WO2023030675A1

WO2023030675A1 - Computer or information technology rack hall cooling equipment

Info

Publication number: WO2023030675A1
Application number: PCT/EP2022/025287
Authority: WO
Inventors: Trine SAABY; Kim Henrik Stadel DEVALD; Mark Luxford
Original assignee: New Nordic Data Cooling Aps
Priority date: 2021-09-01
Filing date: 2022-06-21
Publication date: 2023-03-09
Also published as: GB2610393A; GB202112478D0; EP4218376A1

Abstract

Computer or information technology rack hall cooling equipment comprising at least two rows (202 and 204) of racks (10), in which the racks (10) are provided with respective rear door heat exchangers (18). The rows (202 and 204) are substantially parallel to one another to provide an aisle (208) between them. Each rear door heat exchanger (18) faces the aisle (208). A coolant manifold (40) extends along the aisle (208) connected to provide coolant to the rear door heat exchangers (18). In a first aspect, there are two or more such manifolds (40) and along each row (202, 204) racks (10) which have their rear door heat exchangers (18) connected to a first one of the manifolds (40) alternate with racks (10) which have their rear door heat exchangers (18) connected a) to the other of the said two manifolds (40) if there are only two manifolds, or (b) if there are more than two such manifolds (40) to another of the manifolds (40), and the rear door heat exchangers (18) of racks (10) of a first one of the said two rows (202) of racks (10) connected to the said first one of the manifolds (40) oppose rear door heat exchangers (18) of racks (10) of the said other of the two rows (204) of racks (10) connected (a) to the said other of the said two manifolds (40) if there are only two manifolds (40), or (b) if there are more than two manifolds (40) to another of the manifolds (40). In a second aspect, a first set of racks (10) of two rows of racks (202 and 204) has its rear door heat exchangers (18) connected to a first electronic control unit (250) to be controlled thereby and a second set of racks (10) of the two rows of racks (202 and 204) has its rear door heat exchangers (18) connected to a second electronic control unit (252) to be controlled thereby, the first and second control units (250 and 252) also being connected to one another to enable each to detect a fault in or a fault detected by the other and to control the rear door heat exchangers (18) to which it is connected to compensate for such a fault.

Description

[0001] Computer or information technology rack hall cooling equipment

[0002] The present invention relates to computer or information technology rack hall cooling equipment, especially but not exclusively computer or information technology rack hall cooling equipment which provides heat for a city hot water system.

[0003] Computer or information technology (IT) rack halls need to provide cooling air for the air inputs of computer racks typically in conformity with service level agreements (SLAs) . Among other criteria, these set the upper temperature limit for such cooling air. This is especially critical for rack halls which also provide coolant at a set temperature to supply heat to a city hot water system.

[0004] An IT rack hall may comprise a number of pods. Each pod may comprise two substantially parallel rows of racks. The air output from the racks may be cooled by respective rear door heat exchangers (RDHxs) . The RDHxs may be provided with coolant from a coolant manifold extending along the pod. A problem encountered by such a construction of IT rack hall is that if a malfunction occurs with supply of coolant via the manifold, or with an electrical or electronic control of the pod, or some other malfunction, the air output from the affected rack or racks may be exces sive and cause a local hotspot which may extend to the air input side of the racks , exceeding the SLA limit .

[ 0005] The present invention seeks to provide a remedy .

[ 0006] According to a first aspect of the present invention , there is provided computer or information technology rack hall cooling equipment comprising at lea st two rows of racks , in which the racks are provided with respective rear door heat exchangers , in which the rows are substantially parallel to one another to provide an ai sle between them with each rear door heat exchanger facing the ais le , and in which a coolant manifold extends along the ais le connected to provide coolant to the rear door heat exchangers , characterised in that there are two or more such manifolds and along each row racks which have their rear door heat exchangers connected to a f irst one of the manifolds alternate with racks which have their rear door heat exchangers connected a ) to the other of the said two manifolds if there are only two manifolds , or (b ) if there are more than two such manifolds to another of the manifolds , and in that the rear door heat exchangers of racks of a first one of the said two rows of racks connected to the said first one of the manifolds oppose rear door heat exchangers of racks of the said other of the two rows of racks connected ( a ) to the said other of the said two manifolds if there are only two manifolds , or (b ) if there are more than two manifolds to another of the manifolds . [0007] Such a construction is less likely to provide an unacceptable hotspot in the surrounding air in the event of a blockage in one of its manifolds.

