Sam Ali Posted January 5, 2019 Share Posted January 5, 2019 Hello everyone. I'm new to Cadtutor. I recently started learning Revit. As I was following a tutorial video, I got confused when the tutor connected the return duct to the VAV. I looked online to see if that's possible and found a couple of designs where the duct is connected to the AHU. Why the duct is connected to VAV in some designs, and in others connected to the AHU? I attached the image from the tutorial video. I really appreciate any help from you. Thank you, Quote Link to comment Share on other sites More sharing options...
tzframpton Posted January 7, 2019 Share Posted January 7, 2019 I'm no engineer but I think if the above-ceiling space is not a plenum return space then you have to duct the return back directly to the unit if it's a fan powered VAV unit. -TZ Quote Link to comment Share on other sites More sharing options...
RobDraw Posted January 7, 2019 Share Posted January 7, 2019 That kind of design is quite common around here with VRF becoming the latest in energy efficient designs. This is similar in that the "AHU" is only supplying ventilation (outside) air. The VAV needs more air to condition the space so the room air is returned back to the VAV. There should also be a separate exhaust system sized close to the ventilation air. This exhaust air might go through an ERV for preconditioning of the ventilation air. Quote Link to comment Share on other sites More sharing options...
tzframpton Posted January 7, 2019 Share Posted January 7, 2019 I don't believe the above screenshot is a VRF system, as you would mix your O/A in the return plenum controlled by motorized dampers. The above screenshot shows duct going directly into the inlet which leads me to believe this is supply and not outside air because the R/A is not being mixed. Again I'm no engineer so I could be wrong on this one. -TZ Quote Link to comment Share on other sites More sharing options...
RobDraw Posted January 7, 2019 Share Posted January 7, 2019 It is not a VRF system. I was saying that it is similar to what it being done with VRF systems. I think this might be what is called a Demand Ventilation system. I did it a couple of schools with the same configuration where there was an unoccupied mode in which the ventilation air could be shut down during certain hours. The return to the VAV would allow for conditioning the space without any ventilation air. Quote Link to comment Share on other sites More sharing options...
tzframpton Posted January 7, 2019 Share Posted January 7, 2019 Gotcha, thanks for clarifying Rob. -TZ Quote Link to comment Share on other sites More sharing options...
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