Method, device and refrigeration system for controlling the speed of a variable frequency compressor

Abstract

The embodiment of the application discloses a rotating speed control method, device and refrigerating system of a variable frequency compressor. The variable frequency compressor is applied to an environmental test equipment. An inner box of the environmental test equipment is provided with an evaporator and a heater. The rotating speed control method comprises the following steps: obtaining an exhaust temperature of the variable frequency compressor, an evaporation temperature of the evaporator, an outlet superheat degree, a heating capacity of the heater, a current temperature of the inner box of the environmental test equipment and a temperature at a preset time point before the current time point; determining a change rate of the current temperature and the temperature at the preset time point according to the current temperature and the temperature at the preset time point; and adjusting a current rotating speed of the variable frequency compressor according to the exhaust temperature, the evaporation temperature, the outlet superheat degree, the heating capacity and the change rate. The embodiment of the application discloses a rotating speed control method, device and refrigerating system of a variable frequency compressor, which can reduce energy consumption and improve energy-saving effect.

Description

Technical Field

[0001] The embodiments of the present invention relate to compressor control technology, and more particularly to a method, device and refrigeration system for controlling the speed of a variable frequency compressor. Background Technology

[0002] For refrigeration systems used in environmental testing equipment, the cooling effect is a crucial factor affecting its application, and the variable frequency compressor within the system is a key component. When different cooling effects are required, this can be achieved by adjusting the speed of the variable frequency compressor and reliably controlling that speed. However, existing speed control methods for variable frequency compressors often suffer from poor reliability when adjusting the speed, such as increasing it. This leads to higher energy consumption in the refrigeration system and negatively impacts its energy-saving performance. Summary of the Invention

[0003] This invention provides a method, apparatus, and refrigeration system for controlling the speed of a variable frequency compressor, in order to reduce energy consumption and improve energy-saving performance.

[0004] In a first aspect, embodiments of the present invention provide a speed control method for a variable frequency compressor. The variable frequency compressor is applied to an environmental testing equipment, the environmental testing equipment having an evaporator and a heater installed inside. The speed control method includes:

[0005] Obtain the discharge temperature of the variable frequency compressor, the evaporation temperature of the evaporator, the outlet superheat, the heating capacity of the heater, the current temperature of the inner chamber of the environmental test equipment, and the temperature at a preset time before the current time.

[0006] Determine the rate of change of the current temperature and the temperature at the preset time based on the current temperature and the temperature at the preset time.

[0007] The current speed of the variable frequency compressor is adjusted based on the exhaust temperature, evaporation temperature, outlet superheat, heating amount, and rate of change.

[0008] Optionally, based on the current temperature and the temperature at a preset time, determine the rate of change of the current temperature and the temperature at the preset time, including:

[0009] Based on the current temperature and the temperature at the preset time, determine the difference between the current temperature and the temperature at the preset time, as well as the time difference between the current time and the preset time;

[0010] The ratio of the difference to the time difference is used as the rate of change.

[0011] Optionally, the current speed of the variable frequency compressor can be adjusted based on the exhaust temperature, evaporation temperature, outlet superheat, heating capacity, and rate of change, including:

[0012] When the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, and the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature, if the rate of change is greater than or equal to the preset speed increase temperature difference, then the current speed of the variable frequency compressor is controlled to increase by the preset value.

[0013] Optionally, the current speed of the variable frequency compressor can be adjusted based on the exhaust temperature, evaporation temperature, outlet superheat, heating capacity, and rate of change, including:

[0014] When the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, and the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature, if the heating amount is less than or equal to the preset heating amount deviation, the current speed of the variable frequency compressor is controlled to increase by the preset value.

[0015] Optionally, the current speed of the variable frequency compressor can be adjusted based on the exhaust temperature, evaporation temperature, outlet superheat, heating capacity, and rate of change, including:

[0016] When the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, and the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature, if the outlet superheat is greater than or equal to the sum of the preset maximum superheat and the preset superheat difference, then the current speed of the variable frequency compressor is increased by the preset value.

