A common failure mode in newly converted immersion facilities is undersizing the outdoor heat rejection loops for mid-summer peak temperatures. In regions like Gyeonggi-do, where July and August temperatures frequently reach 35°C with 85% relative humidity, relying on standard catalogue ratings derived at 25°C ambient air guarantees thermal throttling.
Understanding the Approach Temperature (Delta-T)
In a closed-loop immersion cooling architecture, heat moves through two distinct thermal boundaries:
- Primary Loop: Dielectric fluid absorbs heat from ASIC chip heatsinks and transfers it through a brazed plate heat exchanger to an intermediate treated water/glycol loop.
- Secondary Loop: The water/glycol mixture is pumped to outdoor dry coolers where ambient air cools the fluid before returning to the heat exchanger.
The approach temperature is the difference between the dry cooler fluid leaving temperature and the outdoor ambient dry bulb temperature. In hot summer conditions (35°C ambient), achieving a 42°C supply fluid to the plate exchanger requires an approach Delta-T of no more than 7°C. This requires substantially more finned coil surface area than standard industrial refrigeration units.
The Role of Adiabatic Pre-Cooling
During the 20 to 30 hottest peak afternoon hours of the summer, high-efficiency adiabatic misting pads can depress the incoming air temperature toward the ambient wet bulb temperature (typically 27°C–28°C in Korea). This provides an emergency 5°C to 7°C buffer without consuming water year-round.
Seminar Calculation Exercises
During our heat management seminars, participants work through real hydraulic spreadsheets, inputting specific hashboard wattages (e.g., 3,500W per Whatsminer M56S immersion unit) to size pipe diameters, pump head pressure, and dry cooler motor kilowatts accurately.