JP4462436B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a refrigeration apparatus applied to an air conditioner or the like, and more specifically, a receiver tank (gas-liquid separator) and a supercooling heat exchanger (SC (subcool) heat between a condenser and an evaporator. And a refrigerating apparatus in which a liquid level detecting means is provided in the receiver tank.

  As shown in FIG. 6, the air conditioner includes an outdoor unit 1 and an indoor unit 20, and in the split type, they are connected via a predetermined pipe. As a basic configuration, the outdoor unit 1 is provided with a compressor 2, a four-way valve 3, an outdoor heat exchanger 4 having an outdoor fan 4a, and, for example, an expansion valve 5 as a throttle mechanism, and a refrigerant return side low-pressure pipe Is connected to an accumulator 7.

  On the other hand, the indoor unit 20 is provided with an indoor heat exchanger 21 having an indoor fan 21a. As shown in this example, for example, two indoor units 20a and 20b are connected to one outdoor unit 1. For example, an expansion valve 23 is provided as a throttle mechanism in each of the indoor units 20a and 20b in order to provide a long piping length for connecting them and a degree of freedom of installation.

  In addition, a receiver tank (gas-liquid separator) 6 for adjusting excess refrigerant is provided between the expansion valve 5 on the outdoor unit 1 side and the expansion valve 23 on the indoor unit 20 side. In the multi-room air conditioner in this example, a variable speed compressor 2a and a constant speed compressor 2b by inverter control are used as the compressor 2 of the outdoor unit 1.

  During the cooling operation, as indicated by the solid line arrow in FIG. 6, the high-temperature and high-pressure gas refrigerant generated by the compressor 2 is sent to the outdoor heat exchanger 4 and condensed by heat exchange with the outdoor air, and the high-temperature and high-pressure liquid Becomes a refrigerant. This high-temperature and high-pressure liquid refrigerant passes through the expansion valve 5 and the check valve 5a connected in parallel thereto (the pressure loss here is designed to be negligible) and flows into the receiver tank 6. . The high-temperature and high-pressure liquid refrigerant is sent from the receiver tank 6 to the indoor heat exchangers 21 and 21, and is reduced in pressure by the electronic expansion valve 23 on the indoor unit side to become a low-temperature and low-pressure two-phase refrigerant. The two-phase refrigerant cools the room air by exchanging heat with the room air, and heats itself and evaporates to become a low-temperature and low-pressure gas refrigerant. The low-temperature and low-pressure gas refrigerant is returned to the compressor 2 through the four-way valve 3 and the accumulator 7 as a flow path switching valve. Thus, during the cooling operation, the outdoor heat exchanger 4 side becomes a condenser, and the indoor heat exchangers 21 and 21 side become evaporators.

  On the other hand, the four-way valve 3 is switched during the heating operation, and the high-temperature and high-pressure gas refrigerant generated by the compressor 2 is sent to the indoor heat exchangers 21 and 21, as indicated by the broken line arrows in FIG. The room air is heated by heat exchange, and is cooled and condensed to become a high-temperature and high-pressure liquid refrigerant. This high-temperature and high-pressure liquid refrigerant is depressurized by the electronic expansion valve 23 on the indoor unit side to become a two-phase refrigerant, enters the receiver tank 6 through the connection pipe, and is depressurized by the expansion valve 5 to be a low-temperature and low-pressure two-phase refrigerant. Become. And it heats and evaporates by heat exchange with outdoor air in the outdoor heat exchanger 4, and becomes a low-temperature low-pressure gas refrigerant. This low-temperature and low-pressure gas refrigerant is returned to the compressor 2 via the four-way valve 3 and the accumulator 7. Thus, at the time of heating operation, the outdoor heat exchanger 4 side becomes an evaporator, and the indoor heat exchangers 21 and 21 side become condensers.

  As described above, particularly in a multi-room air conditioner in which a plurality of indoor units are connected to one outdoor unit, the operation mode (cooling or heating), the operating indoor unit capacity, and the indoor / outdoor temperature Since the amount of refrigerant required for operation varies depending on conditions, the receiver tank 6 is provided to adjust the amount of excess refrigerant. However, the refrigerant flow rate required by the expansion valve 5 during heating operation is adjusted. There are cases where it cannot be secured.

