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daylighting controls and arrows

asked 2016-11-30 16:18:27 -0500

Matt Koch gravatar image

updated 2016-12-01 13:24:43 -0500

So, I am continuing to try to figure out how to use daylighting controls. In a particular, I am running one model with and another without daylighting controls in each exterior windowed zone. I created the one with form the one without by using the "Add Daylight Sensor at the Center of Space" measure. By the the way, that alone was not sufficient, I then also had to manually add illuminance maps for each daylighting controlled zone, because OpenStudio would show an error without them - is that intended behavior?

Anyway, it turns out, with an Illuminance Setpoint of 45 fc, I use MORE electricity with daylighting controls than without daylighting controls, and I am puzzled by that. My windows have U-0.7, SHGC-0.25 and VT-0.275, so granted there is not much daylight to begin with. Also, my Minimum Light Output Fraction is 0.2, with a Minimum Input Power Fraction of 0.3. Furthermore, I have selected Continuous/Off for the Lighting Control Type, plus 1 as the Number of Stepped Control Steps, 1 as the Probability Lighting will be Reset and 1 as the Number of Daylighting Views.

Any thoughts on why daylighting controls might cause more energy usage in this scenario?

Furthermore, I noticed that the daylighting controls in the SketchUp plugin have little arrows associated with them. Is there a particular direction these arrows should point in - towards the windows, perhaps? Could misaligned daylighting controls be the reason for the above observations?

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answered 2016-12-01 09:38:19 -0500

Alex Vlachokostas gravatar image

Just some thoughts:

-The BCL places the Daylight Sensor at the center of the room (as its name implies). Maybe your room is too deep and the window size is small. Therefore a daylight control in the middle of the room might work to your disadvantage. The daylight sensor keeps trying to meet the 45 fc target and as a result, it overworks the electric lights.

-The OS daylight sensor has a horizontal arrow which should be pointing to the window and a vertical arrow that should be pointing up.

-Action items: Change the location of the daylight control to a one closer to the window. Also try: 1, ! Lighting Control type.

Hope that helps.

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Thank you Alex! My rooms are fairly narrow, and my windows fairly tall, so location in the center of the room should be OK. But, as it turns out, my original message was based on a false analysis. Basically, instead of comparing a case with DCL to a case without DLC, I accidentally compared a case with DLC using a reference glazing to several other cases with DLC using alternate glazing. So the odd behavior was almost certainly caused by the varying glazing properties. And thanks for clarifying the arrow directions!

Matt Koch gravatar image Matt Koch  ( 2016-12-01 13:18:20 -0500 )edit

However, now I am looking closer at the results of a case with and without DLC, using the same glazing. In the EP Lighting Summary, without DLC it has 58,800.0 W & 684.9 GJ and with DLC it has 55,742.4 W & 471.1 GJ. The 58,800.0 W seem to be a direct result of summing up the products of area and lighting power density for each zone, while I suppose the 55,742.4 W reflect the benefit of daylighting.

However, in the EP Demand Summary, I see 92,920 W for both without and with DLC. Where might this number com from? Especially since the EP Usage Summary still shows 684.9 GJ and 471.1 GJ?

Matt Koch gravatar image Matt Koch  ( 2016-12-01 13:27:39 -0500 )edit

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Asked: 2016-11-30 16:18:27 -0500

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Last updated: Dec 01 '16