Staged spray indirect evaporative cooling system

Abstract

To provide a heat exchanger assembly, an indirect evaporative heat exchanger including the heat exchanger, and methods of operating the same.SOLUTION: The heat exchanger assembly includes at least one tube, a plurality of sections, and a plurality of nozzles. The at least one tube is configured to (1) have a process fluid flow therethrough in a first direction and (2) have a heat-scavenging cooling medium flow across the outer surface of the tube in a second direction intersecting the first direction. The sections are aligned in the first direction. The nozzles are located above the at least one tube. At least one of the nozzles is located in each of the sections and configured to selectively discharge a coolant onto a portion of the tube in the section.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to cooling systems and systems and methods for controlling the same, and in particular to airflow cooling systems using indirect evaporative cooling. Particularly suitable applications are, for example, in data center cooling systems. [Background technology]

[0002] Servers in data centers generate a lot of heat and require cooling. One cooling system used for data centers is an indirect evaporative cooling system, such as the Oasis™ indirect evaporative cooling system manufactured by Munters, Inc., USA. The “Oasis” system includes a polymeric air-to-air cross-flow tube heat exchanger. In this system, process air flows through the inside of the tubes and heat rejection air flows across the outside of the tubes. The process air is cooled by transferring its heat to the heat rejection air. On cold and cool days, the polymeric tube heat exchanger runs dry as an air-to-air heat exchanger. The heat rejection air indirectly cools the data center air by normal heat exchange without using any water. When the ambient temperature rises to a certain point, water is pumped from a water sump into a spray nozzle, which wets the outside surface of the polymer tubes, coating the tubes with a thin film of water. The heat rejection air evaporates the water on the outside surface of the tubes, extracting heat from the recirculating data center air flowing through the tubes. The multiple nozzles of the system are positioned and configured to wet the entire length of the polymeric heat exchanger tubes when water is sprayed from the nozzles. Summary of the Invention [Problem to be solved by the invention]

[0003] While the "Oasis" system offers several advantages over other cooling systems, including less water consumption, even further reduction in water consumption is desired. The invention described herein provides such a reduction in water consumption, and provides additional benefits in cold weather conditions and an emergency back-up system. [Means for solving the problem]

[0004] In one aspect, the present invention relates to an indirect evaporative heat exchanger. The indirect evaporative heat exchanger includes a heat exchanger assembly, a plurality of nozzles, a water reservoir, at least one pump, a temperature sensor, and a controller. The heat exchanger assembly includes at least one tube having a first end, a second end, and an exterior surface. The at least one tube is configured such that (1) a process fluid flows therethrough in a first direction from the first end to the second end, and (2) a heat removal cooling medium flows across the exterior surface in a second direction intersecting the first direction. The heat exchanger assembly also includes a plurality of sections aligned in the first direction, each section including a portion of the at least one tube. The plurality of nozzles are positioned above the at least one tube. At least one nozzle of the plurality of nozzles is (1) located within each of the plurality of sections and (2) configured to selectively emit cooling liquid onto a portion of the tube within each section. The water reservoir is positioned below the at least one tube. The water reservoir is configured to collect the cooling liquid emitted from the plurality of nozzles and flowing across the tube. The at least one pump is configured to circulate water from the water sump to nozzles located in at least one section of the heat exchanger. The temperature sensor is configured to detect a control temperature. The controller is communicatively coupled to the temperature sensor and configured to receive a signal from the temperature sensor indicative of a temperature detected by the temperature sensor and operate the pump to circulate coolant from the water sump to nozzles located in one section of the heat exchanger to prevent freezing of the coolant in the water sump when the temperature detected by the temperature sensor is below a predetermined threshold.

[0005] In another aspect, the invention relates to a method for preventing freezing in a water sump of an evaporative heat exchanger, the method including a heat exchanger assembly including at least one tube having a first end, a second end, and an exterior surface. The at least one tube is configured such that (1) a process fluid flows therethrough in a first direction from the first end to the second end, and (2) a heat removal cooling medium flows across the exterior surface in a second direction intersecting the first direction. The heat exchanger assembly also includes a plurality of sections aligned in the first direction, each section including a portion of the at least one tube. The method includes the steps of determining that a control temperature is below a predetermined threshold, circulating a cooling fluid from the water sump to at least one nozzle located in a section of the heat exchanger, ejecting the circulated cooling fluid from the at least one nozzle onto a portion of the tube in the section of the heat exchanger in which the nozzle is located, and collecting the cooling fluid ejected from the at least one nozzle and flowing across the tube in the water sump.

