propylene glycol vs. methyl alcohol in loop

[minn]

I last posted about a year ago complaning of irritants in my home that appeared to be coming from my horizontal loop that contained methyl alcohol.My combustible gas detector went off around the pump flanges and canister in the basement. Anyway, a month ago I had the system flushed of the MA and filled with food grade propylene glycol , not only to ease my mind but to also satisfy a requirement by the state to receive a rebate. A few days ago I noticed the geo running longer than usual to meet demand so this morning I took some readings. My EWT was about 39.5 which is good, but my discharge air coming out of register was 77 during 1st stage and when 2nd stage kicked in the max discharge temp was 85. The system then ran for 1 hour 12 minutes to meet demand and it's only 20 degrees outside. When alcohol was in system 1st stage was 84 degrees and 2nd ran about 93/94 discharge air. Can the glycol be that much less efficient or could there be another problem?
P.S. the irritants in the home have disappeared since installing glycol.

[Lambo]

Although the heat transfer rate of propylene is slightly better, it's viscosity is much greater than that of what you had. This may simply be affecting the volume of the heat transfer medium (Glycol) circulating throughout the system. You may have to increase your pumping capacity.

[minn]

Thanks Lambo,
Right now I have 2 inline Grundfos circ pumps that appear to be single speed(not sure what HP). Would I just need to replace those with the next biggest HP ones or is it more complicated than that?

[Lambo]

Minn, my last post were my initial thoughts after reviewing some data comparing the two types of glycol. There are correction factors for required pump volume for glycol as compared to straight water, but I can't find any data that would support my previous comments.
I would be more concerned about proper mixture percentages and that the right type of glycol was used. I have attached a file that offers some good information.

[minn]

Lambo, thanks for the attachment. I replaced the alcohol with a 25 % mixture of inhibited propylene glycol/deionized water that is manufactured for geo loops. It came in a 55 gal drum that was pre-mixed.
I was told to expect a slight decrease in efficency but I wasn't expecting more than a 10 % drop in discharge air temp.
We are expecting -25 degrees(30 to 40 below windchills) next week and I think I will have to shut down the geo and go back to my LP furnace.
Would a slight loss of refrigerant(r-410) cause a loss of discharge air temps? Im trying to think of everything.
Any help would be appreciated.
Thanks

[supertek65]

you need to know the specific heat of the MA and that of the glycol at 25% mixture

from there it is simple!

btu= gpm x 500 x delta t x specific heat

[RoBoTeq]

What kind of system do you have where the fluid in the loop is exposed to your home?

Propylene glycol DOES NOT have as good heat transfer, and it is harder to pump. What you are seeing is about right from changing to propylene glycol.

[minn]

My system is a horizontal closed loop (1year old). What was happening was the "fumes" from the Methyl Alcohol were escaping around the pump flanges and the flow center canister screw cap. There was a mist of liquid laying on the pump flanges. There was no dripping, just a mist or coating around the flanges. I tightened the flange bolts but that didn't help. I silicone greased the threads on the canister and that did help. My combustible gas detector still picked up at the pump flanges. Must be physics thing with the alcohol, I dont know.
I am disappointed by the 9 degreee drop in the supply discharge air after switching to glycol. It seems to me a huge difference fron 94 to 85 degrees.
My question is can this be remedied by larger pump capacity and would that be larger horsepower or more RPM?

[supertek65]

nobody can answer that without knowing this formula as it applies to your system

you have to know the specific heat of your fluid

you have to know the GPM and to know that , you need pump curve and head!

you need to know the specific heat of the MA and that of the glycol at 25% mixture

from there it is simple!

btu= gpm x 500 x delta t x specific heat

My system is a horizontal closed loop (1year old). What was happening was the "fumes" from the Methyl Alcohol were escaping around the pump flanges and the flow center canister screw cap. There was a mist of liquid laying on the pump flanges. There was no dripping, just a mist or coating around the flanges. I tightened the flange bolts but that didn't help. I silicone greased the threads on the canister and that did help. My combustible gas detector still picked up at the pump flanges. Must be physics thing with the alcohol, I dont know.
I am disappointed by the 9 degreee drop in the supply discharge air after switching to glycol. It seems to me a huge difference fron 94 to 85 degrees.
My question is can this be remedied by larger pump capacity and would that be larger horsepower or more RPM?

[mstrblstr3]

Sounds like someone put way to much methanol in your system.
It should be a 10 percent solution and I've never had any leaks with the waterfurnace supplied pumps and equiptment. Methanol is in all my systems and they all qualify for all government rebates is michigan. Guess whats in windshield washer fluid? I hope you didn't replace all that fluid at your own cost.:

[farbeondriven]

Sounds like someone put way to much methanol in your system.
It should be a 10 percent solution and I've never had any leaks with the waterfurnace supplied pumps and equiptment. Methanol is in all my systems and they all qualify for all government rebates is michigan. Guess whats in windshield washer fluid? I hope you didn't replace all that fluid at your own cost.:

ditto. Hell I've heard of guys using windshield washer fluid in geo systems. We always buy the premix 5 gal pails of methanol from our equipment supplier.

[crash11]

Yeah I put methanol in my loop, and I haven't had a single problem. No leaks whatsoever. I did a 20% methanol mix.

Is your loop holding a slight positive pressure?

[arc8]

The loop field is sized by your Heat Load.
Once that's determined, your antifreeze is determined and usually all the time; Methanol is the best. The reynolds number is the highest and propylene glycol is the lowest which is not good, hardly ever.

And if you do use PG, you would need a little more pumping power.

Anyway, you should never have a leak in the system, it's very unsafe since Methanol is flammable. Get the contractor to fix it.

I still would use Methanol but I would make sure that there are no leaks (repair them).

BTW, 20% is a safer bet unless your source LWT doesn't drop below 32F ever!