U.S. patent application number 13/143633 was filed with the patent office on 2011-11-03 for cooling apparatus and method.
This patent application is currently assigned to LEANECO APS. Invention is credited to Daniel Rene Hagen Pedersen.
Application Number | 20110265983 13/143633 |
Document ID | / |
Family ID | 40379324 |
Filed Date | 2011-11-03 |
United States Patent
Application |
20110265983 |
Kind Code |
A1 |
Pedersen; Daniel Rene
Hagen |
November 3, 2011 |
COOLING APPARATUS AND METHOD
Abstract
Cooling apparatus providing two independent heat exchangers (18,
20) serially arranged with respect to a heat flow (42), each heat
exchanger being connected to a respective independent chiller (32,
34). The apparatus incorporates an element of redundancy in order
to effect an increase in operational efficiency, by being
switchable between a first operation mode in which both chillers
operate in a free cooling mode and a second operation mode in which
a first chiller operates in a free cooling mode and a second
chiller operates in a forced cooling mode.
Inventors: |
Pedersen; Daniel Rene Hagen;
(Brabrand, DK) |
Assignee: |
LEANECO APS
Kolding
DK
|
Family ID: |
40379324 |
Appl. No.: |
13/143633 |
Filed: |
January 8, 2010 |
PCT Filed: |
January 8, 2010 |
PCT NO: |
PCT/EP2010/050161 |
371 Date: |
July 7, 2011 |
Current U.S.
Class: |
165/279 ;
165/200 |
Current CPC
Class: |
F25B 2309/06 20130101;
F25B 41/00 20130101; F25B 2400/06 20130101; F28F 27/02
20130101 |
Class at
Publication: |
165/279 ;
165/200 |
International
Class: |
F25B 41/00 20060101
F25B041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 8, 2009 |
GB |
0900268.4 |
Claims
1. Apparatus for cooling heat flow from a heat source, the
apparatus comprising: a first heat exchanger and a second heat
exchanger arranged serially to receive the heat flow, the first
heat exchanger being closer to the heat source than the second heat
exchanger, each heat exchanger being connected to a respective
coolant distribution circuit arranged to transfer coolant through
its heat exchanger; and a first chiller and a second chiller for
cooling the coolant from the first and second heat exchangers
respectively, wherein the apparatus is switchable between: a first
operation mode in which both the first and second chiller operate
in a free cooling mode; and a second operation mode in which the
first operates in a free cooling mode and the second chiller
operates in a forced cooling mode.
2. Apparatus according to claim 1, in which the first and second
chiller are both selectively operable in a free cooling mode or a
forced cooling mode, and which is switchable to a third operation
mode in which both the first and second chiller operate in the
forced cooling mode.
3. Apparatus according to claim 2, wherein the first and second
chillers each include a compressor selectively connectable into the
respective coolant distribution circuit.
4. Apparatus according to claim 3, wherein each chiller includes a
bypass circuit for diverting coolant past the compressor when
operating in the free cooling mode.
5. Apparatus according to claim 1, wherein the second chiller
includes an auxiliary cooling circuit that is independent of the
coolant distribution circuit connected to the second heat
exchanger, the auxiliary cooling circuit conveying auxiliary
coolant that is in thermal communication with the coolant
distribution circuit connected to the second heat exchanger to cool
the coolant in the coolant distribution circuit connected to the
second heat exchanger.
6. Apparatus according to claim 5, wherein a compressor is
connected into the auxiliary cooling circuit when the second
chiller operates in a forced cooling mode.
7. Apparatus according to claim 1 including a detector arranged to
measure temperature or pressure of the coolant transferred out of
the first heat exchanger, wherein the apparatus is arranged to
switch to the second operation mode based on measurement made by
the detector.
8. Apparatus according to claim 1, wherein the heat exchangers are
mounted on the door of a server rack.
9. Apparatus according to claim 1, wherein the heat exchangers are
evaporators.
10. Apparatus according claim 1, wherein the coolant is liquid
CO.sub.2.
11. A server rack comprising: one or more servers mounted therein;
an air circulation unit arranged to direct a flow of air through
the rack to draw heat away from the servers; and apparatus
according to claim 1 arranged to cool the flow of air, wherein the
heat source is the server(s) and the first and second heat
exchangers are arranged serially to receive the flow of air, the
first heat exchanger being closer to the servers than the second
heat exchanger.
12. A data centre comprising an enclosed space housing a plurality
of server racks according to claim 11.
13. Apparatus for cooling heat flow from a heat source, the
apparatus comprising: a plurality of first heat exchangers and a
plurality of second heat exchangers arranged as a plurality of
first and second heat exchanger pairs serially mounted relative to
respect to the heat flow, the first heat exchanger in each pair
being closer to the heat source than the second heat exchanger; a
first common coolant distribution circuit connected to the
plurality of first heat exchangers to transfer coolant
therethrough; a second common coolant distribution circuit
connected to the plurality of second heat exchangers to transfer
coolant therethrough; and a first chiller arrangement and a second
chiller arrangement for cooling the coolant output from the
plurality of first heat exchangers and the plurality of second heat
exchangers respectively, wherein the apparatus is switchable
between: a first operation mode in which both the first and second
chiller arrangements operate in the free cooling mode; and a second
operation mode in which the first chiller arrangement operates in
the free cooling mode and the second chiller arrangement operates
in the forced cooling mode.
14. Apparatus according to claim 13, in which both the first and
second chiller arrangements are selectively operable in a free
cooling mode or a forced cooling mode, and which is switchable to a
third operation mode in which both the first and second chiller
arrangements operate in the forced cooling mode.
15. Apparatus according to claim 13, wherein each common coolant
distribution circuit comprises a plurality of parallel cool
outputs, each cool output being connected to deliver coolant to a
respective heat exchanger on the circuit.
16. Apparatus according to claim 13, wherein each common coolant
distribution circuit comprises a common hot input connected to
receive coolant from a plurality of heat exchangers on the
circuit.