[0008] There may be only two such manifolds.

[0009] This has an economy of parts.

[0010] If there are only two such manifolds, both racks immediately adjacent to each and every one of the racks of both rows, apart from the racks at the ends of the rows, may have their rear door heat exchangers connected to the same one of the two manifolds, the rear door heat exchanger of the said one of the racks, between the immediately adjacent racks, being connected to the other of the manifolds .

[0011] This provides an even mix of the air exiting those rear door heat exchangers connected to a blocked manifold in the event of such a blockage with air exiting those connected to the other manifold.

[0012] Each rear door heat exchanger may be provided with a fan driven by an electric motor, the latter being connected to a processor unit of the rear door heat exchanger which can vary the speed of the electric motor.

[0013] This enables an efficient operation of the rear door heat exchanger.

[0014] Each rear door heat exchanger may be provided with a heat-exchange pipe having a valve connected to a processor unit of the rear door heat exchanger which can vary the degree to which the valve is open .

[ 0015] Thi s also enables an efficient operation of the rear door heat exchanger .

[ 0016] According to a second aspect of the present invention , there is provided computer or information technology rack hall cooling equipment comprising at lea st two rows of racks , in which the racks are provided with respective rear door heat exchangers , in which the rows are substantially parallel to one another to provide an ais le between them with each rear door heat exchanger facing the ais le , and in which at least one coolant manifold extends along the ais le connected to provide coolant to the rear door heat exchangers , characterised in that a f irst set of racks of the said two rows of racks has its rear door heat exchangers connected to a first electronic control unit to be controlled thereby and a second set of racks of the said two rows of racks has its rear door heat exchangers connected to a second electronic control unit to be controlled thereby, the first and second control units also being connected to one another to enable each to detect a fault in or a fault detected by the other and to control the rear door heat exchangers to which it is connected to compensate for such a fault .

[ 0017 ] There may be provided information computer or technology rack hall cooling equipment made in accordance with the foregoing paragraph which sets out the aforesaid second aspect of the present invention and also in accordance with the foregoing paragraph which sets out the aforesaid first aspect of the present invention with or without any one of the features set out in the intervening paragraphs .

[0018] Th e said first set of racks referred to in the paragraph which sets out the second aspect of the present invention may be constituted by those racks which are referred to in the paragraph which sets out the first aspect of the present invention as having their rear door heat exchangers connected to a first one of the manifolds.

[0019] This provides an effective control of the equipment.

[0020] Each manifold may be provided with both a coolant supply line and a coolant drainage line across which the heat-exchange pipes of those rear door heat exchangers which are connected to that manifold are connected.

[0021] This provides an efficient supply of coolant to and drainage of coolant from the rear door heat exchangers.

[0022] The present invention extends to a computer or information technology rack hall comprising a multiplicity of pods each comprising cooling equipment in accordance with the first and/or the second aspect of the present invention .

[0023] This provides an efficient means of maintaining the

SLA for the hall. [0024] In such a hall, all the manifolds of all the pods may have coolant supply lines connected at both ends to common main coolant supply pipes of the hall, and coolant drain lines connected at both ends to common main coolant drainage pipes of the hall.

[0025] This provides an efficient use of coolant supply and drainage .

[0026] Both ends of the coolant supply lines and coolant drainage lines of the manifolds may be provided with shutoff valves.

[0027] This enables a leaking manifold or a manifold to which is connected a leaking heat-exchange pipe to be isolated.

[0028] The shut-off valves may be connected to be controlled by the control units.

[0029] This enables such isolation to be performed automatically .

