US20060005571A1

US20060005571A1 - Refrigerant system with reheat function provided by auxiliary heat exchanger

Info

Publication number: US20060005571A1
Application number: US10/886,383
Authority: US
Inventors: Alexander Lifson; Michael Taras
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2004-07-07
Filing date: 2004-07-07
Publication date: 2006-01-12
Also published as: WO2006016987A2; WO2006016987A3

Abstract

In disclosed embodiments of this invention, the main flow of refrigerant is subcooled by another refrigerant stream in an auxiliary heat exchanger. The auxiliary heat exchanger is either an economizer heat exchanger or a liquid-suction heat exchanger. In the case of the economizer heat exchanger, the smaller tapped portion of the refrigerant is returned into the intermediate compression stage. In the case of the liquid-suction heat exchanger, the refrigerant leaving the evaporator subcools the refrigerant in the main line as it leaves the condenser. In either case, the refrigerant approaching the evaporator is subcooled and greater cooling capacity is achieved. At the same time, the reheat function is provided by passing a stream of air over the auxiliary heat exchanger. This air additionally cools both refrigerant flows in the auxiliary heat exchanger, which is desirable as it further increases the subcooling of the liquid refrigerant and also reduces the temperature of the vapor refrigerant entering the compressor. This results in improved system efficiency and capacity, while at the same time air is being dehumidified in a reheat cycle.

Description

BACKGROUND OF THE INVENTION

This application relates to the provision of a reheat function in a refrigerant system wherein an auxiliary heat exchanger is utilized to subcool refrigerant approaching an evaporator.
Refrigerant systems are utilized to control the temperature and humidity of air in various environments. In a typical refrigerant system, a refrigerant is compressed in a compressor and delivered to a condenser. In the condenser, heat is exchanged between outside ambient air and the refrigerant. From the condenser, the refrigerant passes to an expansion device, at which the refrigerant is expanded to a lower pressure and temperature, and then to an evaporator. In the evaporator heat is exchanged between the refrigerant and the indoor air, to condition the indoor air. When the refrigerant system is operating, the evaporator cools the air that is being supplied to the indoor environment. In addition, as the temperature of the indoor air is lowered, moisture usually is also taken out of the air. In this manner, the humidity level of the indoor air can also be controlled.
In some cases, the air, that is brought to provide a comfort environment in a conditioned space, may need to be additionally dehumidified to provide the desired humidity level. This has presented design challenges to refrigerant cycle designers. One way to address such challenges is to utilize various schematics incorporating reheat coils. In many cases, the reheat coils, placed on the way of indoor air stream are employed for the purpose of reheating at least a portion of the air supplied to the conditioned space after it has been overcooled in the evaporator, where the moisture has been removed.
One of the options available to a refrigerant system designer to increase efficiency and capacity of the refrigerant system is to employ an auxiliary economizer circuit. In the economizer circuit, a portion of the refrigerant flowing from the condenser is tapped and passed through an economizer expansion device and then to an economizer heat exchanger. This tapped refrigerant subcools a main refrigerant flow that also passes through the economizer heat exchanger. The tapped refrigerant leaves the economizer heat exchanger, usually in a vapor state, and is injected back into the compressor at an intermediate compression point (or in case of two compressors connected in series, the injection is taken place into the point between the low and high pressure compressors). The main portion of refrigerant flow leaving the condenser is additionally subcooled after passing through the economizer heat exchanger. The main portion of the refrigerant flow then passes through a main expansion device and then to an evaporator. This main flow will have a higher cooling capacity because it was additionally subcooled in the economizer heat exchanger. An addition of economizer circuit thus provides enhanced system performance. In an alternate arrangement, a portion of the refrigerant is tapped and passed through the economizer expansion device after being passed through the economizer heat exchanger (along with the main flow). In all other aspects this arrangement is identical to the configuration described above.
Another option to increase the system capacity and efficiency is to utilize a liquid-suction heat exchanger. The purpose of the liquid-suction heat exchanger is to boost system performance by providing extra subcooling to liquid refrigerant exiting the condenser coil through the heat transfer interaction with the refrigerant vapor exiting the evaporator. Although during this heat transfer interaction the refrigerant density and subsequently mass flow rate at the compressor suction are undesirably reduced, in general, the combined effect of the liquid-suction heat exchanger addition allows for overall system performance enhancement.
Recently, the assignee of this application has developed a system that combines the reheat coil and economizer cycle. However, variations of this basic concept have yet to be fully developed.

