WO2011073668A1

WO2011073668A1 - Data centre building and method

Info

Publication number: WO2011073668A1
Application number: PCT/GB2010/052117
Authority: WO
Inventors: Paul Rogers
Original assignee: Bripco BVBA
Current assignee: Bripco BVBA
Priority date: 2009-12-17
Filing date: 2010-12-16
Publication date: 2011-06-23
Anticipated expiration: 2012-06-17
Also published as: GB0922095D0

Abstract

A data centre building (100) comprises a rack room (140) comprising a plurality of racks (143) housing computer servers, at least one cold aisle (144), and at least one hot aisle (145). The data centre building (100) comprises a first set of air circulating devices, provided external to the rack room for example in an air optimiser unit (111), for transporting cooling air (118) from a cold aisle (144) via a rack (143) into a hot aisle (145). One or more racks (143) optionally comprise a second set of air circulating devices for cooling the rack- mountable electronic components. The cooling power of the first set of air circulating devices is greater than the cooling power of the second set of air circulating devices (if present). The first set of air circulating devices is used as the primary means for transporting cooling air (118).

Description

Data centre building and method

Background of the Invention

The present invention relates to a data centre building and a method of operating a data centre.

A data centre is a late 20^th Century development that has grown as a response to the increasing demand for computer processing capability and a recognition of the importance of information technology (IT) in the place of every business and organisation today. Whereas smaller organisations have sufficient processing power with laptops, PCs and occasionally servers, larger organisations require higher capacity centralised processing to serve a wide range of needs and applications. A few years ago this capacity was supplied by large mainframe computers, but more recently the method used has been to provide data centres comprising many networked computer servers known as "blades" installed in racks enabling controlled and modular expansion of capacity. The racks also typically house storage systems and/or telecommunications equipment such as routers to handle data flow between the computer servers and data flow between the data centre and the outside world. It is conventional to provide each rack component, for example a server, with a cooling fan. Servers are typically provided as electronic components housed within a metal casing or box that includes grilles or vents front and rear to facilitate the flow of cooling air through the casing or box and over the electronic components to cool the components during use. A fan inside the casing or box causes or assists the flow of cooling air through the casing or box. It is also known to sell rack-mountable computer servers without fans. For example, the Californian company, Stealth.com Inc., sells a rack-mountable computer server called the "SR-2625F - Fanless 2U Rack Server". Also, certain low heat generating rack mountable components or high heat endurable components may be mounted in a rack and not be provided with an integrated fan. Many such fanless components can not be packed in close proximity to one another and do not lend themselves well to scaleabilty, efficient use of space or reliability, as a result of the need to manage the heat that would otherwise be generated.

WO2007/149855 discloses a data centre racking arrangement in which there are two stacks of half-depth servers in a single rack. In one of the arrangements envisaged by WO2007/149855, the fans which would normally be located within the chassis of each server are mounted in the rack but external to the server chassis. The fans, being provided in the racks, are still local to the racks. Thus, whilst WO2007/149855 proposes the use of fanless servers, the arrangement proposed in WO2007/149855 still requires the use of many fans in the racks. Such an arrangement might not provide a particularly efficient means of cooling the servers, and also reduces the density of computer servers able to be provided in the space defined by the racks. Also, the racks, being designed for half-sized servers, do not appear to be configured to accept standard sized IT equipment for use in standard- sized racks.

The present invention seeks to provide an improved data centre building or an improved method for cooling a data centre. Alternatively or additionally, the present invention seeks to provide a data centre building and/or improved method for cooling a data centre that mitigates one or more of the above mentioned disadvantages.

Summary of the Invention In accordance with a first aspect of the present invention, there is provided a data centre building comprising a rack room,

the rack room comprising

(i) a plurality of racks, each rack housing a plurality of rack- mountable electronic components, the majority of which preferably being computer servers,

(ii) one or more cold regions, defined at least partly by the layout of the racks, the one or more cold regions including at least one cold aisle, and

(iii) one or more hot regions, defined at least partly by the layout of the racks, the one or more hot regions including at least one hot aisle, the data centre building comprising a first set of air circulating devices for transporting cooling air to said one or more cold regions, then via the racks, to said one or more hot regions, at least some of the cooling air passing from a cold aisle via a rack into a hot aisle, thus cooling the rack-mountable electronic components in the racks,

the first set of air circulating devices preferably being provided external to the rack room,

the rack room optionally comprising a second set of air circulating devices for cooling the rack-mountable electronic components, each of the air circulating devices of the second set (if present) being provided by a rack, the cooling power of the first set of air circulating devices being greater than the cooling power of the second set of air circulating devices (if present).

The first set of air circulating devices is typically provided external to the rack room, although the first set of air circulating devices may in certain embodiments be provided in the rack room.

A rack room will typically comprise a floor, a ceiling, one or more walls, and preferably one or more doors providing personnel access to the rack room. In certain embodiments, one or more walls of the rack room may be defined by front or rear sides of a row of racks. In the case where a rack defines a wall of a room, such a rack may be considered as being within the room. However, if one considers the side of the row of racks that faces the room to define one or more walls of the room, then it may in certain

embodiments be more appropriate to consider those racks and the servers therein, or a substantial part of such racks/servers, to be outside the room. There may be a plurality of rack rooms in the data centre building. At least some of the rack rooms may be located directly adjacent to each other. There may in certain embodiments be no dedicated wall between adjacent rack rooms.

There may be at least 10 racks per rack room, preferably more than 20 racks per rack room. The data centre building may include more than two rack rooms. Preferably, however, there are fewer than ten rack rooms per floor of the building. Each rack may have more than 10 slots for insertion of separate rack-mountable electronic components. Each rack may have more than twenty such slots. Thus, each rack room may, when operating at full capacity, accommodate over 500 separate servers (and/or other separate rack-mountable electronic components), and possibly more than 1,000.

The circulation of cooling air to the racks may be performed under a controlled pressure regime. An air circulation control unit may be provided to control such a process. Pressure sensors may for example be provided to provide a measure of pressure in different regions of the data centre building. The control unit may be arranged to receive signals representative of the pressure so measured, such signals being used to control the cooling of the data centre. The cooling and/or the pressure regime may be adjusted by means of controlling (preferably automatically) controllable vents located between different regions of the data centre. For example, such controllable vents may be located in the path of the cooling air, such a path for example extending from the source of cooling air via said one or more cold regions, then via the racks, to said one or more hot regions. There may of course be many cooling air paths, there being for example a path of cooling air for each of many independent cold regions / hot regions. The controllable vents preferably divide the or each cooling air path into two or more discrete sections.

