U.S. patent application number 13/217866 was filed with the patent office on 2012-03-01 for cooling systems and methods.
Invention is credited to Richard D. Osbaugh.
Application Number | 20120048514 13/217866 |
Document ID | / |
Family ID | 45695579 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120048514 |
Kind Code |
A1 |
Osbaugh; Richard D. |
March 1, 2012 |
COOLING SYSTEMS AND METHODS
Abstract
A cooling system for a server may include an evaporator that is
in thermal communication with the server so that the evaporator
absorbs heat generated by the server. An inlet end of a condenser
is fluidically connected to an outlet end of the evaporator,
whereas an outlet end of the condenser is fluidically connected to
an inlet end of the evaporator. A working fluid disposed within the
evaporator and the condenser is substantially free of lubricant.
The working fluid absorbs heat generated by the server in the
evaporator, changing from a liquid phase to a vapor phase. The
working fluid releases heat in the condenser, changing from the
vapor phase back to the liquid phase. The phase changes of the
working fluid in the evaporator and the condenser result in
pressure changes sufficient to cause the working fluid to circulate
between the evaporator and the condenser in a self-sustaining,
phase-change thermodynamic cycle.
Inventors: |
Osbaugh; Richard D.;
(Lakewood, CO) |
Family ID: |
45695579 |
Appl. No.: |
13/217866 |
Filed: |
August 25, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61377791 |
Aug 27, 2010 |
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Current U.S.
Class: |
165/104.21 |
Current CPC
Class: |
H05K 7/20827
20130101 |
Class at
Publication: |
165/104.21 |
International
Class: |
F28D 15/02 20060101
F28D015/02 |
Claims
1. A cooling system for a server, comprising: an evaporator having
an inlet end and an outlet end, said evaporator being in thermal
communication with said server so that said evaporator absorbs heat
generated by the server; a condenser having an inlet end and an
outlet end, the inlet end of said condenser being fluidically
connected to the outlet end of said evaporator, the outlet end of
said condenser being fluidically connected to the inlet end of said
evaporator; and a working fluid disposed within said evaporator and
said condenser, said working fluid being substantially free of
lubricant, said working fluid absorbing heat generated by the
server in said evaporator, the absorbed heat changing said working
fluid from a liquid phase to a vapor phase in the evaporator, said
working fluid releasing heat in said condenser, the released heat
changing said working fluid from the vapor phase to the liquid
phase in said condenser, the phase changes of said working fluid in
said evaporator and said condenser resulting in pressure changes
sufficient to cause said working fluid to circulate between said
evaporator and said condenser in a self-sustaining, phase-change
thermodynamic cycle.
2. The cooling system of claim 1, wherein said condenser is located
at an elevation that is higher than an elevation of said
evaporator.
3. The cooling system of claim 1, wherein said working fluid
changes from the liquid phase to the vapor phase at a temperature
of about 18.degree. C. at a pressure of about 1 bar.
4. The cooling system of claim 3, wherein said working fluid
comprises a halocarbon fluid.
5. The cooling system of claim 4, wherein said halocarbon fluid
comprises 1,1,1,3,3-pentafluoropropane.
6. The cooling system of claim 1, wherein the server includes a
heat discharge member and wherein said evaporator is in direct
thermal communication with the heat discharge ember of the
server.
7. The cooling system of claim 1, wherein said evaporator and said
condenser comprise fluid conduits therein, and wherein said fluid
conduits comprise diameters sufficiently large to reduce a velocity
of said working fluid flowing therein below a level at which a
pressure head loss would prevent said working fluid from
circulating through said cooling system in the self-sustaining,
phase-change thermodynamic cycle.
8. A method for cooling a server, comprising: evaporating a working
fluid contained in an evaporator in thermal communication with the
server, the working fluid being substantially free of lubricant,
said evaporating producing a working fluid stream in a vapor state;
supplying the working fluid stream in the vapor state to a
condenser; condensing the working fluid in the vapor state to
produce working fluid stream in a liquid state; and returning the
working fluid stream in the liquid state to the evaporator, wherein
phase changes of the working fluid in the evaporator and the
condenser result in pressure changes sufficient to cause the
working fluid to circulate between the evaporator and the condenser
in a self-sustaining, phase-change thermodynamic cycle.
9. The method of claim 8, wherein the working fluid stream in the
vapor state and said the working fluid stream in the liquid state
flow at velocities that are below a level at which a pressure head
loss would prevent the working fluid from circulating through the
evaporator and the condenser in the self-sustaining, phase-change
thermodynamic cycle.
10. The method of claim 8, wherein said evaporating is conducted at
a pressure of about 1 bar.
11. The method of claim 10, wherein said evaporating is conducted
at a temperature of about 18.degree. C.
12. The method of claim 8, wherein said supplying comprises
supplying the working fluid stream in the vapor state to the
condenser that is located at an elevation that is higher than an
elevation of the evaporator.