17. Apparatus according to claim 14, wherein either or both of the
first and second chiller arrangements comprise a plurality of
chillers connected in parallel to the respective coolant
distribution circuit, each chiller being selectively operable in a
free cooling mode or a forced cooling mode.
18. Apparatus according to claim 13, wherein the heat flow is a
forced air current flowing from the heat source.
19. A method of cooling heat flow from a heat source, the method
comprising: delivering coolant independently to a first heat
exchanger and a second heat exchanger from a first coolant transfer
circuit and a second coolant transfer circuit respectively, the
first and second heat exchangers being arranged serially to receive
the heat flow, the first heat exchanger being closer to the heat
source than the second heat exchanger; measuring temperature or
pressure of the coolant transferred out of the first heat
exchanger; and controlling the operation modes of a first chiller
connected to the first coolant transfer circuit and a second
chiller attached to the second coolant transfer circuit based on
the measuring temperature or pressure, wherein the method includes
operating the first chiller in a free cooling mode and operating
the second chiller in a forced cooling mode if the temperature or
pressure of the coolant transferred out of the first heat exchanger
exceeds a threshold.
Description
FIELD OF THE INVENTION
[0001] This invention relates to cooling equipment, e.g. for air
conditioners, electrical appliances or the like, in which fluid
coolant is circulated between a absorbing region where it absorbs
energy from the surrounding environment and a cooling region where
it emits energy to the surrounding environment.
BACKGROUND OF THE INVENTION
[0002] Electrical appliances, e.g. televisions, PCs, servers and
the like, emit heating during operation. In the case of information
technology (IT) equipment it is often necessary for operation to be
continuous. Problems, e.g. malfunction, may occur if the equipment
overheats, so it is important to control the temperature of the
surrounding environment.
[0003] Air conditioning may be used to control the temperature of a
space, e.g. room, warehouse or the like, that contained heat
generating equipment. Conventional air conditioning apparatus
operates to cool air, which is subsequently circulated in the space
to control the temperature.
SUMMARY OF THE INVENTION
[0004] At its most general, the invention provides cooling
apparatus which incorporates an element of redundancy in order to
effect an increase in operational efficiency. Put simply, the
invention involves providing two (or more) independent heat
exchangers which are serially arranged with respect to a heat flow
and operate to extract the full benefit of free cooling.
[0005] The invention also proposes targeted cooling, i.e. locating
heat exchangers at heat sources to provide localised cooling rather
than global cooling seen in conventional air conditioners.
[0006] In a development of the targeted cooling concept, the
invention may also provide a scalable cooling apparatus, whereby
the same principles may be used to build cooling systems on widely
varying scales.
[0007] According to one aspect of the invention there may be
provided apparatus for cooling heat flow from a heat source, the
apparatus comprising: a first heat exchanger and a second heat
exchanger arranged serially to receive the heat flow, the first
heat exchanger being closer to the heat source than the second heat
exchanger, each heat exchanger being connected to a respective
coolant distribution circuit arranged to transfer coolant through
its heat exchanger; and a first chiller and a second chiller for
cooling the coolant from the first and second heat exchangers
respectively, wherein the apparatus is switchable between: a first
operation mode in which both the first and second chiller operate
in a free cooling mode; and a second operation mode in which the
first chiller operates in a free cooling mode and the second
chiller operates in a forced cooling mode.
[0008] The improved efficiency of the apparatus may be achieved by
maintaining operation of the first chiller in the free cooling mode
even when its coolant may be approaching its critical point. For
example, if the heat flow causes the temperature of the coolant
and/or system pressure in the first heat exchanger to rise above a
threshold level, e.g. the boiling point of the coolant, the second
heat exchanger may still operate to cool the heat flow to a desired
temperature, e.g. a set room temperature. The apparatus may be
arranged to switch into the second operation mode if the
temperature of the coolant and or the system pressure in the second
heat exchanger rises above a threshold level (which may be set
slightly lower than the critical point of the coolant). Thus in
both the first and second operation modes full use is made of the
free cooling capability of the first chiller. The threshold level
may be determined based on any one or more of the temperature of
the heat flow, e.g. at the output from the second heat exchanger,
the ambient temperature and the system pressure in each heat
exchanger.
[0009] Having more than one heat exchanger at the heat source may
also provide an element of redundancy. In the event that one of the
cooling circuit becomes inoperative (e.g. due to malfunction or
servicing) the other circuit may be operate alone. In that case,
the single operating chiller may be arranged to operate in the
forced cooling mode immediately if the temperature of the coolant
and/or pressure in the heat exchanger exceeds the threshold
level.
[0010] The first and second chiller may both be selectively
operable in a free cooling mode or a forced cooling mode. The
apparatus may also be switchable to a third operation mode in which
both the first and second chiller operate in the forced cooling
mode. To operate efficiently, the apparatus may be arranged to
switch into the third operation mode if the temperature of the
coolant in the second heat exchanger when operating in the forced
cooling mode rises above a threshold level (which may be set
slightly lower than the critical point of the coolant).
[0011] The heat source may be any appliance that produces heat
during operation. For example, the heat source may be a computer,
e.g. PC or server.
[0012] The heat flow may be forced, e.g. on an air current directed
away from the heat source. For example, the heat source or one or
more of the heat exchangers may have a fan associated therewith for
blowing the surrounding air in the direction of the heat flow. The
first and second heat exchangers may be arranged in series in the
path of the heat flow, with the first heat exchanger arranged to
receive the heat flow first, i.e. at the hotter end of the
temperature gradient across the exchangers. The heat exchangers may
incorporate passageways to permit a medium carrying the heat flow,
e.g. air, therethrough. The heat flow may be convective.
[0013] The heat source may be contained in a space having a
internal temperature separated from an external environment having
an ambient temperature that is lower than the internal temperature.