The pressure regime may comprise maintaining differential pressures as between the pressure in a cold aisle and the pressure in a hot aisle, so that air flow is encouraged from the cold aisle to the hot aisle. The pressure regime may comprise maintaining differential pressures as between the pressure in a hot aisle and a downstream pressure, for example outside the building, to encourage extraction of air away from the hot aisle. The pressure regime may comprise maintaining differential pressures as between the pressure in a cold aisle and an upstream air supply duct. The differential pressure may be required upstream of a cold aisle simply to enable differential pressures downstream. The pressure differential between two successive points on the airflow route (for example either side of the racks or either side of an air intake dividing a rack room from an airflow) may be greater than 5Pa, is preferably greater than 10 Pa, and preferably less than lOOPa.

It is preferred that the cooling power of the second set of air circulating devices (if present) is less than 50% (further preferably less than 30% and further more preferably less than 10%) of the cooling power of the first set of air circulating devices. The cooling power of a fan or a set thereof may be measured or calculated by measuring the volume of the cooling air flow per unit time and measuring the temperature of the air flow. Alternatively, the cooling power of a set of fans may be defined simply by reference to the volume of air that passes through the racks per unit time. For example, the cooling power of the first or second set of fans may be defined as the volume of air that passes through the racks per second when each fan in the set is operating at the maximum speed that such each fan would be expected to operate at during the lifetime of the data centre.

The volume of air flow per unit time able to be independently generated by the first set of air circulating devices may be greater than the volume of air flow per unit time able to be independently generated by the second set of air circulating devices. It is preferred that the volume of air flow per unit time able to be independently generated by the first set of air circulating devices is at least three times (and more preferably at least five times and further more preferably at least ten times) greater than the volume of air flow per unit time able to be independently generated by the second set of air circulating devices.

The second set of air circulating devices (if present) may comprise fewer air circulating devices than the first set of air circulating devices. The second set of air circulating devices (if present) may comprise fewer than 50% (and possibly fewer than 30%> and possible fewer than 10%) of the number of air circulating devices in the first set.

It is preferred that the second set of air circulating devices (if present) comprises fewer operational air circulating devices than the first set of air circulating devices. It is further preferred that the number of operational air circulating devices of the second set of air circulating devices (if present) is fewer than 50% (and further preferably fewer than 30% and further more preferably fewer than 10%) of the number of air circulating devices in the first set. It will be appreciated that an operational air circulating device is one that is arranged to operate to assist with moving cooling air through the racks during at least some part of the normal operation of the data centre building. The racks may for example be arranged to be filled substantially entirely with fanless servers or other fanless components. However, there may be a need to install in the rack one or more components that have integrated fans. There may therefore be operational fans in the second set of fans, even though in respect of the or each component that is associated with each such fan there is no need for the airflow through the component to be controlled or enhanced by the operation of its own fan.

The second set of air circulating devices (if present) may comprise more air circulating devices, albeit inoperative air circulating devices, than the first set of air circulating devices. The first set of air circulating devices may comprise fewer than 50% (and possibly fewer than 30% and possible fewer than 10%) of the number of air circulating devices (albeit inoperative air circulating devices) in the second set.

In one possible embodiment of the invention, a majority of the electronic components include a fan, such fans together forming the second set of air circulating devices, but at least a majority, and preferably all, of said second set of air circulating devices are rendered inoperative.

It will be appreciated that an inoperative air circulating device is one that is prevented from assisting with moving cooling air through the racks at all times during operation of the data centre building. For example, an air circulating device may be present but not powered. An air circulating device may be present and powered, but controlled so as never to be operated, and thus be considered as rendered inoperative. It will be seen that an air circulating device will either be arranged to be an inoperative air circulating device (one that never operates) or an operational air circulating device (one that is arranged to operate, but perhaps for only part of the time). Thus, even if the second set of air circulating devices, if not rendered inoperative, would have a cooling power greater than that of the first set of air circulating devices, the fact that they are, in this embodiment of the invention, rendered inoperative ensures that the cooling power of the first set of air circulating devices is greater than the cooling power of the second set of air circulating devices.

It is preferred that there are no air circulating devices provided in any of the racks in the rack room for cooling the rack-mountable electronic components. However, one or more racks may be provided with an air circulating device.

It is preferred that a majority of the rack-mounted electronic components are fanless components.

It is preferred that at least one of the racks (preferably more than one of the racks, more preferably the majority of the racks and further more preferably all of the racks) is not provided with an air circulating device for cooling the rack-mounted electronic components.

It is preferred that at least 60%, preferably at least 80% and further more preferably at least 90% of the rack-mounted components are computer servers. Such servers are well- known to those skilled in the art, and are typically blade servers.

One or more of the rack-mounted components may be provided with a cooling air input side on a first side of the rack, a cooling air exhaust side on a second side of the rack, and an in-rack cooling airflow path extending from said first side to said second side. The one or more in-rack cooling airflow paths may be arranged to facilitate the extraction of heat from heat-generating components. The one or more in-rack cooling airflow paths may be arranged to provide the primary means for cooling the rack-mounted components.

One or more of the rack-mounted electronic components (preferably more than one rack-mounted electronic component, further more preferably a majority of rack-mounted electronic components and most preferably each rack-mounted electronic component) may be provided with a cooling air input side on a first side of the rack, a cooling air exhaust side on a second side of the rack, and an in-rack, preferably fanless, cooling airflow path extending from said first side to said second side. The in-rack, preferably fanless, cooling airflow paths are typically arranged to facilitate the extraction of heat from heat-generating components and are typically the primary means for cooling the rack-mounted components. The rack is preferably so arranged that there are no in-rack fans arranged to assist airflow via each in- rack cooling airflow path. Alternatively, there may be cooling fans in the racks that are inoperative or otherwise do not contribute, in any significant manner, (and preferably not at all) to the cooling of the rack-mounted components.

The rack typically requires an air pressure difference to be applied across the rack, with the air pressure at the first side being higher than the air pressure at the second side in order for sufficient cooling air to flow along the fanless airflow paths for the rack-mounted components to function without overheating.

The provision of in-rack fanless airflow cooling paths is preferred when the rackmounted electronic component is a computer server.

One or more rack-mounted components (preferably one or more server, more preferably more than one server, further more preferably between 30 and 50% of servers) may be provided with more than one fanless cooling airflow path.

The in-rack fanless cooling airflow path typically extends across the face of each component.

The racks may be provided with blanking plates to ensure that substantially all of the cooling air that flows via the racks flows through or over a rack-mounted component, such as a server. The cold and hot regions of the data centre building may be arranged to be enclosed, or otherwise sealed, such that flow of cooling air from the cold regions to the hot regions is only via a rack. Proper control and entrainment of cooling air may be important for improving efficiency.

The first set of air circulating devices may be positioned upstream of the racks. There may be one or more cooling airflow paths extending from the first set of air circulating devices via one or more cold aisles, to the racks. Upstream of the one or more cold aisles there may be one or more large air supply ducts. It is preferred that two or more cold aisles are supplied with cooling air by means of one common air supply duct. The one or more air supply ducts may be defined by personnel access corridors. One or more controllable vents may be associated with the air flowing via each cold aisle, respectively. The or each air supply duct is preferably entirely located above floor level. A central control unit may be provided for controlling the one or more controllable vents. The one or more cold aisles may be connected to the cooling air supply duct by means of such a controllable vent. A personnel access door may also be provided between the cooling air supply duct and the or each cold aisle. The controllable vent may form part of the door or be provided separately from the door. There may be at least two pairs of adjacent rows of racks. A hot aisle may be defined between one such pair of rows of adjacent racks, in which pair, the second sides of the racks face each other. A cold aisle may be defined between another such pair of rows of adjacent racks, in which pair, the first sides of the racks face each other.

