JP7526958B2 - Refrigeration Cycle Equipment - Google Patents

Description

This disclosure relates to a refrigeration cycle device.

Patent Document 1 discloses a refrigeration system equipped with multiple compressors arranged in series to compress a refrigerant, and a bypass refrigerant circuit that bypasses a portion of the refrigerant in the circulating main refrigerant circuit between the multiple compressors.

A portion of the refrigerant in the main refrigerant circuit is expanded by an electronic expansion valve located in the bypass refrigerant circuit, and after heat exchange with the refrigerant flowing through the main refrigerant circuit, it is bypassed between the multiple compressors, merges with the refrigerant discharged from the low-stage compressor among the multiple compressors, and is sucked into the high-stage compressor.

The discharge temperature of the high-stage compressor is constantly detected, and if it is predicted that the discharge temperature of the high-stage compressor will exceed the upper limit, the opening of the electronic expansion valve in the bypass refrigerant circuit is temporarily increased to lower the discharge temperature.

JP 2009-192164 A

This disclosure provides a highly reliable refrigeration cycle device that can suppress increases in discharge temperature and discharge pressure without exceeding the upper limit of the operating range, even when the discharge temperature and discharge pressure increase and approach the upper limit of the operating range.

The refrigeration cycle device disclosed herein includes a compression mechanism composed of a compression rotating element, a utilization side heat exchanger that heats a utilization side heat medium with the refrigerant discharged from the compression rotating element, an intermediate heat exchanger, a first expansion device, and a heat source side heat exchanger, which are connected in sequence by piping, a bypass refrigerant circuit in which the refrigerant branched from the piping between the utilization side heat exchanger and the first expansion device is decompressed by a second expansion device, and then heat exchanged with the refrigerant flowing through the main refrigerant circuit in the intermediate heat exchanger, and is merged with the refrigerant being compressed by the compression rotating element, a discharge temperature detection means for detecting the discharge temperature of the compression rotating element, a discharge pressure detection means for detecting the discharge pressure of the compression rotating element, and a control device, and is characterized in that when the discharge pressure of the compression rotating element is higher than a predetermined pressure and the discharge temperature of the compression rotating element is higher than a predetermined temperature, the control device increases the opening degree of both the first expansion device and the second expansion device.

According to the present disclosure, it is possible to provide a highly reliable refrigeration cycle device that can suppress increases in the discharge temperature and discharge pressure without exceeding the upper limit of the operating range, even when the discharge temperature and discharge pressure increase and approach the upper limit of the operating range.

1 is a block diagram of a refrigeration cycle according to a first embodiment of the present invention; In the refrigeration cycle device of the first embodiment, a pressure-enthalpy diagram (P-h diagram) when the opening degree of only the second expansion device is increased In the refrigeration cycle device of the first embodiment, a pressure-enthalpy diagram (P-h diagram) when the opening degree of only the first expansion device is increased In the refrigeration cycle device of the first embodiment, the pressure-enthalpy diagram (P-h diagram) when the opening degree of the first expansion device and the opening degree of the second expansion device are increased.

Below, the embodiments will be described in detail with reference to the drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted.

The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

(Embodiment 1)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 3. FIG.

[1-1. Configuration]
In FIG. 1 , the refrigeration cycle device includes a main refrigerant circuit 8 and a bypass refrigerant circuit 6 .

The main refrigerant circuit 8 is formed by sequentially connecting a compression mechanism 1 composed of a compression rotating element, a utilization side heat exchanger 2 which serves as a radiator, an intermediate heat exchanger 5, a first expansion device 3, and a heat source side heat exchanger 4 which serves as an evaporator with piping, and uses carbon dioxide ( _CO2 ) as the refrigerant.

The compression mechanism 1 is composed of a high-stage compression section 11 and a low-stage compression section 12. In the user-side heat exchanger 2, the user-side heat medium is heated by the refrigerant discharged from the compression mechanism 1.

In FIG. 1, the compression rotating element is shown as a two-stage compression mechanism consisting of a low-stage compression section 12 and a high-stage compression section 11, but it can also be applied to a single compression mechanism. In the case of a single compression mechanism, the position where the refrigerant from the bypass refrigerant circuit 6 is sucked in can be midway through the compression of the compression rotating element, the compression rotating element up to the position where the refrigerant from the main refrigerant circuit 8 and the refrigerant from the bypass refrigerant circuit 6 join can be the low-stage compression section 12, and the compression rotating element after the position where the refrigerant from the bypass refrigerant circuit 6 joins can be the high-stage compression section 11.