[0017] Secondly, embodiments of the present invention also provide a speed control device for a variable frequency compressor. The variable frequency compressor is applied to an environmental testing equipment, the environmental testing equipment having an evaporator and a heater installed inside. The speed control device includes:

[0018] The data acquisition module is used to acquire the discharge temperature of the variable frequency compressor, the evaporation temperature of the evaporator, the outlet superheat, the heating capacity of the heater, the current temperature of the inner chamber of the environmental test equipment, and the temperature at a preset time before the current time.

[0019] The rate determination module is used to determine the rate of change of the current temperature and the temperature at the preset time based on the current temperature and the temperature at the preset time.

[0020] The speed control module is used to adjust the current speed of the variable frequency compressor based on the exhaust temperature, evaporation temperature, outlet superheat, heating amount, and rate of change.

[0021] Optionally, the rate determination module includes:

[0022] The difference determination unit is used to determine the difference between the current temperature and the temperature at the preset time, as well as the time difference between the current time and the preset time, based on the current temperature and the temperature at the preset time.

[0023] The rate determination unit is used to determine the rate of change by taking the ratio of the difference to the time difference.

[0024] Thirdly, embodiments of the present invention also provide a refrigeration system, including a variable frequency compressor, a controller, a heater, and an evaporator. The variable frequency compressor, the heater, and the evaporator are all electrically connected to the controller. The heater and the evaporator are all connected to the variable frequency compressor through pipes. The speed control device as described in any one of claims 7-8 is integrated into the controller.

[0025] Optionally, the refrigeration system also includes a condenser, which is connected to the evaporator and the variable frequency compressor via piping.

[0026] Optionally, the refrigeration system may also include an electronic expansion valve, which is located in the passage connecting the evaporator and the inverter compressor.

[0027] The present invention provides a method, apparatus, and refrigeration system for controlling the speed of a variable frequency compressor. The variable frequency compressor is applied to an environmental testing equipment. The inner chamber of the environmental testing equipment is equipped with an evaporator and a heater. The method acquires the discharge temperature of the variable frequency compressor, the evaporation temperature of the evaporator, the outlet superheat, the heating capacity of the heater, the current temperature of the inner chamber of the environmental testing equipment, and the temperature at a preset time prior to the current time. Based on the current temperature and the temperature at the preset time, the rate of change of the current temperature and the temperature at the preset time is determined. The current speed of the variable frequency compressor is adjusted based on the discharge temperature, evaporation temperature, outlet superheat, heating capacity, and rate of change. The method, apparatus, and refrigeration system provided by the present invention, by adjusting the current speed of the variable frequency compressor based on the discharge temperature, evaporation temperature, outlet superheat, heating capacity, and rate of change, can improve speed control reliability, thereby reducing energy consumption and improving energy-saving effects. Attached Figure Description

[0028] Figure 1 This is a flowchart of a speed control method for a variable frequency compressor provided in Embodiment 1 of the present invention;

[0029] Figure 2 This is a structural block diagram of a refrigeration system provided in Embodiment 1 of the present invention;

[0030] Figure 3 This is a flowchart of a speed control method for a variable frequency compressor provided in Embodiment 2 of the present invention;

[0031] Figure 4 This is a structural block diagram of a refrigeration system provided in Embodiment 2 of the present invention;

[0032] Figure 5 This is a flowchart of another speed control method for a variable frequency compressor provided in Embodiment 2 of the present invention;

[0033] Figure 6 This is a structural block diagram of a speed control device for a variable frequency compressor provided in Embodiment 3 of the present invention. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0035] Example 1