  This point will be described with reference to the Mollier diagram of FIG. 7 showing changes in the refrigerant state during the heating operation. The low-pressure gas refrigerant at point A is sucked into the compressor 2 and compressed to become high-pressure gas refrigerant at point B. This high-pressure gas refrigerant is condensed in the indoor heat exchanger 21 to become a high-pressure liquid refrigerant at point C. This high-pressure gas refrigerant is depressurized by the indoor unit expansion valve 23, and pressure loss in the connection pipe is also added, so that it becomes a two-phase refrigerant at point D at the inlet of the receiver tank 6. The two-phase refrigerant is decompressed by the outdoor unit expansion valve 5, and becomes a low-pressure two-phase refrigerant at point E on the outlet side of the outdoor unit expansion valve 5. The low-pressure two-phase refrigerant is evaporated by the outdoor heat exchanger 4 and returns to the point A.

  Here, the problem is that it is not possible to guarantee that the liquid refrigerant is always accumulated in the receiver tank 6 when the heating operation is performed in the cycle of FIG. If the liquid refrigerant does not accumulate in the receiver tank 6, the passage flow rate in the outdoor unit expansion valve 5 cannot be ensured, and the operation of reducing the evaporation capacity in the outdoor heat exchanger 4 → decreasing the low pressure → insufficient in the heating capacity will result.

  Further, if it is attempted to secure the passage flow rate in the outdoor unit expansion valve 5 in a state where liquid refrigerant does not accumulate in the receiver tank 6, an unnecessarily large expansion valve (electronic expansion valve) must be used, which increases costs. It becomes.

  Thus, in the conventional refrigeration apparatus, the passage flow rate of the outdoor unit expansion valve is insufficient during the heating operation, and the heating capacity may be insufficient. In order to perform an ideal heating operation, it is necessary to supply the refrigerant flow rate required by the evaporator (outdoor heat exchanger) by controlling the outdoor unit expansion valve.

  The refrigerant flow rate required in the evaporator is determined by the operating compressor capacity, outdoor load (outside air temperature), and heat exchange area. If the heat exchange area is unchanged, the refrigerant flow rate required by the evaporator is determined by two conditions of the operating compressor capacity and the outdoor load. If the flow rate of the outdoor unit expansion valve is less than this required flow rate, the heating capacity will be insufficient due to the low pressure drop, and if it is too high, the operation will be wet and the reliability of the compressor will be reduced.

  As a method of controlling the refrigerant flow rate suitable for the required flow rate with the outdoor unit expansion valve, there is a method of Patent Document 1. In the invention described in Patent Document 1, each temperature (or pressure) on the suction side and the discharge side of the compressor detected only on the outdoor unit side during heating operation, the temperature of the outdoor heat exchanger, and the polytropic index of the compressor Thus, the target discharge refrigerant temperature is calculated, and the opening degree of the outdoor unit expansion valve is controlled so that the actual discharge temperature of the compressor follows this target discharge refrigerant temperature.

JP 2004-116978 A

  However, the invention described in Patent Document 1 is also based on the premise that liquid refrigerant is accumulated in the receiver tank. Otherwise, the control itself is not realized.

If the liquid refrigerant does not accumulate in the receiver tank, the reason why the flow rate at the outdoor unit expansion valve cannot be secured is that the mass flow rate through the outdoor unit expansion valve is qm [kg / s], and the outdoor unit expansion valve The flow coefficient conversion of the opening is Cv [no unit], the differential pressure between the inlet side and outlet side of the outdoor unit expansion valve is ΔP [MPa], and the refrigerant density at the inlet side of the outdoor unit expansion valve is D [kg / m ^3]. ]
qm = Cv × (ΔP × D) ^0.5 / Const
It becomes. In other words, when the liquid refrigerant does not accumulate in the receiver tank and the two-phase state is reached, the density of the refrigerant rapidly decreases, and the flow rate cannot be secured.

  FIG. 8 is a graph showing the relationship between the dryness and density of the two-phase refrigerant. In this graph, the point of dryness = 0 is the saturated liquid state, and it can be seen that the refrigerant density rapidly decreases when entering the two-phase region from that state.

  Accordingly, an object of the present invention is to control the liquid level in the receiver tank so that the passage flow rate is insufficient in the outdoor unit expansion valve during heating operation.

  In order to solve the above problems, the present invention includes a refrigeration cycle that includes a compressor, a flow path switching valve, a condenser, and an evaporator, and selectively performs cooling operation and heating operation by switching the flow path switching valve. In a refrigeration apparatus in which a receiver tank and a supercooling heat exchanger are connected between the condenser and the evaporator, and a liquid level detection means is provided in the receiver tank, during heating operation, Control means for controlling the opening degree of the expansion valve of the supercooling heat exchanger based on a liquid level detection signal from the liquid level detection means is provided (claim 1).

  In the present invention, when the liquid level in the receiver tank detected by the liquid level detection means is lower than a predetermined value, the control means sets the opening of the expansion valve of the supercooling heat exchanger. When the liquid level is higher than a predetermined value, the opening degree of the expansion valve of the supercooling heat exchanger is controlled to be reduced (Claim 2).

