How does increasing the chilled water supply temperature impact the overall PUE of a data center, and why?

Increasing the chilled water supply temperature generally improves the overall PUE (Power Usage Effectiveness) of a data center because it allows for more efficient operation of the chillers. Chillers consume a significant amount of energy in a data center, and their efficiency is directly related to the temperature difference between the chilled water they supply and the return water they receive. Raising the chilled water supply temperature reduces this temperature difference, making it easier for the chillers to remove heat. This means the chillers consume less energy per unit of cooling provided. Furthermore, a higher chilled water supply temperature enables greater use of 'free cooling' methods, such as air-side or water-side economizers. These economizers use outside air or water to cool the data center, reducing the reliance on mechanical chillers and significantly lowering energy consumption. The higher the chilled water supply temperature, the more hours per year that free cooling can be utilized. This reduction in chiller energy consumption directly translates into a lower PUE, as PUE is calculated as total facility energy divided by IT equipment energy. By reducing the total facility energy used for cooling, while the IT equipment energy remains the same, the overall PUE improves.