QUESTION:

Am I correct in believing windows are "open" when Natural Ventilation is selected in Zone Management and "closed" when "None" is selected?

Also, when opening windows is there a need to alter Air Change Rates in Zone Management (If not, what does this refer to?)

ANSWER:

When a zone's HVAC system is set to Natural Ventilation, ECOTECT assumes that the occupants will automatically open the windows whenever the outside air temperature is within the defined comfort band or closer to it than the current indoor zone temperature. If not the windows are assumed closed.

During an inter-zonal adjacency calculation ECOTECT calculates the potential for cross-ventilation, looking at the area and orientation of each window in each zone (Note that it only looks at this on an individual zone basis - it cannot work out how air flows through and between zones - for this you will need CFD). This allows it to apply an additional air change rate when the windows are opened based on the total zonal window area and a factor based on the area of windows in both adjacent and opposite walls.

You are right in thinking that setting a zone's HVAC system to None assumes the windows are never opened and uses only the defined zone air change rate.

If you want to manually control the ventilation in your model, to set up a night-purge system for example, you can set the zone HVAC system to None and then apply a complex schedule to the air-change rate - effectively simulating the opening and closing of windows at times of your own choosing. However, in this case you have total control over the amount of air flow by setting the maximum value and using the hourly profiles in the schedule to moderate it.