JP7341341B2 - air conditioner - Google Patents

Description

The present invention relates to an air conditioner, and particularly to an air conditioner that executes a defrosting operation mode.

An air conditioner that heats or cools a room consists of an outdoor unit installed outdoors and an indoor unit installed indoors.The indoor unit and outdoor unit have a heat exchanger that exchanges heat between air and refrigerant. It is equipped with a heat exchanger, a blower fan that blows air through the heat exchanger, and refrigerant piping that connects the outdoor unit and the indoor unit.

The outdoor heat exchanger of the outdoor unit absorbs heat from the outside air (heat absorption) in the case of heating operation to heat the room, and releases heat to the outside air (heat radiation) in the case of cooling operation to cool the room. It has functions.

Therefore, during heating operation, if the evaporation temperature of the refrigerant inside the outdoor heat exchanger falls below the freezing point (0°C), frost forms on the surface of the heat exchange fins of the outdoor heat exchanger. When frost grows and fills the spaces between the heat exchange fins of the outdoor heat exchanger, the air blowing performance, especially the air volume, decreases, resulting in a phenomenon in which sufficient heat absorption is not possible. Therefore, in an air conditioner equipped with a heating function, a defrosting operation mode is executed to melt the frost that has formed.

In this defrosting operation mode, an example of defrosting using outdoor air is described in International Publication No. 2017/145762 (Patent Document 1). The air conditioner described in Patent Document 1 defrosts air by using outdoor air as a heat source to melt frost, and the operation at this time is called "outside air defrosting operation."

In the outside air defrosting operation of Patent Document 1, the refrigerant is prevented from flowing to the outdoor heat exchanger to be defrosted (hereinafter referred to as a defrosting heat exchanger), while the refrigerant is Refrigerant is allowed to flow through the frost heat exchanger.

In addition, the flow of outdoor air during the outdoor air defrosting operation is controlled by driving the outdoor ventilation fan to open both the first opening/closing flap and the second opening/closing flap, and then the defrosting heat exchanger and the non-defrosting heat exchanger. Allows outdoor air to flow through both sides of the container.

As described above, in the outside air defrosting operation of Patent Document 1, the defrosting heat exchanger absorbs heat from the outdoor air for defrosting, and the non-defrosting heat exchanger also absorbs heat, and the non-defrosting heat exchanger absorbs heat. This operation uses an indoor heat exchanger to radiate the heat obtained for heating.

However, this outside air defrosting operation is based on the premise that it is only performed when the temperature of the outdoor air is higher than the freezing point, and the outside air that is higher than the freezing point is passed through the defrosting heat exchanger to remove frost. . Note that here, since the refrigerant is not allowed to flow into the defrosting heat exchanger, defrosting is performed by heat exchange using only outdoor air in the defrosting heat exchanger.

On the other hand, during defrosting operation when the temperature of the outdoor air is lower than the freezing point, the refrigerant is also flowed into the defrosting heat exchanger, and the outdoor air and the refrigerant in the defrosting heat exchanger exchange heat, thereby defrosting. The temperature of the refrigerant in the heat exchanger is increasing.

In normal heating operation before starting defrosting operation, the defrosting heat exchanger functions as an evaporator, so the refrigerant temperature within the defrosting heat exchanger is lower than the outdoor air temperature. Then, when the temperature of the outdoor air is lower than the freezing point, the temperature of the refrigerant in the defrosting heat exchanger is raised to near the temperature of the outdoor air by blowing the outdoor air into the defrosting heat exchanger through which the refrigerant flows. be able to. As a result, it becomes possible to reduce the thermal energy required in the subsequent defrosting operation.

In addition, defrosting operation when the temperature of the outdoor air is lower than the freezing point is only an operation performed as a pre-stage to full-scale defrosting operation such as "refrigerant defrosting operation" or "reverse refrigerant defrosting operation". This is to reduce the thermal energy required for defrosting. Here, "refrigerant defrost operation" is to defrost by supplying a portion of high-temperature gas from the compressor to the defrost heat exchanger, and "reverse refrigerant defrost operation" is to switch from heating operation to cooling. After switching to operation, high-temperature gas from the compressor is supplied to the defrosting heat exchanger to perform defrosting.

International Publication No. 2017/145762

In Patent Document 1, when the temperature of outdoor air is higher than the freezing point, one of the two outdoor heat exchangers is used as a defrosting heat exchanger to flow outdoor air to perform defrosting, while the other non-defrosting heat exchanger is used as a defrosting heat exchanger. An air conditioner is described that continues heating operation by evaporating refrigerant in a heat exchanger.

Furthermore, in the air conditioner described in Patent Document 1, when the temperature of the outdoor air is lower than the freezing point, the outdoor air is not used for the purpose of defrosting, but the defrosting heat exchanger enters full-scale defrosting operation. As a preliminary step, heating operation is carried out from a technical standpoint by providing thermal energy to the refrigerant to reduce the heat required for defrosting.

However, when the temperature of the outdoor air is lower than the freezing point, a low-temperature refrigerant is flowing through the defrosting heat exchanger, so frost may accumulate during the transition to refrigerant defrosting operation or reverse defrosting operation, causing frost to form. There is a possibility that phenomena such as growth may occur. This causes a problem that the subsequent defrosting time becomes longer.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air conditioner that enables an outside air defrosting operation using outside air and maintains heating capacity even under conditions where the outside air temperature is lower than the freezing point.

