Refrigerant Selection for High-Density Data Center Cooling
Two announcements in the space of a week say something useful about where data center cooling is heading. On 21 September 2026, Daikin Applied Europe and CTS Group unveiled a modular cooling concept for high-density computing, with projected power usage effectiveness as low as 1.09 in Nordic climates and below 1.20 in Middle Eastern conditions. On 22 September 2026, LG announced that its 2.6 MW coolant distribution unit had qualified as an NVIDIA DSX Ready CDU, its third qualification after 600 kW and 1 MW models.
Both are liquid cooling stories. Neither removes the vapor-compression machine from the building. Liquid cooling moves heat from the chip to the facility water loop very efficiently; something still has to reject that heat to ambient, and in many climates, for at least part of the year, that something is a chiller. Which means an operator who has never thought about refrigerant regulation is about to make a twenty-year decision that depends on it.
What Actually Governs the Refrigerant Decision
Capacity and Lift
Direct-to-chip cooling runs warmer facility water than legacy air cooling does, which is the point: a higher chilled water setpoint means less lift across the compressor and better efficiency, and more hours where the chiller can be unloaded or bypassed entirely in favor of free cooling. Refrigerant selection interacts with this directly, because volumetric capacity and the shape of the pressure-enthalpy envelope determine compressor sizing and how gracefully the machine handles part load. A data center's load profile is unusually flat compared with comfort cooling, which changes what matters: sustained efficiency at design conditions counts for more than seasonal turndown.
Condensing Temperature at High Ambient
The Daikin and CTS figures illustrate the point neatly. The same architecture is projected at 1.09 in a Nordic climate and below 1.20 in Middle Eastern conditions, and much of the gap reflects the cost of rejecting heat to a hot ambient. Refrigerants with lower critical temperatures lose capacity and efficiency faster as condensing temperature climbs. If the site is hot, this constrains the candidate list before any regulatory question is asked.
The Regulatory Envelope
Under EPA's Technology Transitions program, implemented under the AIM Act, chillers and data center cooling equipment are subject to GWP limits with compliance dates that differ by application:
Data centers, computer room air conditioning and information technology equipment cooling is its own subsector, with a 700 GWP limit and a compliance date of 1 January 2027 for both manufacture or import and installation.
Comfort cooling chillers carry a 700 GWP limit, with a compliance date of 1 January 2025 for both manufacture or import and installation.
Industrial process refrigeration chillers carry a 700 GWP limit, with a compliance date of 1 January 2026 for exiting fluid at or above -30°C and 1 January 2028 for exiting fluid from -50°C to -30°C. EPA's reconsideration rule published on 26 May 2026 added a 1 January 2030 date for chillers in semiconductor manufacturing equipment with a charge of 100 lb or less.
The consequential question for a data center is which subsector the equipment falls into. EPA created the data center subsector so that this equipment is evaluated on its own terms rather than as comfort cooling or industrial process refrigeration, but equipment at the boundary, such as a chiller serving both a data hall and occupied space, still needs a deliberate call. That determination drives the applicable compliance date, and it should be made deliberately, in writing, with the current rule text and EPA's sector restriction tables in front of you, rather than assumed from how a vendor describes the machine. Regulatory status also has a second-order effect worth naming: a refrigerant's position in the phasedown affects long-term service availability and cost over an asset life that may run past 2036.
Separately, since 1 January 2026, EPA's Emissions Reduction and Reclamation rule under 40 CFR Part 84 Subpart C requires leak repair for appliances holding 15 lb or more of refrigerant containing an HFC with a GWP above 53, and it treats data center cooling equipment as air conditioning, which carries a 10% leak rate threshold.
Safety Classification, Charge and the Machinery Room
ASHRAE Standard 34 assigns a safety group based on toxicity and flammability. ASHRAE Standard 15 and, for applicable equipment, UL 60335-2-40 then set what follows from that group: permitted charge for a given occupancy and space, machinery room requirements, ventilation, refrigerant detection and mitigation.
