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# length of overhang based on energy modeling results

I am sorry if my question is so long, Related to the answer of @rpg777, in my previous question here, To find length of my shades, I have run the simulation of two alternatives with two different shading length, one has 1.00m length and second one has 1.20m. and now I would like to know based on my energy modeling result which alternative is better to choose? Thanks in advance for any help and suggestion.

To see the result of cooling/heating I have watched annual overview in OS.

Alternative a)

Alternative b)

To see the result of daylight availability, I ran Radiance in OS and in resultview, I thought that I have to check Daylight sensor illuminance.(but I do not know am I right or not?)

Alternative a)

Alternative b)

To see the result of glare probability, I thought its better to see Mean illuminance map.

Alternative a)

Alternative b)

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The "best" design depends upon several factors -- and their weights, and those weights are subjective. Again this is more of a general design/engineering question and not a building energy modeling question. But we can answer it in the context of BEM as you've provided a lot of good info here about your process.

Your first step of looking at the annual energy end uses is great, and in this case it shows a negligible difference between the two options. Looking at the actual overhang configurations, the energy use data back up the suspicion that there's little difference between the two designs. You need to explore the ends of the envelope further. Again the resources I listed in my response to your other post will be helpful for this. Start with a base case model, with no overhangs at all, to really see what you're dealing with here.

Now in terms of the glare control question, I would look at the useful daylight illuminance (UDI) rather than the mean illuminance. UDI illustrates the percentage of time a given space receives between 100 and 3,000 lux. I really like this metric, both for quantifying the, well, the utility of the daylight vis a vis energy savings from controls, but also the glare potential (or lack thereof), since the metric penalizes a design for over-illumination (>3,000 lux). This is using task plane horizontal illuminance as a proxy, but it's a reasonably quick way to look at a whole space or a whole building. You could also place glare sensors in your model and get annual vertical eye illuminance and draw your own conclusions that way. Unfortunately we do not have an elegant reporting measure that takes this daylight metric data and presents it to you like the default EnergyPlus output (this is a drag). You need to go into the text file output and parse it and visualize it some way, either with Excel or R or whatever. At any rate, the data can be found in the output directory of your run directory, e.g.:

[your_model]/run/[radiance_measure]-UserScript-0/radiance/output/daylight_metrics.csv

I recommend peeping at this video for some more details as well.

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@rpg777 , Thank you for your really informative answer.I have seen your really helpful video as well,(this is my new question that because of images I had to do in this way unfortunately I could not upload them in comments )_any way as a test I ran my model once with NO shading and second time with shading. And I got these results of UDI.

and it would be really appreciated that if I know with these UDIs how can I know using shading for my building is useful? for example may I know what is the difference of UDI= 0.35 and UDI= 0.16 and which one is good?

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The lower the UDI, the less percentage of time the daylight illuminance criterion was met. For example, with shading, the daylight illuminance in the "East_Classroom_GF" space was between 100 and 3000 lux for 16% of the daylight and occupied hours, and equal to or greater than the lighting setpoint (500lux) only 1% of the time (this is DA). Again, "good" is whatever meets your needs. There isn't enough room in a comment to explain this properly, nor is this website the right place for the discussion.

( 2016-07-07 14:31:34 -0600 )edit

@rpg777, Thank you so much.

( 2016-07-11 23:53:44 -0600 )edit