Computer Room Air Conditioning CRAC CRAH

Depending on the audience we speak to, either those new to the industry or those coming in from ancillary industries, such as indoor agriculture or archival and medical imaging spaces, they have often asked us what the main difference is between precision and comfort cooling.  In simplified terms:

  • Precision cooling is air conditioning specifically designed for IT equipment in places like data centers and computer rooms.  Precision Cooling Systems are also purpose-built for the indoor agriculture market, whether that be for cannabis or a multitude of vertical farming crops.
  • Comfort cooling is designed for people.

Many will incorrectly try to implement precision cooling systems into rooms occupied with people thinking “Cold air is just cold air, right?” Wrong. Places like those differ from computer rooms and data centers because they have a much lower, inconsistent heat load and have a higher need for dehumidification since people add humidity to a room while IT equipment does not.

Sensible Cooling vs. Latent Cooling

Sensible cooling is used to remove heat, while latent cooling is used to remove moisture. Spaces with high density heat loads and little need for dehumidification require high sensible cooling capability and low latent cooling capability. This would generally be a 0.8 to 1.0 sensible heat ratio (SHR) where the ratio is represented as sensible cooling over total cooling. Spaces like these require precision cooling.

In data room applications where there are rapid temperature swings, high or low humidity can have negative effects on the room’s electronics. High, low, or fluctuating temperatures are capable of corrupting and even shutting down entire data systems. For precision air systems with lower than 1 SHR, a humidifier is often included to put moisture back into the room.

Precisely Controlling Humidity

While too high an amount of humidity can cause condensation, deterioration, and corrosion of the IT equipment, too low an amount will increase static electricity which may fry electrical components. When IT equipment is generally running 24 hours a day, 365 days a year, means the precision cooling system will also have to be constantly running.

Comfort cooling is completely different than precision cooling. People don’t produce nearly as much heat as computer servers do, but we do produce humidity. This means there is a higher need for latent cooling to remove moisture. Comfort cooling applications typically need an SHR of 0.65 to 0.8. Use of comfort cooling systems is also intermittent, generally only 8-12 hours a day and not necessarily every day throughout the year. If the air conditioning system happens to fail, people will be in uncomfortable conditions, but it is not crucial to be able to get the system up and running immediately like you would in a data center to protect these mission critical environments.

Standard comfort cooling is designed to handle low density heat loads, not the high-density loads, or precise temperature and humidity control IT room applications require. Precision air systems provide year-round, reliable operation with the flexibility necessary to meet any applications. Without the proper cooling equipment, applications sensitive to temperature and/or humidity, which are not controlled precisely, will compromise uptime, reliability, efficiency and ultimately affect profitability  for a company.

PRECISION

  • High Density Heat Loads
  • Precise Temperature & Humidity
  • Designed for 24/7 operations
  • 80%-100% Sensible | 20% Latent

COMFORT

  • Low density Heat Loads
  • General Conditions for Humans
  • Intermittent use 8-12 Hours a Day
  • 65%-80% Sensible | 35% Latent

Types of Precision Cooling Systems

CRAC vs. CRAH Diagram

Computer Room Air Conditioning (CRAC) unit, similar to the A/C in your home, operates using a direct expansion (DX) refrigeration cycle. Cooling is accomplished by blowing air over a cooling coil filled with refrigerant. The refrigerant is kept cool by a compressor located inside the unit. The excess heat is then expelled using ambient air, water, or a glycol mixture.

   

Computer Room Air Handler (CRAH) unit, unlike a CRAC unit, uses fans and chilled water coils to remove heat. Because CRAH units do not have compressors, they consume less energy and are more efficient than CRAC units. Typically, chilled water is supplied to the CRAH units from a chilled water supply like a chiller.

Now that you know the basics of precision cooling, you can be assured that Data Aire offers a wide variety of CRACs and CRAHs to fit your environmental control needs. Our mission critical technology is engineered into each of our precision air conditioners and air handlers. Whether you need a comprehensive cooling system for a mission critical datacom facility or need an application-specific equipment for unique and constant environments, Data Aire delivers the environmental control solution that’s tailored for our customers.