GB2409510A

GB2409510A - Heat exchanger for an air conditioning system

Info

Publication number: GB2409510A
Application number: GB0505751A
Authority: GB
Inventors: Malcolm Heys
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2001-05-17
Filing date: 2001-05-17
Publication date: 2005-06-29
Anticipated expiration: 2021-05-17
Also published as: GB2375596B; GB2375596A; GB2409510B; GB0505751D0; GB0112032D0

Abstract

A heat exchanger (14) for an air conditioning system comprising a first manifold (40); a second manifold (42) spaced from, and substantially parallel to, the first manifold; a plurality of substantially parallel tubes (44) extending between and fluidly connecting the first and second manifolds; an inlet (46) connected to one of the manifolds; an outlet (48) connected to one of the manifolds; at least one separation wall (50) positioned inside each manifold such that fluid normally flows though the heat exchanger with at least three passes; and bypass means (52) associated with one of the manifolds which, when open, fluidly connects said one manifold with the inlet to reduce the number of passes by at least one. The system has a reduced flow path through the heat exchanger during heat pump mode of the air conditioning system for improved efficiency and reduced ice formation.

Description

24095 1 0 lIEAT EXCHANGER FOR.N AIR CO - ITIOMNG SYSTEM

Technical Field

The present invention relates to heat exchanger for an air conditioning system for the passenger compartment of a motor vehicle, and more particularly to a heat exchanger for an air conditiorng shyster wll-,,ch can provide both heating and cooling for the passenger compartment.

Background of the Invention

Air conditioning systems for the passenger compartments of motor vehicles are well known. In general, these systems comprise an inside heat exchanger (located within, or associated with, the passenger compartment) and an outside heat exchanger (located outside the passenger compartment). A pair of fluid passages connect the heat exchangers to allow the circulation of fluid through the heat exchangers. An expansion device is positioned in one of the fluid passages. A compressor and accumulator/dryer is positioned in the other fluid passage. When fluid is pumped by the compressor through the outside heat exchanger, the expansion device, the inside heat exchanger and the accumulator/diyer in succession, air passing through the inside heat exchanger is cooled as the air flows into the passenger compartment. When fluid is pumped in the reverse direction through the inside heat exchanger, the expansion device, the outside heat exchanger and the accumulator/dryer in succession, air passing through the inside heat exchanger is heated as the air flows into the passenger compartment. A reversing valve is positioned in the other fluid passage to provide the required flow direction for the fluid. A disadvantage of this known system is that, in heat pump mode, a large pressure drop can occur in the outside heat exchanger which results in low refrigerant flow to the compressor. This is especially known in systems having dual inside heat exchangers which, necessarily, require an oversized outside heat exchanger. This can result in poor performance during heat pump mode. Also, during heat pump mode, ice can form on the outside heat exchanger which reduces the efficiency of the heat exchanger. Removing the ice during a 'de-ice' mode is difficult in certain areas of the outside heat exchanger as the refrigerant fluid temperature in these areas approaches ambient temperature.

US-A-5174373 and US-A-5826649 describe heat exchangers where the flow path of the refrigerant fluid is redistributed to reduce pressure drop or to improve the refrigerant quality (that is, refrigerant fluid flow upwards) through the passes through the heat exchanger.

Sururnarv of the Invention It is an object of the present invention to provide a heat exchanger for an air conditioning system in which the above mentioned disadvantages are overcome, or their effects are reduced.

A heat exchanger in accordance with the present invention for an air conditioning system comprises a first manifold; a second manifold spaced from, and substantially parallel to, the first manifold; a plurality of substantially parallel tubes extending between and fluidly connecting the first and second manifolds; an inlet connected to one of the manifolds; an outlet connected to one of the manifolds; at least one separation wall positioned inside each manifold such that fluid normally flows through the heat exchanger with at least three passes; and bypass means associated with one of the manifolds which, when open, fluidly connects said one manifold with the chalet or the il 'et to red-ucc the number cJf passes by at 'east one.

