HK1133066B - Economized refrigerant system with vapor injection at low pressure - Google Patents

Description

Economic refrigerating system with low-pressure steam injection

Technical Field

The present invention relates to a refrigeration system having a vapor injection function, such as by an economizer cycle, wherein vapor injection is limited to only the low pressure portion of the compression cycle.

Background

In many applications, a refrigeration system is utilized to condition the environment. In particular, air conditioners and heat pumps are used to cool and/or heat a secondary fluid, such as air, entering an environment. The cooling or heating load of the environment may vary with changes in ambient conditions, occupancy levels, sensible and latent load demands, and with adjustments to temperature and/or humidity set points by occupants of the conditioned space.

Thus, a refrigerant system may be provided with fine control and a number of optional components and features to adjust cooling and/or heating capacity. Well-known options include: refrigerant can be bypassed back to the suction line, the refrigerant having been at least partially compressed by the compressor. This function is also referred to as an unloader function. This additional step of operation is used to reduce system capacity.

The use of economizer cycles (economiser cycles) is also known. The economizer cycle provides system performance enhancement by diverting a portion of the refrigerant flow downstream of the condenser under certain conditions. The tapped refrigerant passes through a separate expansion device and then through the economizer heat exchanger in heat exchange relationship with the main refrigerant flow flowing through a separate conduit within the economizer heat exchanger. Within the scope of the present invention, a flash tank is also considered to be one type of economizer heat exchanger, as is well known in the art. The tapped refrigerant cools the main refrigerant, so that the main refrigerant flow has a greater cooling potential when it reaches the evaporator. The tapped refrigerant is returned to an intermediate point in the compression cycle through a vapor injection line. It is also known that an economizer cycle can provide an additional unloading step while enhancing operational control and reducing the life cycle cost of the plant. In addition, greater benefits can be achieved when the economizer cycle is combined with various means of compressor unloading.

One known system configuration with a scroll compressor utilizes a vapor injection line as part of the unloading operation. In such an arrangement, a portion of the refrigerant may be rerouted from the compression chamber into the vapor injection line, then through the unloader valve, and ultimately to the suction line leading to the compressor suction port.

In many vapor compression devices, particularly in air conditioning applications having a relatively low pressure ratio (the ratio of compressor discharge pressure to compressor suction pressure), the economizer and unloader features described above have not been fully utilized. Some reasons are related to the following: in such low pressure ratio applications, the temperature differential within the economizer heat exchanger is small to provide significant benefits, but the pulsation losses associated with the vapor injection lines/ports become more significant and difficult to control.

In the past, the injection line communicated with the compression chambers for a majority of the time during compressor operation. For example, in a scroll compressor, as a first scroll member orbits relative to a second scroll member, at some point in the orbit cycle, the wraps come together to seal the compression chambers from the suction port. Vapor injection into the scroll compressor is produced by an injection line that passes refrigerant from the economizer heat exchanger or flash tank to an intermediate injection point within the scroll compressor. The vapor is injected into a separate compression chamber that is generally sealed from the suction and discharge ports. In the past, the steam injection time was controlled to last for most of the vortex plate orbiting cycle. The injection port is thus exposed to almost the entire range of pressure variation within the scroll compression chamber connected to the injection port. This results in two major pulsation (sloshing) and throttling losses which are detrimental to efficient compressor operation. These losses occur because: at the beginning of the cycle, when the pressure in the scroll compression chambers is low, the injected refrigerant will fill the compression chambers. However, since the pressure in this compression chamber will increase towards the end of the compression process, the refrigerant will be forced back into the injection line. This results in high sloshing losses due to refrigerant moving into and out of the compression chamber. Throttling caused by pressure drop in the injection line and through the injection ports also contributes to such losses.

Overcoming this loss has proven to be a challenge for incorporating an economizer cycle in such refrigeration systems for air conditioning applications where any losses associated with the economizer cycle are extremely severe. The idea of combining the unloader line with the economizer cycle also introduces additional problems. This problem occurs when the unloading operation becomes less efficient than desired. During system unloading operation, when vapor is returned from the intermediate compression port to the suction line, excess compression power is consumed to compress the refrigerant to a higher pressure before the refrigerant is bypassed back to the suction line. In particular, when the compressor has compressed the refrigerant to the point where the injection port is closed, a significant amount of power has been wasted compressing the refrigerant which is now bypassed back to the compressor suction line. Therefore, compressor unloading has not been successfully utilized in the past.

