WO2002037919A1

WO2002037919A1 - Climate control of an outdoor cabinet

Info

Publication number: WO2002037919A1
Application number: PCT/SE2001/002261
Authority: WO
Inventors: Klas Hedberg; Anders Lundgren
Original assignee: Emerson Energy Systems AB
Current assignee: Vertiv Sweden AB
Priority date: 2000-10-30
Filing date: 2001-10-17
Publication date: 2002-05-10
Anticipated expiration: 2003-04-30
Also published as: SE0003950L; AU2001296148A1; SE519476C2; SE0003950D0

Abstract

The present invention relates to an outdoor cabinet (1) housing electrical equipment (27). The cabinet comprises two substantially concentrically arranged casings (23, 33) forming an intermediate space (35). This space is used as a duct for an external air flow. An external air inlet (15) and a heat exchanger unit (57) is arranged in a door (11) of the cabinet and at least one external air fan (71) is arranged for blowing air into the space. External air outlets (17) are arranged at a side of the cabinet opposite the door side (11). Thus an external air flow entering the cabinet through the external air inlet (15) has to travel a long distance until it reaches the external air outlets (17). Hereby, sound generated by the fan motion (71) is effectively damped. At the same time the external air flow inside the duct (35) is removing the heat contribution due to solar radiation.

Description

Climate control of an outdoor cabinet

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an outdoor cabinet housing electrical, heat generating equipment.

DESCRIPTION OF RELATED ART

Telecommunication equipment and other electrical equipment housed in outdoor cabinets such as base station cabinets generate heat during operation. Unless this heat is removed the electrical equipment will become overheated, which can jeopardise function and performance of the base station. To this end the electrical equipment need to be cooled. Forced convection is normally utilised, i.e. fan controlled air flow(s) carry away rejected and excessive heat, thereby maintaining a proper temperature within the closed cabinet.

One way of cooling the electrical equipment is to employ a heat exchanger unit mounted in the door of the cabinet. Internal and external air flows are passing through the heat exchanger unit on mutual separated sides. The internal air flow is circulated within the cabinet absorbing heat generated by the electrical equipment, which is transferred to the external air flow inside the heat exchanger unit, which in '■. turn forwards it to the ambient atmosphere outside the cabinet. Inlet and outlet lou- vres are arranged in the door admitting the external air flow to enter and exit the heat exchanger unit, while internal and external air fans are ensuring and maintaining the internal and the external air flows through the heat exchanger unit.

GB 2 277 767 shows such a base station cabinet. However, the external air fan is arranged in the vicinity of the outlet louvre. Thus, sound caused by the fan motion is transmitted to the cabinet surroundings. This is usually perceived as noise pollution and is considered as a serious problem, since base station cabinets are frequently located in densely built-up areas.

Normally, not only the heat rejection from electrical equipment has to be taken into consideration when designing an outdoor cabinet, but also the contribution due to solar radiation. The solar radiation is heating the cabinet walls and the heat is transferred into the interior of the cabinet putting great demands upon the cooling. A common solution to this problem is to provide the cabinet walls with insulation material as well as further increase the air flows through the cabinet.

However, an increased air flow make the noise pollution grow worse.

Furthermore, if insulation material or fans with greater capacity are required the total cost for the cabinet increases.

SUMMARY

The present invention seeks to overcome the above mentioned drawbacks.

Thus, an object of the present invention is to provide an outdoor cabinet having a less noisy operation mode, while an appropriate temperature within the cabinet is maintained.

'■• This object is accomplished by means of an outdoor cabinet housing electrical, heat generating equipment, which comprises a first casing for said electrical equipment; a door mounted to the cabinet providing access to the first casing; a heat exchanger unit arranged in, and supported by the door; an internal air duct system extending through the electrical equipment and being in flow communication with a first side of the heat exchanger unit; at least one internal air fan arranged for circulation of an internal air flow within the internal air duct system; an external air duct system, separated from the internal duct system, being in flow, communication with a second side of the heat exchanger unit; at least one external air fan arranged for transfer of an external air flow within the external air duct system from an external air inlet, via the heat exchanger unit, to external air outlets; wherein said internal and external air flows are adapted to co-act in a heat exchanging manner inside the heat exchanger unit for controlling the temperature within the first casing, so as to maintain function and performance of the electrical equipment. The outdoor cabinet is characterised in that said external duct system is defined in a space between said first casing and a second casing surrounding the first casing; the at least one external air fan is arranged downstream the heat exchanger unit for blowing air into the external air duct system; and the external air outlets are arranged on a side opposite the door side.

