US20100122540A1

US20100122540A1 - Thermoelectric cooler for economized refrigerant cycle performance boost

Info

Publication number: US20100122540A1
Application number: US12/597,975
Authority: US
Inventors: Michael F. Taras; Alexander Lifson
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2007-06-19
Filing date: 2007-06-19
Publication date: 2010-05-20
Also published as: HK1142387A1; CN101688706B; EP2156110A1; WO2008156482A1; CN101688706A

Abstract

A refrigerant system incorporates an economizer circuit, and a thermoelectric cooler to provide a performance boost to the conventional economized refrigerant system. A thermoelectric cooler cools the refrigerant either directly in a main refrigerant circuit, or in an economized circuit, or both.

Description

BACKGROUND OF THE INVENTION

This application relates to a refrigerant system having an economizer circuit, wherein a thermoelectric cooler provides additional cooling and a performance boost to assist the conventional economizer circuit.
Refrigerant compressors circulate a refrigerant through a refrigerant system to condition a secondary fluid. Typically, in a basic refrigerant cycle, a compressor compresses a refrigerant and delivers it to a heat rejection heat exchanger.
Refrigerant from the heat rejection heat exchanger passes through an expansion device, in which its pressure and temperature are reduced. Downstream of the expansion device, the refrigerant passes through a heat accepting heat exchanger, and then back to the compressor. As known, the heat accepting heat exchanger is typically an evaporator. The heat rejecting heat exchanger is a condenser, in subcritical applications, and a gas cooler, in transcritical applications.
One option in a refrigerant system design to enhance performance is the use of an economizer, or so-called vapor injection function. When an economizer function is activated, a portion of refrigerant is tapped from a main refrigerant stream downstream of the heat rejection heat exchanger. In one configuration, this tapped refrigerant is passed through an auxiliary expansion device, to be expanded to an intermediate pressure and temperature, and then this partially expanded tapped refrigerant passes in heat exchange relationship with a main refrigerant flow in an economizer heat exchanger. In this manner, the main refrigerant is cooled such that it will have a greater thermodynamic potential when it reaches the heat accepting heat exchanger. The tapped refrigerant, typically in a superheated thermodynamic state, is returned to an intermediate compression point in the compressor downstream of the economizer heat exchanger. As known, there are other arrangements involving economizer heat exchangers as well as flash tanks that provide similar functionality. One other option which has been recently proposed for incorporation into refrigerant systems is the use of a thermoelectric cooler. The thermoelectric cooler essentially takes advantage of specific thermoelectric properties of dissimilar semiconductor materials and is based on two phenomena—the Peltier effect and Seebeck effect concurrently taking place during operation of the thermoelectric device. The Peltier effect is associated to the release or absorption of a finite heat flux at the junction of two electrical conductors, made from different materials and kept at constant temperature, at the presence of electric current. Similarly, the Seebeck effect is related to the same arrangement, where the two junctions are maintained at different temperatures, which would create a finite potential difference, and an electromotive force that would drive an electric current in the closed-loop electric circuit. The Peltier and Seebeck effects are presented simultaneously in the thermoelectric cooler that is preferably made from the materials that have dissimilar absolute thermoelectric powers. The finite electric current passing through the two junctions triggers two heat transfer interactions with two cold and hot reservoirs kept at different temperatures. For steady thermoelectric cooler operation, heat fluxes associated with the two junctions should have opposite signs. If the external system maintains potential difference and drives electric current against this difference, the two junction system becomes a thermoelectric cooling device.
A typical thermoelectric cooler consists of an array of P-type and N-type semiconductor elements that act as the two dissimilar conductors. The P-type material has an insufficient number of electrons and the N-type material has extra electrons. These electrons in the N-type material and so-called “holes” in the P-type material, in addition to carrying an electric current, become a transport media to move the heat from the cold junction to the hot junction. The heat transport rate depends on the current passing through the circuit and the number of moving electron-hole couples. As an electric current is passed through one or more pairs of P-N elements, there is a decrease in temperature at the cold junction resulting in the absorption of heat from the object to be cooled. The heat is carried through the thermoelectric cooler by electron transport and released at the hot junction as the electrons move from a high to a low energy state. Although the thermoelectric devices are inherently irreversible, since heat and electric current must flow through the circuit during their operation, they do not have moving parts that makes them extremely reliable. Further, the refrigerant of the conventional vapor compression system is replaced by electrons carrying energy from a cold junction to a hot junction, created by two conductors with dissimilar absolute thermoelectric powers and connected electrically in series and thermally in parallel. To date, the use of thermoelectric coolers has only been proposed to be positioned downstream of a heat rejection heat exchanger in a conventional refrigerant cycle. Such thermoelectric coolers have never been proposed for providing an additional performance boost to an economizer cycle. Performance enhancement of economized refrigerant systems becomes especially crucial in a view of a limited capability of the economizer cycle in the air conditioning application range and continuously raising efficiency standards. Furthermore, alternate refrigerants, such as carbon dioxide operating in a transcritical regime, require extra means, in addition to the economizer function, to achieve the performance levels comparable to the performance levels of refrigerant systems charged with conventional refrigerants.

