The cooling process in a data center can be broken down into three stages:
- The condenser water side
- The evaporator side
- The load side
This process ensures that excess heat is redirected from the servers to the condenser units and cooling towers, and then to the outside environment. Thus, the vapor you see coming from cooling towers is steam, not smoke.
The role of the cooling tower is essential to the overall efficiency of the data center. When the condenser water temperature, which is circulating to the cooling tower, is lower, the compressor will be less taxed in its job. For every pound of water that is evaporated in the cooling tower, as much as 1,000 BTUS (British Thermal Units) can be absorbed from the data center building.
A couple important questions to ask when you are evaluating the effectiveness of a cooling tower:
- How do you evaluate its performance?
- What factors impact how effective it will be?
One of these factors involves understanding the specific cooling tower’s wet bulb temperature. The wet bulb temperature will vary depending on where the cooling tower and data center are located, and what the weather conditions are in that location (particularly concerning humidity). Of course, when a climate is more humid, less evaporation can occur; when a climate is less humid, more evaporation can occur (think Phoenix versus Miami—both are generally very warm, but Phoenix has dry heat, while Miami has high levels of humidity).
Wet bulb temperature is the lowest temperature that the cooling tower can reach, given the current weather environment. The ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) handbook has a list of wet bulb temperatures for all significant locations in the U.S. Make sure you know what the wet bulb temperature is where your data center is located.
Determining the optimal operating range for your cooling tower can be a tricky process. You will need to compare the kilowatt consumption for both the pump(s) and the chillers under various circumstances. Make sure you account for the array of variables that may affect these values.
It is also important to remember that the higher the temperature of the water leaving the cooling tower (approach), the smaller the cooling tower, and the lower the temperature of the water leaving the cooling tower, the larger the cooling tower.
In our next blog we will cover fans in the data center.