Non-barrier PEX in heating systems

Solid_Fuel_Man

Friend of mine recently dug a trench between his house and garage. Against my advice he put 2 non-barrier pex runs in a 2.5" conduit with 3 90's. This isnt a long run, maybe 30' total (15' each way). 

He wants to put a boiler in the garage/workshop and send heat to the house, and vice versa. 

This would be a glycol loop with a FPHX in the house where an oil boiler is. 

How would chemical/glycol do with this non-barrier tube? I want to try and pull it out and replace, but he said that may be impossible....

hot_rod

The temperature has an awful lot to do with O2 ingress. In your case it sounds like 180F or so in the non-barrier section? So you will have a lot of O2 ingress.

The choice is all non ferrous components, or an ongoing chemical regiment involving oxygen scavengers. I think the open system steel OWF basically add a sodium sulfite yearly to sponge up the O2?

With glycols, the manufacturers offer "boost" packages which probably accomplish the same function, replenishing the O2 scavenger. It wouldn't surprise me if that boost in Na2 SO3.

STEVEusaPA

If it's in conduit, how hard to yank it out and pull barrier pex thru it? And maybe if it's oversized you could go with a smaller pipe diameter.

hot_rod

Electrical conduit with long sweep ells? do they even make 2-1/2", or is that OD he is measuring. What size pex inside? I would guess 2- 3/4 pex would be a tight squeeze inside 2" PVC.

Solid_Fuel_Man

He has three 3/4" water pex in what he called 2.5". I have not seen the conduit, it was behind a pile of building materials. 

I want him to pull it out. He was thinking domestic water, supply&return. I would go with a 1/2" domestic to save space and pull 3/4 supply&returns. 

Originally before he did this project my advice was 1" hePEX S&R in a 4" conduit with a single 90 sweep ell. 

hot_rod

Yikes, pulling Pex through 3 turns! What would help a bunch is if you could warm up the tube some how. At 180 Pex turns into a much softer and easier to manipulate tube.

Zman

So is the non barrier pipe only exposed to the FPHX and associated trim, not the boiler?
If so, it might be easier to make all those parts non ferrous and leave the tubing...

kcopp

Dont you just love it when you give good advice to people...then they go and do whatever they want and expect you to fix it. May be best to walk away from this one.

Solid_Fuel_Man

I'm not going to fix it, he is....or he can use it however he wants to and end up with an expensive water maint program. 

He did a big garage reno and poured a new slab etc. I think this just had no thought put into it, as he really has no experience with this stuff. He is a boiler engineer, but industrial steam planslts and closed loop pex really have nothing in common.  

There will be two boilers, one in garage (wood) which will end up with glycol and this short pex run. The fphx will be inside by his oil boiler. I've suggested he at least pipe the rest with 1.25" iron or copper. 

The 3/4 is a bottle neck and the wrong stuff. 

hot_rod

Such a short run, I'd be more inclined to have him dig it up and do it right?

Ironman

They do make 2.5" electrical conduit and it's not that uncommon, especially in commercial.

Solid_Fuel_Man

We all shoot ourselves in the foot every now and then. He certainly did on this one with the small conduct and the unnecessary bends. It was hand dug and under 4 feet of frozen ground now.

Could this simply be treated as an open system as far as chemicals/glycol are concerned? 

hot_rod

So it is a sealed pressurized system, or open like a non pressurized OWF?

If it is open to atmosphere, no pressure OWF type you do not want glycol. Glycol goes bad quickly if exposed to O2. Even a 5 gallon bucket goes bad when not sealed tightly.

With a closed pressurized non barrier tube system you could use glycol, test it yearly and you will need to boost every so many years.
The indicator is dropping Ph, so the glycol goes in at say 9- 10 ph, drops into the 8's then the 7's, glycolic acid is formed and attacks all the metals.

Dow suggest when it drops into the 7's flush and replace, it would take so much inhibitor to get it back in to the 9-10 ph. Of course they sell glycol I have seen it drop much lower, and usually a history of pin holes, expansion tanks first, is an indication the glycol has gone bad.

Over heating destroys glycol quickly also. Solar thermal that goes into stagnation often can ruin glycol in a years time. 325F is what most glycol is rated for, some of the HD fluids a bit higher. Flat plate solar collectors can stagnate over 400F, evac tube can push 600F.

Solid_Fuel_Man

It's a closed loop pressurized system. 

I just did the flow calc and came up with 20feet of head at 6gpm. That's on the high side of reasonable. At least a 009 or Alpha can take care of it. 

hot_rod

Workable, non barriers is also💰