HW Air Separator / Exp Tank Location

[BronYrAur]

Attached is a Thermal Solutions sketch showing the air separator on the leaving side of the boilers. I understand this from a temperature/dissolved air perspective, but this puts the expansion tank on the discharge side of the pump. That is unless I put the expansion tank on the suction side and air separator on the discharge side. Historically, I have always kept the two close together.

My system will be as shown with only boiler pumps and zone pumps. there will be no "primary" pump circulating the main loop between boilers and zones. the boiler pumps will handle all of that circulation. Should I split them up, put them both on the suction side, or leave them where shown?

Thanks for your feedback.

Steve

 

[ChrisConley]

As the expanion tank as the 'point of no pressure change' in the system is located downstream of your circulators means that your primary boiler circulator/system circulators will be dropping the system pressure by their head throughout the entire system. If the boiler pumps have enough head this can drop you to negative, regardless you can have air entrainement problems.

I'd move the expansion tank to the suction / return side of the assembly. Air seperator works better with hot, low pressure water. If you can't have both, then hot is good.

Constant speed or variable?

 

[walkes]

A few thoughts...

Are the boilers capable of variable flow? If they are you could replace the boiler pumps with modulating two-way valves and put the circulator on the main loop downstream of the expansion tank location.

The way you currently have it piped the flow may reverse in the main loop. When you have a circulator there it would probably have a check valve.

The extra circulator in the main loop may not be a bad thing, the pressure drop would be minimal. Look at the overall pumping/head loss numbers.

 

[BronYrAur]

Thank for the comments. I'm trying to avoid another pump and would like to keep constant flow with the individual boiler pumps. I think I'll just move the ET to the suction side if there are no issues with that.

 

[sspeare]

Listen to ChrisConley. Whatever you do, get that expansion tank as close to the SUCTION side of your pump as possible, And, per walkes, you should consider a circulator in the "main loop".

 

[hollandhvac]

I have downloaded a PDF once about expansion tanks, which I wanted to upload, but the system does not like it.

The document title is Practical Guide; Understanding of expansion taks ASHREA Journal March 2003.

May be google it and you can download it from there.