  As a preferred aspect of the present invention, the control means has priority over the control of the liquid level in the receiver tank so that the cooling refrigerant of the supercooling heat exchanger returned to the compressor side does not become a damp refrigerant. And the superheat control of the said supercooling heat exchanger is performed (Claim 3).

  In the present invention, the liquid level detection means is a pressure reducing unit that depressurizes the refrigerant flowing in the liquid level detection pipe and at least one liquid level detection pipe having one end connected to a predetermined height portion of the receiver tank. Means, heating means for heating the refrigerant in the liquid level detection pipe, and temperature detection means for detecting the temperature of the refrigerant heated by the heating means, and the other end of the liquid level detection pipe Is connected to the cooling side pipe of the supercooling heat exchanger, and the refrigerant used for detecting the liquid level is caused to flow through the supercooling heat exchanger and uses the latent heat of evaporation (claim 4).

  The liquid level detection means detects the phase state of the refrigerant in the receiver tank at a position where one end of the liquid level detection pipe is connected based on the refrigerant temperature obtained from the temperature detection means. (Claim 5).

  According to a preferred aspect of the present invention, the heat generated from the refrigerant discharge pipe of the compressor is used as the heating means (Claim 6).

  The present invention includes a compressor, a flow path switching valve, a condenser, and an evaporator, and includes a refrigeration cycle that selectively executes a cooling operation and a heating operation by switching the flow path switching valve. In a refrigeration system in which a receiver tank and a supercooling heat exchanger are connected between the receiver and a liquid level detection means provided in the receiver tank, the liquid level from the liquid level detection means during heating operation Based on the detection signal, the opening degree of the expansion valve of the supercooling heat exchanger is controlled, that is, when the liquid level in the receiver tank detected by the liquid level detecting means is lower than a predetermined value, the supercooling heat Control the direction to increase the opening degree of the expansion valve of the exchanger, and if the liquid level is higher than the predetermined value, control the direction to reduce the opening degree of the expansion valve of the supercooling heat exchanger. Liquid refrigerant is always stored in the tank. Since the passage flow rate required by the outdoor unit expansion valve is secured, it never runs out heating capacity.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 5, but the present invention is not limited to this. FIG. 1 is a schematic diagram showing an overall configuration of an example in which the refrigeration apparatus of the present invention is applied to an air conditioner. FIG. 2 is a schematic diagram of a liquid level detection means of a receiver tank, a supercooling heat exchanger, FIG. 3 is a Mollier diagram for explaining the operation of the liquid level detection means, FIG. 4 is a Mollier diagram for explaining the operation of the supercooling heat exchanger, and FIG. 5 is a receiver tank. It is a schematic diagram for demonstrating the heat exchange state with the external air in.

  First, the overall configuration of the air conditioner according to this embodiment will be described with reference to FIG. This air conditioner includes an outdoor unit 10 and an indoor unit 20. The outdoor unit 10 and the indoor unit 20 are of a split type in which they are connected via a predetermined piping member. However, the indoor unit 20 may be of a wall-mounted type, a ceiling embedded type, or a floor type. Note that the air conditioner in this embodiment is a multi-room air conditioner, and the two indoor units connected in parallel with the same configuration are connected to the indoor unit 20 in the same manner as the conventional example described in FIG. 20a and 20b are included.

  This air conditioner includes a heat pump type refrigerant circuit capable of cooling operation and heating operation. Therefore, the outdoor unit 10 includes, as a basic configuration, a compressor 11, a four-way valve 12 as a flow path switching valve, an outdoor heat exchanger 13 having an outdoor blower fan 13a, a receiver tank (gas-liquid separator) 14, and a parallel configuration. In this case, the receiver tank 14 is provided with a liquid level detecting means 30, and the receiver tank 14 is subjected to supercooling heat exchange. A device 40 is connected. In this example, the compressor 11 includes a variable speed compressor 11a controlled by an inverter and a constant speed compressor 11b.

  Referring to FIG. 2, the liquid level detection means 30 includes, for example, a first liquid level detection pipe 31 connected to an upper limit position of the receiver tank 14, a second liquid level detection pipe 32 connected to an intermediate position, and a lower limit. Three liquid level detection pipes 33, which are third liquid level detection pipes 33 connected to the positions, are provided.

  Each of the liquid level detection pipes 31, 32, 33 is provided with capillary tubes 31a, 32a, 33a as pressure reducing means, and on the downstream side thereof, heating means 34 for heating the decompressed refrigerant is provided. ing. The heating means 34 may be provided on the upstream side of the capillary tubes 31a, 32a, 33a.