The heat exchangers may be located in the space with the heat
source to absorb the heat energy therein. The chillers may be
arranged in the external environment. Free cooling may mean release
of energy from the coolant with substantially no (i.e. very low)
energy cost. For example, free cooling may be release of heat
energy from the coolant to the external environment. Free cooling
may be achieved by passing the coolant through a heat exchanger
located in the external environment. If the ambient temperature is
low enough the heat exchanger will operate to emit heat from the
coolant to the external environment. Forced cooling may mean
release of heat energy with an energy cost, e.g. an energy input.
For example, forced cooling may be achieved using conventional
compressor based cooling, i.e. in which the pressure of the coolant
is increased to increase its temperature to increase a temperature
gradient and hence cooling efficiency.
[0014] Each coolant distribution circuit may operate convectively
or may have a pump for circulating the coolant. Each coolant
distribution circuit may comprise a cool input for receiving
coolant from a chiller, a cool output for directing coolant to a
heat exchanger, a hot input for receiving coolant from the heat
exchanger and a hot output for directing coolant to the
chiller.
[0015] The apparatus may include a detector arranged to measure
temperature or pressure of the coolant transferred out of the
second heat exchanger (i.e. temperature or pressure at the hot
input of the relevant coolant distribution circuit), wherein the
apparatus is arranged to switch to the second operation mode based
on measurement made by the detector. As mentioned above, to achieve
efficient operation, the apparatus may switch to the second
operation mode only when the temperature or pressure of coolant
from the second heat exchanger exceeds a threshold. Even then the
first chiller continues to operate in the free cooling mode. No
detector may be needed for the first heat exchanger.
[0016] The first and second chillers may each include a compressor
connected to the respective coolant distribution circuit. Each
chiller may include a bypass circuit for diverting coolant past the
compressor when operating in the free cooling mode. The first
chiller may be arranged only to operate in the free cooling mode,
so may comprise a passive coolant distribution circuit.
[0017] The second chiller may include an auxiliary cooling circuit
that is independent of the coolant distribution circuit connected
to the second heat exchanger. The auxiliary cooling circuit may
convey auxiliary coolant that is in thermal communication with the
coolant distribution circuit connected to the second heat exchanger
to cool the coolant in the coolant distribution circuit connected
to the second heat exchanger. The coolant in the coolant
distribution circuit may thus be isolated, which may prevent
contamination. Indeed, the coolant distribution circuit may in
itself be a passive circuit; a compressor may be connected into the
auxiliary cooling circuit when the second chiller operates in a
forced cooling mode. The auxiliary cooling circuit may be part of a
conventional, e.g. off the shelf, cooling device.
[0018] Thermal communication between the auxiliary coolant and the
coolant in the coolant distribution circuit connected to the second
heat exchanger may be achieved by providing an auxiliary heat
exchanger, e.g. a plate heat exchanger, at an interface between the
auxiliary cooling circuit and the coolant distribution circuit
connected to the second heat exchanger.
[0019] The auxiliary coolant may be the same or different from the
coolant flowing through the first and second heat exchangers. The
auxiliary coolant may be CO.sub.2, water, NH.sub.3 or the like.
[0020] The first chiller may be configured in the same way as the
second chiller, i.e. with its own auxiliary cooling circuit.
[0021] To provide localised cooling, the heat exchangers may be
mounted on the heat source, e.g. on the door of a server rack. The
heat exchangers may be evaporators, e.g. conduits arranged to carry
liquid coolant which evaporates when energy is absorbed. The
coolant may be CO.sub.2.
[0022] In another aspect, the invention may provide a server rack
comprising: one or more servers mounted therein; an air circulation
unit arranged to direct a flow of air through the rack to draw heat
away from the servers; and apparatus as described above arranged to
cool the flow of air, wherein the heat source is the server(s) and
the first and second heat exchangers are arranged serially to
receive the flow of air, the first heat exchanger being closer to
the servers than the second heat exchanger. In this aspect the
cooling occurs at the rack itself, whereby the heat flow does not
substantially affect the surrounding air temperature. Such targeted
cooling may be more efficient.
[0023] In another aspect, the invention may provide a data centre
comprising an enclosed space housing a plurality of server racks as
described above. The chillers may include heat exchangers located
outside the enclosed space, e.g. in a low temperature external
environment, for use when operating in the free cooling mode.
[0024] In yet another aspect, the invention may provide apparatus
for cooling heat flow from a heat source, the apparatus comprising:
a plurality of first heat exchangers and a plurality of second heat
exchangers arranged as a plurality of first and second heat
exchanger pairs serially mounted relative to respect to the heat
flow, the first heat exchanger in each pair being closer to the
heat source than the second heat exchanger; a first common coolant
distribution circuit connected to the plurality of first heat
exchangers to transfer coolant therethrough; a second common
coolant distribution circuit connected to the plurality of second
heat exchangers to transfer coolant therethrough; and a first
chiller arrangement and a second chiller arrangement for cooling
the coolant output from the plurality of first heat exchangers and
the plurality of second heat exchangers respectively, wherein the
apparatus is switchable between: a first operation mode in which
both the first and second chiller arrangements operate in the free
cooling mode; and a second operation mode in which the first
chiller arrangement operates in the free cooling mode and the
second chiller arrangement operates in the forced cooling mode.
This aspect is similar to the first aspect mentioned above, but may
further provide scalability and/or additional redundancy.
[0025] As above, both the first and second chiller arrangements may
be selectively operable in a free cooling mode or a forced cooling
mode, and which is switchable to a third operation mode in which
both the first and second chiller arrangements operate in the
forced cooling mode.
[0026] Each common coolant distribution circuit may comprise a
plurality of parallel cool outputs, each cool output being
connected to deliver coolant to a respective heat exchanger on the
circuit. A coolant distribution circuit may be arranged to support
a predetermined number of heat exchangers, which may be provide as
connectable modules.
[0027] Each common coolant distribution circuit comprises a common
hot input connected to receive coolant from a plurality of heat
exchangers on the circuit. The heat exchangers may thus be provided
as parallel connected modules.
