Magnetic bearing compressor protection
By using magnetic bearings and controllers to monitor the speed and pressure difference of the rotating shaft in a vapor compression system, the problem of protecting the bearing from damage in traditional systems is solved, thus achieving stable system operation and ensuring the safety of bearing protection.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CARRIER CORP
- Filing Date
- 2021-07-07
- Publication Date
- 2026-06-16
AI Technical Summary
In traditional vapor compression systems, the rotating shaft of a shut-down compressor may damage the protective bearing while it is still rotating. Existing check valves are at risk of failure and cannot effectively prevent the rotating shaft from stopping after shutdown.
By introducing a magnetic bearing into the vapor compression system, combined with a controller that monitors the rotational speed of the rotating shaft and the pressure differential of the check valve, the magnetic bearing is kept in active mode until the rotating shaft reaches an acceptable threshold speed, and switches to inactive mode or closes the isolation valve when the check valve fails.
This effectively prevents or mitigates the damage to the rotating shaft caused by placing it on the protective bearing after shutdown, reduces the risk of check valve failure, and ensures stable system operation.
Smart Images
Figure CN113899094B_ABST
Abstract
Description
[0001] Cross-references to related applications
[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 705,599, filed July 7, 2020, the contents of which are incorporated herein by reference in their entirety. Background Technology
[0003] A vapor compression system (e.g., a refrigeration unit) typically includes at least one compressor, a condenser, an expansion valve, and an evaporator. Refrigerant circulates through the vapor compression system to cool a medium (e.g., air). The refrigerant exits the compressor(s) at high pressure and high enthalpy through multiple discharge ports. The refrigerant then flows through the condenser at high pressure, releasing heat to an external fluid medium. The refrigerant then flows through the expansion valve, which expands the refrigerant to a low pressure. After expansion, the refrigerant flows through the evaporator, absorbing heat from another medium (e.g., air). The refrigerant then re-enters the compressor(s) through multiple suction ports, completing the cycle.
[0004] A compressor typically comprises a motor rotor and a motor stator housed within a compressor housing. The rotor is fixed to and rotates with a rotating shaft, while the stator is fixed inside the compressor housing. Depending on the type of compressor, magnetic bearings may be used to levitate the rotating shaft while the compressor is operating. Touchdown bearings are commonly used in compressors with magnetic bearings to provide smooth rotation of the shaft and protect the rotor when the compressor is stopped. Touchdown bearings can be in the form of ball bearings or sleeve bearings. If the rotating shaft is placed on a touchdown bearing while it is still rotating, these touchdown bearings are susceptible to damage because they are traditionally not lubricated.
[0005] When multiple compressors are used in combination (e.g., in a situation where at least one compressor is shut down while at least one other compressor remains operational), the pressure generated by the operating compressor may cause the rotating shaft of the shut-down compressor to continue rotating even after shutdown. Traditionally, this problem is addressed by using one or more check valves. For example, a check valve may be placed between the compressor that may be shut down (e.g., based on load requirements) and the condenser and / or the compressor that may remain operational. However, if the check valve fails, the compressor that remains operational may prevent the rotating shaft of the compressor being shut down from stopping. As mentioned above, if the rotating shaft is placed on a protective bearing while it is still rotating, the protective bearing may be damaged.
[0006] Therefore, a method is still needed to prevent or at least mitigate the situation where the rotating shaft of a compressor being shut down is placed on a protective bearing while it is still rotating. Summary of the Invention
[0007] According to one embodiment, a method for operating a vapor compression system is provided, the vapor compression system including a first compressor, a second compressor, a condenser, and at least one check valve disposed between the first compressor and the condenser. The method includes the step of sending a shutdown command to at least one of the first compressor and the second compressor, the first compressor and the second compressor including a rotating shaft and a magnetic bearing. The magnetic bearing includes an active mode and an inactive mode. In the active mode, the magnetic bearing suspends the rotating shaft. The method includes the step of monitoring at least one of the rotational speed of the rotating shaft and the differential pressure across the check valve for a preset time, wherein the magnetic bearing remains in the active mode for at least the preset time.
[0008] According to an additional or alternative embodiment, the preset time is less than ten minutes after the shutdown command is sent.