  Although the specifications of the capillary tubes 31a, 32a, and 33a may be arbitrarily determined on condition that they are the same, a capillary tube having an inner diameter of 0.8 mm and a length of 1000 mm can be used as an example. In this example, strainers 31c, 32c, and 33c for preventing clogging of the capillary tube are provided upstream of the capillary tubes 31a, 32a, and 33a.

  An electric heater or the like may be used as the heating unit 34, but it is preferable to use heat generated from the refrigerant discharge pipe of the compressor 11. For this purpose, a part of the pipe may be welded along the refrigerant discharge pipe.

  Each of the liquid level detection pipes 31, 32, 33 is provided with temperature sensors 31b, 32b, 33b made of, for example, a thermistor for detecting the temperature of the heated refrigerant. The liquid level detection pipes 31, 32, 33 are finally combined into one after the refrigerant is heated by the heating means 34, and connected to the cooling side pipe of the supercooling heat exchanger 40 via the electromagnetic valve 35. The

  The refrigerant temperature detected by each of the temperature sensors 31b, 32b, 33b is input to the control means 50 composed of a microcomputer, for example, and the control means 50 determines the liquid level in the receiver tank 14 based on the detected refrigerant temperature. Determine level and phase state.

  Here, the liquid level in the receiver tank 14 is between the upper limit position and the intermediate position, the gas refrigerant flows through the first liquid level detection pipe 31, and the second and third liquid level detection pipes 32. , 33, the operation of the refrigerant liquid level detection means 30 will be described on the assumption that liquid refrigerant flows. Since the second liquid level detection pipe 32 and the third liquid level detection pipe 33 are placed under the same conditions, the third liquid level detection pipe 33 will be described on the liquid refrigerant side.

  In the first liquid level detection pipe 31, the inlet point of the capillary tube 31a is A1, the outlet point is C1, and the detection point of the temperature sensor 31b is E1. In the third liquid level detection pipe 33, the inlet point of the capillary tube 33a is B1, the outlet point is D1, and the detection point of the temperature sensor 33b is F1.

  In the pressure system, the pressure in the receiver tank 14 is the discharge pressure Ph, the saturation pressure at the detection points E1 and F1 is Pm, and the pressure on the outflow side of the solenoid valve 35 is Pl. Each of these pressures is measured by a pressure sensor (not shown).

  When the electromagnetic valve 35 is opened, the gas refrigerant flows through the first liquid level detection pipe 31 and the liquid refrigerant flows through the third liquid level detection pipe 33. Each refrigerant is decompressed equally in the capillary tubes 31a and 33a, and as shown in the Mollier diagram of FIG. 3, point A1 is in the state of point C1, and point B1 is in the state of point D1.

  Since C1 point and D1 point are both on the pressure line of Pm, they are at the same temperature. Thereafter, the first liquid level detection is performed by heating by the heating means 34 (preferably heat exchange with the refrigerant discharge pipe of the compressor 11). The temperature of the gas refrigerant on the piping 31 side rises from point C1 to point E1 in the overheated region. Even in the case of the non-fluorocarbon type R410A, the temperature TE at the point E1 is preferably higher by 10 ° C. or more than the temperature TC at the point C1 (TE> TC + 10 ° C.).

  On the other hand, since the refrigerant on the third liquid level detection pipe 33 side is a liquid refrigerant, the enthalpy rises even after the pressure is reduced and heated, but the temperature does not change and exists in the saturation region, and the point D1 has the same temperature. It just moves to F1 point. That is, the temperature TD at the point D1 and the temperature TF at the point F1 are the same temperature (TD = TF).

  The control means 50 compares the temperature TE at point E1 detected by the temperature sensor 31b with the temperature TF at point F1 detected by the temperature sensor 33b, and determines the liquid level in the receiver tank 14. . In this case, since TE> TF, it is determined that the liquid level is between the upper limit position and the lower limit position. In this case, since the temperature difference is large, high reliability is obtained in the determination result.

  By the way, when the detected temperature TE of the temperature sensor 31b and the detected temperature TF of the temperature sensor 33b are equal, the receiver tank 14 is assumed to have only two types of gas refrigerant or liquid refrigerant. In order to be able to determine the overall phase state in the receiver tank 14, the control means 50 performs the following processing.

  That is, the saturation temperature T (Pm) obtained from the pressure Pm at the point F1 is set as the reference temperature Ts, the reference temperature Ts is compared with the detected temperature TF obtained from the temperature sensor 33b, D is set as a predetermined value, and TF− When Ts <D is satisfied, it is determined that the receiver tank 14 is in a state of only liquid refrigerant, and when TF−Ts <D is not satisfied, the receiver tank 14 is in a state of only gas refrigerant.

