Compressor system for refrigerating unit

Abstract

The invention relates to a compressor system for a refrigeration unit, comprising a plurality of compressors (1), a first compressor (1) having a speed-independent continuous capacity control device (6), said compressor system being adapted to control the first compressor (1) as a master compressor and to turn on and off a subsequent compressor (1) as a slave compressor, therefore, the capacity requirement of the refrigerating unit is met, and the service life of the system compressor (1) is prolonged. For this purpose, each compressor (1) has a speed-independent continuous capacity control device (6) for pulse width modulation control on the basis of the valve opening time, and meanwhile, one of the other compressors (1) can serve as a main compressor to be controlled by the compressor system through adjustment, and the first compressor and the subsequent compressor (1) which serves as a slave compressor when necessary are started and stopped, so that the capacity requirement of the refrigerating unit is alternately met.

Description

Technical Field

[0001] This invention relates to a compressor system for a refrigeration unit, comprising multiple compressors, wherein a first compressor has a speed-independent continuous capacity control device. The compressor system can be adjusted to control the first compressor as the master compressor and to start and stop the other compressors as slave compressors, thereby meeting the capacity requirements of the refrigeration unit. This compressor system is described in US Patent US 2019 / 063805A1. This invention also relates to methods for controlling and modifying such a compressor system. Background Technology

[0002] A refrigeration circuit is a system used to cool equipment such as food freezers to the required temperature. The refrigerant moving in the closed circuit undergoes a series of phase changes: first, the gaseous refrigerant is compressed by a compressor. Then, the gaseous refrigerant condenses and releases heat in a subsequent heat exchanger. Then, due to pressure changes, the liquid refrigerant expands through a throttle element such as an expansion valve or capillary tube. In the downstream second heat exchanger (evaporator), the refrigerant evaporates, absorbing heat at a low temperature (boiling cooling). The cycle can then restart. This process must be maintained by providing mechanical work (drive power) from an external source via a compressor.

[0003] In large refrigeration units such as cold storage facilities or server rooms, compressor systems equipped with multiple compressors are typically used to provide the required capacity. Usually, one compressor handles the base load, which is continuously adjusted via a frequency converter and speed control. This compressor acts as the main compressor in the system. The remaining load is typically handled by turning other compressors on and off. Following the base load principle, these compressors operate as slave compressors.

[0004] The main drawback of this design is that the main compressor operates for an excessively long time, leading to wear and tear on mechanical components. Therefore, the lifespan of the main compressor is typically several times shorter than that of the secondary compressor.

[0005] Therefore, the purpose of this invention is to provide a compressor system and method of the above type to extend the service life of the compressor in the system. Summary of the Invention

[0006] This invention achieves this objective by means of the following: each compressor has a speed-independent continuous capacity control device based on valve opening time pulse width modulation control, and the compressor system can be adjusted to control one subsequent compressor as the master compressor and to turn on and off the first compressor and other subsequent compressors as slave compressors when applicable, thereby alternately meeting the capacity requirements of the refrigeration unit.

[0007] This invention is based on the consideration of extending the service life of the main compressor by reducing the load on the main compressor. To this end, its operating time needs to be shortened by temporarily shutting down the main compressor. However, to achieve this, the second compressor needs to be adjusted to continuously regulate its output to achieve the desired capacity control. However, since frequency converters are relatively complex components, achieving this using existing frequency converters requires a significant investment of effort. Therefore, other power control systems should be employed, namely speed-independent power control systems, which are technically easier to implement. This allows the system to alternately use other compressors as the main compressor, thereby balancing operating time and reducing wear.

[0008] The entire compressor system employs a symmetrical design, ensuring that each compressor in the system has the aforementioned speed-independent continuous capacity control device. This means that each compressor can be used alternately as the main compressor, and the symmetrical design allows for optimal adjustment of the operating time of each compressor.

[0009] Furthermore, by controlling the valve opening time, particularly through pulse width modulation control based on the valve opening time, speed-independent continuous power control can be achieved. Such systems can achieve continuous power control using fast-switching solenoid valves without the need for frequency converters.

[0010] In a preferred design of the system, each compressor also features a mechanical graded capacity control device. When each compressor employs a reciprocating piston compressor structure, its mechanical graded capacity control device is preferably based on cylinder block shut-off. This type of graded control device allows each compressor to operate at only 50% capacity (four-cylinder model) or 33% and 66% capacity (six-cylinder model) with relatively low technical investment, unaffected by continuous control. This avoids capacity jumps when other compressors start and stop, even if the control range of the main compressor is small (the control coefficient (CF) is reduced).