[0006] In another aspect, the invention relates to a cooling system. The cooling system includes an indirect evaporative heat exchanger configured to cool a process fluid, a mechanical cooling system, and a controller. The indirect evaporative heat exchanger includes at least one tube, a plurality of sections, and a plurality of nozzles. The at least one tube has a first end, a second end, and an exterior surface. The at least one tube is configured such that (1) the process fluid flows therethrough in a first direction from the first end to the second end, and (2) a heat removal cooling medium flows across the exterior surface in a second direction intersecting the first direction. The plurality of sections are aligned in the first direction. Each section of the plurality of sections includes a portion of the at least one tube. The plurality of nozzles are located above the at least one tube. At least one nozzle of the plurality of nozzles is (1) located within each of the plurality of sections and (2) configured to selectively discharge water onto a portion of the tube within each section. The mechanical cooling system includes an evaporative coil configured to (1) flow therethrough and (2) cool the process fluid. The controller has a water loss mode responsive to a loss of water supply event. The controller is configured to selectively release water from nozzles located within one section of the indirect evaporative heat exchanger to cool the process fluid in the water loss mode and to operate the mechanical cooling system to cool the process fluid.

[0007] In yet another aspect, the present invention relates to a method of operating a cooling system during a loss of water supply event, the method including determining that a water supply to the cooling system from a normal water supply line is interrupted and cooling a process fluid with the indirect evaporative heat exchanger. The indirect evaporative heat exchanger includes at least one tube, a plurality of sections, and a plurality of nozzles. The at least one tube has a first end, a second end, and an exterior surface. The at least one tube is configured such that (1) a process fluid flows therethrough in a first direction from the first end to the second end, and (2) a heat removing cooling medium flows across the exterior surface in a second direction intersecting the first direction. The plurality of sections are aligned in the first direction. Each section of the plurality of sections includes a portion of the at least one tube. The plurality of nozzles are located above the at least one tube. At least one nozzle of the plurality of nozzles is located within each of the plurality of sections. The process fluid is cooled by selectively discharging water from nozzles located within a section of the indirect evaporative heat exchanger. The method further includes operating a mechanical cooling system to cool the process fluid. The mechanical cooling system includes an evaporator coil configured to have the process fluid flow therethrough.

[0008] In yet another aspect, the present invention relates to an indirect evaporative heat exchanger. The indirect evaporative heat exchanger includes a heat exchanger assembly and a plurality of nozzles. The heat exchanger assembly includes a plurality of straight tubes. Each tube has a first end, a second end, and an exterior surface. Each tube is configured for (1) process fluid to flow therethrough in a first direction from the first end to the second end, and (2) a heat removal cooling medium to flow across the exterior surface in a second direction intersecting the first direction. The heat exchanger assembly also includes a plurality of sections aligned in the first direction. Each section includes a portion of each of the plurality of tubes. The plurality of nozzles are positioned above the plurality of straight tubes. At least one nozzle of the plurality of nozzles is (1) located within each of the plurality of sections and (2) configured to selectively emit cooling fluid onto a respective portion of the plurality of tubes within each section.

[0009] In yet another aspect, the invention relates to a method for cooling a process fluid in an indirect evaporative heat exchanger, the method including flowing process fluid in the first direction through a plurality of straight tubes of a heat exchanger assembly from a first end to a second end of each tube. The heat exchanger assembly has a plurality of sections, and a portion of each of the plurality of tubes is contained within each section of the heat exchanger assembly. The method also includes flowing a heat rejection cooling medium across an exterior surface of each tube in a second direction intersecting the first direction to cool the process fluid. The method further includes selecting at least one nozzle of a plurality of nozzles when the flow of the heat rejection cooling medium alone is not sufficient to cool the process fluid to a target temperature. The at least one nozzle of the plurality of nozzles is located within each section of the heat exchanger assembly. The method further includes ejecting a cooling liquid from a nozzle selected in the selecting step onto a portion of the plurality of tubes in a corresponding section of the indirect heat exchanger assembly to further cool the process fluid.