Two points are worth making plainly, because both get muddled in general discussion.
First, a safety group is not a transport classification. ASHRAE Standard 34 classification and DOT hazard classification for shipping and storage are separate systems answering separate questions, and a product's designation under one tells you nothing definitive about its treatment under the other. Both need checking independently.
Second, the design consequences of a safety group are a constraint set, not a verdict. An A2L refrigerant in a machine located and detected as the standards require is a code-compliant installation, widely used and well characterized. An A1 refrigerant does not remove the need for a machinery room assessment either, because charge limits, pressure relief and oxygen displacement all still apply. The honest summary is that the safety group determines which set of engineering requirements you design to, and every set is satisfiable. Chiller product lines in service today span both groups; R-1234ze(E), R-515B, R-513A, R-454B and R-32 all appear in current chiller duty.
Reading the Two Announcements Carefully
A note on evidence, because both announcements are worth reading with a clear eye:
The Daikin and CTS PUE figures are described as projections. Reporting indicates full-scale factory testing validated the concept's ability to handle demanding AI workloads, but the PUE numbers are not measured results from an operating facility. Treat them as a design target, not a performance guarantee.
The LG announcement is a qualification against a reference design. NVIDIA DSX Ready means the unit meets the applicable DSX reference design requirements for AI factory infrastructure. That is a meaningful signal about integration, not a performance ranking.
The LG release cites TrendForce data projecting that liquid cooling penetration for AI chips rises from 14% in 2024 to approximately 60% by 2027. That is a third-party market projection carried in a vendor release, and it should be read as such.
A Short Diligence List
Determine which Technology Transitions subsector your cooling equipment falls into, including whether it sits in the data center subsector, and record the reasoning. Do it before procurement, not after.
Confirm the applicable GWP limit and compliance date against the current rule text, including any revision made by the May 2026 reconsideration rule.
Confirm the leak repair and recordkeeping obligations under 40 CFR Part 84 Subpart C that apply at the charge size you are specifying.
Model performance at your site's design ambient, not at a reference condition, and ask for the assumptions behind any efficiency figure a vendor quotes.
Establish the machinery room, charge, detection and ventilation requirements that follow from the candidate refrigerant's safety group under ASHRAE Standard 15 and, where applicable, UL 60335-2-40, and confirm them against local code.
Check transport and storage handling requirements separately from the safety group, since they are governed by a different classification system.
Ask what the service and refrigerant supply picture looks like in year fifteen, not year one.
Why a Refrigerant Manufacturer Is Writing This
Data center operators are making long-lived decisions inside a regulatory framework that now includes a dedicated subsector for their equipment, on a schedule that runs to 2036. FluoroFusion blends and packages refrigerants across safety classifications, holds HFC consumption allowances, and operates as an EPA-certified reclaimer. For a data center, that means we can supply service refrigerant for the life of the asset and reclaim it when the equipment is retired. We are not going to tell you which refrigerant belongs in your chiller from a blog post. We will say that the determination in item one of that list is the one most likely to be made casually and regretted later.
Sources
Cooling concept delivers PUE below 1.2 in hot climates, Cooling Post
New patented cooling concept, Climate Control News, 21 September 2026
LG Electronics' 2.6-Megawatt Coolant Distribution Unit Qualifies as NVIDIA DSX Ready CDU, 22 September 2026
LG 2.6MW CDU is NVIDIA approved, Cooling Post
Technology Transitions HFC Restrictions by Sector, US EPA (last updated 28 August 2026)
Regulatory Actions for Technology Transitions, US EPA
Technology Transitions Final Rule Fact Sheet, updated May 2026, US EPA
Emissions Reduction and Reclamation Program fact sheets, US EPA
ANSI/ASHRAE Standard 15 and ANSI/ASHRAE Standard 34
Frequent Questions on the Phasedown of Hydrofluorocarbons, US EPA
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