JP3939292B2 - Air conditioner - Google Patents

Description

  The present invention relates to an air conditioner.

2. Description of the Related Art Conventionally, an air conditioner that performs cooling and heating by performing compression refrigeration cycle control using at least two heat exchangers is known. In such an air conditioner, in order to increase energy efficiency, the refrigerant superheat degree of the evaporator in the cooling mode and the refrigerant subcool degree of the condenser in the heating mode are accurately detected, and these are detected. It is necessary to perform control within a predetermined temperature range. In that case, it is necessary to accurately know the evaporation pressure or condensation pressure in the heat exchanger, but it is known to use a temperature sensor instead of an expensive pressure sensor.
In addition, an apparatus has been proposed in which a temperature sensor is arranged at each inlet / outlet of the heat exchanger to estimate the degree of refrigerant superheat or the degree of refrigerant subcooling.
For example, Patent Literature 1 describes an air conditioner that calculates a refrigerant saturated vapor pressure or a refrigerant saturated condensing pressure in a heat exchanger based on a gradient of a refrigerant pressure-saturation temperature curve.
Further, Patent Document 2 describes the degree of opening of the expansion valve by obtaining the temporary superheat degree from the output difference of the temperature sensors respectively provided at the inlet and outlet of the evaporator and estimating the superheat degree from the refrigerant side pressure loss characteristic of the evaporator. A control device for an electric expansion valve that performs the above control is described.
JP-A-9-152237 (page 2-4, FIGS. 1 and 2) Japanese Patent Laid-Open No. 10-38398 (page 4-7, FIGS. 1 and 5)

However, the conventional air conditioner as described above has the following problems.
In the technique described in Patent Document 1, the refrigerant saturated vapor pressure or the saturated condensation pressure is calculated from the temperature detected by a temperature sensor attached to one place of the heat exchanger, so the refrigerant-side pressure loss of the heat exchanger is ignored. The calculated value deviated from the actual value. Therefore, there has been a problem that the energy efficiency of the refrigeration cycle is inferior to the optimum state.
In the technique described in Patent Document 2, the difference between the temperature sensors provided at the entrance and exit of the evaporator is used as the temporary superheat degree, and the superheat degree is estimated from the refrigerant-side pressure loss characteristics of the evaporator, so that the superheat degree can be estimated more accurately. However, it is necessary to obtain the refrigerant-side pressure loss characteristics of the evaporator according to the operating state by actually measuring each system. There was a problem that it took a lot of work to do so.

  The present invention has been made in view of the above problems, and is an air conditioner capable of controlling a refrigeration cycle to an optimum state by controlling the refrigeration cycle with high accuracy with a simple and low-cost configuration. The purpose is to provide.