The object of the present invention is to solve the above-mentioned problems.

Disclosure of Invention

In the disclosed embodiment of the invention, the vapor injection line is exposed to the compression chamber only for a limited period of the compression cycle. In the prior art, the vapor injection is typically exposed to the compression chamber for a significant amount of time, typically over 50% of the time during an operating cycle. In the present invention, however, the compression chamber communicates with the vapor injection port less than 50% of the time during one operation cycle. More preferably, in the disclosed embodiments, the communication time is less than 35%. In one disclosed embodiment, a flow control device, such as a snap action valve, is positioned on the steam injection line near the steam injection port to control the timing at which the steam injection will occur. The controller opens and closes this valve so that it only allows communication between the vapor injection line and the compression chamber for a relatively short period of time during operation of the scroll compressor.

As a preferred embodiment of the invention, the injection line begins to communicate with the at least one compression chamber at any time during a period of one-tenth of the compressor on cycle before any of the compression chambers is exposed to the suction port and two-tenths of the compressor on cycle after any of the compression chambers is isolated from the suction port.

Preferably, the compressor operates at a pressure ratio of 2 to 8, which is the ratio of discharge pressure to suction pressure.

The present invention thus solves the above mentioned problems.

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

FIG. 1 illustrates a refrigeration system incorporating the present invention;

FIG. 1A shows an alternative arrangement;

fig. 2 shows an example of a vapor injection port of a refrigeration compressor.

Detailed Description

In fig. 1, a refrigeration system 10 is shown including a compressor 11, an evaporator 26, a main expansion device 24, and a condenser 16. As shown, the economizer heat exchanger 18 is communicated to the compressor 11 by an economizer injection line (or so-called vapor injection line) 20.

The compressor 11 may be a scroll compressor, and includes: an orbiting scroll member 12 with a generally spiral wrap 13; and a fixed scroll member 14 with a generally spiral wrap 15. As is well known, these wraps interfit to define compression chambers. As shown, for example, the economizer injection line 20 delivers refrigerant into the compression chambers through the vapor injection ports 203 and wrap 15 of the fixed scroll member. Such a structure is well known.

Line 20 passes through an economizer expansion device 115 and then through the economizer heat exchanger 18. As is known, the refrigerant in the main liquid line 113 is cooled in the economizer heat exchanger by passing the tapped refrigerant through the expansion device 115 and the heat exchanger 18 in heat exchange relationship with the refrigerant in the main circuit. As is known, the economizer injection line 20 is shown returning tapped refrigerant to the compressor 11 at some intermediate point in the compression cycle.

As further known, an optional unloader or bypass line 17 selectively communicates the economizer injection line 20 to the suction line 111. With the unloader valve 19 open, a portion of the partially compressed refrigerant may flow from an intermediate port (described below) of the scroll member to a line 20, into the unloader line 17 and through the unloader valve 19, and ultimately to a suction line 111. Suction line 111 communicates with suction port 201 to deliver refrigerant back into compressor 11. Typically, the economizer expansion valve 115 does not communicate with the vapor injection port 203 when the unloader valve 19 is open. If the expansion valve 115 does not have closing capability, an additional closing device may be provided on the economizer injection line 20 to isolate the expansion valve 115 from the vapor injection port 203 of the compressor 11. Such structures and flow configurations are also known.

As shown in fig. 2, the fixed wrap 15 is preferably of a "hybrid type" and, as shown, has a thickness that varies along its circumferential extent. As shown in this example, the injection ports 23 and 27 are formed through the wrap 15. The injection ports 23 and 27 may have varying sizes. Further, it is preferable to form the injection ports 23 and 27 at a position of a part of the wrap 15 which is not the minimum thickness of the wrap. Thicker wraps additionally ensure that a jet of sufficient size can be formed through the wrap. As shown, a discharge port 28 is formed through the back surface of the fixed scroll member as shown. The injection ports may also be formed through the base of the fixed scroll member as is known in the art.

