HK1137801B - A refrigerant system with a suction modulation valve having adjustable opening and the operation method thereof - Google Patents

Description

Refrigerant system having suction modulation valve with adjustable opening and method of operating same

Technical Field

The present application relates to refrigeration systems.

Background

In the refrigerant systems to which this application relates, a suction modulation valve (or other type of valve having a small controlled opening in the closed position) is provided with a pulse width modulation control to regulate refrigerant system capacity. The minimum opening size of the suction modulation valve is maintained to ensure that the suction pressure inside the compressor casing downstream of the suction modulation valve does not drop below a specified value. However, this minimum opening size is adjusted in response to the conditions under which the system is operating to ensure that the suction pressure within the compressor is close to the minimum allowable and not undesirably high.

Refrigeration systems are known and are used to condition secondary fluids. As one example, an air conditioning system cools and dries air delivered into a climate controlled environment. Refrigeration systems generally include a compressor that compresses a refrigerant and delivers the refrigerant to a first heat exchanger through a discharge line. From the first heat exchanger, the refrigerant passes through an expansion device and then through a second heat exchanger. The refrigerant then returns to the compressor.

Under various conditions, the refrigeration system may provide excess capacity to cool or heat the secondary fluid supplied to the climate-controlled environment. Many methods are known for reducing the capacity of a refrigeration system.

One known method of reducing capacity is to provide a pulse width modulation control for a suction valve located upstream of the compressor to control the amount of refrigerant moving from the second heat exchanger to the compressor. In a pulse width modulation control for a suction valve, the valve is rapidly cycled (opened and closed) to limit the amount of refrigerant flowing to the compressor. This in turn limits the amount of refrigerant compressed in the compressor and the flow of refrigerant circulating through the refrigeration system, resulting in a reduced capacity of the refrigeration system and providing more efficient operation.

One challenge with such operation is that the pressure within the compressor shell should not be reduced below certain limits defined by compressor reliability considerations. As a rough guideline, it is desirable to maintain the pressure within the compressor shell at least 1 psia. However, when the suction modulation valve is fully closed during the pulse width modulation control cycle, at times, the pressure within the compressor housing may decrease below this particular minimum pressure. In this case, a spark may occur at the tip for the compressor motor, which may cause damage to the tip. This phenomenon is known as the "corona discharge" effect and is undesirable.

Thus, it is known in the art that there is a need to provide a minimum "leak" opening for the suction valve that would otherwise be closed during the pulse width modulation cycle to prevent compressor suction from entering the deep vacuum region. Also, in another approach, a branched bypass line around the pulse width modulation valve containing a small inner diameter capillary tube or small orifice has been proposed in the past to prevent compressor suction from entering the deep vacuum by providing an alternative small "leak" path to facilitate refrigerant flow into the compressor. While the prior art does provide better control of capacity, the "leak" opening is typically sized to ensure that the suction pressure in the compression casing exceeds a certain minimum pressure at all operating conditions.

However, when the suction valve is in the closed position, the downstream pressure inside the compressor shell varies considerably for an opening of constant size, depending on the pressure upstream of the opening. The evaporator pressure can vary by at least one order of magnitude depending on the operating conditions of the refrigeration system. Thus, in the prior art, under high pressure operating conditions at the evaporator, the suction pressure inside the compressor will also be much higher than what can be considered desirable for the minimum pressure in order to avoid the "corona discharge" effect. It is undesirable to have the suction pressure substantially exceed this threshold because it reduces the efficiency of the refrigerant system operating in the pulse width modulated mode. Thus, the prior art fails to effectively control the suction pressure inside the compressor to just exceed an acceptable threshold value under all operating conditions while avoiding "corona discharge".

