ASHRAE Journal - September 2023 - 45

TECHNICAL FEATURE
spaces, greenhouses, controlled environmental
agriculture and similar spaces have increased in the
last fi ve years and, as a result, Standard 90.1-2022 now
addresses these applications.
Other parts of the standard use (or are based on) the
term " lumens, " but lumens are for humans. Lumens
are based on the human visual system (a mathematical
function based on cones in the retina of the eye ),
but plants do not have cones and need a different
metric. The standard has adopted photosynthetic
photo effi cacy (PPE) as the metric for the horticultural
lighting requirements. PPE recognizes that plants
create energy via photosynthesis. PPE is the measure of
the visible, infrared and ultraviolet light produced per
unit of energy. The unit for PPE is micromole (µmol)
per joule (J). You don't have to dust off your chemistry
textbooks-the higher the µmol/J value, the more
effi ciently the light source provides photosynthetic
photon fl ux per input electric power. PPE is a metric
developed in ANSI/ASABE S640, Quantities and Units
of Electromagnetic Radiation for Plants (Photosynthetic
Organisms).
This requirement does not apply to small indoor
horticultural or greenhouse spaces/buildings. A
facility must have at least 40 kW of connected load
dedicated to horticultural lighting, which is probably
on the order of 1,000 ft2 (93 m2) of indoor grow facility
or greenhouse, before the requirement needs to be
considered.
Greenhouses have glass roofs and allow daylight to
enter the space. Therefore, the PPE requirement for
greenhouses is 1.7 µmol/J. In contrast, indoor grow
buildings that have opaque roofs as a result have
higher PPE requirements of at least 1.9 µmol/J.
The required PPE values are achievable with some
high-pressure sodium lamps. Very few metal halide
lamps meet the requirement. Many LED sources
and fi xtures can meet the horticultural lighting
requirements; however, verify the information-which
reputable vendors should be able to provide-to
determine if the product under consideration can meet
the requirement.
Alterations
Moving into the main body of Section 9, Lighting,
Standard 90.1-2022 Addendum p revised the
alterations (Section 9.1.3) requirements for interior
lighting. Previous versions of Standard 90.1 included
some vagaries when determining if an alteration met
the requirements to increase the energy effi ciency of
the lighting system.
The 2022 edition established specifi c thresholds
to determine if the project meets the conditions for
an alteration. Within an interior space, if 2,000 W
of existing interior lighting is replaced, the project
must meet all the requirements of Section 9. If less
than 2,000 W is replaced, the new lighting must meet
certain lighting controls requirements of Section 9.4.1
and either use 50% less power than the existing system
being replaced or comply with the Space-by-Space
(Table 9.5.2.1-1 and 9.5.2.1-2) compliance method.
Exterior alterations are a little different. If more than
10 luminaires or more than 20 linear ft (6 linear m) of
luminaires are being replaced, the new lighting must
meet all the requirements of Section 9. If not, any
new lighting must meet a subset of lighting controls
in Section 9.4.1 and either have 50% lower wattage or
meet the wattage requirements of Table 9.4.2-2.
Luminaire Wattage
Standard 90.1-2022 Addendum z revised the
methodology for determining the power allotment
for track lighting. Track lighting can be a challenge
for lighting projects. Lighting drawings often do not
indicate the number of track heads, but rather just
the linear amount (feet) of track. Track is designed to
be functional and allow occupants to add or subtract
track heads as necessary. For line-voltage track, e.g.,
track that is directly supplied with either 120 V or
277 V, Standard 90.1 has long established a maximum
allowable power per linear foot (W/linear foot).
Track that is powered by a transformer or driver
is limited by the power rating of that device. In
contrast, line-voltage track is not limited, and a
power rating was necessary. An estimate of the power
of the track was necessary. Previous versions of
Standard 90.1 required users to assume 30 W/linear ft
(98 W/linear m) for line-voltage track. This value was
based on a mixture of incandescent, halogen and other
light sources. Since 2015, LEDs have become more
prevalent, and since 2019 they have been the de facto
light source for lighting projects. Standard 90.1-2022
requires users to assume 10 W/linear ft (33 W/linear m)
for line-voltage track.
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