  As described above, according to the liquid level detection means 30 provided in the present invention, a large temperature difference between the liquid refrigerant and the gas refrigerant is obtained by taking out the refrigerant from the receiver tank 14 and heating the refrigerant after decompressing the refrigerant. Therefore, the liquid level in the receiver tank 14 can be reliably detected. Even when only the liquid refrigerant or the gas refrigerant is contained in the receiver tank 14, the phase state can be detected.

  Next, the supercooling heat exchanger 40 is a double heat exchanger in which an inner cooling side pipe (inner pipe) 41 and an outer cooled side pipe (outer pipe) 42 are coaxial pipes. The liquid refrigerant taken out from the receiver tank 14 is passed through the outer cooled side pipe 42, and the liquid refrigerant taken out from the bottom of the receiver tank 14 is passed through the inner cooling side pipe 41 to the expansion valve for the supercooling heat exchanger. The refrigerant is depressurized at 43 and brought into a low-pressure gas state.

  In this embodiment, the refrigerant flowing through the liquid level detection pipes 31, 32, 33 of the liquid level detection unit 30 is finally combined into one after the refrigerant is heated by the heating unit 34. And is supplied to the cooling side pipe 41 inside the supercooling heat exchanger 40 on the downstream side of the expansion valve 43 for the supercooling heat exchanger.

  Contrary to the above example, the liquid refrigerant taken out from the receiver tank 14 is flowed using the inner pipe 41 as the cooled pipe, and the pressure is reduced by the expansion valve 43 for the supercooling heat exchanger using the outer pipe 42 as the cooling pipe. However, the refrigerant in the low pressure gas state and the refrigerant from the liquid level detection means 30 may be flowed.

  Each indoor unit 20a, 20b includes an indoor heat exchanger 21 having an indoor blower fan 21a, and an expansion valve 23 is provided as a decompression means for each indoor unit 20a, 20b, and the flow rate is adjusted by the expansion valve 23. .

  One end of the indoor heat exchanger 21 is connected to the outdoor heat exchanger 13 via the expansion valve 23, the supercooling heat exchanger 40, the receiver tank 14 and the outdoor unit expansion valve 15, and the other end is connected via the four-way valve 12. It is selectively connected to either the compressor 11 or the accumulator 15.

  During the cooling operation, the four-way valve (flow path switching valve) 12 is switched as shown by the solid line in FIG. 1, and the refrigerant is a non-return check in parallel with the compressor 11 → the four-way valve 12 → the outdoor heat exchanger 13 → the outdoor unit expansion valve 15. It flows from the valve 15 a → the receiver tank 14 → the supercooling heat exchanger 40 → the indoor unit expansion valve 23 → the indoor heat exchanger 21 → the four-way valve 12 → the accumulator 15 → the compressor 11. In this case, the outdoor heat exchanger 13 acts as a condenser, and the indoor heat exchanger 21 becomes an evaporator.

During this cooling operation, the temperature detected by the evaporation temperature detection thermistor 22a provided at a refrigerant inlet side of the indoor heat exchanger 21 TH _in, the detection of superheat (SH) detecting thermistor 22b provided on the refrigerant outlet side When the temperature is TH _out , the control unit (not shown) of the indoor unit 20 controls the indoor unit expansion valve 23 as follows to perform target SH control (maximum capability control).

That is, the actual SH is SH _R (= TH _out −TH _in ), the target SH is SH _T , and when SH _T <SH _R , control is performed to throttle the expansion valve 23, and SH _T > SH _R In this case, the expansion valve 23 is controlled to open. In general, SH _T = 1 to 3 ° C. is set in order to maximize the ability.

Regarding the relationship with the room temperature control, the target SH is set according to the difference between the set temperature T _SET (usually 18 to 30 ° C.) of the indoor unit 20 and the indoor temperature T _ROOM detected by a temperature sensor (not shown). Change (SH _T ). That is, when T _ROOM -T _SET is small, the expansion valve 23 is throttled to increase the target SH _T , and when T _ROOM -T _SET is large, the expansion valve 23 is opened and the target SH _T is decreased.

  During the heating operation, the four-way valve 12 is switched as indicated by a chain line in FIG. 1, and the refrigerant is the compressor 11, the four-way valve 12, the indoor heat exchanger 21, the indoor unit expansion valve 23, the supercooling heat exchanger 40, and the receiver. It flows from the tank 14 to the outdoor unit expansion valve 15 to the outdoor heat exchanger 13 to the four-way valve 12 to the accumulator 15 to the compressor 11. In this case, the indoor heat exchanger 21 acts as a condenser, and the outdoor heat exchanger 13 becomes an evaporator.