Disclosure of Invention

In one disclosed embodiment of the invention, control of the suction modulation valve uses a pulse width modulation controller to operate the suction modulation valve to reduce refrigeration system capacity. When the valve is in the closed position, the controller varies the size of the minimum opening or "leak" opening in the valve depending on the refrigerant system operating conditions. In one disclosed embodiment, the control refrigerant system operating condition will be the pressure upstream of the suction modulation valve. This pressure is typically associated with, and closely approximates, the pressure inside the evaporator. The evaporator pressure may be measured by one of the sensors and the registered value is related to the desired minimum opening of the suction modulation valve to achieve the minimum desired pressure within the compressor shell. It is known that the smaller the opening of the valve, the greater the pressure drop across the valve, and therefore, for the same upstream evaporator pressure, the downstream compressor suction pressure can be controlled by varying the size of this opening. In this way, this problem of the prior art is eliminated: during periods when the suction modulation valve is in the closed position, the suction pressure is made to far exceed the minimum threshold pressure within the compressor shell at higher evaporator pressure conditions.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

Drawings

Figure 1 is a schematic diagram of a refrigeration system incorporating the present invention.

Figure 2 shows the operation of a prior art pulse width modulation controller.

Fig. 3A and 3B illustrate the problem with prior art systems.

Fig. 4 is a graph illustrating the features of the present invention.

Detailed Description

A refrigeration system 20 is illustrated in fig. 1. The refrigeration system 20 incorporates a compressor 22 that compresses a refrigerant and delivers the refrigerant downstream to a condenser 24. The refrigerant from the condenser 24 passes through an expansion device 26 and then to an evaporator 28. Refrigerant from the evaporator 28 passes through a suction modulation valve 30 and back to the compressor 22. As is known, the controller 34 for the suction modulation valve 30 may provide pulse width modulation control to rapidly vary the size of the opening through the valve 30 between the open and closed positions in order to limit the amount of refrigerant passing from the evaporator 28 to the compressor 22. In this way, a reduction in capacity during part load operation of the refrigeration system 20 may be achieved.

As shown in fig. 2, the refrigerant system capacity cycles between a maximum value (fully open suction modulation valve) and a minimum value (closed suction modulation valve with minimum opening) over time, thereby making the average capacity less than full capacity without pulse width modulation control.

Fig. 3A and 3B illustrate the disadvantages of the prior art. As described above, a certain "leakage" path is typically maintained through the suction modulation valve to ensure that a relatively small amount of refrigerant does reach the compressor 22, and thus a minimum suction pressure is maintained within the compressor housing 52. The minimum pressure is between 0Between 5psia and 3 psia. As set forth above, the motor 50 for the compressor pump unit 51 is received within the compressor housing 52. If the pressure within the compressor housing 52 becomes too low, an undesirable "corona discharge" effect may occur. For this reason, a refrigerant "leak" path is typically provided to prevent the compressor from entering the deep vacuum region. However, the size of this minimum "leakage" path is typically designed to ensure that the pressure will never drop below a particular minimum pressure (e.g., 1psia) under all operating conditions. For example, as shown in FIG. 3B, if the minimum desired upstream pressure P_{Upstream of}Equal to 30psia, the minimum opening is sized so that the downstream pressure P at the suction modulation valve closed position is_DownstreamIs 1 psia. However, P at 100psia_{Upstream of}At the pressure value, P is shown in FIG. 3A for the same amount of opening of the suction modulation valve 30_DownstreamAbout 6psia, but for most efficient operation would require the same pressure of 1psia downstream of the suction modulation valve.

