Hydronic System - Routing - Prevent Air Trap

[Vusal Quliyev]

Dear HVAC Experts,
As you know there are some rules about hydronic heating systems routing(i.e. Fan Coil Unit system) in order to prevent air trap in the system which will lead heating capacity reduction.
I prepared one example and need your thought about this situation:
- High rise building.
- LTHW Fan Coil system for heating.
- Pipes enters to the level goes down connects to main pipe at corridor. Then pipe connection will be from up only until fan coil units. (See photo for information)
- We have Automatic Air Vent at the top of the shaft.

What do you think? Is there any risk of air trap in the system?

I wonder if there is any research or standard about this routing?

 

[nuuvox000]

We typically put an air vent at the top of each fan coil.

 

[HVAC-Novice]

Put de-aerators in the highest pipe based on flow direction. so for supply and return they will be on opposite sides. Fluid flows horizontally and at the elbow that drops down, there should be the deaerator.

 

[Vusal Quliyev]

Dear Experts,
many thanks for information.
Any research information about this topic?
We already have air vent at fan coil units and air vent at top of shaft. Do i need additional air vent? Where i should put this vent. Can you point in the picture please.

 

[HVAC-Novice]

what research information do you require? air bubbles rise in water. Water flow can carry air with it (if above a certain speed, typically 2 fpm), but not so well when flowing downwards. Buoyancy doesn't need further proof or research

Imagine when a system is built, it is full of air. then you fill it with water (typically somewhere at the bottom where the boiler is). without fluid flow you can imagine where air collects. and with pump running, you can imagine where the water has a hard time to move the air with it (i.e. flowing downwards. that is why I said above to put the deaerator in the highest horizontal pie at the end (where it flows toward right before the pipe drops down).

Keep in mind, air also will be dissolved from the water during operation and at lower flow. so you will have air for some weeks of operation and slow velocity. so that is why I recommended de-aerators where I did.

Your system may have multiple high points, so you need more than one location.