The cold aisles and/or hot aisles may be substantially straight along their length. The data centre building may be so arranged that a plurality of cold aisles are interleaved between a multiplicity of hot aisles. It will be appreciated that a "cold aisle" may be "cold" in the sense that it is upstream of the rack storage area in the direction of flow of cooling air, in use. It will also be appreciated that a "hot aisle" may be "hot" in the sense that it is downstream of a rack in the direction of flow of air from the racks that has, in use, been heated by rack mountable electronic components in the racks. The hot aisle may be hot in the sense that the temperature in the hot aisle is, once a steady state has been achieved during operation, typically higher than the temperature in the cold aisle.

The cold aisle and/or hot aisle may in use act as a large air duct. Whilst the cold aisle and/or hot aisle may have a relatively large cross-section, it is preferred that cross-sectional area of the hot aisle and/or cold aisle is not excessively wide or tall, for example to assist with the entraining of the air flow. For example, the maximum dimension of the aisle (for at least 90% of its length) within the plane of the cross-section of the aisle is preferably less than 4m and more preferably less than 3m. The aisle is preferably elongate in geometry.

The hot aisle may be sized to permit personnel access. The hot aisle may for example be in the form of a personnel corridor. The cold aisle may be sized to permit personnel access. The cold aisle may for example be in the form of a personnel corridor. For an aisle to be suitable for use as a personnel corridor it may need to have a minimum width and/or a minimum height, for example along at least 90% of its length. The personnel corridor may for example have a height greater than 1.5m above the floor. The personnel corridor may have a large cross-sectional area, namely an area greater than 2m2, and preferably greater than 3m2.

The cooling air flow path from upstream of the rack room, then via said one or more cold regions, then via the racks to said one or more hot regions, is entirely above floor-level.

The floor may be defined as the surface on which the racks stand. The data centre building may be so arranged that cooling air is transported to the one or more cold aisles under the control of a central air circulation control system. The central air circulation control system may receive a plurality of different inputs concerning one or more of temperature, air velocity, air humidity and air pressure. The central air circulation control system may, in use, control the temperature and/or humidity of the cooling air being supplied to cool the components in the racks. The central air circulation control system may, in use, control the speed or pressure at which the cooling air is supplied.

For example, there may be a requirement to maintain a certain pressure differential region, for example there being a certain minimum pressure difference across the racks. There may be a requirement to maintain the temperature in the hot regions below a certain maximum value.

In data centres of the prior art it is common to provide under-floor air ducts. Certain embodiments of the present invention do not employ such under-floor ducts. There is therefore no need to have a high raised floor in embodiments of the present invention. The upper surface of the floor may be less than 500mm above the base of the building, for example. Better use may therefore be made of the vertical space available in a building of a given height.

It is preferred that at least one rack has space for at least 16 rack-mountable components, more preferably at least 24 rack-mountable components and further more preferably at least 42 rack-mountable components.

At least one rack may comprise a relatively large number of servers. For example, the number of servers may be equivalent to at least 40 servers per 42 unit rack, and preferably at least equivalent to 80 servers per 42 unit rack. It may be possible for the number of servers to be equivalent to at least equivalent to 120 servers per 42 unit rack. The packing of so many servers in such a space may be achieved by means of providing specially adapted servers. Each server is preferably provided without any cooling fan. Each server may be provided without any external casing for that individual server. Each server may be arranged such that at least one processor chip on the board, or a heat sink connected thereto, is directly exposed to the cooling air passing from the cold aisle via the rack into the hot aisle (i.e. without needing to pass via a vent that is unique to that particular server).

At least one (preferably more than one and more preferably each) rack may accommodate 20 or more servers. There may be at least four such racks, each

accommodating at least 10 servers, preferably 20 or more servers.

It will be appreciated that a 42-unit rack is a conventional size of rack and typically has a height of about 2m and a width of about 600mm. When cooling air passes via the racks, the air may pass through the rack-mountable electronic components, particularly when each rack-mountable electronic component comprises a casing arranged to allow air to flow therethrough. When cooling air passes via the racks, the air may pass around the rack-mountable electronic components, particularly when each rack-mountable electronic component does not comprise a casing. The air may when passing around a rack-mountable electronic component still extract significant heat from the component. Cooling air may pass both around and through the rack-mountable electronic components.

The air pressure at the first side may be at least 3 Pascal (preferably at least 5 Pascal, more preferably at least 8 Pascal and further more preferably at least 10 Pascal) greater than at the second side.

One or more racks may be housed in a cabinet. There may be one cabinet per rack. One cabinet may alternatively accommodate many racks. The cabinet preferably has a vent or vents provided on its front face. The cabinet may have a vent or vents provided on its rear face.

The air circulating devices of the second set (if present) may be provided by a rack by means of the rack accommodating the air circulating devices within the space in the rack, for example within one or more of the rack-mountable electronic components. The air circulating devices of the second set (if present) may be provided directly adjacent to the rack.

In accordance with a second aspect of the present invention, there is provided a data centre building comprising a rack room,

the rack room comprising

(i) a plurality of racks, each rack housing a plurality of rack- mountable electronic components, the majority of which being computer servers,

the rack room optionally comprising a second set of air circulating devices for cooling the rack-mountable electronic components, each of the air circulating devices of the second set (if present) being provided by a rack,

the number of air circulating devices in the first set of air circulating devices being greater than the number of air circulating devices in the second set of air circulating devices (if present).

It is further preferred that the second set of air circulating devices (if present) comprises fewer than 50% (and further preferably fewer than 30% and further more preferably fewer than 10%) of the number of air circulating devices in the first set.

The cooling power of the first set of air circulating devices may be greater than the cooling power of the second set of air circulating devices.

It is preferred that the cooling power of the second set of air circulating devices (if present) is less than 50% (further preferably less than 30% and further more preferably less than 10%) of the cooling power of the first set of air circulating devices.

The data centre building of the second aspect of the present invention may comprise those features described above in relation to the data centre building of the first aspect of the present invention. For example, the volume of air flow per unit time able to be independently generated by the first set of air circulating devices may be greater than the volume of air flow per unit time able to be independently generated by the second set of air circulating devices. It is preferred that the volume of air flow per unit time able to be independently generated by the first set of air circulating devices is at least three times (and more preferably at least five times and further more preferably at least ten times) greater than the volume of air flow per unit time able to be independently generated by the second set of air circulating devices.