The bypass refrigerant circuit 6 is branched off from the main refrigerant circuit 8 by piping between the user side heat exchanger 2 and the intermediate heat exchanger 5, and is connected by piping up to the middle of the compression process between the low stage compression section 12 and the high stage compression section 11.

The bypass refrigerant circuit 6 is provided with a second expansion device 7. A portion of the high-pressure refrigerant that has passed through the user-side heat exchanger 2 is decompressed by the second expansion device 7 to become an intermediate-pressure refrigerant, which exchanges heat with the high-pressure refrigerant flowing through the main refrigerant circuit 8 in the intermediate heat exchanger 5, and merges with the refrigerant flowing through the main refrigerant circuit 8 during compression between the low-stage compression section 12 and the high-stage compression section 11.

The user-side heat medium heated in the user-side heat exchanger 2 is used for heating and the like at a user-side terminal (not shown). Water or antifreeze is used as the user-side heat medium.

In the main refrigerant circuit 8, a discharge temperature sensor 15, which is a discharge temperature detection means, and a discharge pressure sensor 16, which is a discharge pressure detection means, are provided in the discharge piping of the compression mechanism 1. The discharge temperature detected by the discharge temperature sensor 15 and the discharge pressure detected by the discharge pressure sensor 16 are input as data into the control device 20.

The control device 20 is preset with a threshold value of a predetermined temperature that is a first predetermined value lower than the discharge temperature value that is the upper limit of the operating range of the refrigeration cycle device, and a predetermined pressure that is a second predetermined value lower than the discharge pressure value that is the upper limit of the operating range of the refrigeration cycle device.

The discharge temperature value that is the upper limit of the operating range of the refrigeration cycle device, and the discharge pressure value that is the upper limit of the operating range of the refrigeration cycle device, are values at which the control device 20 stops operating the refrigeration cycle device.

When the discharge temperature detected by the discharge temperature sensor 15 and the discharge pressure detected by the discharge pressure sensor 16 exceed their respective threshold values, the control device 20 controls the opening degree of the first expansion device 3 and the opening degree of the second expansion device 7 to be increased.

The discharge pressure sensor 16 is provided in the main refrigerant circuit 8 from the discharge side of the compression mechanism 1 to the upstream side of the first expansion device 3, and is capable of detecting the pressure of the high-pressure refrigerant in the main refrigerant circuit 8.

Figures 2 to 4 show the change in pressure-enthalpy diagram (P-h diagram) when the opening degree of the first expansion device or the opening degree of the second expansion device is increased in the refrigeration cycle device of this embodiment 1.

Figure 2 shows the change in the refrigeration cycle when the opening of only the second expansion device 7 is increased, with the solid line showing the state before the opening is increased and the dashed line showing the state after the opening is increased.

Figure 3 shows the change in the refrigeration cycle when the opening of only the first expansion device 3 is increased, with the solid line showing the state before the opening is increased and the dashed line showing the state after the opening is increased.

Figure 4 shows the change in the refrigeration cycle when the opening of the first expansion device 3 and the opening of the second expansion device 7 are increased, with the solid line showing the state before the opening is increased and the dashed line showing the state after the opening is increased.

In Figures 2 to 4, the upper limits of the operating range of the refrigeration cycle device for both discharge temperature and discharge pressure are indicated by dashed lines, and points a to e and points A to B correspond to the respective points in the configuration diagram of the refrigeration cycle device shown in Figure 1.

[1-2. Operation]
The operation and function of the refrigeration cycle apparatus constructed as above will now be described.

First, the operation of the refrigeration cycle device will be explained based on Figures 1 and 2.

In the refrigeration cycle device before the opening of the second expansion device 7 is increased (solid line), the high-pressure refrigerant (point a) compressed in the high-stage compression section 11 and discharged from the compression mechanism 1 dissipates heat in the user-side heat exchanger 2, branches off from the main refrigerant circuit 8 at the refrigerant branching point A, is decompressed to an intermediate pressure by the second expansion device 7 to become an intermediate-pressure refrigerant (point e), exchanges heat in the intermediate heat exchanger 5, and merges with the refrigerant in the main refrigerant circuit 8 compressed in the low-stage compression section 12 during the compression process located between the high-stage compression section 11 and the low-stage compression section 12 (point B).