[0036] Figure 1 This is a flowchart of a variable frequency compressor speed control method provided in Embodiment 1 of the present invention. This embodiment is applicable to situations where the speed of the variable frequency compressor is increased. The variable frequency compressor is used in environmental testing equipment, and the inner chamber of the environmental testing equipment is equipped with an evaporator and a heater. The method can be executed by a variable frequency compressor speed control device, which can be implemented by software and / or hardware. The device can be integrated into the controller of the refrigeration system. The method specifically includes the following steps:

[0037] Step 110: Obtain the discharge temperature of the variable frequency compressor, the evaporation temperature of the evaporator, the outlet superheat, the heating capacity of the heater, the current temperature of the inner chamber of the environmental test equipment, and the temperature at a preset time before the current time.

[0038] The environmental testing equipment's inner chamber can also be equipped with a temperature sensor. The variable frequency compressor's speed control device can be electrically connected to the temperature sensor to obtain the current temperature of the inner chamber and the temperature at a preset time prior to the current moment. The variable frequency compressor's speed control device can also be electrically connected to the variable frequency compressor, evaporator, and heater to obtain the variable frequency compressor's exhaust temperature, the evaporator's evaporation temperature, outlet superheat, and the heater's heating capacity.

[0039] Step 120: Determine the rate of change of the current temperature and the temperature at the preset time based on the current temperature and the temperature at the preset time.

[0040] The rate of change of the current temperature TPV(n) and the preset temperature TPV(nx) is [TPV(n)-TPV(nx)] / [t(n)-t(nx)], where t(n) is the current time and t(nx) is the preset time.

[0041] Step 130: Adjust the current speed of the variable frequency compressor according to the exhaust temperature, evaporation temperature, outlet superheat, heating amount and rate of change.

[0042] For example, Figure 2This is a schematic diagram of a refrigeration system provided in Embodiment 1 of the present invention. (Reference) Figure 2 The refrigeration system includes a variable frequency compressor 10, a controller 20, an evaporator 30, and a heater 40. The variable frequency compressor 20, evaporator 30, and heater 40 are all electrically connected to the controller 20. The evaporator 30 and heater 40 are both connected to the variable frequency compressor 10 via pipes. The speed step control device, as described in any embodiment of the present invention, is integrated into the controller 20. The refrigeration system also includes a condenser and an electronic expansion valve. The condenser is connected to the evaporator 30 and the variable frequency compressor 10 via pipes. The electronic expansion valve is located in the passage connecting the evaporator 30 and the variable frequency compressor 10.

[0043] Specifically, the controller 20 can control the speed of the variable frequency compressor 10. For example, when the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, and the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature, if the rate of change is greater than or equal to the preset speed increase temperature difference, then the current speed of the variable frequency compressor is controlled to increase by the preset value. The unit for the preset speed decrease temperature difference is ℃ / s.

[0044] It should be noted that the values ​​of each preset value in this embodiment can be determined according to the actual speed control requirements, and are not limited here.

[0045] The variable frequency compressor speed control method provided in this embodiment acquires the discharge temperature of the variable frequency compressor, the evaporation temperature of the evaporator, the outlet superheat, the heating capacity of the heater, the current temperature of the inner chamber of the environmental testing equipment, and the temperature at a preset time before the current time. Based on the current temperature and the temperature at the preset time, the rate of change of the current temperature and the temperature at the preset time are determined. The current speed of the variable frequency compressor is adjusted based on the discharge temperature, evaporation temperature, outlet superheat, heating capacity, and rate of change. This variable frequency compressor speed control method, by adjusting the current speed of the variable frequency compressor based on the discharge temperature, evaporation temperature, outlet superheat, heating capacity, and rate of change, can improve speed control reliability, thereby reducing energy consumption and improving energy-saving effects.

