ASHRAE Journal - September 2023 - 50

TECHNICAL FEATURE
with zones that are limited to
600 ft2 (56 m2). The general
lighting in the occupied zone is
permitted to automatically turn
on to full upon occupancy, while
the lighting in other unoccupied
zones is also permitted to turn
on, but to no more than 20%
power (Figure 3).
Occupants had expressed
dissatisfaction with the zone size
and the darkness within their
field of view as they looked across
the office toward unoccupied
workstations. This change allows
all the lighting to turn on, but
to a low level (not more than
20%). Turning on the lighting
allows for even distribution and
reduces occupant dissatisfaction
in spaces. Occupant-driven
controls still enable energy savings.
Interior Lighting Power
Three prescriptive compliance approaches,
Simplified Building Method (Section 9.3), Building
Area Method (Section 9.5.1) and Space-by-Space
Method (Section 9.5.2) are available. Each method
requires users to comply first with lighting power
limits and then lighting controls.
For power, projects have a lighting power allowance
(LPA). The LPA is determined by multiplying the area by
a lighting power density (LPD) value. The LPD value is
specified in each of the applicable compliance pathways.
TABLE 2 Sample interior lighting power density values, Standards 90.1-2016, 2019
and 2023.
SPACE TYPE
Classroom
Corridor
Conference Room
Enclosed Offices*
Large (Open Plan) Offices
Warehouse - Medium/Bulky
90.1-2016,
W/ft2
0.92
0.66
1.07
0.93
0.81
0.35
90.1-2019,
W/ft2
0.71
0.41
0.97
0.74
0.61
0.33
90.1-2023,
W/ft2
0.72
0.44
0.88
0.73
0.56
0.33
*Enclosed office size designations changed from 250 ft2 to 150 ft2 in Standard
90.1-2023.
50
ASHRAE JOURNAL ashrae.org S E PTEM B ER 2023
FIGURE 3 Open office with the dimmer lighting over the
desk operating at 20% output, Chicago.
Standard 90.1 has a model used
to develop the LPD values (which
users reference to determine
the lighting power budget). The
model creates the LPD for the
Space-by-Space method tables.
The values for the Building
Method and Simplified Building
Methods are then based on
the values in the Space-bySpace
tables. The Standard
90.1 lighting model is updated
each cycle to reflect changes in
lighting practice, incorporate
new luminaire data and reflect
updates from more efficient
equipment.
Table 2 shows a sample of
spaces in the Space-by-Space
table. The LPD values for
some spaces (e.g., classroom,
corridor) increased between 2019 and 2022. The
increase was due to a combination of factors
including changes in lighting recommendations,
revised inputs and assumptions and incorporation
of new or modified design practices. Similarly, the
LPD values reduced for many spaces (e.g., conference
rooms, open plan offices) for the same reasons.
Finally, in some spaces there was no change in value
(e.g., warehouse-medium/bulky).
Overall, a 4% reduction in the interior lighting
power density values occurred in Standard 90.1-2022
compared to Standard 90.1-2019.
Lighting Power Allowances
Within the Space-by-Space Compliance Method,
users have an option for additional power if the
standard prescriptive values are not sufficient for
their needs. Section 9.5.2.2 of Standard 90.1-2022 is
Additional Interior Lighting Power (previously this was
Section 9.6.3).
The lighting power density values for decorative
lighting in this section were evaluated and resulted in
a reduction from 0.75 W/ft2 to 0.70 W/ft2 (8 W/m2 to
7.5 W/m2). The retail values were also reduced. Both
changes result from LED luminaires becoming more
efficient and allowing for potential savings.
MICHAEL MYER
http://www.ashrae.org
ASHRAE Journal - September 2023

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