In order to solve the above problems, in the invention described in claim 1, at least two heat exchangers, a compressor, and an expansion valve used for the condenser and the evaporator are arranged on the flow path, and the refrigerant is supplied to the flow path. An air conditioner that circulates and performs compression refrigeration cycle control, an inlet / outlet temperature sensor that detects a refrigerant inlet / outlet pipe temperature of at least one of the heat exchangers, and the at least one heat exchanger An intermediate refrigerant temperature sensor provided at an intermediate part of the refrigerant flow path in the internal refrigerant passage, an intermediate refrigerant pressure calculating means for calculating an intermediate refrigerant pressure in the heat exchanger from a temperature detected by the intermediate refrigerant temperature sensor, Refrigerant pressure correction means for calculating a refrigerant side saturation pressure by correcting a refrigerant side pressure loss from an intermediate part of the refrigerant flow path to an outlet of the at least one heat exchanger to an intermediate part refrigerant pressure; A saturation temperature calculation means for calculating the refrigerant saturated vapor temperature or the refrigerant saturated liquid temperature by converting the refrigerant side saturation pressure calculated by the above into a temperature, and the inlet / outlet temperature provided on the outlet side of the at least one heat exchanger Superheat degree / supercooling degree calculating means for calculating a refrigerant superheat degree or a refrigerant supercooling degree from the outlet side temperature detected by the sensor and the refrigerant saturated vapor temperature or the refrigerant saturated liquid temperature, and the superheat degree / supercooling degree calculating means. Expansion valve control means for controlling the opening degree of the expansion valve so that the refrigerant superheat degree or the refrigerant supercooling degree calculated in step 4 falls within a predetermined temperature range, and the refrigerant pressure correcting means includes the intermediate refrigerant. A unit of the at least one heat exchanger, wherein a refrigerant circulation amount is calculated based on the intermediate refrigerant pressure calculated by the pressure calculation means, and is calculated from the intermediate refrigerant pressure and the refrigerant circulation amount. By calculating the refrigerant flow resistance per a, a configuration which is adapted to calculate the refrigerant pressure loss to the outlet of said at least one heat exchanger from an intermediate portion of the refrigerant passage.
According to the present invention, based on the detected temperature detected by the intermediate unit refrigerant temperature sensor to calculate the intermediate portion the refrigerant pressure in the heat exchanger by the intermediate portion the refrigerant-pressure calculating means, the refrigerant pressure correction means to the intermediate part refrigerant pressure Calculate the refrigerant side saturation pressure with the refrigerant side pressure loss corrected, calculate the refrigerant saturated vapor temperature or refrigerant saturated liquid temperature by converting the refrigerant side saturated pressure using the saturation temperature calculation means, and calculate the superheat / supercool degree The refrigerant superheat degree or the refrigerant cooling degree can be calculated from the outlet side temperature detected by the inlet / outlet temperature sensor on the outlet side of the heat exchanger and the refrigerant saturated vapor temperature or the refrigerant saturated liquid temperature. As a result, without using a pressure sensor or the like, it is possible to accurately determine the degree of refrigerant superheat or the degree of refrigerant cooling according to the operating state using a cheaper temperature sensor.
And since such a refrigerant superheating degree or a refrigerant-cooling degree by the expansion valve control means controls the opening degree of the expansion valve so as to fall within a predetermined temperature range, can be controlled to the optimum state of the refrigeration cycle.

According to a second aspect of the present invention, in the air conditioner according to the first aspect, the intermediate refrigerant temperature sensor is provided substantially at the center in the length direction of the refrigerant flow path in the heat exchanger. To do.
According to the present invention, since the intermediate refrigerant temperature sensor is provided at substantially the center in the length direction of the refrigerant flow path of the heat exchanger, a stable temperature can be detected regardless of the operating state. It can be calculated with high accuracy.

According to a third aspect of the present invention, in the air conditioner according to the first or second aspect, the refrigerant flow path of the heat exchanger has a flow path bent portion that is bent outward and protrudes, and the flow path The bent portion is provided with the intermediate refrigerant temperature sensor.
According to this invention, attachment and maintenance of the intermediate part refrigerant temperature sensor are facilitated.

  According to the air conditioner of the present invention, the refrigerant-side pressure loss correction can be performed with a simple configuration in which the temperature detected by an inexpensive temperature sensor is converted to the intermediate refrigerant pressure. Since the saturation pressure can be obtained with high accuracy, and the opening degree of the expansion valve can be controlled using the high degree of refrigerant superheat or the high degree of refrigerant supercooling, the refrigeration cycle can be controlled to the optimum state.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1A is a schematic explanatory diagram including a functional block diagram for explaining a schematic configuration of an air-conditioning apparatus according to an embodiment of the present invention. FIG. 1B is also a detailed functional block diagram of a part thereof.

The schematic configuration of the air conditioner 1 according to the embodiment of the present invention includes a compressor 2, a four-way valve 8, an outdoor heat exchanger 4 (heat exchanger), an expansion valve 7, an indoor heat exchanger 9 (heat exchanger), It consists of a control unit 50 and constitutes a compression refrigeration cycle. Thus, it is possible to operate by switching between cooling and heating.
Hereinafter, for the sake of convenience, the case of the cooling operation will be mainly described. That is, the refrigerant is described as circulating in the order of the compressor 2, the outdoor heat exchanger 4, the expansion valve 7, and the indoor heat exchanger 9 (in the arrow direction in FIG. 1A). In this case, the outdoor heat exchanger 4 functions as an evaporator, and the indoor heat exchanger 9 functions as a condenser. Unless otherwise specified, the terms upstream side, downstream side, inlet side, and outlet side are used based on the refrigerant flow. Needless to say, these directions are reversed during heating operation.