[0028] Similarly, either or both of the first and second chiller
arrangements may comprise a plurality of chillers connected in
parallel to the respective coolant distribution circuit, each
chiller being selectively operable in a free cooling mode or a
forced cooling mode. Each chiller may be provided in a selectively
connectable module to facilitate disconnection and reconnection
during servicing, load redistribution or the like.
[0029] In yet another aspect, the invention may provide a method of
cooling heat flow from a heat source, the method comprising:
delivering coolant independently to a first heat exchanger and a
second heat exchanger from a first coolant transfer circuit and a
second coolant transfer circuit respectively, the first and second
heat exchangers being arranged serially to receive the heat flow,
the first heat exchanger being closer to the heat source than the
second heat exchanger; measuring temperature or pressure of the
coolant transferred out of the first heat exchanger; and
controlling the operation modes of a first chiller connected to the
first coolant transfer circuit and a second chiller attached to the
second coolant transfer circuit based on the measuring temperature
or pressure, wherein the method includes operating the first
chiller in a free cooling mode and operating the second chiller in
a forced cooling mode if the temperature or pressure of the coolant
transferred out of the first heat exchanger exceeds a threshold. In
the method the first chiller may thus be held in the free cooling
mode even if the cooling achieved in that mode is not enough to
reduce the temperature of the heat flow to the desired level.
[0030] The invention may be implemented using sustainable
refrigerants as the coolant. In the situation where the coolant
from the first heat exchanger is gaseous, it may be desirable to
have a blow out valve to prevent overpressure in the distribution
circuit. This is undesirable or impractical with non-sustainable or
toxic refrigerants.
[0031] The invention incorporates redundancy in a modular
architecture by cooling each heat source with a passive or forced
heat flow redundant evaporator. This redundancy also acts to
improve operational efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Examples of the concepts outlined above are discussed in
detail with reference to the accompanying drawings, in which:
[0033] FIG. 1 is a schematic block diagram of cooling apparatus
that is an embodiment of the invention;
[0034] FIG. 2 is a schematic block diagram showing components of a
cooling apparatus that is an embodiment of the invention;
[0035] FIG. 3 is a schematic block diagram showing a plurality of
evaporators arranged serially with respect to a heat flow;
[0036] FIG. 4 is a schematic block diagram of a data centre that is
an embodiment of the invention;
[0037] FIG. 5 is a schematic block diagram of modular cooling
apparatus that is another embodiment of the invention;
[0038] FIG. 6 is a graph showing power consumption against ambient
temperature for a chiller assembly suitable for use in the
invention; and
[0039] FIG. 7 is a schematic block diagram showing components of a
cooling apparatus that is another embodiment of the invention.
DETAILED DESCRIPTION
Further Options and Preferences
[0040] The present invention may provide a flexible solution to the
problem of cooling a data centre efficiently. The invention may
utilize natural and non-water-based refrigerants. The invention may
provide scalable apparatus, e.g. to enable tailored control of
cooling system, e.g. in accordance with a business plan or proposed
development. The scalability may also enable increases in the
overall power density of a rack to be catered for, thus supporting
the development of high power density blade servers and network
equipment.
[0041] By providing heat exchangers associated with particular heat
sources, the invention may limit or remove the need for forced
airflow, which is standard in conventional cooling solutions.
Similarly, the invention may remove the need for computational
fluid dynamics (CFD) analysis of air flow patterns within a space
to be cooled, and particularly the change of such patterns during
operation, service and maintenance. This may be advantageous, in
that predicting whether or not a certain airflow in data centre
provides the right cooling capacity for a given operation pattern
can be one of the most complex tasks in data centre management. The
present invention may obviate this task.
[0042] FIG. 1 illustrated an architecture for a cooling apparatus
10 that is an embodiment of the invention. In this embodiment, the
apparatus 10 comprises three main parts: an evaporator assembly 16,
a coolant distribution unit (CDU) 12, and a hybrid chiller assembly
14.
[0043] The evaporator assembly 16 comprises two sets 18, 20 of
multiple parallel heat exchangers (which in this embodiment are
evaporators, e.g. HVAC coils or the like). The sets 18, are coupled
in series with respect to the direction of heat flow 22 from a heat
source (indicated by an arrow in the drawing). For example, the
sets 18, 20 may be arranged to formed multiple parallel pairs of
serially arranged evaporators. Heat from the heat source thus first
enters a first set 18 of evaporators (indicated as Evaporator a in
the drawing). After the heat flow 22 passes through the first set
18 of evaporators, i.e. after the cooling effect of the first set
18 of evaporators is imparted to the heat flow, the heat flow 22
passes through a second set 20 of evaporators first (indicated as
Evaporator b in the drawing). Thus heat flow entering the second
set 20 of evaporators has already been exposed to the first set 18
of evaporators. This embodiment illustrates two serial sets of
evaporators. There may be three or more sets arranged in series
with respect to the heat flow. Furthermore, although this
embodiment illustrates a plurality of evaporators in each set, each
set may have only one evaporator. Other types of heat exchanger may
be used instead of evaporators.
[0044] The CDU 12 is a system which distributes coolant (e.g.
natural refrigerant such as liquid CO.sub.2) to the evaporator
assembly 16. The CDU 12 is a modular arrangement comprising a
plurality similar or identical modules 24, 26. There is at least
one module per set of evaporators. In this embodiment, a first
distribution module 24 (CDUa) is connected via first input and
output conduits 28 to the first set 18 of evaporators and a second
distribution module 26 (CDUa) is connected via second input and
output conduits 30 to the second set 20 of evaporators. The sets
18, 20 of evaporators thus have independent coolant circuits; there
is no mixing of coolant circulating in the first and second
evaporators.
[0045] The heat source may be contained in an enclosed space, e.g.
a room or warehouse. The evaporators are located with the heat
source in the enclosed space (which may be referred to herein as
the interior). The CDU 12 need not be contained in the interior.
