Radiant heat

[Hangernail]

I recently built a new shop with in slab radiant heat. The heat source is an outdoor wood boiler that circulates water through a heat exchanger. The radiant system is a closed loop system with glycol/water mixture. It's been running for about a week and it just doesn't seem to be getting warmer than 10 degrees. The boiler pipes are circulating fine at roughly 180 degrees and the glycol in the closed loop seems to be getting heat from the exchanger (180 degrees at heat exchanger and 100 at supply manifold after mixing valve). The returns have never got any warmer than about 65 and the temperature in the shop has never gotten above 10 degrees Celsius. I have tried a few times to purge more air out of the closed loop and am not having any success. Any ideas or suggestions would be much appreciated.

 

[FishScreener]

Did you insulate under the slab? You have a Delta T, of 115-degrees, so the heat is going somewhere.

 

[Diehard]

"(180 degrees at heat exchanger and 100 at supply manifold after mixing valve)" sounds like a big drop.
What is your arrangement?
Did you use PEX tubing?

 

[Hangernail]

Did you insulate under the slab? You have a Delta T, of 115-degrees, so the heat is going somewhere.

I put 3 inches of rigid insulation under the entire slab

 

[Hangernail]

This is a picture of the complete setup

 

[Diehard]

Why not adjust the temperature a bit higher to your manifold? I thought I saw PEX says up to 115 degrees.
Don't know what the flow rate is on that circulator but I would think having a little higher flow rate would help.
Although from what you say and how it looks, I can see where purging it properly could be a challenge. Seems like you need another hose end valve and possibly an isolation valve to help direct the purging through all sections of piping.
You said. "you have tried a few times to purge more air out of the closed loop and am not having any success.", which sounds like you have reason to believe there's more air in thee. Since it's a glycol loop, I assume you have to pump it through from a glycol source. A connection to enter the closed loop and a connection to return to your "purging" pump.

BTW...Where I'm from, those "Dual Check Valves with Intermediate Atmospheric Vent" type backflow preventers I see on your automatic water make-up line are for "non-health hazard applications"(Like residential boilers, for example). Which means they are typically not approved for make-up to a glycol system. What is required is a "Reduced pressure zone backflow preventer"(Expensive). And in most, if not all of the US, requires annual testing by a certified tester.
However, depending on your authorities, you could possibly get by, by not having a fixed piped connection to the potable water system.
I wouldn't even ask about the heat exchanger.
I used to be a cross connection inspector and a certified tester. That's how I noticed it.