ASHRAE Journal - March 2021 - 57

TECHNICAL FEATURE

(2011, 2015 and 2017) using archetype
models for small, medium and large
ofﬁce buildings, schools and multiunit residential buildings (MURBs).
Simulations were performed using
the U.S. Department of Energy's
EnergyPlus V9.1 in different Canadian
climate zones; Victoria, Windsor,
Ottawa, Edmonton and Whitehorse,
which represent NECB Climate Zones 4
through 8, respectively.

TABLE 1 Differences in EPD and equivalent full-load hours, ASHRAE Standard 90.1-2016 and NECB 2017.
BUILDING TYPE

Ofﬁce
School
Multiunit
Residential
Buildings

Background
Review of Plug Load Assumptions in Energy Codes and Standards
In different energy codes and standards, default
schedules and EPD values for plug loads are provided
based on building type. These values are used to represent plug loads in building simulations for demonstrating compliance with these codes and standards. A recent
review by O'Brien, et al.,3 which reviewed energy codes
in 23 regions across the world, indicated that speciﬁed
EPD values varied by nearly a factor of six between different countries (0.24 W/ft2 to 1.49 W/ft2 [2.6 W/m2 to
16 W/m2]). The review suggested the variation in plug
load schedules was not as considerable as EPD values,
yet some differences were observed, particularly with
regard to estimates of nighttime plug load use.
Within the Canadian context, although schedules
and EPD values are relatively similar in both NECB and
ASHRAE Standard 90.1, Table 1 summarizes the main
differences for ofﬁce buildings, schools and MURBs.
Equivalent full-load hours per year for plug loads were
calculated based on the plug load schedules speciﬁed in
each case for weekdays and weekends.
Little information could be found regarding the
development of EPDs and related schedules in the
NECB. A review of the different versions of NECB also
showed that plug load schedules have not changed
since 1997-the year in which Canada's ﬁrst building
energy code was published. However, previous ASHRAE
research projects reported on the development of EPDs
and related schedules for ofﬁce buildings for ASHRAE
Standard 90.1. In particular, ASHRAE Research Project
RP-10934 presented the development process of hourly
plug load density proﬁles for weekdays and weekends
for ofﬁce buildings. The data analyzed in that project
consisted of hourly monitored lighting and receptacle

METRIC

ASHRAE STANDARD 90.1

NECB 2017

Equipment Power Densities

0.75 W/ft2

0.7 W/ft2

Equivalent Full-Load Hours

2,899 h/yr

3,697 h/yr

Equipment Power Densities

W/ft2

0.46 W/ft2

Equivalent Full-Load Hours

2,725 h/yr

3,193 h/yr

Equipment Power Densities

0.5

W/ft2

0.46 W/ft2

Equivalent Full-Load Hours

5,715 h/yr

3,713 h/yr

0.5

loads in 46 ofﬁce buildings around the United States,
which were used to derive plug load schedules.
Abushakra, et al.,5 surveyed available data sets of
monitored commercial end use electricity data, which
were used as part of ASHRAE RP-10934 and indicated
that data used in ASHRAE RP-1093 were collected in the
1980s and early 1990s. Although building occupancy
patterns have signiﬁcantly changed since then (e.g., due
to new societal trends such as teleworking, co-working,
and other ﬂexible work arrangements), assumptions
regarding plug loads have not reﬂected these changes.
More recent ASHRAE projects (e.g., ASHRAE RP-1482,
ASHRAE RP-17426) aimed to revise EPD values with
newer values to reﬂect developments in equipment
power management capabilities. However, analysis of
different versions of ASHRAE Standard 90.1 and its user
manuals shows that only EPD values have changed over
the years; plug load schedules have not.

Review of Previous Studies on Plug Load Use in Existing Buildings
As indicated above, energy codes and standards specify
EPD and schedules for plug loads based on building
type. However, previous studies showed these values
and their use proﬁles widely varied between existing
buildings, even those of the same type. Studies that
focused on analyzing plug loads in existing buildings
are discussed in this section, and a summary of their
reported EPDs is provided in Table 2.
Several studies focused on analyzing plug load use
in ofﬁce buildings and highlighted wide discrepancies
in EPD and daily use patterns. For example, Bennet,
et al.,7 indicated electricity use varied widely between
32 tenants of ofﬁce towers in eastern Ontario and
that plug load use was lower than ASHRAE design values during occupied hours. Harris and Higgins8 also
reported a wide range of EPD and related schedules
based on data from 17 ofﬁce buildings in the United
States, which were categorized into high (1.6 W/ft2
MARCH 2021

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