Since the cabinet is provided with two substantially concentrically arranged casings a gap is formed between them, which gap surrounds the electrical equipment on almost all sides. Using this gap as a duct for an external air flow heat exchange is not only accomplished inside the heat exchanger, but also through convection between the external air flow and the second casing (heat exchange is certainly also accomplished between the external air flow and the first casing, but is more or less insignificant in comparison with the heat exchange accomplished in the heat exchanger unit).

Thus, the heat due to the solar radiation is not transferred into the cabinet, but is taken care of by the external air flow, which remove the heat to the ambient atmosphere. At the same time the sound due to the external air fan motion has to travel a '■ long way through the duct until it reaches the external air outlets. Hereby, the sound is absorbed and damped by the walls, so the sound transmitted to the cabinet surroundings is substantially reduced compared to the prior art solution, where the external air fan is located in close proximity to the external air outlets "facing" the exterior of the cabinet. The heat exchanger unit is also an obstacle to the sound transmission from the fan to the external air inlet, since the at least one external air fan is arranged downstream the heat exchanger unit. Preferably, a plurality of external air fans are arranged vertically on top of each other. Hereby, the external air flow is uniformly distributed in the external air duct system, which secures an uniform cooling.

Suitably, the external air duct system is adapted to provide a curved path for the external air flow downstream the at least one external air fan and/or the external air duct system is provided with sound absorbing material. Hereby, the sound transmitted to the cabinet surrounding is even more subdued.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. la is a perspective front view of an outdoor cabinet according to the present invention;

Fig. lb is a perspective rear view of the outdoor cabinet in fig. la;

Fig. 2 shows an interior view of the outdoor cabinet in fig. la-b;

Fig. 3a is a schematic cross-sectional side view of the outdoor cabinet in fig. 2 showing an air flow in an internal air duct system;

Fig. 3b is a schematic cross-sectional top view of the outdoor cabinet in fig. 3a showing the air flow in the internal air duct system;

Fig. 4a is a schematic cross-sectional top view of the cabinet in fig. 3a showing an air flow in an external air duct system;

Fig. 4b is a schematic cross-sectional side view of the cabinet taken along line I-I in fig. 4a showing the air flow in the external air duct system; Fig. 4c is a schematic cross-sectional front view of the cabinet taken along line II-II in fig. 4a showing the air flow in the external air duct system;

Fig. 5a shows a partly sectioned view of a door of the cabinet having four external air fans and two internal air fans;

Fig. 5b is a sectioned view of the door in fig. 5a showing the internal and external air flow through the heat exchanger unit.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. l and lb show a front view and a rear view, respectively of an outdoor cabinet 1 intended for use in a telecommunication system. The cabinet 1 is adapted to accommodate electrical, heat generating equipment, such as telecommunication equipment or the like. The cabinet comprises two outer side walls 3, 5, an outer rear wall 7, an outer roof 9 and a door 11 forming a weather resistant outer casing, later referred to as a second casing. The door 11 is mounted to the cabinet 1 by means of not shown hinges, and is pivotable about a vertical hinge axis, so as to be openable and closable, thereby permitting access to the electrical equipment. A knob 13 or a handle is attached to the door to facilitate opening and closing of the door.

Front side louvres or air inlets 15 are arranged in the door 11 to admit an external air flow to enter the cabinet 1. These external air inlets 15 are arranged vertically at one v long side of the door, in the vicinity of, and in parallel with a not shown vertical hinge axis. The outer rear wall 7 is provided with vertically arranged rear side louvres or air outlets 17. These external air outlets 17 admit the external air flow, entering the cabinet via the external air inlets, to exit the cabinet. The roof 9 is protruding from the outer rear wall of the cabinet, approximately 50 mm, thereby creating an overhung 19. A lower edge part of this overhung or protruding portion has not shown openings, which also serve as an outlet for the external air flow. This feature is further explained with reference to fig.4b. The cabinet is moreover ar- ranged on a mounting base 21, so as to be firmly secured to the ground, and to facilitate opening and closing of the door without interference with the ground.

Fig. 2 through 3 shows interior views of the outdoor cabinet. The interior of the cabinet comprises an inner rack 23, which is provided with slots or shelves 25 adapted to accommodate electrical, heat generating equipment, further referred to as electrical units 27. The electrical units are vertically stacked on top of each other within the slots, thereby creating a horizontal space between each electrical unit 27. During operation heat is generated by the electrical units 27, which has to be re- moved to avoid overheating, so as to maintain function and performance of the electrical units.