A feature of the present invention is that the outdoor heat exchanger of the outdoor unit is divided into a plurality of parts, and each of the divided outdoor heat exchangers has a gas header, a liquid side distributor, and an outdoor expansion valve, and The divided outdoor heat exchangers are arranged horizontally side by side in the outdoor unit, and in the defrosting operation mode during heating operation, outdoor air is supplied to both divided outdoor heat exchangers by an outdoor fan. If the temperature of the outdoor air is lower than the freezing point, fully close the outdoor expansion valve connected to the outdoor heat exchanger that is to be defrosted among the divided outdoor heat exchangers. Only the fully closed outdoor heat exchanger is defrosted by the sublimation action of outdoor air.

According to the present invention, defrosting using outdoor air is possible while continuing heating operation even under conditions where the temperature of outdoor air is lower than the freezing point.

FIG. 1 is an external perspective view illustrating a schematic configuration of an outdoor unit of an air conditioner. FIG. 2 is an external perspective view illustrating the internal configuration of an outdoor unit of the air conditioner. It is a cycle system diagram explaining the refrigeration cycle of an air conditioner. It is a flowchart at the time of the outside air defrosting operation which becomes embodiment of this invention. It is an external perspective view of the outdoor heat exchanger of an air conditioner. It is a schematic diagram explaining the flow of the refrigerant of the outdoor heat exchanger of an air conditioner. It is a partial perspective view of the heat exchange fin of the outdoor heat exchanger which becomes embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail using drawings, but the present invention is not limited to the following embodiments, and various modifications and applications can be made within the technical concept of the present invention. is also included within the scope.

First, before describing embodiments of the present invention, the background why the present invention is required will be explained using FIGS. 1 to 3. Note that the outdoor unit used in this embodiment is a top-flow type outdoor unit that has an outdoor fan at the top of the casing. This top-flow type outdoor unit has the advantage that the heat exchanger can be small compared to the required heating and cooling capacity, and is suitable for VRF (Variable refrigerant flow) type air conditioners used in buildings such as commercial buildings. It is widely applied.

As shown in FIG. 1, the outdoor unit used in the embodiment of the present invention includes a first outdoor fan 22, a second outdoor fan 23, two bell mouths 25, and a first outdoor heat exchanger 20. It is composed of a second outdoor heat exchanger 21, a front panel 29, and the like. These two outdoor heat exchangers are arranged horizontally side by side in the outdoor unit, and one outdoor fan 22, 23 is provided for each outdoor heat exchanger 20, 21. It is installed in

FIG. 2 shows a perspective view of the outdoor unit shown in FIG. 1 with the outdoor fans 22, 23, bell mouth 25, and front panel 29 removed to reveal the inside. A compressor 10, a refrigerant tank 28, an accumulator 24, and a control panel 26 are arranged inside the outdoor unit. The control panel 26 is equipped with input/output units for sensors attached to the outdoor unit, electrical components for controlling the operation of the compressor 10 and the outdoor fans 22 and 23, and the like. The refrigerant tank 28 is installed in the middle of the refrigeration cycle, and is used to absorb the difference in the amount of refrigerant required within the cycle between cooling operation and heating operation.

FIG. 3 shows a cycle diagram of the refrigeration cycle. In buildings such as commercial buildings, for example, air conditioners called VRF systems are used, which are equipped with one or more outdoor units and multiple indoor units connected to the outdoor units via refrigerant piping. There is.

Such an air conditioner is called a "multi-air conditioner system." In this embodiment, a VRF type air conditioner is targeted, and FIG. 3 also shows an outline of a VRF type refrigeration cycle. A plurality of indoor units are connected to the outdoor unit through connection piping. Further, FIG. 3 shows the refrigeration cycle during heating operation.

During normal heating operation, high-temperature refrigerant gas discharged from the compressor 10 passes through the refrigerant pipe 11 and the four-way valve 12 and flows into the gas-side blocking valve 13 . From here, an indoor unit 103 and a gas-side blocking valve 13 are connected by a gas-side connection pipe 101 . The gas refrigerant flowing out from the gas-side blocking valve 13 flows to the indoor heat exchanger 104 in the indoor unit 103. Note that the indoor units 103 are provided in two different living rooms 107. Of course, it is also possible to provide more rooms than this.

Air is passed through the indoor heat exchanger 104 by an indoor fan 105, and the air absorbs heat from the refrigerant and is supplied into the room, thereby warming the room. Inside this indoor heat exchanger 104, the refrigerant is cooled and liquefied. The liquefied liquid refrigerant passes through the indoor expansion valve 106, passes through the liquid side connection pipe 102, and flows to the liquid side blocking valve 14.

The refrigerant flowing into the outdoor unit 100 from the liquid-side blocking valve 14 is first divided into a first outdoor expansion valve 15 and a second outdoor expansion valve 16 housed in the outdoor unit 100 and flows therethrough. Thereafter, the liquid passes through a liquid distributor (not shown) and flows to the first outdoor heat exchanger 20 and the second outdoor heat exchanger 21. In this embodiment, a first heat exchanger temperature sensor 17 is installed in the first outdoor heat exchanger 20 and a second heat exchanger temperature sensor 17 is installed in the piping between the liquid distributor and the outdoor heat exchanger 21. A heat exchanger temperature sensor 18 is attached.

