Questions about wind pressure coefficient in natural ventilation

Hi,everyone. I’ve been using “SET EP air flow” to simulate a natural ventilation, but i can’t find where to input the wind pressure coefficient value from different angles.
So do anybody know how to input these data?


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The EP_Airflow component models ventilation air flow rate as function of wind speed, and stack-effect, or an input design flow rate. So it isn’t simulating a pressure difference to calculate ventilation rates. For that you need the EnergyPlus methods from the Airflow Network Group, which hasn’t been integrated in Honeybee yet. As such, it doesn’t take wind pressure coefficients as an input.

If you have wind pressure coefficients from a uniquely sheltered site, and want to understand the ventilation impact then at least one of these methods, the wind and stack ventilation method via the EnergyPlus’ Airflow Group won’t work. It’s based on the vector sum of the volumetric flow of local wind speed, and stack effect velocity, at your zone height. So rather then wind pressure, that aspect of flow rate is approximated from the wind speed and direction, derived from the wind speeds at the airport station, and can only account for changes in height and direction of wind - not local geometry. If that’s all you’re looking to account for, it’ll work, but not if you’re looking approximate complex local site conditions.

However, there is also the design flow rate method (which HB does have). I’m only speculating here, but I wonder if you can find a way to generate a list of design flow rates (i.e flow/area, ACH) using your wind pressure coefficients, then perhaps you can account for local conditions reflected in your wind pressure coefficients. I’m thinking specifically of what some of the Butterfly users were suggesting here: Wind pressure on facade to calculate infiltration rate - Another potential way to link Butterfly to Honeybee.

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Thanks for your detailed explanation. I will try to find that.


@SaeranVasanthakumar @HongningLan


Just wanted to check if there are any developments regarding the integration of Cp values (acquired through CFD methods) in Honeybee (and in turn, EnergyPlus)

Many thanks in advance,



I’m not working on any specific pipeline for bringing CFD outputs to EnergyPlus, however I will be working on integrating the EP AirFlow Network into Honeybee[+] soon, which can be improved with pressure coefficients from a CFD study (I’ve done this in the past).