Refrigeration – Structural installation – With electrical component cooling
Reexamination Certificate
2000-09-12
2001-10-23
Doerrler, William (Department: 3744)
Refrigeration
Structural installation
With electrical component cooling
C062S267000, C165S104330, C361S701000
Reexamination Certificate
active
06305180
ABSTRACT:
This invention relates to a cooling system for use in cooling electronic equipment which includes electronic units mounted in racks. Such units typically have a ventilated casing and a fan for cooling the components in the casing, but when several units are stacked closely on racks, the usual ventilation is not effective and some units can become overheated and fail. The invention is directed to dealing with this problem.
In the past, analogs electronic circuitry was more openly constructed so that it could be cooled when forced air was supplied to the room in which it was installed. Therefore, when such analog equipment was installed on racks, it could be cooled by cooling air in the room in which the rack or racks were installed. However, with the trend towards greater u se of digital equipment, digital electronic circuitry is often now housed in units of a modular construction, each of which usually includes a casing of a modular size (such as 600mm.×500 mm), designed to fit into a corresponding space in a rack, the rack housing a column of such electronic units, mounted one above the other, and several racks being positioned side by side in a room which is normally temperature controlled. The electronic units and racks are designed as neat columns and rows, so that the front panels are flush with one another. Whilst this provides a more aesthetic appearance, at least some of the electronic units are then susceptible to overheating, as will be explained in more detail below.
Generally speaking, in dividual electronic units contain components which generate heat when the unit is supplied with electrical power. However, such electronic units are adapted to be cooled and maintained at a safe operating temperature by “on-board” air cooling means including an inlet and outlet in the casing, and an internal fan for inducing a flow of cool ambient air from the inlet to the outlet which flows over the components. Whilst such air cooling means is satisfactory for individual electronic units when located in free air, a problem of overheating can occur when the electronic units are stacked closely together on adjacent racks. This overheating can occur despite gaps between adjacent racks and despite providing a rear air space behind the racks. The rear air space is normally much larger than the intermediate space between the racks, because it accommodates cabling, but these air spaces do not provide a reliable way of cooling rack mounted electronic units (especially digital) since not enough air flow can take place.
The latter problem is aggravated by the increasing number of racks, positioned side by side, in the same room and also by reducing the width of the air gaps between racks (to conserve space). For example, whilst a column of electronic units mounted in a first rack are closest to the incoming ambient “cold” air and can be sufficiently cooled, the air heated by passage through each of these units can rise in temperature by some 5° to 10° C. Whilst this heated air can escape from the air outlets of the electronic units in the first tack into the gap between the racks, if the air inlets of the electronic units in the second adjacent rack are positioned at the same modular height as the air outlets of the electronic units in the first rack, then the fans in the units of the second rack can induce this heated air (rather than colder ambient air from the side air spaces or rear air spaces) which then flows into the downstream units and causes the air temperature to rise. This occurs with electronic units which are positioned at the same modular heights in every pair of adjacent racks, whereby the air temperature rises progressively and cumulatively from one end of the racks to the other. For example, the increase in temperature, from rack to rack, can be sufficient to produce a final exit air temperature in excess of some 50° C. As the electronic units are not intended to work at such a temperature, the life expectancy of overheated electronic units is considerably reduced, for example, sometimes to even just a few weeks. Such overheating clearly cannot be tolerated, not only due to the high cost of replacing expensive electronic units, but also due to the problems of downtime, inconvenience and refitting.
This problem cannot be solved by increasing the air throughput of the internal fans, since the heated air from an outlet of an upstream electronic unit will still be supplied to the air inlet of the adjacent downstream electronic unit and the air gaps between the adjacent racks (and the rear air space) would not allow enough cold ambient air to be drawn into the air inlets of downstream electronic units prevent some from overheating (due to the cumulative rise in temperature).
Attempts to deal with this problem by cooling the air in the room in which the electronic units are installed have not been entirely successful. More effective cooling can be achieved by ducting cold air in channels beneath floor level, and running the channels to rear air spaces behind the electronic units in the racks. However, a rack of say ten electronic units may generate about 1 kilowatt of heat, whereby 10 kilowatts of heat would be produced by the electronic units in 10 adjacent racks. Due to space limitations, only narrow gaps are left between adjacent racks and this creates too much fluidic impedance for efficient cooling by forced chilled air. The rear air space is often comparatively large, but it is obstructed by large amounts of cabling and it is at the rear of the electronic units, not at the sides where there is close proximity between upstream air outlets that face downstream air inlets when modular electronic units are stacked at corresponding heights. Therefore, whilst overheating can be reduced by ducting cold air via floor voids, it has proved to be an unreliable method. Moreover, over-cooling ambient air is inefficient.
A problem facing the invention is not only to cool individual electronic units by a required amount, but also to provide uniform cooling of many electronic units in several adjacent racks. For example, electronic units designed to operate at room temperature may ideally be maintained at a generally uniform ambient temperature within the range of 20° to 24° C. Whilst it may be comparatively simple to maintain racks of upstream electronic units at such a temperature, since they are first in receiving in coming cool air, the problem remains of maintaining a sufficient cooling from rack to rack since downstream electronic units are more susceptible to overheating. Moreover, it is necessary to avoid overcooling of upstream electronic units, since this could give rise to the problems of condensation.
The problem faced by the invention is to provide an inexpensive but efficient method of coolinlg rack mounted electronic units which aims to provide a predetermined and substantially uniform operating temperature for the electronic units in adjacent racks.
The invention solves this problem by providing a cooling system for electronic units mounted in racks, each of said units having a casing with an air inlet, an air outlet and a device for inducing a flow of ambient air from the inlet to the outlet to cool the contents of the electronic unit;
the cooling system comprising at least one chiller unit for location between adjacent upstream and downstream racks, the chiller unit having means for connection to a heat extraction device so that when the chiller unit receives air heated in transit through one or more units in an upstream rack, beat is removed from the air by the chiller unit before it is returned to ambient.
The chiller unit can be constructed in any way which enables the heat to be extracted from a heated air stream and thereby remove heat from the rack mounted electronic equipment. Devices which can achieve this are usually termed “heat sinks”. They can include a reservoir of coolants, the reservoir having walls with a large surface area to encourage heat transfer. This surface area can be augmented by fins or equivalent surface formation either attached to or
Fields Simon David
Holland Michael James
Miller David Jonathan
Sams Ian James
British Broadcasting Corporation
Doerrler William
Dubno Herbert
Jones Melvin
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