How harnessing waste heat can help unlock energy efficiencies for data centers

Driven by regulation, cost pressures and resource constraints, today’s operators are regularly being tasked to do more with less. In a reality where only 35-50% of the input fuel is converted into electricity, and the rest is released into the atmosphere, there is a massive opportunity for operators to take advantage and find better and more strategic ways to utilize waste heat.

That’s where absorption chillers and the technology behind them enter the picture.

Reusing waste heat: no longer just a suggestion

In the European Union, heat export mandates are beginning to require waste heat reuse, and this shift is already leading to projects where the warmth from servers is piped into district heating grids. Even in regions without such requirements, the economic and environmental benefits are prompting wider adoption – especially in situations where grid electricity is constrained or water is scarce.

This has brought attention to absorption chillers and the technology behind them.

“Absorption chillers can be driven by waste heat from combined heat and power (CHP) systems, providing beneficial cooling to the data centers,” says Rajesh Dixit, Senior Director, Global Product Management, Building Technologies & Solutions, Johnson Controls. “The heat of rejection from the absorption cycle can be rejected to dry coolers, which means no water loss. In a futuristic scenario, absorption heat pumps may be serving the cooling needs of the data center, and the heat of rejection of the cycle can be used for beneficial heating purposes.”

Absorbing waste heat

Simply put, absorption chillers offer a different approach to cooling. Unlike mechanical chillers, which rely on electrically driven compressors, absorption systems use waste heat as their primary energy source.

“The beauty of an absorption chiller is for every two megawatts of cooling, you would need only 25 kilowatts of input electrical energy to run that unit – compared to more than 500 kilowatts for an electrical chiller,” explains Ivo Eiermann, Product Manager, Absorption Chillers & Heaters EMEA, Johnson Controls. “This is a significant impact, as you’re not dependent on the electrical grid at all to produce cooling.”

In most cases, absorption chillers are used to supplement (rather than replace) mechanical cooling. They are particularly valuable when on-site generation – CHP plants, small modular reactors (SMRs) or fuel cells – produces abundant waste heat. Their design makes them adaptable and able to operate without evaporative cooling in hot, arid regions – like Texas, Arizona and the Middle East – by having the ability to reject heat to condenser water loops above the ambient in these climates. This makes them particularly interesting for the growing data centers landscape.

“As data centers increasingly adopt on-site power generation, they inadvertently create a valuable byproduct: waste heat, available in proximity to the site’s chilled water demand,” said Mihir Nandkeolyar, Director, Technology Strategy & Business Development, Thermal Management, Johnson Controls. “This convergence of thermal energy and cooling demand presents a compelling opportunity for absorption chillers. By harnessing waste heat, these systems deliver chilled water with a fraction of the electrical input required by traditional electric chillers – unlocking both energy efficiency and sustainability in one elegant solution.”

Beyond cooling – waste heat repurposed

Waste heat can also be put to work beyond the data center itself. In Europe, where district heating networks are common and legislation mandates that heat cannot be wasted, operators are increasingly pairing waste heat with heat pumps to raise waste heat temperatures for integration into municipal systems. The objective of such process is to create a dual benefit of cooling the data center while supplying heat to local communities. By turning waste heat into a resource, absorption chillers could potentially offer data centers a way to reduce carbon emissions, conserve water and improve operational efficiency.

“It makes economic sense for the waste heat to be put to use for either heating or cooling,” says Dixit.

Decades of innovation

For operators navigating the pressures of rising demand and sustainability mandates, Johnson Controls provides the technology and expertise to make that possible through decades of experience in thermal innovation.

With innovative and proprietary heat exchanger designs – developed by a leading global R&D engineering team with end-of-line testing capabilities in-house – customers can be confident that Johnson Controls systems integrate seamlessly with a variety of on-site energy sources.

Want to get the most out of your data center? Johnson Controls draws upon hundreds of successful data center projects worldwide to address the industry’s most pressing challenges. We’ll help you adapt to rapid technological change, easily source products and services across the globe and meet demanding local requirements.

Learn more about how Johnson Controls can be your dedicated global data center solutions partner: https://www.johnsoncontrols.com/industries/data-centers

FAQs about heat waste and absorption chillers

1. What is pushing the conversation around waste heat recovery?
With the exponential growth of data centers and AI factories, operators are facing increasing constraints and challenges. There is a need to explore and adopt technological solutions that can tackle the increasing demands while still meeting sustainability requirements.

2. How can absorption chillers help data centers use waste heat?
Absorption chillers use waste heat as their primary energy source. Because they rely on thermal energy instead of large compressors, they can deliver chilled water with only a fraction of the electrical input needed by traditional electric chillers.

3. What are potential benefits of absorption chillers for data centers?
A few of the key benefits include reduced electrical demand, improved sustainability and efficiency, and the ability to operate in hot or arid regions.

4. Can waste heat be used beyond a data center?
Yes. In regions with district heating networks – especially in Europe – waste heat can be integrated into municipal heating systems. This could potentially provide community heating while helping a facility manage its thermal load.