- A CRAC (Computer Room Air Conditioner) or CRAH (Computer Room Air Handler) unit is part of air-based cooling systems commonly used in data centers. Here’s how they differ from direct liquid cooling (DLC) systems:
- CRAC/CRAH Overview
Component | Description |
CRAC | A self-contained unit with a compressor that cools air using refrigerant coils. |
CRAH | A chilled water-based unit using coils fed by a building chilled water system. |
Cooling Method | Cools the room air and circulates it across IT equipment via raised floors or ceiling plenum. |
Cooling Fluid Contact | Indirect – air contacts equipment; chilled water or refrigerant cools the air, not the electronics. |
- Direct Liquid Cooling (DLC) Overview
Component | Description |
Cooling Method | Liquid (often water-based) is brought directly to the chip or cold plate inside the server. |
Heat Transfer | Heat from processors is removed by the fluid and carried to a CDU (cooling distribution unit) or heat exchanger. |
Cooling Fluid Contact | Direct (to the hardware interface) – not open to the environment, but thermally in contact with chips. |
- Key Differences Between CRAC/CRAH and DLC
Feature | CRAC/CRAH | DLC |
Cooling Medium | Air | Liquid (usually water/glycol) |
Efficiency | Lower (air has poor heat capacity) | Higher (direct contact, better thermal transfer) |
Space Use | Requires hot/cold aisles and raised floors | Reduces space footprint |
Heat Density Support | Moderate (< 10 kW/rack typical) | Very high (up to 100 kW/rack or more) |
Maintenance Risk | Lower for leaks (air cooled) | Higher if leaks occur in server |
Filtration Need | Basic air filters | Micron-level filtration and purity critical |
- Summary
- CRAC/CRAH = traditional room-level air cooling
- DLC = advanced, chip-level liquid cooling
- DLC is significantly more efficient, compact, and demanding in terms of water quality, making proper chemical treatment and filtration far more critical than in CRAC/CRAH setups.