I simulated the amount of airflow through a room but the result was way too high though and I can’t figure out why. I had tried to change the type of ventilation to 1; it led to a different result but one which was even more unrealistic.
It’s the first time I do a simulation so it might be a beginner’s mistake.
tutorialmodell.3dm (89 KB)
airflowing_kahlschlag.gh (561 KB)
Julian,
Thanks for posting. I am thinking that I will change the default values of this component as I am realizing that almost everyone sets up the component incorrectly the first time that they try it. I have opened an issue here and I will make these changes to the defaults soon:
https://github.com/mostaphaRoudsari/Honeybee/issues/547
For your case, you have only one window on one side of your building and so you do not get any wind-driven cross ventilation (only buoyancy-driven stack ventilation from that one window). So you need to set the wind discharge coefficient to 0. The correct way to set up your model for your case is like so:
As you will see in the attached file, you get much lower airflows this way.
-Chris
airflowing_kahlschlag_CWM.gh (552 KB)
Hi Chris,
thanks a lot for your answer!
I think I set it up incorrectly because actually I do want have two windows facing east and west respectively though the window facing west is more than twice as big as the one facing east (I hope this is not critical yet). I updated again, now it says so in the ReadMe and I got volumes between like 3-17m3/s again.
At this point I just stopped and calculated: Is it possible, that an airflow volume of 3-17m3/s in this case is not so unrealistic after all? It would mean, in the most extrem case, bit more 21km/h wind speed at the opening.
What do you think? Is it possible that I just misestimated the values to expect?
You might guessed it: I’m still architecture student. : /
airflowing_kahlschlag.gh (561 KB)
Julian,
21km/h isn’t an unreasonable wind speed at the window but I should admit that the default means of calculating window-based wind-driven cross ventilation assumes that there are even-sized windows on each side of the zone. As such, you might want to make just 2 custom wind and stack objects that both have an effective area of the smaller window but have opposite angles2North (for this, you can use 2 SetEPAirflow components in tandem). You also might want to decrease this area further to account for other obstructions like insect screens (if you have them). If you are mostly counting on the wind, it might also be a good idea to set the stackDischargeCoeff to 0. So, in total, your wind speed is probably a bit less than what you currently have but I don’t think that you are too far off.
-Chris
Thanks a lot!
Dear Chris,
Suppose we have a thermal zone with 2 windows in the same size, one on the north wall, the other on the south wall, which fit the criteria of window-based wind-driven cross ventilation as you explained.
May I ask how to use two setEPAirFlow components in tandem, as you suggested, to specify the _windowAngle2North?
I noticed that in your natural ventilation demo file on Hydra, there are three thermal zones, two of them have windows facing opposite directions. However, only one zero value is assigned to the _windowAngle2North input node on the setEPAirFlow components for the 2) Custom Chimney Object workflow.