Hydronic heating help.

[Roundgunner]

I built a 1200 SF apartment above my garage for my daughter and her family. I used ½ inch pex under the floor. The heat comes from the outdoor wood boiler water on the return to boiler run after it has gone thru my house by 2 closely spaced Ts on the 1” main loop. I have a mixing valve to keep the heat under the floor at 125 or less, it is a nice heat and I wish I had it in my house. This system has been working for 4-5 years now.
The problem is that I have 3 zones for them, each has it’s own pump drawing from a 1” into the ½ “ through a manifold. One of the pumps sometimes becomes air bound and free spins. Once when I was not home to shut it down it cooked the bearing. I replaced it and now the new one has become air bound already this year. I cannot understand why it gets air.
This zone only has 2 loops off the manifold, they heat the bath room then each drop down 10 feet to go thru a baseboard to give some heat to a hallway and a pool room we don’t use during the winter. The water goes back up and into a return line with a check valve.
I don’t understand the terms describing the power of the pump. It seems like the weight of the water going down 8 feet would equal the weight of the water being lifted back up the 8 feet to the return manifold. I’m afraid the pump is cavitating. I’m including some photos to try to help understand the layout of the system and problem.
I would like to understand the problem so I can find the fix. Any thoughts would be great!

 

[Roundgunner]

The insulated 1” lines are supply and return from the OWB running across the garage ceiling. The uninsulated 1” furthest from the garage door spring is the supply line for the upstairs with a T to the pump. The manifold breaks it down to 2 ½ inch lines.

 

[Roundgunner]

This shows one loop dropping down, passing thru the wall to go thru the base board and return back up to go to the return to boiler. You can also see one side of the second loop coming down.

 

[Roundgunner]

This shows the second loop dropping down, passing thru the wall to go thru the base board and return back up to go to the return to boiler.

 

[Roundgunner]

 

[E Yoder]

A couple questions:
Is the pump that's making issues strapped horizontal up in the ceiling and is it higher than the top of the wood boiler? If so that's a good way to trap air bubbles. It's in a vacuum if it's an open system. The slightest leak can pull in air.
The lower you can get the pump and mount it vertical can help.
What wood boiler is it?

 

[E Yoder]

More details on the piping would help too. Small things can sometimes make a big difference.

 

[jebatty]

Circulators are not pumps. Look at lack of Net Positive Suction Head as the cause of your problem. Your may be able to figure out what can be done to solve your problem by reading up on NPSH.

Pumps - NPSH (Net Positive Suction Head)

An introduction to pumps and the Net Positive Suction Head (NPSH).

www.engineeringtoolbox.com

 

[Roundgunner]

A couple questions:
Is the pump that's making issues strapped horizontal up in the ceiling and is it higher than the top of the wood boiler? If so that's a good way to trap air bubbles. It's in a vacuum if it's an open system. The slightest leak can pull in air.
The lower you can get the pump and mount it vertical can help.
What wood boiler is it?

Profab Empyre Elite II 200
Those pumps and the booster pump on the 1" main manifold are about the same height as the OWB. The Empyer self stores about 125 gallons and will idle at 180 then kick back on at 175. I have this pipe diagram and photos of the main distribution manifold in the garage.

 

[Roundgunner]

The photo of the front of the house may help understand the piping challenges.

 

[Roundgunner]

Circulators are not pumps. Look at lack of Net Positive Suction Head as the cause of your problem. Your may be able to figure out what can be done to solve your problem by reading up on NPSH.

Pumps - NPSH (Net Positive Suction Head)

An introduction to pumps and the Net Positive Suction Head (NPSH).

www.engineeringtoolbox.com

Thank you. I didn't understand any of that except the general idea of lowering the pump. I will try to bring it down the wall on the outside of the drywall to see how it goes.

 

[E Yoder]

It's a complex enough piping situation I'd have to actually see it to pinpoint what specific changes need to happen. Details really matter in something like this, pump sizing, trapping air, flow rates, which circs come on when, (they can affect each other) etc. What was mentioned about not enough pressure on the inlet of the pump/circ could very well be an issue.