For example, if the enclosed space is defined within a building,
the CDU 12 may be located outside the building, e.g. exposed to the
outside environment.
[0046] The CDU 12 may also handle coolant flow control based on
real time measurements of performance parameters of coolant in the
first and second input and/or output conduits. The performance
parameters may include any one or more of pressure, flow
temperatures, evaporator assembly input and output temperatures,
ambient temperature (i.e. temperature of the outside environment),
and actual or predicted power usage of the heat source (which may
be an electrical appliance such as a server or communication
equipment, e.g. networking apparatus etc.).
[0047] In this embodiment, the hybrid chiller assembly 14 comprises
two sets 32, 34 of multiple hybrid chillers. The purpose of each
chiller is to condense (i.e. cool) evaporated (i.e. heated) coolant
received from the CDU 12 and return it to the CDU 12 for
recirculation to the evaporator assembly 16. Each set 18, 20 of
evaporators has a corresponding set 32, 34 of hybrid chillers to
maintain isolation of the coolant between the first and second sets
of evaporators. Each set 32, 34 of hybrid chillers is therefore
connected to the relevant distribution module by an independent
input and output conduit. Thus, in the illustrated embodiment a
first set 32 of hybrid chillers (indicated as Hybrid Chiller a in
the drawing) is connected to first distribution module 24 by first
input and output conduits 36 to receive, cool and output coolant
from the first set 18 of evaporators. Similarly a second set 34 of
hybrid chillers (indicated as Hybrid Chiller b in the drawing) is
connected to second distribution module 26 by second input and
output conduits 38 to receive, cool and output coolant from the
second set 20 of evaporators. Each set of hybrid chiller may
include only one hybrid chiller.
[0048] A hybrid chiller is a cooling system having two operating
modes. One mode is a free cooling mode, in which the hybrid chiller
works substantially passively as a so-called free cooler, gas
condenser, or dry cooler. In this mode cooling occurs directly on
the evaporated refrigerant without increasing its working pressure.
In practice operating in this mode may include transferring the
coolant through a heat exchanger in a low temperature environment
outside the enclosed space containing the heat source. The low
temperature environment may be in the open air. Night and/or cold
season temperatures in some areas of the world (e.g. northern
Europe, northern states of the US, etc.) may be low enough to
enable operation in the mode for a coolant such as CO.sub.2 or the
like. The other operating mode is a forced cooling mode in which an
energy input is required to achieve cooling. An example of the
forced cooling mode is compressor-based cooling, in which the
coolant pressure is temporarily increased, which makes it possible
to cool even at high ambient temperatures.
[0049] Whilst the embodiment illustrates hybrid chillers, i.e.
chillers that can switch between the two operating modes described
above, this need not be essential. Each set of chillers may be made
up of one or more free coolers and one or more forced coolers.
However, having hybrid chillers may be advantageous in terms of
providing increased energy efficiency and coping with redundancy
demands.
[0050] FIG. 2 shows components of each of the main parts of one of
the cooling circuits of the cooling apparatus 10 shown in FIG. 1.
In this embodiment, the heat source is an IT rack 40 (e.g. a server
rack containing one or more servers). The IT rack 40 may have a
inbuilt fan for circulating air flow through the rack. The air flow
may carry heat away from the IT rack 40 and hence may represent the
heat flow 42 away from the heat source. Two heat exchangers 44, 46
are arranged serially in the direction of the heat flow 42. The
heat exchangers 44, 46 may be attached to the IT rack 40, e.g.
mounted on its back door.
[0051] The cooling circuit connected to the second heat exchanger
46 is illustrated in more detail. The circuit connected to the
first heat exchanger is independent of the illustrated circuit.
[0052] The second heat exchanger 46 is connected to a CDU module 48
by feed conduits 50, 52. A first conduit 50 is a cool output from
the CDU module 48 which feeds coolant into the heat exchanger 46. A
second conduit 52 is a hot input to the CDU module 48 which
transfers heated coolant away form the heat exchanger 46. The CDU
module 48 consists of valves 54, 56 which may be arranged to
operate as hot plugs, leakage protection and flow controllers for
coolant flowing in the first and second conduits 50, 52
respectively. The CDU module 48 may include a pump 58 for driving
the coolant. The pump is optional (i.e. the circuit may operate by
convection), but has the advantage of extending the distance
between the hybrid chiller(s) and the evaporator assembly.
[0053] The CDU module 48 is connected to the hybrid chiller 60 by a
pair of conduits 62, 64. A first conduit 62 is a hot output from
the CDU module 48 which transfers heated coolant to a reservoir 66
in the hybrid chiller 60. A second conduit 64 is a cool input to
the CDU module 48 which transfers cooled, e.g. liquid, coolant from
the reservoir 66 to be sent to the heat exchanger 46. A pump 68 to
drive the circuit may be provided on the second conduit 64.
[0054] The reservoir 66 acts as a coolant receiver/buffer. The
reservoir 66 retains liquid coolant (which can be transferred out
via the second conduit 64) but has a gas outlet 70 that delivers
heated coolant to a condenser 72 for cooling. Cooled, e.g. liquid,
coolant from the condenser 72 is delivered back to the reservoir 66
via liquid inlet 74. A pressure relief valve 76 may be provided
after the condenser 72 as a safety blow out mechanism.
[0055] In the embodiment there are two paths from the gas outlet 70
to the condenser 72. A first path 78 passes through a compressor
80, which acts to increase temporarily the pressure (and hence
temperature) of the gas to facilitate cooling in the condenser 72.
The second path 82 bypasses the condenser. A bypass valve 84 is
provided on the second path 82 to enable the system to select which
path the gas may take.
[0056] When the bypass valve 84 is open the hybrid chiller operates
in a free cooling mode. When the bypass valve 84 is closed the
hybrid chiller operates in a forced cooling mode.