The inner rack constitutes a first casing 23, which houses and completely surrounds the stacked electrical units on all sides except at a front side 31 facing the door. A second casing 33 comprised by the outer rear wall 7, the two outer side walls 3, 5 and the outer roof 9, are surrounding the first casing on a small distance. Accordingly, an intermediate space 35 or gap is defined between the first 23 and the second 33 casing. This space 35 is adapted to work as an external air duct system 35 for the external air flow, which will be more exhaustively explained later with reference to fig.4a-c.

A radial fan 37 is, as shown in fig. 3a, arranged above each electrical unit 27 and is adapted to remove heat generated by the electrical units and transfer it to a continu- ' ous internal duct system 39 having air inlets 41 and an air outlet 43 arranged at the front side 31 of the electrical units. The air outlet 43 is arranged above the air inlets 41. The internal air duct system 39 extends from the air inlets 41 and passes by the electrical units 27 to a rear duct portion 45, arranged between a rear inner wall 47 of the first casing 23 and a rear side 48 of the electrical units. Further, the rear duct portion 45 connects to an upper duct portion 49, arranged between a ceiling of the first casing 23 and the electrical units, which finally debouches at the air outlet 43. The air inlets 41 and the air outlet 43 are, when the door 11 of the cabinet is closed, in flow communication with corresponding openings 51, 53 arranged in the door. These openings 51, 53 are constituted by an upper air intake 53, in flow communication with the air outlet 43 and two lower exhaust openings 51, in flow communi- cation with the air inlets 41 , via a space 55 in front of the rack.

The door 11 is supporting a heat exchanger unit 57 through which an internal air flow and a not shown external air flow circulate, which flows are interacting in a heat exchanging manner on mutually separated, first and second sides of the heat exchanger unit. The function of the heat exchanger unit will be more detailed explained with reference to fig. 5a-b. The external air flow is taken from the ambient atmosphere outside the cabinet through the external air inlets. The internal air flow is comprised from the air heated by the electrical units 27 and which is circulated inside the cabinet.

As can be seen from fig. 3a-b also the internal air flow within the cabinet is shown. The direction of the internal air flow is indicated by the arrows. A thick arrow indicates a cool air flow, while a thin arrow indicates a less cool air flow. Heat generated by the electrical units 27 is by means of the internal air fans 37 transferred to the rear duct portion 45, where it rises towards the ceiling. It leaves the cabinet 1 through the upper air outlet 43 and the thus heated air flow enters the heat exchanger unit 57 inside the door through the upper air intake 53 and the heat is emitted inside the heat exchanger unit 57, thus absorbed by the external air flow, which ' forwards it to the ambient atmosphere. Two exhaust fans 59 exhaust the thus cooled internal air flow, when leaving the heat exchanger unit 57, into the space 55 defined between the door 11 and the front side 31 of the electrical units 27. This cooled internal air flow is entering the air inlets 41, and will once again absorb heat generated by the electrical equipment. This closed loop behaviour is continuously repeated during operation. A not shown sealing strip or door gasket is mounted to a front edge of the first casing 23 and is adapted to seal against the door 11, when the door is closed, so as to separate the interior of the first casing 23 from the external air duct system 35. In this way the interior of the first casing is protected from the affection of airborne particles as well as moisture entering the external air inlets.

Referring now to fig. 4a-c where the external air duct system is shown. As mentioned earlier the external air duct system 35 is formed by the intermediate space between the first and the second casing 23, 33, which extends from the external air inlets 15, arranged in the door 11 , to the external air outlets 17 arranged in the outer rear wall 7 of the second casing 33. The intermediate space 35 comprises a side intermediate space 61 having an inlet 63 and a rear intermediate space 65 having the external air outlets 17 as indicated by fig. 4a, but also by a top intermediate space 67 defined between the outer roof 9 and the ceiling of the first casing 23.

The inlet 63 of the side intermediate space 61 is arranged at the front side 31 of the cabinet facing the door 11 and is in flow communication with a corresponding fan outlet 69 arranged in the door 11. Four radial fans 71 are mutually vertically arranged on top of each other in the door 11 downstream the heat exchanger unit 57 and are adapted to blow external air, via the inlet 63, into the side intermediate space 61 for circulation of the external air flow.

Accordingly, during operation the radial fans 71 draw external air from the ambient ' atmosphere, via the external air inlets 15, through the heat exchanger unit 57. This is indicated by the arrows, where a thick arrow indicates a cool air flow, while a thin arrow indicates a less cool air flow. Inside the heat exchanger unit 57 heat from the internal air flow is absorbed by the external air flow, which air flow is exhausted into the side intermediate space 61 via the inlet 63. The external air flow is deflected substantially perpendicularly to the left before it arrives to the rear intermediate space 65, thus providing a curved path for the external air flow downstream the external air fans. When the external air flow reaches the external air outlets 17 it is ex- hausted to the ambient atmosphere. An external air flow is also passing through top intermediate space 67 between the outer roof 9 and the ceiling as indicated in fig. 4b-c. The external air flow passing through the top intermediate space 67 exits the cabinet through the openings arranged in the protruding portion 19 of the outer rear wall 7, as mentioned earlier.