The high-pressure refrigerant flowing through the main refrigerant circuit 8 after dissipating heat in the user-side heat exchanger 2 is cooled by heat exchange with the intermediate-pressure refrigerant (point e) flowing through the bypass refrigerant circuit 6, and is depressurized in the first expansion device 3 in a state in which the enthalpy has been reduced (point b).

The refrigerant in the main refrigerant circuit 8, which has been decompressed by the first expansion device 3 and is in a two-phase gas-liquid state, evaporates in the evaporator 4 by absorbing heat from the outside air and becomes gaseous, returns to the suction side (point d) of the compression mechanism 1, and is compressed in the low-stage compression section 12 of the compression mechanism 1.

Under operating conditions where high-temperature water needs to be discharged when the outside air temperature is low and heating capacity is required, the rotation frequency of the compression mechanism 1 needs to be increased, and not only does the discharge temperature of the compression mechanism 1 exceed the threshold value, but the discharge pressure of the compression mechanism 1 is also operating at a state close to the threshold value.

The dashed line shows the change in the refrigeration cycle when the opening of the second expansion device 7 is increased.

When the opening degree of the second expansion device 7 is increased, the amount of low-temperature refrigerant flowing through the bypass refrigerant circuit 6 increases, and the temperature during compression (point B) where the refrigerant flowing through the bypass refrigerant circuit 6 and the refrigerant flowing through the main refrigerant circuit 8 merge decreases.

The refrigerant whose temperature has dropped and merged is compressed in the high-stage compression section 11 and discharged from the compression mechanism 1. The discharge temperature (point a) of the discharged refrigerant drops and can be made below a threshold temperature, suppressing an increase in the discharge temperature.

However, because the amount of refrigerant flowing through the bypass refrigerant circuit 6 increases, the amount of refrigerant flowing into the compression mechanism 1 increases and the discharge pressure rises. As a result, the discharge pressure exceeds the threshold value.

Next, the operation of the refrigeration cycle device will be explained based on Figures 1 and 3.

The operation of the refrigeration cycle device before the opening of the first expansion device 3 is increased (solid line) is the same as the operation before the opening of the second expansion device 7 in Figure 2 is increased, so a description is omitted.

When the outside air temperature is low and heating capacity is required, and operating conditions require high-temperature water to be discharged, the rotation frequency of the compression mechanism 1 must be increased, and not only does the discharge pressure of the compression mechanism 1 exceed the threshold value, but the discharge temperature of the compression mechanism 1 is also operating at a temperature close to the threshold value.

The broken line shows the change in the refrigeration cycle when the opening degree of the first expansion device 3 is increased. When the opening degree of the first expansion device 3 is increased, the amount of refrigerant flowing through the main refrigerant circuit 8 increases, and the amount of refrigerant flowing through the bypass refrigerant circuit 6 decreases. Therefore, the discharge pressure of the compression mechanism 1 decreases, and can be reduced below the threshold value.

However, because the amount of refrigerant flowing through the bypass refrigerant circuit 6 decreases, the temperature rises midway through compression (point B) when the refrigerant flowing through the bypass refrigerant circuit 6 and the refrigerant flowing through the main refrigerant circuit 8 join together.

As a result, the discharge temperature (point a) of the refrigerant compressed in the high-stage compression section 11 and discharged from the compression mechanism 1 rises and exceeds the threshold value.

In this way, when the opening degree of only the second expansion device 7 is increased, the discharge temperature decreases but the discharge pressure increases. Also, when the opening degree of only the first expansion device 3 is increased, the discharge pressure decreases but the discharge temperature increases.

Under operating conditions where it is necessary to discharge high-temperature water at low outside temperatures that require heating capacity, both the discharge temperature and discharge pressure are close to the upper limits of the operating range of the refrigeration cycle device, i.e., both the discharge temperature and discharge pressure exceed their respective threshold values.

However, when the ambient environment of the refrigeration cycle device changes and the discharge temperature exceeds a threshold value, simply increasing the opening of the second expansion device 7 will cause the discharge pressure to exceed the threshold value, making it impossible to achieve proper operation of the refrigeration cycle.

