ASHRAE Journal - February 2023 - 45

FEATURE
in establishing the overarching boundaries and
limitations of when the standard applies and when it
does not.
The Title is obvious: Energy Standard for Data Centers.
The Purpose is stated as " ...this standard is to establish
the minimum energy effi ciency requirements of data
centers for
a. design, construction, and a plan for operation
and maintenance; and
b. use of on-site or off-site renewable energy
resources. "
The purpose of 90.4, therefore, is to establish a
" design " standard and a " plan " for operations and maintenance,
allowing for consideration of renewable energy
sources to meet the effi ciency requirements. It does not
include any requirement that the constructed facility
be verifi ed as operating effi ciently-only that it be engineered
and designed to be capable of effi cient operation,
and that this capability be demonstratable to an authority
having jurisdiction (AHJ). There is neither a requirement
for owners or end users to use all the capabilities,
nor is there a requirement for an AHJ to inspect and verify
that the facility is meeting the intended effi ciencies.
Simply stated, Standard 90.4 is a design standard meant
to make effi ciency compliance realistic for both the engineers
and the AHJ without impairing the reliability and
availability of mission critical facilities. Owners wanting to
verify operational compliance can turn to other sources.
However, the design must still include a " plan for
operations and maintenance. " Even if no mechanism
exists to enforce operations compliance, it still
requires the design team to provide information to
the owner as to how the design should be used to
realize the effi ciencies provided by the design. This
aspect takes on high importance with data centers
due to the typical need for redundant systems and
equipment to provide the required reliability. This, in
turn, results in excess capacities and, therefore, less
than maximum effi ciencies.
Complying with Standard 90.4 ensures that, even with
these redundancies, a high level of effi ciency is still realized.
Further, since data centers typically have day-one
loads much smaller than their ultimate design capacity
ratings, opportunities exist to optimize mechanical
energy effi ciencies by applying the affi nity laws (energy
used is proportional to the cube of rotational speed) by
spreading loads across redundant systems and equipment.
Likewise on the electrical side, operating electrical
equipment at low load conditions, particularly uninterruptible
power supplies (UPSes) typically results in
reduced effi ciency. Therefore, fi nding the " sweet spot, "
both electrically and mechanically, may require strategies
and operating plans that optimize infrastructure
effi ciency based on variable load profi les. Since these
variables must be addressed to meet the Standard 90.4
requirements, it is only right that apprising the owner of
90.1
90.4
Removed the exemption for
data centers in 2010
Applies to computer rooms
(<10 kW or 20 W/ft2) of
conditioned fl oor space
Prescriptive standard
First published in 2016.
90.1's
Data center
alternative
compliance path.
90.1
Compliance with
other building
aspects
FIGURE 1.
Standards
90.1 and 90.4
demarcation and
interrelationship.
F E B R U A RY 2 0 2 3 ashrae.o rg ASHRAE JOURNAL
45
Applies to data centers
and some computer rooms
>10 kW or 20 W/ft2 of
conditioned fl oor area
Specifi cally defi ned MLC
and ELC
Performance-based
standard
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ASHRAE Journal - February 2023

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