Hi All,
I just got back comments on my models for a LEED project and the reviewer
commented that I needed to account for occupancy sensors. I had done this
by switching the lighting schedule to the occupancy schedule in rooms with
occupancy sensors, does anyone know if this is an appropriate way to model
occupancy sensors? Is there a tool built into equest that allows you to
account for them a different way?
Thanks in advance,
____________________________
Michael Shields
Michael,
There are a couple different ways to account for occupancy sensors for
LEED but you need to follow Appendix G Table G3.2 of ASHRAE 90.1.
Basically you're allowed to reduce the lighting by the percentage listed
in the above table, 10% for most buildings. You can do this by either
reducing the lighting power input for the spaces by 10% under the
Internal Loads tab or create a lighting occupancy sensor schedule that
has hourly fractions that are 10% less than your regular lighting
schedule. You also need to make sure that you apply this lighting
credit to any spaces that are required by minimum code to have automatic
lighting controls specified under Section 9.4.1. Table G3.1 Number 6
has a good explanation of this process for the baseline and proposed
building.
Thanks,
Matthew Larson, LEED AP BD+C
Reducing the lighting power density is a easy for you and acceptable for
USGBC way.
Just a note: the adjustment in Table G3.2 does NOT apply to spaces
mandated to have those controls under 9.4.1 - it only applies to spaces
where these controls are optional. Table G3.1(6) says:
"g. For automatic lighting controls in addition to those required for
minimum code compliance under Section 9.4.1, credit may be taken for
automatically controlled systems by reducing the connected lighting
power by the applicable percentages listed in Table G3.2.
Alternatively, credit may be taken for these devices by modifying the
lighting schedules used for the proposed design, provided that credible
technical documentation for the modifications are provided to the rating
authority."
(italics as used in the referenced standard)
There is quite a bit of discussion on Table G3.2 in the list archives
that you can browse. You can adjust the LPD in your proposed model (not
baseline - baseline does not include the controls) or instead you can
explain to the reviewers the methodology you used to determine the
occupancy schedule and why it is appropriate that the lighting schedule
mirror the occupancy schedule for rooms with controls. No need to run
the model if you have the evidence to support your method and your
method is allowed by Appendix G, which it clearly is in Table
G3.1(6)(g).
Your review comment does bring up an interesting point: the language in
the standard is not absolute. Appendix G does not explicitly state that
you are required to take credit for occupancy controls and therefore
include them in the model, it only states that you MAY take credit for
them. The model is more conservative if credit is not taken for
occupancy controls. If you have much less than a clear picture of how
the occupants are going to use the building you should weigh the
uncertainty of the occupancy inputs against the energy reduction
achieved by including the controls in the model. You may determine that
it is not appropriate to include occupancy control savings in the model
and the language in the standard would support that decision.
Jeremy R. Poling, PE, LEED AP+BDC
For clarification, we have gotten comments from GBCI requiring us to
include automatically controlled lighting systems in the mandated spaces
per Section 9.4.1 in the baseline model so we have applied the
adjustments in the baseline to those required spaces. I would think you
could just not use the adjustment credit in the baseline or proposed
(even if there are occ sensors in the proposed) for spaces that are
mandated so no credit is taken for having those occupancy sensors. It
seems like Jeremy is referring to the latter method of not giving credit
to the mandated spaces in either model. It seems that the point of the
comment is to ensure the project doesn't get credit for occupancy
sensors in spaces where it is mandated under 9.4.1 so either way should
work. W e have had no problems just applying the credit to the baseline
and proposed for mandated spaces. However Jeremy's method seems to line
up with the Table G3.1(6) statement better. This could just be another
case of review comment inconsistencies.
Thanks,
Matthew Larson, LEED AP BD+C
I have seen the reviewers request documentation verifying that automatic lighting controls were NOT included in the baseline model.
Very specifically, Table G3.1(6) for the baseline states:
?Lighting power in the baseline building design shall be determined using the same categorization procedure (building area or space function) and categories as the proposed design with lighting power set equal to the maximum allowed for the corresponding method and category in Section 9.2. No automatic lighting controls (e.g. programmable controls or automatic controls for daylight utilization) shall be modeled in the baseline building design, as the lighting schedules used are understood to reflect the mandatory control requirements of this standard.?
The language there is pretty clear: shall = mandatory, therefore, no automatic controls are to be included in the baseline model (understanding that the lighting schedules already account for the mandatory provisions). So I?m not certain if your reviewer accidently asked for the controls to be in the baseline when they meant to ask for you to verify that they weren?t.
Either way, just remember that not every change to the model requested by a reviewer will necessarily be legitimate. The amount of information required for submittal is such a small portion of the knowledge that went into the design of the building and the construction of the model, so rarely will the reviewer have as detailed of a view of the design as you the modeler should have. In addition, they only get 25 business days (including QA time) to review something that may have taken you at least two or more times that amount of time, so they realistically may not have enough time to catch EVERY detail and nuance to the project. If you have a strong reason for running the model with certain parameters and can backup that decision with design documents and specific sections of the code, that is an acceptable response to a review comment.
Jeremy R. Poling, PE, LEED AP+BDC
After reading your responses and rereading the comments from the reviewer I believe that in my case the reviewer wanted to make sure it was done as Jeremy has interpreted ASHRAE (not including a reduction in lighting power for either model). Having thought about it more unless you have a strong support for changing the schedule it seems that the 10% reduction in power level is the easiest and least questionable way to take advantage of lighting control savings, although if you have pre and post usage hours for a similar project you could possibly justify a change in schedule.
Thanks for all the feedback.
We always apply the 10% to the Baseline and Proposed models for the ASHRAE mandated spaces even if they technically offset.
The Proposed model should mimic the actual design as closely as possible so the Baseline reductions come along for the ride.
Fred Betz PhD., LEED AP