[0010] These and other aspects, objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings. [Brief description of the drawings]

[0011] [Figure 1] 1 is an elevational view of a data center using a cooling system according to a preferred embodiment of the present invention; [Diagram 2] FIG. 2 is a perspective view of an indirect heat exchanger of the cooling system shown in FIG. [Diagram 3] FIG. 3 is a detailed view of the indirect heat exchanger shown in FIG. 2 showing detail 3 of FIG. 2. [Figure 4] 3 shows one tube of the indirect heat exchanger shown in FIG. 2. [Diagram 5] FIG. 2 is a schematic diagram of an indirect heat exchanger of the cooling system shown in FIG. [Figure 6] 2 is a schematic diagram of an indirect heat exchanger of the cooling system shown in FIG. 1 showing an alternative arrangement of nozzles. [Figure 7] FIG. 4 is a schematic diagram of the indirect heat exchanger shown in FIG. 3 illustrating a first stage operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] FIG. 1 illustrates a data center 100 having a cooling system 110 according to a preferred embodiment of the present invention. Although the cooling system 110 is shown and described in relation to the data center 100, the cooling system 110 is not limited to this application and may be used in other suitable air cooling applications. Electronic devices such as servers are mounted in a number of racks 102, which are arranged in a number of rows in the data center 100 to form aisles 104, 106 between the rows. One aisle 104 is a cold aisle and the other aisle 106 is a hot aisle. Cool supply air 112 from the cooling system 110 is directed to the cold aisle 104 using, for example, ducts 108. The supply air 112 then passes from the cold aisle 104 through the racks and into the hot aisle 106. As the air passes through the racks 102, it draws heat from the electronic devices and hot air enters the hot aisle 106. This air is then returned to the cooling system 110 as hot return air 114. The supply air fans 116 are used to draw return air 114 from the data center 100, pass the return air 114 through the cooling system 110 (where it is cooled), and return the cooled return air 114 to the data center 100 as supply air 112.

[0013] The cooling system 110 uses an indirect heat exchanger 200 to cool the return air 114. FIG. 2 is a perspective view of the indirect heat exchanger 200, and FIG. 3 is a detail view showing detail 3 of FIG. 2. The indirect heat exchanger 200 includes a heat exchanger assembly 210 having a plurality of tubes 212. While any suitable shape may be used, in this embodiment, each tube 212 is generally rectangular with rounded ends (see FIG. 3). The tubes 212 are oriented vertically, with the long dimension of the generally rectangular tubes 212 being vertical. A plurality of tubes 212 are arranged in horizontal rows with gaps 214 between adjacent tubes 212. The tubes 212 are also arranged vertically. Vertically, each row is staggered with the row above or below. In this embodiment, the centerline of the tubes 212 in one row is aligned with the centerline of the gaps 214 between the tubes 212 in the rows above and below. However, instead of a staggered arrangement, any suitable arrangement may be used including, for example, vertically aligning the tubes 212. The tubes 212 are supported at each end by header plates 218.

[0014] The return air 114 is directed through the tubes 212 by the supply air fan 116. The tubes 212 in this embodiment are straight and extend in a first direction A (horizontally in this embodiment), so that the return air 114 travels through the tubes 212 in the first direction A as a process fluid. As the return air 114 travels through the tubes 212, it is indirectly cooled by the heat rejection air 122 (see FIG. 4). The heat rejection air 122 is drawn across an outer surface 216 of each tube 212 (see FIG. 4) by the heat rejection air fan 124 (see also FIG. 1). In this embodiment, the heat rejection air 122 is fresh air drawn from the outdoor environment surrounding the cooling system 110. Also in this embodiment, the indirect heat exchanger 200 is a cross-flow heat exchanger. The heat rejection air 122 is drawn across the outer surface 216 of each tube 212 in a second direction B that intersects the first direction A. In this embodiment, the second direction B is perpendicular to the first direction A. When the outside temperature is cool enough, the indirect heat exchanger operates dry as an air-to-air heat exchanger. However, when the outside temperature increases, water can be discharged from a number of nozzles 220 located above the heat exchanger assembly 210. As shown in FIG. 4, the water flows down around the outside (exterior surface 216) of each tube 212. As the heat removal air 122 flows across the exterior surface 216 of each tube 212, evaporative heat transfer effectively cools the return air 114 flowing through the inside of the tubes 212. The header plate 218 separates the heat removal air 122 from the return air 114 and the supply air 112.

[0015] As shown in FIG. 5, the indirect heat exchanger 200 of this embodiment is divided into a number of sections 230 along a first direction A. Although any suitable number of sections 230 may be used, the indirect heat exchanger 200 of this embodiment has three sections 230. Also, in this embodiment, the sections 230 are equally distributed over the length of the tubes 212, with each section including 1 / 3 of each tube 212, although other suitable distributions may be used. The first section 232 is the first 1 / 3 of the tubes 212 closest to the end of the tubes 212 where the return air 114 enters the tubes 212. The third section 236 is also referred to as the end section, and is the last 1 / 3 of the tubes 212 closest to the exit of the tubes 212. The second section 234 is the middle 1 / 3 between the first section 232 and the third section 236.