In accordance with a third aspect of the present invention, there is provided a rack suitable for use in the data centre building of the first and/or second aspects of the present invention.

The rack of the third aspect of the present invention may comprise those features discussed above in relation to the data centre building of the first and/or second aspects of the present invention.

In accordance with a fourth aspect of the present invention, there is provided an air- cooled computer server rack in which there is housed a plurality of servers, the servers comprising heat-generating components which generate heat when the servers are operated, wherein

a majority of the servers in the rack comprise

a cooling air input side on a first side of the rack,

a cooling air exhaust side on a second, opposite, side of the rack, and a fanless cooling air flow path extending from the first side to the second side, the fanless cooling air flow paths being arranged to facilitate the flow of cooling air via regions in the rack that allows the cooling air to extract heat from the heat-generating components,

the fanless cooling air flow paths being the primary means for cooling the servers, and the rack requiring an air pressure difference to be applied across the rack, resulting in the air pressure at the first side being higher than the air pressure at the second side, in order for sufficient cooling air to flow along the fanless cooling air flow paths in order for the servers in the rack to function without over-heating.

It is preferred that each of the servers in the rack comprises

a cooling air input side on a first side of the rack,

a cooling air exhaust side on a second, opposite, side of the rack, and a fanless cooling air flow path extending from the first side to the second side, the fanless cooling air flow paths being arranged to facilitate the flow of cooling air via regions in the rack that allows the cooling air to extract heat from the heat-generating components.

The rack of the fourth aspect of the present invention may comprise those features discussed above in relation to the data centre building of the first aspect of the present invention.

The rack of any of the first to fourth aspects of the invention may comprise a single column of spaces for rack-mountable component. The rack may be so arranged that each rack-mountable component is mounted horizontally so that the component extends across at least 75% of the usable width of the rack. The rack may be so arranged that at least some of the rack-mountable components are mounted vertically in rows of many vertically mounted components. More than 5 such vertically mounted components may extend across the width of a single rack. There may be 8 or more in such a row. Each rack may be configured such that the main load bearing uprights of the rack are provided at each of its four corners, but not elsewhere. Many such racks may be provided side by side to define a wall of racks. The racks may be housed in cabinets. Each rack may be defined at least partly by a cabinet. The cabinet preferably has vents front and back to ensure good airflow.

It will be appreciated that a data centre building may be in the form of a data centre having its own dedicated building such that the primary function and purpose of the data centre building is one of being a data centre. The data centre building may alternatively be in the form of building in which only part of the building accommodates a data centre.

In accordance with a fifth aspect of the invention there is provided a method of operating a data centre building, for example a data centre building according to any aspect of the present invention described or claimed herein. The data centre building may for example comprise one or more cold aisles, one or more hot aisles, and a plurality of racks, arranged in one or more rows, each row being located between a hot aisle and a cold aisle, each rack housing a plurality of rack-mountable electronic components, the majority of which being computer servers.

The data centre building may comprise a first set of air circulating devices not located in any of the cold aisles, hot aisles and the racks. The method may include a step of using the first set of air circulating devices as the primary means for transporting cooling air such that air flows to at least one of the cold aisles, and then via the racks to at least one of the hot aisles, thus cooling the rack-mountable electronic components in the racks.

Any non-negligible contribution to the movement of cooling air via the cold aisles, the racks, and via the hot aisles may be provided solely by air circulating devices located upstream of the cold aisles.

The method may include a step of cooling racks of separate rack-mountable electronic components by operating the first set of air circulating devices to transport cooling air (which may be in the form of air from outside the data centre building at ambient air temperature) to the racks, preferably without utilising refrigerant-based active cooling. At least some of the air may then be removed from the racks and exhausted to outside the building via at least one air exhaust. At least some of the air may be removed from the racks and recirculated within the building. The first set of air circulating devices preferably provide a sufficient pressure differential, for example as compared to the air pressure immediately outside the building, to be able independently to cause air to be circulated via the racks such that the air moves through the racks at a rate of at least 20m³s^_1 per rack room (or optionally at least 10 mV¹ per rack room, or optionally at least 8 mV¹ per rack room, or optionally at least 5m³s^_1 per rack room). Such rates might represent the higher end of the likely range of operational air circulation rates. The data centre building may be arranged to operate at low IT demand levels with circulation rates of the order of only 0.3m³s^_1 per rack room, or perhaps only 0. lmV¹ per rack room. In the case where there are for example, three or more (or optionally five or more) rack rooms in a building, or a floor thereof, air may be moved at a rate of at least 50m³s^_1 within the building (or floor of the building, as the case may be), when operating at high demand for example (or optionally at a rate of at least lOmV¹, or possibly at least lOOmV¹, within the building). It will be understood that in certain embodiments, the air may be moved at lower rates, say less than 50m³ s^"1 within the building, but greater than lmV¹. Alternatively or additionally, air may be circulated at a rate of at least 0.4m³s^_1 per rack. If there are 24 racks in a rack room, such a rate would be equivalent to about lOmV¹ per rack room. Air may be circulated at a rate of at least 0.005m³s^_1 per rack, optionally at a rate of at least 0.05m³s^_1 per rack, and possibly at a rate of at least 0.15m³s^_1 per rack. Air may be circulated at a rate of at least lmV¹ per rack, and possibly at rates as high as at least 5m³s^_1 per rack. Alternatively or additionally, air may be circulated at a rate of at least 0.002m³s^_1 per slot in the racks in the room. If there are 40 racks in a rack room and 40 slots per rack, such a rate would be equivalent to about 3.2m³s^_1 per rack room. Alternatively or additionally, air may be circulated at a rate of at least 0.005m³s^_1 per rack slot, preferably at a rate of at least 0.008m³s^_1 per rack slot. At low demand, the air may be circulated at a rate of as little as 0.00024mV¹ per rack slot. If there are 24 racks in a rack room and 40 slots per rack (of which at any given time 10 or more are each closed over by a blanking strip thereby restricting or preventing the flow of air therethrough), such a rate may be equivalent to less than 0.2m³s^_1 per rack room. Air may be circulated at a rate of at least 0.0 lmV¹ per rack slot, or possibly at least 0.15m³s^_1 per rack slot (such rates again representing the higher end of the range of likely operational circulation rates). Thus, in an embodiment of the invention, a sufficiently large volume of air per second is used to effect "ambient air" cooling of the separate rack-mountable electronic components in the data room. There may therefore be less of a need for use of refrigerant-based active cooling. In certain embodiments of the invention, there is for example no need for CRAC units to be provided. This means of cooling may be used even when the ambient air temperature outside is higher than 20 degrees Celsius. Preferably, the method includes a step of operating the data centre and cooling it by means of airflows where the rate of air circulation is greater than 5m³ s^"1 per rack room and also a step, performed at a different time, of operating the data centre and cooling it by means of airflows where the rate of air circulation is less than lmV¹ per rack room. The first set of air circulating devices may be arranged to provide a flow of cooling air accrording to any of the aforementioned flow rates. For example, any of the aforementioned flow rates may be achieved substantially entirely by means of the first set of air circulating devices.