The first outdoor heat exchanger 20 corresponds to the first outdoor fan 22, and the second outdoor heat exchanger 21 corresponds to the second outdoor fan 23. Outdoor air is flowed to 20 and 21. Further, an outside air temperature sensor 19 is arranged around the outside of the second outdoor heat exchanger 21 to detect the temperature of the outdoor air sucked in by the outdoor blower fan 23.

The gas refrigerant evaporated and gasified in the first outdoor heat exchanger 20 and the second outdoor heat exchanger 21 passes through the four-way valve 12, passes through the accumulator 24, returns to the compressor 10, and is compressed by the compressor 10 again. The action compresses it into a high-temperature, high-pressure gas. By repeating these steps, heating operation can be continued.

On the other hand, during cooling operation, the four-way valve 12 connects the discharge pipe of the compressor 10, the first outdoor heat exchanger 20, and the second outdoor heat exchanger 21, and connects the gas-side blocking valve 13 and the accumulator 24. , the connection at the four-way valve 12 is switched.

As a result, the flow direction of the refrigerant flowing into the first outdoor heat exchanger 20, the second outdoor heat exchanger 21, and the indoor heat exchanger 104 is reversed. Further, during cooling operation, the gas refrigerant condenses and liquefies in the first outdoor heat exchanger 20 and the second outdoor heat exchanger 21, and the liquid refrigerant evaporates and gasifies in the indoor heat exchanger 104. By repeating these steps, the cooling operation can be continued.

During heating operation, the refrigerant that returns from the indoor unit 103 to the liquid-side blocking valve 14 of the outdoor unit 100 via the liquid-side connection pipe 102 is depressurized by the first outdoor expansion valve 15 and the second outdoor expansion valve 16, and is reduced to a low temperature. It becomes a low-pressure gas-liquid two-phase state and flows to the first outdoor heat exchanger 20 and the second outdoor heat exchanger 21.

Outdoor air is flowed through the first outdoor heat exchanger 20 and the second outdoor heat exchanger 21 by a first outdoor ventilation fan 22 and a second outdoor ventilation fan 23, and the refrigerant is passed through the first outdoor heat exchanger 20. The pressure is reduced so that the temperature is lower than the temperature of the outdoor air flowing through the second outdoor heat exchanger 21. Therefore, the refrigerant in the first outdoor heat exchanger 20 and the second outdoor heat exchanger 21 absorbs heat from the outdoor air and evaporates.

At this time, if the temperature of the refrigerant flowing to the outdoor heat exchangers 20, 21 is lower than the freezing point, frost may grow (frost formation) on the surfaces of the outdoor heat exchangers 20, 21. Since frost blocks the air passages of the heat exchange fins of the outdoor heat exchangers 20 and 21, the amount of air flowing through the outdoor heat exchangers 20 and 21 decreases, resulting in a decrease in heating performance.

Therefore, generally, the heating operation is temporarily stopped, the refrigeration cycle is switched to the cooling operation, and the high temperature discharge gas (refrigerant gas) of the compressor 10 is flowed to the outdoor heat exchanger 20, A reversible refrigerant defrosting operation is being performed to warm up the air conditioner 21 and melt the frost. Since the heating operation is temporarily stopped during this reverse refrigerant defrosting operation, the supply of warm air to the room may be temporarily stopped, resulting in a decrease in comfort.

Additionally, a flow path connecting the discharge port of the compressor 10 is provided at the gas side outlets of the outdoor heat exchangers 20 and 21 in addition to the flow path flowing to the normal four-way valve, and these two flow paths are switched. There is also known a refrigerant defrosting/heating operation in which a switching valve is added so that the discharge gas of the compressor 10 flows only to the defrosting heat exchanger targeted for defrosting.

According to this refrigerant defrosting operation, high-temperature refrigerant gas can be supplied from the discharge port of the compressor 10 to only one of the two outdoor heat exchangers 20 and 21, so that quick defrosting is possible. It becomes possible. In addition, the other outdoor heat exchanger can perform normal heating operation, so indoor heating can continue.

However, since the outdoor heat exchangers 20 and 21 require switching valves and additional connecting piping, the product cost increases.Also, since the compressor is operated and the thermal energy generated thereby is used for defrosting, There are issues such as it leading to energy loss.

On the other hand, as described in Patent Document 1, an outdoor heat exchanger is divided into two parts, and an outdoor expansion valve is provided in each of the divided outdoor heat exchangers, so that when the temperature of outdoor air is higher than the freezing point, Also known is an outside air defrosting operation in which the outdoor expansion valve of the defrosting heat exchanger on one side is closed and air is sent by an outdoor fan to defrost the air.

In the method of Patent Document 1, when the temperature of the outdoor air is higher than the freezing point, the outdoor expansion valve of the defrosting heat exchanger on one side is fully closed to stop the refrigerant supply, without stopping the compressor, to defrost with outdoor air. As a result, the frost adhering to the surface of the defrosting heat exchanger melts and becomes water, which is removed downward by gravity. Furthermore, it becomes possible to continue the heating operation using the other remaining non-defrosting heat exchanger.