13. A cooling system for a server having a heat discharge member,
comprising: an evaporator having an inlet end and an outlet end,
the evaporator being in direct thermal communication with the heat
discharge member of the server; a condenser having an inlet end and
an outlet end, the condenser being located at a higher elevation
than the evaporator; a supply conduit connecting the outlet end of
the condenser to the inlet end of the evaporator; a return conduit
connecting the outlet end of the evaporator to the inlet end of the
condenser; and a working fluid disposed within the evaporator, the
condenser, the supply conduit, and the return conduit, wherein the
working fluid enters the inlet end of the evaporator in a liquid
phase and absorbs heat from the heat discharge member thereby
transitioning the working fluid from the liquid phase to a vapor
phase, the working fluid in the vapor phase exits the outlet end of
the evaporator and travels though the return conduit before
entering the inlet end of the condenser, wherein the working fluid
in the vapor phase discharges heat to ambient thereby transitioning
the working fluid in the vapor phase to the liquid phase before
traveling through the supply conduit back to the evaporator.
14. The cooling system of claim 13, wherein the working fluid has a
boiling point of about 15.degree. C. (60.degree. F.) at about 1.01
bar (1 atm).
15. The cooling system of claim 13 further comprising a pump
connected to the supply conduit.
16. The cooling system of claim 13, further comprising a controller
operatively associated with the supply conduit, wherein the
controller controls the supply of the working fluid to the
evaporator.
17. The cooling system of claim 13, further comprising a compressor
connected to the return conduit.
18. The cooling system of claim 17, wherein the compressor
comprises a magnetically-driven compressor.
19. The cooling system of claim 13, wherein the evaporator
comprises a microchannel heat exchanger.
20. The cooling system of claim 13, wherein the condenser comprises
a microchannel heat exchanger.
21. The cooling system of claim 13, wherein the condenser comprises
a cooling tower.
22. A method for cooling a server having a heat discharge member,
comprising: supplying a working fluid in a liquid phase to an
evaporator in direct thermal communication with the heat discharge
member of the server; discharging heat from the heat discharge
member of the server to the evaporator; transferring the discharged
heat from the heat discharge member to the working fluid in the
liquid phase, wherein the working fluid in the liquid phase absorbs
the discharged heat; transitioning the working fluid into a vapor
phase; supplying the working fluid in the vapor phase from the
evaporator to a condenser located at a higher elevation than the
evaporator, wherein the working fluid in the vapor phase is
supplied from the evaporator to the condenser by a pressure
differential caused by the condensation of the working fluid in the
condenser; cooling the working fluid in the vapor phase with the
condenser; transitioning the working fluid in the vapor phase to
the liquid phase; and supplying the working fluid in the liquid
phase back to the evaporator.
23. The method for cooling a server of claim 22, wherein the
working fluid has a boiling point of about 15.degree. C.
(60.degree. F.) at about 1.01 bar (1 atm).
24. The method for cooling a server of claim 22 further comprising:
monitoring a temperature of the working fluid in the evaporator;
and changing the supply of working fluid to the evaporator
depending on the temperature of the working fluid.
25. The method for cooling a server of claim 22, wherein supplying
the working fluid in the liquid phase back to the evaporator
comprises pumping the working fluid in the liquid phase from the
condenser to the evaporator.
26. The method for cooling a server of claim 22, wherein supplying
the working fluid in the vapor phase from the evaporator to the
condenser comprises pumping the working fluid in the vapor phase
from the evaporator to the condenser.
27. The method for cooling a server of claim 26 further comprising:
monitoring a condensation temperature of the condenser and a
temperature of the working fluid in the vapor phase; and bypassing
the pumping of the working fluid in the vapor phase from the
evaporator to the condenser when the condensation temperature is
less than the temperature of the working fluid in the vapor
phase.
28. The method for cooling a server of claim 22 further comprising,
storing the working fluid in a liquid receiver prior to supplying
the working fluid to the evaporator.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/377,791, filed on Aug. 27, 2010, which is
hereby incorporated herein by reference for all that it
discloses.
TECHNICAL FIELD
[0002] The present invention relates to cooling systems in general
and more particularly to cooling systems and methods for cooling
servers located in data centers.
BACKGROUND
[0003] Data center cooling systems are known in the art and are
commonly used to cool computer servers and other electronic
equipment located within data centers. Such cooling systems are
configured to maintain specific temperatures and humidity levels to
prevent the servers and other electronic equipment from overheating
and malfunctioning. Typical data centers use complex computer room
air conditioning ("CRAC") systems. In general, CRAC systems intake
room temperature air from the data center and discharge cold air
into the data center to maintain the desired temperature range and
humidity level. However, such air conditioning units have high
power demands and are relatively inefficient, leading to increased
operational costs. Indeed, in many cases, the cooling systems
consume as much, if not more, energy than the computer equipment
itself.
[0004] As an alternative to conventional air conditioning systems,
data center designers have proposed various types of low energy,
non-refrigerant-based cooling systems. Examples of such low energy,
non-refrigerant-based systems include "airside" and "waterside"
economizers. While such systems can be made to work in many
applications, they are not without their own problems. For example,
airside economizers are perceived as introducing various air
quality issues, such as the introduction of corrosives and
dust/dirt. It is also difficult to maintain a consistent humidity
level with airside economizers. Waterside economizers carry with
them risks associated with water piping and associated leakage
issues and also suffer problems associated with the operation of
cooling towers during freezing weather. In addition, waterside
economizers consume considerable amounts of water.
[0005] Consequently, a need remains for an improved cooling system
for computer and data centers that does not suffer from the
problems associated with current systems. Ideally, such a system
should be capable of providing effective cooling for computer
systems, but without the high energy demands of refrigerant-based
systems. Additional advantages could be realized if such an
improved system solved the problems associated with airside and
waterside economizer systems.