Fig. 5a is a partly sectioned view of the door 11 showing the fan outlet 69, intended for the external air flow, together with the radial fans 71. It can be appreciated that the radial fans 71 are vertically arranged on top of each other at one side of the door. Moreover, the exhaust fans 59 intended for the internal air flow as well as the upper air intake 53 in the internal air duct system are also shown.

Fig. 5b is a sectioned view of the door 11 showing the heat exchanger unit 57 as well as the internal and the external air flow through it. The heat exchanger unit 57 is in the form of four cross-flow heat exchangers, having first 73 and second 75 sides, respectively. The first side 73 is intended for the internal air flow, while the second side 75 is intended for the external air flow. Accordingly, the internal duct system 39 is in flow communication with the first side 73 of the heat exchanger unit, while the external air duct system is in flow communication with the second side 75 of the heat exchanger unit. The external air flow passes through the heat exchanger unit 57 substantially horizontally, while the internal air flow passes through the heat exchanger unit substantially vertically from top to bottom. This is indicated by arrows.

Furthermore, the internal air flow is divided into two sub-internal air flows, each passing through two of the heat exchangers, thus arranged in series. The external air flow, on the other hand, is divided into four sub-external air flows, each passing through one of the heat exchangers, thus arranged in parallel. Due to this arrangement the heat exchanger unit can be made in a smaller size, i.e. fit into a door hav- ing a less thickness, while maintaining a good cooling capacity. Even though the invention has been described with reference to base station cabinets to be employed in a telecommunication system it is conceivable to use the cabinet with other electrical equipment and for other purposes, such as cabinets housing rectifier equipment in a power supply system.

The intermediate space or external air duct system is preferably provided with sound absorbing material for suppressing noise caused by the radial fans. While the fans are not "seeing" the external air inlets and outlets the noise of the fans are even more suppressed.

The external air duct system may also be provided with labyrinth means forming a curved path for the air flow.

It is of course also conceivable to use a different amount of fans than four, and the invention is not restricted to the use of cross flow heat exchangers, both counter flow heat exchangers and parallel flow heat-exchanger are possible.

Claims

1. An outdoor cabinet (1) housing electrical, heat generating equipment (27), comprising:

- a first casing (23) for said electrical equipment (27);

- a door (11) mounted to the cabinet providing access to the first casing (23);

- a heat exchanger unit (57) arranged in, and supported by the door (11);

- an internal air duct system (39) extending through the electrical equipment (27) and being in flow communication with a first side (73) of the heat exchanger unit;

- at least one internal air fan (37, 59) arranged for circulation of an internal air flow within the internal air duct system (23);

- an external air duct system (35), separated from the internal duct system (23), being in flow communication with a second side (75) of the heat exchanger unit;

- at least one external air fan (71) arranged for transfer of an external air flow within the external air duct system (35) from external air inlets (15), via the heat exchanger unit (57), to external air outlets (17);

said internal and external air flows being adapted to co-act in a heat exchanging manner inside the heat exchanger unit (57) for controlling the temperature within the first casing, so as to maintain function and performance of the electrical equipment,

characterised in that - said external duct system (35) is defined in a space between said first casing (23) and a second casing (33) surrounding the first casing;

5 - said at least one external air fan (71) is arranged downstream the heat exchanger unit (57) for blowing air into the external air duct system (35); and

- said external air outlets (17) are arranged on a side opposite the door side (11).

i 0

2. Outdoor cabinet according to claim 2, wherein a plurality of external air fans (71) are arranged vertically on top of each other.

3. Outdoor cabinet according to any of claim 1-2, wherein said external air duct system (35) is adapted to provide a curved path for the external air flow down-

15 stream said at least one external air fan (71).

4. Outdoor cabinet according to claim 3, wherein said curved path is comprised by at least one substantially right-angled curve.

!0 5. Outdoor cabinet according to any of claim 1 -4, wherein said heat exchanger unit (57) comprises a plurality of cross-flow heat exchangers, said internal air flow being adapted to serially pass the cross-flow heat exchangers in a vertical direction, while the external air flow being adapted to parallelly pass the cross-flow heat exchanger in a horizontal direction.

!5

6. Outdoor cabinet according to any of claim 1-5, wherein said external air duct system is provided with sound absorbing material.