Cooling system with indirect humidity determination

1. A cooling system for a data center having equipment racks disposed therein, the equipment racks having electronic equipment therein, the cooling system comprising:

a cooling unit;

a controller coupled to the cooling unit;

a temperature sensor disposed near an air inlet of each equipment rack at which relative humidity is to be calculated by the controller (“Temp Sensor Location”), each temperature sensor coupled to the controller;

a relative humidity sensor disposed to sense relative humidity at a location in the data center or near an air return inlet of the cooling unit and an associated temperature sensor disposed with the relative humidity sensor, the relative humidity sensor and associated temperature sensor coupled to the controller;

the controller measuring with the relative humidity sensor relative humidity at the location at which the relative humidity sensor is disposed and measuring with the associated temperature sensor disposed with the relative humidity sensor a temperature of air thereat;

the controller calculating a dew point based on the measured relative humidity and temperature of air measured at the relative humidity sensor;

the controller measuring with the temperature sensor at each Temp Sensor Location a temperature of air at each Temp Sensor Location and indirectly determining a relative humidity thereat by calculating the relative humidity thereat based on the temperature of air measured at that Temp Sensor Location and the calculated dew point.

2. The system of claim 1 wherein the air inlet of each equipment rack is a Temp Sensor Location and has one of the temperature sensors disposed thereat.

3. The system of claim 2 wherein a location near an air supply outlet of the cooling unit is also a Temp Sensor Location and has a temperature sensor disposed thereat.

4. The system of claim 3 including a display coupled to the controller on which the relative humidities can be displayed.

5. The system of claim 3 wherein the controller controls the cooling unit to control a relative humidity at one or more of the Temp Sensor Locations, the controller calculating a control relative humidity set point for each such Temp Sensor Location based on a relative humidity set point for the Temp Sensor Location entered into the controller, the calculated dew point and the temperature of air measured at that Temp Sensor Location, the controlling controller controlling the cooling unit to control the relative humidity at that Temp Sensor Location based on the calculated control relative humidity set point for that Temp Sensor Location and the relative humidity at that Temp Sensor Location calculated by the controller.

6. The system of claim 1 wherein the relative humidity sensor and associated temperature sensor are disposed in the cooling unit near the air return inlet of the cooling unit.

7. The system of claim 1 wherein the relative humidity sensor and associated temperature sensor are a combined sensor.

8. In a data center having equipment racks disposed therein, the equipment racks having electronic equipment therein and a cooling unit for cooling the data center, a method of indirectly determining relative humidity at one or more locations in the data center having a temperature sensor disposed thereat but not a relative humidity sensor (“Temp Sensor Locations”), each temperature sensor disposed at a Temp Sensor Location coupled to a controller, the method comprising:

measuring with a controller and a relative humidity sensor coupled to the controller and disposed at a location in the data center or near an air return inlet of the cooling unit the relative humidity at the location where the relative humidity sensor is disposed;

measuring with the controller and a temperature sensor coupled to the controller and disposed at the location where the relative humidity sensor is disposed a temperature of air at that location;

calculating with the controller a dew point based on the measured relative humidity and the temperature of air measured at the location where the relative humidity sensor is disposed;

measuring with the controller and the temperature sensor at each Temp Sensor Location a temperature of air at each Temp Sensor Location;

indirectly determining the relative humidity at each Temp Sensor Location by calculating with the controller the relative humidity based on the calculated dew point and temperature of air measured at that Temp Sensor Location.

9. The method of claim 8 wherein the Temp Sensor Locations include air inlets of the equipment racks.

10. The method of claim 8 wherein the Temp Sensor Locations include an air supply outlet of the cooling unit.

11. The method of claim 8 wherein measuring the relative humidity and the temperature of the air at the location at which the relative humidity sensor is disposed includes measuring the relative humidity and the temperature of air near an air return inlet of the cooling unit.

12. The method of claim 11 wherein measuring the relative humidity and the temperature of the air near the air return inlet of the cooling unit includes measuring the relative humidity and the temperature of air in the cooling unit near the air return inlet of the cooling unit.

13. The method of claim 8 including displaying the relative humidities on a display coupled to the controller.

14. The method of claim 8 including controlling the cooling unit with the controller to control relative humidity at one or more of the Temp Sensor Locations by calculating with the controller a control relative humidity set point for each such Temp Sensor Location based on a relative humidity set point for the Temp Sensor Location entered into the controller, the calculated dew point and the temperature of air measured at that Temp Sensor Location, and controlling the cooling unit with the control to control the relative humidity at that Temp Sensor Location based on the calculated control relative humidity set point for that Temp Sensor Location and the relative humidity at that Temp Sensor Location calculated by the controller.