I want to run a simulation to look at wind and temperature around buildings. The case is located in a high latitude and very cold climate, we want to look at the air temperature and wind speed in outdoor spaces near the exterior walls at a very cold day (-30 Celsius) to be able to predict peak of energy demand. I followed the instructions for solar heating and wind load and have some questions:
- Does a very low air temperature e.g. -30 pose a problem for simulation? The tutorial for solar heating says: "Apply the sky radiation temperature to the exterior surface of the dome. This temperature typically falls within a narrow range, roughly between 0 and 30 °C."
- The instructions for dimensions of exterior air volume differ between wind and solar analysis. The solar heating tutorial suggests to build a volume 20 times wider that the objects and with a height 10 times larger than height of the objects. These dimensions for wind analysis are much smaller (width 4 times of the actual object and the height is suggested to be 3 times bigger). Wat dimensions ARE approapriate hen döing Båth tonetter?
- Is there a way to include indoor air temperature of buildings, without the need to create air volume for indoor spaces?
Solved! Go to Solution.
Solved by Jon.Wilde. Go to Solution.
I can help here I'm sure
Thanks,
Jon
Many thanks Jon,
For the exterior volume, I used width and length in accordance to wind loading instruction (width 5 times bigger and length 6 time bigger than dimensions of the object) and for the height, I made external volume's height, 10 times bigger than the the object as suggested by solar heating tutorial.
Regards, Saeed
OK - feel free to share an image if you like, tough to picture.
Thanks,
Jon
Two images are attached, one showing the exterior and the other is a closer look at temperature patterns. I have faced some other issues during/after the simulation and I would like to ask about them:
- I have used concrete for the walls, air temp outdoor is -30 and indoor air temp is +20, wind vel: 3.6 m/s. looking at the temperature, the air gets pretty warm near the walls (5 to 10 C). I thought that had to do with the conductivity value of concrete. then modified concrete and changed the value to 0.4. the results didn't change that much between to scenarios one with default concrete and one with modified. Are there some other parameters to modify?
- The wind tutorial suggests to have Automatic Forced Convection = On if heat transfer is important. When I used this the simulation got interrupted (Message: Analysis has stopped because the Solver has exited Unexpectedly). I ran the simulation without AFC and it worked successfully. (Sorry if it was a naive question. I have a background in architecture.) Is it alright with Automatic Forced Convection = off? and the gravity setting (earth - 1, 0, 0)
To include humidity to external volume, I chose moist air and assigned temp and humidity to it, then run the solve with humidity on. Is there something more to consider regarding humidity?
Best regards, / Saeed
The air looks great, nice 🙂
Make sure you have not applied a boundary condition internally to the model, they can only be on a boundary - hence my suggestion to suppress the internal air from the mesh, creating a void where you can apply a temperature. If you sandwich a boundary condition between two materials, you will have problems.
It looks to me like you have the internal 'air' meshed and not supressed.
AFC runs flow first and thermal second. This is only OK if you are not looking at natural convection, where they are related to one another. So if you are running with gravity (do you need to?) I would leave it off as you have.
Hope that helps.
Thanks again Jon,
The gravity settings (Earth, 1, 0, 0) was suggested in solar heating tutorial. (http://help.autodesk.com/view/SCDSE/2014/ENU/?guid=GUID-14DA299D-BD93-44E1-BCB6-0C924EF3FD4E)
Kind regards/ Saeed E
Hi Saaed,
No problem. We just need to be sure we understand why we are applying everything. We need gravity if we are looking at natural convection, so that as the air density reduces it knows what direction to rise.
As you have forced convection here, the effect is likely to be very small indeed and can typically be ignored 🙂