SUMMARY OF THE INVENTION
[0006] A cooling system for a server according to one embodiment of
the present invention may include an evaporator having an inlet end
and an outlet end. The evaporator is in thermal communication with
the server so that the evaporator absorbs heat generated by the
server. An inlet end of a condenser is fluidically connected to the
outlet end of the evaporator, whereas an outlet end of the
condenser is fluidically connected to the inlet end of the
evaporator. A working fluid disposed within the evaporator and the
condenser is substantially free of lubricant. The working fluid
absorbs heat generated by the server in the evaporator, changing
from a liquid phase to a vapor phase. The working fluid releases
heat in the condenser, changing from the vapor phase back to the
liquid phase. The phase changes of the working fluid in the
evaporator and the condenser result in pressure changes sufficient
to cause the working fluid to circulate between the evaporator and
the condenser in a self-sustaining, phase-change thermodynamic
cycle.
[0007] In another embodiment, a cooling system for a server having
a heat discharge member may include an evaporator having an inlet
end and an outlet end that is in direct thermal communication with
the heat discharge member of the server. A condenser having an
inlet end and an outlet end is located at a higher elevation than
the evaporator. A supply conduit connects the outlet end of the
condenser to the inlet end of the evaporator. A return conduit
connects the outlet end of the evaporator to the inlet end of the
condenser. A working fluid disposed within the evaporator, the
condenser, the supply conduit, and the return conduit enters the
inlet end of the evaporator in a liquid phase and absorbs heat from
the heat discharge member thereby transitioning the working fluid
from the liquid phase to a vapor phase. The working fluid in the
vapor phase exits the outlet end of the evaporator and travels
though the return conduit before entering the inlet end of the
condenser, wherein the working fluid in the vapor phase discharges
heat thereby transitioning the working fluid in the vapor phase to
the liquid phase before traveling through the supply conduit back
to the evaporator.
[0008] Also disclosed is a method for cooling a server that
includes the steps of: Evaporating a working fluid contained in an
evaporator in thermal communication with the server, the working
fluid being substantially free of lubricant, the evaporating
producing a working fluid stream in a vapor state; supplying the
working fluid stream in the vapor state to a condenser; condensing
the working fluid in the vapor state to produce working fluid
stream in a liquid state; and returning the working fluid stream in
the liquid state to the evaporator, wherein phase changes of the
working fluid in the evaporator and the condenser result in
pressure changes sufficient to cause the working fluid to circulate
between the evaporator and the condenser in a self-sustaining,
phase-change thermodynamic cycle.
[0009] Another method may involve the steps of: Supplying a working
fluid in a liquid phase to an evaporator in direct thermal
communication with the heat discharge member of the server;
discharging heat from the heat discharge member of the server to
the evaporator; transferring the discharged heat from the heat
discharge member to the working fluid in the liquid phase, wherein
the working fluid in the liquid phase absorbs the discharged heat;
transitioning the working fluid into a vapor phase; supplying the
working fluid in the vapor phase from the evaporator to a condenser
located at a higher elevation than the evaporator, wherein the
working fluid in the vapor phase is supplied from the evaporator to
the condenser by a pressure differential caused by the condensation
of the working fluid in the condenser; cooling the working fluid in
the vapor phase with the condenser; transitioning the working fluid
in the vapor phase to the liquid phase; and supplying the working
fluid in the liquid phase back to the evaporator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Illustrative and presently preferred exemplary embodiments
of the invention are shown in the drawings in which:
[0011] FIG. 1 is a pictorial diagram of one embodiment of a cooling
system for cooling servers provided in a server rack;
[0012] FIG. 2 is an enlarged side view in elevation of the server
rack, heat discharge member, and evaporator that may be utilized in
one embodiment to form the direct thermal communication between the
heat discharge member and evaporator;
[0013] FIG. 3 is a rear view of the server rack and evaporator
arrangement of FIG. 2 more clearly showing the relative positioning
of the heat discharge member and evaporator; and
[0014] FIG. 4 is a pictorial diagram of another embodiment of the
cooling system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] One embodiment of a cooling system 10 according to the
teachings of the present invention is illustrated in FIG. 1 as it
may be used to cool a plurality of servers 24 located in a data
center 20. Briefly, but as will be described in much greater detail
herein, the cooling system 10 involves a self-sustaining,
phase-change thermodynamic cycle 12 that does not require the use
of separate pumping apparatus to move a working fluid 40 within the
system 10. Instead, the working fluid 40 circulates within the
system 10 due to pressure differences resulting from fluid phase
changes occurring within the system 10.
[0016] The cooling system 10 may comprise a condenser 50 and an
evaporator 60 that are fluidically connected together. More
particularly, a supply conduit 74 may be used to fluidically
connect an outlet end 54 of condenser 50 with an inlet end 62 of
evaporator 60. A return conduit 76 may be used to fluidically
connect an outlet end 64 of condenser 60 with an inlet end 52 of
condenser 50. In the particular embodiment illustrated in FIG. 1,
the condenser 50 is located at an elevation that is higher than an
elevation of evaporator 60, as depicted schematically in FIG. 1.