The method of the invention may include the use of a suitably arranged control apparatus. For example, the control apparatus may be arranged to receive inputs, from which measures of outside air temperature and relative humidity may be ascertained. The control apparatus may be arranged to receive at least one input from an air temperature sensor that measures directly or indirectly the temperature of air in a cold aisle. The control apparatus may be arranged to receive at least one input from an air temperature sensor that measures directly or indirectly the temperature of air in a hot aisle. The control apparatus may be arranged to receive at least one input from an air temperature sensor located on, within or directly adjacent to a rack of rack-mountable electronic components. There may be a separate temperature sensor associated with each rack. The method of cooling the rack- mountable electronic components may include controlling the cooling provided to ensure that the measured temperature of the air exiting the racks is no greater than a threshold temperature, which may for example be 37 degrees Centigrade.

The control apparatus may be arranged to receive at least one input from a humidity sensor that measures directly or indirectly the humidity of air in a cold aisle. The control apparatus may be arranged to receive at least one input from a humidity sensor that measures directly or indirectly the humidity of air in a hot aisle.

The control apparatus may be arranged to receive at least one input from an air pressure sensor located within the data centre building. The control apparatus may for example be arranged to receive at least one input from a pressure sensor that measures directly or indirectly the pressure of air in a cold aisle. The control apparatus may be arranged to receive at least one input from a pressure sensor that measures directly or indirectly the pressure of air in a hot aisle.

It will be appreciated that other aspects of the invention may require a control unit, or multiple control units, requiring further inputs. The control apparatus may control the speed of the first set of air circulating devices, for example one or more fans that make up the first set of air circulating devices. The control apparatus may control the adjustment of adjustable apertures, for example air-flow control vents.

The method may include a step of cooling racks of separate rack-mountable electronic components by controlling the rate of supply of cooling air to the racks in dependence on the temperature of air being passed out from the racks. The method may include a step of cooling racks of separate rack-mountable electronic components by controlling the rate of supply of cooling air to the racks in dependence on the pressure of air in the air supply path upstream of the racks. The step of controlling the rate of supply of cooling air to the racks may include one or both of varying the speed of the speed of the first set of air circulating devices and adjusting the effective aperture size of one or more adjustable apertures, for example air- flow control vents. For example, the method may include varying the speed of the speed of the first set of air circulating devices in dependence on the pressure of air in the air supply path upstream of the racks. The method may include adjusting the effective aperture size of one or more adjustable apertures in dependence on the temperature of air being passed out from the racks. The method may include a step of maintaining a pre-set minimum pressure differential across the racks. The method may include a step of controlling the temperature and humidity of the cooling air supplied. The method may include a step of controlling the temperature and humidity of the cooling air supplied in dependence on the temperature and humidity outside the building. The method may include a step of controlling the temperature and humidity of the cooling air supplied in dependence on the temperature and humidity as measured by one or more temperature and humidity sensors, some of which possibly being located in the hot aisle and/or the cold aisle.

The control apparatus may comprise one or more programmable control units. The method of the invention may be implemented by means of suitably programmed control units.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the following figures of which:

Figure 1 shows a schematic plan view of an embodiment of an example of a data centre building in accordance with the present invention; Figure 2 shows a schematic perspective view of an embodiment of an example of a rack used in the data centre building of Figure 1 ;

Figure 3 shows a data centre building according to a further embodiment of the

invention, showing the building when viewed from above; and

Figure 4 shows a row of racks populated with server blades as used in the racks of the data centre building shown in Figure 3.

Detailed Description Figure 1 shows a data centre building 1. The building 1 is rectangular with external walls 2. The building is divided into front and rear sections by an internal dividing wall 2a, located approximately one third of the length of the building from the rear external wall.

The rear section (on the left in Figure 1) defines an air optimisation room 3, which provides a system of circulating cooling air in the building 1. Ambient air 4 is drawn into the air optimisation room 3 through an ambient air intake 5 in the rear external wall by a set of fans 6. Ambient air 4 can be treated/cooled in the air optimisation room and this air 4a is then used for cooling. If the ambient air outside the building 1 is sufficiently cool, the ambient air may be used as cooling air, without requiring any active cooling by the air optimisation room 3. Cooling air 4a passes into the front section of the building 1 through a controllable aperture 40 in the internal dividing wall 2a.

The front section (on the right in Figure 1) of the building 1 defines a rack room 8. The rack room 8 houses two rows of racks 9. The racks 9 extend away from the internal dividing wall 2a, towards the front of the building. Each rack row extends approximately out to two thirds of the length of the front section of the building. Although only shown schematically in Figure 1 , there are 20 racks in each row, each rack housing up to 40 items of IT equipment (typically server blades). There may therefore be a many as 1,600 items of IT equipment in the racks. A blanking panel 10a extends between the front ends of the two racks, thereby defining a cold region or "cold aisle" 11a between the internal dividing wall 2a, the two racks 9 and the blanking panel 10a. The flow of cooling air into the cold aisle 11a delivered between the two rows of racks is illustrated schematically by arrows 7a. Of course the air flow in the cold aisle is in reality more complicated. A hot region 1 lb is defined on the other side of the racks 9 and the blanking panel 10a. Air is caused to exhaust from the hot region l ib though a hot air exit 12 in the front external wall of the building.

In use, ambient air 4 is drawn into the air optimisation room 3 through the ambient air intake 5 by the set of fans 6. The set of fans 6 also urge air through the controllable aperture 40 as cooling air 4a. The ambient air 4 may be cooled (for example, using refrigeration or other cooling techniques) prior to being urged through controllable aperture 40. The cooling air 4a enters the rack room 8 into the cold region 11a. The cooling air 4a moves through the racks 9 in the rack room 8 to reach the hot region l ib and in the process cools the electronic components mounted in the racks 9. The resulting hot air 13 coming off the racks 9 then leaves the rack room 8 through the hot air exit 12.

The volume of air flow through the building is at least 12m³s^_1. Such a high rate of supply of air is sufficient to cool the IT equipment in the room via ambient air cooling alone for ambient air temperatures of up to 24 degrees Celsius.

In the present example, there are no cooling fans attached to the racks 9 and all of the servers in the racks are either fanless or have fans that have been rendered inoperative;

substantially all of the cooling of the racks is provided by the flow of air generated by the set of fans 6.

