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# Lighting energy consumption of 15th floor is higher than 14th floor.

I am modeling a 15-story residential building. Each story has 4 apartment units. I have two problems.

Problem : Lighting energy consumption of 15th floor is higher than 14th floor.

Case A (See images): I modeled 4 thermal zones (each include 15 vertical apartment units). The result of lighting energy consumption of different floors: 1-Floor: 9895, 2-Floor: 9890, 7-Floor: 9560, 14-Floor: 9502, and 15-floor: 10068 kWh. There is big jump between 14th and 15th floor. Lighting energy consumption must decrease, not increase. After adding a 16th floor, I re-simulated the 15th floor, then the result dropped 9392 kWh. How it is possible that the lighting energy consumption of 15th floor is higher than 14th floor? How can I fix this problem?

Case B In order to solve this problem, I considered each apartment unit as a single zone and I created 60 zones in total. And re-simulated. Average ligthing floor consumption is 11819, Which is higher than all above. How it is possible?

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3
1. What simulation engine are you using?
2. Are you using daylighting controls?
3. Have you confirmed that the lighting inputs and geometry/floor area are the same on each floor?
( 2016-07-27 12:08:43 -0600 )edit

Can you upload the images now that you have a bit more karma please?

( 2016-07-27 13:40:06 -0600 )edit

Are there any zone or zone group multipliers?

( 2016-07-27 14:47:59 -0600 )edit

Hi David, I am using OpenStudio-1.11.0.4313b0e0d9-Win64. Radiance Parameters : Coarse, the default one. I modeled in Sketchup 2016. Lighting Control Type: Continuous. I copied and paste the first floor for 15 times vertically. So, the lighting inputs and geometry/floor area are the same on each floor.
Hi Julien, how do I upload pictures, the attachment or upload option is gone. Hi Arhmage, No, there are not any zone or zone group multipliers.
Thank you,

( 2016-07-28 02:41:44 -0600 )edit

Hum you might need 20 of karma, I'm not sure

( 2016-07-28 06:23:09 -0600 )edit

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The mid floors make sense; less ground reflectance going up. It's consistently your top floor that is the anomaly.

In that case, you may have some different construction materials happening that are changing how much daylight is bounced around the room. Since the top level is the driving factor, check to see if you have a different internal reflectance going on with the underside of your roof surface as compared to an internal ceiling surface.

I had something similar happen once when modeling radiant surfaces vs non-radiant surfaces. It took me HOURS to figure out what was going on, but the floor construction was the culprit.

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I wonder if perhaps your ground plane is too small. You might be getting a different amount of ground glow at the higher floors.

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Last updated: Sep 13 '16