Cooling

Immersion & Hydro Cooling

How liquid-cooled miners work, the loop components, coolant rules, and the water/fluid faults air techs never see.

Why liquid at all

Air is a poor conductor; water and dielectric fluids carry far more heat per unit volume than air. Chips run ~20 °C cooler, so makers push more current through the same silicon - liquid SKUs deliver higher hashrate AND better J/TH, run quiet, and shrug off dust.

HYDRO = a sealed water loop through cold plates; the miner stays dry inside.
IMMERSION = the whole miner is submerged in non-conductive dielectric fluid, fans removed.
Universal startup rule: cooling ON before the miner ON; miner OFF before cooling OFF.

The hydro loop

Water block on the boards -> internal manifold -> quick-disconnects -> rack manifold -> CDU -> dry cooler -> back.

The CDU (Coolant Distribution Unit) holds the pump, a plate heat exchanger isolating the miner loop from the facility loop, a filter, and sensors.
Use the exact manufacturer-approved fluid for the model and loop, with that fluid-specific pH, conductivity, inhibitor and freeze-protection limits. There is no universal DI-water/glycol recipe or shared pH band.
S21 XP Hydro envelope: flow 8-10 L/min, pressure ≤3.5 bar, min inlet temp ~20 °C to start (colder won't boot / risks condensation); outlet up to ~65-70 °C.
You monitor: inlet/outlet temp + delta-T, per-board flow, pressure, pump status, coolant level, pH/conductivity, and leaks.

Immersion

Use the exact miner/fluid OEM preparation procedure. A purpose-built immersion model may need no conversion; do not remove labels, fans or seals without that procedure. Verify fluid/seal compatibility and SDS controls.

Single-phase (dominant in mining): fluid stays liquid, convects to a heat exchanger. Simpler, cheaper, safer.
Two-phase: fluid boils on the chips and condenses up top - thermally superior but costly sealed fluids (3M Novec) with vapor loss/PFAS concerns. Rare in mining.
Never mix fluids (conductive slurry risk). Flash points are >200 °C.

Fluid	Type	~Cost/L	Notes
BitCool BC-888	Synthetic, single-phase	$15-25	Purpose-built, best longevity
Mineral oil	Petroleum, single-phase	$3-8	Cheap, oxidizes, degrades rubber
3M Novec 7100	Fluorocarbon, two-phase	$80-150+	Enterprise only, being phased out

Liquid-specific faults

Symptom	Cause & field fix
WM 5070/5071/5072 'water velocity abnormal'	Per-board flow fault: confirm pump running, check kinks/clogged filter, verify coolant level + QDs seated, confirm 8-10 L/min; if flow truly normal, replace the velocity sensor.
Rising outlet temp / delta-T, flow normal	Heat isn't rejecting: clean the dry cooler, check its fan, check the facility loop / exchanger fouling.
Antminer hydro won't start	Inlet water below ~20 °C blocks boot - check inlet temp first.
Leak vs condensation	Leak = sustained pooling at a fitting + dropping reservoir; condensation = diffuse film from a cold line below dew point, reservoir steady -> insulate / raise inlet temp / drop humidity.
Pump failure	No/low flow, low pressure, no vibration, grinding -> replace pump (spreading over-temp follows).

Relieve the ≤3.5 bar water pressure and use dripless quick-disconnects before you separate a hydro line. Immersion tank failures can flood a room - use drip trays/containment.

Why liquid at all

HYDRO = a sealed water loop through cold plates; the miner stays dry inside.

IMMERSION = the whole miner is submerged in non-conductive dielectric fluid, fans removed.

Universal startup rule: cooling ON before the miner ON; miner OFF before cooling OFF.

The hydro loop

Water block on the boards -> internal manifold -> quick-disconnects -> rack manifold -> CDU -> dry cooler -> back.

The CDU (Coolant Distribution Unit) holds the pump, a plate heat exchanger isolating the miner loop from the facility loop, a filter, and sensors.

Use the exact manufacturer-approved fluid for the model and loop, with that fluid-specific pH, conductivity, inhibitor and freeze-protection limits. There is no universal DI-water/glycol recipe or shared pH band.

S21 XP Hydro envelope: flow 8-10 L/min, pressure ≤3.5 bar, min inlet temp ~20 °C to start (colder won't boot / risks condensation); outlet up to ~65-70 °C.

You monitor: inlet/outlet temp + delta-T, per-board flow, pressure, pump status, coolant level, pH/conductivity, and leaks.

Immersion

Single-phase (dominant in mining): fluid stays liquid, convects to a heat exchanger. Simpler, cheaper, safer.

Two-phase: fluid boils on the chips and condenses up top - thermally superior but costly sealed fluids (3M Novec) with vapor loss/PFAS concerns. Rare in mining.

Never mix fluids (conductive slurry risk). Flash points are >200 °C.

Fluid	Type	~Cost/L	Notes
BitCool BC-888	Synthetic, single-phase	$15-25	Purpose-built, best longevity
Mineral oil	Petroleum, single-phase	$3-8	Cheap, oxidizes, degrades rubber
3M Novec 7100	Fluorocarbon, two-phase	$80-150+	Enterprise only, being phased out

Liquid-specific faults

Symptom	Cause & field fix
WM 5070/5071/5072 'water velocity abnormal'	Per-board flow fault: confirm pump running, check kinks/clogged filter, verify coolant level + QDs seated, confirm 8-10 L/min; if flow truly normal, replace the velocity sensor.
Rising outlet temp / delta-T, flow normal	Heat isn't rejecting: clean the dry cooler, check its fan, check the facility loop / exchanger fouling.
Antminer hydro won't start	Inlet water below ~20 °C blocks boot - check inlet temp first.
Leak vs condensation	Leak = sustained pooling at a fitting + dropping reservoir; condensation = diffuse film from a cold line below dew point, reservoir steady -> insulate / raise inlet temp / drop humidity.
Pump failure	No/low flow, low pressure, no vibration, grinding -> replace pump (spreading over-temp follows).

Relieve the ≤3.5 bar water pressure and use dripless quick-disconnects before you separate a hydro line. Immersion tank failures can flood a room - use drip trays/containment.