[0016] In this embodiment, the indirect heat exchanger 200 is physically separated into three sections by two dividers 238 and a header plate 218. The dividers 238 are similar to the header plate 218. Like the header plate 218, the dividers 238 are plates through which the tubes 212 extend, and in this embodiment, the dividers 238 extend the entire height and width of the heat exchanger assembly 210. The dividers 238 provide structural support to the tubes 212, especially in embodiments where the tubes 212 are long. Additionally, when water is discharged in some sections (as described further below), the dividers 238 act as a barrier to help contain the discharged water to the particular section 230 of the heat exchanger assembly 210 that is discharging water.

[0017] In this embodiment, there are three nozzles 220 used to distribute water over the length of each tube 212. A first nozzle 222 is located in the first section 232 and is used to distribute water over the portion of the tube 212 in the first section 232. A second nozzle 224 is located in the second section 234 and is used to distribute water over the portion of the tube 212 in the second section 234. A third nozzle 226 is located in the third section 236 and is used to distribute water over the portion of the tube 212 in the third section 236. Instead of a single nozzle, multiple nozzles 220 may be used in each section, and thus the first, second and third nozzles 222, 224, 226 may be a first, second and third nozzle set. For example, multiple nozzles may be used in each section 230 as seen in Figure 2 to ensure that when water is discharged from nozzles 220 in one section 230 of the indirect heat exchanger 200, the entire width of the rows in the heat exchanger assembly 210 is wetted. Multiple nozzles may also be used in each section 230, for example, to ensure that when water is discharged from nozzles 220 in one section 230, the entire portion of each tube 212 in that section of the heat exchanger assembly 210 is wetted. Figure 6 shows a schematic diagram of an indirect heat exchanger 200 having multiple nozzles 220 in each section 230.

[0018] Since the indirect heat exchanger 200 is divided into multiple sections 230, the indirect heat exchanger 200 can be wetted in stages, instead of operating with the entire length of each tube 212 dry or wet. Staging allows the return air 114 to be cooled first in one or more dry sections 230, and then water is used in the remaining sections 230 downstream of the dry sections to achieve the target temperature of the supply air 112. As mentioned above, when the outside temperature is cool enough, the indirect heat exchanger 200 operates dry as an air-to-air heat exchanger. When the heat removal air 122 alone is not sufficient to cool the return air 114 to the target temperature of the supply air 112, water may be discharged from nozzles 220 in at least one section 230 of the indirect heat exchanger 200.

[0019] As shown in Fig. 7, for example, water is discharged from the nozzles 226 in the third section 236 of the indirect heat exchanger 200. Thus, the return air 114 is first cooled only by the heat rejection air 122 in the first section 232 and the second section 234 before the water is used to achieve the improved heat exchange provided by indirect evaporative cooling (IEC) in the third section 236. If the discharge of water from the nozzles 220 in only one section 230 of the indirect heat exchanger 200 is not sufficient to cool the return air 114 to the target temperature of the supply air 112, water may be discharged from the nozzles 220 in the additional sections 230. For example, water may be discharged from the nozzles 224, 226 in the second and third sections 234, 236, and the first section 232 may run dry. Thus, the additional sections 230 may be operated until water is discharged from the nozzles 220 in all sections 230 of the indirect heat exchanger 200. Staged operation of the indirect heat exchanger 200 has the advantages of better temperature control and reduced water consumption when transitioning from 100% dry heat exchange mode to IEC mode compared to a non-staged indirect heat exchanger.

[0020] The cooling system 110 includes a controller 130 for operating the cooling system 110 including the indirect heat exchanger 200 as shown in FIG. 5. In this embodiment, the controller 130 is a microprocessor-based controller including a processor 132 for performing various functions as described further below, and a memory 134 for storing various data. The controller 130 may also be referred to as a CPU. In one embodiment, control of the cooling system 110 is implemented in the form of a set of instructions stored in the memory 134 and executed by the processor 132. Thus, the controller 130 is communicatively coupled to various pumps and valves within the system, which may be operated as described further below. In addition, the controller 130 may also be communicatively coupled to input and display devices, as appropriate.