[0009] According to an additional or alternative embodiment, the method further includes the step of switching the magnetic bearing from an active mode to an inactive mode when the rotational speed reaches an acceptable threshold.
[0010] According to additional or alternative embodiments, the acceptable threshold is less than 50 RPM.
[0011] According to an additional or alternative embodiment, the method further includes the step of sending a shutdown command to another of the first compressor or the second compressor when the rotational speed does not reach an acceptable threshold within a preset time.
[0012] According to an additional or alternative embodiment, the method further includes the step of activating an alarm when the rotational speed does not reach an acceptable threshold within a preset time.
[0013] According to an additional or alternative embodiment, the method further includes the step of closing an isolation valve disposed between the evaporator and at least one of the first compressor and the second compressor when the rotational speed does not reach an acceptable threshold within a preset time.
[0014] According to another aspect of this disclosure, a vapor compression system is provided, comprising a condenser, a first compressor, a second compressor, a check valve, and a controller. The condenser transfers heat from a working fluid to an external fluid medium. The first and second compressors are in fluid communication with the condenser. At least one of the first and second compressors includes an electric motor, a magnetic bearing, and a protective bearing. The electric motor drives a rotating shaft. When in an active mode, the magnetic bearing suspends the rotating shaft. The magnetic bearing is disposed adjacent to the electric motor. The protective bearing is configured to rotate and support the rotating shaft when the magnetic bearing is in an inactive mode. The protective bearing is disposed adjacent to the rotating shaft. The check valve is in fluid communication with the condenser and at least one of the first and second compressors. The controller is configured to control at least one of the first and second compressors. The controller is configured to receive a shutdown command from at least one of the first and second compressors. The controller communicates with at least one sensor disposed within at least one of the first and second compressors. The sensor is configured to monitor at least one of the rotational speed of the rotating shaft and the differential pressure across the check valve for a preset time. The controller maintains the magnetic bearing in an active mode for at least the preset time.
[0015] According to an additional or alternative embodiment, the preset time is less than ten minutes after the stop command is sent to the controller.
[0016] According to an additional or alternative embodiment, when the rotational speed reaches an acceptable threshold, the controller switches the magnetic bearing from active mode to inactive mode.
[0017] According to additional or alternative embodiments, the acceptable threshold is less than 50 RPM.
[0018] According to an additional or alternative embodiment, if the rotational speed does not reach an acceptable threshold within a preset time, the other of the first compressor or the second compressor stops.
[0019] According to an additional or alternative embodiment, the controller activates an alarm when the rotational speed does not reach an acceptable threshold within a preset time.
[0020] According to an additional or alternative embodiment, the vapor compression system further includes an isolation valve disposed between the evaporator and at least one of the first compressor and the second compressor, the isolation valve being configured to prevent working fluid from flowing into the first compressor.
[0021] According to additional or alternative embodiments, the isolation valve is a solenoid valve.
[0022] According to an additional or alternative embodiment, the isolation valve communicates with a controller configured to close the isolation valve when the rotational speed of the first compressor's rotating shaft does not reach an acceptable threshold within a preset time.
[0023] According to additional or alternative embodiments, the external fluid medium includes at least one of the following: an air source and a water source.
[0024] According to additional or alternative embodiments, the working fluid is a refrigerant. Attached Figure Description
[0025] The subject matter of this disclosure is specifically pointed out and expressly claimed in the claims at the end of the specification. The following description of the drawings should not be construed as limiting in any way. Referring to the drawings, the same element numbers are the same:
[0026] Figure 1 This is a schematic diagram of a vapor compression system including a condenser, a first compressor, and a second compressor according to one aspect of the present disclosure, wherein a controller is configured to control at least one of the first compressor and the second compressor.
[0027] Figure 2 This is based on one aspect of the disclosure. Figure 1 The cross-sectional side view of the first compressor shown depicts the protective bearing located adjacent to the rotating shaft.