SUMMARY OF THE INVENTION

In disclosed embodiments of this invention, an auxiliary heat exchanger is provided and placed on the way of predominantly liquid refrigerant flow downstream of the condenser and upstream of the evaporator, and this main flow of refrigerant in the auxiliary heat exchanger is further subcooled by another refrigerant stream. In the case of the economizer heat exchanger, the latter, smaller portion of the refrigerant is evaporated and returned into the intermediate compression stage. In case of liquid-suction heat exchanger, the refrigerant in the main suction line, that is predominantly in a vapor state, before flowing into the compressor suction port, subcools the refrigerant in the main liquid line, as it leaves the condenser. In either case, the refrigerant approaching the evaporator is subcooled such that a greater cooling capacity is provided. With these arrangements, the refrigerant flow returning to the compressor through the intermediate port, in the case of the economizer heat exchanger, or through the suction port, in case of the liquid-suction heat exchanger, is being preheated by the opposite stream that is being subcooled. The present invention utilizes this preheating effect to provide a reheat function.
More specifically in the embodiment dealing with the liquid-suction heat exchanger, refrigerant downstream of the evaporator is utilized to subcool the refrigerant approaching the evaporator. In this case, a portion of the suction line leading to the compressor inlet or liquid suction heat exchanger itself is placed in the path of at least a portion of an airflow passing over the evaporator. As described above, the reheat function is operable to heat the air to a desired temperature, while providing the air dehumidification in the evaporator. As the air is heated while passing over the liquid-suction heat exchanger, it cools the refrigerant in this liquid-suction heat exchanger, which is desirable, as it improves the system capacity and efficiency.
In other embodiments, the subcooling function is provided by an economizer circuit. As is known, an economizer circuit includes a heat exchanger receiving a main flow of refrigerant and a smaller, tapped flow of refrigerant. The tapped flow of refrigerant subcools the main flow of refrigerant. The tapped flow of refrigerant is returned to an intermediate point in the compression cycle of the compressor. Since the smaller, or tapped flow, has subcooled the main flow of refrigerant, this tapped refrigerant is being evaporated or pre-heated, as it passes through the economizer heat exchanger. Thus, if the economizer heat exchanger or its return line to the compressor are placed in the heat transfer relationship with the airflow passing over the evaporator, then the refrigerant in this line is cooled by this airflow. This additional cooling of refrigerant vapor, as it enters the intermediate injection port, is desirable, as it improves system capacity and efficiency. At the same time, the reheating of the airflow is accomplished and dehumidification function is provided.
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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first schematic of a refrigerant system.
FIG. 2 shows a second schematic of a refrigerant system.
FIG. 3 shows a third schematic of a refrigerant system.
FIG. 4 shows a fourth schematic of a refrigerant system.
FIG. 5 shows an exemplary heat exchanger.
FIG. 6 shows a second embodiment heat exchanger.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A refrigerant system 20 is illustrated in FIG. 1 having a compressor 22 delivering a refrigerant to a condenser 24. An auxiliary heat exchanger 26 (liquid-suction heat exchanger in this case) is positioned downstream of the condenser 24, and upstream of a main expansion device 28. The refrigerant passes through an evaporator 30 downstream of the main expansion device 28, and an air moving device 32 moves air over the evaporator 30, with the air then being moved into an environment to be conditioned. As can be seen in FIG. 1, downstream of the evaporator 30, the refrigerant once again enters an auxiliary liquid-suction heat exchanger 26 at point 34, and exits at point 36, subcooling the refrigerant passing to the main expansion device 28. Thus, when the refrigerant reaches the evaporator 30, it will have a greater cooling capacity than it otherwise would possess. As can be appreciated, the refrigerant passing from the condenser 24 to the main expansion device 28 is generally in a liquid state, while the refrigerant passing from point 34 to 36 is generally a vapor.
As shown in FIG. 5, the heat exchanger 80, receives the liquid refrigerant passing to the main expansion device 28 through a central tube 82 (or multiple tubes), and receives the vapor refrigerant through an inlet port 84. The vapor refrigerant then enters the space confined between a heat exchanger shell 86 and the central tube 82. After heat transfer interaction with the liquid refrigerant inside the tube, the heated vapor refrigerant exits through an outlet port 88. Thus, the two flows of refrigerant are maintained separated within the heat exchanger 80 and communicate with each other through the heat transfer interaction only. It is known to a person ordinarily skilled in the art that, the heat exchanger can have enhanced heat transfer surfaces (such as fins, ribs, etc) located on the outside or inside portion of the heat exchanger shell 86 in order to improve the heat transfer between the two refrigerant flows and surrounding air. The internal and external surfaces of the tube 82 can also be similarly enhanced to boost the heat transfer between the two refrigerant streams. In the heat exchanger exhibited in FIG. 5, the refrigerant vapor, being on the shell side, is in direct heat transfer interaction with surrounding air. Another heat exchanger configuration, with the refrigerant liquid being on the shell side, is also possible, and selection of a particular design depends on the application requirements and specifics. Thus, the connections can simply be reversed such that the liquid refrigerant is on the shell side. Finally, as shown in FIG. 6, in an embodiment 200, both the vapor and the liquid are exposed to the outside environment or air, with a vapor flow path 202, and a liquid flow path 204. Obviously, the heat exchanger 200 can have various flow patterns and configurations, including multiple channels on both liquid and vapor sides. It should be noted that the heat exchanger designs shown in FIGS. 5 and 6 are exemplary and many other concepts and configuration variations are also permissible to obtain full benefits of the invention teachings.