[0030] Respective trays may be provided underneath the heatexchange pipes of the rear door heat exchangers and underneath the manifolds, the trays being provided with leakage sensors to detect the presence of leaked coolant therein which sensors are connected to the control units.

[0031] This enables a control unit to shut off a manifold which is leaking or which has a leaking heat-exchange pipe connected to it in dependence upon signals issued by the leakage sensors. [ 0032 ] An example of computer or information technology rack hall cooling equipment constructed in accordance with the present invention and an example of a computer or information technology rack hall constructed in accordance with the present invention will now be described with reference to the accompanying drawings in which :

[ 0033] Figure 1 shows a diagrammatic plan view of a rack of a pod of racks of a computer or IT rack hall , the pod of racks embodying the present invention ;

[ 0034 ] Figure 2 shows a diagrammatic plan view of a pod of racks of a computer or IT rack hall , the pod of racks embodying the present invention , each rack of which pod is as shown in Figure 1 ; and

[ 0035] Figure 3 shows a diagrammatic plan view of a computer or IT rack hall embodying the present invention , comprising a multiplicity of pods as shown in Figure 2 .

[ 0036] A computer or IT rack 10 shown in Figure 1 comprises a hous ing 12 extending from an air inlet front face 14 to an air outlet rear face 16 which is covered by a rear door heat exchanger 18 . The hous ing 12 provide s a series of slots 19 at respective different levels into which are slid a number of blade servers 20 to form a stack of such servers . The stack of servers can be cooled by air pas sing from the front to the rear of the hous ing 12 under the action of fans 22 within the blade servers 20 . [0037] In addition, the passage of air in this way through the housing 12 can be assisted or effected by a fan 30 of the rear door heat exchanger 18. The fan 30 has a span greater than half the width of the housing 12, and is driven by an electric motor 32 mounted on the rear door heat exchanger 18. The rear door heat exchanger 18 is also provided with a meandering heat-exchange pipe 34 which extends approximately evenly over the area of the rear face 16 of the housing 12 to cool the air exiting the housing 12. The pipe 34 has a coolant inlet end 36 connected to a coolant supply line 38 of a coolant manifold 40 via a connection line 42, and a coolant outlet end 44 connected to a coolant drainage line 46 of the coolant manifold 40 via a connection line 48.

[0038] Temperature sensors 50, 52, 54 and 56 are located to measure the temperatures of coolant, in this case water, in the lines 38, 42, 46 and 48 respectively and are connected electrically to send signals indicative of those temperatures to a processor unit 58 of the rear door heat exchanger 18. A temperature sensor 60 is also located to provide a measure of the temperature of the air upstream of the rear door heat exchanger 18 and is connected to send signals indicative of that temperature to the processor unit 58.

[0039] Differential pressure sensor parts 62 and 63 are provided upstream and downstream respectively of the rear door heat exchanger 18 to provide a measure of the pressure differential between the pressures of the air at those locations. The sensor parts 62 and 63 are also connected to the processor unit 58.

[0040] A liquid sensor 64 is also located to sense the presence of leaked coolant in a collecting tray 66 underneath the pipe 34, and is connected electrically to the processor unit 58 to send a leaked coolant indicator signal thereto in the event of such leakage.

[0041] In addition to signals received by the processor unit 58 from the various sensors referred to, the processor unit 58 is also electrically connected to a valve 68 in the connection line 42 which valve 68 serves to adjust the amount of coolant flowing through the heat exchange pipe 34, and is also electrically connected to the electric motor 32 to control the speed of rotation of the fan 30 to maintain a pressure drop across the rear door heat exchanger 18 of typically -2Pa whilst keeping the flow rate of air substantially to a minimum necessary to obtain the desired temperatures.

[0042] In the event of a leak detected by the liquid sensor 64, the processor unit 58 will shut the valve 68.