On the other hand, when the temperature of the outdoor air is lower than the freezing point, in order to reduce the thermal energy required for defrosting operation, the outdoor expansion valve of the defrosting heat exchanger is opened to supply refrigerant to the defrosting heat exchanger. The temperature of the refrigerant inside the defrosting heat exchanger is raised to near the temperature of the outdoor air. After that, a refrigerant defrosting operation using high-temperature refrigerant gas or a reverse refrigerant defrosting operation is performed.

However, when the temperature of the outdoor air is lower than the freezing point, a low-temperature refrigerant is flowing through the defrost heat exchanger, so frost may re-deposit during the transition to refrigerant defrost operation or reverse defrost operation. , there is a risk that phenomena such as frost growth may occur. This causes a problem that the subsequent defrosting time becomes longer.

In order to solve this problem, the present embodiment is characterized in that by actively using the sublimation effect of frost, the outside air defrosting operation is performed even when the temperature of the outside air is lower than the freezing point. In this type of outside air defrosting operation, even if the temperature of the outside air is lower than the freezing point, the relative humidity is less than 100%, and the supply of refrigerant to the defrosting heat exchanger is stopped. This is based on the fact that in the absence of cooling by a refrigerant, the frost on the heat exchange fins will dissipate into the blown outdoor air due to sublimation.

Therefore, when the temperature of the outdoor air is lower than the freezing point, the outdoor expansion valve of the defrosting heat exchanger is fully closed to stop the flow of low-temperature refrigerant, and the outdoor fan continues to blow air, resulting in a sublimation effect. Defrosting becomes possible.

Here, the defrosting time by this sublimation action varies depending on the temperature and humidity of the outdoor air. Therefore, it is difficult to manage the completion of the defrosting period at a predetermined time. In the present embodiment, monitoring the amount of power of the outdoor fan corresponding to each outdoor heat exchanger is used as an indicator of completion of defrosting.

That is, in the outside air defrosting operation, it is possible to determine that defrosting is complete when the amount of electric power during defrosting has recovered to the level before frost formation, while maintaining the outdoor ventilation fan at the same rotation speed. The frosting power threshold for determining that frosting has occurred and the defrosting power threshold for determining that defrosting has been completed are determined by calculating the amount of power of the outdoor fan after and before frosting in advance. , these amounts of power can be used as a reference for the above-mentioned judgment.

Here, in FIG. 3, the outdoor ventilation fan is provided in each of the divided outdoor heat exchangers 20 and 21, but it may also be a single outdoor ventilation fan. The reason is that in the outside air defrosting operation, air is blown to both of the divided outdoor heat exchangers 20 and 21.

In addition, when switching to outside air defrosting operation, the outdoor expansion valve of one defrosting heat exchanger is fully closed, so unless the opening degree of the outdoor expansion valve of the other non-defrosting heat exchanger is increased, or Unless the compressor rotation speed is lowered, the evaporation temperature inside the outdoor heat exchanger or the compressor suction pressure will decrease.

A decrease in the evaporation temperature of the outdoor heat exchanger accelerates the growth of frost and leads to an increase in the amount of frost formed. Further, a decrease in refrigerant pressure at the suction section of the compressor leads to a decrease in the amount of refrigerant circulation, which also leads to a decrease in heating capacity. Furthermore, a decrease in the rotational speed of the compressor itself leads to a decrease in the amount of refrigerant circulated and a decrease in heating capacity.

On the other hand, if the opening degree of the outdoor expansion valve of the non-defrosting heat exchanger that continues heating operation is greatly increased, the number of rotations of the outdoor fan will increase and the heat exchange capacity of the outdoor heat exchanger will be reduced. If there is no refrigerant, gasification of the refrigerant will be insufficient and liquid refrigerant will be supplied to the compressor. However, since there is an accumulator connected to the compressor, the liquid refrigerant is temporarily stored here and a large amount of liquid refrigerant is immediately supplied to the compressor, which will not cause the compressor to malfunction. It is possible that the compressor may malfunction due to excess liquid refrigerant flowing back into the compressor.

Therefore, in this embodiment, in addition to fully closing the outdoor expansion valve on the side of the defrosting heat exchanger, as shown in FIG. 51, and a hot gas regulating valve 52 that can adjust the refrigerant flow rate is provided between the hot gas bypass 51. That is, the accumulator 24 is provided in the middle of the refrigerant passage connecting both the suction side of the compressor 10 and the divided outdoor heat exchangers 20 and 21, and the accumulator 24 and the discharge side of the compressor 10 are connected to each other by hot gas bypass. 51, and the hot gas bypass 51 is provided with a hot gas regulating valve 52 that can adjust the flow rate of refrigerant.

As a result, when the refrigerant gasification in the non-defrosting heat exchanger is insufficient, the high temperature refrigerant gas coming out of the discharge port of the compressor 10 is returned to the accumulator 24, thereby evaporating the liquid refrigerant in the accumulator 24. be able to. Thereby, the specific entropy and circulation amount of the refrigerant flowing to the indoor unit 103 can be maintained, and the heating capacity can be maintained.

In particular, in this embodiment, when performing an outside air defrosting operation in a heating operation in which the rotational speed of the outdoor ventilation fans 22 and 23 is not increased, the defrosting heat exchanger, for example, the first While fully closing the first outdoor expansion valve 15 corresponding to the outdoor heat exchanger 20, the opening degree of the second outdoor expansion valve 16 corresponding to a non-defrosting heat exchanger, for example, the second outdoor heat exchanger 21 is increased. move in the direction. Furthermore, the hot gas regulating valve 52 provided in the hot gas bypass 51 connecting the compressor stage suction port to the discharge port of the compressor 10 via the accumulator 24 is opened to increase the rotation speed of the compressor 10. make it work.