The orbiting scroll member includes a wrap 13, which wrap 13 may also be "compound-type" and extends from a base. The base includes grooves 44 and 46 formed in the base of the scroll member.

During operation of the scroll compressor, orbiting scroll member 12 will move relative to stationary scroll member 14 such that the base of orbiting scroll member 12 slides over the tip of stationary wrap 15. With the configuration shown in fig. 2, during the compression cycle, the injection ports 23 and 27 are brought into communication when they overlap the grooves 44 and 46. At this time, injection of the economizer refrigerant flow into the compression chambers 50 and 51 may be performed. Preferably, communication between the injection ports 23 and 27 and the compression chambers is achieved, for example, by the grooves 44 and 46 when the refrigerant pressure in the compression chambers 50 and 51 is lower than the pressure in the economizer injection line 20. Under such conditions, the economizer refrigerant flow is directed into compression chambers 50 and 51. It is also important to minimize or avoid communication between injection line 20 and compression chambers 50 and 51 when the pressure in compression chambers 50 and 51 exceeds the refrigerant pressure in economizer injection line 20. Thus, pulsation (sloshing) of the refrigerant "in and out" of the compression chambers 50 and 51 is avoided. Finally, it is often important to provide the above-described refrigeration communication immediately after the compression chambers 50 and 51 are closed (or about to be closed) from the suction port 201 of the compressor 11 in order to achieve the maximum temperature differential within the economizer heat exchanger 18. It should be noted that an example of this is shown in fig. 2: how fluid through the economizer port can be selectively blocked or unblocked at a particular time during the compression cycle. Other arrangements in the positioning of the economizer injection ports that allow for limited time injection are also possible. Accordingly, the arrangement shown in FIG. 2 is shown for illustrative purposes only.

If additional enhancements are required to the timing of the injection event as described in the arrangement shown in FIG. 2, a fast-acting flow control device, such as a valve 150, may be provided on the economizer injection line 20 as shown in FIG. 1. This valve 150 may be controlled by the system controller 301 such that the valve 150 opens only immediately after the scroll wraps 15 and 13 are in contact or are about to be in contact to seal the compression chambers 50 and 51 from the suction port 201. Valve 150 is closed at a time long before compression chambers 50 and 51 are in communication with discharge port 28, at which point the pressure in the compression chambers is preferably still less than or equal to the refrigerant pressure in economizer injection line 20. In essence, the timed opening of the valve 150 in fig. 1 functions similarly to the "valve opening" and "valve closing" of the injection ports 23 and 27 by the grooves 44 and 46 in fig. 2. This valve 150 may be used in conjunction with the arrangement shown in fig. 2 or independently of the arrangement. It should be understood that the valve 150 may be disposed inside or outside of the compressor housing. The case of being externally provided is shown in fig. 1. Alternatively, the valve 150 may be disposed inside the housing as shown in FIG. 1A. The valve may also be attached to the housing.

In the disclosed embodiment, the vapor injection ports 23 and 27 are only in communication with the compression chambers 50 and 51 for less than 50% of the compression cycle time. In a preferred disclosed embodiment, this communication time is less than 35%. The precise timing of this communication results in improved efficiency of the economizer cycle. It has also been found that when the system is operating in a non-economizer mode (economizer branch is shut off and bypass line is closed), particularly if the vapor injection port and vapor injection line begin to communicate immediately after compression chambers 50 and 51 are closed, the average pressure in the injection line will not exceed 1.75 times the suction pressure. This low pressure in the injection line also results in more efficient operation of the system in the non-economizer mode.

In a similar manner, the efficiency of the bypass unloading operation is also improved when valve 19 is open and a portion of the partially compressed refrigerant is bypassed back to compressor suction 201. Because the refrigerant is bypassed early in the compression process, unnecessary over-compression of the bypassed refrigerant, which results in additional power consumption, is avoided.

It should be appreciated that a system designer may consider different priorities regarding system performance improvement depending on the emphasis on capacity or efficiency. While both methods may benefit from the disclosed invention, the start of steam injection should begin as early as possible from a capacity boost perspective, while for efficiency improvement the start of steam injection should be consistent with capacity-power optimization (still located in the low pressure region). In other words, in the latter case, efficiency optimization should be achieved between the capacity increase obtained due to the greater temperature difference within the economizer heat exchanger, and the additional power consumption due to the injected refrigerant flow being compressed by the compressor.