[0028] Figure 3 This is a flowchart illustrating a method of operating a vapor compression system according to one aspect of the present disclosure, the vapor compression system including a first compressor, a second compressor, a condenser, and at least one check valve disposed between the first compressor and the condenser. Detailed Implementation
[0029] As described below, a vapor compression system and a method of operating the vapor compression system in such a manner as to prevent or at least mitigate the placement of a rotating shaft on a protective bearing while it is still rotating are provided. The vapor compression system includes a first compressor and a second compressor. Depending on load requirements, one of the compressors can be shut down while the other remains operational. For example, under partial load operation, the first compressor can be shut down while the second compressor remains operational. A check valve can be used to prevent the working fluid (e.g., refrigerant) and pressure from the operating compressor (e.g., the second compressor) from flowing back into the compressor being shut down (e.g., the first compressor). Although the vapor compression system described herein includes a check valve, it relies less on check valves than conventional vapor compression systems because it helps to keep the magnetic bearing in an active mode while monitoring at least one of the rotational speed of the rotating shaft and the pressure differential of the check valve after the compressor has been shut down.
[0030] Now refer to the attached diagram, Figure 1The diagram shows a vapor compression system 800 including a condenser 500, a first compressor 100, and a second compressor 200. It should be understood that the vapor compression system 800 may include any system (e.g., a refrigeration unit, etc.) having a condenser 500 and multiple compressors 100, 200, each of which includes a rotating shaft 140. Figure 2 (As shown in the image). Figure 1 As shown, the vapor compression system 800 includes a controller 600 configured to control at least one of a first compressor 100 and a second compressor 200. Figure 1 As shown, the vapor compression system 800 may include a first compressor 100, a second compressor 200, a condenser 500, an expansion valve 400, and an evaporator 300. The vapor compression system 800 may be configured to circulate a working fluid (e.g., a refrigerant such as R-134A) through the vapor compression system 800 to provide cooling to a medium (e.g., air, water, etc.). Although R-134A is mentioned, it should be understood that other types of refrigerants may also be used.
[0031] As described above, sometimes the vapor compression system 800 may require a higher cooling capacity (which requires a higher refrigerant flow rate), while at other times, a lower cooling capacity (which requires a lower refrigerant flow rate) is needed. To provide a continuous and effective supply of the required refrigerant charge, the vapor compression system 800 includes a first compressor 100 and a second compressor 200. These compressors may be replicas of the same compressor (e.g., having the same dimensions and construction) or may be different (e.g., different dimensions or different constructions). It is conceivable that at least one of the compressors (e.g., the first compressor 100) includes a magnetic bearing 110, a protective bearing 120, and a rotating shaft 140. Figure 2 (as shown in the image).
[0032] Figure 2 Depicting Figure 1 The image shows a cross-sectional side view of the first compressor 100. Although not shown, it should be understood that the second compressor 200 can be constructed in the same manner as the first compressor 100. Figure 2As shown, the first compressor 100 includes an electric motor 130, a magnetic bearing 110, and a protective bearing 120. The electric motor 130 drives a rotating shaft 140. When in an active mode (e.g., at least when the first compressor 100 is in operation), the magnetic bearing 110 suspends the rotating shaft 140. The first compressor 100 can be considered to be in operation when it is generating positive pressure to force working fluid through the vapor compression system 800. It should be understood that the magnetic bearing 110 includes an active mode (e.g., when a magnetic field is generated to suspend the rotating shaft 140) and an inactive mode (e.g., when no magnetic field is generated). The magnetic bearing 110 is disposed adjacent to the electric motor 130. When the magnetic bearing 110 is in an inactive mode, the protective bearing 120 supports the rotating shaft 140. The protective bearing 120 is disposed adjacent to the rotating shaft 140.
[0033] As described above, the vapor compression system 800 may include a check valve 150 in fluid communication with the first compressor 100 and the condenser 500. Figure 1 (As shown in the figure). When the first compressor 100 is being shut down (e.g., when the vapor compression system 800 is operating under partial load), the check valve 150 helps to stop the backflow of working fluid from the second compressor 200 (e.g., when the second compressor 200 is operating) into the first compressor 100. The check valve 150 also helps to ensure that the rotating shaft 140 of the first compressor 100 stops rotating when the first compressor 100 is shut down. As shown, in some cases, both the first compressor 100 and the second compressor 200 may each include check valves 150 and 250, respectively.
