ASHRAE Journal - March 2023 - 22

COLUMN DATA CENTERS
TABLE 2 Potential reduction in capital and energy costs related to a chillerless data center with 1 MW ITE load in various climates.
DETAILS
CLIMATE
ZONE
1A
2A
2B
3A
3B
3C
4A
4B
4C
5A
5B
5C
6A
6B
7
8
REPRESENTATIVE
CITY
Miami
Tampa, Fla.
Tucson
Atlanta
El Paso, Texas
San Francisco
New York
Albuquerque, N.M.
Seattle
Buffalo, N.Y.
Denver
Port Angeles, Wash.
Rochester, Minn.
Great Falls, Mont.
International Falls, Minn.
Fairbanks, Alaska
MAX
ANNUALIZED MLC
(ITE >300 kW)
0.26
0.23
0.17
0.21
0.17
0.14
0.18
0.14
0.14
0.16
0.15
0.14
0.16
0.14
0.14
0.13
MLC
SCENARIO 1
0.21
0.20
0.17
0.17
0.15
0.18
0.15
0.13
0.15
0.13
0.12
0.15
0.12
0.11
0.11
0.09
a net CapEx savings of $438,310 for a data center with a
1 MW ITE design load.
Impact on Data Center Energy Consumption
For a chilled water system, the energy savings would
accrue from the reduction (or elimination) of chiller
energy during the course of a year. Parasitic energy to
be included in the analysis includes: (a) the increase in
cooling tower fan energy to provide 100% economizer
cooling for the entire year, and (b) increased fan
energy required to operate CRAH units at higher
airflow rates when server fans ramp up. It should be
noted that in the case of (b), the chillerless data center
is assumed to be equipped with more CRAH units than
the baseline design, and these CRAH units can operate
at low fan speeds except during the hours of the year
when the cold aisle supply temperature is significantly
above the baseline x-factor temperature of 68°F
(20°C). As such, the annualized cooling air distribution
fan energy of a chillerless design will typically be less
than the fan energy associated with a standard chiller
MLC
SCENARIO 2
0.08
0.07
0.06
0.06
0.06
0.06
0.06
0.05
0.05
0.05
0.05
0.05
0.0S
0.05
0.05
0.05
NET X-FACTOR
1.41
1.34
1.14
1.17
1.08
1.13
1.11
0.97
1.04
1.03
0.94
1.00
1.02
0.90
0.97
0.86
ANNUAL ENERGY
COST SAVINGS
(75% ITE)
$94,242
$90.488
$82,093
$76,976
$72,035
$87,275
$65,641
$56,914
$73,577
$56,959
$51,154
$68,904
$50,531
$45,722
$43,747
$34,217
CAPITAL COST SAVINGS
($/MW)
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
$438,310
plant design with fewer CRAH units. The exact tradeoff
depends on the ambient wet-bulb distribution of
the site in question.
Table 2 compares the potential reduction in CapEx costs
and the potential reduction in energy (OpEx) costs while
using x-factor variable supply temperature control. For
reference, ASHRAE Standard 90.4-20194 mechanical
load component (MLC) factors are also shown, as well as
the MLCs calculated for both the baseline (chiller) and
the x-factor (chillerless) designs.*
Table 2 provides general information on the variation in
energy use of Scenario 1 (the water-cooled chilled water
baseline) and Scenario 2 (water-cooled chillerless data
center) for representative cities in each of the U.S.-based
ASHRAE Climate Zones. To make sure the baseline
system is reasonably aligned with standard designs,
MLC values are compared to the MLC targets contained
in Standard 90.4-2019. There was reasonable alignment
in this regard, with the baseline system slightly above
Standard 90.4-2019 in only three climate zones, and
slightly below in all others.
*ASHRAE Standard 90.4-2022 was not available as a reference for this column, but will be published in 2023.
22
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