Could oxygen level in hydronic heating system be too low? 4

[payton34]

A question has been raised in a Canadian pulp mill. Could the O2 level be too low causing the system to airlock and reduce heat transfer efficiency. We all know about diffusion but what is the limit?

 

[GMcD]

Hmmm sounds like it's more simple- too much air in a hydronic pipe? Vent the air out, eliminate air locks. Normally one does NOT want very much O2 in a hydronic system as it will corrode ferrous components pretty quick. The whole idea is to keep the friggin' air OUT of the hydronic system in the first place. The only time air/O2 will diffuse through hydronic pipes on a molecular scale is in many types of plastics, non-oxygen barrier piping.

 

[payton34]

I'm just wondering when is too much of a good thing not a good thing? The industry standard for O2 diffusion rate is 0.1/liter/day at 40 C. When does dead water become an issue? Marginal quality water can lead to the delopment of scale, sediment deposits, or the creation of sludge in the heat exchanger which will reduce heat transfer efficiency. Pulp Mills spend millions on heat.

 

[GMcD]

I'm not sure what that "industry standard" is that you refer to - is it for plastic pipe? steel or black-iron pipe? What wall thicknesses?

Normally, in my world of Building Hydronic systems, after the initial fill with clean water, it's treated with inhibitors and other chemical treatment to remove minerals, scale, sludge, etc. AND some kind of permamanent air extractor (Airtrol) is used to remove all the air from the system. If an anti-freeze mixture is required, then inhibited glycol of various types (as required for the application) is mixed in to the system. Some other systems such as geo-exchange systems, that may run at low temperatures, sometimes use a methanol solution for anti-freeze to keep the viscosity in control.

 

[payton34]

The industry standard is for reference only. Its the German Industry Standards(DIN). It does refer too plastic pipe.

In your opinion there is nothing good that could ever come from infusing the water in a hydronic heating system with Oxygen. At any level for any reason.

 

[GMcD]

Not an opinion, but a fundamental fact. Dissolved oxygen in a closed loop hydronic system will lead to all sorts of operating problems. Read up on hydronic heating systems for the last 50 years and note that the key fundamental issues are bleeding air out of the systems, and using proper chemical treatment and inhibitors to minimize dissolved oxygen in the fluid.

 

[leDouche]

GMcD...I totally agree with you. I am in the Testing, Adjusting, and Balancing field. The largest hurdle I have to overcome when working on a hydronic balancing project is AIR in the system. There is nothing worse, in my opinion. An Airtrol (depending on what type of Airtrol)will take the dissolved air out of a system at or near the pumps, and air bleeders installed at the lowest point of solubility (generally the highest point of the system) will take the air out at that point. I have yet to see an enclosed hydronic system where air is a helpful factor.
SO...Bleed air, fill with liquid, repeat until ALL of the air is out of a system. Keep in mind that a lot of air bleeders installed at the high point WILL let air IN to the system if it is not 100% full. Shoot for about 10 psi at the high point. Sometimes, perhaps on a shutdown or something similar, it seems that air will find it's way to the high point, rather than being entrained "midstream"...so my point is, it may be helpful to shut a system off and wait for air to bleed out.
I apologize for the lenghty reply, I am sure there is a thread on this topic somewhere else...

 

[payton34]

I'm not talking about air but infusing the water with Oxygen for time to time.

 

[quark]

Can't you say what is bothering you? Generally, there are no advantages but all problems if you have air or oxygen in your system, unless you bother about aerobic micro oraganism

 

[lilliput1]

Air bubbles & low velocity vs turbulent flow will decrease heat transfer.

 

[payton34]

What about a mircoporus filter that the water in the closed loop would bypass through that would filter any salts or any mirco impurities from the stagnet water?

 

[GMcD]

I think we are still not understanding what the specific issue is - as I've said above - oxygen in a closed loop hydronic heating systems is bad! Don't do it! Get it out! What specifically is the problem you are trying to solve? If the heating system is a closed loop, where are these salts or micro-impurities coming from? Do you not have a proper strainer and sidestream filter at the circulating pump station?

 

[kenvlach]

payton34,
"PEX Tubing is used to distribute water in PEX Plumbing, Radiant Heat, and other Hydronic Heating Systems. When using PEX Tubing for heating purposes, Oxygen Barrier PEX such as ThermaPEX, Wirsbo hePEX, Mr. PEX-al-PEX, and Multicor PEX-al-PEX Tubing should be used."

http://www.pexsupply.com/CategoryPr...tm_campaign=PEX+Tubing&osadcampaign=googlePex

FYI, Oxygen Barrier means keeping oxygen out of the system.