[0046] Example 2

[0047] Figure 3 This is a flowchart of a variable frequency compressor speed control method provided in Embodiment 2 of the present invention. This embodiment is applicable to situations where the speed of the variable frequency compressor is increased. The variable frequency compressor is used in environmental testing equipment, and the inner chamber of the environmental testing equipment is equipped with an evaporator and a heater. The method can be executed by a variable frequency compressor speed control device, which can be implemented by software and / or hardware. The device can be integrated into the controller of the refrigeration system. The method specifically includes the following steps:

[0048] Step 210: Obtain the discharge temperature of the variable frequency compressor, the evaporation temperature of the evaporator, the outlet superheat, the heating capacity of the heater, the current temperature of the inner chamber of the environmental test equipment, and the temperature at a preset time before the current time.

[0049] Step 220: Based on the current temperature and the temperature at the preset time, determine the difference between the current temperature and the temperature at the preset time, as well as the time difference between the current time and the preset time.

[0050] Step 230: Use the ratio of the difference to the time difference as the rate of change.

[0051] Step 240: When the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, and the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature, if the rate of change is greater than or equal to the preset speed increase temperature difference, then control the current speed of the variable frequency compressor to increase by the preset value.

[0052] Step 250: When the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, and the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature, if the heating amount is less than or equal to the preset heating amount deviation, then control the current speed of the variable frequency compressor to increase by the preset value.

[0053] Step 260: When the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, and the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature, if the outlet superheat is greater than or equal to the sum of the preset maximum superheat and the preset superheat difference, then control the current speed of the variable frequency compressor to increase by the preset value.

[0054] For example, Figure 4 This is a schematic diagram of a refrigeration system provided in Embodiment 2 of the present invention. The controller 10 in the refrigeration system controls the rotational speed Comp_rpm_present of the variable frequency compressor 20, such as controlling the rotational speed Comp_rpm_present+Δrpm_step_increase. Figure 5 This is a flowchart of another speed control method for a variable frequency compressor provided in Embodiment 2 of the present invention. (See reference) Figure 5 The method includes the following steps:

[0055] Step 1: Obtain T_comp_out, Comp_rpm_present, T_evap, TQ_heater_output, dT_superheating_C1, TPV(n), and TPV(nx).

[0056] Where T_comp_out is the discharge temperature of the variable frequency compressor, Comp_rpm_present is the current speed of the variable frequency compressor, T_evap is the evaporation temperature of the evaporator, dT_superheating_C1 is the outlet superheat, TQ_heater_output is the heating capacity of the heater, TPV(n) is the current temperature of the inner chamber of the environmental test equipment, and TPV(nx) is the temperature at a preset time before the current time.

[0057] Step 2: Determine whether T_evap is greater than or equal to T_evap_limiting_min, whether Comp_rpm_present is less than Comp_rpm_base_max, and whether T_comp_out is less than or equal to T_comp_out_limiting; if yes, proceed to Step 3; otherwise, end.

[0058] Where T_evap_limiting_min is the preset minimum evaporation temperature, Comp_rpm_base_max is the preset maximum base speed, and T_comp_out_limiting is the preset limit speed that increases the exhaust temperature.

[0059] Step 3: Determine whether [TPV(n)-TPV(nx)] / [t(n)-t(nx)] is greater than or equal to dT_rpm_increase, or TQ_heater_output is less than or equal to TQ_heater_output_up_diff, or dT_superheating is less than or equal to dT_superheating_max+dT_superheating_rpm_increase; if yes, proceed to step 4; otherwise, end.

[0060] Where [TPV(n)-TPV(nx)] / [t(n)-t(nx)] is the rate of change of the current temperature and the temperature at the preset time, dT_rpm_increase is the temperature difference increased by the preset rotation speed, TQ_heater_output_up_diff is the preset heating amount deviation, dT_superheating_max is the preset maximum superheat, and dT_superheating_rpm_increase is the superheat difference increased by the preset rotation speed.

[0061] Step 4: Control Comp_rpm_present + Δrpm_step_increase.

[0062] Where △rpm_step_increase is the preset value for the increase in rotational speed.

