LBT2PH: Ventilation in ACH

Hi @edpmay, is there a way to specify ventilation rates in air changes per hour? I’m going through your tutorials and the “Set TFA params” command appears to only take m3/h, which means I need to get all the room volumes and make the conversion for each room, then enter it manually in Rhino.

I know you prefer the manual way but in my case I’ve got a fairly large building with many rooms and would prefer to automate this in Grasshopper.

I have tried the following but get an error message: (26.1 KB)

Just realised it works if I give it a base program

However, when I go to the PHPP, I can see that the total ACH is set to 0.25 instead of 0.3 as specified:

Is this because the total ACH refers to the ACH per GFA but what I’m specifying in HB is the ACH per GFA?

Hi @MaxMarschall

Glad you were able to get it working. And yes I think you are exactly right: the difference there is that in PH-models they want to use the ‘net-interior’ volume as the reference volume for all of those items (ventilation, infiltration) whereas E+ uses gross volume. So yeah: 0.25ACH wrt the gross will be a higher ACH wrt the net. Frustrating I know - would be much easier if everyone used the same reference dims.

But to your question: no - I hadn’t thought to include a ‘setter’ for ACH-based ventilation flow I’m afraid. That’s a great idea though and I’'ll be sure to add to the V2 we’re working on. For the time being I think you’d need to calc the airflow rates manually for each space I’m afraid.

Sorry about that!

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Thanks for clarifying and no need to apologise! Thanks for putting out this great tool and developing it further.

I think that this has mostly been addressed via this topic:

The only thing that wasn’t really addressed there is the ability to get net volume instead of gross volume. I think this is something that I would add if I addressed this issue:

So, if this is something that you think you’ll want sooner than later, than :+1: that issue and I’ll prioritize it.


Hi @chris. I know this quite a old post but I was curious to know if this feature will be implemented soon!. Any thought on this?

There have just been other things that have been taking priority, @Asisnath . The honeybee-energy OpqaueConstruction classes already has a thickness property, so if someone wanted to implement this, all that they would have to do is subtract these thicknesses from the floor areas. The only part that requires a little extra work is identifying the edges between Walls and Floor Faces but this should be straightforward with ladybug_geometry.

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