Study finds warmer water cools data centres more efficiently
A study of data centres in Frankfurt and Miama found that using higher temperature water resulted in energy savings of between 41% and 64%. A small increase in capital expenditure for additional air cooling systems, redesigned cooling coils and additional adiabatic coolers to compensate for the warmer water is offset by reduced energy costs
Energy efficiency is an issue that concerns all who are involved with the design and operation of data centres. The cooling function in general, and the operation of water chillers in particular, are large consumers of power accounting for 60 to 85% of the overall cooling-system energy consumption. As a result data centres are designed to minimise the use of chillers and focus on less power-hungry systems such as air coolers and cooling towers.
One approach to reducing water chiller energy consumption is to design the cooling system so that a higher outlet water temperature from the chillers can be tolerated while maintaining a sufficient cooling effort. In this way, chillers consume less energy by not having to work as hard. Among the trade-offs are installing more air-handling units inside the IT space to offset the higher water-coolant temperatures, in addition to the need for redesigned equipment such as coils, to provide adequate cooling efforts when the chilled water temperature (CHW) exceeds 20ºC. Using adiabatic, or evaporative, cooling can also improve the heat dissipation. Each approach requires an additional capital investment, but results in lower long-term operating expenses due to the improved energy efficiency.
Schneider collected data from a data centre in Frankfurt in a temperate climate to compare to the tropical monsoon climate of Miama, Florida. This found that an increased capital cost of 13% in both cases resulted in energy savings of between 41% and 64%, paying back the upgrade costs in under three years.
Another benefit was the improvement in the PUE (Power Usage Effectiveness) rating. This is calculated by dividing the total amount of power consumed by a data centre by the power consumed by its IT equipment alone, and was reduced by 14% in Miami and 16% in Frankfurt.
A white paper on “How Higher Chilled Water Temperature Can Improve Data Center Cooling System Efficiency” is at www.apc.com/wp?wp=227