[0057] The condenser 72 is exposed to an ambient temperature, e.g.
an external temperature outside the enclosed space containing the
IT rack. A fan 86 may blow air at the ambient temperature over the
condenser 72 to facilitate cooling of coolant therein.
[0058] The circuit may also include a auto fill storage unit 88
connected to deliver extra coolant to either the CDU module 48 or
hybrid chiller 66. In this embodiment the auto fill storage unit 88
has a first delivery conduit 90 for transferring coolant to the hot
output 62 of the CDU module 48 and a second delivery conduit 92 for
transferring coolant to the gas outlet 70 of the reservoir 66. Each
delivery conduit 90, 92 has a respective control valve 94, 96
arranged to control flow rate therethrough.
[0059] FIG. 3 illustrates the series connection of multiple
evaporators 100, 102, 104, 106 with respect to a heat flow 108.
Each evaporator is connected to an independent circuit C1, C2, C .
. . , Ci, e.g. as described above with respect to FIG. 2. In this
way the cooling apparatus may be seen as a modular cooling system
constructed around a redundant set of serially arranged
evaporators. The (2 or more) evaporators may each be air to
refrigerant micro tube heat exchangers. Each evaporator is coupled
in a dedicated cooling circuit, in such a way that each evaporator
in an assembly has a dedicated cooling circuit connecting it to an
outdoor chiller, condenser or the like.
[0060] By using a set of paralleled or a single outdoor hybrid
chiller for each cooling circuit, which hybrid chiller either
operates as a free cooling condenser, or as a transcritical
compressor based chiller, increased efficiency and multilevel
redundancy may be achieved when compared with conventional cooling
systems.
[0061] In a further development of the embodiments discussed
herein, the CDU may allows several evaporators to be connected to
share a common coolant circuits and redundant coolant feed to and
from outdoor chillers. This may facilitate scalability, i.e. the
ability to increase the number of paralleled hybrid chillers or
evaporator sets. The CDU also provides integrated safety and
service mechanisms such as limp home on faults, leakage detection,
plug and play addition of evaporators, and filling of
refrigerant.
[0062] FIG. 4 shows a cooling apparatus which makes use of the
modular concept discussed herein. This drawing illustrates a data
centre 110 having a wall 112 which separates an enclosed indoor
space 114 from outside 116. A plurality of server racks 118 are
arranged in the enclosed inside space 114. Each rack 118 has an
evaporator assembly 120 mounted on its rear door. In the
illustrated embodiment the data centre 110 has four rows of eight
racks. Each row of racks has its own CDU 122. Each evaporator
assembly 120 has a plurality of serially arranged heat exchangers.
The CDU 122 comprises a plurality of CDU modules (not shown) each
of which connects to a plurality of parallel heat exchangers, one
heat exchanger per rack in the row. Thus, although each rack has a
plurality of heat exchangers with independent coolant circuit, the
coolant circuits are shared between the racks, i.e. all of the
first heat exchangers may be connected (e.g. in parallel) to a
common coolant circuit.
[0063] Each CDU 122 may be connected to a main CDU (MCDU) 124, e.g.
by two or more forward and return flow path pairs to provide
redundancy. Thus there may be at least four connections from each
CDU 122 to a MCDU 124. The MCDU 124 may be optional; it may be
possible to couple a CDU 122 directly to a hybrid chiller assembly
126. In FIG. 4 the CDUs in the two rows on the left are shown as
paralleled on to a common pipe installation; this may be
beneficial, e.g. to reduce installation costs.
[0064] The hybrid chiller assembly is arranged outside 116. The
assembly comprises a plurality of hybrid chiller independently
connected to the MCDU 124. Details of the connection are discussed
below with reference to FIG. 5.
[0065] Each evaporator 120 in FIG. 4 could be implemented as any
one of a rear door assembly, a dedicated cooling rack, a hot aisle
roof, a rack side panel, a blade chassis, or a embedded rack cooler
unit. Alternatively, the heat exchangers may include a heat sink or
heat pipe.
[0066] In operation, a control system (not shown) may handle system
operation, fault detection and coolant handling. The evaporator
assemblies may include thermal monitoring systems (which may be
wireless or hardwired) and fire extinguishing valves controlled by
the CDU evaporation/exhaust of the natural refrigerant. The CDU may
be arranged to stabilise the average indoor temperature, e.g. to a
reference value which may be selectable. The CDU may includes a
controller arranged to operate based on measured values or any one
or more of ambient (e.g. outdoor) temperature, chiller operating
modes, indoor temperatures, evaporator performance measurements
heat source measurements, and coolant pressure and temperature. The
CDU may also be arranged to measure indoor temperatures, either
through a wireless sensor array or hardwired thermal sensors
distributed in the data centre.
[0067] The CDU may also detect and isolate any leakage, hose or
pipe bursts, blockages, or other abnormal behaviour. After
isolating any leakage the CDU may control the auto fill storage to
re-establish the lost amount of coolant within the affected
circuits. The CDU can therefore handle any issues with
availability, if such incidences should occur.
[0068] Where each CDU may connect to a plurality of heat
exchangers, each connection may have a hot plug mechanism to handle
unplugging and plugging of additional CDUs or evaporator
assemblies.
[0069] In emergencies, e.g. a fire in cooled equipment such as a
complete rack where the measured temperature indicates the a given
burst is due to a fire, the cooling apparatus in the affected area
can be shutdown without affecting other systems. The fire may thus
be extinguished while all remaining systems are kept up and
running.
[0070] The hybrid chiller assembly may control the working pressure
of the coolant within each circuit. Each hybrid chiller may operate
as a free cooler, which is a condenser unit without compressor,
thus not changing the pressure of the evaporated coolant, or as a
forced cooler, e.g. as a energy consuming compressor-based
condenser, where the pressure of the coolant is increased above its
critical point. Selecting the operation mode may be controlled by
the hybrid chiller itself, based on ambient temperature, working
pressure, and a maximum allowed room temperature (interior
temperature). Hybrid chillers located outside may have a safety
blow out valve, in case of over pressure in the system. Thus making
sure that a blow out would occur outside rather than inside.
