# US 2021/0243919 A1 · Data center coolant switch > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0243919 A1 - Document ID: US20210243919A1 - Status: Published application - Kind: A1 - Application number: 17/150,357 - Filed: 2021-01-15 - Published: 2021-08-05 - Earliest claimed: 2011-07-15 - Assignees: International Business Machines Corporation - Applicants: International Business Machines Corporation - Inventors: Madhusudan K. Iyengar; Pritish R. Parida; Mark D. Schultz - Web page: https://patentgrep.com/patent/US20210243919A1 ## CPC - H05K 7/20836: {Thermal management, e.g. server temperature control} - F28D 15/00: Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls {; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies (F28D17/00, F28D19/00, F28D20/00 take precedence)} - H05K 7/2079: {within rooms for removing heat from cabinets} - F25B 25/005: {using primary and secondary systems} - F25B 47/006: {for preventing frost} - F25B 2313/009: indoor unit in circulation with outdoor unit in first operation mode, indoor unit in circulation with an other heat exchanger in second operation mode or outdoor unit in circulation with an other heat exchanger in third operation mode - F25B 2700/2106: of fresh outdoor air - H05K 7/20218: {using a liquid coolant without phase change in electronic enclosures (in cabinets of standardized dimensions H05K7/20536; in server cabinets H05K7/20709; in vehicle electronic casings H05K7/20845; in power control electronics H05K7/2089; in displays H05K7/20954)} - H05K 7/20254: {Cold plates transferring heat from heat source to coolant} - H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS - F28D: HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT (fluid heaters having heat generating means and heat transferring means F24H; furnaces F27; details of heat-exchange apparatus of general) - F25B: REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS ## Abstract A data center cooling system has an indoor portion wherein heat is absorbed from components in the data center, and an outdoor heat exchanger portion wherein outside air is used to cool a first heat transfer fluid (e.g., water) present in at least the outdoor heat exchanger portion of the cooling system during a first mode. When an appropriate time has been reached to switch from the first mode to a second mode, the outdoor heat exchanger portion of the data cooling system is switched to a second heat transfer fluid, which is a relatively low performance heat transfer fluid (compared to the first fluid). It has a second heat transfer fluid freezing point, lower than the first heat transfer fluid freezing point, and sufficiently low to operate without freezing when the outdoor air temperature drops below a first predetermined relationship with the first heat transfer fluid freezing point. ## Claims ### Claim 1 A system comprising: an indoor portion wherein heat is absorbed from components in a data center during a first mode; an outdoor heat exchanger portion wherein outside air is used to cool a first heat transfer fluid present in at least the outdoor heat exchanger portion during the first mode, the first heat transfer fluid having a first freezing point; a control unit configured to determine that an appropriate condition is met to switch from the first mode to a second mode, wherein the appropriate condition is a threshold condition; a switch configured to switch from the first mode to the second mode, the switch switching the outdoor heat exchanger portion to a second heat transfer fluid, in preparation for operation in the second mode; and wherein the second heat transfer fluid has a second freezing point lower than the first freezing point, wherein the second freezing point is lower than a lowest expected outdoor operating air temperature. ### Claim 2 (depends on 1) The system of claim 1, wherein the outside air is used to cool the second heat transfer fluid present in at least the outdoor heat exchanger portion during the second mode, wherein the control unit is configured to determine that a second appropriate condition has been met to switch from the second mode back to the first mode, and wherein the switch responsive to the control unit determining that the second appropriate condition is met to switch from the second mode back to the first mode, is configured to switch the outdoor heat exchanger portion back to the first heat transfer fluid. ### Claim 3 (depends on 1) The system of claim 1 wherein: the first heat transfer fluid comprises water; and the second heat transfer fluid comprises one of antifreeze and an antifreeze-water mixture. ### Claim 4 (depends on 3) The system of claim 3, wherein the antifreeze comprises ethylene glycol and the antifreeze-water mixture comprises an ethylene glycol-water mixture. ### Claim 5 (depends on 1) The system of claim 1, further comprising: a single loop passing through the data center to the outdoor heat exchanger portion; a first tank to store the first heat transfer fluid; and a second tank to store the second heat transfer fluid; wherein the switch comprises a valve arrangement configured to: isolate the first and second tanks during steady-state operation; allow the first heat transfer fluid