While the specifically disclosed embodiments are shown with respect to a scroll compressor, other types of compressors, such as screw compressors, rotary compressors, reciprocating compressors, or any refrigerant compressor that may incorporate an economizer cycle, can utilize 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 (22)

1. A refrigeration system comprising:

a compressor for compressing refrigerant and delivering the refrigerant downstream to a condenser, an expansion device downstream of the condenser, an evaporator downstream of the expansion device, refrigerant flowing from the compressor through the condenser, the expansion device, the evaporator, and back to a suction line of the compressor;

an economizer cycle including a flow splitting device that splits a portion of refrigerant from a main refrigerant flow in a liquid line and that passes the split refrigerant through an economizer expansion device and then through an economizer heat exchanger where it exchanges heat with the main refrigerant flow and returns to the compressor through an injection line;

the compressor further includes: a compression pump unit driven through a compression cycle, a suction port, and a discharge port, and operable to receive refrigerant and compress the refrigerant toward the discharge port, the compressor communicating an injection of refrigerant from the injection line into the compression pump unit and into at least one injection port, and the injection time being less than 50% of one compressor cycle.

2. The refrigeration system of claim 1, wherein: the time of the injection is less than 35% of one compressor run.

3. The refrigeration system of claim 1, wherein: the compression pump unit comprises at least one compression chamber connected to the injection line.

4. The refrigeration system of claim 3, wherein: the injection line begins to communicate with the at least one compression chamber at any time during a time period that is one-tenth of a compressor operating cycle before any compression chamber is exposed to the suction port and two-tenth of a compressor operating cycle after any compression chamber is isolated from the suction port.

5. The refrigeration system of claim 1, wherein: the timing of the injection is controlled by selectively blocking and unblocking the injection line.

6. The refrigeration system of claim 5, wherein: the blocking and the switching are controlled by a flow control device.

7. The refrigeration system of claim 6, wherein: the flow control device is located external to the compressor.

8. The refrigeration system of claim 6, wherein: the flow control device is located inside the compressor.

9. The refrigeration system of claim 6, wherein: the flow control device is controlled by a system controller.

10. The refrigeration system of claim 6, wherein: the flow control device is a snap-action valve.

11. The refrigeration system of claim 5, wherein: the blocking and the switching are controlled by opening and closing of the at least one injection port.

12. The refrigeration system of claim 11, wherein: the opening and closing of the at least one injection port is controlled by a groove on the base of the orbiting scroll member.

13. The refrigeration system of claim 1, wherein: the injection line is also in communication with an unloader line having an unloader valve disposed thereon and which may be opened to allow at least a portion of the partially compressed refrigerant to flow back through the injection line to the suction port.

14. The refrigeration system of claim 1, wherein: the compression pump unit is a scroll compressor.

15. The refrigeration system of claim 1, wherein: the compressor operates at a pressure ratio of 2 to 8, which is the ratio of discharge pressure to suction pressure.

16. The refrigeration system of claim 1, wherein: the refrigeration system includes an unloader line having a pressure ratio of pressure within the injection line to suction pressure of less than 1.75 when the injection line and the unloader line are blocked.

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

providing a compression pump unit provided with a suction port and a discharge port and operable to receive a sucked refrigerant and compress the sucked refrigerant toward the discharge port through a compression cycle;

the compressor is also provided with an injection line for communicating an injection of refrigerant into the compression chambers during the compression cycle, and the injection of refrigerant is limited to 50% of one compressor cycle.

18. The method of claim 17, wherein: the injection of refrigerant is limited to 35% of one compressor cycle.

19. The method of claim 17, wherein: the refrigeration system includes an unloader line including a valve that is selectively opened to allow refrigerant from a compression chamber to flow through the injection line back to the suction port.

20. The method of claim 17, wherein: the compression pump unit is a scroll compressor.

21. The method of claim 17, wherein: the compressor operates at a pressure ratio of 2 to 8, which is the ratio of discharge pressure to suction pressure.

22. The method of claim 17, wherein: the refrigeration system includes an unloader line having a pressure ratio of pressure within the injection line to suction pressure of less than 1.75 when the injection line and the unloader line are blocked.