This increases the opening degree of the outdoor expansion valve 16 corresponding to the second outdoor heat exchanger 21, which is a non-defrosting heat exchanger for continuing heating operation, while maintaining the refrigerant circulation amount. The evaporation temperature of the frost heat exchanger is not lowered too much, and the risk of frost formation can be suppressed.

In addition, the liquid refrigerant that has not been completely evaporated in the non-defrosting heat exchanger (second outdoor heat exchanger 21) that continues the heating operation is transferred to a portion of the refrigerant gas discharged from the compressor 10 before reaching the accumulator 24. can be evaporated by hot gas supplied to the

Along with this, the compressor 10 needs to compress the refrigerant extra by the amount of evaporation of this refrigerant, so in order to maintain the amount of refrigerant circulating to the indoor unit, it is necessary to increase the rotation speed of the compressor. be. However, compared to the case where the energy of the compressor 10 is used for defrosting, all the energy of the compressor 10 is used for heating, so the loss of energy is small.

FIG. 4 shows a flowchart when executing the outside air defrosting operation of this embodiment. This control flow is executed by a microcomputer built into the control panel 26.

<<Step S10>>
First, in step S10, the system waits for the timing to execute the defrosting operation mode during the heating operation. For example, in a state where heating operation is being performed, the defrosting operation mode is activated at interrupt timing that is generated at predetermined time intervals. When the interrupt timing arrives, the defrosting operation mode is activated and the process moves to step S11.

<<Step S11>>
In step S11, it is determined whether the power amount of the outdoor ventilation fan exceeds the frosting power threshold, and if it is determined that frosting has not occurred, the process returns to step S10 and waits for the interrupt timing to arrive. become. On the other hand, it is determined whether the electric power amount of the outdoor fan exceeds the frosting power threshold, and if it is determined (estimated) that frosting has occurred, the process moves to step S12.

<<Step S12>>
In step S12, the temperature of the outdoor air is measured by the outdoor air temperature sensor 19, and when the temperature of the outdoor air continues to be lower than the freezing point for a predetermined period of time, a defrosting operation mode using sublimation, which is a feature of this embodiment, is executed. In this case, the process moves to step S14. On the other hand, if the outdoor temperature is higher than the freezing point, the process moves to step S13.

<<Step S13>>
In step S13, another defrosting mode is started. Other defrosting modes have little relevance to this embodiment, so their explanation will be omitted, but for example, a refrigerant defrosting operation may be used.

<<Step S14>>
In step S14, since it has been determined in step S11 that there is frost and that the outdoor temperature is lower than the freezing point in step S12, startup of the outside air defrosting operation using sublimation action is started. When the start-up of the outside air defrosting operation using the sublimation action is started, specific control steps starting from the next step S15 are executed.

<<Step S15>>
In step S15, even if the outside air defrosting operation by sublimation is started, the rotational speed of the compressor 10 and the rotational speeds of the first outdoor ventilation fan 22 and the second outdoor ventilation fan 23 are maintained as they are. There is. In this way, the reason why the rotation speeds of the first outdoor ventilation fan 22 and the second outdoor ventilation fan 23 are maintained is to perform defrosting by sublimation in the defrosting heat exchange, and to absorb heat in the non-defrosting heat exchanger. This is to allow heating operation to continue. Further, the rotational speed of the compressor 10 at this time is smaller than a predetermined value. Then, the process moves to step S16 while maintaining this state.

<<Step S16>>
In step S16, the first outdoor expansion valve 15 corresponding to the first outdoor heat exchanger (defrosting heat exchanger) 20 to be defrosted is fully closed. Further, the second outdoor expansion valve 16 corresponding to the second outdoor heat exchanger 21 that is not subject to defrosting (non-defrosting heat exchanger) is controlled to an opening degree based on the discharge gas temperature of the compressor 10, etc. It is operated as follows.

Then, the amount of refrigerant flowing to the second outdoor heat exchanger 21 increases by the amount that the first outdoor expansion valve 15 is closed, and the amount of refrigerant whose pressure is reduced by the second outdoor expansion valve 16 increases. Therefore, the suction refrigerant pressure (Ps) of the compressor decreases. Since this reduces the heating capacity, the process moves to step S17 shown below.

<<Step S17>>
In step S17, first, it is determined whether the rotational speeds of the first outdoor fan 22 and the second outdoor fan 23 can be increased. If the current rotational speeds of the first outdoor ventilation fan 22 and the second outdoor ventilation fan 23 can be increased, the process moves to step S18, and if the current rotational speed cannot be increased, the process moves to step S20.

<<Step S18>>
In step S18, the rotation speeds of the first outdoor fan 22 and the second outdoor fan 23 are increased to improve the evaporation pressure of the refrigerant in the first outdoor heat exchanger 20 and the second outdoor heat exchanger 21. Make it. Here, the increase in the rotation speed of the first outdoor ventilation fan 22 can hasten the completion of outside air defrosting due to the sublimation action of the first outdoor heat exchanger 20, and also increases the rotation speed of the second outdoor ventilation fan 21. The increase leads to improved evaporation of the refrigerant inside the second outdoor heat exchanger 21. When the rotational speeds of the first outdoor fan 22 and the second outdoor fan 23 are increased, the process moves to step S19.