Downstream of the point 36, the refrigerant passes into a suction line 41 leading back to a line 44 to direct the refrigerant back to the compressor 22. An enhanced heat transfer surface 42 is preferably placed on or built into the suction line 44. This heat transfer surface and the portion of the suction line are placed in the airflow having passed over the evaporator 30. A worker of ordinary skill in the art would recognize how and when to control flow control devices, such valves 40 and 48, to either bypass the heat exchange portion 42, or pass the refrigerant through the heat exchange portion 42 when a reheat function is desired. It should also be noted that valves 40 and 48 and line 46 can be removed altogether if the reheat option is to remain operational all the time. The valves 48 and 42 can also be combined into a single three-way valve. Also, the valves 40 and 48 could be fixed or regulating flow control devices.
While the air reheating function is provided, the temperature of the refrigerant in the heat exchange portion 42 will be reduced as air temperature is expected to be colder than refrigerant temperature in the heat exchange portion 42. This reduction in the refrigerant temperature is desirable, as it will improve capacity and efficiency of the refrigerant system by increasing the density and consequently the mass flow rate of the refrigerant entering the compressor 22.
FIG. 2 shows a refrigerant system 50 that is similar to the FIG. 1 embodiment, however, the auxiliary liquid-suction heat exchanger 126 is itself placed in the path of the airflow provided by the air moving device 32. The temperature of the refrigerant vapor is reduced by the airflow, which is beneficial to improving the system performance, as it reduces the temperature of the refrigerant entering the compressor, as well as provides additional subcooling of the liquid refrigerant entering the expansion device to boost system performance. Depending on the liquid-suction heat exchanger configuration, either vapor refrigerant or liquid refrigerant is placed on a shell side of the auxiliary heat exchanger 26 into direct heat transfer interaction with the air form air moving device 32.
FIG. 3 shows yet another embodiment 52 wherein a tap 55 taps a refrigerant through an economizer expansion device 58. The tapped refrigerant from the line 55 passes through an economizer heat exchanger 54. A main portion of the flow (or all the flow, if the tap is located downstream of the economizer heat exchanger 54, on its main leg) also passes through the economizer heat exchanger 54 toward the main expansion device 28. As is known, the refrigerant in the main flow is subcooled within the economizer heat exchanger 54. A three-way valve 56 downstream of the economizer heat exchanger 54 on the tap line 55 selectively taps the refrigerant into a line 59, if the reheat function is desired, or taps refrigerant into the by-pass line 60, if no reheat function is desired. If the three-way valve 56 activates the reheat function, then a heat exchange portion 90 will be in the path of air having passed over the evaporator 30 as it has been driven by the air moving device 32. While the air reheating function is provided, the temperature of the refrigerant in the heat exchange portion 90 will be reduced, as air passing over the heat exchange portion 90 is colder than refrigerant in the 90. This is desirable, as it will improve capacity and efficiency of the refrigerant system by increasing the density and lowering the temperature of the refrigerant entering the compressor 22 through its intermediate compression port. On the other hand, if the reheat function is not desired, the three-way valve 56 is positioned to direct the refrigerant through a bypass line 60, at which it will re-enter the line 64 at a point 62. This refrigerant is thus returned to an intermediate compression point in the compressor 22 without having provided the reheat function. Again, an appropriate control manages the three-way valve 56 to either provide the reheat function or avoid it, depending upon sensible and latent capacity demands. It should also be noted that the valve 56 and line 60 can be removed altogether, if the reheat option to remain operational all the time. Of course, the three-way valve 56 can be substituted by a pair of the conventional valves as well as be of the metering nature by either modulation or pulsation techniques.
FIG. 4 shows a refrigerant system 70, again having an economizer heat exchanger 154. In this embodiment, the auxiliary economizer heat exchanger itself is placed in the path of the airflow from the air moving device 32, providing the desired reheating function. At the same time, as the air temperature passing over the auxiliary economizer heat exchanger is expected to be colder than the temperature of the refrigerant passing through the heat exchanger, the temperature of the refrigerant in the heat exchanger is reduced. The refrigerant temperature reduction is beneficial to the system performance (resulting in enhanced system capacity and efficiency), as it increases refrigerant subcooling entering the main expansion device as well as reducing the temperature of the refrigerant vapor entering the compressor intermediate compression port.
The refrigerant flow through the economizer heat exchanger can be arranged in either counterflow or parallel flow configuration (only parallel flow arrangement is illustrated in the schematics). Also, with another variation, the tapped portion of the refrigerant can be tapped either upstream of the economizer heat exchanger (as shown in the schematics) or downstream of the economizer heat exchanger. If it is tapped upstream, then only a portion of the refrigerant exiting the condenser will pass through the main leg of the economizer heat exchanger, with the remaining portion of the refrigerant passing through the secondary leg leading to the intermediate compression port. In case of the tap located downstream of the economizer heat exchanger, the main leg of the economizer heat exchanger will carry all the flow exiting the condenser. In this case, the tapped portion of the refrigerant will enter the economizer heat exchanger on the secondary leg downstream of the economizer heat exchanger, subcooling the refrigerant in the main leg.
Although preferred embodiments of this invention have 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