SUMMARY OF THE INVENTION

In disclosed embodiments of this invention, refrigerant systems are provided with economizer circuits. A thermoelectric cooler is operable to provide an additional performance boost to the economized refrigerant system by providing extra cooling either to an economized refrigerant flow or directly to a main refrigerant flow or both. In either case, a thermoelectric cooler can be positioned upstream or downstream of an economizer, in relation to a respective refrigerant flow. In all disclosed refrigerant system configurations, the thermoelectric cooler allows for additional cooling of the main refrigerant flow and its temperature reduction upstream of the main expansion device. Therefore, the thermodynamic cooling potential of the refrigerant flow entering an evaporator and the overall performance of the refrigerant system are increased.
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. 1A shows a first schematic.

FIG. 1B shows a second schematic.

FIG. 2A shows a third embodiment.

FIG. 2B shows a fourth schematic.

FIG. 3A shows a fifth schematic.

FIG. 3B shows a sixth schematic.

FIG. 4A is a P-h diagram for FIGS. 1A, 1B, 2A and 2B.

FIG. 4B is a P-h diagram for FIGS. 3A and 3B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An economized refrigerant system 20 is illustrated in FIG. 1A. As known, a compressor 22 compresses a refrigerant and delivers it downstream to a heat rejection heat exchanger 24. As also known, the heat rejection heat exchanger 24 is a gas cooler for a transcritical cycle and a condenser for a subcritical cycle. From the heat rejection heat exchanger 24, the refrigerant passes through an economizer heat exchanger 26. In this embodiment, a main refrigerant flow passes through the economizer heat exchanger 26, and a tap refrigerant line 30 taps a portion of the refrigerant from a main refrigerant line 28 downstream of the economizer heat exchanger. The tap line 30 passes through an economizer expansion device 32, and then once again through the economizer heat exchanger 26. In the expansion device 32, the tapped refrigerant is expanded to an intermediate pressure and temperature, and therefore can cool the refrigerant in the main refrigerant line 28 during heat transfer interaction in the economizer heat exchanger 26. The refrigerant from the tap refrigerant line 30 passes through an injection refrigerant line 34 back to an intermediate compression point at the compressor 22.
Refrigerant in the main refrigerant line 28 downstream of the economizer heat exchanger 26 passes through a main expansion device 40, and then through a heat accepting heat exchanger (evaporator) 42. From the heat accepting heat exchanger 42, the refrigerant passes back to the compressor 22.
The economized refrigerant system described above is generally known in the art. The present invention enhances performance of this known economized refrigerant system by including a thermoelectric cooler 38 downstream of the economizer heat exchanger 26. Thermoelectric cooler 38 provides further cooling to the refrigerant in the main refrigerant line 28 by providing a thermal contact between a cold junction of the thermoelectric cooler 38 and a refrigerant in the main refrigerant line 28. Moreover, the thermoelectric cooler 38 also cools the refrigerant which is tapped into the tap refrigerant line 30, and thus provides even greater thermodynamic cooling potential for the tapped refrigerant and a higher heat transfer rate between the main refrigerant in the main refrigerant line 28 and tapped refrigerant in the tap refrigerant line 30, in the economizer heat exchanger 26. The thermoelectric cooler 38 may be of any type or configuration known in the art. For instance, the hot junction of the thermoelectric cooler 38 may be cooled by an air stream. In embodiments, the components may be positioned such that a single air moving device moves air over both the gas cooler 24 and the thermoelectric cooler 38 to reject heat from both components. Alternatively, separate air moving devices can be utilized. Obviously, other heat rejection means from the hot junction of the thermoelectric cooler 38 are also feasible. The attachment of the cold junction of the thermoelectric cooler 38 to the main refrigerant line to provide sufficient thermal contact can be, for instance, by a mechanical contact, brazing, soldering, welding, gluing, or any other means.
Analogously to the FIG. 1A embodiment 20, the tap refrigerant line 30 for the economizer circuit can be positioned upstream of the thermoelectric cooler 38. Similar benefits can be achieved in this configuration as well.
