ASHRAE Journal - November 2019 - 12

TECHNICAL FEATURE

Process Energy Index

A Metric to Characterize
Commercial Building
Process Loads, Energy Use
BY ROGER CHANG, P.E., BEMP, FELLOW ASHRAE; DRURY B. CRAWLEY, PH.D., BEMP, FELLOW ASHRAE

With an ever-increasing focus on low-energy buildings, energy benchmarking has
become even more important. The predominant metric for benchmarking commercial office building energy use continues to be the energy use intensity (EUI). Use of
EUI alone can mask poor performance, as the metric does not explicitly capture variation due to a partially occupied building or a building with a low net-to-gross floor
area ratio.
Low-energy buildings require the participation of an
engaged occupant group to realize process energy use
savings. Yet, there is also a need to achieve energy efficiency without compromising user productivity.
Benchmarking often starts with an EUI target, either
determined using the U.S. Environmental Protection
Agency's ENERGY STAR Target Finder (www.energystar.
gov/buildings/tools-and-resources/target-finder-0) or
based on the Architecture 2030 challenge framework
(https://architecture2030.org). What if we built targets
starting with a building's process load? Although there is
some movement within ASHRAE/IES Standard 90.1 and
California's state energy code (Title 24) to regulate these
loads, they are typically unregulated, leaving them to be a
point of focus later in a design process than they should be.
Based on a high-performance building project previously featured, the Wayne Aspinall Federal Building, the

design team found that ASHRAE standard utilization
schedules had poor correlation to measured process
load energy use profiles.1 When tenants were questioned about their use, they became frustrated at being
encouraged to reduce equipment energy use that would
compromise function. In interacting with tenants over
an 18-month period, we were brought to a new way of
viewing energy use. What if design teams focused on a
building level coefficient indexed to a building's process
load, in addition to EUI?

PEI Metric Definition
The proposed metric is termed process energy index
(PEI), the ratio of building energy use divided by process
energy use. This metric has similarities to the power
usage effectiveness (PUE) metric used for data centers,2 but with broader application to a wide range of

Roger Chang, P.E., LEED Fellow, is senior engineering leader with DLR Group in Washington, D.C. Drury B. Crawley, Ph.D., is director, building performance products at Bentley
Systems in Washington, D.C.
12

ASHRAE JOURNAL

ashrae.org

N O V E M B E R 2 0 19


http://www.energystar.gov/buildings/tools-and-resources/target-fi nder-0 http://www.energystar.gov/buildings/tools-and-resources/target-fi nder-0 https://www.architecture2030.org

ASHRAE Journal - November 2019

Table of Contents for the Digital Edition of ASHRAE Journal - November 2019

Contents
ASHRAE Journal - November 2019 - Intro
ASHRAE Journal - November 2019 - Cover1
ASHRAE Journal - November 2019 - Cover2
ASHRAE Journal - November 2019 - 1
ASHRAE Journal - November 2019 - Contents
ASHRAE Journal - November 2019 - 3
ASHRAE Journal - November 2019 - 4
ASHRAE Journal - November 2019 - 5
ASHRAE Journal - November 2019 - 6
ASHRAE Journal - November 2019 - 7
ASHRAE Journal - November 2019 - 8
ASHRAE Journal - November 2019 - 9
ASHRAE Journal - November 2019 - 10
ASHRAE Journal - November 2019 - 11
ASHRAE Journal - November 2019 - 12
ASHRAE Journal - November 2019 - 13
ASHRAE Journal - November 2019 - 14
ASHRAE Journal - November 2019 - 15
ASHRAE Journal - November 2019 - 16
ASHRAE Journal - November 2019 - 17
ASHRAE Journal - November 2019 - 18
ASHRAE Journal - November 2019 - 19
ASHRAE Journal - November 2019 - 20
ASHRAE Journal - November 2019 - 21
ASHRAE Journal - November 2019 - 22
ASHRAE Journal - November 2019 - 23
ASHRAE Journal - November 2019 - 24
ASHRAE Journal - November 2019 - 25
ASHRAE Journal - November 2019 - 26
ASHRAE Journal - November 2019 - 27
ASHRAE Journal - November 2019 - 28
ASHRAE Journal - November 2019 - 29
ASHRAE Journal - November 2019 - 30
ASHRAE Journal - November 2019 - 31
ASHRAE Journal - November 2019 - 32
ASHRAE Journal - November 2019 - 33
ASHRAE Journal - November 2019 - 34
ASHRAE Journal - November 2019 - 35
ASHRAE Journal - November 2019 - 36
ASHRAE Journal - November 2019 - 37
ASHRAE Journal - November 2019 - 38
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ASHRAE Journal - November 2019 - Cover3
ASHRAE Journal - November 2019 - Cover4
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