In addition, when the ambient environment of the refrigeration cycle device changes and the discharge pressure exceeds the threshold, simply increasing the opening of the first expansion device 3 will cause the discharge temperature to exceed the threshold, making it impossible to operate the refrigeration cycle appropriately.

Therefore, when the control device 20 controls the opening of both the first expansion device 3 and the second expansion device 7 to be larger, the refrigeration cycle changes from the solid line to the dashed line as shown in Figure 4.

In other words, it is possible to provide a highly reliable refrigeration cycle device that can suppress increases in discharge temperature and discharge pressure without causing the discharge pressure and discharge temperature to exceed their respective threshold values, i.e., without exceeding the upper limit of the operating range.

The control device 20 is preset with a threshold value of a predetermined temperature that is a first predetermined value lower than the discharge temperature value that is the upper limit of the operating range of the refrigeration cycle device, and a predetermined pressure that is a second predetermined value lower than the discharge pressure value that is the upper limit of the operating range of the refrigeration cycle device.

Then, when the discharge temperature detected by the discharge temperature sensor 15 and the discharge pressure detected by the discharge pressure sensor 16 exceed their respective threshold values, the control device 20 controls the first expansion device 3 and the second expansion device 7 to increase their opening.

As a result, in order to lower the discharge temperature, the opening of the second expansion valve is increased and the amount of low-temperature refrigerant mixed in is increased. Even if the amount of refrigerant flowing into the compression mechanism 1 increases and the discharge pressure rises, the opening of the first expansion valve is increased to increase the amount of refrigerant flowing through the main refrigerant circuit 8, thereby reducing the increased discharge pressure.

Furthermore, the control device 20 controls the opening of the first expansion device 3 to be increased after increasing the opening of the second expansion device 7.

As a result, the amount of low-temperature refrigerant merging from the bypass refrigerant circuit 6 is increased, and then the amount of pressure reduction in the main refrigerant circuit 8 is reduced. The amount of pressure reduction in the main refrigerant circuit 8 can be controlled while detecting the increase in discharge temperature caused by the decrease in the refrigerant flow rate in the bypass refrigerant circuit 6 by reducing the amount of pressure reduction in the main refrigerant circuit 8 with the discharge temperature sensor 15.

Furthermore, the control device 20 controls the change in the opening degree of the second expansion device 7 so that the higher the discharge temperature of the compression mechanism 1, the greater the change in the opening degree.

As a result, the higher the discharge temperature of the compression mechanism 1, the more quickly the flow rate of low-temperature refrigerant joining from the bypass refrigerant circuit 6 can be increased.

Specifically, the control device 20 controls the amount of change in the opening degree of the second expansion device 7 to be greater the greater the temperature difference between the discharge temperature of the compression mechanism 1 and the threshold value.

As a result, the discharge temperature of the compression mechanism 1 is continuously detected, so that an excessive rise in the discharge temperature can be detected more quickly and reliably, and the opening degree of the second expansion device 7 can be controlled.

[1-3. Effects, etc.]
As described above, in the first embodiment, the refrigeration cycle apparatus includes the compression mechanism 1 composed of a compression rotating element, the utilization side heat exchanger 2 that heats the utilization side heat medium with the refrigerant discharged from the compression rotating element, the intermediate heat exchanger 5, the first expansion device 3, and the heat source side heat exchanger 4, which are sequentially connected by piping, the main refrigerant circuit 8, the bypass refrigerant circuit 6 in which the refrigerant branched from the piping between the utilization side heat exchanger 2 and the first expansion device 3 is decompressed by the second expansion device 7, and then heat exchanged with the refrigerant flowing through the main refrigerant circuit 8 in the intermediate heat exchanger 5, and merges with the refrigerant being compressed by the compression rotating element, the discharge temperature detection means 15 that detects the discharge temperature of the compression rotating element, the discharge pressure detection means 16 that detects the discharge pressure of the compression rotating element, and the control device 20, and is characterized in that when the discharge pressure of the compression rotating element is higher than a predetermined pressure and the discharge temperature of the compression rotating element is higher than a predetermined temperature, the control device 20 increases the opening degree of both the first expansion device 3 and the second expansion device 7.

