Computer Room Air Conditioning
CRAC & CRAH

Computer Room
Air Conditioniners
(CRAC & CRAH)

Computer Room Air Conditioning / Computer Room Air Conditioners / CRAC / CRAH

Computer Room Air Conditioners/Air Handlers are a staple of data center design, providing precise temperature and humidity control for mission critical environments. Engineered for 24x7x365 operation, CRACs provide recurrent heat exchange: accepting the heat energy generated by IT equipment, cooling it, and returning it back to the equipment.

Traditional data center cooling has used CRAC/H units and a raised floor plenum (like below) to distribute chilled air to data center racks.
 

CRAC / CRAH view from Cold Aisle - Computer Room Air Conditioner & Raised Floor Plenum

 

Environmental Control
CRACs supply chilled air (measured in cubic feet per minute) within a specific temperature range (the current ASHRAE specification is 64.4 deg F to 80.6 deg F) to satisfy the cooling demands of IT equipment. CRACs have design specifications for supply air, return air, and refrigerant temperature, all of which affect its operation and performance.

Capacity
Capacities for CRAC and CRAH units are typically measured in tons, which can be converted to kilowatts (kW) or British Thermal Units (BTU/hr) depending on user preference

CRAC vs. CRAH
Though they serve the same purpose, there is a fundamental difference between a CRAC and CRAH:
• A Computer Room Air Conditioner includes an internal compressor, using the direct expansion of refrigerant to remove heat from the data center.
• A Computer Room Air Handler includes only fans and a cooling coil, often using chilled water to remove heat from the data center.

Heat Rejection
Both technologies will require outdoor heat rejection sources. CRAC units are connected to remote condensers, while CRAH units are traditionally connected to chiller systems.

The 42U Advantage
42U partners with leading manufacturers of CRAC/CRAH solutions including Liebert and APC.

How much can your organization save by having more efficient cooling in your Data Center?

As much as 40% of a data center's energy bill is from cooling equipment. Try our new Interactive Data Center Efficiency Calculator and find out how you can start improving your data center efficiencies now!

Issue: Understanding the Efficiency Metrics Best Practice: Adoption and use of PUE/DCiE
In furtherance of its mission, The Green Grid is focused on the following: defining meaningful, user-centric models and metrics; developing standards, measurement methods, processes and new technologies to improve data center performance against the defined metrics.
- The Green Grid

Measurements like watts per square foot, kilowatts per rack, and cubic feet per minute (cfm) are ingrained in data center dialogue. Until recently, no standard measurement existed for data center efficiency. Enter the Green Grid, a consortium promoting responsible energy use within critical facilities. The group has successfully introduced two new terms to the data center lexicon: Power Usage Effectiveness (PUE) and Data Center Infrastructure Efficiency (DCiE).