[0021] FIG. 5 is a schematic diagram of the indirect heat exchanger 200. When water is discharged from the nozzle 220, it flows across the tubes 212 of the heat exchanger assembly 210, and any water that is not evaporated during the cooling process is collected in a water sump 242. At least one pump 244, 246 is used to circulate the water from the water sump 242 to the nozzle 220. In the indirect heat exchanger 200 shown in FIG. 5, the first pump 244 is fluidly connected to the nozzle 226 in the third section 236. The second pump 246 is fluidly connected to the nozzles 222, 224 in the first and second sections 232, 234. The stage valve 248 is located between the second pump 246 and the nozzle 222 of the first section 232. When operating in the first stage of the IEC mode, the controller 130 may operate the first pump 244 to circulate water from the water sump 242 and discharge water from the nozzle 226 in the third section 236. In the first stage, the controller 130 does not operate the second pump 246. In the second stage, the stage valve 248 is closed to isolate the nozzle 222 in the first section 232 from the second pump 246, and both the first and second pumps 244, 246 are operated to discharge water from the nozzles 224, 226 in the second and third sections 234, 236. The third stage is similar to the second stage, except that the stage valve 248 is open to also discharge water from the nozzle 222 in the first section 232. Although described with two pumps 244, 246 and a single stage valve 248, any suitable number of pumps and stage valves may be used in various combinations to achieve the desired staging of the indirect heat exchanger 200.

[0022] There are several additional benefits that may be gained by incorporating a staged spray approach. In cooling applications, since the indirect heat exchanger 200 is typically unable to meet the required cooling load under all operating conditions, a supplemental mechanical cooling system 300 may also be included in the cooling system 110 (see FIG. 1). The mechanical cooling system 300 includes a cooling coil 302 located in the flow path of the return air 114. In the embodiment shown in FIG. 1, the cooling coil 302 is located downstream of the indirect heat exchanger 200 and is configured to cool the return air 114 after it has been cooled by the indirect heat exchanger 200. Any suitable mechanical cooling system may be used, including systems that use direct expansion refrigerant or chilled water to cool the cooling coil 302.

[0023] In this embodiment, the mechanical refrigeration system 300 is a direct expansion (DX) refrigeration system 300 that uses a conventional refrigeration cycle. The direct expansion refrigeration system 300 includes a compressor (not shown) that increases the pressure and temperature of the refrigerant after the cooling coil 302 before it is cooled in the condenser 304. In this embodiment, the condenser 304 of the direct expansion refrigeration system 300 may be located above the indirect heat exchanger 200 and cooled by the heat rejection air 122. Other suitable configurations for the condenser 304 may be used, including, for example, being located in an air stream other than the heat rejection air 122, separate from the indirect heat exchanger 200. The refrigerant passes through an expansion valve (not shown) to reduce its pressure and temperature before returning to the cooling coil 302.

[0024] The mechanical cooling system 300 is typically referred to as a trim cooling system because it is typically sized only to provide the balance of the cooling required after the indirect evaporative cooling process of the indirect heat exchanger. In critical cooling applications such as data center cooling, performance must be guaranteed. If the trim cooling system (mechanical cooling system 300) is not fully sized, a water reservoir must be provided by the facility to maintain full cooling capacity during a water loss event. Such a reservoir may be provided by a water storage tank 320 (see FIG. 5). The storage tank 320 is typically sized based on peak water evaporation demands during a sustained time interval, e.g., 24 or 48 hours. Hourly weather data for the typical year (TMY) is evaluated to identify peak water usage periods. The indirect heat exchanger 200 described herein allows for a significant reduction in the size of this backup water storage tank 320.

[0025] As shown in FIG. 5, water is supplied to the indirect heat exchanger 200 via a supply tube 312. In this embodiment, water may be supplied to the indirect heat exchanger 200 by discharging water from a supply nozzle 314 located above the heat exchanger assembly 210. The water discharged from the supply nozzle 314 flows across the tube 212 and into the water basin 242, similar to the nozzle 220 used for recirculation. A supply valve 316 may be opened or closed to control the supply of water from the supply tube 312 to the indirect heat exchanger 200. Water may be supplied to the indirect heat exchanger 200 using other suitable configurations. For example, instead of filling the water basin 242 using the supply nozzle 314, the supply tube 312 may directly pour into the water basin 242.

[0026] The supply line 312 may be connected to various water sources. One water source may be the water source used under normal operating conditions. The normal water source may be any suitable water source used by the facility in which the cooling system 110 is located. Such a normal water source may include water from a municipal water main, a well, or the like. As shown in FIG. 5 , this normal water source is connected to the supply line 312 by a normal water supply line 322. A normal water supply valve 324 is used to disconnect the normal water supply line 322 from the supply line 312. As mentioned above, water may also be provided to the cooling system 110 by a backup water source. The backup water supply may be stored in a water storage tank 320. The water storage tank 320 is fluidly connected to the supply line 312 by a backup water supply line 326, and a backup water supply valve 328 is used to disconnect the backup water supply line 326 (and the water storage tank 320) from the supply line 312.

