Glycol in whole system or Heat Exchanger for half ?

Antitorque

Hey guys,

I've been enjoying reading all the posts here and have picked up a lot of good tips. However I can't find a good answer to my question.
I'm doing my first Hydronic heat system that has a snow melt / exterior garage heating requirement. (Denver, CO.) The interior basement space is 1600 square feet, the garage is 600 and the snow melt for the patio is 80 square feet. My question is would it be prudent to make the whole system glycol as opposed to using a heat exchanger along with extra pump and expansion tank in the gylcol loop. ( I would combine the garage heat and snow melt ) I know I would incur less efficiency, higher glycol costs and probably the cost of an axiom feeder system but I figure this would be easier to install.
Any thoughts?

mattmia2

those are the 2 options. since the snow melt is very low temp the hx for that isn't really an issue. What d you want to use to heat the garage? With radiant i the slab you can probably keep the boiler side temps in a range where it is condensing, if you use a unit heater or panel radiators you probably won't be in the condensing range on the boiler side, if yo want to use a modcon for efficiency.

mattmia2

glycol is more difficult to pump, transfer heat to, and has a lower specific heat than water.

Antitorque

mattmia2 said:

glycol is more difficult to pump, transfer heat to, and has a lower specific heat than water.

So larger pumps and higher temps ?   And all the areas are pex tubes in insulated slab concrete, 

mattmia2

the higher viscosity usually isn't enough of a difference it would change what you would do but the lower specific heat and transfer become important in sizing your emitters (designing your tubing in this case) and sizing your heat exchanger if you use one. there are derating factors depending on the concentration.

JohnNY

I hate glycol.
I hate glycol.
I hate glycol.

I hate the smell. I hate the sticky. I hate the buckets. I hate the refractometer. I hate the cost. I hate the calculations to get the right mixture. I hate maintaining the mixtures. I hate having a leak.

I just finished a system that took over 200 gallon of Cryotek to get to a 30% mixture. A Hoffman 79 in the middle of the system leaked and drained 4 stories of my mixture into a floor drain. Getting this right again is a nightmare of cost and effort.

Avail yourself to as little involvement with glycol as you possibly can. Trust me.

Edited to add:
Only about 25% of that system was vulnerable to freezing. After the last big loss event, I got the engineers to agree to add a heat exchanger. Now, my portion of the system is 100% water and only the HVAC company's portion which supplies heat to rooftop air handlers is filled with 30% glycol.

ChrisJ

Glycol is much worse at transferring heat than water.
That's why we do not run straight antifreeze in cars.

But, @JohnNY How do you really feel about glycol?

hot_rod

tommay said:

All glycol, skip the heat exchangers. Unfortunately, glycol cost have gone up due to shipping weight and supply chain issues involved due to the "pandemic" they want us to believe in, but incorporating it now will save you a lot in the future. No worries about frozen pipes, it has detergents and oils to keep the lines clean and will last ten years or more depending on temperature and run time. I use Cryotek, in both my solar hot water systems and heating systems that are susceptible to freezing. Glycol is better than water when absorbing and distributing heat is considered. This is why it is used in cars... Hopefully you understand or realize that the snow melt system in your driveway can act as a solar hot water collector 3/4's of the year....make it a separate zone and you can hook up to a simple side arm heat exchanger with a bypass and aquastat. If it is a new install....insulate with some 1/2 rigid insulation or more, with foil face, under the tubing before burying.

I have worked with 3 different glycol manufacturers doing trainings and webinars, never heard of detergent being in hydronic glycol blends.  One ingredient is a film provider that helps protect the piping and components, the opposite of a detergent?

As for oil, glycol is “cracked” from either crude oil or bio glycols from corn or other plant base. It pretty much is oil with ph buffers, oxygen scavengers, film providers and coloring added

Food grade glycol, also from oil😋 is used as a food additive, preserving and flavor enhancer, also listed on some tooth paste tubes.

