Add the Ability to Model Naturally Ventilated Building Typologies

[chriswmackey]

For a while, I have been curious about the effect of natural ventilation on UHI and I think that we should find some way of adding this in as we build future versions of the UWG. I think we can do it by simply cutting out the cooling and boosting up the airflow to the indoors when the indoor temperature gets above a certain threshold (using the same mechanism that we currently use to account for infiltration). We can have the airflow calculated based on simple orifice equations, which are well-documented in the EnergyPlus reference on WindAndStack objects: https://bigladdersoftware.com/epx/docs/8-7/input-output-reference/group-airflow.html#zoneventilationwindandstackopenarea

[saeranv]

I think this is a good idea as all the variables in the orifice equations are already available to us, and as wind changes non-linearly with height, and urban types (surface roughness) it'll provide useful feedback for different urban typologies.

Regarding the wind equation:

What are your thoughts on accounting for wind direction when we simplify the different wall orientations to a single "infinite" canyon? The area of the windows is already weighted in Dragonfly, but it seems like we should also multiply wind magnitude by the cosine of angle between our "infinite" canyon wall, and grasshopper model wall.

[chriswmackey]

@saeranv , I was actually thinking that, by default, we should assume airflow driven only by bouyancy and there will be a parameter on the building class that adds wind driven cross ventilation in the cases where the user feels this is relevant. I imagine that most tall urban buildings can't easily achieve wind-driven cross ventilation unless they were designed to have a thin profile and relatively minimal interior obstructions.

For wind direction in the cases where there is cross-ventilation, I think we can assume that Half of the buildings are oriented towards the wind and half are not. So we can use an average between these two to assess the total wind-driven air flow.