[0071] Turning again to FIG. 1, operation of the system is as
follows. A basic mode of operation is where both sets of hybrid
chillers 32, 34 operate in free cooling mode. This mode works when
the ambient temperature is such that the coolant can be condensed
without compression. As the ambient temperature and/or the heat
energy of the heat flow increases, the coolant in the first set 18
of evaporators (i.e. the evaporators which see the heat flow at its
hottest) may approach its critical point. Above this temperature
and pressure the remaining cooling capacity of the first set of
evaporators falls away. However, the second set 20 of evaporators
receives the heat flow after cooling by the first set, and so the
system may still operate to maintain the inside temperature at a
set reference value.
[0072] If changes in the temperature and/or pressure of the coolant
in the second circuit causes it to approach its critical point, the
second set 34 of hybrid chillers may be switched to the forced
cooling mode, in which they actively cool the coolant by increasing
its pressure (e.g. by transcritical CO.sub.2 cooling), thus
increasing the coolant temperature above ambient temperature to
facilitate cooling it down before lowering the pressure again. This
is a standard approach in compressor-based cooling.
[0073] However, the first set 32 of hybrid chillers stays in the
free cooling mode at this time. Thus even though some forced
cooling is taking place, this is only after the free cooling
benefit of the first set 18 of evaporators has occurred. This may
reduce the amount of forced cooling that is necessary, which may
improve overall efficiency.
[0074] Thus, the main difference between the first and second sets
32, 34 of hybrid chillers is that the second set 34 may change to
compressor mode before the first set 32, to extend to the highest
possible degree the operation in free cooling mode of the first
cooling circuit.
[0075] A further operational mode may be both cooling circuits
operating in forced cooling mode. This may occur e.g. if the
ambient temperature is too high for free cooling to be effective
(e.g. when the ambient temperature approaches the critical
temperature of the coolant).
[0076] By controlling each system like described above it is
possible to maintain a reliable and cost effective system, which
increases the year of year power usage efficiency of a data centre
in for instance Denmark to 96% from below 50%, while also
minimising the wear and thus increasing the lifetime of the cooling
apparatus. The possible power saving is discussed below with
reference to FIG. 6.
[0077] FIG. 5 shows in more detail the redundancy feature of
cooling apparatus that is an embodiment of the invention. In FIG. 5
the heat source 130 (e.g. a plurality of server racks) emits a heat
flow 132. An evaporator assembly 134 is arranged in the path of the
heat flow 132. The evaporator assembly comprises two sets of heat
exchangers arranged such that the heat flow passes through them. A
first set of heat exchangers is located closer to the heat source
130 that an second set. The sets of heat exchangers are fed coolant
from coolant distribution unit (CDU) 140 via respective input
conduits 136. The heat exchangers in each set may be connected in
parallel to their respective input conduit 136. The sets of heat
exchangers transfer heated coolant to the CDU 140 via respective
output conduits 138. The heat exchangers in each set may be
connected in parallel to their respective output conduit 138. As in
earlier embodiments, the coolant for the first heat exchangers is
isolated from the coolant for the second heat exchangers throughout
the circuit. Accordingly the apparatus provides a first hybrid
condenser 142 for coolant from the first heat exchangers and a
second hybrid condenser 144 for coolant from the second heat
exchangers. To provide redundancy, each hybrid condenser 142, 144
may comprise a plurality of modules. The modules in each hybrid
condenser 142, 144 are connected to the CDU 140 via a respective
modular interface 146, 148. The purpose of the modular interface is
to direct the coolant to certain modules in the hybrid condenser.
The modular interface may provide user control over how many and
which particular modules are used, e.g. to promote efficiency and
enable servicing and maintenance to take place without shutdown of
the apparatus.
[0078] Each modular interface 146, 148 is also connected to a
service unit, which may perform the auto fill storage function
described above.
[0079] The cooling apparatus described herein may be redundant in
its construction, e.g. through the provision of multiple
evaporators, each having its own cooling circuit, CDU module and
dedicated hybrid chiller. With two evaporators per heat flow, the
apparatus may easily achieve 2N redundancy (i.e. where no single
point of failure will interrupt overall operation).
[0080] However, the benefits of such redundancy are greatly
extended when the system is scaled up. For example, if the system
is designed to cope with a maximum power of 30 kW from a server
rack, the more racks there are the more free capacity that may be
available because loads vary between racks. Since all non-cooled
heat sources will contribute to a shared increase in room
temperature, this free capacity may operate as a global redundancy
for the other racks.
[0081] For example, consider a data centre with 300 kW IT power
usage creating approximate 300 kW heat. If this is divided up in 40
racks at 7.5 kW per rack, and the cooling capacity of the
evaporator assembly on each rack is 30 kW, the redundancy on its
cooling capacity may be 2N+39.
[0082] If the rear door of a rack is opened, the heat flow from
that rack may escape the local evaporator assembly. This heat will
dissipate in the enclosed space and hence effectively be divided
among other racks. Whilst in this circumstance the local evaporator
may cause a loss in efficiency, this is far outweighed by the
ability of the apparatus to use existing air flow from the servers,
i.e. there may be no need to circulate air within the enclosed
space.
[0083] FIG. 6 is a graph that schematically illustrates the
potential power saving achievable by using the invention. A bold
line on the graph shows the power consumed by the hybrid chiller
assembly of the invention as the ambient temperature varies. A
dotted line shows the power consumed by a chiller assembly
connected to a circuit in which there is only one heat exchanger.
Clearly, as ambient temperature increases the efficiency of free
cooling decreases. In a system with only one heat exchanger
(evaporator), the switch to forced cooling must occur as soon as
the temperature of the coolant in the heat exchanger approaches the
boiling point of the coolant. This is indicated at ambient
temperature T.sub.1 in FIG. 6. Where there are two or more
evaporators, both evaporators may be able to continue to operate in
a free cooling mode beyond ambient temperature T.sub.1.