[0027] During a water supply loss event where the normal water supply provided through the normal water supply line 322 is interrupted, the cooling system 110 may operate in a water loss mode. In this embodiment, the water loss mode involves shifting the cooling burden from the indirect heat exchanger 200 to the mechanical cooling system 300. If the outside temperature is not low enough to cool the return air 114 only with the heat rejection air 122, the mechanical cooling system 300 operates to its maximum capacity instead of discharging water from the nozzles 220 of the indirect heat exchanger 200 while the heat rejection air fan 124 operates to provide maximum airflow of the heat rejection air 122. And, if necessary, the indirect heat exchanger 200 may operate with indirect evaporative cooling only on a portion of the section 230 of the heat exchanger assembly 210. For example, the mechanical cooling system 300 may be sized such that the mechanical cooling system 300 and the indirect heat exchanger 200 operating in a first stage are sufficient to provide the required cooling capacity based on peak design conditions. As discussed above, in the first stage, water is discharged from nozzles 226 in the third section 236 of the indirect heat exchanger 200. Operating the cooling system 110 in this manner conserves a significant amount of water during a water loss event compared to operating the cooling system 110 with full water spray, thereby reducing the amount of stored water required and the size of the water storage tank 320.

[0028] The water loss mode may be activated when the normal water supply is found to be interrupted. An operator manually activates the water loss mode when they determine that the normal water supply is interrupted, but the water loss mode may also be activated automatically. As shown in FIG. 5, the water supply sensor 136 is located in the normal water supply line 322. The water supply sensor 136 is communicatively coupled to the controller 130 and sends a signal to the controller 130 when the water supply sensor 136 detects that the normal water supply is interrupted. Upon receiving the signal from the water supply sensor 136, the controller 130 activates the water loss mode. In the water loss mode, the normal water supply valve 324 is closed and the backup water supply valve 328 is opened to switch the water supply from the normal water supply to the backup water supply stored in the water storage tank 320. The controller 130 then operates the cooling system 110 in the water loss mode as described above. The data center 100 may include a building management system (BMS) that controls various aspects of the data center 100, including the water supply to the cooling system 110. If data center 100 includes a BMS, the BMS sends a signal that is received by controller 130 to operate cooling system 110 in water loss mode. Controller 130 may operate water supply valves 324, 328 in response to a signal received from the BMS, but water supply valves 324, 328 may be operated by the BMS to activate (or deactivate) the water loss mode.

[0029] When the indirect heat exchanger 200 operates at ambient temperatures close to freezing, incorporating a staged spray approach also provides water conservation benefits. Because the indirect heat exchanger 200 can typically provide full cooling using only the heat rejection air 122 at temperatures well above freezing, the water system (including the sump 242) is typically drained as the ambient temperature approaches freezing, without any concerns about freezing. In areas that frequently experience nighttime drops toward freezing, but heat up during the day and require indirect evaporative cooling, this can result in frequent filling and draining of the sump 242, wasting water each time the sump 242 is drained. In applications with variable cooling loads, sump heaters are often used to keep the sump water surviving low temperatures. This approach is acceptable, but requires energy to run the heater. However, in facilities with more consistent heat loads, such as the data center 100, staged water spraying can provide a more efficient approach.

[0030] When the outside temperature reaches a predetermined threshold, the indirect heat exchanger 200 operates in a first stage. In the first stage, water is circulated from the sump 242 to the nozzles 222 of the first section 232 by the first pump 244. The water expelled from the nozzles 222 extracts enough heat from the return air to keep the entire sump 242 warm enough to prevent freezing. Alternatively, instead of measuring the outside temperature and using a predetermined threshold based on the outside temperature, the temperature of the water in the sump 242 can be measured and the predetermined threshold can be based on the temperature of the water in the sump 242.

[0031] When an operator determines that the temperature has dropped below a predetermined threshold, the indirect heat exchanger 200 may operate in the first stage to prevent freezing, or the indirect heat exchanger 200 may automatically initiate this operation. As shown in FIG. 5, the temperature detector 138 is configured to measure the temperature of the outside air or the temperature of the water in the water sump 242. The temperature detector 138 is communicatively coupled to the controller 130 and transmits the temperature of the outside air (or the water in the water sump 242) to the controller 130. The controller 130 receives the temperature of the outside air (or the water in the water sump 242) from the temperature detector 138, and when the controller 130 determines that the temperature has dropped below a predetermined threshold, the controller 130 operates the first stage of the indirect heat exchanger 200 as described above to prevent the water in the water sump 242 from freezing.

