A global blueprint for how gigawatt-scale AI Factories can re-use waste heat with absorption chillers

Driven by growing power constraints, increasing AI workloads and ambitious sustainability targets, data centers are having to do more with every unit of energy consumed. To meet the relentless AI demands, operators are increasingly turning to on-site generation sources such as CHP plants, fuel cells and small modular reactors.

These systems deliver reliable electricity, but they also produce an abundance of waste heat – a resource that (up until recently) has been largely left untapped. When natural gas is used to generate electricity, only 35-50% of the input fuel becomes usable power. The rest is lost as waste heat.

Rather than rejecting this thermal energy into the atmosphere, forward-thinking operators are exploring ways to capture and reuse it. Absorption chillers offer a compelling pathway. They transform waste heat into valuable cooling capacity to help AI Factories simultaneously improve efficiency, resilience and sustainability.

Thermally driven absorption chillers with on-site power generation

Reference Design Guide 407 from Johnson Controls is the latest in a series of global reference design guides for gigawatt-scale AI data centers. The design guide outlines how to plan and design a 1-Gigawatt (1GW) AI Factory that is built around thermally driven absorption chillers. The guide places a strong emphasis on how data center operators can capture waste heat from on-site generation and re-use it to deliver cooling with minimal electric consumption.

Reference Design Guide 407 includes the following key information:

• A map of the full thermal chain, from capturing heat at chip level to managing the final atmospheric rejection
• An architecture that integrates CHP generators, absorption chillers, dry coolers, CRAHs, FCWs and CDUs in a single, modular system
• A breakdown of compute clusters, required equipment, thermal chain elements and how absorption chillers are used within integrated heat and power systems
• An outline of intended AI Factory goals and how the design helps achieve them

The combination of absorption chillers and dry coolers outlined in the guide overcomes the conventional PUE vs WUE trade-off. For many years, there was a perceived inverse relationship between achieving a lower PUE and increasing WUE, with conventional cooling designs ]operating along a water-energy trade-off curve. However, advances in cooling designs are demonstrating that this trade-off is not always necessary. Similar to Reference Design Guide 401 and Reference Design Guide 402, the latest technical blueprint allows data center operators to improve both metrics simultaneously. The integrated system can achieve PUE of 1.23 and WUE of 0.

Critical outcomes for gigawatt-scale AI Factories

Reference Design Guide 407 from Johnson Controls was developed in collaboration with Lynk Engineers – a multidisciplinary firm with over 40 years of experience at delivering integrated energy, cooling and critical infrastructure solutions for mission-critical facilities.

The approach outlined in the design guide delivers the following critical outcomes for AI Factories compared to using generator-powered electric chillers:

• 44% reduction in cooling electrical load: one integrated system delivers two ways to win with either more compute (+97MW with same fuel input) or lower fuel consumption (43% reduction in chiller plant CO₂ emissions with same IT load)
• Lower PUE with zero water trade-off: PUE of 1.23 and a WUE of 0 through absorption cooling with dry coolers
• Grid-independent, resilient operation: on-site generation with redundancy ensures continuous cooling
• Modular, scalable deployment: 1:1 pairings of generators to chillers enable scaling without redesign

Energy considerations that are shaping the future of AI

More than ever before, the efficient energy usage of data centers is being placed under the microscope by those both inside and outside the industry.

Facilities face severe power constraints and operate within hard limits, determined by regional power grids and caps set by local utility operators. Data center operators also face increasingly stringent sustainability objectives and demanding cooling requirements.

"A vast amount of heat produced by on-site power generators is essentially thrown away — dissipated into the air. We see a huge opportunity when that energy is put to work instead," said Katie McGinty, Vice President and Chief Sustainability and External Relations Officer, Johnson Controls. "By converting waste heat into useful cooling, we're turning a resource already bought and paid for into an asset rather than a disposal liability. Every megawatt we can shift from cooling to computing capacity helps customers increase the revenue potential of their facilities and accelerates time to value by significantly cutting pressure on the grid. That's the kind of innovation that supports AI growth, lowers costs and helps communities and businesses get more from existing energy resources."

Download the latest Reference Design Guide from Johnson Controls

The latest reference design guide follows recent releases of Reference Design Guide 402 and Reference Design 401. These two guides – which were designed for the emerging class of AI Factories – provide an outline for a water-cooled chiller plant (Reference Design Guide 402) and an air-cooled chiller plant (Reference Design Guide 401).

For more information and to download all guides, follow the link below.

FAQs

What is the YORK® YHAU absorption chiller?

The YORK YHAU is a series of absorption chillers manufactured by YORK (Johnson Controls). Unlike conventional electric centrifugal or screw chillers, the YORK YHAU produces chilled water using heat energy rather than relying primarily on electrically driven compressors.

The YORK YHAU comes in a range of models. These can be either single effect or double effect, which refers to the number of stages used to boil the refrigerant. They can also be powered by a range of sources including steam, hot water or direct fired with natural gas.

What are absorption chillers and how do they work?

Absorption chillers are cooling systems that use waste heat as their primary energy source. They can recover the waste heat from on-site generation and use it as their primary energy source, instead of grid electricity. In addition, water is used as the natural refrigerant. This process results in reduced electrical demand, improved sustainability, enhanced efficiency and the ability to operate in hot or arid regions.

What is the Silent-Aire CDU?

The Silent-Aire CDU (Coolant Distribution Unit) is a versatile alternative to traditional air conditioning systems that is designed to meet the high-performance demands of liquid-cooled AI Factory operators. By enabling placement near the equipment that requires cooling, the Silent-Aire CDU helps conserve energy and eliminates the need to circulate coolant over a large area.