1. A refrigerant system comprising:

a compressor for compressing refrigerant and delivering the refrigerant to a condenser;

a main expansion device positioned downstream of said condenser, and an evaporator positioned downstream of said main expansion device, and an air moving device for passing air over said evaporator; and

an auxiliary heat exchanger, a first refrigerant stream being subcooled in said auxiliary heat exchanger by a second refrigerant stream returning toward said compressor, and at least one of said first or second refrigerant streams placed in a path of air driven by said air moving device over said evaporator to provide a reheat function.

2. The refrigerant system as set forth in claim 1, wherein a flow control device selectively communicates said second flow stream of refrigerant downstream of said auxiliary heat exchanger being returned to said compressor, either through a reheat portion that is in a path of said air to provide a reheat function, or can bypass said second flow stream of refrigerant into a bypass line to be returned directly to said compressor without providing the reheat function.

3. The refrigerant system as set forth in claim 2, wherein a flow control device is positioned in each of a line leading to said reheat portion, and said bypass line.

4. The refrigerant system as set forth in claim 1, wherein said auxiliary heat exchanger is placed in said path of air to provide said reheat function.

5. The refrigerant system as set forth in claim 1, wherein said auxiliary heat exchanger is an economizer heat exchanger, and there being a tap for said second stream of refrigerant for being tapped from a first flow of refrigerant and being passed through an economizer expansion device, said tapped refrigerant exchanging heat with said first flow of refrigerant in said economizer heat exchanger.

6. The refrigerant system as set forth in claim 5, wherein said tapped flow of refrigerant being returned to an intermediate compression portion in said compressor.

7. The refrigerant system as set forth in claim 1, wherein a return line for returning refrigerant to said compressor is placed in said path of air.

8. The return line as set forth in claim 7, wherein at least a portion of this line has enhanced heat transfer surfaces to promote heat transfer between the refrigerant in said return line and air in said air path.

