We're having difficulty getting Solatubes to calculate correctly for the prescriptive (option 2) method. The required ratio of top-lighting aperture sf to floor area inaccurately reflects the performance of the Solatube (we feel). We contacted the Solatube company and they agree. They have never used the prescriptive method to assist with LEED applications; they said they usually use simulation method (option 1). Solatube said they have been on projects that submitted a combination of Option 1 and 2 - Option 2 for the windows and Option 1 for the Solatubes. Is this possible?? What I really would like to know is if there any way that anyone knows of to calculate Solatubes with the prescriptive method more accurately.
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TODD REED
Energy Program SpecialistPA DMVA
LEEDuser Expert
889 thumbs up
August 10, 2011 - 8:11 am
The prescriptive method is a means to provide projects some type of guidelines that will get them some daylighting scenarios that would be better if they had not even considered daylight. It is method of formulas and rules. It is not a method that can effectively or accurately provide projects teams information about the performance of their daylighting scenarios.It is not meant for anything other than punched openings in a building envelope.
Your not going to get the actual performance of the solartube using the prescriptive method. You will need to use a combination of methods as Solar tube had mentioned. When simulating soar tubes you will actually simulate them as electric lights. You can get the IES file from Solar Tube to do this.
Matt Nolan
LEED APBelay Architecture
8 thumbs up
August 10, 2011 - 9:47 pm
Dana,
I'm working on a project which will also attempt to earn the daylighting credit with the prescriptive approach, and is also using Solatube skylights. I would be interested in what your outcome was if you have had your project reviewed- and how you chose to document the Solatubes.
We have an approach we used during design - allowing us to decide how many we needed, how to space them, and we expected it to comply with the LEED requirements, but it hasn't been submitted yet. I don't want to post our idea on the forum in-case it's incorrect- (then it will just confusion), but we can compare notes if you haven't submitted yet. Here is my contact mnolan (at) BelayArchitecture (dot) com -thanks!
James Geers
Architect, LEED AP, Director of Sustainable DesignSFA Architects Inc.
3 thumbs up
November 24, 2014 - 11:58 am
I have used Solatubes in projects and they have IES illumination files for different sun angles for each model. Using the modeling option it is very easy to determine the sun angle for 9 am an 3 pm place the appropriate IES file in a simple lighting program and determine your lighting fc. I believe Solatube may even do these calculations for you. If you combine it with other daylighting options you can easily do the calculations yourself it program such as 3d Studiomax which came as an add on with my version of REVIT.
Jill Perry, PE
ConsultantJill Perry, LLC
LEEDuser Expert
440 thumbs up
November 24, 2014 - 4:49 pm
For clarity, Solatubes cannot be documented with the prescriptive option. To document your use of Solatubes you must simulate them. You can either simulate all of the regularly occupied spaces turning in the entire documentation under the simulation option, or you can document the spaces that don't have Solatubes with the prescriptive option and submit the simulation and the prescriptive calculations together under the combination option.