One Primary Loop, Many Cooling Architectures

Direct-to-chip cooling, immersion cooling, CRAH and CRAC systems may look very different at the point of heat capture, but they all rely on the same fundamentals:

  • A stable supply temperature
  • Predictable heat transfer performance
  • Reliable flow, pressure and chemistry
  • Consistent heat rejection capability

In a hybrid data centre, the primary closed loop supports air handling units for room-level cooling, while simultaneously feeding CDUs that service direct-to-chip or immersion deployments. This makes primary cooling not just a utility, but a shared critical system that underpins the entire cooling architecture.

Thermal Fluids: The Invisible Enabler

At the centre of primary cooling performance is the thermal fluid itself — most commonly a glycol-based solution. Fluid selection is not a commodity decision; it directly influences heat transfer efficiency, pumping energy, material compatibility, environmental impact and long-term reliability.

Key considerations include:

  • Correct glycol type and concentration to balance freeze protection, heat transfer and viscosity
  • Low-toxicity formulations, particularly important where systems interface with sensitive environments or sustainability targets
  • Additive packages that protect against corrosion, scaling and biological growth

An incorrectly specified or degraded thermal fluid increases pumping energy reduces heat exchanger effectiveness and introduces hidden failure modes that erode uptime over time.

Balancing Performance and Safety: Propylene vs Ethylene Glycol

Traditional ethylene glycol (EG) offers excellent heat transfer properties and lower viscosity than propylene glycol (PG) but is toxic and requires stringent handling and spill protocols. Propylene glycol, in contrast, is much less toxic and safer for enclosed environments and personnel exposure—making it a preferred choice for data centres concerned with operational safety and environmental compliance.

That said, standard propylene glycols often have lower thermodynamic performance compared to EG blends, creating a performance-safety trade-off that designers and operators must address. This is where advanced fluids like Castrol On Primary Loop DTX provide a compelling alternative.

Introducing Castrol On Primary Loop DTX

Castrol On Primary Loop DTX is an advanced glycol solution engineered for data centre primary cooling loops. It combines the low toxicity profile of propylene glycol with performance characteristics that approach those of ethylene glycol systems—yielding a formulation especially suited to today’s high-performance cooling demands. By optimising the thermodynamic and hydrodynamic behaviour of the fluid, DTX helps maintain efficient heat transfer in closed-loop chilled water loops without compromising on safety. This synergy is particularly attractive in critical infrastructure where both human safety and system efficiency are paramount.

Fluid Condition, Management and Monitoring

Primary cooling efficiency is not static. Over time, thermal fluids degrade due to thermal stress, contamination, oxidation and dilution. Without active fluid management and monitoring, performance slowly drifts away from design intent — often unnoticed until failures occur.

Best practice primary cooling strategies therefore include:

  • Regular fluid analysis to assess inhibitor health, contamination and degradation
  • Proactive fluid maintenance and correction rather than reactive replacement
  • Ongoing system monitoring to ensure temperature differentials, flow rates and pressures remain optimised

This approach supports not only efficiency, but also predictability, which is essential for high-density computing environments.

Designing for Uptime, Efficiency and Sustainability

From a Chiller-to-Chip perspective, primary cooling is the first and most important design decision. It defines how effectively heat can be removed, how resilient the system is under variable loads, and how sustainably the data centre can operate over its lifecycle.

DC Cooling Solutions focus on this foundational layer — combining a unique range of thermal fluids and performance enhancing additives, together with expertise in fluid dynamics, cooling system design and chem-mech site services to ensure that advanced cooling architectures deliver real-world results, not just theoretical performance.

In an era of rising densities and hybrid cooling systems, the message is clear: get the primary cooling right first — everything else depends on it.