FIG. 4 shows the suction modulation valve downstream pressure (P) for three different minimum opening sizes (e.g., opening A1, opening A2, and opening A3) through the pulse width modulation valve when the valve is in the closed position_Downstream) -suction modulation valve upstream pressure (P)_{Upstream of}) A graph of (a). The larger the opening, for the same P_{Upstream of}P of pressure_DownstreamThe greater the pressure. As indicated in fig. 4, a1 is the largest minimum opening size, A3 is the smallest minimum opening size, and a2 is the smallest opening size between the a1 and A3 opening sizes. As can be seen from fig. 4, when the valve has a maximum minimum opening size a1, when the upstream pressure P is_{Upstream of}Equal to 30psia, the downstream pressure P_DownstreamEqual to 1 psia. In addition, for the same opening A1, when P_{Upstream of}When equal to 100psia, P_DownstreamEqual to 6 psia. However, it is desirable to have a downstream pressure P of 1psia_DownstreamIrrespective of the upstream pressure P_{On the upper part Swimming device}. By having an adjustable minimum suction regulating valve opening, i.e. when P_{Upstream of}At a pressure equal to 30psia, the minimum suction modulation valve opening must be at A1, andwhen P is present_{Upstream of}With a pressure equal to 100psia, the minimum suction modulation valve opening must be at A3 to achieve this P of 1psia_DownstreamAnd (4) pressure.

As can be appreciated from FIG. 1, the pressure sensor 32 may be disposed upstream of the suction modulation valve 30 to measure the upstream pressure P_{Upstream of}. Another sensor 44 may be disposed downstream of the suction modulation valve 30 to measure the pressure P downstream of the suction modulation valve 30_Downstream(this downstream pressure corresponds to and typically closely approximates the suction pressure inside the compressor shell). As can be seen from the graph in FIG. 4, a downstream pressure P is selected that provides a desirable 1psia when the suction modulation valve is in the closed position_DownstreamThe desired area "a" of the minimum suction modulation valve opening. It should be noted that the exemplary fig. 4 shows only three curves for different area "a" openings, and that a more accurate graph will develop more closely spaced lines corresponding to area "a" so that the desired area "a" can be accurately selected by interpolating between the lines corresponding to the areas shown on this graph. The control 34 therefore not only drives the suction modulation valve 30 to have a pulse width modulated movement between the open and closed positions, but also depends on the operating conditions (and in particular the upstream pressure P of the suction modulation valve 30)_{Upstream of}) To adjust the minimum opening for the suction modulation valve 30 to maintain a P of 1psia_DownstreamPressure, irrespective of the upstream pressure P_{Upstream of}. Thus, the pressure within the compressor housing 52 can always be maintained near a minimum pressure (e.g., 1psia) rather than higher than desired (resulting in irreversible efficiency losses in the operation of the refrigeration system 20).

As an alternative to developing the graph shown in FIG. 4, the refrigerant system 20 may have a feedback control, which may be based on a downstream pressure P being measured_DownstreamThe pressure sensed by the sensor 44 to regulate the amount of minimum opening for the pulse width modulation valve 30. If the sensor 44 measures P when the pulse width modulation valve 30 is in the closed position_DownstreamIs much higher than 1psia, the minimum opening size for the pulse width modulation valve 30 is reduced.Downstream pressure P_DownstreamIn the event that the positive trend is to fall below 1psia, the minimum opening size for the suction modulation valve 30 is increased. Controller 34 may also operate in a learn mode, or may be operated when controller 34 learns about upstream pressure P_{On the upper part Swimming device}What amount of opening is needed to maintain a downstream pressure P of approximately 1psia_DownstreamIn a time mode.

The chart presented in fig. 4 is exemplary and shown for illustrative purposes only, as the exact shape of the curve will depend on the particular compressor size and type, refrigerant type, etc. Except for the measurement P being dependent on the upstream pressure_{Upstream of}In addition, other parameters may be measured to fine tune the establishment of the minimum opening area required for the pulse width modulated valve 30 in the closed position (e.g., temperature upstream and downstream of the valve, etc.). Although a scroll compressor is used to illustrate the present invention, other compressor types will fall within the scope of the present invention, including, for example, rotary, screw and reciprocating compressors. The present invention is applicable to various types of systems and may include refrigeration container and truck trailer systems, supermarket installations, residential air conditioning and heat pump systems, and rooftop units. Finally, as noted above, other valve types capable of adjusting the minimum opening size will be within the scope of and may equally benefit from the present invention.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims (20)

