Utilizing Fan Coil Unit return to fullfill fresh air requirements

[tj00889]

TL;DR

Hello,
I'm currently working on an HVAC Villa project in Dubai where the client has requested that he does not wish to pay for a dedicated fresh air fan to provide fresh air. He added that the common method of doing this in commercial projects in Dubai is to extend a fresh air duct from outside to the FCU return plenum as shown in the drawing. Can this provide sufficient control of how much fresh air will enter to be compliant with ASHRAE 62.1 and what problems can I expect.
Thank you very much

 

[russ_watters]

Great question, with multiple facets/layers. I'll get back with more when I have more time, but yes you are right to be concerned about outside air/62.1 compliance. Also, this configuration will not adequately control humidity. It's a bad idea, but unfortunately a common shortcut.

Question for you: are the fans constant or variable speed? Always running or cycling?

 

[tj00889]

Great question, with multiple facets/layers. I'll get back with more when I have more time, but yes you are right to be concerned about outside air/62.1 compliance. Also, this configuration will not adequately control humidity. It's a bad idea, but unfortunately a common shortcut.

Question for you: are the fans constant or variable speed? Always running or cycling?

The fans are constant speed and cycling.
What I am worried about is if the positive pressure buildup in the room would stop fresh air supply all together. There is also the issue that seeing as there is no way to maintain the building at positive pressure with this configuration, I was wondering if there is anything in ashrae i could use that states that maintaining the building at positive pressure is a requirement or at least a suggestion for better indoor air quality