ASHRAE Journal - October 2014 - 62

2014 ASHRAE TECHNOLOGY AWARD CASE STUDIES

Since 100% or a very large fraction
of outdoor air is used all the time
unless we need to run the system in
recirculation mode, the indoor air
quality is excellent. The air flows
over a wet media that captures dust
particles and also provides excellent
filtration of outdoor contaminants
as well as enhanced indoor air quality. So far, we have never had to run
the system in a complete recirculation mode.

PUE of cooling equipment).

COOLING EQUIPMENT ENERGY USE PER UNIT IT ENERGY CONSUMPTION
MONTH

ELECTRICITY USE BY AIR
MOVING FANS IN DATA
HALL, KWH/KWH OF THE IT
EQUIPMENT

ELECTRICITY USE BY AIR
MOVING FANS IN UPS
HALL, KWH/KWH OF THE
IT EQUIPMENT

ELECTRICITY USE BY
CHILLER COOLING
PLANT, KWH/KWH OF
THE IT EQUIPMENT

TOTAL ELECTRICITY USED
FOR COOLING DATA CENTER,
KWH/KWH OF THE IT
EQUIPMENT

Jan 13

0.058

0.009

0.001

0.068

Feb 13

0.040

0.010

0.000

0.050

Mar 13

0.050

0.011

0.006

0.066

Apr 13

0.053

0.010

0.002

0.065

May 13

0.071

0.011

0.002

0.084

Jun 13

0.099

0.013

0.018

0.130

Jul 13

0.114

0.014

0.113

0.242

Aug 12

0.087

0.020

0.070

0.178

0.068

0.017

0.019

0.104

0.054

0.014

0.000

0.069

0.053

0.013

0.000

0.067

0.049

0.012

0.000

0.061

0.067

0.013

0.019

0.099

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O CT O B E R 2 0 1 4

FIGURE 1 Plot of energy use by components of cooling equipment as a fraction of

the IT energy consumption (contributing components of the partial PUE).

1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0

Annual

Nov. 2012

Dec. 2012

Oct. 2012

Sep. 2012

Jul. 2013

Aug. 2012

May 2013

Jun. 2013

Apr. 2013

Mar. 2013

Feb. 2013

IT Energy

IT Equipment Energy Use
Chiller Plant
UPS Hall Fans
AHU Hall Fans

Jan. 2013

Several innovations, as well as best
Sep 12
practices we learned from operatOct 12
ing other data centers, were impleNov 12
mented here.
Dec 12
Humidification. The system
Annual
uses the waste heat from the IT
equipment to evaporate water into moisture instead of
using energy to generate steam. Moving hot dry air over
a wet media to cool it is a well-known technology, but its
use to primarily humidify air has not yet found its way in
the industry. The hot air from the IT equipment, mixed
with cold outdoor dry air, flows over a wet media where
it picks up moisture and gets humidified as shown in
Figure 3.
The air is cooled in the process, which is also known as
evaporative cooling. The cooling is certainly helpful but
incidental in this application; the primary objective is to
get free humidification. In West Jordan, Utah, humidification is needed for more than 78% of the hours in a
year when outdoor dew-point temperature is below the
current minimum acceptable dew-point temperature
of 41.9°F (5.5°C) as shown in Table 2, which also shows a
quick comparison of number of hours when free cooling is available with conventional air-side economizer as
well as with the installed cooling system.
The solution provides complete free humidification
and cooling for 74% of the time and partial free cooling
for the remaining 26% of the time with the controls setpoints that we had selected. It has the ability to provide
free cooling and humidification for 99% of the time if
supply air temperatures of 72°F (22°C) are acceptable.
In comparison, the conventional economizer provides
free cooling for only 73% of the time, but requires

kWh/kWh of IT Equipment Energy Use

Innovations in Energy Efficiency

TABLE 1 Energy use by components of cooling equipment as a fraction of the IT equipment energy use (partial

humidification energy for 78% of the time. The large
number of hours when humidification is needed in cold
climates explains why conventional humidification
systems with steam required more energy than cooling
energy saved from cold outdoor air, and economization
was shunned by the industry.
Controls. Conventional controls are based on dry-bulb
temperatures and use feedback from the discharge air
temperature to control sensible cooling. The innovation
in controls is based on using the wet-bulb temperature
of the incoming air for control of humidification. This
also provides stable supply air temperature and prevents

ASHRAE Journal - October 2014

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