Combined chiller and free cooling system for operation at low ambient temperature

1. A system comprising:

a first set of coils configured to:

receive a coolant from a first coolant line;

transfer heat from the coolant to outdoor air; and

provide the coolant to a second coolant line;

a second set of coils configured to:

receive the coolant from a third coolant line, wherein the third coolant line is disposed in series with and coupled to the first coolant line;

transfer heat from the coolant to outdoor air; and

provide the coolant to a fourth coolant line, wherein the fourth coolant line is disposed in series with and coupled to the second coolant line;

a first valve configured to regulate a flow of the coolant between the first coolant line and the third coolant line, the first valve being disposed between the first coolant line and the third coolant line;

a second valve configured to regulate the flow of the coolant between the second coolant line and the fourth coolant line, the second valve being disposed between the second coolant line and the fourth coolant line;

a third valve positioned and configured to regulate the flow of the coolant between the fourth coolant line and a fifth coolant line, wherein the fifth coolant line is coupled to a water evaporator and a three-way valve;

the three-way valve configured to regulate the flow of the coolant between the fifth coolant line, the third coolant line, and a coolant input line;

a fourth valve positioned and configured to regulate the flow of the coolant from the second coolant line to a water condenser;

a compressor configured to compress a refrigerant provided to the water condenser; and

a controller coupled to the first valve, second valve, third valve, fourth valve, three-way valve, and the compressor, the controller comprising a processor configured to:

receive a temperature measurement and an indoor setpoint temperature;

determine, based on a comparison of the temperature measurement to the indoor setpoint temperature, that the system should operate in a low-temperature operating mode;

after determining that the system should operate in the low-temperature operating mode:

cause the first valve to be in an open position such that the flow of the coolant is allowed between the first coolant line and the third coolant line;

cause the second valve to be in the open position such that the flow of the coolant is allowed between the second coolant line and the fourth coolant line;

cause the third valve to be in the open position such that the flow of the coolant is allowed between the fourth coolant line and the fifth coolant line;

cause the fourth valve to be in a closed position such that the flow of the coolant is prevented between the second coolant line and the water condenser; and

cause the three-way valve to be in a position such that the flow of the coolant is:

allowed between the coolant input and the third coolant line; and

prevented between the fifth coolant line and the third coolant line.

2. The system of claim 1 , wherein:

the temperature measurement is a measurement of an outdoor temperature; and

the processor is configured to determine that the system should operate in the low-temperature operating mode by:

determining a difference between the outdoor air temperature and the indoor setpoint temperature; and

determining that the difference is greater than a predefined threshold value.

3. The system of claim 1 , wherein:

the temperature measurement is a measurement of a coolant temperature of the coolant in the fifth coolant line;

the processor is configured to determine that the system should operate in the low-temperature operating mode by determining that the coolant temperature is less than a threshold value.

4. The system of claim 1 , wherein:

the temperature measurement is a measurement of an outdoor temperature; and

the processor is configured to:

determine that the outside temperature is less than a threshold value; and

in response to determining the outside temperature is less than the threshold value, cause each of the first valve and the second valve to move to a closed position.

5. The system of claim 1 , the system further comprising, for each coil of the first set of coils and the second set of coils, at least a corresponding fan.

6. The system of claim 1 , wherein the processor is further configured to, after determining that the system should operate in the low-temperature operating mode, cause the compressor to turn off.

7. The system of claim 1 , wherein the system further comprises:

a coolant pump configured, when turned on, to provide the flow of coolant from the first set of coils and the second set of coils to the water condenser; and

wherein the processor is further configured to, after determining that the system should operate in the low-temperature operating mode, cause the coolant pump to turn off.

8. A method of operating a combined chiller/free cooling system, the method comprising:

receiving a temperature measurement and an indoor setpoint temperature;

determining, based on a comparison of the temperature measurement to the indoor setpoint temperature, that the combined chiller/free cooling system should operate in a low-temperature operating mode, wherein the combined chiller/free cooling system comprises:

a first set of coils configured to:

receive a coolant from a first coolant line;

transfer heat from the coolant to outdoor air; and

provide the coolant to a second coolant line;

a second set of coils configured to:

receive the coolant from a third coolant line, wherein the third coolant line is disposed in series with and coupled to the first coolant line;

transfer heat from the coolant to outdoor air; and

provide the coolant to a fourth coolant line, wherein the fourth coolant line is disposed in series with and coupled to the second coolant line;

after determining that the combined chiller/free cooling system should operate in the low-temperature operating mode:

causing a first valve to be in an open position such that a flow of coolant is allowed between the first coolant line and the third coolant line, the first valve being disposed between the first coolant line and the third coolant line;

causing a second valve to be in the open position such that the flow of the coolant is allowed between the second coolant line and the fourth coolant line, w the second valve being disposed between the second coolant line and the fourth coolant line;

causing a third valve to be in the open position such that the flow of the coolant is allowed between the fourth coolant line and a fifth coolant line, wherein the fifth coolant line is coupled to a water evaporator and a three-way valve;

causing a fourth valve to be in a closed position such that the flow of the coolant is prevented from the second coolant line to a water condenser; and

causing the three-way valve to be in a position such that the flow of the coolant is:

allowed between a coolant input of the combined chiller/free cooling system and the third coolant line; and

prevented between the fifth coolant line and the third coolant line.