1. A refrigeration system, comprising:

a compressor having a pump unit and a motor, the motor and the pump unit mounted within a housing, the compressor delivering refrigerant to a first heat exchanger, refrigerant passing from the first heat exchanger through an expansion device and to a second heat exchanger, refrigerant passing from the second heat exchanger through a suction valve and back to the compressor, refrigerant that has passed through the suction valve passing into the compressor housing and into a chamber housing the electric motor; and

a controller for the suction valve, the controller being operable to rapidly cycle the suction valve between an open position and a closed position to regulate capacity of the refrigeration system, and the suction valve maintaining a minimum opening area in the closed position, the controller selecting the minimum opening area to ensure that the pressure within the housing for the compressor approaches a minimum predetermined pressure when the controller has moved the suction valve to its closed position.

2. The refrigerant system as set forth in claim 1, wherein said suction valve is a suction modulation valve.

3. The refrigeration system of claim 1 wherein the minimum predetermined pressure is between 0.5psia and 3 psia.

4. The refrigerant system as set forth in claim 1, wherein said minimum opening is selected by said controller based on a pressure associated with said second heat exchanger.

5. The refrigerant system as set forth in claim 4, wherein said pressure is measured at a location downstream of said second heat exchanger and upstream of said suction valve.

6. The refrigerant system as set forth in claim 4, wherein a relationship between said pressure and said minimum opening for said suction valve is determined to ensure that the pressure within said compressor shell approaches said minimum predetermined pressure, and said controller utilizes said relationship to select said minimum opening.

7. The refrigerant system as set forth in claim 1, wherein said minimum opening is selected by said controller based on a pressure measurement indicative of said pressure within said compressor shell.

8. The refrigerant system as set forth in claim 7, wherein said control decreases said minimum opening if said pressure within said compressor shell is above an expected pressure.

9. The refrigerant system as set forth in claim 7, wherein said control increases said minimum opening if said pressure within said compressor shell is below an expected pressure.

10. The refrigerant system as set forth in claim 1, wherein said rapid cycling of said suction valve is performed by a controller using a pulse width modulation technique.

11. A method of operating a refrigeration system comprising the steps of:

(1) providing a compressor having a pump unit and a motor, the motor and the pump unit being mounted within a housing, the compressor delivering refrigerant to a first heat exchanger, refrigerant passing from the first heat exchanger through an expansion device and to a second heat exchanger, refrigerant passing from the second heat exchanger through a suction valve and back to the compressor; the refrigerant having passed through the suction valve is delivered into the compressor housing and into a chamber housing the electric motor; and

(2) rapidly cycling the suction valve between an open position and a closed position to regulate capacity of the refrigeration system, and maintaining a minimum opening area in the closed position, the controller selecting the minimum opening area to ensure that the pressure within the housing for the compressor approaches a minimum predetermined pressure when the controller has moved the suction valve to its closed position.

12. The method of claim 11, wherein the suction valve is a suction modulation valve.

13. The method of claim 11, wherein the minimum predetermined pressure is between 0.5psia and 3 psia.

14. The method of claim 11, wherein the minimum opening is selected by the controller based on a pressure associated with the second heat exchanger.

15. The method of claim 14, wherein the pressure is measured at a location downstream of the second heat exchanger and upstream of the suction valve.

16. The method of claim 14, wherein a relationship between the pressure and the minimum opening for the suction valve is determined to ensure that the pressure within the compressor shell approaches the minimum predetermined pressure, and the controller uses the relationship to select the minimum opening.

17. The method of claim 11, wherein the minimum opening is selected by the controller based on a pressure measurement indicative of the pressure within the compressor shell.

18. The method of claim 17, wherein the controller decreases the minimum opening if the pressure within the compressor housing is higher than expected.

19. The method of claim 18, wherein the controller increases the minimum opening if the pressure within the compressor shell is below an expected pressure.

20. The method of claim 11, wherein the rapid cycling of claim 2 occurs with a pulse width modulation control of the suction valve.