9. The refrigerant system as set forth in claim 5, wherein a three-way valve selectively directs refrigerant from said tap and downstream of said economizer heat exchanger either into said path of air, or to bypass said path of air when a reheat function is not desired.

10. The refrigerant system as set forth in claim 5, wherein said economizer heat exchanger itself is placed in the path of said air.

11. The refrigerant system as set forth in claim 1, wherein said two refrigerant flows are maintained separately within said auxiliary heat exchanger.

12. The refrigerant system as set forth in claim 1, wherein said auxiliary heat exchanger has said first refrigerant stream surrounded by said second refrigerant stream, and such that said second refrigerant stream is exposed to said air.

13. The refrigerant system as set forth in claim 1, wherein said second refrigerant stream is surrounded by said first refrigerant stream, and such that said first refrigerant stream is exposed to said air.

14. The refrigerant system as set forth in claim 1, wherein both said first and second refrigerant streams in said auxiliary heat exchanger are exposed to said air.

15. A refrigerant system comprising:

a main expansion device positioned downstream of said condenser, and an evaporator positioned downstream of said main expansion device, an air moving device for passing air over said evaporator; and

an auxiliary heat exchanger, said auxiliary heat exchanger cooling a refrigerant passing from said condenser toward said evaporator, said refrigerant being cooled by a downstream refrigerant returning to said compressor downstream of said evaporator, and a refrigerant line of said downstream refrigerant passing to said compressor being placed in a path of air driven by said air moving device downstream of said evaporator to provide a reheat function.

16. The refrigerant system as set forth in claim 15, wherein a flow control device selectively communicates said second flow of refrigerant downstream of said auxiliary heat exchanger being returned to said compressor, either through a reheat portion that is in a path of said air to provide a reheat function, or can bypass said second flow of refrigerant into a bypass line to be returned directly to said compressor without providing the reheat function.

17. The refrigerant system as set forth in claim 16, wherein a flow control device is positioned in each of a line leading to said reheat portion, and said bypass line.

18. The refrigerant system as set forth in claim 15, wherein said auxiliary heat exchanger is placed in said path of air to provide said reheat function.

19. A refrigerant system comprising:

an economizer heat exchanger, said economizer heat exchanger cooling a first refrigerant stream passing from said condenser toward said evaporator, said first refrigerant stream being subcooled in said economizer heat exchanger by a tapped refrigerant which is returned toward said compressor downstream of said economizer heat exchanger, and a refrigerant return passing to said compressor downstream of said economizer heat exchanger being placed in a path of air driven by said air moving device downstream of said evaporator to provide a reheat function.

20. The refrigerant system as set forth in claim 19, wherein said tapped flow of refrigerant being returned to an intermediate compression portion in said compressor.

21. The refrigerant system as set forth in claim 19, wherein at least one flow control device selectively directs refrigerant from said tap and downstream of said economizer heat exchanger either into said path of air, or to bypass said path of air when a reheat function is not desired.

22. The refrigerant system as set forth in claim 19, wherein said economizer heat exchanger itself is placed in the path of said air driven by said air moving device

23. The refrigerant system as set forth in claim 19, wherein said refrigerant streams in said economizer exchanger is arranged in counterflow configuration

24. The refrigerant system as set forth in claim 19, wherein said refrigerant streams in said economizer exchanger is arranged in parallel flow configuration

25. The refrigerant system as set forth in claim 19, wherein said tapped flow of refrigerant is tapped upstream of the said economizer heat exchanger.

26. The refrigerant system as set forth in claim 19, wherein the said tapped flow of refrigerant is tapped downstream of the said economizer heat exchanger.

27. A method of operating a refrigerant system comprising the steps of:

(1) providing a compressor for compressing refrigerant and delivering to a condenser, a main expansion device downstream of said condenser and an evaporator downstream of said main expansion device, and an air moving device for passing air over the evaporator;

(2) providing an auxiliary heat exchanger with a first refrigerant stream being subcooled in said auxiliary heat exchanger by a second refrigerant stream that is returned to said compressor;

(3) placing a portion of said second refrigerant stream in a path of air moved by said air moving device; and

(4) operating said refrigerant system, and passing said second refrigerant stream in said path of said air, and passing air over said portion, prior to said second refrigerant stream being returned to said compressor, when reheat function is desired and bypassing said portion when reheat function is not desired.