What is the difference between CRAC and CRAH?

CRAC uses direct expansion refrigerant and operates independently. CRAH uses chilled water from a central plant, is more efficient at scale, and requires coordinated chiller automation.

How is cooling controlled in a data center?

PID loops maintain supply air temperature, VFDs modulate fan and pump speeds, and sequencing logic stages chillers based on load demand — integrated through BMS or SCADA.

Cooling Automation in Data Centers

Quick Answer

Cooling automation in data centers uses PID control for supply air temperature, VFDs for fan and pump speed modulation, sequencing logic for chiller staging, and economizer controls for free cooling. Integration with BMS and SCADA provides centralized monitoring and optimization.

CRAC vs CRAH

CRAC — Direct expansion refrigerant cooling, self-contained, common in smaller data centers
CRAH — Chilled water coil with central chiller plant, more efficient at scale, requires coordinated plant automation

Temperature Control

PID loops maintain supply air temperature setpoints. The process variable is the supply air temperature sensor; the control output drives a chilled water valve (CRAH) or compressor staging (CRAC). See Allen-Bradley PID configuration for PLC-based loop setup.

Chiller Staging

Lead/lag sequencing starts and stops chillers based on cooling demand. Load-based staging adds chillers when the running units approach capacity and removes them when demand drops, preventing short-cycling and optimizing efficiency.

Free Cooling

Economizer logic engages free cooling (air-side or water-side) when outside conditions permit — reducing or eliminating compressor operation. Automated switchover based on outside air temperature and humidity maximizes free cooling hours. See enteliWEB scheduling for BMS-based automation.

Frequently Asked Questions