Abstract:
A server rack cooling system is described, aspects directed to a heat exchanger and a closed cooling air duct extending at least between the housing of the devices and the heat exchanger, which cooling air duct feeds the heated cooling air leaving the housing to the heat exchanger before it is released to the environment.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This utility patent application claims benefit under 35 U.S.C. §119 of European Patent Application Number 10 170 111.8, filed on Jul. 20, 2010. 
       TECHNICAL FIELD 
       [0002]    The invention is related to a cooling system for cooling waste heat-producing electronic devices, in particular computer racks. 
       BACKGROUND 
       [0003]    In order to assure functioning of electronic devices, these have to be cooled and the produced waste heat has to be discharged and/or dissipated. In known server racks, the cooling air is sucked in from the server room, led along the electronic devices for cooling and blown off again into the server room using a fan or a ventilator. Because of this, a high heat load develops in the server rooms of data centres due to the waste heat produced by the servers. So far, heat discharge from such rooms has been carried out by transporting the heated air. However, since air is a very bad heat conductor, very high air mass flows have to be circulated in order to achieve the necessary cooling power. Transport efficiency for the circulated air or the driving power of the ventilators, respectively, and re-cooling the circulated air by means of cooling units constitute a considerable cost factor for data centers. 
       SUMMARY 
       [0004]    A problem to be solved by the present invention is to provide a more efficient cooling for encased electronic devices, in particular for computer racks. 
         [0005]    This problem is solved by the subject-matter of the claims, wherein the subclaims define preferred embodiments of the present invention. 
         [0006]    Although the present invention is described in the following as to be used for cooling server racks, it is absolutely conceivable to cool other devices producing waste heat by means of the cooling system according to the invention. 
         [0007]    The cooling system according to the invention comprises a heat exchanger and a closed cooling air duct which feeds the heated cooling air leaving the housing into the heat exchanger before it is released to the environment and which extends at least between a housing of the devices and the heat exchanger. 
         [0008]    In other words, the heated cooling air is according to the invention no longer blown by the fan out from the device housing into the server room. Rather, the heated cooling air is directly led to a heat exchanger where the heat is extracted again from the cooling air. Only the cooled air is then blown into the server room again. 
         [0009]    Thus, the heat is according to the invention discharged directly where it is generated. The air in the server room is therefore no longer heated and thus does not need to be expensively cooled again. In this manner, energy may be saved which is necessary for transporting the air from the server room to a cooling unit and/or refrigerator and back again from the cooling unit to the server room. 
         [0010]    Another advantage of the present invention consists in that it uses the present cooling fan of the server to lead the cooling air past the heat exchanger. Thus, no fan of its own has to be provided for the cooling system according to the invention which further reduces the energy expenditure for the cooling. Of course it is conceivable to provide an additional fan in order to, for example, compensate for a higher pressure loss during flow through the heat exchanger. 
         [0011]    According to a preferred embodiment, a liquid cooling medium flows through the heat exchanger, water being particularly cost-efficient as a cooling medium, wherein it is absolutely conceivable to add additives to it such as for example anti-freeze agent. Of course, other liquid cooling media are also suitable for being employed in the cooling system according to the invention. 
         [0012]    While with hitherto existing cooling systems the air heated by the devices and transported out of the server room has to be re-cooled again by refrigerators at high energy expense before being transported back into the server room, it suffices with the present invention to re-cool the liquid cooling medium heated in the heat exchanger outside of the server room in a further heat exchanger. This may happen for example in a wet or dry cooling tower which makes employment of energy-expensive refrigerators superfluous almost all-the-year. 
         [0013]    According to a further preferred embodiment, the cooling medium flows through the heat exchanger transversely to the flow direction of the heated air. It therefore is a matter of a cross flow heat exchanger. Experiments have shown that this is a convenient design for the present invention. 
