Chilled water coils 2

[djacks02]

We know that it is usual practice to pipe chilled water to coils counter flow in respect to airflow. Another words the coldest water on the leaving air side of the coil.

Question, is there any documentation that dictates whether the supply and return should be high or low on the coil?

 

[quark]

Generally air trapped inside, if allowed to go in the direction of water flow, will reduce the formation of vapor lock. As a natural phenomenon air always flows up, so return line should be high.

Regards,

 

[speco]

The most common practice is to arrange the piping to the coil such the the water flow is counterflow to the air. This gives the best performance since the LMTD is higher in counterflow.

It is also good practice to have vent and drain connections at the high and low points on the coil to provide to getting rid of trapped air. These connections also allow for hydrotesting and draining of the coil at the factory. In any closed-loop system, there should be a surge tank at the high point in the system to allow for venting, too.

 

[TBP]

In addition to the any entrapped or dissolved air moving up to be pushed out of the water coil, the water is also warming up, and will tend to rise. The air is cooling, and will tend to fall. The chilled water would go in the bottom, and out the top, the air will go in the top, and out the bottom. If you've got something that's tending to happen naturally anyway, and you can arrange things such that it helps you, why fight it? Use it.

 

[ChasBean1]

quark/TBP: dead on. Use engineering sense per those two posts and documentation isn't required.

 

[lilliput1]

Counterflow is very important for heat transfer. You will not be able to attain design leaving conditions if flow is not arranged counterflow.