  Here, the operation and effect of the supercooling heat exchanger 40 will be described. The reason for using the supercooling heat exchanger 40 is to increase the refrigeration effect mainly by supercooling the refrigerant (liquid saturated state at this time) taken out from the receiver tank 14 during the cooling operation to bring it into a liquid state. It is.

  Referring to the Mollier diagram of FIG. 4, the Mollier diagram of the refrigeration cycle when the supercooling heat exchanger 40 is not used is A → B → C → D. Point A is on the liquid saturation line at the outlet of the receiver tank 14. Point B is the outlet side of the indoor heat exchanger 21, point C is the suction side of the compressor 11, and point D is the discharge side of the compressor 11. The refrigeration effect of this refrigeration cycle is ΔIb, and the cooling capacity Qb in the indoor unit 20 is represented by Qb = qmb × ΔIb [kW], where the refrigerant circulation amount is qmb.

  On the other hand, the Mollier diagram of the refrigeration cycle when the supercooling heat exchanger 40 is used is E → F → C → D. That is, when the refrigerant at point A is supercooled by the supercooling heat exchanger 40, the refrigerant changes to point E. The refrigeration effect of this refrigeration cycle is ΔIf, and the cooling capacity Qf in the indoor unit 20 is represented by Qf = qmf × ΔIf [kW] where the refrigerant circulation amount is qmf.

  In this case, since a part of the refrigerant is bypassed to the accumulator 15 side by the supercooling heat exchanger 40, qmb> qmf is satisfied. However, since ΔIb <ΔIf, the refrigeration cycle using the supercooling heat exchanger 40 Has higher ability and efficiency. In other words, normally, the supercooling heat exchanger 40 is designed so that Qb <Qf.

  Note that the C point is common to the two refrigeration cycles, but this is due to the control of the expansion valve 23 on the indoor unit 20 side, and the SH (superheat, degree of superheat) shown in FIG. As described above, control is performed so as to follow a target value (for example, 3 ° C.). Therefore, on the Mollier diagram, the refrigeration effect is enhanced by the amount of increased supercooling.

  Another reason for using the supercooling heat exchanger 40 is that when the piping between the outdoor unit 10 and the indoor unit 20 is long, the pressure loss in the liquid piping increases, so that the Mollier diagram of FIG. Moreover, when the refrigerant state at the outlet of the outdoor unit 10 is point A, the refrigerant state is point G on the front side of the expansion valve 23 on the indoor unit 20 side.

  In a refrigeration cycle that does not use the supercooling heat exchanger 40, the liquid refrigerant easily becomes a two-phase refrigerant if there is a pressure loss. When the refrigerant enters a two-phase state on the front side of the expansion valve 23 of the indoor unit 20, refrigerant noise is generated from the expansion valve 23. This is a big problem as an air conditioner.

  On the other hand, in the refrigeration cycle using the supercooling heat exchanger 40, since the refrigerant at the outlet of the outdoor unit 10 is sufficiently subcooled, even if there is a pressure loss in the piping system, the indoor unit 20 The refrigerant can be kept in a liquid state before the expansion valve 23. Referring to the Mollier diagram of FIG. 4, even if the refrigerant at point E changes to point H due to pressure loss in the piping, the refrigerant is still in the liquid region, so no refrigerant noise is generated from the expansion valve 23. .

  In the present invention, as described above, the refrigerant used in the liquid level detection means 30 is supplied to the cooling side pipe 41 of the supercooling heat exchanger 40. As described above, since the refrigerant used for the liquid level detection has latent heat of vaporization of Q = qm × (Ic−If) [kW], the supercooling of the liquid refrigerant flowing in the cooled pipe 42 is performed. Can be used effectively.

The expansion valve 43 for the supercooling heat exchanger is detected by the control means 50 of the outdoor unit 10 with the detected temperature TL _in at the refrigerant inflow side temperature sensor 44 of the cooled pipe 42 and the detected temperature TL at the refrigerant outflow side temperature sensor 45. Control is performed so that the temperature difference from _out (TL _in −TL _out : this is supercooling) follows the target value.

In parallel with this, the expansion valve 43 for the supercooling heat exchanger is a temperature between the detected temperature TG _in at the refrigerant inflow side temperature sensor 46 of the cooling side pipe 41 and the detected temperature TG _out at the refrigerant outflow side temperature sensor 47. The difference (TG _in −TG _out : superheat in the supercooling heat exchanger 40) is controlled to be a certain level or more. This super heat control is performed in order not to return the wet refrigerant (refrigerant having latent heat of evaporation) to the suction side of the refrigeration cycle, that is, to prevent a loss of capacity.