         [0014]    With hitherto existing server racks, cooling air flows through them in their horizontal direction while with a particularly preferred embodiment of the present invention, the heat exchanger is provided at the rear side of the device housing or the server rack, respectively, at which the heated cooling air emanates. Because the density of the cooling medium in the heat exchanger decreases with increasing temperature and the cooling medium strives to rise upward in a vertical direction, transport of the cooling medium due to its natural buoyancy is supported with a vertical arrangement of the cooling medium duct. Thus, the cross flow design is the most suitable one with a heat exchanger arranged at the server rack on the rear side. It is, however, also conceivable to arrange the heat exchanger at another place in the device housing, such as for example at the upper or lower side of the server rack, such that counterflow or co-current designs may turn out to be suitable. It is further conceivable to provide the heat exchanger at a place different from the device housing or the server rack, respectively, as long as the heated cooling air escaping from the device housing is transported to the heat exchanger on the direct way in order to be released in a re-cooled state into the server room only after passing the heat exchanger. For this, for example, a cooling air tube extending from the server rack to the heat exchanger would be conceivable. 
         [0015]    Preferably, capillary tubes are employed with the heat exchanger according to the invention for leading the cooling medium. In this manner, the heat exchanger generates only a very low pressure loss in the cooling air flow so that a sufficient cooling air flow can be maintained only by the fan present in the server and a separate fan for compensation of the pressure loss in the heat exchanger is not necessary. Just as advantageously, the heat exchanger with capillary tubes is not prone to soiling and therefore easy to maintain. 
         [0016]    Further, plural capillary tubes may be integrated into a composition, wherein the capillary tubes can be positioned or switched in parallel and therefore have a common intake and a common drain and/or outlet. It would, however, also be conceivable to switch the capillary tubes serially so that the cooling medium passes through them one after the other. 
         [0017]    Furthermore, a planar design of the capillary tubes composition is preferred in which the capillary tubes of one composition extend in parallel in a plane. Such a design is also called a capillary tube mat. 
         [0018]    The heat exchanger according to the invention can according to a preferred embodiment have plural such compositions which are integrated to form a register, wherein it is possible to switch individual ones, plural ones or all of the compositions in parallel and/or serially. A parallel switching of the compositions is preferred, though, such that the cooling medium having equal temperature passes through them. Also preferred is an alignment of the compositions transverse to the flow direction of the cooling air such that the cooling air flow passes the individual compositions one after the other after leaving the server rack. However, an alignment of the compositions would be just as conceivable in which the cooling air flows against the individual compositions in parallel, flow of the cooling air thus running in the plane of the individual compositions. 
         [0019]    A further embodiment of the cooling medium duct, in particular the capillary tubes, comprise a plastic material, in particular polypropylene (PP), polyethylene (PE), polyester or polyethylene terephthalate (PET), the cooling system according to the invention improved to be even more maintenance-friendly, because the capillary tubes made of polypropylene are corrosion-resistant and therefore clogging them by rust particles need neither be feared. Equally, such capillary tubes are dirt-repellent so that the heat exchanger may neither be clogged as easily by dirt introduced with the cooling air. Accordingly, capillary tubes completely made of polypropylene are especially preferred. 
         [0020]    Furthermore, the heat exchanger of the cooling system according to the invention can be surrounded by a casing which is connected to the housing of the devices to be cooled or the server rack, respectively, wherein, as already suggested further, the casing of the heat exchanger can be installed at an arbitrary location of the device housing, wherein a rear-side arrangement of the heat exchanger housing on the server rack may be preferred. In order to improve access and therefore also the maintenance friendliness of the heat exchanger, the heat exchanger housing may be installed pivotably on the device housing such that the heat exchanger can be pivoted away from the device housing along with the casing for maintenance purposes. 