One of the racks 9 is now described in more detail with reference to Figure 2. Figure 2 shows a perspective view of part of a rack 9. The rack 9 comprises a plurality of rack mounts, mounted one on top of another, each rack mount being provided with one or more servers. The rack mount 20 has been mostly omitted for the purpose of clarity. The rack mounts above and below rack mount 20 have been omitted for the purpose of clarity. Rack mount 20 is provided with a plurality of electrical components, in this case blade servers 21, 22, 23, 24, 25, 26, 27, 28. Vent apertures (only two of which are labelled for clarity, 30) are provided for each blade server. Each server comprises a heat sink (not shown) that allows for conduction of heat away from heat sensitive components of the server. Each heat sink has fins to allow for transfer of heat from the heat sink to the cooling air passes over and past the heat sink. Cooling air 4a enters the rack room 8 and passes into cold region 11a. Cooling air 4a then passes through vent apertures 30 and into the airflow path between adjacent servers. The cooling air 4a in the airflow path contacts, and removes heat from, the servers as it passes over the face of the blade servers partly by means of the heat sinks. The air (now heated) enters hot region 1 lb. The racks are not themselves provided with cooling fans. The rack mounts (not shown) above and below rack mount 20 are also provided with servers in the same manner as shown in Figure 2.

The rack shown in Figure 2 is a 42 unit rack, and shows eight vertical blade servers mounted horizontally across the rack. The space occupied by the eight servers would normally be filled by four servers each housed in a dedicated slot. The server-packing capacity of the rack is thus effectively approximately doubled.

The airflow generated by the set of fans 6 cools the servers in the racks, and thus facilitates the use of server racks which are not themselves provided with cooling fans.

Figure 3 shows a rectangular data centre building 100 with external walls 110 and a flat roof of a further embodiment. The building has three rack room modules 140. Each rack room module 140 is identical in configuration. Each rack room comprise two rows 143 of racks, and a cold aisle 144 defined therebetween. One of the rows of racks effectively defines one extreme side of the rack room. The row of racks on the opposite side is separated from the opposite extreme side of the rack room by a hot aisle 145. It will be seen that the row of racks that divides adjacent rack rooms can be views as a wall defining the boundary between adjacent rooms. In the configuration shown in Figure 3, three cold aisles are interleaved between four hot aisles. The three cold aisles are each fed with cooing airs from a single air supply corridor 123. The four hot aisles 145 all feed a single hot air exhaust corridor 132.

The rear section (on the left in Figure 3) defines an air optimisation room 111, which provides a system of circulating cooling air in the building 100. Ambient air (represented by arrows 118a) can enter the air optimisation room 111 through an ambient air intake 113 in the rear external wall. Ambient air 118a can be treated/cooled in the air optimiser room and this air 118a is then used for cooling. If the ambient air outside the building 100 is sufficiently cool, the ambient air may be used as cooling air, without requiring any active refrigerant- based cooling by the air optimisation room 111. The cooling air then passes into the front section of the building 100 and passes (see arrow 118b) along an air supply corridor 123.

The racks accommodate computer servers and other IT equipment. The majority of the computer servers are either fanless or have fans that have been rendered inoperative. Cooling of the components mounted in the fans is thus provided substantially entirely by cooling air supplied by the air optimiser room 111. Such an arrangement can enhance efficiency of the data centre and further reduce the power requirements of the data centre, thus enabling the provision of a data centre with a very low power usage efficiency (PUE). . At one end of each rack room (the upper end in Figure 3), spanning across the ends of both rows of racks, is a cold aisle blanking panel 147 which closes off the cold aisle 144. At the top of both rows of racks 143 are over-rack blanking plates designed to stop cold air travelling over the racks 143 between the top of the racks and the ceiling of the rack room module 140. Hence, air can only leave the cold aisle 144 through the racks 143. There is no personnel access possible from the cold aisle 144 directly to the other side of the racks 143.

The data centre building of the embodiment shown in Figure 3 is modular in construction. There are six modules consisting of (moving left to right along Figure 3) an air optimisation module 111, a plant room module three rack room module 140 and a personnel module, which in Figure 3 facilitates personnel entry into the data centre building and the hot and cold aisles.

When a data centre building 100 is required to be built in a given location, the different modules can be individually delivered on trucks, such as 40 foot articulated or flat bed trucks. The buildings are typically less than 4.2m high and therefore are readily transported via road or rail. The modules can then be craned into place using integral lifting eyes (not shown) on the modules or using slings. The building 100 can be sited on a flat area of concrete. Alternatively, the building 100 can be placed on concrete blockwork if the site is not level or if the level of the building 100 is to match an existing building level. Each module comprises a steel framework and the walls (if present), roof and floor of each module are made of corrugated steel.

Cooling air 118a from the air supply corridor 123 can enter the cold aisle 144 of each rack room module 140 through controlled vents provided by respective cooling air intake grilles 142 positioned in personnel access doors (not shown) that divide each cold aisle from the air supply corridor. The vents that are controllable by a process control panel (located in the plant room) so that a desired air pressure regime can be achieved. The hot air from the racks 143 can leave the rack room modules 140 through the hot aisles 145. The hot air then reaches the hot air exhaust corridor 132.

On the upper wall (as viewed in Figure 3) of each rack room module 140, adjacent to the hot air exhaust corridor 132, is a hot air exhaust outlet grille 146 with adjustable vents that are controlled in use by the process control panel so that the amount of hot air that is exhausted from the building 100 through the hot air outlet grills 146 can be controlled. Hot air from the hot air exhaust corridor 132 may alternatively be recirculated via return air grille 125 and passed back to the air optimiser unit to be mixed with air from atmosphere, or to be used alone as the air that supplied the air optimiser unit.

The air optimisation module 120 contains an air optimisation unit which contains various air treatment apparatus, including a set of fans, air filters, humidification apparatus and an active DX cooling system. The humidification apparatus is used to provide adiabatic cooling during use. The air optimisation unit also contains an air mixing box (not shown) for mixing the air return from the hot aisles and ambient air taken from outside the building.

In use, ambient air 118 enters the air optimisation room 111 through the ambient air intake 113. The ambient air 118 is cooled/treated as necessary in the air optimisation room 111 resulting in cooling air 118b, which enters the rack room 140, into the cold aisle 144, via the vents in the doors on the ends of the cold aisles. The cooling air 118c moves over the racks 143 in the rack room 140 to reach the hot aisles 145 and in the process cools the equipment in the racks 143. The resulting hot air coming off the racks 143 then leaves the hot aisles and passes into the hot air exhaust corridor 132. It will of course be appreciated that the hot air is simply the result of the cooling air 118c having been heated by the equipment in the racks 143 and is otherwise essentially the same air. As such the operation may be considered as involving the flow of cooling air into the rack room 140, the flow of cooling air via the racks 143 and then the flow of cooling air (then heated by the racks such that the "cooling air" may then have less, if any, ability to cool) out of the rack room. As such "hot air" or "exhaust air" can be considered as heated or used "cooling air".