[0011] Specifically, the compressor system is preferably adjusted to alternately use each compressor equipped with a speed-independent continuous capacity control device as the main compressor, thereby achieving equalization of the operating time of each compressor. In other words, each compressor periodically takes over the task of the main compressor, resulting in equalized operating time. In this case, the start-up of the secondary compressor is also used for basic load changes, that is, ideally, the compressor with the shortest current operating time is always started as the secondary compressor.

[0012] The above objectives can also be further achieved by using the control method of the compressor system described above, wherein the operating time of each compressor is balanced by alternately using each compressor equipped with a speed-independent continuous capacity control device as the main compressor.

[0013] In a further preferred embodiment of the method, the cycle number of the power controller for each compressor cylinder group is balanced. Power control is achieved through pulse width modulation (PWM) signals, and by incorporating the possibility of cylinder group deactivation, the PWM signals can be applied alternately only to a single cylinder group, effectively combining cylinder deactivation with PWM control. This also enables synchronized cycle time, i.e., the period during which each cylinder group is active due to the activation pulse, thereby compensating for wear between cylinder groups within the compressor.

[0014] Preferably, within a specified time interval, the runtime of each compressor and / or the cycle time of the cylinder group capacity controller remain the same, with a deviation within 20%, preferably within 10%. For example, the control objective could be to equalize the deviation of the runtime of all compressors to within 10% within a weekly cycle.

[0015] To further address this issue, a method is adopted to modify a compressor system comprising multiple compressors. The first compressor has a continuous capacity control device. The compressor system is adjusted to control the first compressor as the master compressor and to start and stop other compressors (which are slave compressors) to meet the capacity requirements of the refrigeration unit. At least one other compressor is equipped with a continuous capacity control device. Each continuous capacity control device is adjusted to be a speed-independent capacity control device based on valve opening time pulse width modulation control. The compressor system is further adjusted to control one of the subsequent compressors as the master compressor and to start and stop the first compressor and, where applicable, the remaining subsequent compressors (which are slave compressors) to alternatively meet the capacity requirements of the refrigeration unit.

[0016] The advantages of this invention are specifically reflected in the following aspects: The compressor design employing a valve-controlled, speed-independent capacity control system enables the equalization of compressor operating time, thereby creating a uniform load on all mechanical components. This extends the compressor's service life. Furthermore, optimal CF coefficients can be achieved at any time of year and under any operating conditions. Uniform operation also reduces switching cycles. Optimal local loads can be achieved regardless of which main compressor is currently active. The identical design of all compressors also offers advantages in performance testing and maintenance. Attached Figure Description

[0017] Referring to the accompanying drawings, examples of embodiments of the present invention will be explained in more detail. Wherein:

[0018] Figure 1 A refrigeration circuit of a compressor system equipped with multiple compressors is shown. Detailed Implementation

[0019] Figure 1A schematic diagram of a refrigeration circuit K is shown. The following explanation of refrigeration circuit K is based on a compressor system consisting of three compressors 1 connected in parallel. The refrigerant compressed by compressor 1 is sent to condenser 2, where it is cooled and liquefied. From there, the refrigerant flows through refrigerant manifold 3 and injection valve 4 into evaporator 5, where it expands and absorbs heat, achieving the desired cooling effect. The gaseous refrigerant flowing out of evaporator 5 then flows back to compressor 1, where it is compressed and the cycle begins again.

[0020] The refrigeration circuit K is part of a refrigeration unit (not shown in detail), such as a refrigeration unit in a server room or food cold storage. It includes numerous other components, but these are omitted because their description is irrelevant to the function of the invention shown herein, such as oil separators, safety valves, etc. The refrigeration circuit K can also be more complex, for example, having multiple pressure stages.

[0021] Based on the capacity requirements of the refrigeration unit, the capacity of the parallel compressor 1 in the compressor system needs to be adjusted. This can be achieved by continuously adjusting one compressor 1 as the main compressor, for example, within a range of 10%-100% of its maximum capacity. If the refrigeration unit requires a higher capacity, such as when the heat input of the room to be cooled increases or during summer operation, additional subsequent compressors 1 can be added as slave compressors. These compressors 1 have only fixed capacity levels, so fine-tuning of the capacity is still performed by the main compressor.

[0022] To balance the operating time and wear of compressor 1 and thus extend its service life, the compressor system in this design example is symmetrical; each compressor 1 is equipped with two capacity regulators 6, controlled by a central control unit 7. In this design example, compressor 1 is adjusted to function as a four-cylinder compressor. Each capacity regulator 6 in each compressor 1 operates on one of the two cylinder banks of each compressor 1. The capacity regulator 6 is a stepless, speed-independent capacity regulator. Corresponding solenoid valves are installed in the cylinder head, and these solenoid valves are controlled by pulse-width modulation signals to achieve stepless capacity control.

