Hi all
We are working in an office project that we would like to apply to the commercial interior LEED Certification. The office is in an existing building, with a surface of 1.500 m2. The building has a curtain wall envelope that used a simple glass that not match entirely the specification in the table 5.5-1 zone 1. The glass is compound with one layer that has a U value of 5.814 and a SHGC of 0.258. The second layer has the same U value and a SHGC of 0.51. We cannot modify the fenestration area.
According to ASHRAE 90.1-2010 the WWR has to be < 40%, but reviewing the information and how there are different points of view regarding the scope of the project we would like to ask:
1. Do we have to build internal walls in order to achieve the WWR < 40%? Or because this is an existing building the curtain wall is out of the scope?
2. In case that we do not consider the office envelope, if we go with the Option 2. Prescriptive Compliance, the same option apply in the EAC2?
Thank for your support
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
July 1, 2019 - 12:02 pm
There is an exception in CI v4 that does not allow you to use the existing envelop conditions - Exception: the baseline project envelope must be modeled according to Table G3.1(5) (baseline), Sections a–e, and not Section f.
So the baseline must be modeled according to Appendix G including the <40% WWR limit. In the case of the modeling approach (Option 1) you will simply pay a penalty in the energy performance. Since this is not a mandatory provision and it is outside your scope of work you do not have to comply.
Under Option 2 this system is outside the scope of work so you also do not have to comply with the prescriptive envelop requirements.
Waleed AlGhamdi
Sustainability EnablerEskew+Dumez+Ripple
20 thumbs up
July 1, 2019 - 12:09 pm
Without getting into the specifics of the project, the 40% max WWR figure is for the baseline model. A proposed design can exceed that figure in ASHRAE 90.1 2010 but with a penalty. This means that you'll need to compensate by additional savings elsewhere (HVAC, lighting, DHW, etc).
Interior walls are not considered in the WWR calculation. The definition (Section 3.2) is "wall area, gross: the area of the wall measured on the exterior face from the top of the floor to the bottom of the roof."
Having said that, unfortunately, the LEED credit language explicitly requires the project to follow "Table G3.1(5) (baseline), Sections a–e, and not Section f." which means your project will be penalized for WWR in excess of 40% and for a fenestration system that falls short of the requirements in Table G3.1(5).
Carlos Dobobuto
July 1, 2019 - 1:23 pm
Dear Marcus and Waleed
Thanks for answer our question.
Best regards
Carlos Dobobuto