All flow of cooling air from the air supply corridor 123, via the cold aisle 144, via the racks 143, to the hot aisle 145 (and also flow of air along the hot air exhaust corridor 132) occurs above floor level. There are no under-floor air ducts under the racks or under the cold aisles for supplying cooling air thereto. Also, the air supply corridor 123, the cold aisle 144, and the hot aisle 145 (and also the hot air exhaust corridor 132) have a height of at least 2m and a width of at least 1.5m and are therefore sufficiently tall and wide enough for personnel access. The rack room module 140 also contains sensors for measuring the air temperature, humidity level, and air pressure. These and other such sensors are connected to the process control panel in the plant room. The sensors (only some of which being shown in Figure 3) comprise a temperature sensor and humidity sensor for measuring the psychrometric characteristics of the outside air; a temperature sensor, a humidity sensor and a pressure sensor for measuring the physical characteristics of the air in the air supply corridor; further temperature sensors, humidity sensors and pressure sensors for measuring the physical characteristics of the air in each of the cold aisles; pressure sensors for measuring the air pressure in each of the hot aisles; capillary tube temperature sensors 134 on the back of each rack for measuring the average temperature of the air exhausted from the slots of the racks; and a temperature sensor, a humidity sensor and at least one pressure sensor for measuring the physical characteristics of the air in the hot air exhaust supply corridor.

In use, the data centre building 100 of Figure 3 operates to cool the racks 143 in the rack room module(s) 140 by generating a sufficient quantity, velocity and pressure of cooling air 118a in the air optimisation unit 122. The air optimisation unit 122 also filters the air using air filters and performs humidification / de-humidification on the air, as necessary. The cooling process is controlled by the process control panel located in the plant room and will now be described in further detail. The principle control philosophy employed is that air supplied to the racks should have psychrometric characteristics within a certain range. In the present case, the control process is performed to supply cooling air at a temperature of between about 18 and about 24 degrees Centigrade and with a moisture content between acceptable preset limits. Cooling demand of the IT equipment in the racks is ascertained via measuring the temperature of air expelled from the racks, and is met by increasing (or decreasing) the flow of air to such racks. The process control panel controls the various grilles/vents and controls the cooling, humidification and other air treatments in the air optimiser room 111 in dependence on the inputs received as follows.

The cooling regime used is determined by the characteristics of the outside air. In a first scenario, the outside temperature is too low to be used safely to cool the servers. The control panel causes the vents to recirculate the hot air from the hot air exhaust corridor 132. The cold air from outside is mixed with as much or as little hot air from the hot air exhaust corridor 132 as is required to heat the cold outside air sufficiently for it to be safe for use as cooling air. If the outside air reaches a certain temperature (a second scenario), it then becomes more efficient to direct all of the hot air from the hot air exhaust corridor 132 to outside the building via the exhaust vents 146 and to use only outside air as the cooling air. In either of the two aforementioned scenarios, extra cooling is not required to be provided by the air optimiser unit. In a third scenario, the outside temperature is too high (for example, above 24 degrees Centigrade) to be used for cooling air without being additionally cooled by the air optimiser unit. In this scenario, the air optimiser unit cools the outside air to about 24 degrees. In a fourth scenario, the exhaust air has a temperature that is lower than the outside air. In such a scenario, it is more efficient to fully recirculate the air within the data centre and use the hot air exhausted from the racks as the source of the air to be treated by the air optimiser unit to provide the cooling air. Cooling of air in the air optimisation unit 111 is achieved by using a humidification unit to cause adiabatic cooling of the air and/or refrigerant-based active/mechanical cooling.

The rate of supply of air to the respective cold aisles is determined by cooling demand. If a row of racks has a greater need for cooling, the temperature of the air passing from the rack row will be higher. The vents to each cold aisle are controlled to open if the temperature of air passing from a rack, as measured by a capillary tube sensor in the hot aisle, exceeds a threshold value, for example 37 degrees C. If the vent to a particular cold aisle is fully open, and still there is a demand for greater cooling by racks being supplied with air from that cold aisle, then the speed of the set of fans in the air optimiser unit is increased. The flow of air is maintained to be as low as possible. Thus, the cold aisle having the greatest cooling demand will have vents that are fully open and the set of fans in the air optimiser unit will operate at such a speed that the temperature of air passing from the hottest rack associated with that cold aisle is as close to, but not greater, than the threshold value. The flow of air through the data centre must however be maintained such that there is a controlled pressure regime, with a pressure gradient sufficient to ensure that air flows in the intended direction within the data centre. If the pressure differential between one region of the data centre and another downstream region falls below a threshold value then the speed of the fans in the air optimiser unit are increased. The vents to each cold aisle are controlled to close if the temperature of air passing from a rack, as measured by a capillary tube sensor in the hot aisle, falls below the threshold value. The vents in the doors to the cold aisles are never fully closed and there will therefore always be at least some airflow into each cold aisle (unless the associated racks have no operational heat-generating components installed therein).

It will be appreciated that there may also be a need to control the humidity of the air in the rack room 140. The process control panel receives inputs on the humidity of the air in the various parts of the data centre building and controls humidification de- humidification apparatus in the air optimisation unit 122 so that satisfactory air humidity is delivered.

The volume of air flow through the building may, during certain conditions (for example when outside temperature is relatively high and/or IT loads are relatively high), be at least 12m³s^_1. The air optimiser module has the capacity to generate air flow through the building at a rate as high as at least 40m³s^_1 (i.e. more than about lmV¹ per rack and about 0.025m³s^_1 per rack slot, assuming that substantially all air flowing through the building passes via a rack slot). The volume of air flow through the building may during other occasions be about 0.3m³s^_1, during certain conditions. Such a rate of supply of air may still be sufficient to cool the IT equipment in the single rack room of the building by means of ambient air cooling alone for ambient air temperatures of up to 24 degrees Celsius.

In order for the cooling and power-usage efficiency to be improved the entrainment of air is important. Blanking panels may be used to ensure efficient use of cooling air. Figure 4 is a schematic drawing showing a row of racks of servers of the kind that are used in the data centre building shown in Figure 3. Figure 4 shows a row of racks 143 in perspective view. The rack frames are made of metal. Each rack is an open fronted 42u standard universally compatible server rack. The racks 143 are joined together in rows by filler pieces in the form of vertically extending blanking strips (the position of which being indicated by arrow 143c) that seal over the adjacent abutting edges of the racks of each adjacent pair. A gasket seal is also provided around the top of the racks 143 to provide a seal between the ceiling, or in the case where the rack does not extend up to ceiling height, the blanking panel between the ceiling and the rack. Such seals and filler pieces ensure that air can only flow out of the cold aisle 144 via the server slots in the racks.

The rack may be filled with twenty upright server blades 121 arranged side-by- side across the width of the rack. The server blades 121 are mounted on a chassis that is then inserted into a rack, the weight of the servers being supported by the support structure defining the slots at the upper and lower ends of the chassis. The height of the upright server blades are such that 8 conventional slots are occupied by the chassis that holds the servers 121. Five such chassis may by supported by a single rack, thus equating to one hundred servers being held by a 42-u rack, thereby more than doubling the capacity of a single rack. Areas of a rack not holding any such chassis of servers 121 are sealed off with front-facing blanking panels 143f. Alternatively or additionally, individual empty slots in the rack, whether conventional horizontal slots or vertical slots in a chassis mount, may be sealed off with individual blanking strips.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described. Those skilled in the art will realise that a rack may comprise rack-mounted electrical components other than blade servers.