FIG. 1B shows an embodiment 50, which is similar to the embodiment 20 depicted in FIG. 1A, other than in the location of the thermoelectric cooler 52. Here, the thermoelectric cooler 52 is positioned intermediate the economizer expansion device 32, and the economizer heat exchanger 26. In this case, the thermoelectric cooler can be made more compact, since it has to cool only a portion of refrigerant tapped into the tap refrigerant line 30. This embodiment provides higher temperature difference between a refrigerant in the main refrigerant line 28 and a refrigerant in the tap refrigerant line 30, leading to a higher heat transfer rate in the economizer heat exchanger 26. Obviously, the thermoelectric cooler can also be positioned between the tap point 33 and the economizer expansion device 32.
FIG. 2A shows yet another embodiment 60. In the embodiment 60, a portion of refrigerant is tapped into the refrigerant line 30 upstream of the economizer heat exchanger 26, and passed through a thermoelectric cooler 62 prior to reaching the economizer expansion device 32. Again, refrigerant in the tap refrigerant line 30 will be colder, and thus will be able to cool the refrigerant in the main refrigerant line 28 to an even greater extent, in the economizer heat exchanger 26.
FIG. 2B shows an embodiment 70 that is similar to the embodiment 60 of FIG. 2A, other than locating the thermoelectric cooler 72 downstream of the economizer expansion device 32.
FIG. 3A shows still another embodiment 80 where the economizer heat exchanger 26 of previous embodiments is replaced by a flash tank 44. Economized systems with a flash tank are known in the art. The flash tank separates liquid and vapor refrigerant phases, with the liquid phase flowing through the main circuit and the vapor phase delivered to an intermediate compression point in the compressor 22. A thermoelectric cooler 46 is placed between the economizer expansion device 32 and the flash tank 44 to provide extra liquid content in the refrigerant mixture flowing into the flash tank 44 and an additional performance boost to the refrigerant system 80.
FIG. 3B shows another embodiment 90, which is similar to the embodiment 80 of FIG. 3A, with the exception that a thermoelectric cooler 48 is positioned between the flash tank 44 and the main expansion device 40. In this case, rather than increasing the liquid content in the two-phase mixture flowing into the flash tank 44, the thermoelectric cooler 48 further cools the liquid exiting the flash tank 44, thus enhancing performance of the refrigerant system 90.
The benefits of providing a thermoelectric cooler at the locations as shown in this application can be seen from the P-h diagrams of FIGS. 4A and 4B. In general, the P-h diagram depicted in FIG. 4A shows additional capacity provided by a thermoelectric cooler for the refrigerant systems having an economizer circuit containing an economizer heat exchanger, as shown in FIGS. 1A, 1B, 2A and 2B. Similarly, FIG. 4B shows benefits provided by a thermoelectric cooler for the refrigerant systems including a flash tank, as exhibited in FIG. 3B.
The economized refrigerant systems incorporating thermoelectric coolers disclosed in this invention can be used in both conventional subcritical applications, as shown in FIG. 4A, and transcritical applications, as exhibited in FIG. 4B. Since transcritical applications, such as those employing carbon dioxide as a refrigerant, are inherently less efficient, the thermoelectric cooler would be the most advantageous in those applications. Also, since the augmentation provided by an economizer cycle for air conditioning applications is limited by a reduced pressure ratio, the thermoelectric cooler integration would provide additional benefits for air conditioning applications, especially in a view of continuously raising efficiency standards and diminishing returns of standard performance enhancement methods.
Furthermore, the thermoelectric cooler can provide additional flexibility in unloading economized refrigerant systems. Turning the thermoelectric device on will supply additional capacity to compensate for thermal load demand in the conditioned space. On the other hand, switching the thermoelectric device off will allow for unloading of the refrigerant system when only part-load capacity is required to meet the space demand.
It should be pointed out that many different compressor types could be used in this invention. For example, scroll, screw, rotary, or reciprocating compressors can be employed. The refrigerant systems that utilize this invention may have various options and enhancement features, such as, for instance, tandem components, reheat circuits, intercooler heat exchangers, etc., and can be used in many different applications, including, but not limited to, air conditioning systems, heat pump systems, marine container units, refrigeration truck-trailer units, and supermarket refrigeration systems.
While 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 it downstream to a heat rejection heat exchanger, the refrigerant from the heat rejection heat exchanger passing through a main expansion device, and then to a heat accepting heat exchanger before being returned to said compressor;