The compressor 2 is for compressing a gaseous refrigerant, and any type of compressor used in a compression refrigeration cycle may be used.
A temperature sensor 12 for detecting the refrigerant discharge temperature _Thd is provided at the discharge port of the compressor 2. A temperature sensor 11 for detecting the refrigerant suction temperature _Ths is provided at the suction port.
The four-way valve 8 is a switching valve for connecting the discharge port and the suction port of the compressor 2 to the refrigerant flow paths 3a and 3d in a switchable manner. That is, according to the switching control signal, the discharge port and the suction port are connected to the refrigerant flow paths 3a and 3d, respectively, during cooling (see FIG. 1A). It is connected to 3a. As a result, the circulation direction of the refrigerant on the flow path can be switched.

The outdoor heat exchanger 4 is connected to the downstream side of the refrigerant flow path 3a and is arranged outside, includes a fan 6 for blowing outdoor air, and performs heat exchange for exchanging heat between the refrigerant and the outdoor air. It is a vessel. Any type of heat exchanger may be used, but in the present embodiment, a plurality of heat transfer tubes 4a and 4b (refrigerant flow in the heat exchanger) that are folded by repeating flat S-shaped bending. The example of the finned-tube heat exchanger which provided the radiation fin between (path) was shown. Note that the number of heat transfer tubes is not limited to two, but may be more, but each has substantially the same length and is provided so that the pressure loss of the refrigerant is substantially the same.
Further, the heat transfer tubes 4 a and 4 b form branch flow paths that are branched and joined on the inlet side and the outlet side of the outdoor heat exchanger 4. A temperature sensor 20A (entrance / entrance temperature sensor) for detecting the inlet temperature is provided on the inlet side, and a temperature sensor 20B (entrance / exit temperature sensor) for detecting the outlet temperature is provided on the outlet side.

Further, the heat transfer tubes 4 a and 4 b include a bend portion 4 c that protrudes outward from a fin or the like among the bent portions and can be easily approached from the outside of the outdoor heat exchanger 4. And the temperature sensor 5 (intermediate part refrigerant | coolant temperature sensor) for detecting the temperature of the refrigerant | coolant there is provided in the bend part 4c in the intermediate part of the length direction of the heat exchanger tube 4a.
An appropriate type of temperature sensor can be adopted.
The position of the intermediate portion does not need to be in the center if an accurate position with respect to the length of the heat transfer tube 4a is known, but in order to perform stable temperature detection regardless of the operation state, the length of the heat transfer tube 4a It is preferable that the center be approximately the center.

The expansion valve 7 is for decompressing and expanding the refrigerant radiated by the outdoor heat exchanger 4, and is connected to the downstream side of the refrigerant flow path 3 b extending from the outlet side of the outdoor heat exchanger 4.
And it is set as the structure which can be electronically controlled by the control unit 50 mentioned later, and an opening degree is controlled by the control signal of the control unit 50. FIG.

The indoor heat exchanger 9 is connected to the downstream side of the refrigerant flow path 3c and is disposed indoors. The indoor heat exchanger 9 includes a fan 6 for blowing indoor air, and is a heat exchanger for exchanging heat with indoor air. In this embodiment, it is a fin tube heat exchanger similar to the outdoor heat exchanger 4, and corresponds to the heat transfer tubes 4a, 4b, the bend portion 4c, the temperature sensor 5, and the temperature sensors 20A, 20B of the outdoor heat exchanger 4. The heat transfer tubes 9a and 9b, the bend portion 9c, the temperature sensor 10, and the temperature sensors 21A and 21B are provided. Since each structure and arrangement are the same as in the case of the outdoor heat exchanger 4, the description thereof is omitted.
And the refrigerant | coolant circulation flow path for performing a compression-type refrigeration cycle is constructed | assembled by connecting the upstream of the refrigerant flow path 3d to the exit of the indoor heat exchanger 9. FIG.