The teaching of the present invention is not limited to a data room or a rack in which the racks are not themselves provided with any cooling fans. Indeed, some racks may be provided with cooling fans, especially for the cooling of electrical components which generate lots of heat. The racks, including for example components mounted in the racks, may include some operational fans and some inoperative fans.

A rack may include both upright servers mounted on a dedicated chassis which is shaped so as to be received in a multiplicity of slots in the rack and horizontally arranged servers that are received one to a slot.

The blade servers could each be provided with a casing of a generally cuboidal shape, facilitating close-packing of the servers. The casings may include vents both on their front faces and their rear faces.

The blade servers could each be provided in the form of an open board without a casing. When the blade servers are provided without casings, each server may be provided with mounting means facilitating their mounting in the rack. The servers may be mounted vertically. There may be an air gap between adjacent servers providing an airflow path for cooling air to cool the servers.

The racks and aisles defined by the racks need not be straight and/or rectangular in plan-view.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.

Claims

1. A data centre building comprising a rack room, wherein

the rack room comprises:

a. a plurality of racks, each rack housing a plurality of rack-mountable electronic components, the majority of which being computer servers,

b. one or more cold regions, defined at least partly by the layout of the racks, the one or more cold regions including at least one cold aisle, and

c. one or more hot regions, defined at least partly by the layout of the racks, the one or more hot regions including at least one hot aisle,

the data centre building comprises a first set of air circulating devices for transporting cooling air to said one or more cold regions, then via the racks, to said one or more hot regions, at least some of the cooling air passing from a cold aisle via a rack into a hot aisle, thus cooling the rack-mountable electronic components in the racks,

the first set of air circulating devices being provided external to the rack room, the rack room optionally comprises a second set of air circulating devices for cooling the rack-mountable electronic components, each of the air circulating devices of the second set (if present) being provided by a rack, and

the cooling power of the first set of air circulating devices is greater than the cooling power of the second set of air circulating devices (if present).

2. A data centre building according to claim 1 wherein the cooling power of the second set of air circulating devices (if present) is less than 50% of the cooling power of the first set of air circulating devices.

3. A data centre building according to claim 2, wherein the cooling power of the second set of air circulating devices (if present) is less than 10%> of the cooling power of the first set of air circulating devices.

4. A data centre building according to any preceding claim wherein the volume of air flow per unit time able to be independently generated by the first set of air circulating devices is greater than the volume of air flow per unit time able to be independently generated by the second set of air circulating devices (if present).

5. A data centre building according to claim 4, wherein the volume of air flow per unit time able to be independently generated by the first set of air circulating devices is at least three times greater than the volume of air flow per unit time able to be independently generated by the second set of air circulating devices (if present).

6. A data centre building according to any preceding claim wherein a majority of the racks are not provided with an air circulating device arranged to cool the rack-mounted components.

7. A data centre building according to any preceding claim, wherein a majority of the electronic components are fanless components.

8. A data centre building according to any of claims 1 to 6, wherein a majority of the electronic components includes a fan, such fans together forming the second set of air circulating devices, and wherein second set of air circulating devices are rendered inoperative.

9. A data centre building according to any preceding claim wherein at least 60% of the rack-mounted components are computer servers.

10. A data centre building according to any preceding claim, wherein the rack-mountable electronic components are each provided with a casing arranged to allow the cooling air to flow through the rack-mountable electronic component.

11. A data centre building according to any of claims 1 to 9, wherein each rack- mountable electronic component does not have an external casing that is unique to the rack- mountable electronic component and each rack-mountable electronic component is arranged to allow the cooling air to flow around and over the rack-mountable electronic component.

12. A data centre building according to any preceding claim wherein one or more of the rack-mounted components are provided with a cooling air input side on a first side of the rack, a cooling air exhaust side on a second side of the rack, and an in-rack cooling airflow path extending from said first side to said second side, the one or more in-rack cooling airflow paths being arranged to facilitate the extraction of heat from heat-generating components and are the primary means for cooling the rack-mounted components, and the rack is so arranged that there are no in-rack fans arranged to assist airflow via any of the in- rack cooling airflow paths.

13. A data centre building according to any preceding claim wherein one or more of the rack-mounted components are provided with a cooling air input side on a first side of the rack, a cooling air exhaust side on a second side of the rack, and an in-rack cooling airflow path extending from said first side to said second side, the one or more in-rack cooling airflow paths being arranged to facilitate the extraction of heat from heat-generating components and are the primary means for cooling the rack-mounted components, and wherein, in use, a pressure difference is applied across the rack, with the air pressure at the first side being sufficiently higher than the air pressure at the second side in order for sufficient cooling air to flow along the in-rack cooling airflow path for the rack-mounted component to function without overheating.

14. A data centre building according to any preceding claim including at least two pairs of adjacent rows of racks in which one or more of the rack-mounted components are provided with

a. a cooling air input side on a first side of the rack,

b. a cooling air exhaust side on a second side of the rack, and

c. an in-rack cooling airflow path extending from said first side to said second side, the one or more in-rack cooling airflow paths being arranged to facilitate the extraction of heat from heat-generating components and are the primary means for cooling the rack-mounted components, wherein

a hot aisle is defined between one such pair of rows of adjacent racks, in which pair, the second sides of the racks face each other, and

a cold aisle is defined between another such pair of rows of adjacent racks, in which pair, the first sides of the racks face each other.

15. A data centre building according to any preceding claim, wherein both the hot aisle defined between adjacent racks and the cold aisle defined between adjacent racks are sized to permit personnel access.

16. A data centre building according to claim 14 or claim 15, wherein both the hot aisle defined between adjacent racks and the cold aisle defined between adjacent racks are sized to permit personnel access.

17. A data centre building according to any preceding claim, wherein the cooling air flow path from upstream of the rack room, then via said one or more cold regions, then via the racks to said one or more hot regions, is entirely above floor-level.

18. A data centre building according to any preceding claim wherein the rack comprises a packing of servers equivalent to at least 80 servers per 42 unit rack.

19. A method of operating a data centre building, wherein the data centre building comprises

a. one or more cold aisles,

b. one or more hot aisles,

c. a plurality of racks, arranged in one or more rows, each row being located between a hot aisle and a cold aisle, each rack housing a plurality of rack-mountable electronic components, the majority of which being computer servers, and

d. a first set of air circulating devices not located in any of the cold aisles, hot aisles and the racks, and wherein

the method includes a step of using the first set of air circulating devices as the primary means for transporting cooling air such that air flows to at least one of the cold aisles, and then via the racks to at least one of the hot aisles, thus cooling the rack-mountable electronic components in the racks.

20. A method according to claim 19, wherein any non-negligible contribution to the movement of cooling air via the cold aisles, the racks, and via the hot aisles is provided solely by air circulating devices located upstream of the cold aisles.