However, other arrangements are possible, as will be described in
further detail herein. In addition, the evaporator 60 in the
embodiment illustrated in FIG. 1 is arranged so that it is in
direct thermal communication with the heat discharge member 26 of
servers 24. As used herein, the term "direct thermal communication"
means that substantially all of the heat (represented by arrows 28)
discharged from heat discharge member 26 of servers 24 is conducted
directly to the evaporator 60, i.e., without passing through an
intermediate medium (e.g., open room air) and without substantial
heat transfer to such intermediate medium. Alternatively, other
arrangements for the evaporator 60 possible, as will also be
described in further detail herein.
[0017] In operation, the condenser 50 provides the working fluid 40
in a liquid phase 44 to the evaporator 60 via supply conduit 74. In
the evaporator 60, heat 28 discharged from the heat discharge
member 26 of servers 24 is absorbed by the working fluid 40. The
heat absorbed changes the working fluid 40 from the liquid phase 44
to a gas or vapor phase 42. Thereafter, the working fluid 40 in the
liquid phase 44 (i.e., as a working fluid stream in the vapor
phase) is conducted to the condenser 50 via the return conduit 76.
In the condenser 50, heat (represented by arrows 58) from the
working fluid 40 in the vapor phase 42 is released into a suitable
cooling medium (e.g., air or water). The amount of heat released
causes the working fluid 40 to re-condense into the liquid phase
44. The working fluid 40 in the liquid phase 44 (i.e., as a working
fluid stream in a liquid state) is then supplied back to the
evaporator 60 via supply conduit 74 to complete the
self-sustaining, phase-change thermodynamic cycle 12.
[0018] The phase changes of the working fluid 40 occurring in
condenser 50 and evaporator 60 result in pressure changes that are
sufficient to cause the working fluid 40 to circulate between the
condenser 50 and evaporator 60 in a self-sustaining manner. More
specifically, the vaporization of the working fluid 40 in the
evaporator 60 results in an increase in the vapor pressure of the
working fluid 40. The increase vapor pressure of the working fluid
40 in the evaporator 60 is greater than the vapor pressure of the
condensing working fluid 40 in the condenser 50. The resulting
pressure difference causes the working fluid 40 to flow within the
system 10, thereby dispensing with the need, at least in certain
embodiments and operating at certain temperature regimes, to
provide separate pumps or compressors to move the working fluid
40.
[0019] Because the present invention does not require the use of
pumps or compressors, the working fluid 40 may be substantially
free of lubricants. In addition, there is no need in the present
invention to achieve any particular minimum velocity for the
various working fluid streams (e.g., the working fluid stream in
the vapor state leaving the evaporator 60 and the working fluid
stream in the liquid state leaving the condenser 50), in order to
provide a sufficient flow of lubricant to a pump or compressor. To
the contrary, it is generally preferred to design the cooling
system 10 of the present invention so that the velocities of the
various working fluid streams are below a level at which pressure
head losses would prevent the working fluid 40 from circulating
through the cooling system 10 in the self-sustaining manner
described herein. In one embodiment, such velocity reductions may
be achieved by providing the system 10 with fluid conduits (e.g.,
condenser and evaporator coils 56 and 66, as well as the supply and
return conduits 74 and 76) having sufficiently large diameters or
cross-sectional flow areas.
[0020] Moreover, even in embodiments that may utilize a pump or
compressor (typically on an as-need basis only), the pressure-head
increase that may need to be provided by such a pump or compressor
will still be significantly below the pressure head required in
conventional, refrigerant-based systems. Consequently, even in
embodiments utilizing pumps or compressors, the cooling system of
the present invention will still require much less energy during
operation compared to conventional, refrigerant-based systems.
[0021] Still other advantages may be associated with the particular
working fluid 40 selected as the heat transfer medium. In one
embodiment, the working fluid 40 is selected so that the required
phase changes (e.g., from liquid to vapor and back again) occur at
moderate pressures, typically on the order of atmospheric pressure
or slightly above atmospheric pressure. The moderate pressures
involved with such a working fluid 40 dispense with the need to
provide expensive, high-pressure tubing, conduits, evaporators,
condensers, and related equipment, thereby further reducing the
cost and complexity of the cooling system 10 compared to
conventional, refrigerant-based cooling systems.
[0022] For example, in many embodiments, the cooling system
according to the present invention may utilize any of a range of
non-metallic tubing or piping for the supply and return conduits 74
and 76. Similarly, the condenser 50 and evaporator 60 need not be
constructed or rated to work with the high working pressures
typically associated with conventional server cooling systems. The
installation cost of the cooling system 10 is therefore
significantly reduced relative to traditional refrigeration-based
cooling systems.
[0023] Yet other advantages of the cooling system 10 may be
realized in embodiments in which there is direct thermal
communication between the heat discharge member 26 of server 24 and
the evaporator 60 of cooling system 10. For example, the direct
thermal communication between these two elements or components
substantially reduces the amount or quantity of heat 28 from
servers 24 that is released into the environment of the data center
20, thereby significantly reducing the heat load on the data center
cooling system 20. Indeed, in many embodiments, the data center
cooling system 20 need not be provided with any additional cooling
capacity, other than that which normally would be required for a
room of comparable size but without the added heat load from the
servers 24.
