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Lighting power density for Multifamily

asked 2017-03-22 08:02:37 -0600

updated 2017-04-03 13:22:14 -0600

Background: I'm modeling a 7 story multi-family building. The developer wants to design things at a very high level of energy performance, including lighting and plans to provide LED lighting in all rooms. As a result, the occupants won't need to provide their own lighting at all (though I'm sure there will be some). ASHRAE 90.1-2010 specifies maximum lighting power density for multifamily as 0.6 w/sq.ft., which is a fairly stringent requirement. I'm wondering if ASHRAE has assumed a typical lighting design for multifamily, which in my experience includes minimal hard-wired lights, perhaps only in the kitchen, bathrooms and hallway. In that scheme, the overall LPD would be pretty low and occupant-provided lights would become plug loads and unregulated - but would also remain identical for the Baseline and Proposed designs. I want to claim savings for the plug loads if this is the case. (Neither the 90.1 document nor its User Manual address this) Question: For my Proposed scenario (LED lights hard-wired and provided in every space), is it consistent with ASHRAE's assumptions to reduce my plug loads for the Proposed case because we're providing more lighting than is normal for multifamily occupancy?

Full Disclosure: I'm not trying to game the system, but want to be sure I don't leave energy points on the LEED table - so to speak.

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answered 2017-03-22 10:04:01 -0600

updated 2017-03-22 10:05:50 -0600

ASHRAE 90.1 does not regulate dwelling unit lighting power*, so strictly following Appendix G modeling you would keep the lighting power the same in both models. (Note: the 0.6 W/SF is for multifamily whole-building method, so that's the value that would apply to common areas, corridors, etc. Just not dwelling units).

As with everything ASHRAE, the Rating Authority can provide a methodology for showing savings for unregulated loads. LEED Interpretation 1712 has provided an exceptional calculation methodology that I've used in the past to show savings for hard-wired dwelling unit lighting, however as you can see that applies to V2 and V3 projects only. I'm not sure if there has been a similar interpretation for LEED V4 projects.

*This (PDF link) ASHRAE interpretation.

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As usual for you, that's very helpful - Thanks!

Jim Dirkes gravatar image Jim Dirkes  ( 2017-03-22 10:44:37 -0600 )edit

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Asked: 2017-03-22 08:02:37 -0600

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Last updated: Mar 22 '17