The case of where did the air come from, this Fridays case.

RayWohlfarth

In this weeks case, I talk about how air gets inside a hydronic loop. For years, I read about pumping away and the reasons for doing so and never really got it. I can be thick headed my family says. I couldn't imagine how much difference it would make to have the circulator on the supply versus the return. The other question I had was how could air enter a closed system if the circulator was on the return and not enter if it was on the supply. I will share my epiphany this Friday.

dko

Can't find it at the moment but watched a video demonstration by Hot Rod with a pump setup showing how air can be pulled in through the air vent.

edit: found
https://www.youtube.com/watch?v=jTXEdxGerd8

Derheatmeister

Deep temperature setbacks can also allow Oxygen ingest based on natures ways of trying keep things balanced.

Sylvain

In addition to Hot Rod demo, here an article:
https://www.deppmann.com/blog/monday-morning-minutes/hydronic-expansion-tanks-pumped-into-point-pressure-change/
It also contains a video demo and a link to a B&G manual: "Air Management Sizing And Installation Instructions For Hydronic Heating/Cooling Systems"
I have recently found this site which has a lot of useful information.
Look at the content table on the right side of the "window".

RayWohlfarth said:

The other question was how could air enter a closed system if the circulator was on the return and not enter if it was on the supply.

Answer in the last example of the article.

EBEBRATT-Ed

The way I remember it if you pump away from the ex tank the piping restriction in the system shows up as a increase in discharge pressure and the suction pressure remains at 15psi (or whatever the system requires).

If you pump toward the ex tank the system piping restriction show up as a negative suction pressure if the system has a larger head loss and the suction pressure stays relatively unchanged.

For the average small house it doesn't matter much.

If you pump towards the ex tank and the suction goes minus you can suck air in to an air vent.

RayWohlfarth

Thanks Gentlemen I had heard it could pull it into a vacuum according to an old old BG Little Red School House video.What I didnt realize is air is entrained in the water and the system pressure keeps it managed, When the pump starts, it drops the pressure and allows the bubbles to expand. I love that I learn something new all the time about out industry. https://youtube.com/watch?v=9HynvMU4jO8

Sylvain

RayWohlfarth said:

I love that I learn something new all the time ...

So do I.
After seeing the answer, I searched about air separator and venting.
This caleffi video speaks about dissolved air in water, some PEX tubes being permeable to oxygen and the best place for the air separator:
https://www.heatinghelp.com/systems-help-center/coffee-with-caleffi-air-vents-and-air-separators/

RayWohlfarth

Thanks @Sylvain

leonz

Hello Ray,

I can add to this from my personal experience as well.

Two heating seasons ago I had vacuum condition in my baseboard heating system that occurred between heating seasons that took me a while to isolate.

The vacuum gauge was pegged and It turned out that the packing compression nuts that sealed the
water level gauge in my steel compression were a tiny bit loose and after tightening them a 1/4 turn that eliminated the vacuum.

Since then, I have had no issues, the steel compression tank is 2/3 full of water as it should be and I have lots of heat.

RayWohlfarth

@leonz Isn't that funny how something so small can cause such headaches

leonz

It's nice not dealing with screaming circulator, that's for sure.