“Trane” air handler vents, coils

Mx2

I’m observing multiple central heating and cooling coils (4’x10’) in air handling units to maintain facility temps. On the side, towards the top of each air handler a 1/4” pipe exits the unit and is labeled “vent” where it 90s up and goes to a valve and the valve is closed and plugged.
The boiler is in adjacent room, (water tube boiler) glycol/water mix, there are the usual air separator etc.

Question is: i’m curious why there are no individual active vents on these coils? (in my mind I am trying to reason the difference between a large commercial system versus a home baseboard system.) The 2” inlet and outlet to each coil is in the center so I see a potential of air being trapped, so I’m not sure if this has been overlooked? Not an issue(?) or engineer, expected those to be manually manipulated if the system is ever opened after start up(?) or maybe they’re just not needed in such a system.
Your thoughts?

Thanks in advance.

ScottSecor

I suspect there may have been an automatic air vent installed in the top of the threaded ball valve. Perhaps it was removed as it was leaking or on rare occasion sometimes they can allow air to enter the system.

If the air handler is providing plenty of heat and cooling, I would suggest leaving it alone. If there are issues, I would install a drain cock in the top of the valve, hook up a short garden hose and bleed any air stuck in the coil.

EBEBRATT-Ed

It's because of the glycol mixture. Glycol tends to foam and doesn't get along real well with automatic air vents. Usually with glycol you install some automatic vents to help vent the system and then either remove them or leave the vent in place and shut the valve.