The control unit 50 is a unit including control means for operating such a compression refrigeration cycle and performing control so that the energy efficiency is operated in an optimum state.
The schematic configuration includes a temperature detection unit 14, a superheat / cooling degree calculation unit 15, an expansion valve control unit 16, an operation mode control unit 18, a compressor control unit 17, and a four-way valve control unit 19.
These specific configurations may employ appropriate means. For example, it may be configured independently as a circuit board member on which each appropriate electric circuit is configured, or may be realized by a program incorporated in a microcomputer provided with appropriate input / output interfaces and storage means.

The temperature detection unit 14 includes temperature detection means 14a and 14b.
The temperature detection means 14a includes a compressor discharge temperature T _hd detected by the temperature sensors 11, 12, 20A, 20B, 21A, and 21B, a compressor suction temperature T _hs , an outdoor unit inlet temperature t ₁ , and an outdoor unit outlet temperature T _1. This is a means for converting the indoor unit inlet temperature t ₂ and the indoor unit outlet temperature T ₂ into digital signals that can be numerically processed.
Temperature detecting means 14b may bend the temperature _T bV detected by the temperature sensor 5 and _10, the _{T bL,} a means for converting the numerical operations processable digital signals.

As shown in FIG. 1 (b), the superheat degree / cooling degree calculation unit 15 includes temperature signal intermediate part refrigerant pressure calculation means 15a, refrigerant pressure correction means 15b, and saturation temperature calculation means 15c output from the temperature detection means 14b. And a superheating degree / supercooling degree calculating means 15d.
The intermediate refrigerant pressure calculation means 15a refers to the bend temperature T _bV and T _bL input from the temperature detection means 14b by referring to the temperature-pressure characteristics of the refrigerant, so that the corresponding vapor pressure _Pe (intermediate refrigerant pressure) is obtained. ), A means for calculating the condensation pressure P _c (intermediate refrigerant pressure).
For the temperature-pressure characteristics of the refrigerant, an approximate expression is created in advance and the coefficient data is stored. Alternatively, it may be stored as table data.

The refrigerant pressure correction means 15b averages the vapor pressure _Pe and the condensation pressure _Pc input from the intermediate refrigerant pressure calculation means 15a, respectively, and calculates the refrigerant-side pressure loss amount according to the position in the length direction of the intermediate part. This is a means for _adding and calculating the refrigerant saturated vapor pressure P _esV and the refrigerant saturated liquid pressure P _csL at the outlet of the outdoor heat exchanger 4 or the indoor heat exchanger 9.

The saturation temperature calculation means 15c is based on the refrigerant temperature / pressure characteristics, and from the refrigerant saturation vapor pressure P _esV and refrigerant saturation liquid pressure P _csL input from the refrigerant pressure correction means 15b, the refrigerant saturation vapor temperature T _esV and the refrigerant saturation respectively. This is means for calculating the liquid temperature _TcsL .

The superheat / supercooling degree calculation means 15d includes a refrigerant saturated vapor temperature T _esV input from the saturation temperature calculation means 15c, a refrigerant saturated liquid temperature _TcsL, and an outdoor unit outlet temperature T ₁ input from the temperature detection means 14a. from respective differences between the indoor unit outlet temperature T _2, which is a means for calculating the refrigerant superheating degree SH, the refrigerant supercooling degree SC.

  The expansion valve control means 16 determines the refrigerant superheat degree SH in the cooling operation and the refrigerant in the heating operation according to the refrigerant superheat degree SH and the refrigerant supercool degree SC input from the superheat degree / cooling degree calculation unit 15. This is a means for controlling the opening degree of the expansion valve 7 so that the degree of supercooling SC falls within a predetermined range.