         [0021]    According to a further preferred embodiment, the heat exchanger housing has the essentially same cross-section in the flow direction of the heated air as the device housing. In other words, the heat exchanger housing has the corresponding measurements of the respective side at the device housing at which the heat exchanger housing with the heat exchanger is attached. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The present invention is illustrated in more detail in the following by way of  FIGS. 1 to 3 . It can comprise the features shown therein individually as well as in any sensible combination thereof. In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. It is shown in: 
           [0023]      FIG. 1  depict a schematic side view of the cooling system according to the invention on a server rack; 
           [0024]      FIG. 2  depict a side view of a capillary tube composition of  FIG. 1 ; 
           [0025]      FIG. 3   a - 3   c  disclose three-side-views of a heat exchanger according to  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    In  FIG. 1 , a schematic side view of a server rack  2  with heat exchanger casing  11  attached to it is shown. The heat exchanger casing  11  is attached to the rear side of the device housing  2  and therefore at the location at which the air current  3  entering through the front side of the server rack  2  leaves the server rack  2  again or would enter the environment/the server room  5 , respectively. The current of the cooling air  3  is illustrated in  FIG. 1  by the parallel arrows. The heat exchanger seated in the in the casing  11  comprises a register  10  formed by plural capillary tube compositions  6  positioned or switched in parallel. The cooling air duct  4  consists in the embodiment shown here of a circumferential lip seal arranged between heat exchanger casing  11  and server rack  2  and running on and stuck into the casing  11 , which enables an airtight connection of sever rack  2  and the heat exchanger casing  11 . 
         [0027]    The internal, not shown cooling fans of the servers  2  convey the warm waste air  3  of the devices through the register  10  through which water flows and in which the waste heat is extracted from the air  3  and transferred onto the cooling medium water. The heated cooling water is transported to the outside in a closed pipe circuit and re-cooled there, wherein the cooling system according to the invention replaces the hitherto conventional ventilation equipment of the server room. 
         [0028]    Not shown are the upper and lower side mountings with concealed pin hinges attached between the server rack  2  and the heat exchanger casing  11 , which allow to pivot the heat exchanger casing  11  away from the server rack  2  without having to dismount the connectors for the cooling medium for maintenance jobs on the servers and/or the on the cooling register. 
         [0029]    In  FIG. 2  a planar composition  7 , a so-called capillary tube mat with plural capillary tubes  6  is shown which extends in parallel in a vertical direction between two distribution lines. The length of the capillary tubes  6  is set in accordance with the respective height of the rack casing. The lower distribution line has an inlet  8  while the upper distribution line has a drain and/or outlet  9 . In the example shown here, the flexible connecting tubes DN15 can thus be connected to the composition  7  so that the cooling water flows through the composition  7  from bottom to top. 
         [0030]    In  FIGS. 3   a - 3   c,  a 3-side-view of a heat exchanger  1  according to the invention is shown which comprises a register  10  of twenty capillary tube mats  7  and a heat exchanger casing  11  which surrounds the capillary tube mat register  10  at four sides and leads the cooling air flow  3  running in direction S through the register  10 . In the steel sheet casing  11  of the heat exchanger  1  mounting bores are provided into which the individual capillary tube mats  7  can be mounted and/or hung, wherein the casing  11  on the coupling side between server rack  2  and heat exchanger  1  is formed as a flange. Furthermore visible are the inlets  8  and the drains  9  which are formed separately for each capillary tube mat at opposing side walls of the casing  11 . The inlets and drain ( 8 ,  9 ) provided separately for each capillary tube mat allow for an arbitrary switching of the capillary tube mats  7 , wherein a parallel switching of the capillary tube mats  7  in the register  10  is preferred. By having a certain offset in height of the inlets and drain ( 8 ,  9 ), it is possible to reduce a distance and/or clearance between the capillary tube mats  7  in order to receive a more compact register  10 . 
         [0031]    In the embodiment of  FIGS. 3   a - 3   c,  capillary tube mats manufactured by Clina having the type Orimat G10 are used, the capillary tubes of which have an outer diameter of 3.4 mm and an inner diameter of 2.3 mm. The capillary tubes are made of polypropylene and thermically welded together with an upper and a lower distribution line, wherein the number of capillary tube mats in a cooling register is variable and can be adapted to the actual heating power of a server rack. The shown capillary tube mats reach a cooling power of about 66 W per mat at a water entry temperature of ca. 18° C. In the example shown here, 20 capillary tube mats  7  are arranged behind one another, the inlets and drains of which are connected in parallel. Because of this, the heat exchanger shown here reaches a total cooling power of 12 KW. The cooling powers considerably increase with decreasing water entry temperatures.