Every commercial high efficiency boiler loop I've ever seen or designed runs a glycol mix. Heat exchanger or not, everyone uses glycol. Just too much liability and it's not exactly 'easy' to fix a burst pipe in a slap or elsewhere.
As I say all the time, med-large commercial systems are night and day different from resi systems. Glycol inhibits heat transfer more than plain water..
OK, I told my self I wasn't going to post much more about hvac because it seems to bother some people, the fact that I am only in my mid 30's I can't possibly know wtf I am talking about... But here I go, lol...
I want to share what I think about glycol.
First, if you are going to use glycol, use DOW brand, make sure to buy the inhibitor version, not just glycol, I have seen the old purple st8 stuff eat ss in less than 2 years...
So first everyone is crazy about efficiency, so lets talk about what glycol does to how much energy you use- it is thicker- viscosity goes from something like 1.3 cP {plain water} to 3.3 cP for a glycol/water mix set at around -8. So its harder to circulate, need a larger pump to get desired flow rates..
Next - corrosive, NO MATTER WHAT, it is more corrosive than water, even if you mix it to -5 and run all the inhibitors...
Next - It doesn't last forever, its NOT free to start with I have done floors that used $1500 worth of chem on more than a few occasions and then told the customer "we should change this in 4-5 years"!!! I have showed them on paper that is cheaper to not use anti freeze and install another back up heating unit to circulate the floor incase the primary goes down... Now I know this is NOT the thinking that some of the guys that have "50" years in the business would say, but the math doesn't lie, $1500 of chems and $200 in labor every 5 years or spend the initial $5K for a back up boiler that will last 50 years...
Last one I will talk about is efficiency, you have to heat it hotter to get the same energy, its hard to explain but glycol {propylene and ethylene both and almost equal} inhibit heat transfer more than water.
If we call water {which freezes at 0 degrees} 100% thermal conductivity {in actual numbers its something like .585 w/(mk) but not to confuse anyone, ignore that and call it 100% } a water and glycol mix that freezes around -8 degrees would be 88% , so you loose 12% {and that is the good stuff from a company like atec or dow}.. So throw 12% away, thats what it boils down to...
So since it is all about money, lets add it up 12% thermal transfer lost, $100 {for a small system} lost every 5 years {if you do it yourself}, and the corrosive factor that is going to shorten your equipments life span by 20% {that is my number, I made up from my experience, no scientific back up for that, lol , sorry}...
This is why I tell people I am installing rad systems for that want anti frze to look over all the other options..
A back up boiler, piped in with a hydraulic separator {purpose built or close tees}, this is easy with gas, since for most floors, a basic rinnai water heater, or tiny cast iron boiler will do this for $800-$1500, you wont need all the trim since it is already there, the unit will last a LONG time since you will only use it in an emergency, I have done this many times, and what I do it schedule service for them units in the winter, and while I am servicing their primary I let the secondary run the system for a couple hours, then switch it back, it makes sure everything is OK and it runs the unit at least once a year, but the customer is capable of running ti the same way as a test, since it is piped in in a manner that allows simple conversion from a to b...
1-isolate as much of the system from the glycol as you can, so no glycol in the boiler, just in one side of the FPHX, the manifolds, and the floor.
2- rinse and change it every 4 years {3 is better 5 is the longest I would go}.
3-use good stuff, test it with the proper device {not a ball float meter, lol} refractometers can work well, don't just do percents, some companies say 20% and I trust my refractometer more than their ball park and in every case I can put less than the % they specify for desired fp.
4- materials, dont use orings {mechanical seals}, don't use iron/steel pipe- use s/s, cross linked poly, etc.
1 more thing to keep in mind, install an alarm so the floor sensor knows when the boiler is off, don't wait to say "is it cold in here", this will give you a head start, it takes a pretty long time to freeze a floor, this will give you time to get everything fixed so you don't have to worry about your glycol count...
I can obviously go on and on, but I don't want to ruffle any feathers, I am not writing this stuff to be a douche, I am trying to help someone with a fresh idea, vs the same old ideas from 50 years ago...
I will go on record as saying that antifreeze is the devil, lol If you can get away with not having it, do yourself a favor and don't have it, BUT on the other hand I will admit, its not as easy as just draining it out or not using it, you need to be proactive about what happens when anti frz would be needed, a genny for when the power goes out, a back up source of warm water {depending on the size of your building this could be a 40 gallon gas or electric water heater}, and most important an alarm that lets you know where there is an issue, this can also be as simple as a thermostat {t87} mounted 5"s from the floor and set to a temp that would allow you to know the floor isnt keeping up {say your primary is set at 65 yu could set the floor stat at 63 if its 63 at the floor and the primary tstat is at 65 something is not running}, you wire that to a simple 12v wall wart and car buzzer, you hear the buzzer you know to check the heat. I know a lot of boilers have alarm contacts, but that wont warn you if a circuit goes air bound, a manifold seals shut, a circulator stops, etc...
SO good luck, please read my posts as just another idea, I am not trying to show anyone up or bust balls, just giving a fresh take that a lot of people never heard before, that is all, if it helps someone, good, if you don't like my ideas, post yours, I love debates and I have an open mind, convince me of a better way and I will preach that..
ONE more NOTE- I have fixed a bunch of frozen {pex in cement} floors {well maybe 20 over the years}, they don't break all over and they are easier than you would think to fix, I use my thermal imager to find the frozen spots, demo saw to cut her open {or the bosch chipper depending on the floor}, uponor expansion fittings for the repair {they flow the best since they have the largest id}, then re-pour what we removed... I think the cheapest floor I ever fixed was a small house, had OLD antifrz in it, boiler went out for about 3 days, they were using electric heaters and when they got the parts to their wall hung boiler in the mail {weren't in stock locally} it was too late, floor froze and they kept the circ on like they were told, but didnt matter, too cold. It had 2 breaks close to each other, the bill was $4800, the insurance company covered it, as they did for EVERY floor I ever repaired, no questions asked, they come out check it, call to fix it and pay.... So its not the end of the world, while it certainly ***** and should be avoided, its not like you are ripping up an entire floor {which if it was needed the insurance co would pay for that too}...
This is why I always say to insulate the floor very well, reflective and foam and what ever you can afford, throw it under there...