[0043] A pod 200 of racks 10 is shown in Figure 2. The pod 200 comprises two rows of racks 202 and 204, each rack 10 of which is constructed in the same way as the rack 10 shown and described herein with reference to Figure 1. There are 22 racks in each row 202 and 204 , so that in the Figure 2 construction there are 44 racks which constitute the pod 200 of racks , although only 24 are shown in that Figure with the central racks being omitted for the sake of clarity, to enable a whole pod to be fitted within a single drawing without each rack appearing too small . The rows 202 and 204 are substantially parallel to one another to provide an ai sle 208 between them . Each rear door heat exchanger 18 of each rack 10 faces the ais le 208 .

[ 0044 ] Two coolant manifolds 40 extend along the ais le 208 . Each manifold has a first line 38 extending along its length within which coolant is held at a first pre s sure , the first line 38 constituting a supply line to supply coolant to rear door heat exchangers 18 of the pod . Each manifold 40 also ha s a second line 46 extending along it s length within which coolant is held at a lower pre s sure than the said first pres sure , the second line 46 constituting a drainage line to take away coolant from rear door heat exchangers 18 of the pod .

[ 0045] Both ends of both coolant supply lines 38 are provided with motorised shut-of f valves 220 , and both ends of both coolant drainage lines 46 are provided with motorised shutoff valves 222 .

[ 0046] Viewing Figure 2 from left to right , what is shown as the first rack 10 of what appears in the Figure as the upper of the two rows of racks 202 of the pod 200 has the coolant inlet end of the heat exchange pipe of it s rear door heat exchanger 18 connected to the supply line 38 of what appears in Figure 2 a s the lower of the manifolds 40 and the coolant outlet end of that pipe connected to the drainage line 46 of that manifold . Likewise the third, fifth and every odd numbered rack of the upper row counting from left to right . On the other hand, again viewing Figure 2 f rom left to right , what i s shown a s the second rack 10 of what appears in that Figure as the upper of the two rows of racks 202 of the pod 200 ha s the coolant inlet end of the heat exchange pipe of it s rear door heat exchanger 18 connected to the supply line 38 of what appears in Figure 2 as the upper manifold 40 and the coolant outlet end of that pipe connected to the drainage line 46 of that manifold . Likewise the fourth , sixth and every even numbered rack of the upper row counting from left to right . In thi s way progres sing along the row of racks 10 , those racks 10 which have their rear door heat exchangers 18 connected to a first one of the two manifolds 40 alternate with racks 10 which have their rear door heat exchangers 18 connected to the other of the said two manifolds 40 . Apart f rom the racks 10 at the very ends of the row , both racks 10 immediately adj acent to each and every one of the racks 10 of the row have their rear door heat exchangers 18 connected to the same one of the manifolds 40 , the rear door heat exchanger 18 of the said one of the racks 10 , between the immediately adj acent racks 10 , being connected to the other of the manifolds 40 .

[ 0047 ] Such alternate connection also applies to the row of racks which appears as the lower of the two rows in Figure 2 , except that what is shown as the f irst rack 10 of what appears in the Figure as the lower of the two rows of racks 204 of the pod 200 has the coolant inlet end of the heat exchange pipe of its rear door heat exchanger 18 connected to the supply line 38 of the upper manifold 40 and the coolant outlet end of that pipe connected to the drainage line 4 6 of that manifold . As a result , the rear door heat exchanger 18 of each rack of a first one of the two rows of racks which i s connected to the upper manifold oppose s the rear door heat exchanger 18 of a rack of the said other of the two rows of racks which is connected to the lower manifold 40 .

[ 0048 ] The two rows of racks 202 and 204 are provided with respective electronic control unit s 250 and 252 . The proce s sor units of the rear door heat exchangers 18 which are connected to the upper manifold 40 are connected to the electronic control unit 250 , and the proces sor units of the rear door heat exchangers 18 which are connected to the lower manifold 40 are connected to the electronic control unit 252 . The electronic control unit 250 is connected to control operation of the shut-of f valves 220 and 222 of the upper manifold 40 , and the electronic control unit 252 is connected to control operation of the shut-off valves 220 and 222 of the lower manifold 40 .

