Data center coolant switch

1. 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 having a first heat transfer fluid 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 having a second heat transfer fluid freezing point lower than the first heat transfer fluid freezing point, the second heat transfer fluid freezing point being sufficiently low to operate the outdoor heat exchanger portion of the data center cooling system without freezing when an outdoor air temperature drops below a first predetermined relationship with the first heat transfer fluid freezing point;

wherein, during the second mode of operation, the heat from the components in the data center is absorbed into the second heat transfer fluid and the outside air is used to cool the second heat transfer fluid in at least the outdoor heat exchanger portion; and

wherein the coolant switch arrangement is further configured to switch the outdoor heat exchanger portion of the data cooling system to the first heat transfer fluid for operation in the first mode of operation in response to the outdoor air temperature reaching a second predetermined relationship with the first heat transfer fluid freezing point.

2. 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.

3. The system of claim 2 , 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.

4. 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.

5. The system of claim 4 , wherein the antifreeze comprises ethylene glycol and the antifreeze-water mixture comprises an ethylene glycol-water mixture.

6. 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 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.

7. 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 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.

8. 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 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.

9. The system of claim 8 , 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.

10. The system of claim 8 , 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.

11. A system comprising:

a data center cooling system configured to operate in a first mode, the data center cooling system having an indoor portion wherein heat is absorbed from components in the data center, the data center cooling system having 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 the first mode, the first heat transfer fluid having a first heat transfer fluid freezing point;

a control unit configure to determine that an appropriate time has been reached to switch from the first mode to a second mode when an outdoor air temperature drops below a first predetermined relationship with the first heat transfer fluid freezing point; and

a switch configured to switch the outdoor heat exchanger portion of the data cooling system to a second heat transfer fluid, in response to the appropriate time being reached, the second heat transfer fluid having a second heat transfer fluid freezing point lower than the first heat transfer fluid freezing point, the second heat transfer fluid freezing point being sufficiently low to operate without freezing when the outdoor air temperature drops below the first predetermined relationship with the first heat transfer fluid freezing point;

wherein, during the second mode, heat from the components in the data center is absorbed into the second heat transfer fluid present in the indoor portion and the outside air is used to cool the second heat transfer fluid present in at least the outdoor heat exchanger portion; and

wherein the control unit is configured to make a second determination that the outdoor air temperature has reached a second predetermined relationship with the first heat transfer fluid freezing point;

wherein the switch is configured to switch the outdoor heat exchanger portion of the data cooling system back to the first heat transfer fluid is response to the second determination.

12. A computer program product useful for controlling a data center cooling system, the computer program product comprising a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising:

computer readable program code configured to operate the data center cooling system in a first mode, the data center cooling system having an indoor portion wherein heat is absorbed from components in the data center, the data center cooling system having 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 the first mode, the first heat transfer fluid having a first heat transfer fluid freezing point;

computer readable program code configured to determine that an appropriate time has been reached to switch from the first mode to a second mode when an outdoor air temperature drops below a first predetermined relationship with the first heat transfer fluid freezing point;

computer readable program code configured to, responsive to the determining, switch the outdoor heat exchanger portion of the data cooling system to a second heat transfer fluid, in preparation for operation in the second mode, the second heat transfer fluid having a second heat transfer fluid freezing point lower than the first heat transfer fluid freezing point, the second heat transfer fluid freezing point being 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;

computer readable program code configured to operate the data center cooling system in the second mode, wherein heat from the components in the data center is absorbed into the second heat transfer fluid and 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; and

computer readable program code configured to switch the outdoor heat exchanger portion of the data cooling system back to the first heat transfer fluid in response to determining that the outdoor air temperature has reached a second predetermined relationship with the first heat transfer fluid freezing point.