Data Center Power Equipment Thermal Guidelines and Best Practices

Overview

The document reproduces the 2015 air-cooled class table with altitude de-rating. The recommended envelope is 18-27 degC; allowable ranges are A1 15-32, A2 10-35, A3 5-40 and A4 5-45 degC. Maximum dew point is 17 degC for A1, 21 degC for A2 and 24 degC for A3/A4, with maximum altitude 3,050 m. Altitude derating is 1 degC per 300 m above 900 m for A1/A2, 1 degC per 175 m for A3 and 1 degC per 125 m for A4.

Rate-of-change limits are in the same table: 5 degC/h for tape and 20 degC/h with no more than 5 degC in 15 minutes for other ITE. Typical locations and service lives of power equipment follow: transformers 20+ years, rack UPS 4-8 years, three-phase floor UPS 10-20 years, central UPS 15-20 years, flywheel 15-20 years. The life gap between rack UPS and central UPS makes replacement frequency a decisive lifecycle-cost factor.

TC 9.9's recommendations are concrete: design power equipment for 40 degC ambient (Class A3), the de-facto standard; rate rack PDUs for at least 60 degC; keep power equipment out of hot aisles because ampacity de-rates; size for temperature excursions; and schedule battery replacement on actual battery temperature rather than room temperature. Supercapacitors are often limited to 45 degC (some 35 degC) non-operating storage. The paper addresses only the temperature envelope and equipment tolerance; it does not cover efficiency or redundancy design. Because it gives general rules rather than per-product derating curves, final selection must be completed with manufacturer data.

Key points

1. Recommended 18-27 degC; allowable A1 15-32, A2 10-35, A3 5-40, A4 5-45 degC.
2. Max dew point A1 17 degC, A2 21, A3/A4 24 degC; max altitude 3,050 m.
3. Altitude derate: A1/A2 1 degC per 300 m above 900 m; A3 1 degC/175 m; A4 1 degC/125 m.
4. Rate of change: 5 degC/h (tape); 20 degC/h and no more than 5 degC in 15 min for other ITE.
5. Design power equipment for 40 degC ambient (A3).
6. Rack PDUs should be rated for at least 60 degC ambient.
7. Service life: transformers 20+ yr; rack UPS 4-8; 3-ph floor UPS 10-20; central UPS 15-20; flywheel 15-20 yr.
8. Supercapacitors often limited to 45 degC (some 35 degC) non-operating storage.

Using it in design

• Encode the A1-A4 table (dry bulb, dew point, altitude derate) as the canonical envelope lookup; site max inlet = classMax - (altitude-900)/derateStep.
• Warn when a rack PDU in a hot aisle is rated below 60 degC ambient.
• Warn when power equipment is located in a hot aisle.
• Drive the battery life model from battery temperature, not room temperature.
• Select power equipment for 40 degC ambient.

Who should read it

Electrical and mechanical designers verifying the thermal tolerance of power equipment in economised or warm-environment sites.

Related standards

• ASHRAE Thermal Guidelines for Data Processing Environments 4th/5th ed.
• IEC 61439
• IEC 62040

Publication details

Authors

ASHRAE TC 9.9

Publisher

ASHRAE TC 9.9

Year

2016

Document number

TC 9.9 White Paper

Document language

English

Source type

Standard

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation