ASHRAE Journal - May 2022 - 58

COLUMN DATA CENTERS
TABLE 3 Evolution of Allowable air-cooled data center environmental conditions.
CLASS
FIRST EDITION
2004
1/A1a Temperature
(Allowable)
1/A1 RH (Allowable)
1/A1 Dew Point (Allowable)
2/A2b Temperature
(Allowable)
2/A2 RH (Allowable)
2/A2 Dewpoint (Allowable)
A3 Temperature (Allowable)
A3 RH (Allowable)
A3 Dewpoint (Allowable)
A4 Temperature (Allowable)
A4 RH (Allowable)
A4 Dewpoint (Allowable)
H1 Temperature (Allowable)
H1 RH (Allowable)
H1 Dewpoint (Allowable)
59°F to 89.6°F
20% to 80%
Max of 62.6°F
50°F to 95°F
20% to 80%
Max of 69.8°F
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
SECOND EDITION
2008
THIRD EDITIONa
2012
59°F to 89.6°F
20% to 80%
Max of 62.6°F
50°F to 95°F
20% to 80%
Max of 69.8°F
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
aClass 1 (Editions 1,2) renamed Class A1 (Editions 3,4,5)
bClass 2 (Editions 1,2) renamed Class A2 (Editions 3,4,5)
allow for " floating setpoint " control of the data center
environment, with lower cooling energy consumption
without higher ITE failure rates on an annualized basis.
Appendices H and I (of the Third, Fourth or Fifth Edition)
provide more detailed analysis and examples.
Fourth Edition Changes
The environmental envelope changes in the Fourth
Edition6 can be found outlined in blue in the fifth column
of Tables 2 and 3. These changes were made after completion
of ASHRAE Research Project RP-1499.
For RP-1499, ASHRAE funded the Electromagnetic
Compatibility (EMC) Laboratory at the Missouri
University of Science and Technology from 2011 to 2014
to investigate the risk of upsets or damage to electronics
related to electrostatic discharge (ESD). Emphasis was
placed on the increase in risk with reduced humidity.
The results from this study showed that a data center
with a low incident rate of ESD-induced damage
operating at 25% RH will maintain a low incident rate
if the relative humidity is reduced to 8%.7 As a result
of this research, the recommended humidity range
was expanded as shown in Table 2, and the allowable
58
ASHRAE JOURNAL ashrae.o rg M AY 2022
humidity range for Classes A1 and A2 was expanded, as
noted in Table 3.
Fifth Edition Changes
The environmental envelope changes in the Fifth
Edition3 can be found in bold in the sixth column of
Table 2. These changes were made after completion of
ASHRAE Research project RP-1755.
For RP-1755, ASHRAE funded the Syracuse University
Mechanical and Aerospace Engineering Department
from 2015 to 2018 to investigate the risk of operating at
higher levels of moisture when high levels of gaseous
pollutants exist.8 The objective was to evaluate the
impact of increasing the recommended moisture level
in support of reducing energy required by data centers.
Five gaseous pollutants were tested under a variety of
temperature and RH conditions-three pollutants that
are pervasive throughout the planet (SO2, NO2 and O3)
and two catalyst pollutants (H2S and Cl2). Pollutant levels
tested were at or near the maximum common concentration
levels existing around the world. The following
changes were made to the recommended envelope
based on this research study:
59°F to 89.6°F
20% to 80%
Max of 62.6°F
50°F to 95°F
20% to 80%
Max of 69.8°F
41°F to 104°F
8% to 85%
10.4°F to 75.2°F
41°F to 113°F
8% to 90%
10.4°F to 75.2°F
N/A
N/A
N/A
FOURTH EDITION
2015
59°F to 89.6°F
8% to 80%
10.4°F to 62.6°F
50°F to 95°F
8% to 80%
10.4°F to 69.8°F
41°F to 104°F
8% to 85%
10.4°F to 75.2°F
41°F to 113°F
8% to 90%
10.4°F to 75.2°F
N/A
N/A
N/A
FIFTH EDITION
2021
59°F to 89.6°F
8% to 80%
10.4°F to 62.6°F
50°F to 95°F
8% to 80%
10.4°F to 69.8°F
41°F to 104°F
8% to 85%
10.4°F to 75.2°F
41°F to 113°F
8% to 90%
10.4°F to 75.2°F
41°F to 77°F
8% to 80%
10.4°F to 62.6°F
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