Data Centre Building Solutions

A CRAC HVAC unit utilises refrigerant and a compressor to cool a room. Designed primarily to cool data centres, CRAC units blow air over a cooling coil and a compressor works to keep the refrigerant in the coil cool. The CRAC unit expels the hot exhaust air using water, air, or a glycol mix.

The CRAC unit absorbs hot air, cools it down, and then blows it up through the perforations in the data centre's raised floor in order to cool the server equipment from below. After cooling the server, the air expelled as hot exhaust gas which is then pulled back into the CRAC unit for cooling.  

Benefits of CRAC HVAC Units

• Best suited to small or low-density data centres.
• Air distribution, humidity, and temperature of the data centre is maintained.
• Heat from servers is absorbed and cool air then distributed to the servers to keep their operating temperatures at peak performance.
• CRAC units work well in small data centres that don't need to scale capacity quickly.
• Units can be added whenever demand requires an increase in cooling capacity.
• CRAC units take up less valuable space as they are usually stand-alone units.
• The units can operate in all outdoor temperature conditions, both cold and hot.

A CRAH HVAC system blows air over cooling coils, similar to a CRAC system, but these cooling coils are filled with chilled water instead of refrigerant. The chilled water is stored in a separate chiller, so when hot air enters the CRAH unit, it transfers the heat to the cold water, and then the water is then pumped back to the chiller.

CRAH units can vary their operation to stabilise fluctuating temperatures and humidity levels in the data centre being controlled. They can also adjust fan speeds to react dynamically as the temperature changes in the controlled space. This creates more stable temperatures and fewer chances of creating condensation or thermal overruns.

Benefits of CRAH HVAC Units

• Best suited to medium to large size data centres.
• CRAH systems are better suited to larger data centres and server farms.
• CRAH units adapt to reduced summer demand and can be more economical to run because water is cheaper than refrigerant.
• These units use less energy as they use "free" air and do not require compressors to be able to achieve the requires cooling levels.
• A CRAH can also improve a building's energy efficiencies by using water that has already been chilled out-of-hours, thereby reducing the need to use peak time energy.

CRAC and CRAH cooling units differ in their cooling mechanisms: CRAC uses refrigerants and compressors, while CRAH relies on chilled water and control valves.

CRAC units have a straightforward operation with typically one mode, making it challenging to adjust cooling based on room requirements. Although simpler in functionality, CRAC systems have more components, necessitating more maintenance and a higher risk of component failures. Regular maintenance is crucial for optimal performance. However, when properly maintained, CRAC units offer proven reliability. They are suitable for data centres with electrical loads below 200kW that demand lower 'availability needs', i.e. a lower level of reliability and resilience is required to ensure uninterrupted access to critical systems and services.

CRAH units employ a more efficient cooling cycle, providing superior heat removal capabilities while maintaining the same energy footprint as CRAC units. Although they may have higher upfront costs for centres with less than 100 kW of electrical IT loads, CRAH systems offer long-term cost-effectiveness. They are designed for data centres with electrical loads of 200kW or more with moderate-to-high availability requirements, i.e. uptime, reliability, redundancy, and fault tolerance are more critical to the operation of the facility.

Maximise your Data Centre's capability and performance with Johnson Controls. Our expertise in HVAC system design, planning, and monitoring allows cutting-edge solutions to be tailored to meet your data centre's present and future needs. From small-scale to large-scale power requirements, we deliver effective, efficient, and sustainable solutions.