The operation mode control means 18 is a means for performing operation control of the air conditioner 1 and performing control for selectively switching between at least cooling and heating operations.
The superheat degree / cooling degree calculation unit 15 is notified of the operation mode of the cooling / heating operation, and the compressor control means 17 is output with a refrigerant compression pressure or the like corresponding to the control temperature to control the four-way valve. A control signal for switching the flow direction of the refrigerant discharged from the compressor 2 is output to the means 19 in accordance with the cooling / heating operation mode.

The operation of the air conditioner 1 will be described focusing on the cooling operation.
FIG. 2 is a schematic PI diagram for explaining the operation of the air-conditioning apparatus according to the embodiment of the present invention. FIG. 3 is a conceptual diagram showing the relationship between the refrigerant superheat degree SH, the refrigerant supercool degree SC, and the energy efficiency COP.

As is well known, a compression-type refrigeration cycle is generally described as a trapezoid with a long upper base on the P-I diagram with the horizontal axis representing enthalpy h and the vertical axis representing pressure P, and the inner angles at the left end being right angles. (Trapezoid P ₁ p ₂ P ₃ p _{4 in} FIG. 2). Then, the state quantity changes along the counterclockwise direction (arrow direction shown in the figure) on the side of the trapezoid. The straight line P ₃ P ₄ represents the change in the evaporator, the straight line p ₄ P ₁ represents the compressor 2, the straight line P ₁ p ₂ represents the condenser, and the straight line p ₂ P ₃ represents the change in the expansion valve 7.
However, this is an ideal case. Actually, the refrigerant-side pressure loss in the evaporator and condenser cannot be ignored, so the straight line P ₃ p ₄ is inclined to become a straight line P ₃ P ₄ (p ₄ > P ₄ ), the straight line P ₁ p ₂ is inclined to become a straight line P ₁ P ₂ (p ₂ > P ₂ ), and changes such that a locus such as a quadrilateral P ₁ P ₂ P ₃ P ₄ is followed. In general, the refrigerant-side pressure loss of the evaporator is larger than the refrigerant-side pressure loss of the condenser.

In such a refrigeration cycle, energy efficiency COP in the cooling operation, a function of the refrigerant superheating degree SH at the evaporator, as shown in FIG. 3, the maximum value Q ₁ with respect to the refrigerant superheating degree SH of the given range A change like curve 40 is shown. Therefore, by the refrigerant superheat degree SH energy efficiency COP to control the operating conditions to take a value between predetermined interval W as a Q ₂ or more, perform cooling operation efficiently in good optimal state.
In the case of heating operation, a similar effect can be obtained by controlling the degree of refrigerant supercooling SC within a predetermined range in the condenser.
The refrigerant superheat degree SH (refrigerant supercool degree SC) can be controlled by the opening degree of the expansion valve 7. Therefore, it is extremely important to accurately detect the refrigerant superheat degree SH (refrigerant supercool degree SC) in order to perform optimal refrigeration cycle control.

Refrigerant superheating degree SH ₀ when the refrigerant pressure loss is not ideal, since the wet vapor pressure p _e in the evaporator and the refrigerant saturation vapor pressure p _ESV are equal, for example, detected by the temperature sensor 10 Temperature calculating the wet steam pressure p _e, it as a refrigerant saturation vapor pressure p _ESV, converted to the saturated steam temperature T _e0, the difference between the indoor unit outlet temperature T ₀ detected by the temperature sensor 21B from,
SH ₀ = T ₀ −T _e0 (1)
As required.

The refrigerant superheat degree SH at the outlet of the indoor heat exchanger during the cooling operation in the present embodiment will be described.
In FIG. 2, a curve 31 represents a saturated liquid line 31a and a saturated vapor line 31b of the refrigerant in a certain operation state.
Curves 32, 33, 34, 35 and 36 show isotherms for a single refrigerant. These are sharp left-up curves on the liquid side with the saturated liquid line 31a as a boundary, and right-down curves on the superheated steam side with the saturated vapor line 31b as a boundary. It becomes a horizontal straight line on the wet steam side between. In the same enthalpy, the higher the pressure, the higher the temperature. In these isotherms, the temperature is shown in parentheses after the sign.