[0032] Although the present invention has been described in certain exemplary embodiments, many additional modifications and variations will be apparent to those skilled in the art from this disclosure. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described. The exemplary embodiments of the present invention are therefore to be considered in all respects as illustrative and not restrictive, and the scope of the present invention should be determined by the appended claims and their equivalents, rather than by the foregoing description. [Explanation of symbols]

[0033] 100 Data Centers 102 LACK Aisles 104 and 106 108 Duct 110 Cooling System 112 Supply air 114 Return Air 116 Supply air fan 122 Deheated air 124 Heat removal air fan 130 Controller 200 indirect heat exchanger 210 Heat exchanger assembly 212 tube 214 Gap 216 Exterior 218 Header Plate 220, 222, 224, 226 nozzles Sections 230, 232, 234, and 236 242 Water Puddle 244, 246 Pump 300 Mechanical Cooling System 302 Cooling coil 304 Condenser 320 Water Storage Tank

Claims

1. 1. An indirect evaporative heat exchanger comprising: at least one tube having a first end, a second end, and an exterior surface, (1) a process fluid flows therethrough in a first direction from the first end to the second end, and (2) a heat removal cooling medium flows across the exterior surface in a second direction transverse to the first direction; a plurality of sections aligned in the first direction, each section including a portion of the at least one tube; a heat exchanger assembly including: a plurality of nozzles positioned above the at least one tube, at least one nozzle (1) positioned within each of the plurality of sections (2) configured to selectively emit cooling fluid onto a portion of the tube within its respective section; a sump located below the at least one tube, the sump configured to collect the cooling liquid emitted from the plurality of nozzles and flowing across the tube; at least one pump configured to circulate water from the sump to nozzles located within at least one section of the heat exchanger; a temperature sensor configured to detect a control temperature; a controller communicatively coupled to the temperature sensor, the controller configured to receive a signal from the temperature sensor indicative of a temperature detected by the temperature sensor, and to operate the pump to circulate coolant from the sump to a nozzle located in a section of the heat exchanger to prevent freezing of the coolant in the sump when the temperature detected by the temperature sensor is below a predetermined threshold; An indirect evaporative heat exchanger comprising:

2. 2. The indirect evaporative heat exchanger of claim 1, wherein said control temperature is at least one of an outside air temperature and a water temperature in said sump.

3. 2. The indirect evaporative heat exchanger of claim 1, wherein the plurality of sections includes three sections, a first section closest to the first end of the tube, a third section closest to the second end of the tube, and a second section between the first and third sections.

4. the plurality of sections includes a terminal section proximate the second end of the tube; The indirect evaporative heat exchanger of claim 1 , wherein the pump is fluidly connected to a nozzle in the terminal section and configured to circulate coolant from the sump to the nozzle located in the terminal section.

5. 2. A method for preventing freezing in a water basin of an evaporative heat exchanger according to claim 1, comprising the steps of: determining, by the controller, that the control temperature is below a predetermined threshold; operating the pump with the controller to circulate coolant from the sump to a nozzle located within one section of the heat exchanger; ejecting the circulating cooling liquid from the at least one nozzle onto a portion of the tubes in the section of the heat exchanger in which the nozzle is located; collecting the cooling liquid discharged from the at least one nozzle and flowing across the tube in the sump; The method includes:

6. 1. An indirect evaporative heat exchanger configured to cool a process fluid, comprising: at least one tube having a first end, a second end, and an exterior surface, (1) the process fluid flows therethrough in a first direction from the first end to the second end, and (2) a heat removal cooling medium flows across the exterior surface in a second direction transverse to the first direction; a plurality of sections aligned in the first direction, each section including a portion of the at least one tube; a plurality of nozzles positioned above the at least one tube, at least one nozzle (1) positioned within each of the plurality of sections (2) configured to selectively emit water onto a portion of the tube within each section; an indirect evaporative heat exchanger comprising: (1) a mechanical cooling system including an evaporator coil configured to flow the process fluid therethrough and (2) to cool the process fluid; a controller having a water loss mode responsive to a loss of water supply event, the controller being configured in the water loss mode to selectively release water from nozzles located within a section of the indirect evaporative heat exchanger to cool the process fluid and to operate the mechanical cooling system to cool the process fluid; A cooling system comprising:

7. a normal water supply conduit configured to supply water to the indirect evaporative heat exchanger during a normal operating mode; 7. The cooling system of claim 6, wherein the controller is further configured to receive a signal indicating that the water supply from the normal water supply line has been interrupted and to operate the cooling system in the water loss mode in response to the received signal.