[ 0049] Respective trays 260 and 262 are provided underneath the upper and lower manifolds 40 , and respective leak sensors 264 and 266 are provided in the trays 2 60 and 262 to detect the presence of any coolant which may have lea ked from the as sociated manifold 40 . The lea k sensors 264 and 266 are connected respectively to the electronic control units 250 and 252 .

[ 0050 ] Th e electronic control units are also connected to one another so that each may detect a fault in the other or via the various sensors connected to the other as des cribed herein . Thus it will be appreciated that a first set of racks of the said two rows of racks 202 and 204 have their rear door heat exchangers 18 connected to a first electronic control unit 250 to be controlled thereby and a second set of racks of the said two rows of racks 202 and 204 have their rear door heat exchangers connected to a second electronic control unit 252 to be controlled thereby, the first and second control units 250 and 252 also being connected to one another to enable each to detect a fault in or a fault detected by the other and to control the rear door heat exchangers 18 to which it is connected to compensate for such a fault .

[ 0051 ] Figure 3 shows a computer or information technology rack hall 300 comprising twelve pods of racks 200 each a s shown in Figure 2 , arranged as six pairs of pods 302 with the pods of each pair being in line with one another and with re spective ends adj acent to one another so that each pair of pods constitutes a row of the arrangement , and the pairs being arranged generally parallel to one another in such a way that they form two columns of pods 304 . Thus the pods are generally parallel to one another or in line with one another and constitute a matrix of six rows 302 and two columns 304 with a gap 306 between the columns 304 .

[ 0052 ] Along the outs ides of each column of pods 304 and along the gap 306 extend two pipes being a main coolant supply pipe 308 and a main coolant drainage pipe 310 . The coolant supply line 38 of every manifold 40 is connected at one of its ends to a main coolant supply pipe 308 which extends along the outside of a column of pods 200 and at the other of it s ends to a main coolant supply pipe 308 extending along the gap 306 . Similarly the coolant drainage line 46 of every manifold 40 is connected at one of it s ends to a main coolant drainage pipe 310 which extends along the outside of a column of pods 200 and at the other of it s ends to a main coolant drainage pipe 310 extending along the gap 306 . One end of each main coolant supply pipe 308 is connected to a coolant input terminal 320 of the hall 300 and one end of each drainage pipe 310 is connected to a coolant output terminal 322 of the hall 300 . [0053] The coolant input terminal 320 is connected to receive coolant from a heat pump system (not shown) of a city hot water system (not shown) and the coolant output terminal 322 is connected to return that coolant to the heat pump system (not shown) of the city hot water system (not shown) at the desired temperature therefor.

[0054] When the computer or information technology rack hall is in operation with the computer blades 20 processing digital electrical signals, the heat so generated is carried away by air which flows through the racks 10 driven by internal fans (not shown) of the blades 20 and/or the fan 30 of the rear door heat exchanger 18. In the embodiment illustrated the SLA limit is 27°C, so air which enters the racks 10 is substantially at a temperature of 27°C. Depending upon the work load of any given rack of blades 10, the temperature of the air reaching the rear door heat exchanger 18 of the rack 10 is in the range from about 35°C to about 40°C. Water as coolant flows through the heat exchange pipe 34 at about 10 litres per minute, being about the minimum flow rate possible to achieve the desired temperatures, and entering the pipe 34 at about the highest possible temperature of about 24°C to achieve the desired temperatures . Heat exchange from the air to the coolant in the heat-exchange pipe 34 of the rear door heat exchanger 18 of each rack 10 cools the temperature of the air so that it exits the rear door heat exchanger 18 of each rack at a temperature of about 26.5°C. This is slightly lower than the SLA limit to take account of the heating effect of staff, lighting and other possible sources of heat within the hall in addition to the blades 20.