<<Step S19>>
In step S19, control is executed to determine the state of heating capacity. Here, assuming that the hot gas regulating valve 52 is not yet open, the refrigerant circulation amount is calculated from the suction pressure (Ps) of the compressor 10 and the rotation speed of the compressor 10, and the amount of the discharge gas of the compressor 10 is calculated. The specific enthalpy amount of the refrigerant supplied to the indoor unit is determined from the pressure (Pd) and temperature (Td), and the ratio at the outlet of the indoor heat exchanger 104 is determined from the degree of subcooling (SC) of the refrigerant at the outlet of the indoor heat exchanger 104. Enthalpy is determined and heating capacity is estimated from these parameters.

If it is determined that the estimated heating capacity does not exceed the predetermined heating capacity threshold, the process returns to step S17 and the control to increase the rotational speed of the first outdoor ventilation fan 22 and the second outdoor ventilation fan 23 is repeated. It turns out. If it is determined that the estimated heating capacity exceeds the predetermined heating capacity threshold, the process moves to step 23.

≪Step S20≫
Returning to step S17, if it is determined that the rotational speed of the first outdoor ventilation fan 22 and the second outdoor ventilation fan 23 cannot be increased any further, control is performed to open the hot gas bypass valve 52 and increase the heating capacity. Is required.

For this reason, in step S20, it is determined whether the rotational speed of the compressor 10 can be increased. If the current rotational speed of the compressor 10 can be increased, the process moves to step S21, and if the current rotational speed cannot be increased, the process moves to step S24.

If it is determined in this control step that the rotation speed of the compressor 10 cannot be increased, as determined in step S17, the rotation speed of the first outdoor ventilation fan 22 and the second outdoor ventilation fan 23 cannot be increased either. Therefore, there is no way to compensate for the lack of heating capacity. In this case, outside air defrosting is ended and another defrosting operation mode such as refrigerant defrosting operation is executed. Note that, in reality, it is unlikely that the process will proceed to step S24.

<<Step S21>>
In step S21, since it is determined in step S20 that the rotation speed of the compressor 10 can be increased, the opening degree of the hot gas regulating valve 52 is increased while increasing the rotation speed of the compressor 10. This makes it possible to increase the heating capacity. When the rotation speed of the compressor 10 is increased and the opening degree of the hot gas regulating valve 52 is increased, the process moves to step S22.

<<Step S22>>
In step S22, control is executed to determine the state of heating capacity. Similarly to step S19, the refrigerant circulation amount is determined from the suction pressure (Ps) of the compressor 10 and the rotation speed of the compressor 10, and the indoor unit The specific enthalpy amount of the refrigerant supplied to the indoor heat exchanger 104 is determined from the degree of subcooling (SC) of the refrigerant at the outlet of the indoor heat exchanger 104, and the heating capacity is estimated from these parameters. are doing.

However, when the hot gas regulating valve 52 is open, the discharge pressure (Pd) of the compressor 10 and the compression The amount of refrigerant circulating to the indoor unit is estimated by subtracting the hot gas bypass refrigerant circulating amount obtained by multiplying the difference in the suction side pressure (Ps) of the unit 10 by a coefficient according to the opening degree of the hot gas regulating valve 52. ing.

Note that the suction pressure (Ps) of the compressor 10 can also be determined from its saturation pressure from the refrigerant evaporation temperature in the heat exchanger 104 in the indoor unit 103, and similarly, the discharge pressure (Pd) of the compressor is: It can also be determined from the condensation temperature of the refrigerant in the indoor heat exchanger 104 in the indoor unit 103.

If it is determined that the estimated heating capacity does not exceed the predetermined heating capacity threshold, the process returns to step S20 and the control to increase the rotation speed of the compressor 10 is repeated. If it is determined that the estimated heating capacity exceeds the predetermined heating capacity threshold, the process moves to step 23.

<<Step S23>>
If it is determined in step S19 and step S22 that the heating capacity is sufficient, it is determined in step S23 that the outside air defrosting operation by sublimation is terminated. As mentioned earlier, this outside air defrosting is determined to be complete when the amount of power of the outdoor fan on the side of the defrosting heat exchanger exceeds a predetermined defrosting power threshold. It is possible to (estimate).

Note that the determination can be made without using the electric power of the outdoor fan. For example, if the object to be defrosted is the first outdoor heat exchanger 20, the temperature of the first heat exchanger temperature sensor 17 may be used as an index.

That is, if the frost has not completely sublimated, the temperature of the first heat exchanger temperature sensor 17 becomes lower than the temperature of the blown outdoor air because the outdoor heat exchanger is cooled by sublimation. Therefore, when the temperature at the first heat exchanger temperature sensor 17 becomes approximately the same as the temperature at the outside air temperature sensor 19, it may be determined that defrosting has ended.

Note that it is necessary to take into account the variations in the temperatures measured by the temperature sensors 17 and 19 to determine the threshold value for determining the end of outside air defrosting. If it is determined that the outside air defrosting has ended, the process moves to step 24.

