MEP engineers specifying cooling systems for data centers are working in a gap. ASHRAE thermal guidelines, which have been the bedrock of data center environmental design for decades, were built around air-cooled environments. The rapid adoption of liquid cooling for high-density AI workloads has outpaced the standards development process, leaving engineers to navigate an evolving landscape where best practices are forming faster than formal guidelines can be published.
This is not an argument against ASHRAE, as the organization is actively developing liquid cooling guidance. But the reality is that projects are being specced and built right now, and engineers need a practical understanding of where current standards apply, where they fall short, and how to fill the gaps responsibly.
Where ASHRAE Thermal Guidelines Stand Today
ASHRAE’s TC 9.9 committee maintains the thermal guidelines that most data center engineers reference for environmental design. The current guidelines define recommended and allowable temperature ranges for air-cooled IT equipment across classes A1 through A4, with A1 being the most tightly controlled environment at 18-27 degrees Celsius dry-bulb on the inlet side.
These classes were designed for servers and networking equipment cooled by air moving through the chassis. They work well for traditional deployments and remain the correct reference for air-cooled portions of hybrid facilities. However, they do not directly address the thermal management of liquid-cooled systems where coolant, not air, is the primary heat transfer medium.
ASHRAE has published supplemental guidance on liquid cooling through its datacom series publications, and TC 9.9 has working groups focused on expanding guidance for direct liquid cooling. But as of early 2026, the formal standard does not yet include prescriptive thermal ranges for liquid cooling supply and return temperatures, coolant chemistry requirements, or system pressure specifications in the same way it does for air-cooled environments.
The Practical Gaps Engineers Are Navigating
When you are specifying a coolant distribution unit for an AI deployment running Blackwell GPUs at 1,200W per processor, you need specific engineering parameters. Today, those parameters come from a combination of GPU manufacturer specifications, CDU vendor documentation, and facility-specific engineering analysis rather than a single unified standard. Here are the areas where engineers are most commonly working without formal ASHRAE guidance:
- Coolant supply temperature ranges: GPU manufacturers typically specify supply temperatures between 25-45 degrees Celsius for single-phase direct liquid cooling. The optimal operating point depends on the specific GPU, workload profile, ambient rejection conditions, and desired PUE. ASHRAE does not yet define recommended versus allowable ranges for these parameters.
- Coolant chemistry and material compatibility: Propylene glycol/water mixtures at various concentrations are common, but specifications for pH, conductivity, inhibitor packages, and maintenance intervals vary by vendor. ASHRAE references coolant considerations in its supplemental publications but does not provide the prescriptive guidance engineers are accustomed to for other systems.
- System pressure and flow requirements: CDU systems operate at specific pressure differentials to maintain adequate flow across cold plates. The engineering calculations are straightforward, but there is no standardized methodology in the ASHRAE framework for sizing these systems across different facility configurations.
- Leak detection and containment: This is an area where ASHRAE guidance would be particularly valuable. Current best practices are borrowed from industrial process cooling and adapted for data center environments, but a data-center-specific standard for leak detection placement, containment volume calculation, and response protocols does not yet exist.
What Is Coming from ASHRAE and When
ASHRAE TC 9.9 has acknowledged the gap and has multiple work items in progress. The next revision of the thermal guidelines is expected to include expanded sections on liquid cooling, including recommended temperature ranges for facility-side and IT-side coolant loops. Working groups are also developing guidance on hybrid environments where air and liquid cooling coexist in the same facility.
Realistically, formal publication of comprehensive liquid cooling standards is a 12-24 month process from where things stand today. That timeline means engineers specifying projects for 2026-2027 deployment will continue working with manufacturer specifications and engineering judgment rather than waiting for ASHRAE to publish.
This is not unusual in rapidly evolving technology sectors. Standards bodies are inherently conservative, and they should be. Publishing premature standards is worse than publishing none. But it does mean that MEP engineers need to be comfortable documenting their engineering basis of design clearly, referencing the sources they are relying on, and building flexibility into their specifications for future standard adoption.
How to Spec Liquid Cooling Systems Today Without Waiting for Standards
Engineers working on projects right now should follow a practical approach:
- Start with GPU manufacturer thermal specifications as the primary design input. NVIDIA, AMD, and Intel all publish detailed thermal management guides for their server platforms that include coolant temperature, flow rate, and pressure requirements.
- Reference CDU vendor engineering documentation for system-level design parameters. Leading CDU manufacturers have developed design guides that address facility integration, piping specifications, and control system requirements.
- Apply ASHRAE 90.4 energy efficiency requirements where applicable. While the thermal guidelines are still catching up to liquid cooling, ASHRAE 90.4 provides energy efficiency standards that apply to cooling system design regardless of the technology used.
- Document your engineering basis of design thoroughly. In the absence of a single comprehensive standard, clear documentation of design inputs, assumptions, and safety factors becomes the record of engineering judgment that supports the project.
- Build flexibility into coolant loop design for future standard compliance. Design pipe sizes, valve arrangements, and control systems to accommodate changes in operating parameters as ASHRAE guidance matures.
- Engage with ASHRAE TC 9.9 activities if your firm has the capacity. Participating in standards development gives you early visibility into the direction of future guidance and allows you to contribute your project experience to the process.
Key Takeaways
ASHRAE standards are evolving, but the pace of liquid cooling adoption in AI data centers means engineers cannot wait for final publications to do their work. The responsible approach is to use the best available engineering data from GPU manufacturers and CDU vendors, apply sound engineering judgment, document decisions clearly, and design systems with enough flexibility to adapt as formal standards mature. The engineers who understand both the current ASHRAE framework and its limitations are the ones best positioned to deliver facilities that perform today and remain compliant tomorrow.
Nautilus Data Technologies collaborates with MEP engineering firms to provide CDU system specifications, integration guidance, and thermal engineering support for liquid cooling projects. Contact our engineering team if you are working on a specification that requires detailed thermal design inputs.