By reducing the length of the flow path through the heat exchanger during a heat pump mode of the air conditioning system, the pressure drop through the heat exchanger is reduced, leading to a more efficient operation of the system. Also, the amount of ice formation on the heat exchanger is reduced.

Brief Description of the Drawings

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of an air conditioning system including a heat exchanger in accordance with the present invention; Figure 2 is a schematic view of the outside heat exchanger of the system of Figure 1 illustrating fluid flow in heat pump mode; and Figure 3 is a schematic view of the outside heat exchanger of the system of Figure 1 illustrating fluid flow in cooling mode.

Description of the Preferred Embodiment

Referring to Figure 1 of the drawings, the air conditioning system 10 is for use in a motor vehicle for heating or cooling the passenger compartment (not shown) of the motor vehicle. The air conditioning system comprises the usual components of a compressor 12, an outside heat exchanger 14 (in accordance with the present invention), an orifice tube or expansion device 16, an inside heat exchanger 18, and an accumulator/dryer 20. The outside heat exchanger 14 is located outside of the passenger compartment. The inside heat exchanger 18 is typically located inside the passenger compartment, although may he positioned outside the passenger compartment but still used to treat air entering the passenger compartment. A first fluid passage 22 fluidly connects the outside heat exchanger 14 with the inside heat exchanger 18 by way of the expansion device 16. A second fluid passage 2q fluidly connects the outside heat exchanger i4 wirn the inside hear exchanger 18 by way of a reversing valve 32. The compressor 12 and the accunulator/dryer 20 fluidly connect with the second fluid passage 24 by way of the reversing valve 32. The compressor 12 has a fluid outlet 26 connected to the reversing valve 32 by way of a third fluid passage 30. The compressor 12 has a fluid inlet 28 connected Lo the reversing valve 32 by way of the accumulator/dryer 20 and a fourth fluid passage 31.

During norrr.al (cooling) operation of the air conditioning system 10, the reversing valve 32 is set to allow fluid flow in the direction X such that air passing through the inside heat exchanger 18 is cooled so that the air conditioning system operates to cool the passenger compartment. In this cooling mode, the refrigerant fluid in the system 10 is pumped by the compressor 12 through the reversing valve 32, the outside heat exchanger 14, the expansion device 16, the inside heat exchanger 18, the reversing valve 32, and the accumulator/dryer 20 in succession before returning to the compressor.

When initial, supplemental, or prolonged heating of the passenger compartment is required, the reversing valve 32 is set to allow fluid flow in the direction Y such that air passing through the inside heat exchanger 18 is heated so that the air conditioning system operates to heat the passenger compartment. In this heat pump mode, the refrigerant fluid in the system 10 is pumped by the compressor 12 through the reversing valve 32, the inside heat exchanger 18, the expansion device 16, the outside heat exchanger 14, the reversing valve 32, and the accumulator/dryer 20 in succession before returning to the compressor.

The outside heat exchanger 14 is shown in greater detail in Figures 2 and 3. The outside heat exchanger 14 comprises first and second manifolds or header tanks 40, 42; and a plurality of tubes 44 fluidly cormecting the first and second manifolds. The manifolds 40, 42 are substantially parallel to one another and spaced apart. The tubes 44 are substantially parallel to one another and extend substantially perpendicular to isle rnanil-olus. First and second ports 46, 48 are formed in tile first marlifoidi at substantially the opposite ends thereof. The first port 46 is fluidly 2.S connected to the first fluid passage 22 and defines an inlet for the outside heat exchanger 14 in heat pump mode, and defines an outlet for the outside heat exchanger in cooling mode. The second port 48 is fluidly connected to the second fluid passage 24 and defines an outlet for the outside heat exchanger 14 in heat pump mode, and defines an mlet for the outside heat exchanger in cooling mode. The location of the ports 46, 48 relative to the first and second manifolds 40, 42 may be changed dependent on the required configuration for the outside heat exchanger 14. Separation walls 50 are located inside the manifolds 40, 42 to define the number of passes for the flow path for the refrigerant fluid through the outside heat exchanger 14. As shown in Figures 2 and 3, the present embodiment has three separation walls, two in the first manifold 40 and one in the second manifold 42, to define four passes for the flow path (as described in more detail below) through the outside heat exchanger 14. The present invention is applicable to an outside heat exchanger having three or more passes for the flow path.

