Brandon White, Engineer, Experimental Research
The choice of cooling method for a data center is driven primarily by water availability, material compatibility, local regulations, and budget constraints. Direct-to-chip (D2C) cooling is a common water-based solution, offering high efficiency—recent benchmarks indicate that 48% of facilities with adequate water resources have adopted it [1]. However, water is a well known fouling medium across many industries, and the same risks apply to data center applications.
Water is favored as a coolant because it is widely available in many regions and has a relatively high heat capacity. However, the nature of the primary water source and any makeup water determines the level of fouling mitigation required. In areas where freshwater is scarce, operators may rely on deep‑well (brackish) water, which contains higher levels of dissolved salts and hardness. Others may use reclaimed process or municipal wastewater, which is often less thoroughly treated and may contain organics, nutrients, or chemicals that are incompatible with cooling loop materials.
A D2C cooling loop, connected to a coolant distribution unit (CDU), is a closed system in which coolant flows through thin cold‑plate heat exchangers that are thermally coupled to the processor package via an integrated heat spreader (HIS) or a dedicated cold‑plate interface (see Figure 1) [1]. The plates are spaced only hundreds of microns apart, and the flow is intentionally laminar to ensure uniform distribution across all plates. Unlike many industrial cooling systems that rely on high velocities to limit fouling, the low‑velocity laminar flow in D2C makes the loop especially sensitive to deposits [2].
As with any standard cooling‑water system, D2C loops are prone to calcium‑carbonate precipitation and other forms of mineral scaling that associated with municipal or well water supplies. These deposits have been managed for decades with softening, filtration, and corrosion‑inhibitor programs. Biofouling presents another significant concern. Microbial films can be 10 – 100% more thermally resistant than calcium carbonate and can readily attach to rough carbonate crystals, further degrading heat transfer. Because many data centers do not routinely monitor water quality, biofilm can develop undetected, making remediation of cold plate exchangers difficult. This highlights the importance of proactive control strategies.
One common approach to limiting microbial growth is the addition of propylene glycol (PG), which is less toxic than ethylene glycol. Industry practice recommends a 25% PG / 75% water blend; concentrations below roughly 17% allow biofilm formation to accelerate. The trade‑off is a ~8% reduction in heat capacity and a noticeable increase in pumping power due to the higher viscosity of the glycol‑water mixture.
For data center owners and operators, selecting the appropriate cooling fluid and understanding its impact on cold‑plate performance is critical. Proper pretreatment—softening, filtration, pH control, corrosion inhibition, and, when needed, biocide or glycol dosing—combined with regular water‑quality monitoring, will minimize scaling and bio‑fouling, can help minimize scaling and biofouling. These measures preserve heat transfer efficiency and protect the significant investment in direct-to-chip cooling systems.
Click here to read more articles in this series.
References
- Open Compute Project, https://www.opencompute.org/ (2023).
- Loraine Huchler, Optimizing heat transfer in single-phase cold-plate liquid cooled systems, 2026 Cooling Technology Instititue Annual Conference, Houston, TX, United States of America (Feb. 8 – 11, 2026).