I have a model with a Chiller hooked to 2 Air Handler Units as depicted in the schematic below.
How do i model the removal of air (50% and 80%) from each zone through to the Exhaust in OpenStudio.
In the case depicted, the easiest is to use a separate AirLoopHVAC for each AHU/Zone combination.
By default, E+ assumes that the ventilation is balanced, so the supply to your zone is the exhaust from your zone. Considering this, you just need to say that for AHU 1 you want 50% of outside air, and automatically 50% will be relieved (exhausted to the outside).
This will be done in the Controller:OutdoorAir attached to the AirLoopHVAC:OutdoorAirSystem.
Think carefully about how your unit is actually working:
If variable volume, do you want the outside air to be 50% of whatever the flow is at that moment, or do you always want a fixed amount like X m3/s or CFM?
If you always want X CFM, just fill the Minimum Outdoor Air Flow Rate. (Or if you have specified the correct DesignSpecification:OutdoorAir, you could let it as autosized)
Minimum Fraction of Outdoor Air ScheduleYou can always add a return fan on your AirLoopHVAC to account for this fan power (see picture above, I have one on the return), though remember it will handle the return air, not just the relief air (but your AHU handles the difference between the two, so you can always do a weighted average of fan power).
One other way would be to use a Fan:ZoneExhaust, but it'll be more complicated and not worth it in your case considering your airflow is coming from an AHU and is balanced. (In OpenStudio under the Thermal Zones tab, you add Fan:ZoneExhaust in the Zone Equipment Column. You won't see it under the HVAC system tab.)
PS: the schematic is slightly confusing, it makes it look like the chiller is part of the air loop. Here you only want to deal with the airflow so you could just exclude it.
To add to Julien's answer, just replace his single speed coils with a Coil:Cooling:Water and connect it to a plant loop with chiller.
Thanks Julien Marrec, where do I find DesignSpecification:OutdoorAir?
@MatthewSteen: I didn't think about putting a screenshot relevant to the chiller situation, good point.
@tajjmann : Multiple places: Space Type and Facility. Typically you should specify it at the Space Type level and then just assign your spaces to said space type (makes more sense). By the way, mark the answer as accepted if you're satisfied so we can close the topic.If not satisfied, let us know what's missing so someone can take a shot at it.
Sorry Julien: I couldn't figure a way around marking the answer as accepted. Finally done. Thanks foe the assistance.
Hello @Julien Marrec, I need to specify "X % of outdoor", could you elaborate on how to do that in "Minimum Fraction of Outdoor Air Schedule"?
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