In accordance with the present invention, bypass means 52 are provided for reducing the number of passes for the flow path through the outside heat exchanger 14 when the system 10 is in heat pump mode. In the present embodiment, the bypass means 52 comprises a bypass fluid passage 54 between the first fluid passage 22 and a bypass port 56 in the first manifold 40, with a check (one-way) valve 58 positioned in the bypass fluid passage.

The bypass port 56 is positioned between the two separation walls 50 in the first manifold 40. The present invention is applicable to other arrangements for the bypass means 52.

In Figure 2, the system 10 is in heat pump mode, and the check valve 58 is open due to the pressure of the refrigerant fluid in the first fluid passage 22. The flow path (as shown by the arrowed line) for the refrigerant fluid has two passes through the outside heat exchanger 14. Such an arrangement reduces the pressure drop through the outside heat exchanger 14 (when compared to an outside heat exchanger with no bypass means). 'finis results in higher suction temperatures and pressures at the compressor inlet 28, and therefore more mass of refrigerant fluid entering the compressor l 2.

As a result, a higher performance for the system 10 is achieved during heat pump mode. Additionally, the passes with no refrigerant fluid passing will not ice up. As these passes are normally the most difficult to de ice (achieved by a period of fluid flow in the direction X), the time for the deice mode may be reduced.

In Figure 3, the system 10 is in cooling mode, and the check valve 58 is closed due to the pressure of the refrigerant fluid in the first manifold 40. The flow path for the refrigerant fluid has four passes through the outside heat exchanger 14. The bypass means 52 therefore has little or no effect on the system 10 during cooling mode.

In the above described embodiment, the bypass means 52 comprises a bypass passage 54 and a check valve 58. The check valve 58 may be replaced by any other suitable type of valve, including a solenoid operated valve which is controlled to be open during heat pump mode, or during predetermined periods during heat pump mode. Further, the valve may positioned inside the first manifold 40 thereby avoiding the need for the bypass passage 54.

The compressor 12 is preferably an electronically variable compressor the operation of which is controlled by an electronic displacement control valve (not shown). An example of a suitable compressor and control valve is described in EP-A-0993977. The compressor 12 is preferably a wobble plate compressor. As an alternative, a swash plate compressor may be used. As a further alternative, the accumulator/dryer 20 may be locate elsewhere in the system 10. A tramway receiver/dryer may alternatively be used in the system 10. An alternative arrangement to a reversing valve 32 may be used for controlling the fluid flow direction through the system 10.

Claims

Claims 1. A heat exchanger for an air conditioning system comprising a

first manifold; a second manifold spaced from, and substantially parallel to, the first manifold; a plurality of substantially parallel tubes extending between and fluidly connecting the first and second manifolds; an inlet connected to one of the manifolds; an outlet connected to one of the manifolds; at least one separation wall positioned inside each manifold such that fluid normally flows through the heat exchanger with at least three passes; and bypass means associated with one of the manifolds which, when open, fluidly connects said one manifold with the outlet or the inlet to reduce the number of passes by at least one.
2. A heat exchanger as claimed in Claim 1, wherein the bypass means comprises a bypass passage fluidly connected between said one manifold and the outlet or the inlet; and a bypass valve positioned in the bypass passage.
3. A heat exchanger as claimed in Claim 2, wherein the said one manifold has two separation walls positioned inside thereof, the bypass passage being fluidly connected to said one manifold between the two separation walls.
4. A heat exchanger as claimed in Claim 2 or Claim 3, wherein the bypass valve is a one-way check valve.
5. A heat exchanger as claimed in Claim 2 or Claim 3, wherein the bypass valve is a solenoid operated valve.
6. A heat exchanger as claimed in Claim 1, wherein the bypass means is positioned in the said one manifold.
7. A heat exchanger as claimed in Claim 6, wherein the bypass means comprises a bypass valve.
8. A heat exchanger substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.