Hi to All,
We are modeling 3 buildings interconnected with each other.
A large canopy is covering?the roof of the buildings and?partially shading?the courtyard within these buildings.
Can we model this canopy in eQuest? How?
Can we model its effect on the cooling load of spaces facing the courtyard?
We are?expecting that solar heat gain will be lower on fenestrations of the rooms/spaces facing courtyard due to shading compared to perimeter spaces facing outside the development.
Thanks in advance.
Reniel
Reniel:
What you need is an exterior shade.
In detailed edit mode, go to Building Shell and select Fixed Shades (or a Building Shade, depending on whether you want the shade to be attached to the building - as it rotates, for instance). A fixed shade remains fixed in space. This is a good way to model adjacent buildings.
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Right click on Fixed Shade and go through the dialog boxes.
Kim E Shinn, PE, LEED AP BD+C, CxA
Here is another illustration shading a courtyard of sorts. You're
looking at the dark grey rectangle in both examples.
I have a followup actually for others familiar with creating building
shades - are they any different in behavior from a window shade, or are
they the same thing simply defined in different ways? More
specifically, do window shades shade buildings and can I define building
shades as a means of modeling multiple vertical fins/horizontal light
shades per window?
NICK CATON, E.I.T.
Window shades only shade their parent window, not the walls. Building shades will shade everything in their shadow, and they rotate with the building if the azimuth is changed. Fixed shades also shade everything in their shadow, but they do not rotate with the building.
DAKOTA KELLEY
Thanks Dakota!
This is good to know as I have a situation where it would probably be less work to explore some specific overhang/fin options within my complex eQuest model vs. trying to build a separate model through my more usual daylight analysis workflows.
Bonus points for your response being 10x more clear than my question =)!
NICK CATON, E.I.T.
At the risk of piling on more information than you really wanted:
App G allows you to take advantage of shading ? so, remove shading from your 90.1 baseline.
You can assign schedules, transparency and reflectance to shades. If you want to model the effect of deciduous trees planted near the building, for instance, you can use a schedule to have greater transparency in the winter (for passive solar heating) and less transparency in the summer for shading.
Kim E Shinn, PE, LEED AP BD+C, CxA
Hi!
Thanks for your replies.
It helps us a lot.
On the model that we're working on,
We already did what?everyone suggested.
We modeled the canopy as fixed shading.
To double check if the model is running as what we're expecting based on cooling load fundamentals,
We modeled full opaque canopy (0 transmittance)?and?1.0 transmittance for comparison purposes only.
After running the model, we had weird results:
0 transmittance
Chilled Water - 104.05 MBTU
Space Heating - 74.8 kwh (X000)
1.0?transmittance
Chilled Water - 109.9 MBTU
Space Heating - 96.2 kwh (X000)
Am I modeling it wrong?
Am I missing something?
Are we having the same results especially with the heating consumption?
What are the areas that I should check first before concluding?
Note that we modeled the systems for both as AUTOSIZING.
Thanks for your assistance.
Reniel
?
Without more specifics, I think we can only give you some general advice/suggestions? I haven?t tried this, but if you?re trying to observe results with/without the shade, maybe you should just delete the shade instead of altering transmittance and see if anything changes?
Overhangs/shades/canopies and the like can both help and hurt over the course of the year. From what we?ve heard I don?t think you?re doing anything wrong in application. I might take these results as a sign you need to carefully reconsider your canopy design with respect to how it is blocking sunlight.
Rather than focusing on overall cooling/heating energy spent, you might do well to identify which specific internal/external load components are changing significantly. If you have any daylighting controls specifically, watch carefully what?s happening to your lighting energy spent.
The increase in heating energy is likely because you?ve eliminated a significant amount of solar gains through fenestrations and opaque walls by blocking the sun during heating months. Remember that building shades are shading more than windows!
In the heating months and from an energy-perspective, a perfect window shade blocks only as much direct sunlight as is required to prevent glare issues through windows. Any other direct light is welcome as a free heating source ? both on windows and opaque walls.
The lesser increase in cooling energy probably has a less direct conglomeration of reasons? That it?s relatively minor suggests it could be a lot of things. I would look at whether your simultaneous cooling/heating hours are changing. For review: In cooling months, a perfect shade blocks (reflects away) direct light incident on windows and opaque walls to minimize solar thermal loads, but still lets indirect light inside windows for daylighting purposes without obstructing views to an unacceptable level.
Another potentially odd daylight/thermal behavior interaction I?ve observed: If you end up really cutting down your lighting energy spent, you might observe a corresponding increase in heating energy spent, as you?re effectively eliminating a heating source in the winter by not running your lights at 100%.
NICK CATON, E.I.T.
Another possible issue on the cooling side: In some climates, and in some building configurations, we see very high cooling loads in the fall, winter and spring (e.g, The Middle East). Ambient temperatures moderate somewhat from summer extremes, but the low solar altitudes are throwing radiation load at the windows at a much more direct angle, frequently ?under? the lip of our overhangs and canopies.
Kim E Shinn, PE, LEED AP BD+C, CxA
Thanks.
I appreciate each of your insights.
The project is in Middle East so everybody can have a clearer picture of the error in numbers.
I'll check Kim's point on low solar altitudes.
I just couldn't relate Nick's point on the numbers that I have.
Please take note that the more transmittance I introduced in the courtyard, the more space heating it requires on spaces facing the courtyard and vice versa.
Is it correct?
I couldn't relate it to cooling-heating fundamentals.
Nick, please confirm your point by clarifying these issues.
Thank you so much.
Reniel
Reniel:
Believe it or not, but I think that the program allows for night-time radiative cooling. So, on a cold winter night, without the canopy, the building cools to the black-body of space. With the canopy, that radiative cooling path is blocked and the building retains heat.
Kim E Shinn, PE, LEED AP BD+C, CxA
Happy to help Reniel =),
I suppose I introduced a number of general points regarding building shade effects that will not all apply to your specific project, so apologies if this wasn?t clear ? just trying to feed some ideas to consider.
I think I understand your results and will restate/summarize them to ensure we?re on the same page:
1. Fully opaque (0% transmittance) results in lower energy figures
2. Fully translucent (100% transmittance) results in higher energy figures
3. Heating varies more than cooling.
4. What you find to be weird/unintuitive in your results is that space heating energy rises with transmittance. Put another way (more clear to my thinking): heating energy spent lowers when you introduce a building shade.
To emphasis one of my suggestions: Do you have daylighting dimming/switching controls? Less daylight resulting in un-dimmed light fixtures means more heat incident from the fixtures, and simultaneously less energy spent for the space heating figure as the lights become a more significant local heat source.
Kim?s suggestion regarding retained radiative heat is another possibility ? While I can?t personally speak to whether that?s actually in play in eQuest between building shades and the rest of the model, I?d definitely like to know if somebody is sure of it!
While shades as a general practice will cause energy to rise in cooling months (by blocking solar gains incident on walls/windows), if you have low winter sun angles and the courtyard facades in question aren?t getting much incident sunshine in the first place (being blocked by other parts of the building), then it would be normal for the shades? expected negative winter effects to lower or be non-existent. In such a situation, otherwise smaller effects including retained radiative heat or lighting space heating as mentioned above could cause the energy figures to swing in an unexpected direction.
Again, I can?t offer any specific answers, but hopefully this offers a bit of guidance that will help you investigate the problem. I?d still encourage you to determine which specific space heating/cooling load components are changing ? they may provide a specific clue as to whether these results are to be expected or an indication something isn?t being modeled correctly.
Best of luck!
NICK CATON, E.I.T.