<<Step S24>>
In step S24, the outside air defrosting operation using the sublimation action is ended, and the control of the outdoor expansion valve 15 and the hot gas regulating valve 52 on the defrosting outdoor heat exchanger side is shifted to the control during normal heating.

In this way, even under conditions where defrosting by sublimation is performed and the temperature of the outdoor air is lower than the freezing point, defrosting using outdoor air is possible while continuing the heating operation.

FIG. 5 shows the structure of an outdoor heat exchanger using round heat transfer tubes. As shown in the figure, the outdoor heat exchangers 20 and 21 are comprised of heat exchanger tubes 34 bent into a U-shape and plate-shaped heat exchange fins 35. In this embodiment, the outdoor heat exchangers are arranged in three rows, with the windward side with respect to the air flow being the first row, and the most leeward row being the third row. As shown in FIG. 5, the heat exchange fins 35 are densely arranged at regular intervals, and the fin pitch, which is the interval, is often 2 mm or less. By narrowing the fin pitch in this way, the heat transfer coefficient to the air on the fin surface improves. This heat transfer coefficient has a correlation with mass transfer such as sublimation, and the higher the heat transfer coefficient, the easier sublimation occurs, and the time required for outside air defrosting can be shortened.

FIG. 6 shows the flow of a part of the refrigerant in the outdoor heat exchanger used in this embodiment. The horizontal direction in FIG. 6 is the column direction, and the first, second, and third columns are counted from the left. In addition, the vertical direction in FIG. 6 is the stage direction, and the number of heat exchanger tubes is counted as 1 stage and 2 stages. The configuration shown in FIG. 6 shows 12 stages, which are part of the outdoor heat exchanger used in this embodiment.

The black arrows in FIG. 6 indicate the flow of refrigerant, and the two-phase flow that exits the outdoor expansion valve 30 during heating operation is distributed by the liquid distributor 31, passes through the capillary 32, and enters each refrigerant path of the outdoor heat exchanger. be swept away. Note that the refrigerant path means a refrigerant flow path. Thereafter, the refrigerant flows into the gas header 33 from the third row of outdoor heat exchangers along the direction of the arrow. The refrigerant that merges at the gas header 33 flows to the four-way valve.

In this embodiment, the heat exchanger temperature sensor 17 (18) is provided, for example, in the middle of the capillary 32 in FIG. 6. During heating operation, this portion remains a two-phase flow because it has not yet been heated by outside air, and can exhibit a temperature close to the evaporation temperature.

Further, the liquid refrigerant inlet/outlet of the outdoor heat exchanger 20 (21) connected from the liquid distributor 31 via the capillary 32 is often located at the most windward row of the outdoor heat exchanger 20 (21). When used as a condenser during cooling operation, the refrigerant near the liquid distributor, which is the closest to the liquid side, is cooled with low-temperature air, and the refrigerant is sufficiently subcooled to improve cooling performance. Because you can.

Frost grows especially in the first row on the windward side of the outdoor heat exchangers 20 and 21. This is because the air with the highest humidity comes into contact with the cooled heat exchange fins 35 first during the heating operation. Therefore, the first row has the greatest influence on the deterioration of the air blowing performance of the outdoor heat exchangers 20 and 21.

As mentioned above, the capillary 32 is often connected to the first column where the amount of frost is the highest. Therefore, in order to detect when frost has melted during defrosting, it is desirable to be able to measure the temperature closest to the area with the most frost. For this reason, the heat exchanger temperature sensors 17 and 18 are provided in the middle of the capillary 32.

FIG. 7 shows the detailed shape of the heat exchange fins 35 employed in this embodiment. In this embodiment, as shown in FIG. 7, fins having offset portions 43 and rib portions 41 cut and raised on the surface between fin collars 42 through which heat transfer tubes 34 pass are used in the outdoor heat exchanger.

The offset portion 43 improves heat exchange performance by dividing the temperature boundary layer formed on the fin surface during normal heat exchange. For example, during cooling, the outdoor heat exchangers 20 and 21 are used as condensers and radiate heat from the refrigerant to the outside air. At this time, the cold air coming from upwind of the fins is warmed by the fins, but naturally this phenomenon is more pronounced near the fin surfaces, and the air temperature near the fins further downwind is lower than that of the air farther away from the fins. becomes higher.

Therefore, when looking only at the fin surface, the temperature difference between the fin and the fin becomes smaller, so the amount of heat exchange becomes smaller. However, the offset portion 43 is located at a distance from the windward fin surface position, and a portion where the temperature rise of the air is not high can be used. Therefore, the offset portion 43 facilitates heat exchange compared to a case where the offset portion 43 is not offset.

Similarly, during outside air defrosting operation, especially when performing defrosting by sublimation when the temperature of the outside air is lower than the freezing point, sublimation is promoted by dividing the boundary layer of humidity distribution formed on the fin surface. In other words, air flowing in from upwind with a constant humidity increases in humidity due to the amount of humidity that has sublimated frost on the fin surface. This increase in humidity is noticeable on the fin surface, similar to the temperature mentioned earlier, and this suppresses the sublimation effect of frost on the fin surface on the leeward side.

On the other hand, with the fins having the offset portions 43, the fins come into contact with air that is away from the windward fin surface, so that the frost can be sublimated by air with a low increase in humidity. Therefore, compared to a fin without the offset portion 43, it is possible to increase the amount of frost that can be sublimated.

