What is ASHRAE TC 9.9 thermal guidelines?
ASHRAE TC 9.9 thermal guidelines are recommendations from ASHRAE Technical Committee 9.9 that define recommended and allowable temperature and humidity envelopes for air at the inlet of IT equipment. They help data center operators balance equipment reliability with cooling energy, and are published in the book Thermal Guidelines for Data Processing Environments.
What it is
TC 9.9 is the ASHRAE technical committee for mission critical facilities, data centers, technology spaces and electronic equipment. Its thermal guidelines define equipment classes, such as A1 to A4, and envelopes for each.
The recommended envelope is where equipment runs reliably with good efficiency. The allowable envelope is wider and can be used for limited periods or to allow more free cooling, with some effect on reliability.
The guidelines focus on air at the server inlet, not the room average. That means cold aisle conditions, rack by rack, are what matter.
Where it is used
Data center designers and operators, IT equipment manufacturers and colocation providers use the guidelines to set operating targets and service level agreements.
Raising setpoints within the recommended envelope is one of the common ways operators reduce cooling energy.
How it is measured
Compliance with the envelope is measured at the inlet, not at the cooling unit return.
- Inlet temperature by rack or aisle
- Humidity or dew point in the space
- Hot spots and recirculation
- Time spent outside the recommended envelope
How Aqueduct helps
Aqueduct tracks inlet conditions by aisle against the envelope, with cooling response and verification.
- aQ AirSafe temperature and humidity sensing by aisle and rack
- Excursions from your chosen envelope flagged with the likely cause
- Cooling setpoints adjusted where control is enabled, with owner approval
- Verified return to range and the energy effect of each change