[0055] At the same time the temperature of the coolant entering the heat-exchange pipe 34 and the temperature of the coolant exiting the heat-exchange pipe 34 of each rear door heat exchanger 18 are dictated by the operating conditions of the heat pump (not shown) of the city hot water system (not shown) , and in this case are 24°C and 34.1°C respectively. Because there are two variables in the operation of each rear door heat exchanger 18, namely the speed of the fan 30 and the degree of opening of the control valve 68 in the connection line 42, it is possible to maintain the desired temperatures of both the air and the coolant exiting the rear door heat exchanger 18 substantially independently of the work load of the blades in the rack, and this is done keeping the flow of coolant through pipe 34 to a minimum sufficient for such maintenance. This is effected by the processor unit 58 of each rack 10, which is programmed to control the speed of the motor 32 and the degree of opening of the valve 68 in the connection line 42 in dependence upon the signals it receives from the sensors 50, 52, 54, 56, 60 and 62.

[0056] In the event of a fault in one of the manifolds 40 or in one of the racks 10 connected to one of the manifolds 40 , for example a lea k from the heat-exchange pipe 34 detected by the liquid sensor 64 of the rack 10 concerned, or a lea k in one of the manifolds 40 itself detected by the leakage sensor 264 or 266 as sociated with the manifold concerned, the fault signal is received by the control unit 250 or 252 as sociated with the manifold concerned which is sues electrical signal s to the four shut-off valves 220 and 222 of the manifold concerned to ensure coolant is not fed into other parts of the equipment at the wrong temperature and also to avoid flooding . In addition , the valves 68 of all the rear door heat exchangers 18 connected to the manifold concerned are also closed, and the speed of the as sociated fan motors 32 is increased . An alarm signal is generated to alert the hall operator . At the same time the other of the control units , by virtue of its connection to the control unit of the manifold concerned, is sues electrical signals to all the proces sor units 58 to which it is connected to increase the speed of the as sociated fan motors 32 and to fully open the as sociated valves 68 to increase the cooling effect of the as sociated rear door heat exchangers and thereby compensate for the hotter air exiting the rear door heat exchangers of the pod concerned through which coolant is no longer flowing . Because of the alternating way the rear door heat exchanges are connected to the two manifolds of the pod concerned, overheated air and overcooled air are mixed very rapidly, reducing the likelihood of an unacceptable hotspot in the hall, thereby maintaining the SLA. At the same time the temperature of the coolant exiting the hall is maintained at the required 34.1°C.

[0057] Information received by all the control units 250 and 252 is relayed to the heat pump (not shown) of the city hot water system (not shown) to control it to meet the coolant delivery temperature and the coolant flow rate requirements of the hall and any other halls of a data centre serviced by the heat pump.

[0058] Many alterations and variations to the illustrated equipment may occur to the reader without taking the resulting construction outside the scope of the present invention. For example there may be more or less racks than forty-four in each pod. There may be more or less than twelve pods in the hall.

[0059] The blade servers or computer blades 20 may be servers other than blade servers or computer blades.

[0060] Th e SLA temperature limit and temperatures required by the city hot water system may be different from the ones given with reference to the illustrated equipment.

[0061] If the racks 10 which have their rear door heat exchangers 18 connected to one of the manifolds 40 are denoted by the letter A and those having their rear door heat exchangers 18 connected to other of the manifolds 40 are denoted by the letter B, so that the racks 10 of one of the rows of the pod 200 shown in Figure 2 , working along the row, may be represented by the sequence ABABABABABAB..., other alternating patterns may be satisfactory in some applications of the invention , such as AABBAABBAABB..., or ABBAABAABBABB..., and so on , as long as there is alternation . Again in some applications some of the rear door heat exchangers of a pod may be connected to the same manifold as the rear door heat exchangers they oppose , provided most of them oppose rear door heat exchangers connected to the other manifold of the pod .

[ 0062 ] There may be three manifolds in each pod instead of j ust the two illustrated, and the pattern of connection may be ABCABCABCABC..., and so on , or variations thereof similar to those given above in relation to an arrangement with j ust two manifolds , again provided there is alternation . Similar considerations apply to the connections of the rear door heat exchangers 18 to the electronic control units 250 and 252 .