9. The method of claim 8 , wherein:

the temperature measurement is a measurement of an outdoor temperature; and

the method comprises determining that the combined chiller/free cooling system should operate in the low-temperature operating mode by:

determining a difference between the outdoor air temperature and the indoor setpoint temperature; and

determining that the difference is greater than a predefined threshold value.

10. The method of claim 8 , wherein:

the temperature measurement is a measurement of a coolant temperature of the coolant in the fifth coolant line;

the method comprises determining that the combined chiller/free cooling system should operate in the low-temperature operating mode by determining that the coolant temperature is less than a threshold value.

11. The method of claim 8 , wherein:

the temperature measurement is a measurement of an outdoor temperature; and

the method further comprises:

determining that the outside temperature is less than a threshold value; and

in response to determining the outside temperature is less than the threshold value, causing each of the first valve and the second valve to move to a closed position.

12. The method of claim 8 , further comprising, after determining that the combined chiller/free cooling system should operate in the low-temperature operating mode, causing a compressor to turn off.

13. The method of claim 8 , further comprising, after determining that the combined chiller/free cooling system should operate in the low-temperature operating mode, causing a coolant pump of the combined chiller/free cooling system to turn off.

14. A controller of a combined chiller/free cooling system comprising a first set of coils configured to receive a coolant from a first coolant line, transfer heat from the coolant to outdoor air, and provide the coolant to a second coolant line; and a second set of coils configured to receive the coolant from a third coolant line, wherein the third coolant line is disposed in series with and coupled to the first coolant line, transfer heat from the coolant to outdoor air, and provide the coolant to a fourth coolant line, wherein the fourth coolant line is disposed in series with and coupled to the second coolant line, the controller comprising:

an input/output interface communicatively coupled to:

a first valve configured to regulate a flow of the coolant between the first coolant line and the third coolant line, the first valve being disposed between the first coolant line and the third coolant line;

a second valve configured to regulate the flow of the coolant between the second coolant line and the fourth coolant line, the second valve being disposed between the second coolant line and the fourth coolant line;

a third valve positioned and configured to regulate the flow of the coolant between the fourth coolant line and a fifth coolant line, wherein the fifth coolant line is coupled to a water evaporator and a three-way valve;

the three-way valve configured to regulate the flow of the coolant between the fifth coolant line, the third coolant line, and a coolant input line;

a fourth valve positioned and configured to regulate the flow of the coolant from the second coolant line to a water condenser; and

a compressor configured to compress a refrigerant provided to the water condenser; and

a processor communicatively coupled to the input/output interface and configured to:

receive a temperature measurement and an indoor setpoint temperature;

determine, based on a comparison of the temperature measurement to the indoor setpoint temperature, that the combined chiller/free cooling system should operate in a low-temperature operating mode;

after determining that the combined chiller/free cooling system should operate in the low-temperature operating mode:

cause the first valve to be in an open position such that the flow of the coolant is allowed between the first coolant line and the third coolant line;

cause the second valve to be in the open position such that the flow of the coolant is allowed between the second coolant line and the fourth coolant line;

cause the third valve to be in the open position such that the flow of the coolant is allowed between the fourth coolant line and the fifth coolant line;

cause the fourth valve to be in a closed position such that the flow of the coolant is prevented between the second coolant line and the water condenser; and

cause the three-way valve to be in a position such that the flow of the coolant is:

allowed between the coolant input and the third coolant line; and

prevented between the fifth coolant line and the third coolant line.

15. The controller of claim 14 , wherein:

the temperature measurement is a measurement of an outdoor temperature; and

the processor is configured to determine that the combined chiller/free cooling system should operate in the low-temperature operating mode by:

determining a difference between the outdoor air temperature and the indoor setpoint temperature; and

determining that the difference is greater than a predefined threshold value.

16. The controller of claim 14 , wherein:

the temperature measurement is a measurement of a coolant temperature of the coolant in the fifth coolant line;

the processor is configured to determine that the combined chiller/free cooling system should operate in the low-temperature operating mode by determining that the coolant temperature is less than a threshold value.

17. The controller of claim 14 , wherein:

the temperature measurement is a measurement of an outdoor temperature; and

the processor is configured to:

determine that the outside temperature is less than a threshold value; and

in response to determining the outside temperature is less than the threshold value, cause each of the first valve and the second valve to move to a closed position.

18. The controller of claim 14 , wherein the combined chiller/free cooling system further comprises, for each coil of the first set of coils and the second set of coils, at least a corresponding fan.

19. The controller of claim 14 , wherein the processor is further configured to, after determining that the combined chiller/free cooling system should operate in the low-temperature operating mode, cause the compressor to turn off.

20. The controller of claim 14 , wherein the processor is further configured to, after determining that the combined chiller/free cooling system should operate in the low-temperature operating mode, cause a coolant pump of the combined chiller/free cooling system to turn off.