Point P ₃ indicates the state quantity at the inlet of the indoor heat exchanger 9, and point P ₄ indicates the state quantity at the outlet of the indoor heat exchanger 9. The pressures are P ₃ and P ₄ , respectively. The respective temperatures are the indoor unit inlet temperature t ₂ and the indoor unit outlet temperature T ₂ and are detected by the temperature sensors 21A and 21B, respectively.
The bend temperature T _bV is detected by the temperature sensor 10. Since the steam pressure P _e of the refrigerant in the bend portion 9c is less than the vapor pressure p _e in the absence of refrigerant pressure loss,
T _bV <T _e0 (2)
(See curves 33 and 34).
The refrigerant saturated vapor pressure P _esV is obtained from the intersection of the saturated vapor line 31b and the straight line P ₃ P _4, and the refrigerant saturated vapor temperature is a temperature T _esV represented by a curve 32 that is an isotherm passing through the point P _esV. is there. As can be seen from FIG.
T _esV <T _bV (3)
It is.
The refrigerant superheat degree SH is
SH = T ₂ −T _esV (4)
It is.

Next, in this embodiment, from the bend portion temperature T _bV, a method of calculating the refrigerant saturated steam temperature T _ESV be described.
The detection outputs of the temperature sensors 5 and 10 are input to the temperature detection means 14b, and the bend temperature _TbL and _TbV are obtained, respectively.
Then, when they are input to the intermediate refrigerant pressure calculation means 15a, the condensation pressure P _c and the evaporation pressure _Pe are calculated. That is, the temperature / pressure characteristic of the refrigerant is preliminarily incorporated in the intermediate refrigerant pressure calculation means 15a as an approximate expression g, for example,
P _c = g (T _bL ) (5)
P _e = g (T _bV ) (6)
Is calculated by

Then the refrigerant pressure compensation means 15b, calculates the refrigerant saturated steam pressure _{P ESV} from the evaporation pressure _{P e.}
For this purpose, the experimental correlation equation f for obtaining the refrigerant circulation amount Gr with the condensation pressure P _c and the evaporation pressure _Pe as parameters for the compressor 2 is incorporated in the refrigerant pressure correction means 15b in advance. That is,
Gr = f (P _c , P _e ) (7)
On the other hand, since the refrigerant flow resistance F per unit length can be described as a function of the refrigerant pressure and the refrigerant circulation amount Gr from the heat exchanger specifications such as the inner diameter of the heat transfer pipe 9a and the inner surface groove shape, it is incorporated. Then the length of the heat transfer tube 9a (the temperature sensor 21A, the length between 21B) as _{L e,} the refrigerant pressure loss dPr of the indoor heat exchanger 9, can be calculated from the following equation.
dPr = F (P _e , Gr) · L _e (8)
Therefore, the refrigerant saturation vapor pressure P _esV is calculated by the following equation.
_{· P esV = P e -dPr (} L b / L e) ··· (9)
Here, the length _Lb is the length from the arrangement position of the temperature sensor 10 to the arrangement of the temperature sensor 21B. In particular, when the temperature sensor 10a is provided at the center in the length direction of the heat transfer tube 9a, (L _b / L _e ) = _½ .
In addition, in the refrigerant pressure correction means 15b, how to incorporate each formula is arbitrary. For example, the equations (7) and (8) may be combined and a correlation approximation equation for obtaining the pressure correction term ΔP _e as in the following equation (10), a data table, and the like may be prepared and incorporated.
ΔP _e = F (P _e , f (P _c , P _e )) · L _e · (L _b / L _e ) (10)
Thus, equation (9) becomes
P _esV = P _e −ΔP _e (9a)
Can be incorporated.
Furthermore, it may be incorporated as a function having (L _b / L _e ) as a parameter.

