Occupancy Sensors

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The only caveat I would add is that the occupancy sensor requirement is
exempt IF the spaces have multi-scene control. So if a space has several
lighting options then an occupancy sensor is not required.

My question on this point is: If occupancy sensors are required, does the
ASHRAE 90.1 LPD for that space already include the reduction for occupancy
sensors? Or is the percent reduction taken on top of the LPD values in 90.1?


Jeffrey G Ross-Bain, PE, LEED, BEMP

Jeff Ross-Bain3's picture
Joined: 2011-09-30
Reputation: 0

As it states that the reductions can be scheduled I would think that the
LPD doesn't include the reduction due to occupancy sensors. However in
saying this do we need to put in the reduction in the mandatory areas as
it is going to be roughly the same savings applied to the baseline and
proposed building?

Rimes, Christie's picture
Joined: 2011-09-30
Reputation: 200


I think you're missing Table G3.2. From a "save yourself a headache"
perspective: I would strongly advise NOT modifying your lighting
schedules to account for occ. sensors, unless you have some kind of
research to back up your modifications. Go with the LPD flow =)!

Simply do not take the LPD credit in areas where occ. sensors are
prescriptively required and not exempted. The 10-15% LPD difference in
these exempted spaces can total up to a significant difference in your
results, depending on your project.

There are multiple discussions on this topic in the equest-users and
bldg-sim archives where we've shared our interpretations of how to
handle these automatic controls requirements/exemptions in explicit
detail. I'd suggest perusing - I've copied a more recent discussion I
was involved in below.

To Jeff's question:

The baseline LPD and scheduling (which should match the proposed
scheduling) are understood to account for any required occupancy

This is made explicit in Table G3.1 - last line under Lighting,
Baseline: "No automatic lighting controls ... shall be modeled in the
baseline building design, as the lighting schedules used are understood
to reflect the mandatory control requirements in this standard."


Nick-Caton's picture
Joined: 2011-09-30
Reputation: 605