[0063] It should be noted that the values ​​of each preset value in this embodiment can be determined according to the actual speed control requirements, and are not limited here.

[0064] The variable frequency compressor speed control method provided in this embodiment adjusts the current speed of the variable frequency compressor according to the exhaust temperature, evaporation temperature, outlet superheat, heating amount and rate of change, which can improve speed control, such as increasing the reliability of speed control, thereby reducing energy consumption and improving energy saving effect.

[0065] Example 3

[0066] Figure 6 This is a structural block diagram of a speed control device for a variable frequency compressor provided in Embodiment 3 of the present invention. The variable frequency compressor is applied to an environmental testing equipment. The inner chamber of the environmental testing equipment is equipped with an evaporator and a heater. The speed control device includes: a data acquisition module 310, a rate determination module 320, and a speed control module 330. The data acquisition module 310 is used to acquire the exhaust temperature of the variable frequency compressor, the evaporation temperature of the evaporator, the outlet superheat, the heating capacity of the heater, the current temperature of the inner chamber of the environmental testing equipment, and the temperature at a preset time prior to the current time. The rate determination module 320 is used to determine the rate of change of the current temperature and the temperature at the preset time based on the current temperature and the temperature at the preset time. The speed control module 330 is used to adjust the current speed of the variable frequency compressor based on the exhaust temperature, evaporation temperature, outlet superheat, heating capacity, and rate of change.

[0067] Optionally, the rate determination module includes: a difference determination unit and a rate determination unit; wherein, the difference determination unit is used to determine the difference between the current temperature and the temperature at the preset time, as well as the time difference between the current time and the preset time, based on the current temperature and the temperature at the preset time; the rate determination unit is used to use the ratio of the difference to the time difference as the rate of change.

[0068] In one embodiment, the speed control module 330 is specifically used to control the current speed of the variable frequency compressor to increase by a preset value when the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature. If the rate of change is greater than or equal to the preset speed increase temperature difference, the variable frequency compressor's current speed is increased by a preset value.

[0069] In another embodiment, the speed control module 330 is specifically used to control the current speed of the variable frequency compressor to increase by a preset value when the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature, and the heating amount is less than or equal to the preset heating amount deviation.

[0070] In another embodiment, the speed control module 330 is specifically used to control the current speed of the variable frequency compressor to increase by a preset value when the evaporation temperature is greater than or equal to the preset minimum evaporation temperature, the current speed is less than the preset maximum reference speed, and the exhaust temperature is less than or equal to the preset limit speed increase exhaust temperature. If the outlet superheat is greater than or equal to the sum of the preset maximum superheat and the preset superheat difference, then the variable frequency compressor's current speed is increased by a preset value.

[0071] The variable frequency compressor speed control device provided in this embodiment belongs to the same inventive concept as the variable frequency compressor speed control method provided in any embodiment of the present invention, and has corresponding beneficial effects. For technical details not detailed in this embodiment, please refer to the variable frequency compressor speed control method provided in any embodiment of the present invention.

[0072] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A rotational speed control method of a variable frequency compressor, characterized by, The variable frequency compressor is applied to an environmental test equipment, an evaporator and a heater are arranged in an inner box of the environmental test equipment, and the rotating speed control method comprises the following steps: obtaining an exhaust temperature of the variable frequency compressor, an evaporation temperature of the evaporator, an outlet superheat degree, a heating amount of the heater, a current temperature of the inner box of the environmental test equipment and a temperature at a preset time point before the current time point; determining a change rate of the current temperature and the temperature at the preset time point according to the current temperature and the temperature at the preset time point; adjusting a current rotating speed of the variable frequency compressor according to the exhaust temperature, the evaporation temperature, the outlet superheat degree, the heating amount and the change rate; the step of adjusting the current rotating speed of the variable frequency compressor according to the exhaust temperature, the evaporation temperature, the outlet superheat degree, the heating amount and the change rate comprises the following steps: when the evaporation temperature is greater than or equal to a preset minimum evaporation temperature, the current rotating speed is less than a preset maximum reference rotating speed, the exhaust temperature is less than or equal to a preset limiting rotating speed increasing exhaust temperature, and the heating amount is less than or equal to a preset heating amount deviation, the current rotating speed of the variable frequency compressor is increased by a preset value.