This makes it possible to provide a highly reliable refrigeration cycle device that can suppress increases in discharge temperature and discharge pressure without exceeding these values, even when the discharge temperature and discharge pressure increase and approach the upper limit of the operating range.

Furthermore, in this embodiment 1, the refrigeration cycle device is characterized in that the control device 20 increases the opening degree of the first expansion device 3 after increasing the opening degree of the second expansion device 7.

This increases the amount of low-temperature refrigerant joining from the bypass refrigerant circuit 6, and then reduces the amount of pressure reduction in the main refrigerant circuit 8.

As a result, the amount of pressure reduction in the main refrigerant circuit 8 can be controlled while also detecting an excessive rise in discharge temperature that accompanies a decrease in the refrigerant flow rate in the bypass refrigerant circuit 6 caused by reducing the amount of pressure reduction in the main refrigerant circuit 8.

As a result, even if the discharge temperature rises quickly, the rise in discharge temperature can be suppressed more effectively in a short period of time, providing a highly reliable refrigeration cycle device.

In addition, in this embodiment 1, the refrigeration cycle device is characterized in that the control device 20 increases the amount of change in the opening degree of the second expansion device 7 as the discharge temperature of the compression rotating element increases.

As a result, the higher the discharge temperature, the faster the flow rate of low-temperature refrigerant joining from the bypass refrigerant circuit 6 can be increased, and the faster the discharge temperature can be reduced.

As a result, even if the discharge temperature is high and exceeds a predetermined temperature, the discharge temperature can be quickly lowered, providing a more reliable refrigeration cycle device.

In addition, in this embodiment 1, the refrigeration cycle device is characterized in that the control device 20 determines the amount of change in the opening degree of the second expansion device 7 based on the temperature difference between the discharge temperature of the compression rotating element and a predetermined temperature.

As a result, the temperature of the refrigerant discharged from the compression mechanism 1 is continuously detected, so that an excessive rise in the discharge temperature can be detected more quickly and reliably, and the second expansion device 7 can be controlled.

This allows the discharge temperature to be lowered quickly, providing a more reliable refrigeration cycle device.

This disclosure provides a highly reliable refrigeration cycle device that can suppress increases in discharge temperature and discharge pressure without exceeding the upper limit of the operating range, even when the discharge temperature and discharge pressure increase and approach the upper limit of the operating range. Therefore, this disclosure is applicable to air conditioners, water heaters, etc.

1 Compression mechanism 2 Heat radiator (use side heat exchanger)
3 First expansion device 4 Evaporator (heat source side heat exchanger)
5 intermediate heat exchanger 6 bypass refrigerant circuit 7 second expansion device 8 main refrigerant circuit 11 high stage compression section 12 low stage compression section 15 discharge temperature sensor (discharge temperature detection means)
16 Discharge pressure sensor (discharge pressure detection means)
20 Control device

Claims (4)

a main refrigerant circuit formed by sequentially connecting a compression mechanism including a compression rotary element, a utilization side heat exchanger that heats a utilization side heat medium with the refrigerant discharged from the compression rotary element, an intermediate heat exchanger, a first expansion device, and a heat source side heat exchanger through piping;
a bypass refrigerant circuit in which a refrigerant branched from the piping between the utilization side heat exchanger and the first expansion device is decompressed by a second expansion device, and then heat-exchanged with the refrigerant flowing through the main refrigerant circuit in the intermediate heat exchanger, and is joined to the refrigerant being compressed in the compression rotary element;
A discharge temperature detection means for detecting a discharge temperature of the compression rotary element;
a discharge pressure detection means for detecting a discharge pressure of the compression rotary element;
A control device,
A refrigeration cycle device characterized in that when the discharge pressure of the compression rotating element is higher than a predetermined pressure and the discharge temperature of the compression rotating element is higher than a predetermined temperature, the control device increases the opening degree of both the first expansion device and the second expansion device. The refrigeration cycle device according to claim 1, characterized in that the control device increases the opening degree of the first expansion device after increasing the opening degree of the second expansion device. The refrigeration cycle device according to claim 1 or 2, characterized in that the control device increases the amount of change in the opening degree of the second expansion device as the discharge temperature of the compression rotating element increases. The refrigeration cycle device according to any one of claims 1 to 3, characterized in that the control device determines the amount of change in the opening of the second expansion device based on the temperature difference between the discharge temperature of the compression rotating element and the predetermined temperature.