Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question

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

asked 2016-07-27 08:17:09 -0500

hlt's avatar

updated 2016-07-28 03:52:08 -0500

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?

edit retag flag offensive close merge delete


  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?
David Goldwasser's avatar David Goldwasser  ( 2016-07-27 12:08:43 -0500 )edit

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

Julien Marrec's avatar Julien Marrec  ( 2016-07-27 13:40:06 -0500 )edit

Are there any zone or zone group multipliers?

Archmage's avatar Archmage  ( 2016-07-27 14:47:59 -0500 )edit

Hi David, I am using OpenStudio- 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,

hlt's avatar hlt  ( 2016-07-28 02:41:44 -0500 )edit

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

Julien Marrec's avatar Julien Marrec  ( 2016-07-28 06:23:09 -0500 )edit

2 Answers

Sort by ยป oldest newest most voted

answered 2016-09-13 00:32:05 -0500

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.

edit flag offensive delete link more

answered 2016-08-02 11:29:34 -0500

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

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Training Workshops

Question Tools

1 follower


Asked: 2016-07-27 08:17:09 -0500

Seen: 216 times

Last updated: Sep 13 '16