Looking at this phenomenon from a macro perspective, the higher the heat transfer coefficient of the fin, the higher the sublimation performance. The rib portion provided on the fin of this embodiment not only improves the strength of the fin, but also contributes to improving the heat transfer coefficient. Therefore, this rib portion 41 also promotes sublimation and contributes to shortening the outside air defrosting time under conditions where the temperature of the outdoor air is lower than the freezing point.

Further, in the embodiment, fins having a pitch of 1.7 mm are used. This is because the fins with the offset portions 43 are used to increase the heat transfer coefficient. On the other hand, if the fins are to be replaced with fins without offset, fins with a smaller fin pitch of about 1.3 mm are desirable.

Further, in this embodiment, the defrosting heat exchanger to be defrosted is supplied with wind having a front wind speed exceeding 1.0 m/s by an outdoor blower fan. This is to constantly supply air with low relative humidity to the defrosting heat exchanger by increasing the air volume, and also to improve the sublimation rate by improving the heat transfer coefficient.

In addition, the first outdoor heat exchanger 20 and the second outdoor heat exchanger 21 of this embodiment are arranged side by side. For example, there is a method of dividing the outdoor heat exchanger into upper and lower parts in the height direction, but in this case, when the upper outdoor heat exchanger is defrosted and the lower part performs heating operation, the upper outdoor heat exchanger is This is to prevent melted frost from freezing on the lower outdoor heat exchanger and accelerating the deterioration of the ventilation performance of the lower outdoor heat exchanger.

If they are arranged side by side as in this embodiment, even when the outdoor air temperature is higher than the freezing point, the melted water of the outdoor heat exchanger to be defrosted will be transferred to the outdoor heat exchanger that continues heating operation. It is possible to suppress the deterioration of heat exchange performance due to flow into the heat exchanger.

Note that the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the embodiments described above are described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to having all the configurations described. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Further, it is possible to add, delete, or replace a part of the configuration of each embodiment with other configurations.

10... Compressor, 11... Refrigerant piping, 12... Four-way valve, 13... Gas side blocking valve, 14... Liquid side blocking valve, 15... First outdoor expansion valve, 16... Second outdoor expansion valve, 17... First heat Exchanger temperature sensor, 18... Second heat exchanger temperature sensor, 19... Outside air temperature sensor, 20... First outdoor heat exchanger, 21... Second outdoor heat exchanger, 22... First outdoor blower fan, 23... Third 2 Outdoor ventilation fan, 24... Accumulator, 25... Bell mouth, 26... Control panel, 27... Bottom installation plate, 28... Refrigerant tank, 29... Front panel, 30... Outdoor expansion valve, 31... Liquid side distributor, 32... Capillary, 33... Gas header, 34... Heat transfer tube, 35... Fin, 37... Heat exchanger temperature sensor, 41... Rib section, 42... Fin collar, 43... Offset section, 51... Hot gas bypass, 52... Hot gas adjustment valve , 100... Outdoor unit, 101... Gas side connecting pipe, 102... Liquid side connecting pipe, 103... Indoor unit, 104... Indoor heat exchanger, 105... Indoor fan, 106... Indoor expansion valve, 107... Living room.

Claims (2)

an outdoor unit having a compressor, a top-flow type outdoor heat exchanger equipped with an outdoor blower fan at the top, and an outdoor expansion valve; an indoor unit having an indoor heat exchanger and an indoor expansion valve; the outdoor unit and the outdoor unit; In an air conditioner equipped with liquid refrigerant piping and gas refrigerant piping that connect to the indoor unit,
The outdoor heat exchanger of the outdoor unit is divided into a plurality of parts,
The outdoor heat exchanger divided into a plurality of parts each has a gas header, a liquid side distributor, and the outdoor expansion valve, and the outdoor heat exchanger divided into a plurality of parts is arranged horizontally inside the outdoor unit. are arranged side by side,
In the defrosting operation mode of the heating operation, the outdoor air fan blows outdoor air to all of the divided outdoor heat exchangers, and if the temperature of the outdoor air is lower than the freezing point, the divided outdoor heat Among the exchangers, the outdoor expansion valve connected to the defrosting outdoor heat exchanger which is the outdoor heat exchanger to be defrosted is fully closed, and the defrosting outdoor heat exchanger is fully closed. In addition to defrosting only the container using the sublimation effect of outdoor air,
An accumulator is provided in the middle of a refrigerant passage connecting both the suction side of the compressor and the divided outdoor heat exchanger, and the accumulator and the discharge side of the compressor are further connected by a hot gas bypass. In addition, the hot gas bypass is provided with a hot gas regulating valve capable of adjusting a refrigerant flow rate,
In the defrosting operation mode, when the outdoor expansion valve is fully closed and the defrosting outdoor heat exchanger is defrosted by the sublimation action of outdoor air,
If it is determined that the rotation speed of the outdoor ventilation fan can be increased, increasing the rotation speed of the outdoor ventilation fan,
When it is determined that the rotation speed of the outdoor blower fan cannot be increased, but when it is determined that the rotation speed of the compressor can be increased, the rotation speed of the compressor is increased, and the hot gas regulating valve is further increased. increase the opening of
An air conditioner characterized by: The air conditioner according to claim 1,
The heat exchange fins of the outdoor heat exchanger are offset fins.
An air conditioner characterized by:

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