to flow from the single loop into the first tank and the second heat transfer fluid to flow from the second tank into the single loop when transitioning from the first mode to the second mode; and allow the second heat transfer fluid to flow from the single loop into the second tank and the first heat transfer fluid to flow from the first tank back into the single loop when transitioning from the second mode to the first mode. ### Claim 6 (depends on 1) The system of claim 1, further comprising: an indoor loop passing through the data center to a liquid-to-liquid heat exchanger; an indoor-outdoor loop passing from the liquid-to-liquid heat exchanger to the outdoor heat exchanger portion; a first tank to store the first heat transfer fluid; and a second tank to store the second heat transfer fluid; and wherein the switch comprises a valve arrangement configured to: isolate the first and second tanks during steady-state operation; allow the first heat transfer fluid to flow from the indoor-outdoor loop into the first tank and the second heat transfer fluid to flow from the second tank into the indoor-outdoor loop when transitioning from the first mode to the second mode; and allow the second heat transfer fluid to flow from the indoor-outdoor loop into the second tank and the first heat transfer fluid to flow from the first tank back into the indoor-outdoor loop when transitioning from the second mode to the first mode. ### Claim 7 (depends on 1) The system of claim 1 further comprising: a first heat transfer fluid indoor loop passing through the data center; a liquid-to-liquid heat exchanger selectively coupled to the first heat transfer fluid indoor loop; a first heat transfer fluid indoor-outdoor loop selectively connectable to the first heat transfer fluid indoor loop and coupled to the outdoor heat exchanger portion; and a second heat transfer fluid loop passing from the liquid-to-liquid heat exchanger to the outdoor heat exchanger portion; wherein the switch comprises a valve arrangement configured to: couple the first heat transfer fluid indoor loop to the first heat transfer fluid indoor-outdoor loop during steady-state operation in the first mode; and couple the first heat transfer fluid indoor loop to the liquid-to-liquid heat exchanger during steady-state operation in the second mode. ### Claim 8 (depends on 7) The system of claim 7, wherein the outdoor heat exchanger portion comprises a first outside heat exchanger coupled to the second heat transfer fluid loop and a second outside heat exchanger coupled to the first heat transfer fluid indoor-outdoor loop. ### Claim 9 (depends on 7) The system of claim 7, wherein the outdoor heat exchanger portion comprises a single outside heat exchanger having a first coil coupled to the second heat transfer fluid loop and a second coil coupled to the first heat transfer fluid indoor-outdoor loop. ### Claim 10 (depends on 1) The system of claim 1, wherein the control unit comprises an outdoor air temperature sensor positioned adjacent the outdoor heat exchanger portion of the data center cooling system to determine whether the outdoor air temperature has reached the first predetermined relationship with the first heat transfer fluid freezing point. ### Claim 11 A method comprising: operating a data center cooling system in a first mode, wherein the data center cooling system has an indoor portion wherein heat is absorbed from components in the data center, and wherein the data center cooling system has an outdoor heat exchanger portion, wherein outside air is used to cool a first heat transfer fluid present in at least the outdoor heat exchanger portion during the first mode, wherein the first heat transfer fluid has a first freezing point; determining that an appropriate condition is met to switch from the first mode to a second mode wherein the appropriate condition is a threshold condition; and switching, responsive to the determining, the outdoor heat exchanger portion to a second heat transfer fluid, in preparation for operation in the second mode, the second heat transfer fluid having a second freezing point lower than the first freezing point, wherein the second freezing point is lower than a lowest expected outdoor operating air temperature. ### Claim 12 (depends on 11) The method of claim 11, further comprising: operating the data center cooling system in the second mode, wherein the outside air is used to cool the second heat transfer fluid present in at least the outdoor heat exchanger portion during the second mode; determining that a second appropriate condition is met to switch from the second mode back to the first mode; and switching, responsive to the determining that the second appropriate condition is met to switch from the second mode back to the first mode, the outdoor heat exchanger portion back to the first heat transfer fluid. ### Claim 13 A data center cooling system comprising: an indoor portion wherein heat is absorbed from components in the data center; an outdoor heat exchanger portion wherein outside air is used to cool a first heat transfer fluid present in at least the outdoor heat exchanger portion of the cooling system during a first mode of operation, the first heat