After two heating seasons freezing point of radiant heat system has gotten lower

capilicious

hi, everyone, long time lurker, first time poster.

I commissioned a radiant in floor (concrete slab) system two years ago, and using a refractometer my freezing point seems to have lowered from around -30 C initially to -40 C now. Has anyone else experienced this? Is it normal due to water evaporation?

thanks,

-Capo

pecmsg

When was it first measured? Was time given for good and through mixing.

-22°F to -40°F is extreme freeze protection. Why so low?

hot_rod

I would chalk that up to meter or operator error.. If this is a closed system the water cannot separate and evaporate out?

The numbers for glycols are

Freeze point, ice crystals form, fluid still flows

Slush point, fluid turns to a slushee, cannot be pumped

Burst point, fluid freezes solid and can break pipes and tubes, even Pex.

It depends on the brand of glycol, generally 30-35% mix is adequate for burst protection.

The higher percentage is harder to pump and transfer heat from. No need to overdo the glycol mix.

pecmsg

30 - 35% is generally all that’s needed

capilicious

thanks for the responses - I’m in a rural area in Canada so if there was a prolonged power outage during a cold snap the outer loops of my system could see some very cold temps. I’m trying to find my notes but I definitely aimed for a little more than 35% glycol by volume (which according to my glycol supplier provides freeze protection to -18 C, which seemed a little too high in my area).

I tested the meter with water and it read 0 deg C, with my car coolant it read -50 C (which is mixed 60% antifreeze as per manufacturers instructions for severe climate eg Eastern Ontario winter ). So don’t think it’s the meter…..

I would entertain the theory that thebinitia measurement was made when the system had not run very much, so it’s possible it was not thoroughly mixed. It is a closed system - I assume only leaks might be past pump seals.

perhaps I’ll try and dilute the fluid with some distilled water and see what happens.

appreciate any other diagnostic suggestions regarding the system or the meter.

-Capo

mattmia2

pretty much any system has some very small leaks at valve packings and things like that but if anything that reduces the concentration as water is added to keep the cold fill pressure up. does it have a tank and pump type auto feeder or some other arrangement like a well tank full of glycol mix and a prv?

pecmsg

Do not confuse freeze protection with Burst Point.

capilicious

• mattmia2: yes I do have an automatic feeder but it has a glycol/water mix in it also. I don’t think it has added anything since the first winter when there might have been a little air in the system.
• pecmsg: not sure what your comment means - the refractometer measures freeze point….

thanks,

capo

pecmsg

Look on the manufactures paperwork it will show Freeze point / Burst point.

30% is more than enough

DCContrarian

"I tested the meter with water and it read 0 deg C, with my car coolant it read -50 C (which is mixed 60% antifreeze as per manufacturers instructions for severe climate eg Eastern Ontario winter ). So don’t think it’s the meter….."

Car antifreeze is a different chemical and requires a different tester. Did you use the same tester both times?

mattmia2

a refractometer will work for both, just need a different scale for ethylene vs propylene glycol.

GroundUp

I think some may be reading this wrong. It's not possible for the freeze point to get lower as time goes on unless you're adding glycol at an elevated concentration. Odds are that your first measurement was not thoroughly mixed yet, or that one of them was simply an error.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1875303#Comment_1875303

unless the stuff in the feeder tank is a higher concentration or maybe the water has evaporated from the feeder tank more readily than the glycol.

pecmsg

https://forum.heatinghelp.com/discussion/comment/1875286#Comment_1875286

Here he said refractometer.

• pecmsg: not sure what your comment means - the refractometer measures freeze point….

pecmsg

Never seen H2O separate once mixed.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1875315#Comment_1875315

a refractometer measures index of refraction which is a function of density among other things

hot_rod

All research indicates once it is mixed it cannot be separates, with the possible exception of freezing the solution.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1875315#Comment_1875315

The refractometer is going to have a different scale for ethylene glycol (car antifreeze) vs. propylene glycol (hydronic antifreeze).

Look at the scale on page 2 of this document:

https://www.richardhouriganinc.com/pdf/ETHYLENE_OR_PROPYLENE.pdf

At a refractometer reading of 1.32 the propylene is about a 50% solution with a freeze point of -20F, the ethylene is a 48% solution with a freeze point of -30F.

Using the wrong scale would easily explain what OP is seeing.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1875329#Comment_1875329

i mean that is how you make liquor by evaporating the ethanol out of the water. what i don't know is about the boiling points and vapor pressures of propylene glycol vs water.

GroundUp

https://forum.heatinghelp.com/discussion/comment/1875305#Comment_1875305

That's….. What I said

Except for the separation thing, which can't happen.

capilicious

here’s a picture i took of the refractometer…..

pecmsg

way too low.