[0034] To control at least one of the first compressor 100 and the second compressor 200, the vapor compression system 800 may include a controller 600. Figure 1 (As shown in the diagram). Controller 600 can be configured to receive a shutdown command from the first compressor 100 (e.g., when partial load operation is required). It should be understood that the shutdown command can be automatically generated based on input from one or more sensors (described below). Controller 600 can communicate with at least one sensor for monitoring the rotating shaft 140 (…) within a preset time period (e.g., for a period of time after the first compressor 100 has stopped). Figure 2 At least one of the rotational speed (shown in the diagram) and the pressure differential on the check valve 150. The controller 600 can help prevent the rotating shaft 140 from being placed on the protective bearing 120 while the rotating shaft 140 is still rotating by keeping the magnetic bearing 110 of the first compressor 100 in an active mode for at least a preset time. In some cases, this preset time is less than ten (10) minutes after the shutdown command of the first compressor 100 is sent to and / or generated by the controller 600. For example, the preset time may be less than three (3) minutes after the first compressor 100 is shut down.
[0035] In some cases, controller 600 may be considered a programmable logic controller (PLC) or programmable controller capable of receiving inputs and outputs from one or more sensors (described below), and may include a processor (e.g., a microprocessor) and memory for storing programs to control components of vapor compression system 800 (e.g., the operation of the first compressor 100 and / or the second compressor 200). The memory may include any one or a combination of volatile memory elements (e.g., random access memory (RAM)), non-volatile memory elements (e.g., ROM, etc.), and / or have a distributed architecture (e.g., various components are located remotely to each other but are accessible by the processor). Controller 600 may be configured to switch magnetic bearing 110 from an active mode to an inactive mode when the rotational speed of rotating shaft 140 reaches an acceptable threshold. The acceptable threshold may be less than 50 RPM. For example, when the first compressor 100 is stopped, controller 600 may keep magnetic bearing 110 in an active mode (e.g., to keep rotating shaft 140 suspended) until rotating shaft 140 rotates at a speed less than 50 RPM.
[0036] If the rotating shaft 140 continues to rotate for an extended period (e.g., longer than a preset time, which could be ten (10) minutes after the first compressor 100 stops), the check valve 150 may have failed. The check valve 150 may be considered failed if it does not prevent working fluid and / or pressure from entering the first compressor 100 when the first compressor 100 stops. The controller 600 may be configured to shut down the second compressor 200 if the rotational speed of the rotating shaft 140 of the first compressor 100 does not reach an acceptable threshold within a preset time. It should be understood that the controller 600 may keep the magnetic bearing 110 in an active mode (e.g., to keep the rotating shaft 140 suspended) after the second compressor 200 stops until the rotating shaft 140 rotates at a speed less than 50 RPM. In addition to shutting down the second compressor 200, or as an alternative, the controller 600 may be configured to activate an alarm (e.g., initiate a visual or audible signal) if the rotational speed of the rotating shaft 140 of the first compressor 100 does not reach an acceptable threshold within a preset time.
[0037] To monitor the rotational speed of the rotating shaft 140 and / or the pressure differential on the check valve 150, the controller 600 may communicate with at least one sensor. In some cases, the sensor is a rotation sensor 160 disposed in the first compressor 100. It should be understood that the controller 600 may also communicate with a rotation sensor 260 disposed in the second compressor 200. The rotation sensors 160, 260 may include any technology capable of determining whether the rotating shaft 140 is rotating and / or at what speed in revolutions per minute (RPM). For example, the rotation sensors 160, 260 may be torque sensors or transducers that convert torque into an electrical signal, which may be transmitted (e.g., via one or more wired or wireless connections) to the controller 600.
[0038] In some cases, the sensors are pressure sensors 170, 270, and 510 located on either side of check valve 150. For example, vapor compression system 800 may include pressure sensor 170 between check valve 150 and first compressor 100, pressure sensor 270 between check valve 250 and second compressor 200, and / or pressure sensor 510 located in condenser 500. It should be understood that vapor compression system 800 may also include pressure sensor 310 located in evaporator 300. Regardless of location, pressure sensors 170, 270, 510, and 310 may include any technology capable of determining internal pressure (e.g., in a conduit or container). For example, pressure sensors 170, 270, 510, and 310 may be strain gauge-based transducers that convert pressure into an electrical signal, which can be transmitted (e.g., via one or more wired or wireless connections) to controller 600. The controller 600 can use pressure readings acquired by pressure sensors 170, 270, 510, and 310 to calculate the pressure differential across check valve 150. This pressure differential can be used to determine whether check valve 150 is operating correctly (e.g., not malfunctioning). For example, if check valve 150 is closed between the first compressor 100 and condenser 500, and the second compressor 200 is operating, the pressure reading downstream of check valve 150 (e.g., from pressure sensor 510 in condenser 500) should be higher than the pressure reading upstream of check valve 150 (e.g., from pressure sensor 170). If the pressure differential is not higher than a minimum (e.g., 100 psi), the controller 600 can determine that check valve 150 has failed.
