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NC-2009 EAp2:Minimum Energy Performance

Area Weighted Average: White Roof, Green Roof, Sloped Roof with Metal Panel and Bulkhead

Our project has three different types roof 1. Sloped roof with a centria metal panel 2. White Roof 3. Green Roof 4. Elevator bulkhead "roof"??? I am assuming that i need the Area weighted average determined first instead of the U-factor for each to input into LEED Minimum Energy Performance Template spreadsheet and ultimately in the energy model as well. Is this correct? Do I have to condsider other thermal benefits in our enery model for the white roof as well, other than listing the SRI? Do I have to condsider other thermal benefits in our enery model for the green roof as well in other to maximize the thermal benefits for building? I maybe be over thinking this part of my question, but will appreciate clarification nonetheless; would the roof of an elevator bulkhead matter in this calculation as well? Best regards, Fatou
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Wed, 02/20/2019 - 17:08

Depending on your modeling software you will need to enter some type of reflectance value for each roof type in the model.  I would not do a weighted average. You need to model reflectance and U-value to simulate the performance of the different roof types. The elevator roof probably does not matter since the space below it is typically unconditioned. See 90.1 Table G3.1 - 5 for both the proposed and baseline modeling guidance on this issue.
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David Eldridge
Energy Efficiency Ninja
Grumman/Butkus Associates
LEEDuser Premium Member
64 thumbs up

Wed, 02/20/2019 - 18:01

For instance if you were using eQUEST, you'd enter each space in the model with its actual roof design. Then you can view a report in the *.sim file that shows an aggregate total for roofs (and walls, and windows) in the model which you could use to populate the LEED form.  

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