transfer fluid is a relatively high performance heat transfer fluid, the first heat transfer fluid having a first freezing point; and a coolant switch arrangement configured to switch the outdoor heat exchanger portion of the data cooling system to a second heat transfer fluid during a second mode of operation, the second heat transfer fluid being a relatively low performance heat transfer fluid, the second heat transfer fluid having a second freezing point lower than the first heat transfer fluid freezing point, and wherein the second freezing point is lower than a lowest expected outdoor operating air temperature; and wherein the relatively high performance heat transfer fluid has a greater efficiency in transferring heat than the relatively low performance heat transfer fluid. ### Claim 14 (depends on 1) The system of claim 1, further comprising a control unit coupled to the coolant switch arrangement and configured to determine that an appropriate time has been reached to switch from the first mode to the second mode, wherein the coolant switch arrangement switches the outdoor heat exchanger portion of the data cooling system to the second heat transfer fluid responsive to the determination by the control unit. ### Claim 15 (depends on 14) The system of claim 14, wherein: the coolant switch arrangement is further configured to operate the data center cooling system in the second mode, wherein the outside air is used to cool the second heat transfer fluid present in at least the outdoor heat exchanger portion of the cooling system during the second mode; the control unit is configured to determine that a second appropriate time has been reached to switch from the second mode back to the first mode; and responsive to the control unit determining that the second appropriate time has been reached to switch from the second mode back to the first mode, the coolant switch arrangement switches the outdoor heat exchanger portion of the data cooling system back to the first heat transfer fluid. ### Claim 16 (depends on 15) The system of claim 15, wherein: the first heat transfer fluid comprises water; and the second heat transfer fluid comprises one of antifreeze and an antifreeze-water mixture. ### Claim 17 (depends on 15) The system of claim 15, wherein the antifreeze comprises ethylene glycol and the antifreeze-water mixture comprises an ethylene glycol-water mixture. ### Claim 18 (depends on 15) The system of claim 15, further comprising: a single loop passing through the data center to the outdoor heat exchanger portion; a first tank to store the first heat transfer fluid; and a second tank to store the second heat transfer fluid; wherein the coolant switch arrangement comprises a valve arrangement configured to: isolate the first and second tanks during steady-state operation; allow the first heat transfer fluid to flow from the single loop into the first tank and the second heat transfer fluid to flow from the second tank into the single loop when transitioning from the first mode to the second mode; and allow the second heat transfer fluid to flow from the single loop into the second tank and the first heat transfer fluid to flow from the first tank back into the single loop when transitioning from the second mode to the first mode. ### Claim 19 (depends on 15) The system of claim 15, further comprising: an indoor loop passing through the data center to a liquid-to-liquid heat exchanger; an indoor-outdoor loop passing from the liquid-to-liquid heat exchanger to the outdoor heat exchanger portion; a first tank to store the first heat transfer fluid; and a second tank to store the second heat transfer fluid; and wherein the coolant switch arrangement comprises a valve arrangement configured to: isolate the first and second tanks during steady-state operation; allow the first heat transfer fluid to flow from the indoor-outdoor loop into the first tank and the second heat transfer fluid to flow from the second tank into the indoor-outdoor loop when transitioning from the first mode to the second mode; and allow the second heat transfer fluid to flow from the indoor-outdoor loop into the second tank and the first heat transfer fluid to flow from the first tank back into the indoor-outdoor loop when transitioning from the second mode to the first mode. ### Claim 20 (depends on 15) The system of claim 15, further comprising: a first heat transfer fluid indoor loop passing through the data center; a liquid-to-liquid heat exchanger selectively coupled to the first heat transfer fluid indoor loop; a first heat transfer fluid indoor-outdoor loop selectively connectable to the first heat transfer fluid indoor loop and coupled to the outdoor heat exchanger portion; and a second heat transfer fluid loop passing from the liquid-to-liquid heat exchanger to the outdoor heat exchanger portion; wherein the coolant switch arrangement comprises a valve arrangement configured to: couple the first heat transfer fluid indoor loop to the first heat transfer fluid indoor-outdoor loop during steady-state operation in the first mode; and couple the first heat transfer fluid indoor loop to the liquid-to-liquid heat exchanger during steady-state operation in the second mode.