[0024] Having briefly discussed one embodiment of the cooling
system 10 according to the present invention, as well as some of
its more significant features and advantages, various exemplary
embodiments and alternative configurations of the cooling system
will now be described in greater detail. However, before proceeding
with the detailed description, it should be noted that while the
cooling system 10 is shown and described herein as it could be used
in a particular application, e.g., to cool server systems, and
having a particular configuration, the present invention could be
used in any of a wide variety of other applications and
configurations, as would become apparent to persons having ordinary
skill in the art after having become familiar with the teachings
provided herein. Consequently, the present invention should not be
regarded as limited to the particular applications and
configurations shown and described herein.
[0025] Referring now primarily to FIGS. 1-3, one embodiment of the
cooling system 10 is shown and described herein as it may be used
to cool one or more servers 24 provided in a data center 20. The
various servers 24 may be provided in one or more server racks 22,
although only a single server rack 22 is shown in FIGS. 1-3. Each
of the servers 24 provided in server rack 22 may include a heat
discharge member 26 through which is discharged heat 28 produced by
various electrical components 29 of server 24. More specifically,
and in one exemplary arrangement, each server 24 may be provided
with one or more fans 30 provided at a position near the back
portion 36 of server 24, adjacent the heat discharge member 26, as
best seen in FIG. 2. In operation, the fan or fans 30 draw air 31
through one or more vents 32 positioned at a front portion 34 of
the server 24. Within the server 24, air 31 is drawn over
electrical components 29. Heat 28 from the electrical components 29
is absorbed by the air 31 as it passes through the server 24. The
heat 28 (i.e., contained in heated air stream 31) is thereafter
discharged via the heat discharge member 26 located at the back
portion 36 of the server 24. See FIG. 3.
[0026] The evaporator 60 of cooling system 10 should be positioned
in thermal communication with the server 24 so that evaporator 60
can carry-away the generated heat. Generally speaking, it is
preferred, but not required, to position the evaporator 60 at a
location where it will be exposed to the highest temperatures
produced by the server 24. So positioning the evaporator 60 will
maximize the evaporator pressure and minimize the need to provide
additional circulation/condensation assistance (e.g., via a
separate pump or compressor system), even with high cooling air
(i.e., condenser) temperatures.
[0027] With the foregoing considerations in mind, in one
embodiment, the evaporator 60 of cooling system 10 may be
positioned with respect to the server 24 so that it is in direct
thermal communication with the heat discharge member 26 of server
24. Such a mounting arrangement will allow heat 28 discharged from
the heat discharge member 26 to be transferred directly to the
evaporator 60, with only minimal amounts being lost to the
environment (e.g., data center 20). That is, instead of being
transferred to ambient air or environment of the data center 20, as
is the case with conventional server cooling systems, the heat 28
discharged from the heat discharge member 26 is transferred
substantially directly to the working fluid 40 contained within
evaporator 60. The direct thermal communication between the heat
discharge member 26 and evaporator 60 may be accomplished in one
embodiment by mounting the evaporator 60 to the back of the server
rack 22, i.e., directly adjacent the heat discharge members 26, by
screws 61 or other fasteners.
[0028] In another embodiment, the evaporator 60 may comprise a
housing configured to encapsulate or enclose the heat-producing
components (e.g., processors) of the servers 24. In such an
embodiment, the working fluid 40 will be in direct contact with the
processors or other heat-producing components of the servers 24.
The encapsulation of the heat producing components will generally
expose the working fluid 40 in the encapsulating evaporator 60 to
higher temperatures, e.g., in the range of about 48.degree. C. to
about 60.degree. C. (about 120-140.degree. F.), compared
embodiments wherein the evaporator 60 is in thermal communication
with cooling air 31 discharged by the server fans 30. Such higher
temperatures will generally result in substantially higher
evaporator pressures that, in most cases, will allow the working
fluid 40 to circulate within the system 10 without the need for
additional pumps or compressors, even with cooling air temperatures
(i.e., for condenser 50) in excess of 38.degree. C. (about
100.degree. F.)
[0029] Referring back now to FIG. 1, in an embodiment wherein the
evaporator 60 is in direct thermal communication with the heat
discharge member 26 of server 24, the evaporator 60 may comprise an
inlet end 62 and an outlet end 64 that are fluidically connected by
one or more coils 66. A plurality of fins or micro-channel heat
transfer elements (not shown) may be thermally associated with the
coils 66 to increase the surface area of the evaporator coils 66,
thereby enhancing the transfer of heat 28 to the working fluid 40
contained within the coils 66. Alternatively, other configurations
for the evaporator 60 are possible, as would become apparent to
persons having ordinary skill in the art after having become
familiar with the teachings provided herein.
[0030] Evaporator 60 may be fabricated from any of a wide range of
materials (typically metals and metal alloys) having a high thermal
conductivity, such as aluminum, copper, and various alloys thereof,
although other materials may be used. Significantly, however, and
depending on the particular working fluid 40 that is used,
evaporator 60 need not be constructed to withstand the high working
pressures typically associated with conventional refrigerant-based
cooling systems.
[0031] Cooling system 10 may also comprise a condenser 50. In one
embodiment, condenser 50 may comprise an inlet end 52 and an outlet
end 54 that are fluidically connected by one or more coils 56. As
was the case for evaporator 60, condenser 50 may also be provided
with a plurality of fins or micro-channels (not shown) to increase
the heat transfer surface area of the condenser coils 56, thereby
enhancing the transfer of heat 58 from the working fluid 40
contained within the coils 56. Alternatively, other arrangements
for the condenser 50 are possible, as would become apparent to
persons having ordinary skill in the art after having become
familiar with the teachings provided herein.