[0039] To protect the first compressor 100 in the event of check valve 150 failure, the vapor compression system 800 may include an isolation valve 700 upstream and / or downstream of the first compressor 100. The isolation valve 700 may be configured to prevent working fluid from flowing into the first compressor 100. In some cases, the isolation valve 700 is a solenoid valve that can communicate with the controller 600. For example, the controller 600 may be configured to close the isolation valve 700 when the rotational speed of the rotating shaft 140 in the first compressor 100 does not reach an acceptable threshold within a preset time and / or when the differential pressure across the check valve 150 is below a minimum (e.g., indicating that the check valve 150 has failed). Once closed, the isolation valve 700 should allow the rotating shaft 140 of the first compressor 100 to decelerate below an acceptable threshold. It should be understood that the controller 600 may hold the magnetic bearing 110 in an active mode (e.g., to keep the rotating shaft 140 suspended) until the rotating shaft 140 rotates at a speed less than an acceptable threshold (e.g., 50 RPM).
[0040] This method of operating the vapor compression system 800 helps prevent or at least mitigate damage to the protective bearing 120 of a compressor that is being shut down (e.g., the first compressor 100). This method 900 can be performed by a controller 600 (e.g., such as the controller 600 described above). This method 900 in... Figure 3 As shown in the diagram. Method 900 can, for example, use... Figure 1 The exemplary vapor compression system 800 shown is used to perform this operation, and the system may include Figure 2 The exemplary first compressor 100 is shown. (As shown) Figure 1 As shown, the vapor compression system may include a first compressor 100, a second compressor 200, a condenser 500, and at least one check valve 150 disposed between the first compressor 100 and the condenser 500. Method 900 provides a step 910 of sending a shutdown command to the first compressor 100. The first compressor 100 includes a rotating shaft 140 and a magnetic bearing 110. The magnetic bearing 110 includes an active mode and an inactive mode. The magnetic bearing 110 is configured to suspend the rotating shaft 140 in the active mode.
[0041] Method 900 provides a step 910 of sending a shutdown command to the first compressor 100. Method 900 also provides a step 920 of monitoring at least one of the rotational speed of the rotating shaft and the differential pressure on the check valve 150 within a preset time period (e.g., within ten (10) minutes after the shutdown command is sent to the first compressor 100). Figure 3As shown, the method provides step 940, which involves switching the magnetic bearing 110 from an active mode to an inactive mode (e.g., no longer suspending the rotating shaft 140) if the rotational speed reaches an acceptable threshold (e.g., less than 50 RPM). However, if the rotational speed does not reach the acceptable threshold within a preset time, the method provides step 930 of keeping the magnetic bearing 110 in an active mode (e.g., to keep the rotating shaft 140 suspended) because the check valve 150 may have failed. As mentioned above, the failure of the check valve 150 can be confirmed by a pressure differential of less than a minimum (e.g., 100 psi). If the check valve 150 has failed, method 900 may provide additional steps of shutting down the second compressor 200 and / or closing the isolation valve 700 to allow the rotating shaft 140 of the first compressor 100 to decelerate below an acceptable threshold. It should be understood that even after the second compressor 200 is shut down and / or after the isolation valve 700 is closed (e.g., until the rotating shaft 140 rotates at less than an acceptable threshold (e.g., 50 RPM), the magnetic bearing 110 may remain in an active mode (e.g., to keep the rotating shaft 140 suspended).
[0042] In the context of describing this invention, the terms “a,” “an,” and “the,” as well as similar indicators, should be construed as encompassing both the singular and plural, unless otherwise stated herein or clarified contradictively by the context. The use of any and all example or exemplary language provided herein (e.g., “such as,” “as,” “for example,” etc.) is intended merely to better illustrate the invention and not to limit its scope, unless otherwise required. No language in the specification should be construed as necessary to represent any unclaimed element in the practice of this invention.
