two-way valve may be closed even when the indoor intake air humidity is a predetermined value or more.
[0058]
In the heating operation, gas injection is not performed when any of the equations (15) to (17) is satisfied.
[0059]
N ≤ Nh0 (15)
To ≧ Toh0 (16)
Ti ≤ Tih0 (17)
Here, Nh0, Toh0, and Tih0 are constants.
[0060]
In step 213, in the case of the cooling operation, the reference value Tss of the compressor suction refrigerant temperature Ts is calculated by the equation (18).
[0061]
Tss = a2 ・ N + b2 ・ Tei + c2 (18)
Here, a2, b2, and c2 are constants. In this embodiment, the temperature of the indoor heat exchanger is used for calculating the reference value of the compressor suction refrigerant temperature. In the case of the heating operation, similarly to the first embodiment, the compressor intake temperature reference value is obtained by the above-described formula (6) or formula (7).
[0062]
In step 216, the downstream side expansion valve opening reference value is obtained by equation (19).
[0063]
P2s = a3 ・ N + b3 ・ To + c3 ・ Ti + d3 + SP (n) (19)
Here, the indoor intake air temperature is also used to calculate the downstream expansion valve opening.
[0064]
According to the present embodiment, the intermediate pressure can be more appropriately maintained by controlling the downstream expansion valve opening degree according to the indoor intake air temperature in addition to the compressor rotation speed and the outside air temperature, so that the gas The effect of performance improvement by injection is maximized. In addition, according to the present embodiment, since the control is performed to close the two-way valve and stop the injection not only by the compressor rotation speed and the outside air temperature but also by the indoor intake air temperature, the performance deterioration due to the liquid injection hardly occurs. ing.
[0065]
【The invention's effect】
As described above in detail, according to the present invention, the effect of performance improvement by gas injection can be maximized. Further, according to the present invention, depending on the conditions of the outside air temperature and the compressor rotation speed, the two-way valve is closed to stop the injection, thereby preventing the performance deterioration due to the liquid injection.
[Brief description of the drawings]
FIG. 1 shows a configuration of an air conditioner according to an embodiment of the present invention.
FIG. 2 is a Mollier diagram showing the operation of a gas injection cycle.
FIG. 3 is a flowchart of expansion valve control.
FIG. 4 is a configuration of an air conditioner according to a second embodiment of the present invention.
FIG. 5 is a flowchart of expansion valve control of the air conditioner according to the second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Compressor, 2 ... Four way valve, 3 ... Outdoor heat exchanger, 4 ... 1st expansion device, 5 ... Gas-liquid separator, 6 ... 2nd expansion device, 7 ... Indoor heat exchanger, 8 ... Injection Piping, 10 ... compressor chamber surface temperature sensor, 11 ... compressor intake refrigerant piping temperature sensor, 12 ... outside air temperature sensor, 14 ... control device.

Claims (1)

A compressor, an outdoor heat exchanger, a first throttle device capable of adjusting an opening degree, a gas-liquid separator, a second throttle device capable of adjusting an opening degree, and an indoor heat exchanger, In an air conditioner comprising an injection pipe for sequentially connecting to constitute a refrigeration cycle and supplying refrigerant from the gas-liquid separator to the compressor,
A means for detecting the compressor rotational speed, a means for detecting the outside air temperature, and a throttle amount of the downstream side throttle device of the two throttle devices according to the detected compressor rotational speed and the outside air temperature. Means and
During cooling operation, when the compressor speed is the same, the lower the outside air temperature, the lower the throttle on the downstream side of the two throttle devices, and during heating operation, when the compressor speed is the same, the outside air temperature is higher An air conditioner having a function of controlling the opening of the downstream side of the two expansion devices.

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