Note: Descriptions are shown in the official language in which they were submitted.
CA 02745301 2011-07-05
Cooling system for encased electronic devices
The invention is related to a cooling system for cooling waste heat-producing
electronic devices, in particular computer racks.
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 centres.
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.
This problem is solved by the subject-matter of claim 1, wherein the subclaims
define
preferred embodiments of the present invention.
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.
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
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heat exchanger before it is released to the environment and which extends at
least
between a housing of the devices and the heat exchanger.
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.
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.
Another advantage of the present invention consists in that it uses the anyway
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.
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.
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
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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.
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.
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.
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Especially 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
imperatively necessary. Just as advantageously, the heat exchanger with
capillary
tubes is not prone to soiling and therefore easy to maintain.
Further preferably, plural capillary tubes may be integrated to into a
composition,
wherein the capillary tubes can be 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.
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.
The heat exchanger according to the invention can according to an especially
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. Especially preferred is a parallel
switching of
the compositions, 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.
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As far as according to a further preferred embodiment 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 can be 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.
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
above,
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 is especially 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.
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.
The present invention is illustrated in more detail in the following by way of
figures 1
to 3. It can comprise the features shown therein individually as well as in
any sensible
combination thereof.
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It is shown in
Fig. 1: a schematic side view of the cooling system according to the invention
on a server rack
Fig. 2: a side view of a capillary tube composition
Fig. 3: three-side-view of a heat exchanger according to the invention
In figure 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 figure 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
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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.
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.
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
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dismount the connectors for the cooling medium for maintenance jobs on the
servers
and/or the on the cooling register.
In figure 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 lows through the composition 7 from bottom to top.
In figure 3, a 3-side-view of a heat exchanger 1 according to the invention is
shown
which comprises a register 10 of 20 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.
In the concrete embodiment of figure 3, 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
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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.
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