[0084] In the apparatus according to the invention, the compressor
in the second cooling circuit is switched on first (when the
temperature of the coolant in its heat exchanger approaches boiling
point). This occurs at temperature T.sub.2 in FIG. 6. Eventually
the ambient temperature may reach a point where the compressor in
the first cooling circuit is switched on (e.g. when the temperature
of the coolant in the heat exchanger of the second cooling circuit
approaches boiling point despite operating in the forced cooling
mode). This occurs at temperature T.sub.3 in FIG. 6.
[0085] FIG. 6 shows that if the ambient temperature is between
T.sub.1 and T.sub.3 the system of the invention consumes less power
than the single evaporator option. Thus, if the range of typical
outdoor temperatures of a location fall within the range T.sub.1
and T.sub.3 the cooling apparatus of the invention may enable
significant power savings.
[0086] The switch from free cooling to forced cooling in each
circuit may be based on measurements of any one or more of ambient
temperature, pressure and/or temperature of the coolant, room
(inside) temperature. The coolant pressure may be measured in
either the inlet, or exhaust from the chiller, or the receiver of
the particular cooling circuit. The coolant temperature may be
measured in either the inlet, or exhaust from the chiller, or the
receiver of the particular cooling circuit.
[0087] It may be possible to match the cooling apparatus of the
invention to a given rack power density spread through out a
complete data centre. The modular nature of the apparatus may
facilitate changing the capacity and availability of cooling to
follow changes in the data centre through its lifetime.
[0088] A configuration device may be provided to calculate the
exact need for evaporator panel placement and quantity based on
power usage profiles for each rack in a given data centre
configuration. This should be based on varying power usages over
time, due to changing power usage of it equipment caused by
virtualization, load shedding etc.
[0089] The apparatus may be implemented using a combination of room
air conditioning (when panels are shared among several racks) and
dedicated rack cooling (when a panel cools a single rack). All
evaporators will have a positive effect on the entire room cooling,
extending the efficiency benefits of individual rack cooling. This
arrangement may both focus on removing hot spots in the data
centre, by direct cooling of high density racks, and using the
remaining evaporators as standard room air conditioning as a
redundant fall back solution.
[0090] FIG. 7 shows components of each of the main parts of one of
the cooling circuits of a cooling apparatus that is another
embodiment of the invention. Components in FIG. 7 which perform the
same function as those described above with respect to FIG. 2 are
given the same reference numbers and description thereof is not
repeated.
[0091] In this embodiment, the heat exchanger 46 is connected to
receive coolant (in this case CO.sub.2) from a free cooling loop
160, i.e. a coolant distribution circuit without a compressor.
Similarly to the arrangement in FIG. 2, the reservoir 66 has a gas
outlet 170 that delivers heated coolant via conduit 178 to a
condenser 72. In this embodiment there is no compressor on the path
between the reservoir 66 and condenser 72. Liquid coolant from the
condenser 72 is delivered back to the reservoir 66 via liquid inlet
180. In this embodiment there is an auxiliary heat exchanger 182 (a
plate heat exchanger in this embodiment) on the path between the
condenser 72 and the reservoir 66.
[0092] During operation in the forced cooling mode, the coolant
from the condenser 72 is cooled by being brought into thermal
communication with auxiliary coolant in the auxiliary heat
exchanger 182. The auxiliary coolant is cooled in a chiller 184,
e.g. a conventional compressor or the like, where heat extracted
from the auxiliary coolant is transferred to an external
environment. The chiller may comprise a plurality of cascading
cooling loops. The chiller 184 receives heated auxiliary coolant
from the auxiliary heat exchanger 182 via a hot input conduit 186
and conveys cooled auxiliary coolant to the auxiliary heat
exchanger 182 via a cool output conduit 186. The auxiliary coolant
is independent from the coolant in the free cooling loop 160 and
may be different therefrom. For example, the auxiliary coolant may
be water under vacuum, NH.sub.3 or other similar refrigerants, or
heat transferring medias such as oils, glycol etc.
[0093] The embodiment shown in FIG. 7 may be beneficial because it
reduces the risk that CO.sub.2 is contaminated with oil from the
compressor, which may occur in the hybrid chiller arrangement shown
in FIG. 2. Such contamination will over time reduce the efficiency
and cooling capacity of the system.
[0094] The arrangement shown in FIG. 7 also provides advantages in
terms of availability and serviceability, since the system may be
more configurable and maintenance of the compressor and/or chillers
may take place without affecting the closed CO.sub.2 loop. It may
even be possible to shutdown and perform maintenance work on the
chiller while still running the free cooling CO.sub.2 circuit. In
arrangement where there are a plurality of second heat evaporators
connected to the same CDU, there may be a plurality of parallel
auxiliary cooling circuit (i.e. paralleled chillers) in thermal
communication with the cooling distribution circuit.
[0095] The condenser 72 in the FIG. 7 arrangement is also able to
free cool while the chiller 184 is active. The on/off control of
the condenser 72 may be based on the ambient temperature and
temperature of the coolant. Other factors may also be taken into
account, e.g. the time of the day if noise level is to be
controlled.
[0096] As mentioned above, the CDU for the first heat exchanger may
not be operational in a forced cooling mode, i.e. it may not have a
compressor or auxiliary cooling circuit associated therewith.
[0097] The condenser 66 may consist of multiple paralleled or
series coupled condensers with bypass valves for maintenance. A
water spraying system (not shown) may be arranged to spray water on
the condenser(s) to facilitate operation thereof, e.g. to maintain
temperature and/or pressure conditions therein at a configurable
level below the critical point of the coolant. Spraying may occur
before and/or during activation of the chiller. Operation of the
water spraying system may be based on the ambient temperature,
temperature and pressure of the coolant (e.g. as measured by the
detector).
* * * * *