ChrisJ

That's not what a detergent is.

https://en.m.wikipedia.org/wiki/Detergent

the word detergent is derived from the latin adjective detergens, from the verb detergere, meaning to wipe or polish off. detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions.[1] however, conventionally, detergent is used to mean synthetic cleaning compounds as opposed to soap (a salt of the natural fatty acid), even though soap is also a detergent in the true sense.[2] in domestic contexts, the term detergent refers to household cleaning products such as laundry detergent or dish detergent, which are in fact complex mixture of different compounds, not all of which are by themselves detergents.

mattmia2

in cast iron/brass/copper cooling systems it wasn't unusual to run straight water in the summer. once aluminum got involved it required the inhibitors in coolant to keep the aluminum from dissolving in the hot water even in summer

EternalNoob

Specific heat, or specific heat capacity, is not the same as thermal conductivity. Common but annoying confusion. One is a measure of the capacity to hold heat, the other the rate at which heat is transferred. Glycol has both a lower specific heat than water and lower thermal conductivity, meaning it takes less energy to heat it up, and to cool it down, therefore storing less (less capacity). Also, and *unrelated*, a lower transmission rate (conductivity).

WMno57

EG - Ethylene Glycol (toxic, used in cars)
PG - Propylene Glycol (non-toxic, used in homes)
CIs - Corrosion Inhibitors (Silicates, OAT, HOAT, P-HOAT, SI-HOAT) https://en.wikipedia.org/wiki/Antifreeze#Corrosion_inhibitors
Prestone concentrate - EG with CIs
Prestone ready to use - 50/50 EG and H2O with CIs
Evans Waterless Engine Coolant - 100 percent PG with CIs. A niche product that has heat transfer problems. Not used by any OEMs. https://www.evanscoolant.com/

tommay said:

Chrisj, you say we don't run straight antifreeze in cars...why not?

Because it does not transfer heat as well as a 50/50 mix.

tommay said:

If it doesn't contribute to absorbing and transferring heat, through the radiator with a fan blowing on it, why use it all?

100 percent glycol (EG or PG) is only about half as good at transferring heat as H2O. A 50/50 mix is a compromise that transfers heat good enough and doesn't freeze.

tommay said:

Maybe try using straight water in your car for some time, especially in the summer, and see how that works out. Then check the condition of the water after some time, whatever is left of it, because according to you, your car should run cooler with no problems and the antifreeze is only there to keep it from not freezing in the winter and has no other purpose....

Straight H2O can be used if the appropriate CIs for the metals in the system are used. This is done in power plants, some off road industrial vehicles, and some race cars.

tommay said:

Obviously you have access to a dictionary, now get your hands on a chemistry and heat transfer book.

@tommay, Heating Help is unlike most other forums on the Net. There is a unique mix of individuals here. Some have over half a century of real world experience. Others have advanced degrees in Engineering and Science. It is a great place to hang out and learn. I hope you stick around. You may learn a lot here if you are open to learning.

HomerJSmith

Interesting comments! I'm currently reading Is Atheism Dead by Eric Metaxas, a very good read. Basically it is about Science proving the existence of God or Intelligent Design behind the creation of the Universe. I mean life is more than plumbing and hydronic seminars.

The current chapter I'm reading is about water, the miracle molecule, without which, if there was an infinitesimal change in its properties, life would be impossible.

I can't think of anything that absorbs heat energy or releases heat energy as well as water.

I remember my Uncle telling me that when he stopped at a motel in freezing weather that he had to drain the water out of the engine by opening the petcock on the bottom of the radiator. I myself have seen freeze plugs pushed out of engine blocks because of freezing. Then came EG, wow, that was something else.

I agree with johnNY, glycol is a pain in the donkey. It squeezes out of everything. I use it in the same way cars use it because it keeps fluids moving in freezing weather.

Regarding this post, I would use it where needed and not use it where it isn't needed.

I would definitely segregate the house from the outside circuits with a flat plate heat exchanger, pump, expansion tank, air eliminator and mixing valve (Taco I-Series setpoint valve). The cost would be partially offset by the reduced cost of glycol in the house besides which the % of glycol needed in the house and the driveway may be different. Also, because the temp and the operation (only in the winter) of the driveway sys, the glycol's lifespan would be much longer.

Assuming it's a full time residence, I would definitely separate it.

PC7060

tommay said:

Wmno57, fyi I have a degree in Mechanical Engineering and second generation licensed in plg,htg and gas, along with other members of my family, for over 40 years as well as a solar hot water and pv business, so a little knowledge and experience.....You?

Only one degree? Verbal flatulence related to education and experience rarely bolsters any discussion and typically makes 3/4 of the community just tune you out. 

You can always just post your creds in your signature if you feel it’s important. 

ChrisJ

I know of someone else that bragged about how long he had done his job for.  He was wrong too.

