Question:

In the context of a naturally ventilated, passive solar building, discuss the interactions between the different pre-dominant heat and fluid flow paths.

Sample answers:

Within a naturally ventilated passive solar building the main fluid flow will come from infiltration and zone-coupled air flow. Infiltration is caused by leakage of air from outside, while zone coupling is caused by pressure differences and buoyancy forces which are due to temperature differences between coupled volumes of air.
Surface convection is the process were heat flux , emanating at an opaque or transparent surface , is transmitted to an adjacent fluid layer. In a building such as this one , this process can cause buoyancy forces within the heated zones and can affect the heat flux within the building.
Shortwave radiation (either directly from the sun or diffusely) can penetrate an exposed building suface, either by transient conduction or direct transmission through transparent structures. This shortwave radiation will again cause buoyancy forces within the building which will affect the heat flux
Chris Stevens, Environmental Engineering, University of Strathclyde, 1996.

The two predominant fluid flow paths within this building would be infiltration and zone coupled air flow. Where infiltration is caused primarily be air leakage from the outside, and zone coupled air flow is driven by pressure differences and bouyancy forces which are the result of temperature variations between the coupled zones.
Within these flow paths themselves there will be fluid to fluid heat exchange. The predominant heat and fluid flowpaths also interact via surface convection within the building. This is the process by which heat flux is transfered from the interior surface to the adjacent fluid layers. This heat transfer will cause bouyancy forces within the heated space which will in turn affect the fluid flow within that space.
In addition some of the shortwave energy incident on the exterior of the building (either as a result of direct or diffuse solar radiation) will be transmitted into the fluid flowpaths within the building either by transient conduction or direct transmission through transparent structural elements. As with the previous case this heat flux will also have an effect on the fluid flow paths.
Clearly when modelling this type of environment there are a large number of interrelated variables which have to be considered before a reliable model can be arrived at.
Thomas Mullen, Environmental Engineering, University of Strathclyde, 1996.