CRAC vs CRAH: Complete Australian Buyer's Guide

What the acronyms mean

CRAC stands for Computer Room Air Conditioner — a precision cooling unit with an integrated refrigerant compressor. The cooling cycle happens inside the unit using a direct-expansion (DX) refrigeration loop. Heat is rejected via an outdoor condenser.

CRAH stands for Computer Room Air Handler — a precision cooling unit with no compressor inside it. The unit has a chilled-water coil, and the cooling source is a separate centralised chiller plant elsewhere in the building.

Both deliver the same outcome — cool, dehumidified, filtered air at controlled temperature and humidity into a server room or data hall. The difference is where the cooling is generated.

Visual differences

From the outside, CRAC and CRAH look almost identical — same form factor, same airflow direction, same control display. Inside is where they diverge:

• CRAC has a refrigerant compressor (sealed, hermetic), refrigerant pipework, expansion valve, and a connection to an outdoor condenser unit.
• CRAH has only a chilled-water coil, valve, actuator, and pipework connecting to the chiller plant.

The unit nameplate will tell you which it is. "DX" or "Direct Expansion" or "R-410A / R-513A" indicates CRAC. "CW" or "Chilled Water" indicates CRAH.

Cost economics

CRAC and CRAH have very different cost profiles:

CRAC (DX): lower CapEx for small to mid sites because there's no chiller plant. Each unit is a self-contained system. Higher OpEx because compressors are less efficient at part load and refrigerant work is more service-intensive.

CRAH (CHW): higher CapEx because you need a chiller plant. But once you have the plant, adding additional CRAH units is cheap, and the chiller plant runs much more efficiently than distributed compressors at part load.

The crossover point is typically around 500 kW of IT load. Below that, CRAC is more economical. Above, CRAH (with chiller plant) wins on lifecycle cost.

Efficiency at part load

This is the dominant difference for ongoing power costs:

• CRAC compressors at 30% load typically deliver around 0.55 EER. At full load, around 0.90.
• Chiller plants at 30% load can deliver 0.30 EER (lower is better — it's coefficient of performance derived). At full load, 0.20.

Data halls almost never run at full IT load. They run at 30-60% of design capacity for years. The CRAH + chiller combination wins decisively in part-load efficiency, which is where most of the kWh actually get used.

For a 1 MW data centre, the cooling power bill differential between fully-loaded CRAC vs partially-loaded CRAH+chiller can exceed $100,000 per year.

Refrigerant exposure and AS/NZS 5149

CRAC systems contain hydrofluorocarbon (HFC) refrigerant — typically R-410A in older units and R-513A in current low-GWP units. Refrigerant work is licensed under the Australian Refrigeration Council (ARCtick) framework. Service must be performed by RAC1 / RAC2 licensed technicians.

CRAH units typically don't contain refrigerant — they're water-only on the indoor side. The chiller plant has refrigerant but is centralised, simplifying compliance. AS/NZS 5149 applies to the chiller; the indoor CRAH is governed by AS/NZS 3666 (water-system Legionella control instead).

For sites where refrigerant management is a compliance burden (defence, pharma, certain healthcare), CRAH centralises the refrigerant footprint into one location.

Maintenance regime

CRAC: quarterly refrigerant pressure checks, leak detection, refrigerant logbook, compressor electrical testing, condenser coil cleaning (indoor + outdoor), filters, fan motors, humidifier, controls. ARC-licensed technicians required.

CRAH: quarterly water-loop pressure checks, valve and actuator testing, chemical water-quality testing (conductivity, pH, biological), strainers, humidifier, controls. Chiller plant has its own service regime. AS/NZS 3666 compliance review is a separate item.

Maintenance cost is broadly similar across the two. CRAH has slightly less hands-on indoor work but adds the chiller plant and water-loop scope.

When to choose which

CRAC (DX) wins for:

• Small to mid sites < 500 kW IT load
• Sites without a chilled-water plant
• Sites where redundancy comes from multiple distributed CRAC rather than centralised plant
• Sites with intermittent operation (CRAC starts faster than chiller plant)
• Mining and remote sites where centralised plant isn't practical

CRAH (CHW) wins for:

• Large data centres > 500 kW IT load
• Sites with existing chilled-water plant (hospitals, large commercial buildings)
• Sites with high-density / liquid-cooling future requirements
• Sites prioritising part-load efficiency for OpEx targets
• Hyperscale builds where chiller plant economics dominate

Hybrid approaches are common in mid-size data centres — CRAH as the workhorse with one or two CRAC units as backup or for specific high-density rows.

CDW — the third option you should know about

CDW stands for Condenser Water — a CRAC unit that uses a building condenser-water loop (cooling tower or dry cooler) instead of dedicated outdoor condensers per unit. CDW shares some characteristics with both CRAC and CRAH:

• Like CRAC, has a compressor inside the indoor unit
• Like CRAH, uses centralised heat rejection (cooling tower)
• AS/NZS 3666 applies to the cooling tower water side

CDW is common in mid-size data centres (200-800 kW IT) where space for outdoor condensers is constrained but full chiller plant is overkill.

When to call us

We service all three topologies — DX, CDW, CHW — across Australia. If you're evaluating a new build or major refit, we can model the cost and efficiency trade-off for your specific load profile and site conditions.

[Request a Quote](/contact#quick-quote).

References

• AS/NZS 1668.2 — Mechanical ventilation in buildings
• AS/NZS 3666 — Air-handling and water systems
• AS/NZS 5149 — Refrigerating systems
• ASHRAE TC 9.9 — Thermal Guidelines for Data Processing Environments
• Field reliability data from CRAC Services service fleet