WMno57

tommay said:

Wmno57, fyi I have a degree in Mechanical Engineering and second generation licensed in plg,htg and gas, along with other members of my family, for over 40 years as well as a solar hot water and pv business, so a little knowledge and experience.....You?

Just an old DIYer with a 70 YO boiler and bunch of old tools, cars, trucks, tractors, Diesel engines, a Wankel engine, etc. More knowledgeable about Internal Combustion than Hydronics. I do know a bit about automotive coolants and water chemistry. I know why Evans Waterless Coolant is problematic in almost all applications. I also know why water cooled engines are ubiquitous and air cooled/oil cooled engines rare today. Water is by far a better heat transfer medium than glycol, oil, or air.

HomerJSmith

tommay, kudos on your accomplishments. I have found that credentials don't necessarily mean that you know more, but it does, in most case, means that you can charge more. That's kind of a joke.

On this site, we don't criticize the commentator. We criticize the comment. At least, I hope that Erin keeps a pretty good grip on that. Comparing one's accomplishments to another's accomplishments just ends up being a peeing contest. It doesn't add any more knowledge to the post. What I want, is to learn from another's experience and knowledge. That's what the person that posts here, I think, wants, too.

tommay, the web is replete with the illustration comparing the BTUs carrying capacity of a 3/4" pipe to 10" x 14" air duct. The pipe wins out. It all has to do with density, but you are right. Air does collect and release heat energy, readily.

As a side note, one can't measure energy, it not possible. One can only measure the effects of energy.

hot_rod

Some good glycol info here, no need to guess or imagine how it protects

Often what you look for is burst protection. At some temperature glycol gets too thick to pump with a centrifugal type pump.

37% of Dowfrost HD pg gets you -60 burst protection.

Going beyond a 60% blend doesn't add much more protection.

I'd use the lowest % to get the job done, 35- 40% should be plenty for hydronic system protection.

https://www.dow.com/content/dam/dcc/documents/en-us/app-tech-guide/180/180-01286-01-engineering-and-operating-guide-for-dowfrost-and-dowfrost-hd.pdf?iframe=true

mrhemi

I'll throw this recent personal experience out there for your consideration. My own, ten year old home (my build) was completed with a combination of forced air and radiant heat. The forced air is heated via hydronic coil air handler. One of the radiant zones is the attached 1100 sq. ft. garage / workshop. gas fired mod con combi is the source of heat. At the time of install, I decided on a glycol fill due to the remote potential of the garage freezing. Forward 10 years, to last January when the problematic mod con fails (credit to Triangle Tube, they came good for a new mod con) and I am waiting a week during the coldest period of the year for a new boiler. Was I ever glad the system was filled with glycol then! Didn't have to drain the system to prevent freezing while heating the house with the fireplace and a couple of ceramic heaters. Also a fortunate choice made initially was to utilize a storage tank for the DHW from the combi. Because the storage tank in this application is actually an electric hot water tank, wired but never energized, I was able to flip the breaker and have hot water for the duration on the boiler outage.
In hindsight, I do not regret any of my decisions except the original combi mod con design choice.

Erin Holohan Haskell

HomerJSmith said:

On this site, we don't criticize the commentator. We criticize the comment. At least, I hope that Erin keeps a pretty good grip on that. Comparing one's accomplishments to another's accomplishments just ends up being a peeing contest. It doesn't add any more knowledge to the post. What I want, is to learn from another's experience and knowledge. That's what the person that posts here, I think, wants, too.

Well said, @HomerJSmith. Thank you.

Please respect one another and site rules. Let's get back on track.

Antitorque

Thanks for everybody's comments on the subject! After looking closer on the specs of the job and based on the expense and people's dislike of glycol I have decided to install the heat exchanger and associated components for that glycol closed loop. Its two 250' loops vs 1600 square feet of interior space. Thanks again!

Antitorque

So the builder through another wrench in the works. He told me the 80 square feet of patio snow melt tubing is the very same tubing that goes on to heat the 600 square foot garage. (there's a very short distance between house and garage with this patio inbetween) Seems very foolish to not have that a separate controlled zone for each. I can't believe they wouldn't separate the two, it seems very inefficient. How would this affect my btu needs and would it still be possible to heat the patio and have enough water temp left to heat the garage to 50 - 60 degrees? Please excuse my ignorance, this will be my first glycol system.