8. The cooling system of claim 6 , further comprising a backup water supply configured to supply water to the indirect evaporative heat exchanger during the water loss mode.

9. The cooling system of claim 8 , further comprising a backup water supply tank fluidly coupled to the backup water supply line for supplying water to the indirect evaporative heat exchanger.

10. 7. The cooling system of claim 6, wherein the plurality of sections includes three sections, a first section closest to the first end of the tube, a third section closest to the second end of the tube, and a second section between the first and third sections.

11. the plurality of sections includes a terminal section proximate the second end of the tube; The cooling system of claim 6 , wherein during the water loss mode, the controller is configured to selectively release water from nozzles located within the end section.

12. 7. A method of operating the cooling system of claim 6 during a loss of water supply event, comprising: determining that a water supply to the cooling system from a normal water supply line has been interrupted; cooling the process fluid in the indirect evaporative heat exchanger operating in the water loss mode by selectively discharging water from nozzles located within a section of the indirect evaporative heat exchanger and operating a mechanical cooling system to cool the process fluid; The method includes:

13. 1. An indirect evaporative heat exchanger comprising: a plurality of straight tubes, each having a first end, a second end, and an exterior surface, each of the straight tubes configured to (1) allow a process fluid to flow therethrough in a first direction from the first end to the second end, and (2) allow a heat removal cooling medium to flow across the exterior surface in a second direction intersecting the first direction; a plurality of sections aligned in the first direction, each section including a portion of a respective one of the plurality of tubes; a heat exchanger assembly including: a plurality of nozzles positioned above the plurality of straight tubes, at least one nozzle (1) positioned within each of the plurality of sections (2) configured to selectively emit coolant onto a respective portion of the plurality of tubes within each section; An indirect evaporative heat exchanger comprising:

14. 14. The indirect evaporative heat exchanger of claim 13, wherein the plurality of sections includes three sections, a first section closest to the first end of the plurality of tubes, a third section closest to the second end of the plurality of tubes, and a second section between the first and third sections.

15. 14. The indirect evaporative heat exchanger of claim 13, further comprising a valve fluidly connected to a nozzle located within at least one section of the heat exchanger, the valve being configured, when open, to selectively release cooling liquid onto respective portions of the plurality of tubes within that section of the heat exchanger.

16. The indirect evaporative heat exchanger of claim 13 further comprising at least one pump configured to selectively supply coolant to nozzles located within at least one section of the heat exchanger.

17. 17. The indirect evaporative heat exchanger of claim 16, further comprising a sump located below the plurality of straight tubes and configured to collect cooling liquid discharged from the plurality of nozzles and flowing across the plurality of tubes, the pump configured to circulate cooling liquid from the sump to the plurality of nozzles.

18. 14. The indirect evaporative heat exchanger of claim 13, further comprising a controller configured to discharge coolant from nozzles in at least one section of the heat exchanger assembly, the at least one section from which the controller discharges coolant being downstream in the first direction of at least one section of the heat exchanger from which coolant is not discharged from nozzles.

19. 14. The indirect evaporative heat exchanger of claim 13, wherein the heat removal cooling medium is ambient air.

20. 14. The indirect evaporative heat exchanger of claim 13, wherein the process fluid is air.

21. 14. The indirect evaporative heat exchanger of claim 13, wherein the cooling fluid is water.

22. 14. A method for cooling a process fluid in an indirect evaporative heat exchanger according to claim 13, comprising the steps of: flowing a process fluid through the plurality of straight tubes in the first direction; flowing a heat removal cooling medium in the second direction across an exterior surface of each tube to cool the process fluid; selecting at least one nozzle of the plurality of nozzles when the flow of the heat removal cooling medium alone is not sufficient to cool the process fluid to a target temperature; ejecting cooling fluid from the nozzle selected in the selecting step onto a portion of the plurality of tubes in a corresponding section of the indirect heat exchanger assembly to further cool the process fluid; The method includes:

23. 23. The method of claim 22, wherein the plurality of sections includes a first section and a second section, the second section being downstream in the first direction from the first section.

24. The method of claim 23 , wherein the selected nozzles correspond to the second section and the nozzles corresponding to the first section are not selected.

25. 24. The method of claim 23, wherein the first section is closest to the first end of each of the plurality of tubes, the plurality of sections further including a third section closest to the second end of each of the plurality of tubes, the second section being between the first and third sections.

26. The method of claim 25 , wherein the selected nozzles correspond to the third section and the nozzles corresponding to the first and second sections are not selected.

27. 26. The method of claim 25, wherein the selected nozzles correspond to the second and third sections, and the nozzles corresponding to the first section are not selected.

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