ASHRAE Journal - April 2013 - 57

in the rating standard have, to a large degree, been driven by
changes in these publications. Several changes have occurred.
First, IT equipment has been found to be resilient to a wider
range of environmental conditions than previously believed, and
the recommended envelope for ITE inlet conditions, also shown
in the Figure 1 psychrometric chart, is no longer a little box, but
rather a comfortably large envelope, with an inlet temperature
range of 64.4°F to 80.6°F (18°C to 27°C) and 41.9°F (5.5°C)
dew point to 60% RH and 59°F (15°C)
dew point.2
This envelope no longer requires extremely tight control, so the days of adjacent CRAC units fighting each other are
now hopefully only for the history books.
Second, there has been an increasing trend toward the use of hot and
cold aisles, and also of containment to
segregate the cold and hot airstreams.
Both of these trends tend to raise the
return air temperature to CRAC and
CRAH units.
The 2007 standard, with its single return
air rating point of 75°F (23.9°C)/45% RH,
was out of sync with regard to changes
both to ASHRAE’s Thermal Guidelines
for Data Processing Environments, and
to alignment with the industry’s evolving
containment practices.

As data center techs have known for some time, the t-shirt
has replaced the sweater as the most comfortable clothing for
working in most of today’s modern data centers.

Impact to the Industry and the Environment
If a data center could be designed with a return air temperature
of 105°F (40.6°C) instead of 75°F (23.9°C), the impact on the
cooling system and its energy efficiency would obviously be

Major Change to 2012 Ratings
Standard 127-2012 covers four product
application classifications for CRAC
and CRAH units, rather than just one in
the previous (2007) standard. The rating points for the new Classes 2, 3 and
4 are shown in Figure 1, along with the
legacy design points for the 1988–2001
standards (essentially unchanged during
this period), and the 2007 standard.
The 2007 version of the standard uses
a return air temperature of 75°F (23.9°C)
as the basis for rating, while the 2012
version has four application classes. The
return air temperatures of these classes
range between 75°F (23.9°C) for Class 1
to 105°F (40.5°C) for Class 4, all at 52°F
(11.1°C) dew-point temperature.
The new standard thus recognizes that
return air temperatures are as much as
30°F (16.7°C) warmer than in the previous revision of the standard. As Figure 1
shows, the Class 2, 3 and 4 rating conditions are significantly outside both the
ITE inlet recommended conditions and
the Standard 55 comfort zones.
April 2013

www.info.hotims.com/44631-33

ASHRAE Journal

57



ASHRAE Journal - April 2013

Table of Contents for the Digital Edition of ASHRAE Journal - April 2013

ASHRAE Journal - April 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Ground-Coupled Heat Pump and Energy Storage
Fan Efficiency Requirements for Standard 90.1-2013
Technology Award Case Studies:
Geothermal for 5 Ecosystems
Holistic HVAC Design
Standing Columns
Engineer’s Notebook
Data Centers
Emerging Technologies
IAQ Applications
Refrigeration Applications
Special Products
People
International Column
Energy Modeling
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2013 - ASHRAE Journal - April 2013
ASHRAE Journal - April 2013 - Cover2
ASHRAE Journal - April 2013 - 1
ASHRAE Journal - April 2013 - 2
ASHRAE Journal - April 2013 - Contents
ASHRAE Journal - April 2013 - Commentary
ASHRAE Journal - April 2013 - 5
ASHRAE Journal - April 2013 - Industry News
ASHRAE Journal - April 2013 - 7
ASHRAE Journal - April 2013 - 8
ASHRAE Journal - April 2013 - Letters
ASHRAE Journal - April 2013 - Meetings and Shows
ASHRAE Journal - April 2013 - 11
ASHRAE Journal - April 2013 - 12
ASHRAE Journal - April 2013 - 13
ASHRAE Journal - April 2013 - Ground-Coupled Heat Pump and Energy Storage
ASHRAE Journal - April 2013 - 15
ASHRAE Journal - April 2013 - 16
ASHRAE Journal - April 2013 - I1
ASHRAE Journal - April 2013 - I2
ASHRAE Journal - April 2013 - I3
ASHRAE Journal - April 2013 - I4
ASHRAE Journal - April 2013 - 17
ASHRAE Journal - April 2013 - 18
ASHRAE Journal - April 2013 - 19
ASHRAE Journal - April 2013 - 20
ASHRAE Journal - April 2013 - 21
ASHRAE Journal - April 2013 - 22
ASHRAE Journal - April 2013 - 23
ASHRAE Journal - April 2013 - Fan Efficiency Requirements for Standard 90.1-2013
ASHRAE Journal - April 2013 - 25
ASHRAE Journal - April 2013 - 26
ASHRAE Journal - April 2013 - 27
ASHRAE Journal - April 2013 - 28
ASHRAE Journal - April 2013 - 29
ASHRAE Journal - April 2013 - 30
ASHRAE Journal - April 2013 - 31
ASHRAE Journal - April 2013 - Geothermal for 5 Ecosystems
ASHRAE Journal - April 2013 - 33
ASHRAE Journal - April 2013 - 34
ASHRAE Journal - April 2013 - 35
ASHRAE Journal - April 2013 - 36
ASHRAE Journal - April 2013 - 37
ASHRAE Journal - April 2013 - 38
ASHRAE Journal - April 2013 - 39
ASHRAE Journal - April 2013 - Holistic HVAC Design
ASHRAE Journal - April 2013 - 41
ASHRAE Journal - April 2013 - 42
ASHRAE Journal - April 2013 - 43
ASHRAE Journal - April 2013 - 44
ASHRAE Journal - April 2013 - 45
ASHRAE Journal - April 2013 - 46
ASHRAE Journal - April 2013 - 47
ASHRAE Journal - April 2013 - Engineer’s Notebook
ASHRAE Journal - April 2013 - 49
ASHRAE Journal - April 2013 - 50
ASHRAE Journal - April 2013 - 51
ASHRAE Journal - April 2013 - 52
ASHRAE Journal - April 2013 - 53
ASHRAE Journal - April 2013 - Data Centers
ASHRAE Journal - April 2013 - 55
ASHRAE Journal - April 2013 - 56
ASHRAE Journal - April 2013 - 57
ASHRAE Journal - April 2013 - 58
ASHRAE Journal - April 2013 - 59
ASHRAE Journal - April 2013 - Emerging Technologies
ASHRAE Journal - April 2013 - 61
ASHRAE Journal - April 2013 - 62
ASHRAE Journal - April 2013 - 63
ASHRAE Journal - April 2013 - IAQ Applications
ASHRAE Journal - April 2013 - 65
ASHRAE Journal - April 2013 - 66
ASHRAE Journal - April 2013 - Refrigeration Applications
ASHRAE Journal - April 2013 - Special Products
ASHRAE Journal - April 2013 - People
ASHRAE Journal - April 2013 - International Column
ASHRAE Journal - April 2013 - 71
ASHRAE Journal - April 2013 - Energy Modeling
ASHRAE Journal - April 2013 - 73
ASHRAE Journal - April 2013 - Products
ASHRAE Journal - April 2013 - 75
ASHRAE Journal - April 2013 - 76
ASHRAE Journal - April 2013 - 77
ASHRAE Journal - April 2013 - 78
ASHRAE Journal - April 2013 - Classified Advertising
ASHRAE Journal - April 2013 - Advertisers Index
ASHRAE Journal - April 2013 - Cover3
ASHRAE Journal - April 2013 - Cover4
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