What Is PG25 Coolant and Why It Matters in AI Data Centers

As artificial intelligence (AI) and high-performance computing (HPC) workloads continue to scale, data centers are under increasing pressure to manage heat more efficiently. Traditional air cooling methods are reaching their limits, and liquid cooling is rapidly becoming the new standard. Among the various liquid cooling solutions, PG25 coolant—a 25% propylene glycol and 75% water mixture—has emerged as a reliable and efficient thermal transfer fluid. But what exactly is PG25, and why is it so critical in modern data center environments?

🧪 What Is PG25 Coolant?

PG25 coolant is a water-based heat transfer fluid that contains 25% propylene glycol (PG) by volume. Propylene glycol is a non-toxic, hygroscopic organic compound that lowers the freezing point of water and provides corrosion protection when combined with inhibitors.

Key Properties:

• Freezing point: Typically around -10°C (14°F)
• Boiling point: Above 100°C (212°F)
• Low toxicity: Safer than ethylene glycol for use in environments with human exposure risk
• Corrosion inhibitors: Often includes azoles and other additives to protect copper, aluminum, and steel components

❄️ Why PG25 Is Ideal for AI and HPC Cooling

1. Efficient Heat Transfer

Water is one of the best heat transfer fluids available, and PG25 retains much of water’s thermal conductivity while adding freeze protection and corrosion resistance. This makes it ideal for liquid-cooled cold plates, rear-door heat exchangers, and immersion cooling systems^[17].

2. Non-Toxic and Environmentally Friendly

Unlike ethylene glycol, propylene glycol is considered food-grade and is less hazardous in case of leaks or spills. This is especially important in co-location facilities and edge data centers where safety and environmental compliance are critical^[18].

3. Corrosion Protection

PG25 coolants are formulated with inhibitors that protect against galvanic corrosion, scaling, and microbial growth. This is essential in mixed-metal systems commonly found in data center cooling loops^[18].

4. Thermal Stability

PG25 maintains its chemical integrity under the high thermal loads typical of AI and HPC workloads, reducing the risk of breakdown and sludge formation^[18].

🧠 The Role of PG25 in AI Data Centers

AI workloads generate significantly more heat per rack than traditional enterprise applications. With power densities exceeding 30–50 kW per rack, air cooling alone is no longer sufficient. PG25-based liquid cooling systems enable:

• Higher rack densities
• Reduced energy consumption (lower PUE)
• Improved equipment lifespan
• Support for Tier III and IV reliability standards^[17]

🔍 Monitoring PG25 Coolant Health

Despite its advantages, PG25 coolant is not immune to degradation. Over time, it can suffer from:

• pH drift
• Oxidation of glycol
• Depletion of corrosion inhibitors
• Contamination from particulates or microbes

This is why predictive monitoring using technologies like spectrophotometry is essential. Tools like CoolView provide real-time insights into coolant chemistry, enabling proactive maintenance and reducing the risk of downtime.

🌡️ Do You Still Need Freeze Protection in Warm Climates?

Yes — Here’s Why:

• Unexpected Cold Snaps: Even in typically warm regions, rare cold events can occur (e.g., Texas 2021 winter storm). These anomalies can catch systems off guard if they’re not protected.
• Outdoor Equipment Exposure: If your cooling system includes rooftop or external heat exchangers, those components are still exposed to ambient temperatures, which can dip below freezing at night or during seasonal transitions.
• Standardization Across Sites: If you operate multiple data centers, using PG25 across all locations simplifies inventory, maintenance, and training, even if some sites don’t experience freezing.
• Idle or Backup Systems: Redundant cooling loops or backup chillers may sit idle and unheated. These can be vulnerable to freezing even if the primary system is running warm.

🔥 What Is Thermal Stability and Why Does It Matter?

Thermal stability refers to a coolant’s ability to maintain its chemical structure and performance characteristics when exposed to high temperatures over time. In data centers—especially those running AI and HPC workloads—coolants are subjected to continuous thermal cycling and elevated operating temperatures.

Key Aspects of Thermal Stability:

• Resistance to Oxidation: At high temperatures, glycol-based coolants can oxidize, forming organic acids that lower pH and promote corrosion. PG25 is formulated to resist this breakdown, especially when stabilized with corrosion inhibitors^[20].
• Minimal Decomposition: A thermally stable coolant resists decomposition into byproducts like aldehydes, acids, or sludge, which can clog filters and damage pumps^[20].
• Stable Viscosity and Heat Transfer: Thermal stability ensures that the coolant maintains consistent viscosity and thermal conductivity, which is critical for efficient heat transfer and pump performance^[21].
• Longer Service Life: Coolants with high thermal stability require less frequent replacement, reducing maintenance costs and downtime.

How PG25 Performs Under Heat

PG25 coolant is engineered to handle the thermal loads typical of AI data centers, where rack densities can exceed 30–50 kW. Its formulation includes:

• Propylene glycol, which has a higher boiling point than water
• Corrosion inhibitors that remain effective at elevated temperatures
• Additives that prevent scaling and microbial growth

These properties make PG25 a resilient and low-maintenance choice for liquid cooling systems in mission-critical environments^[21].

📊 Coolant Comparison Table

🚀 Final Thoughts

PG25 coolant is more than just a fluid—it’s a critical enabler of next-generation data center performance. As AI and HPC continue to push the boundaries of compute density, PG25 offers a safe, efficient, and scalable solution for thermal management. When paired with intelligent monitoring, it becomes a cornerstone of resilient, high-efficiency infrastructure.