As direct-to-chip liquid cooling becomes standard in high-density data centers, a recent study conducted by BAC finds there is no single heat rejection technology that outperforms others in every instance. The best choice depends on the specific conditions and priorities of each site as opposed to a “one-size fits all” approach. 

The finding reflects a fundamental shift in how modern data centers are designed. As rack densities climb to levels once considered extreme, liquid cooling is being deployed more widely, transferring the bulk of a facility's heat directly to a coolant loop. In many designs, the limiting factor is no longer removing heat inside the IT space, but rejecting it efficiently to the outdoor environment. This shift makes the choice between dry, adiabatic, and evaporative technologies one of the most consequential decisions in facility design today. 

Factors such as free-cooling potential and evaporative effectiveness vary widely by climate, so a cooling approach that proves efficient and practical in one location can fall short in another. The choice also involves inherent tradeoffs: approaches that minimize energy use and peak power demand tend to consume the most water, while those that conserve or even eliminate water use often require more energy and electrical infrastructure. The choice of heat rejection technology is therefore best treated as a site-specific optimization defined by a location's climate, water availability, utility costs, and electrical infrastructure capacity, as well as the operator's sustainability goals and long-term growth plans. 

To reach these conclusions, BAC compared four widely deployed external heat rejection technologies, ranging from fully air-cooled to fully evaporative systems, across six global climate zones ranging from cool maritime conditions to hot, arid environments. The simulations modeled a representative 18 MW high-density facility module across every hour of a full year, using ASHRAE weather data.  Factors such as capital cost, operating cost, peak electrical demand, water consumption, and physical footprint were evaluated for each site. 

The findings arrive as operators face mounting pressure to build faster while managing energy availability, water scarcity, sustainability commitments, and impacts to local communities. The study suggests that early, site-specific evaluation of heat rejection strategy will play an increasingly central role in data center design amid these pressures. 

Interested in learning more? The complete study, executive summary, and supporting materials are available at https://baltimoreaircoil.com/evaluating-data-center-heat-rejection-options