ASHRAE Journal - March 2023 - 53

TECHNICAL FEATURE
modeling in building simulation practice.6 - 8 Key points
include:
* Contrary to standard occupancy schedules and
densities, occupancy is much more variable in reality.
Moreover, common assumptions about occupants tend
to be conservative.
* Occupant behavior is diverse and uncertain, but
often predictable in a probabilistic sense, because occupants
often behave in certain patterns to continuously
improve their comfort.
* Occupants should be recognized as active participants
in buildings rather than mere sources of heat
and air contaminants. In essence, occupants should be
treated as being in a two-way relationship with buildings,
rather than a boundary condition like weather.
* Building design can infl uence occupant behavior,
whereas this is often forgotten during design.
* If inaccurate assumptions are made about occupants
during design, a risk exists for designers to make
suboptimal or non-robust design decisions.
To a large extent, criticisms of current occupant modeling
and design practice can similarly be applied to building
energy codes. This article answers questions such as:
How do codes deal with occupants and how do these vary
by country? What assumptions are made about occupants'
energy-related behaviors? What features can we
learn from existing codes to possibly enhance others?
The 23 regions' building codes and standards were
reviewed as part of a large project of the International
Energy Agency-Energy in Buildings and Communities
Annex 79: Occupant Centric Building Design and
Operation.9 The countries studied include Austria,
Australia, Belgium, Brazil, Canada, China, Denmark,
France, Germany, Hungary, India, Italy, Netherlands,
New Zealand, Norway, Singapore, South Korea, Sweden,
Switzerland, United Arab Emirates, United Kingdom,
United States . They are shown in the map here: https://
tinyurl.com/JournalExtras. For simplicity, we focused
on offi ce buildings, though the work could be extended
to other building types. Considering the magnitude
of this review effort and the number of languages
involved, we had the privilege to work with many international
reviewers (see Acknowledgments and O'Brien,
Tahmasebi, et al.).10
Methodology
Like ASHRAE/IES Standard 90.1, many building codes
and standards around the world provide two main
options for code compliance: the performance path and
the prescriptive path. The performance paths tend to
defi ne occupants and their behaviors using schedules
and densities, whereas prescriptive paths often involve
more qualitative rules. In this study, we review both
types of requirements.
We performed the review in two phases. Phase 1 was
quantitative and focused on comparing the numerical
occupant-related assumptions or requirements
(e.g., schedules, densities and setpoints). The areas that
were considered are schedules and densities/values for
occupancy, cooling and heating temperature setpoints,
plug loads, lighting, domestic hot water, illuminance
and ventilation rates. Only those codes with specifi cations
of this nature were included for each comparison.
Note that such requirements may appear in reference to
either prescriptive or performance paths. For example,
lighting power density is a prescriptive requirement but
is also to be used in the reference building model.
Phase 2 was broader and asked the contributors to provide
occupant-related specifi cations. They were asked to
list at least fi ve instances where the code refers directly
or indirectly to occupants. These requirements were
assessed systematically to understand how occupants
are referred to, how occupants are defi ned and which
systems are assumed to be controlled by occupants.
Results
Phase 1
For Phase 1, Figures 1 to 3 (page 54 and 55) provide the
comparisons of occupancy, lighting and plug loads with
the densities and corresponding schedules. As can be
seen, the densities vary by a factor of two or more across
countries even though the most extreme countries have
similar standards of living. The schedules are generally
not as diverse, though some have a ramp-up period,
while others have abrupt steps in the morning. These
two situations are likely to signifi cantly affect HVAC
equipment sizing and peak loads. We performed some
investigation into the cause of the discrepancies and
found a few hints. Most notably, several of the codes with
the highest occupancy densities were revealed to originate
from safety and egress values. That is, the values are
likely chosen as conservative given the relative importance
of egress in emergencies vs. energy performance.
It is also noteworthy that the occupancy schedules
M A R C H 2 0 2 3 ashrae.org ASHRAE JOURNAL
53
https://tinyurl.com/JournalExtras https://tinyurl.com/JournalExtras http://ashrae.org
ASHRAE Journal - March 2023

Table of Contents for the Digital Edition of ASHRAE Journal - March 2023