[0043] While this disclosure has been described with reference to one or more exemplary embodiments, those skilled in the art will understand that various changes may be made without departing from the scope of this disclosure, and equivalents may be substituted for its elements. Furthermore, many modifications may be made to adapt particular situations or materials to the teachings of this disclosure without departing from the essential scope of this disclosure. Therefore, it is intended that this disclosure be limited to the specific embodiments disclosed as the best mode contemplated for carrying out this disclosure, but rather that this disclosure will include all embodiments falling within the scope of the claims.
Claims
1. A method of operating a vapor compression system, the vapor compression system comprising a first compressor, a second compressor, a condenser, and at least one check valve disposed between the first compressor and the condenser, the method comprising: A shutdown command is sent to the first compressor, which includes a rotating shaft and a magnetic bearing. The magnetic bearing has an active mode and an inactive mode, in which the magnetic bearing suspends the rotating shaft. The rotational speed of the rotating shaft is monitored for a preset time after the first compressor stops, wherein the magnetic bearing remains in the active mode at least during the preset time. If the rotational speed does not reach an acceptable threshold within the preset time, the check valve is determined to have failed; and If the check valve is determined to be faulty, a shutdown command is sent to the second compressor.
2. The method according to claim 1, characterized in that, The preset time is less than ten minutes after the shutdown command is sent.
3. The method according to claim 1, characterized in that, It also includes switching the magnetic bearing from the active mode to the inactive mode when the rotational speed reaches an acceptable threshold.
4. The method according to claim 3, characterized in that, The acceptable threshold is less than 50 RPM.
5. The method according to claim 1, characterized in that, It also includes activating an alarm when the rotational speed does not reach an acceptable threshold within the preset time.
6. The method according to claim 1, characterized in that, It also includes closing the isolation valve located between the evaporator and the first compressor when the rotational speed does not reach an acceptable threshold within the preset time.
7. A vapor compression system, comprising: A condenser is used to transfer heat from a working fluid to an external fluid medium. A first compressor and a second compressor are in fluid communication with the condenser, the first compressor comprising: An electric motor, used to drive a rotating shaft; A magnetic bearing, used to suspend the rotating shaft in the active mode, is disposed adjacent to the electric motor; and A protective bearing is configured to rotate and support the rotating shaft when the magnetic bearing is in an inactive mode, and the protective bearing is disposed adjacent to the rotating shaft. A check valve, which is in fluid communication with the condenser and the first compressor; and A controller configured to control the first compressor, the controller configured to receive a stop command from the first compressor, the controller communicating with a sensor disposed within the first compressor, the sensor configured to monitor the rotational speed of the rotating shaft for a preset time after the first compressor stops, wherein the controller is configured to: The magnetic bearing shall be kept in the active mode for at least the preset time. If the rotational speed does not reach an acceptable threshold within the preset time, the check valve is determined to have failed; and If the check valve is determined to be faulty, a shutdown command is sent to the second compressor.
8. The vapor compression system according to claim 7, characterized in that, The preset time is less than ten minutes after the shutdown command is sent to the controller.
9. The vapor compression system according to claim 7, characterized in that, When the rotational speed reaches an acceptable threshold, the controller switches the magnetic bearing from the active mode to the inactive mode.
10. The vapor compression system according to claim 9, characterized in that, The acceptable threshold is less than 50 RPM.
11. The vapor compression system according to claim 7, characterized in that, The controller activates an alarm when the rotational speed does not reach an acceptable threshold within the preset time.
12. The vapor compression system according to claim 7, characterized in that, It also includes an isolation valve disposed between the evaporator and the first compressor, the isolation valve being configured to prevent the working fluid from flowing into the first compressor.
13. The vapor compression system according to claim 12, characterized in that, The isolation valve is a solenoid valve.
14. The vapor compression system according to claim 13, characterized in that, The isolation valve communicates with the controller, which is configured to close the isolation valve when the rotational speed of the rotating shaft of the first compressor does not reach an acceptable threshold within a preset time.
15. The vapor compression system according to claim 7, characterized in that, The external fluid medium consists of at least one of the following: an air source and a water source.
16. The vapor compression system according to claim 7, characterized in that, The working fluid is a refrigerant.