[0032] Condenser 50 may be fabricated from any of a wide range of
materials (typically metals and metal alloys) having a high thermal
conductivity, such as aluminum, copper, and various alloys thereof,
although other materials may be used. Significantly, however, and
as was the case for evaporator 60, condenser 50 need not be
constructed to withstand the high working pressures typically
associated with conventional cooling systems.
[0033] In one embodiment, condenser 50 is mounted at an elevation
that is higher or greater than the elevation at which is mounted
the evaporator 60. So mounting the condenser 50 at an elevated
location will assist in returning the working fluid (i.e., in a
liquid state or phase 44) to the evaporator 60. In many embodiments
and applications, mounting the condenser 50 so that it is in an
elevated position with respect to evaporator will substantially
reduce or even eliminate (in certain circumstances and operational
regimes) the need to provide a pump or compressor system (not shown
in FIG. 1) to assist in the circulation of the working fluid 40. In
an exemplary installation, the condenser 50 maybe provided on a
roof (not shown) or other elevated location on a building (also not
shown) housing the data center 20.
[0034] The outlet end 54 of condenser 50 may be fluidically
connected to the inlet end 62 of evaporator 60 by a supply conduit
74. Similarly, the outlet end 64 of evaporator 60 may be
fluidically connected to the inlet end 52 of condenser 50 by return
conduit 76. Supply and return conduits 74 and 76 may be
substantially identical to one another, if desired, although they
need not be. They may also be fabricated from any of a wide range
of materials metallic and non-metallic materials, such as metals or
plastics, that would be suitable for the particular application. In
selecting the particular materials and other specifications for the
conduits 74, 76, it should be noted that, in many embodiments, the
operating pressures of the cooling system are considerably below
the operating pressures of conventional, refrigerant-based cooling
systems. Consequently, the conduits 74, 76 need not be capable of
withstanding high pressures. In accordance with the foregoing
considerations, then, in one embodiment, the conduits 74 and 76 may
be fabricated from polypropylene. Use of polypropylene will allow
any joints or junctions in the conduits 74, 76 to be conveniently
made by means of heat fusion, thereby substantially reducing the
likelihood of leaks.
[0035] In considering the design of the system 10, and in
particular the sizes and configurations of the condenser 50,
condenser coils 56, evaporator 60, evaporator coils 66, as well as
the supply and return conduits 74 and 76, it should be noted that
it will be generally preferred to design the system 10 so as to
reduce the velocities of the various working fluid streams (i.e.,
the working fluid stream in the vapor state exiting the evaporator
60 and the working fluid stream in the liquid state exiting the
condenser 50) below a level at which pressure head losses would
prevent the working fluid 40 from circulating through the system 20
in a self-sustaining manner. In one embodiment, such a velocity
reduction may be achieved by increasing the diameters or flow
cross-sectional areas of the various flow conduits involved.
Besides lowering the velocities of the various working fluid
streams, such large area conduits will permit significant mass flow
rates of working fluid 40, thereby increasing the overall heat
transfer rate of the system 10.
[0036] The working fluid 40 of the cooling system 10 should
comprise a working fluid having phase change temperatures (i.e.,
vaporization and condensation temperatures) in a range suitable for
the expected operational temperature ranges of the condenser 50 and
evaporator 60. Moreover, and ideally, those phase change
temperatures should occur at moderate pressures, thereby avoiding
the need to provide the system 10 with components and systems that
are capable of withstanding high operating pressures. Additional
advantages could be realized by selecting a working fluid 40
wherein the pressure increases rapidly with relatively small
increases in temperature.
[0037] Generally speaking, good results can be obtained by
utilizing a working fluid 40 having a boiling point of less than
about 18.degree. C. (65.degree. F.) at about 1.01 bar (1 atm).
Additional advantages may be realized by selecting a working fluid
40 that also has the following characteristics: A low freezing
point (lower than about -109.degree. C. (-165.degree. F.) at about
1.01 bar (1 atm)); a low vapor pressure (less than about 0.172 bar
(25 psia)); a high vapor heat capacity (greater than about 0.8
kJ/kg K (0.2 Btu/lb .degree. F.) at about 1.01 bar (1 atm)); a low
liquid viscosity (less than about 413 Pa s (1 lb/ft hr)); a low
vapor viscosity (less than about 20.7 Pa s (0.05 lb/ft hr)); high
liquid thermal conductivity (greater than about 0.07 W/m K (0.04
Btu/hr ft .degree. F.)); and high vapor thermal conductivity
(greater than about 0.009 W/m K (0.005 Btu/hr ft .degree. F.)). In
addition, it is generally preferred that the working fluid 40 be
substantially free of lubricant. Providing a substantially
lubricant-free working fluid 40 will improve the heat transfer
performance of the system 10.
[0038] By way of example, in one embodiment, the working fluid may
comprise a propane-based halocarbon fluid, such as
1,1,1,3,3-pentafluoropropane (R-245fa), which is readily
commercially available.
