How does IES calculate fresh air loads

[agoyal]

Hi all,

I'm looking to understand how IES is actually calculating the fresh air loads.

Inputs are floor area, occupancy, outside air supply rate (or aux vent depending on how you want to input the information), occupancy profile and outdoor conditions based on the ApLocate information and weather file.

Does IES use the dynamic weather file to calculate outdoor rate (i.e. is it calculating the heating/cooling load using the per hour outdoor conditions) or is it using the design outdoor condition for summer and winter in ApLocate?

Regards,
Anita

[Complex Potential]

Hi agoyal

If you are running a dynamic simulation then the fresh air load will be based on the dynamic weather file external conditions assuming you set the supply condition to be external air.

If you set the supply air external condition to a specified temperature then the room load seen in vista will be the difference between the room temperature and the supply temperature. In such a case, the air side AHU load component (to go from external to supply temperature) would be seen under the building variable section of vista.

Hope this helps.

CP

[agoyal]

Thanks for the response. That does help. I have another question on the same topic.

When I go into vista, what is the best way to take out the fresh air load for heating and fresh air for cooling?

[Complex Potential]

Assuming you have set the fresh air through the air exchanges tab and set the adjacent condition to external air then it should show up as a room variable under "aux vent gain".

If you have set the adjacent condition to a specific temperatre then it gets more complicated because the load then moves from the room to the plant.