ASHRAE 90.1 Baseline LPD and occupancy sensor credit

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All,

This question pertains to a LEED energy model per the ASHRAE 90.1 Appendix
G. Occupancy sensors are required in spaces such as conference rooms and
employee lunch/break rooms per Section 9.4.1.2 and no lighting power
density credit can be taken for their use in the proposed design model.

My question is, do the baseline maximum LPDs prescribed by ASHRAE, say 1.3
W/sf for conference rooms, already account for the power 10 or 15%
adjustment for occupancy sensor use or does the credit have to be manually
applied on top of the 1.3 W/sf in the Baseline model?

Thank you,
Ramana Koti.

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Ramana,

90.1-2007 Table G3.1 section 6 under Baseline Building Performance states: "
. . . No automatic lighting controls (e.g. programmable controls or
automatic controls for daylight utilitzation) shall be modeled in the
baseline building design, as the lighting schedules used are understood to
reflect the mandatory control requirements in this standard."

You should not be adjusting the power density number to simulate lighting
controls, but adjusting the schedules to reflect occupancy sensor operation.
For example, say there are a number of offices and conference rooms in the
proposed building that will have occupancy sensor controls. This should be
simulated by inputting the LPD or actual connected load, and creating a
schedule with a 10% - 15% reduction for each hour of operation per Table
G3.2. In the LEED baseline model, the schedule for the offices would be not
have the occupancy sensor reduction, but the conference room and other
spaces required by 90.1 to have occupancy sensor control would use the
reduced schedule. Clear as mud?

Steven

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Steven, see Table G3.2 of 90.1. Ramana is correct that you can apply
reductions in connected lighting density for occupancy sensors in those
spaces that do not need them (but have them).

Ramana, to answer your question, the LPDs for the baseline model should
not be adjusted per Steven's quote of Table 3.1.

James Hansen, P.E., LEED AP

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Reviewing Table G3.1.6.g., I see more than one right answer. You can
revise either the installed lighting power (LPD) OR the associated
scheduling - I should think both approaches equally acceptable. I
personally revise the LPD values.

This is inherently a "clear as mud" sort of topic since you need to
bounce between so many parts of 90.1 to get the full picture, so I'll
try to bullet the logic simply:

* Prescribed LPD's from chapter 9 are representative of what
should be in the baseline.

* Prescribed baseline are representative of any applicable
required occ. sensors. They should not be modified in any fashion in
the baseline model.

* Proposed lighting LPD's as defined (using either the
space-by-space or whole building method), may apply the prescribed
reductions to the proposed installed LPD (10/15%) BUT ONLY against
fixtures in spaces containing such controls that are not otherwise
required to have them.

A simple example for illustration:

1. Proposed office space and an employee lunch/break room each
have a designed LPD of 0.80

2. Baseline model could use 1.0 W/SF for both spaces (whole
building / 90.1-2007)

3. Since the break room is required to have an occ. sensor, the
proposed break room stays at 0.80 W/SF.

4. Since an office space is not required to have an occ. sensor,
the proposed office space gets a reduction: 10% of 0.80 = 0.08, so the
revised LPD is 0.72 W/SF.

~Nick

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Hi Ramana,

Hope you are doing well. This is a tricky aspect of the ASHRAE90.1. But
if you are modeling for LEED, I would refer to the Advanced Energy
Modeling for LEED: Technical Manual where it explicitly says:

Baseline case: Do not take credit for automatic lighting controls, such
as daylight controls, occupancy controls, or programmable controls.

Proposed Case: Model any daylight-responsive lighting control systems in
proposed design. Also model occupant sensor lighting controls (Table
G3.1, No. 6) in spaces where they are not mandatory; note that such
controls are mandatory in

classrooms, conference rooms and employee lunch and break rooms (Section
9.4.1.2).

So, either I take credit for Occup. Sensors in both the cases for
conf/meeting rooms or not take it.

Hope this helps,

Jude.

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Jim,

My reasoning for adjusting schedules instead of LPD or actual connected kW
is that it's more transparent for the reviewer, because:

The baseline LPDs == 90.1 required values

Proposed model LPDs or directly input kWs == what is on the drawings

You can then have identical "occupancy sensor" schedules in both the models
which is applied where occupancy sensors are required in the baseline
(classrooms, conference, etc), and where occupancy sensors are installed in
the proposed building model.

Steven

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Makes sense (and gets me thinking a bit differently, which is also good.)
Thanks!

James V. Dirkes II, P.E., BEMP , LEED AP

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Thank you all, that confirms my understanding.

RK.

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Just saw this post here and thought I must respond with an additional exception with regards to taking credit for occupancy sensors. ASHRAE 90.1 says that-

" A control device shall be installed that automatically turns lighting off within 30 minutes of all occupants leaving a space, EXCEPT SPACES WITH  MULTI-SCENE CONTROL, in

1. classrooms (not including shop classrooms, laboratory
classrooms, and preschool through 12th grade classrooms),
2. conference/meeting rooms, and
3. employee lunch and break rooms."

I interpret that this implies that I could take also credit for occupancy sensors in conference rooms, break rooms etc as long as they have multi-scene controls. If they dont have multi-scene controls than I will not be able to take credit in my energy model for occupancy sensors installed in these spaces.

Ramya S

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