[0039] The cooling system 10 may be operated as follows to remove
heat 28 from servers 24. Working fluid 40 in a liquid phase or
state 44 enters the inlet end 62 of evaporator 60. The working
fluid 40 in the liquid phase 44 absorbs the heat 28 from the heat
discharge member 26. The working fluid 40 continues to absorb the
discharged heat 28 until it reaches a boiling point and begins to
transition into the vapor phase or state 42. The working fluid 40
in vapor phase 42 ultimately exits the evaporator outlet 64 as a
working fluid stream in the vapor state. During the vaporization
process, the vapor pressure of the working fluid 40 increases
beyond the vapor pressure of the condensing working fluid 40 in
condenser 50. This pressure difference will cause the working fluid
stream in the vapor state to flow into condenser 50. If conduits of
sufficient diameter are provided, or of the system 10 is otherwise
designed with minimal flow restrictions, the pressure head loss
resulting from the flow of working fluid 40 in the system 10 will
be less than the pressure differential resulting from the phase
changes of the working fluid 40. The working fluid 40 will then
flow through system 10 in a self-sustaining manner.
[0040] In the particular embodiment shown and described herein, the
temperature of the air discharged from the heat discharge member 26
of server 24 is at a temperature of about 40.degree. C. (about
104.degree. F.). Working fluid 40 is provided in sufficient amounts
to cool the discharged air to a temperature roughly equal to the
ambient air in the data center 20, about 24.degree. C. (about
75.degree. F.) As explained above, in an embodiment wherein the
working fluid 40 comprises R-245fa, a discharge temperature of
about 40.degree. C. will raise the vapor pressure in the evaporator
60 to a level sufficient to allow the working fluid 40 to circulate
within the system 10 in an self-sustaining manner, even with
moderately high cooling air temperatures at the condenser 50.
Moreover, in an embodiment wherein the evaporator 60 encapsulates
the heat-producing components (e.g., processors) of server 24, or
is otherwise exposed to temperatures in excess of 40.degree. C.
(104.degree. F.), e.g., temperatures in the range of about
48.degree. C. to about 60.degree. C. (about 120.degree. F. to about
140.degree. F.), such excess temperatures will result in even
higher evaporator pressures that will allow the working fluid 40 to
circulate in a self-sustaining manner even when the cooling air
temperature at the condenser 50 exceeds 38.degree. C. (100.degree.
F.)
[0041] After leaving the evaporator 60, the vaporized working fluid
40 enters the condenser 50, whereupon it is condensed. The
condensation process is accomplished by releasing or rejecting heat
from the vaporized working fluid 40 in an amount sufficient to
cause the working fluid 40 to condense. In the particular
embodiment shown and described herein, the working fluid 40 enters
the inlet end 52 of condenser 50 at a temperature of about
40.degree. C. (about 104.degree. F. or higher in some embodiments),
in the vapor state 42. Condensed working fluid 40 (i.e., in the
liquid state 44) is discharged from the condenser 50 (e.g., via
outlet end 54) at a temperature of about 29.degree. C. (about
85.degree. F.). The condensed working fluid 40 then flows to the
inlet end 62 of evaporator 60 whereupon the thermodynamic cycle 12
is repeated.
[0042] As mentioned, the working fluid 40 circulates through the
evaporator 60 and through the rest of the cooling system 10 at
relatively low pressures. In the particular embodiment shown and
described herein, the pressure of the working fluid 40 within the
evaporator 60, condenser 50, return conduit 76, and supply conduit
74 does not typically exceed about 2.07 bar (about 30 psia), and is
generally at about 1.7 bar (about 25 psia). However, in embodiments
wherein the working fluid 40 is exposed to even higher temperatures
(e.g., in a range of about 48.degree. to about 60.degree. C.) in
the evaporator 60, the system pressure will still not normally
exceed about 4.1 bar (about 60 psia). In contrast,
refrigerant-based systems may exceed pressures of 20.7 bar (300
psia), nearly 10 times the pressure at which the present invention
operates. The ability of the cooling system 10 to circulate working
fluid 40 at low pressures allows for relatively inexpensive
low-pressure rated components to be used for the various elements
(e.g., condenser 50, evaporator 60, supply conduit 74, and return
conduit 76) comprising the cooling system 10. Moreover, if a pump
is required or desired in any particular installation, the lower
working pressures of the present invention will allow for lower
pressure pumps to be used, further increasing efficiency and
reducing cost.
[0043] The direct thermal communication between the heat discharge
member 26 and the evaporator 60 more efficiently cools servers 24
by more efficiently transferring heat from the heat discharge
members 26 of the servers 24 to the evaporator 60. The improved
heat transfer capabilities help provide for improved power
efficiency of the data center 20. Power efficiency in the data
center 20 may be measured with power unit effectiveness ("PUE"),
which is a measurement of how efficiently a particular data center
uses its power. PUE is calculated by dividing the total incoming
power to the data center by the power delivered by the servers. The
total incoming power to the data center includes the power
delivered by the servers plus any electrical and mechanical support
systems such as chillers and fans. Lower PUE values are better, as
they indicate more incoming power is consumed by the servers
instead of the support equipment. Traditional data centers
typically have PUE values of about 2.5. In one exemplary
embodiment, the cooling system 10 provides for a more power
efficient data center 20 having a PUE value of about 1.03.
