Dear All,
I'm looking at Table 9.4.5 of ASHRAE 90.1-2007 which lists the maximum allowable LPDs for building exteriors. For building facade lighting, the table reads as follows:
"0.2 W/ft2 for each illuminated wall or surface, OR 5 W / linear foot for
each illuminated wall or surface length"
I'm a bit confused as to why there is a value based on area and another value based on length.
1) If the building facade will be lit by floodlights located at the ground level, will I have to consider the 0.2 W/ft2?
2) If we have a fencing wall, I guess I have the option to use either 0.2 W/ft2 or 5 W/ft, correct? Can I choose the value suits me the most (the one resulting in a higher Wattage allowance)?
Thanks!
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5915 thumbs up
August 15, 2013 - 10:27 am
I am confused by that too. Not sure of the logic behind the linear option. It is our understanding that you can select either option for any facade lighting system. So select the one which results in the higher allowance.
Maya Karkour
EcoConsulting872 thumbs up
August 20, 2013 - 6:32 am
Thanks Marcus,
Just to double check, the linear option is measured horizontally, right (not vertically)?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5915 thumbs up
August 20, 2013 - 10:26 am
I would assume that the linear option would be measured in alignment with the light fixtures. So if they are horizontal you measure horizontal, if they are vertical you measure vertical. This is just my guess. Anyone know more than I about the linear option?
Omer Moltay
Co-founderMimta EcoYapi
201 thumbs up
April 7, 2015 - 9:37 am
We are also struggling to understand this lineer option of 90.1-2007.
We have a facade that is illuminated by horizontal LED luminaires (RGB) at each window frame. This is repeated for each floor. Then, we have continous vertical LED strips, RGB again, illuminating non-transparent vertical strips on the facade. And for the spire, we have the vertical LEDs continuing and additionally three strips of LED fixtures on three sides of portions of s/s mesh that forms the spire.
Using the area method for calculationg the total exterior lighting allowance does not work, produces very low total allowances for the whole facade. We need to use the length of the horizontal component of the illuminated windows and the length of the vertical strips and the area of the spire mesh to calculate the total allowance in order to obtain results comparable to what the lighting designer is planning.
Question is, has any clarification on the use of the lineer option been developed by the USGBC or ASHRAE that may be of use to validate our method of calculation towards the LEED Reviewer?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5915 thumbs up
April 8, 2015 - 9:47 am
I am not aware of any clarification on this issue.
I checked the ASHRAE 90.1-2007 User's Manual and it does not address this issue in any detail.