Thank you all for the responses. I will try to address all the questions here. The piping for the coils is shown below.
@immsk
Has there been a water audit done to see what the actual flow rate and pressure drop through the coil is compared to the original design?
I am not aware of such a study...
We have a air-hot water heat exchanger on an Air handling unit that has uneven heating. Attached photos explain the situation.
The coils are made of copper. The air handlers use 100% outside air. The IR photos show that when the valve opens hot water fills up the supply header but does not...