  As described above, in the present invention, the refrigerant having the latent heat of vaporization used for liquid level detection is caused to flow to the supercooling heat exchanger 40. If the target supercooling is still not reached, the supercooling heat exchanger expansion valve 43 is used. May be controlled as described above.

  The electromagnetic valve 35 of the liquid level detection means 30 may be opened only at the time of liquid level detection. However, according to the present invention, the refrigerant having latent heat of vaporization used for liquid level detection is used for the supercooling heat exchanger 40. Since it can be used effectively as a refrigerant, it is preferable to always open the electromagnetic valve 35 in terms of performance and in order to improve control responsiveness.

During the heating operation, since the outdoor heat exchanger 13 of the outdoor unit 10 functions as an evaporator, the supercooling heat exchanger 40 is also used as one of the evaporators. Again referring to the Mollier diagram of FIG. 7 showing the change in refrigerant state during heating operation, the refrigerant state at the inlet of the receiver tank 14 is point D, and this two-phase refrigerant becomes liquid refrigerant. Is the mass flow rate of the refrigerant flowing into the receiver tank 14 as qm,
Q [kW] = qm [kg / s] × ΔI [kj / kg]
It is necessary to throw away the amount of heat in the receiver tank 14.

  As shown in FIG. 5, the heat exchange amount in the receiver tank 14 is divided into a heat exchange amount Q1 with the container outer wall in the gas portion and a heat exchange amount Q2 with the container outer wall in the liquid portion. Here, the relationship between the heat passage rate K1 in the gas portion and the heat passage rate K2 in the liquid portion is K1> K2 (in the order of 3 to 4 times in the calculation). That is, the larger the gas portion, the greater the amount of heat exchange in the receiver tank 14.

The balance equation for the liquid level in the receiver tank 14 is as follows. The heat transfer area of the gas part and the liquid part is A1 and A2, the temperature of the outside air is T1, and the temperature of the refrigerant is T2.
qm [kg / s] × ΔI [kj / kg]
= Q1 [kW] + Q2 [kW]
= K1 * A1 * (T2-T1) + K2 * A2 * (T2-T1)
It becomes.

Since the heat transfer areas A1 and A2 of the gas part and the liquid part are a function of the liquid level height h and the diameter d of the receiver tank 14,
A1 = πd (h _max −h) + π (d / 2) ²
A2 = πdh + π (d / 2) ²
It is represented by

  From the above, it can be said that the smaller the dryness of the refrigerant flowing into the receiver tank 14 (the smaller the ΔI), the easier the liquid level in the receiver tank 14 comes out, that is, the higher the liquid level.

  Therefore, in the present invention, during the heating operation, the supercooling heat exchanger 40 located on the inflow side of the receiver tank 14 is used to change the dryness of the refrigerant flowing into the receiver tank 14 so that the liquid level is easily produced. Control.

  In the Mollier diagram of FIG. 7, the refrigerant flowing into the receiver tank 14 is a point D (two-phase refrigerant). However, by performing heat exchange with the supercooling heat exchanger 40, the refrigerant state may be brought close to the liquid saturation line. it can. That is, it is possible to control the liquid level in the receiver tank 14 to be easily present.

  More specifically, at least during the heating operation, the liquid level of the receiver tank 14 is monitored by the liquid level detection means 30 with the electromagnetic valve 35 open at all times. When the liquid level is lower than the middle level, for example, the control means 50 controls the opening degree of the expansion valve 43 for the supercooling heat exchanger to open so as to increase the heat exchange amount in the supercooling heat exchanger 40. . Thereby, the liquid level in the receiver tank 14 rises.

  On the other hand, when the liquid level in the receiver tank 14 is higher than the upper limit, the amount of heat exchange in the supercooling heat exchanger 40 is reduced by controlling the opening degree of the expansion valve 43 for the supercooling heat exchanger. To do. Thereby, the liquid level in the receiver tank 14 falls.

  Thus, according to the present invention, the liquid level of the receiver tank 14 can be controlled during the heating operation. Therefore, the liquid refrigerant can be supplied from the receiver tank 14 to the outdoor unit expansion valve 15, and the refrigerant flow rate required by the evaporator (outdoor heat exchanger 13) can be secured. Therefore, there is no shortage of heating capacity.

Note that, as described above, the control unit 50 detects the temperature difference (TG _in) between the detected temperature TG _in at the refrigerant inflow side temperature sensor 46 of the cooling side pipe 41 and the detected temperature TG _out at the refrigerant outflow side temperature sensor 47. -TG _out: refrigerant having a superheat) controls the subcooling heat exchanger expansion valve 43 to be equal to or greater than the constant, wet refrigerant (latent heat of evaporation to the suction side of the refrigeration cycle in the subcooling heat exchanger 40 However, the superheat control is performed with priority over the liquid level control of the receiver tank 14 described above.