Claims

Claims :

1. Computer or information technology rack hall cooling equipment comprising at least two rows of racks , in which the racks are provided with respective rear door heat exchangers , in which the rows are substantially parallel to one another to provide an ais le between them with each rear door heat exchanger facing the ais le , and in which a coolant manifold extends along the ais le connected to provide coolant to the rear door heat exchangers , characterised in that there are two or more such manifolds and along each row racks which have their rear door heat exchangers connected to a first one of the manifolds alternate with racks which have their rear door heat exchangers connected a ) to the other of the said two manifolds if there are only two manifolds , or (b ) if there are more than two such manifolds to another of the manifolds , and in that the rear door heat exchangers of racks of a first one of the said two rows of racks connected to the said first one of the manifolds oppose rear door heat exchangers of racks of the said other of the two rows of racks connected ( a ) to the said other of the said two manifolds if there are only two manifolds , or (b ) if there are more than two manifolds to another of the manifolds . Computer or information technology rack hall cooling equipment according to claim 1 , in which there are only two such manifolds . Computer or information technology rack hall cooling equipment according to claim 2 , in which both racks immediately adj acent to each and every one of the racks of both rows , apart from the racks at the ends of the rows , have their rear door heat exchangers connected to the same one of the two manifolds , the rear door heat exchanger of the said one of the racks , between the immediately adj acent racks , being connected to the other of the manifolds . Computer or information technology rack hall cooling equipment comprising at least two rows of racks , in which the racks are provided with respective rear door heat exchangers , in which the rows are substantially parallel to one another to provide an ais le between them with each rear door heat exchanger facing the aisle , and in which at lea st one coolant manifold extends along the aisle connected to provide coolant to the rear door heat exchangers , characterised in that a f irst set of racks of the said two rows of racks has its rear door heat exchangers connected to a first electronic control unit to be controlled thereby and a second set of racks of the said two rows of racks ha s its rear door heat exchangers connected to a second electronic control unit to be controlled thereby, the first and second control units also being connected to one another to enable each to detect a fault in or a fault detected by the other and to control the rear door heat exchangers to which it is connected to compensate for such a fault . Computer or information technology rack hall cooling equipment which is both according to claim 1 and according to claim 4 . Computer or information technology rack hall cooling equipment according to claim 5 , in which the said first set of racks referred to in claim 1 are constituted by those racks which are referred to in claim 4 as having their rear door heat exchangers connected to a first one of the manifolds . Computer or information technology rack hall cooling equipment according to any preceding claim, in which each rear door heat exchanger is provided with a fan driven by an electric motor , the latter being connected to a proces sor unit of the rear door heat exchanger which can vary the speed of the electric motor . Computer or information technology rack hall cooling equipment according to any preceding claim, in which each rear door heat exchanger is provided with a heat-exchange pipe having a valve connected to a proces sor unit of the rear door heat exchanger which can vary the degree to which the valve is open . Computer or information technology rack hall cooling equipment according to any preceding claim, in which each manifold is provided with both a coolant supply line and a coolant drainage line acros s which the heat-exchange pipes of those rear door heat exchangers which are connected to that manifold are connected . . A computer or information technology rack hall comprising a multiplicity of pods each comprising cooling equipment as claimed in any preceding claim . . A computer or information technology rack hall according to claim 10 , in which all the manifolds of all the pods have coolant supply lines connected at both ends to common main coolant supply pipes of the hall , and coolant drain line s connected at both ends to common main coolant drainage pipes of the hall . . A computer or information technology rack hall according to claim 11 , in which both ends of the coolant supply lines and coolant drainage lines of the manifolds are provided with shut-off valves . . A computer or information technology rack hall according to claim 12 , in which the shut-off valves are connected to be controlled by the control units . Computer or information technology rack hall cooling equipment or a computer or information technology rack hall according to any preceding claim read as appended to claim

4 or any one of claims 5 to 13 read as appended to claim 4 , in which respective trays are provided underneath the heat-exchange pipes of the rear door heat exchangers and underneath the manifolds , the trays being provided with leakage sensors to detect the presence of lea ked coolant therein which sensors are connected to the control units .