an economizer circuit incorporated between the heat rejection heat exchanger and the main expansion device, said economizer circuit including an economizer and an economizer expansion device; and

a thermoelectric cooler provided to enhance performance of the economized refrigerant system.

2. The refrigerant system as set forth in claim 1, wherein the thermoelectric cooler is associated with the economizer circuit.

3. The refrigerant system as set forth in claim 1, wherein said refrigerant system operates at least for a portion of the time in a subcritical cycle.

4. The refrigerant system as set forth in claim 1, wherein said refrigerant system operates at least for a portion of the time in a transcritical cycle.

5. The refrigerant system as set forth in claim 1, wherein said refrigerant system utilizes carbon dioxide as a refrigerant.

6. The refrigerant system as set forth in claim 1, wherein the thermoelectric cooler comprises two semiconductor materials having dissimilar absolute thermoelectric powers.

7. The refrigerant system as set forth in claim 1, wherein the thermoelectric cooler comprises at least one pair of P-type and N-type semiconductor materials.

8. The refrigerant system as set forth in claim 1, wherein the thermoelectric cooler is associated with the main refrigerant circuit.

9. The refrigerant system as set forth in claim 1, wherein said economizer is a heat exchanger type economizer.

10. The refrigerant system as set forth in claim 9, wherein the thermoelectric cooler is associated with the main refrigerant circuit and positioned downstream of the economizer heat exchanger.

11. The refrigerant system as set forth in claim 10, wherein a tap refrigerant line for tapping a portion of refrigerant to an economizer circuit is positioned downstream of the thermoelectric cooler, and then passed through the economizer heat exchanger.

12. The refrigerant system as set forth in claim 10, wherein a tap refrigerant line for tapping a portion of refrigerant to an economizer circuit is positioned upstream of the thermoelectric cooler, and then passed through the economizer heat exchanger.

13. The refrigerant system as set forth in claim 9, wherein a tap refrigerant line for tapping a portion of refrigerant to an economizer circuit is positioned downstream of the economizer heat exchanger, and then passed through the thermoelectric cooler that is associated with the economizer circuit and positioned between the economizer expansion device and economizer heat exchanger.

14. The refrigerant system as set forth in claim 9, wherein a tap refrigerant line for tapping a portion of refrigerant to an economizer circuit is positioned downstream of the economizer heat exchanger, and then passed through the thermoelectric cooler that is associated with the economizer circuit and positioned between a tap point and the economizer expansion device.

15. The refrigerant system as set forth in claim 9, wherein a tap refrigerant line for tapping a portion of refrigerant to an economizer circuit is positioned upstream of the economizer heat exchanger, and then passed through the thermoelectric cooler on its way to the economizer heat exchanger.

16. The refrigerant system as set forth in claim 15, wherein the thermoelectric cooler is positioned upstream of an economizer expansion device and downstream of a tap point.

17. The refrigerant system as set forth in claim 15, wherein the thermoelectric cooler is positioned downstream of an economizer expansion device and upstream of the economizer heat exchanger.

18-20. (canceled)

21. The refrigerant system as set forth in claim 1, wherein a hot junction of the thermoelectric cooler is cooled by one of air, water or glycol solution.

22. The refrigerant system as set forth in claim 1, wherein an air moving device for moving air over the hot junction of the thermoelectric cooler is positioned such that it also moves air over the heat rejection heat exchanger.

23. The refrigerant system as set forth in claim 1, wherein the thermoelectric cooler is used for unloading of the refrigerant system.

24-46. (canceled)