Next, the refrigerant saturation vapor temperature T _esV is calculated from the refrigerant saturation vapor pressure P _esV by the saturation temperature calculation means 15c. For this purpose, the correlation approximate expression H between the refrigerant saturation vapor pressure P _esV and the refrigerant saturation vapor temperature T _esV is incorporated in advance in the saturation temperature calculation means 15c.
Therefore, the refrigerant saturated vapor temperature _TesV is calculated from the following equation.
T _esV = H (P _esV ) (11)

Then, the degree of superheating / cooling degree calculating section 15d, and the refrigerant saturated steam temperature T _ESV inputted by the saturation temperature calculation section 15c, the indoor unit outlet temperature T ₂ that is input from the temperature detecting means 14a, the above equation (4 ) To obtain the refrigerant superheat degree SH.

As described above, according to this embodiment, the refrigerant saturation pressure T _esV can be accurately calculated by correcting the refrigerant side pressure loss, and the refrigerant superheat degree SH can be obtained.
Then, the opening degree of the expansion valve 7 is controlled by the compressor control means 17 so that the value of the refrigerant superheat degree SH falls within a predetermined range.
In a normal cooling operation, for example, T _bV = 5 (° C.), T ₂ = 6 (° C.), T _esV = 3 (° C.), and the refrigerant superheat degree SH = 3 (K). Therefore, when T _bV = T ₂ is considered and the refrigerant superheat degree SH ₀ is used for the control, a large error is included, but it can be seen that the present embodiment enables extremely accurate control.
At this time, it is convenient that the pressure can be calculated by a simple and inexpensive temperature sensor without using an expensive pressure sensor.

In the above description of the operation, the case of the cooling operation has been mainly described. However, the case of the heating operation can be easily understood from the above description.
In the case of heating operation, the operation mode control means 18 and the four-way valve control means 19 switch the connection of the four-way valve 8 to reverse the refrigerant circulation direction. Thereby, since the outdoor heat exchanger 4 functions as an evaporator and the indoor heat exchanger 9 functions as a condenser, in order to control the refrigeration cycle so that energy efficiency is optimal, the refrigerant is supercooled in the condenser. The expansion valve 7 is controlled so that the degree SC falls within a predetermined range.
Calculated refrigerant saturated liquid pressure P _CSL performing pressure compensation the condensing pressure P _c, thereby calculates the refrigerant saturated liquid temperature T _CSL, from the difference between the indoor unit outlet temperature T _2,
SC = T _csL −T ₂ (11)
Is calculated.
However, the indoor unit outlet temperature T ₂ in this case is to adopt the temperature detected by the temperature sensor 21A differs from the above.
In this case, it is needless to say that all the correlation approximation expressions and functions such as the temperature-pressure characteristics of the refrigerant described above are employed in the condenser.
In addition, even when the refrigerant is a mixed refrigerant, the present invention can be similarly applied except that the isotherm has a gradient in the two-phase region.

In the above description, the purpose is to optimize the indoor heating / cooling operation. Therefore, the indoor heat exchanger has been described as an example of control, but outdoor heat exchange is performed using a temperature sensor or the like provided in the outdoor heat exchanger. It goes without saying that the vessel may be the control target.
In general, in a refrigeration cycle system having a plurality of heat exchangers, which heat exchanger is to be controlled can be freely selected, and only the indoor unit is not necessarily controlled. For example, in a multi-system with one outdoor unit and many indoor units, the capacity of the outdoor unit is reduced in order to suppress excessive capacity of the outdoor unit when the number of indoor unit operations is small in order to support all operation patterns. It is possible to make it. In this case, the outdoor unit is controlled during cooling, the degree of supercooling at the outlet of the outdoor heat exchanger (condenser) is increased, and it is used as an index for reducing the effective heat transfer area on the refrigerant side of the condenser. Conceivable.
However, when the object to be controlled is limited to a specific heat exchanger, the inlet / outlet temperature sensor, the intermediate refrigerant temperature sensor, and the like may be provided only in the specific heat exchanger.

