As AI drives unprecedented demands for computing power, the data center industry stands at a critical juncture.
Considering that an average ChatGPT query uses 10 times more power than a Google search, it’s easy to see why billions of dollars are being invested in data centers and extreme measures for powering them – such as Microsoft’s plan to recommission the notorious Three Mile Island nuclear reactor – are all of a sudden back on the table.
Traditional air-cooling systems have hit a performance ceiling, unable to effectively cool today’s high-density server racks. However, our new approach — Hybrid Dry/Adiabatic Cooling (HDAC) — offers a promising solution to address sustainability challenges such as escalating density, power, and water consumption.
Unfortunately, most hyperscale data centers have reached density limits with current air-cooled designs, averaging approximately 11 kW per cabinet. All this while, AI processing and advanced cloud computing are pushing requirements toward 40 kW per cabinet, which in turn requires an unsustainable level of fan energy and increasing contamination risks when using airside economizers. In fact, Nvidia is making noise about racks of 600kW and even more!
To address this power density, today, two primary Direct Liquid Cooling (DLC) technologies are emerging as viable solutions for high-density environments:
- Immersion Cooling (IC): Servers are fully submerged in non-conductive fluid within specialized tanks, with heat exchangers transferring energy to process water and then to heat rejection equipment.
- Rack Fluid Cooling (RFC): Conventional racks are equipped with “cold plate” heat sinks that transfer heat from processors to circulating fluid, which then exchanges heat with a cooling system.
The key advantage of these technologies is their ability to operate at significantly higher inlet fluid temperatures — up to 37°C (98.6°F) and 32°C (89.9°F), respectively.
The HDAC Solution
Shumate Engineering has developed a unique central plant design called Hybrid Dry/Adiabatic Cooling (HDAC) that can effectively handle densities up to 40 kW per cabinet while simultaneously achieving a significantly lower Power Usage Effectiveness (PUE) than any air-cooled system.
At the core of HDAC are Adiabatic Fluid Coolers (AFCs) — heat rejection devices that use fans to induce airflow through a dry adiabatic pad and closed-loop coil. The system operates in dry mode when outdoor temperatures fall below 81.5°F, using zero water. Only when ambient temperatures exceed this threshold does the system activate adiabatic media to assist with heat rejection.
In typical mid-Atlantic climate conditions, this approach can operate without water consumption for approximately 94 percent of the year. The elevated supply water temperature from the AFC serves both the direct liquid cooling equipment and water-cooled chillers that provide cooling for the remaining air-cooled portion of the data center.
Hybrid Approach
What makes HDAC particularly innovative is its hybrid design philosophy. Recognizing that even advanced data centers may still require some air cooling (approximately 20 percent of the total IT load), the system integrates traditional Computer Room Air-Handling Units (CRAHUs) and/or fan walls into a comprehensive cooling solution.
The same elevated supply water from the AFCs passes through the evaporator bundle in the chilled water plant, creating a secondary chilled water loop at lower temperatures to serve air handling components. After leaving the air handling equipment, this fluid then passes through the condenser bundle in the chilled water plant and combines with return water from fluid-cooled equipment before finally returning to the AFCs.
This integrated approach allows for cooling both liquid-cooled and air-cooled equipment with maximum efficiency while minimizing water usage. The chilled water supply to the CRAH equipment operates at 80°F, eliminating condensation risks while still providing effective cooling.
The results are compelling. Calculations show HDAC can achieve an annualized PUE of 1.05 to 1.062 for a hyperscale data center in the mid-Atlantic region, depending on the ratio of air-cooled versus fluid-cooled equipment. This represents a significant improvement over direct adiabatic cooling systems, which typically achieve PUE ratings well above 1.20.
Beyond energy efficiency, HDAC dramatically reduces water consumption compared to traditional cooling tower approaches, which are notoriously water-intensive. Traditional cooling towers operate with 100 percent adiabatic evaporation and typically include a bleed line equal to the evaporation rate to reduce scale buildup, effectively doubling water usage.
The timing of this innovation couldn’t be more serendipitous. The rapid expansion of AI infrastructure is driving unprecedented investment in data center capacity. According to industry analysts, AI-specific data center construction alone is expected to require hundreds of billions in investment over the next decade.
These AI facilities face three core challenges:
- Power density: AI accelerators like GPUs and specialized AI chips generate far more heat per rack than traditional servers.
- Energy costs: The economics of AI infrastructure demands increasingly efficient cooling to remain cost-effective.
- Environmental concerns: Water usage has become a flashpoint for data center development, with many localities restricting new construction based on water consumption concerns.
HDAC addresses all three challenges in one fell swoop. By enabling much higher rack densities, it reduces the data center footprint required for a given computing capacity. The dramatically improved PUE translates to significant operational cost savings. And the near-elimination of water usage for most of the year addresses one of the industry’s most pressing sustainability challenges.
Direct Liquid Cooling implemented through Hybrid Dry Adiabatic Cooling represents one of the most promising approaches for reducing data center PUE while enabling the density required for next-generation computing. As the industry adopts cooling IT equipment with liquid at the heat source, HDAC provides an elegant solution that balances engineering considerations with environmental and financial imperatives, making it a critical enabler for the next wave of AI and cloud computing infrastructure.
