In high-density data centers, liquid cooling is becoming the norm. From rear door heat exchangers to direct-to-chip cooling loops, many facilities rely on propylene glycol and water mixtures to move heat away from servers efficiently and safely. Glycol prevents freezing and corrosion, but it also changes one important property: electrical conductivity.
That matters because most leak detection systems used in these environments rely on conductivity to detect liquid. The higher the glycol concentration, the lower the conductivity, and at some point, your leak detection system may simply stop detecting leaks.
We wanted to find out exactly where that point is.
The Experiment
To better understand the conductivity limits for glycol-based cooling systems, we ran a hands-on test using our LD1 leak detection system and mixtures of propylene glycol and water.
Our goal: determine the maximum glycol concentration that would still trigger the alarm.
Method:
- We mixed glycol and water at 10% increments, from 10% up to 80% glycol.
- For each mixture, we submerged a section of the LD1’s water detection cable.
- We recorded whether the alarm was triggered ("Worked") or not ("Didn’t Work").
Results
| Glycol Concentration | Water Concentration | Alarm Triggered? |
|---|---|---|
| 10% | 90% | ✅ Yes |
| 20% | 80% | ✅ Yes |
| 30% | 70% | ✅ Yes |
| 40% | 60% | ✅ Yes |
| 50% | 50% | ✅ Yes |
| 60% | 40% | ✅ Yes |
| 70% | 30% | ✅ Yes |
| 75% | 25% | ✅ Yes |
| 80% | 20% | ❌ No |
At 80% propylene glycol, the LD1 no longer detected the leak because the mixture was not conductive enough. But at 75%, it still worked. That means the functional limit for conductive leak detection is around 75% glycol.
Typical Data Center Glycol Mixes
Most data center liquid cooling loops run nowhere near that limit. In fact:
- Rear door heat exchanger systems typically use 20–40% glycol.
- Direct-to-chip and cold-plate systems often run 25–50% glycol depending on climate and redundancy design.
- Even in chilled water loops for colder climates, it is rare to exceed 60% propylene glycol.
So in practical terms, most data center systems are well within the safe range for conductive leak detection cables like those used in the LD1 system. Still, knowing your upper limit helps ensure that detection remains reliable, especially if your mixture changes seasonally or across multiple sites.
Takeaways
- Conductivity drops as glycol concentration increases, and above about 75%, standard conductive leak detection cables may no longer trigger.
- Most real-world systems (20–50% glycol) are perfectly compatible with conductive detection.
- For extreme concentrations (75–100%), consider optical or spot-type leak sensors that do not rely on conductivity.
- Always verify detection performance after filling or servicing a loop, since conductivity can vary slightly with temperature and glycol brand.
Why This Matters
Leak detection is a critical line of defense in high-value environments like data centers. Whether you are cooling racks with direct-to-chip liquid loops or using rear door heat exchangers, understanding how glycol affects detection ensures your safety systems are doing their job when it matters most.
At IOThrifty, we are committed to real-world testing that helps engineers design better, safer systems, not just in theory but in practice.