2. The rotation speed control method according to claim 1, characterized by, the step of determining the change rate of the current temperature and the temperature at the preset time point according to the current temperature and the temperature at the preset time point comprises the following steps: determining a difference value of the current temperature and the temperature at the preset time point and a time difference between the current time point and the preset time point according to the current temperature and the temperature at the preset time point; taking a ratio of the difference value to the time difference as the change rate.

3. The rotation speed control method according to claim 1, characterized by, the step of adjusting the current rotating speed of the variable frequency compressor according to the exhaust temperature, the evaporation temperature, the outlet superheat degree, the heating amount and the change rate comprises the following steps: when the evaporation temperature is greater than or equal to a preset minimum evaporation temperature, the current rotating speed is less than a preset maximum reference rotating speed, the exhaust temperature is less than or equal to a preset limiting rotating speed increasing exhaust temperature, and the change rate is greater than or equal to a preset rotating speed increasing temperature difference value, the current rotating speed of the variable frequency compressor is increased by a preset value.

4. The rotation speed control method according to claim 1, characterized by, the step of adjusting the current rotating speed of the variable frequency compressor according to the exhaust temperature, the evaporation temperature, the outlet superheat degree, the heating amount and the change rate comprises the following steps: when the evaporation temperature is greater than or equal to a preset minimum evaporation temperature, the current rotating speed is less than a preset maximum reference rotating speed, the exhaust temperature is less than or equal to a preset limiting rotating speed increasing exhaust temperature, and the outlet superheat degree is greater than or equal to a sum of a preset maximum superheat degree and a preset superheat degree difference value, the current rotating speed of the variable frequency compressor is increased by a preset value.

5. A rotational speed control device of a variable frequency compressor, characterized by comprising: The variable frequency compressor is applied to an environmental test equipment, an evaporator and a heater are arranged in an inner box of the environmental test equipment, and the rotating speed control device comprises: a data acquisition module, which is used for obtaining an exhaust temperature of the variable frequency compressor, an evaporation temperature of the evaporator, an outlet superheat degree, a heating amount of the heater, a current temperature of the inner box of the environmental test equipment and a temperature at a preset time point before the current time point; a rate determining module configured to determine a rate of change of the current temperature and the temperature at the preset time according to the current temperature and the temperature at the preset time; a speed control module configured to adjust a current speed of the variable frequency compressor according to the exhaust temperature, the evaporation temperature, the outlet superheat, the heating amount and the rate of change; the speed control module is specifically configured to, when the evaporation temperature is greater than or equal to a preset minimum evaporation temperature, the current speed is less than a preset maximum reference speed, the exhaust temperature is less than or equal to a preset limit speed increase exhaust temperature, and the heating amount is less than or equal to a preset heating amount deviation, control the current speed of the variable frequency compressor to increase by a preset value.

6. The rotation speed control device according to claim 5, characterized by the rate determining module comprises: a difference determining unit configured to determine a difference between the current temperature and the temperature at the preset time, and a time difference between the current time and the preset time according to the current temperature and the temperature at the preset time; a rate determining unit configured to take a ratio of the difference to the time difference as the rate of change.

7. A refrigeration system characterized by, The speed control device of any one of claims 5-6 is integrated in the controller.

8. The refrigeration system of claim 7, wherein, The speed control device further comprises a condenser, which is communicated with the evaporator and the variable frequency compressor through a pipeline.

9. The refrigeration system of claim 7, wherein, The speed control device further comprises an electronic expansion valve, which is arranged in a passage connecting the evaporator and the variable frequency compressor.

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