[0044] Still other variations and modifications are possible for
the cooling system 10 according to the teachings of the present
invention. For example, and with reference now primarily to FIG. 4,
another embodiment 110 of the cooling system may comprise a
plurality of evaporators 160 associated with corresponding server
racks 122. In addition, the cooling system 110 may also be provided
with a condenser 150 having a fan or blower system 155 operatively
associated therewith. Fan or blower system 155 may be used to
provide additional cooling air to condenser 150 to absorb
additional heat 158 from the condensing working fluid 140 in the
coils 156 of condenser 150.
[0045] The second embodiment 110 may also be provided with
additional components and devices to help circulate working fluid
140 during certain operational modes and temperature regimes
wherein the pressure differential resulting from the phase changes
of the working fluid 40 will be insufficient to circulate the
quantity of working fluid 140 required for the particular heat
load. More specifically, the cooling system 110 illustrated in FIG.
4 may also comprise a compressor 182, a pump 180, and a liquid
receiver 186. The compressor 182 may be provided in the return
conduit 176, in parallel with a bypass valve 185. Pump 180 and
liquid receiver 186 may be provided in the supply conduit 174, as
depicted in FIG. 4. Compressor 182 may be operated in circumstances
wherein the temperature of the cooling medium (e.g., air) provided
at the condenser 150 is too high to fully condense the working
fluid 140. When the compressor 182 is not needed, the working fluid
140 may bypass compressor 182 via bypass valve 185. Pump 180 may
assist in returning the working fluid 140 in a liquid state 144 to
the various evaporators 160, whereas liquid receiver 186 ensures
that the working fluid 140 will be supplied to pump 180 in a liquid
state 144.
[0046] As was the case for the first embodiment 10, the second
embodiment 110 of the cooling system may be operated at pressures
that are considerably lower than the operating pressures of
conventional cooling systems. As a consequence, the compressor 182
and pump 180 need not be designed and configured to operate at high
working pressures. In one embodiment, the compressor 182 may
comprise an oil-less, magnetically-driven compressor having a
variable frequency drive. Alternatively, other types of oil-less
compressor systems that are now known in the art or that may be
developed in the future could also be used. Pump 180 may similarly
comprise a liquid pump suitable for low operating pressures.
Ideally, compressor 182 and pump 180 should be of the type that
will permit the working fluid 140 to remain substantially free of
lubricant.
[0047] The system 110 may also comprise a liquid receiver 186
which, in one embodiment may be operatively associated with
compressor 182. As mentioned above, the liquid receiver 186
separates the working fluid 140 in the liquid phase 144 from the
working fluid 140 in the vapor phase 142. Maintaining a proper
ratio of the working fluid 140 in the liquid phase 144 to the vapor
phase 142 helps to maintain the circulation throughout the cooling
system 110 and otherwise enhances the operation of the cooling
system 110. That is, a sufficient amount of the working fluid 140
in the liquid phase 144 must be supplied to the evaporators 160 to
insure adequate cooling of the servers 124. One factor that affects
the amount of working fluid 140 in the liquid phase 144 is the
ambient temperature of condenser 150 which affects the rate of
condensation of the working fluid 140.
[0048] In one embodiment, the amount of working fluid 140 in the
liquid phase 144 in the liquid receiver 186 is monitored by a
sensor 187. If the working fluid 140 in the liquid phase 144 drops
below a predetermined level, the sensor 187 signals the compressor
182 to assist in compressing the working fluid 140 to increase the
amount of working fluid 140 that is condensed in condenser 150. If
needed, additional amounts of working fluid 140 may also be drawn
from a storage tank 188.
[0049] The system 110 may also be provided with a valve 184
provided at each inlet end of each evaporator 160. Valves 184 may
be modulated to provide working fluid 140 in the liquid state 144
in an amount consistent with the heating load on the associated
evaporator 160. For example, valve 184 can be opened to increase
the amount of working fluid 140 delivered to the evaporator 160 for
increased heat loads from the server 124. Conversely, lower heat
loads on evaporator 160 will allow the valve 184 to be closed,
thereby reducing the amount of working fluid 140 that is delivered
to the evaporator 160.
[0050] Cooling system 110 may also be provided with additional
components and devices, such as one or more temperature sensors 192
and pressure sensors 194. The temperature and pressure sensors 192
and 194 may be provided at various locations throughout the system
110 wherein it might be desired or required to monitor the
temperature or pressure of the working fluid 140. A control system
(not shown) may be operatively connected to the various components
and devices of cooling system 110, such as, for example, the
condenser fan system 155, pump 180, compressor 182, valves 184,
check valve 185, and level sensor 187, to control the function and
operation thereof. More specifically, the control system can then
sense the various operational states, temperatures, and pressures
of the system and operate the various components as required or
desired to achieve a desired operational state or to accommodate
certain changes or cooling demands on the system 110. For example,
the control system may monitor and change the flow rate of the
working fluid 140 throughout the cooling system 110 (e.g., via
operation of the pump 180 and compressor 182). The control system
may also operate the valves 184 to vary the flow rate of the
working fluid 140 to the various evaporators 160, as needed.
[0051] Having herein set forth preferred embodiments of the present
invention, it is anticipated that suitable modifications can be
made thereto which will nonetheless remain within the scope of the
invention. The invention shall therefore only be construed in
accordance with the following claims:
* * * * *