  That is, during the heating operation, the supercooling heat exchanger expansion valve 43 is set so that the liquid level of the receiver tank 14 is preferably at an intermediate level within a range in which the cooling gas refrigerant of the supercooling heat exchanger 40 is not moistened. Control. On the other hand, two independent controls of controlling the outdoor unit expansion valve 15 are performed so that the discharge temperature of the compressor 11 follows the target value.

  As described above, according to the present invention, the liquid level in the receiver tank 14 is controlled by controlling the amount of heat exchange in the supercooling heat exchanger 40 that is positioned in front of the receiver tank 14 during heating operation. It is possible to create a state where it is easy to get out. Therefore, the refrigerant state in front of the outdoor unit expansion valve 15 can be secured in the liquid state during the heating operation, and the shortage of refrigerant supplied to the evaporator (outdoor heat exchanger 13) can be solved.

The schematic diagram which shows the whole structure of the example which applied the freezing apparatus of this invention to the air conditioner. The schematic diagram which expands and shows the liquid level detection means and supercooling heat exchanger of the receiver tank which are the principal parts of this invention. The Mollier diagram for demonstrating the effect | action of the said liquid level detection means. The Mollier diagram for demonstrating the effect | action of the said supercooling heat exchanger. The schematic diagram for demonstrating the heat exchange state with the external air in a receiver tank. The schematic diagram which shows the whole structure of the conventional multi-room type air conditioner. The Mollier diagram which showed the change of the refrigerant | coolant state at the time of the heating operation in the said prior art example. The graph showing the relationship between the dryness and density of a two-phase refrigerant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Outdoor unit 11 Compressor 12 Four-way valve 13 Outdoor heat exchanger 14 Receiver tank 15 Outdoor unit expansion valve 16 Accumulator 20 Indoor unit 21 Indoor heat exchanger 23 Indoor unit expansion valve 30 Refrigerant liquid level detection means 31-33 For liquid level detection Piping 31a to 33a Capillary tube (pressure reduction means)
31b to 33b Temperature sensor 34 Heating means 35 Electromagnetic valve 40 Supercooling heat exchanger 41 Cooling side piping 42 Cooled side piping 43 Expansion valve for supercooling heat exchanger 50 Control means

Claims (6)

A compressor, a flow path switching valve, a condenser, and an evaporator, comprising a refrigeration cycle that selectively executes a cooling operation and a heating operation by switching the flow path switching valve, wherein the condenser and the evaporator In the refrigeration apparatus in which a receiver tank and a supercooling heat exchanger are connected between the receiver tank and liquid level detection means are provided in the receiver tank,
A refrigeration apparatus comprising control means for controlling an opening degree of an expansion valve of the supercooling heat exchanger based on a liquid level detection signal from the liquid level detection means during heating operation.   When the liquid level in the receiver tank detected by the liquid level detecting means is lower than a predetermined value, the control means increases the opening degree of the expansion valve of the supercooling heat exchanger. 2. The refrigeration apparatus according to claim 1, wherein, when the liquid level is higher than a predetermined value, the refrigeration apparatus controls the opening degree of the expansion valve of the supercooling heat exchanger in a direction to throttle.   The control means prioritizes the control of the liquid level in the receiver tank so that the cooling refrigerant of the supercooling heat exchanger returned to the compressor does not become a wet refrigerant. The refrigeration apparatus according to claim 2, wherein superheat control of the exchanger is executed. The liquid level detection means includes at least one liquid level detection pipe, one end of which is connected to a predetermined height portion of the receiver tank, a pressure reduction means for depressurizing the refrigerant flowing in the liquid level detection pipe, Heating means for heating the refrigerant in the liquid level detection pipe, and temperature detection means for detecting the temperature of the refrigerant heated by the heating means,
The other end of the liquid level detection pipe is connected to the cooling side pipe of the supercooling heat exchanger, and the refrigerant used for the liquid level detection is passed through the supercooling heat exchanger and uses the latent heat of evaporation. The refrigeration apparatus according to any one of claims 1 to 3, wherein the refrigeration apparatus is configured as described above.   The liquid level detection means detects the phase state of the refrigerant in the receiver tank at a position where one end of the liquid level detection pipe is connected based on the refrigerant temperature obtained from the temperature detection means. 5. The refrigeration apparatus according to claim 4, wherein The refrigeration apparatus according to claim 4 or 5, wherein heat generated from a refrigerant discharge pipe of the compressor is used as the heating means.

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