[0023] Therefore, the power controller 6 combines mechanical power control with stepless, speed-independent power control. Using this function, the power of each compressor 1 can be controlled in stages by disabling cylinder banks. In this embodiment, a four-cylinder compressor is used, for example, a four-cylinder compressor with power outputs of 50% and 100%. In this way, according to the embodiment, the combination allows the pulse width modulation signal to act only on one cylinder bank. For example, to control the power at 10%, the cycle time of both cylinder banks can be set to 6 seconds per minute, or the cycle time of only one cylinder bank can be set to 12 seconds per minute. When used as a progressive compressor, cylinder deactivation does not use pulse width modulation control; instead, the cylinder bank is directly and completely shut down or opened.

[0024] As shown above, compressor 1, which acts as the main compressor, is essentially in a permanent operating state, while the other compressors 1 are only started as needed. However, since the identical design of each compressor 1 means that each compressor 1 can be used as both a main compressor and a slave compressor, the compressor system shown in the figure can still achieve mutual matching of the operating times of the compressors 1.

[0025] To this end, the control unit 7 is equipped with a corresponding control algorithm that can autonomously determine, based on multiple criteria, which compressor 1 acts as the main compressor and which compressors 1(s) are activated as slave compressors. This can be performed periodically; for example, slave compressors can be periodically replaced or replaced based on actual running time records. The control objective is always to match the running times of the compressors 1, i.e., the compressor 1 with the shortest running time is prioritized for operation. In a further embodiment, the auxiliary compressor 1 can also operate as the main compressor and be continuously controlled until complete continuous control of all compressors 1 is achieved. However, it is crucial to ensure appropriate stability of the control.

[0026] Since the other compressor 1 can initially be started at only a partial capacity, the additional mechanical capacity controller 6 can also optimize the CF coefficient (control coefficient), which is the ratio of the adjustable capacity range of the continuously controlled compressor 1 to the capacity of the next compressor 1 that can be started.

[0027] The design of the compressor system described above allows for the matching of compressor 1 operating times, extending service life while ensuring a high level of quality control across the entire capacity range. This design is particularly advantageous for transcritical refrigeration units, as these units exhibit significant differences in power requirements between winter and summer operation.

[0028] Reference Number List

[0029] 1 compressor

[0030] 2 Condensers

[0031] 3 Refrigerant manifold 4 Injection valve

[0032] 5 Evaporators

[0033] 6 Power Regulator 7 Control System

[0034] K refrigeration circuit

Claims

1. A compressor system for a refrigeration unit comprising a plurality of compressors (1), wherein, The first compressor (1) has a speed independent continuous capacity control (6) wherein the compressor system is arranged to control the first compressor (1) as a master compressor and to switch on and off the subsequent compressors (1) as slave compressors to meet the capacity demand of the refrigeration unit, wherein each compressor (1) has a speed independent continuous capacity control (6) based on valve opening time pulse width modulation control, and the compressor system is further arranged to control one of the subsequent compressors (1) as a master compressor and to switch on and off the first compressor and, if applicable, the remaining subsequent compressors (1) as slave compressors to alternatively meet the capacity demand of the refrigeration unit.

2. The compressor system of claim 1, wherein, Each compressor (1) further comprises a mechanical step capacity control (6).

3. The compressor system of claim 2, wherein, Each compressor (1) is of reciprocating piston compressor design and the mechanical step capacity control (6) is based on cylinder group switching.

4. The compressor system of claim 1, wherein, The compressor system is arranged to alternate the use of each compressor (1) equipped with a speed independent continuous capacity control (6) as a master compressor to achieve equalization of the run times of each compressor (1).

5. The control method of a compressor system according to any one of the preceding claims, wherein, The run times of each compressor (1) are adjusted by alternating the use of each compressor (1) equipped with a speed independent continuous capacity control (6) as a master compressor.

6. The compressor system control method according to the preceding method claim 5, wherein, The cycle times of the power controllers (6) of the cylinder groups of each compressor (1) are equalized.

7. The method of any of the preceding method claims, wherein, The run times of each compressor (1) and / or the cycle times of the power controllers (6) of the cylinder groups of each compressor (1) are kept the same within a predetermined time interval, with a deviation of 20% or less, preferably 10% or less.

8. A method of retrofitting a compressor system comprising a plurality of compressors (1), wherein, The first compressor (1) has a speed independent continuous capacity control (6) wherein the compressor system is arranged to control the first compressor (1) as a master compressor and to switch on and off the subsequent compressors (1) as slave compressors to meet the capacity demand of the refrigeration unit, wherein each compressor (1) is equipped with a speed independent continuous capacity control (6) based on valve opening time pulse width modulation control, and the compressor system is further arranged to control one of the subsequent compressors (1) as a master compressor and to switch on and off the first compressor and, if applicable, the remaining subsequent compressors (1) as slave compressors to alternatively meet the capacity demand of the refrigeration unit.

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