It is the model explanatory drawing for demonstrating schematic structure of the air conditioning apparatus which concerns on embodiment of this invention, and a detailed functional block diagram. It is a typical PI diagram for demonstrating operation | movement of the air conditioning apparatus which concerns on embodiment of this invention. It is a conceptual diagram which shows the relationship between a refrigerant | coolant superheat degree, a refrigerant | coolant supercooling degree, and energy efficiency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air conditioning apparatus 2 Compressor 3a, 3b, 3c, 3d Refrigerant flow path 4 Outdoor heat exchanger (heat exchanger)
4a, 4b, 9a, 9b Heat transfer tube (refrigerant flow path in heat exchanger)
4c, 9c Bend part (flow path bending part)
5, 10 Temperature sensor (intermediate refrigerant temperature sensor)
7 Expansion valve 8 Four-way valve 9 Indoor heat exchanger (heat exchanger)
14b Temperature detection means 15a Intermediate refrigerant pressure calculation means 15b Refrigerant pressure correction means 15c Saturation temperature calculation means 15d Superheat / supercooling degree calculation means 16 Expansion valve control means 50 Control units 20A, 20B, 21A, 21B Temperature sensors (entrance / exit temperatures) Sensor)
T _bV , T _bL Bend part temperature SH Refrigerant superheat degree SC Refrigerant supercool degree _Pe evaporation pressure (intermediate part refrigerant pressure)
_PC condensation pressure (intermediate refrigerant pressure)
T ₁ outdoor unit outlet temperature (outlet temperature)
T ₂ indoor unit outlet temperature (outlet temperature)

Claims (3)

An air conditioner that performs compression refrigeration cycle control by disposing at least two heat exchangers used in a condenser and an evaporator, a compressor, and an expansion valve on a flow path, and circulating a refrigerant in the flow path.
An inlet / outlet temperature sensor for detecting a refrigerant inlet / outlet pipe temperature of at least one of the heat exchangers;
An intermediate refrigerant temperature sensor provided in an intermediate part of the refrigerant flow path in the at least one heat exchanger;
An intermediate refrigerant pressure calculating means for calculating an intermediate refrigerant pressure in the heat exchanger from a temperature detected by the intermediate refrigerant temperature sensor;
Refrigerant pressure correcting means for calculating refrigerant side saturation pressure by correcting refrigerant side pressure loss from the intermediate part of the refrigerant flow path to the outlet of the at least one heat exchanger to the intermediate part refrigerant pressure;
Saturation temperature calculation means for calculating the refrigerant saturated vapor temperature or the refrigerant saturated liquid temperature by converting the refrigerant-side saturation pressure calculated by the refrigerant pressure correction means into a temperature;
The degree of superheat for calculating the degree of refrigerant superheat or the degree of refrigerant subcooling from the outlet side temperature detected by the inlet / outlet temperature sensor provided on the outlet side of the at least one heat exchanger and the refrigerant saturated vapor temperature or refrigerant saturated liquid temperature. / Supercooling degree calculation means,
Expansion valve control means for controlling the degree of opening of the expansion valve so that the refrigerant superheat degree or the refrigerant supercooling degree calculated by the superheat degree / supercooling degree calculating means falls within a predetermined temperature range;
The refrigerant pressure correcting means is
The unit length of the at least one heat exchanger is calculated from the intermediate part refrigerant pressure and the refrigerant circulation amount by obtaining the refrigerant circulation amount based on the intermediate refrigerant pressure calculated by the intermediate refrigerant pressure calculating means. By calculating the refrigerant flow resistance per unit,
An air conditioner characterized in that a refrigerant-side pressure loss from an intermediate portion of the refrigerant flow path to an outlet of the at least one heat exchanger is calculated .   The air conditioner according to claim 1, wherein the intermediate refrigerant temperature sensor is provided at a substantially center in a length direction of a refrigerant flow path in the heat exchanger.   The refrigerant flow path of the heat exchanger has a flow path bending portion that protrudes by bending outward, and the intermediate portion refrigerant temperature sensor is provided in the flow path bending portion. 2. The air conditioning apparatus according to 2.

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