Ethylene or Propylene glycol for HVAC system

[EnergyProfessional]

I'm aware of the general pros and cons for both types. Most older HVAC systems we have use ethylene glycol due to slightly better efficiency. But there also is the concern the toxicity could be a hazard (handling errors, spills etc.). Some newer systems we have use propylene glycol for that reason. I also always hear rumors there will be more restrictions on ethylene glycol.

I know geothermal and solar use propylene glycol and those are specific types for the relevant temperatures. I don't want to make those part of the discussion. I'm strictly talking about regular HVAC (e.g. boiler heat).

Do you see newer HVAC glycol projects using propylene glycol, even if ethylene is legal?

 

[IRstuff]

EG also has a ever-so-slight advantage in freezing point. In any case, the putative efficiency advantage of EG will likely continue to win out, since cost is more often the driver than anything else.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[EnergyProfessional]

IRstuff: I didn't mention, we usually use 30% glycol for HVAC and if it freezes (not bursting) it is fine. I looked it up and for 40% PG it is 7°F, for EG also 7.3°F. So for 30% not really a difference.

Our OAT design temperature is -15°F. But In this particular installation the AHU is indoors and we add the typical freezestat. So even if it gets slushy, it can thaw again. For outdoor equipment we use 50%, and there EG has a 5°F advantage. There seems to be quite a pump energy penalty for PG at low temps (chiller). But for heating systems the difference seems small.

I have a hard time judging the toxicity. Here it even says EG degrades faster. So if there is a spill, it should be fine after 30 days. EG is supposed to be toxic when one drinks 100ml. but if is only 30% EG, I find it hard to believe one would accidentally drink a large amount.

I swear I saw a Trane Engineer Newsletter where they compared EG vs. PG systems and had examples of the added pump energy for chilled water. But I can't find it right now. My current project is heating and I played a bit with the heater manufacturer software and using PG vs. EG would degrade performance by 3% or so (same flowrate). So if we increase flowrate for PG a bit to have the same output, and added viscosity, we may look at 10% more pump power? Or am I off in my math?

 

[IRstuff]

Not sure where they got their information; the ads of scantily clad women would seem to deprecate the answers. An MSDS is more informative:

https://rsc.aux.eng.ufl.edu/_files/msds/2/Dowfrost-HeatTransferFluid.pdf

http://www.ciscochem.com/assets/propylene-glycol,-industrial-sds.pdf

although some MSDS are less sanguine. Nevertheless, we know that we're not supposed to have exposed EG because dogs can certainly get to it and get sick. PG is ingestible in small quantities:

https://foodinsight.org/questions-a...ylene glycol can be,its intended uses in food

and is present in a number of common foods:

https://www.leaf.tv/articles/foods-drinks-with-propylene-glycol/

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[itsmoked]

Not just dogs, any animal thinks it smells interesting and they all think it's sweet. Which = bad results.

PG is used in ice cream isn't it? (Crappy ice cream I'd never eat.)

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

Yup

https://www.leaf.tv/articles/foods-drinks-with-propylene-glycol/[/URL]]Foods Containing Propylene Glycol
Many foods containing a laundry list of ingredients also contain propylene glycol. Some of the more common packaged foods containing it include dried soups and seasoning blends, marinades and salad dressings and baking mixes for products such as cakes, pancakes and muffins. In the beverage world, soft drinks, flavored teas, powdered drink mixes and alcoholic beverages may also contain propylene glycol. It is also used in some flavoring extracts for baking, as well as in some types of food coloring.

Propylene glycol is also quite common in fast foods, bread-based products, highly processed snack foods, flavored popcorn and cake frosting. Pre-made, mass-distributed baked desserts such as brownies, cakes and cupcakes may also contain this chemical. Even some ice cream flavors contain propylene glycol.

Marshmallows, dried coconut shreds and even some cans of nuts contain propylene glycol, as it helps retain an acceptable moisture level in these foods.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[EnergyProfessional]

I did some comparison with the UH manufacturer sizing software and pressure drop in Revit.
Base case is 10 gpm with 30% EG. With 1.25"pipe that gave me a pressure drop of 2.848 ftH20/100ft at assumed 100°F and 0.6psi for the unit heater. dT is 24.6°F

To get the same heat output with 30% PG, I need to increase flow to 11.4 gpm. that increases Uh pressure drop to 0.8 psi and pipe to 3.6743 ftH20/100ft. So 29% more pressuredrop for piping and 33% more for the heater. dT is reduced to 21.5°F. So around 3°F less, which will have some impact on efficiency of a condensing boiler.

So with more flow requirement I also may need larger pipes and units at some point. So there is a potential upfront-cost penalty with PG.

I think the toxicity is a bit overblown. Yes, it is toxic, but so is regular boiler water with the inhibitors etc. End it isn't like people have an EG tap right next to a beer tap and accidentally drink EG. I also think the food-grade PG is a bit a lie, since PG for HVAC systems has corrosion inhibitors and pH buffers etc. I'm also more concerned about environmental damage when there is a leak. but EG seems to degrade faster.

There also may be a pump performance penalty pumping the more viscous PG. I'll do some dummy pump sizing next.

Edit: I did some more sizing. If I leave the flowrate the same, the UH loses about 3.2% performance and pressure drop will rise by 2". I guess one could live with that, but in some locations may require a larger unit heater, or a pipe a bit larger (but not all over the project).
but if I want 100% of the heating performance, flow needs to increase by 14%, and pressure rises by 29%. that also would lead to about 30% more pump power (based on some mockup sizing, but those were different pumps in both scenarios). And with 14% more flow, there will be quite a few locations requiring larger pipes. i haven't analyzed the impact on the boiler. But i suspect with PG the overall flowrate needs to be higher, dT will be less. So so we also run into lower condensation rates.

If I need to install a larger UH, it also has a larger fan that needs more electricity. There are many ways to make a Pg system perform. But in general we tlak about a few% more material/equipment cost, a bit more pump power, and a bit lower combustion efficiency for condensing boilers.

 

[IRstuff]

since PG for HVAC systems has corrosion inhibitors and pH buffers etc

True, but the level of those substances is considerably lower, i.e., a dog, or other animal, could potentially lap up some amount of PG antifreeze and not get sick, which isn't necessarily the case with the equivalent amount of EG, since EG itself is toxic. The Dowfrost MSDS is for a commercial coolant with an inhibitor

https://rsc.aux.eng.ufl.edu/_files/msds/2/Dowfrost-HeatTransferFluid.pdf

and says for ingestion, "No emergency medical treatment necessary"

I have no dog in this hunt, so it's what it is and I wouldn't been surprised if the decision gets swayed toward EG.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[GT-EGR]

I trace back the anti-EG sentiment to the link below. Heavily regulated and compliant Facilties see EG as one more potential item to track. PG doesn’t have anything out there like this so it is casually regarded at times as the safe alternative.

https://rcrapublic.epa.gov/files/14163.pdf

 

[EnergyProfessional]

Here the SDS for EG.
I sent the SDS to someone who does environmental work here to hear her opinion.

I kind of see the advantage of PG in food and other industries.

I didn't mean to say regular PG or other HVAC water are as toxic as EG. I meant to state none of the fluids is something I or any mechanic would drink (well, there are people who lick door knobs, so you never know...). So the added toxicity to humans isn't really a problem here (non-food application).

I think the Acute dermal toxicity of EG is a realistic danger if spills happen and no PPE are used. From the SDS:
Acute dermal toxicity
Prolonged skin contact is unlikely to result in absorption of harmful amounts. Repeated skin
exposure to large quantities may result in absorption of harmful amounts. Massive contact
with damaged skin or of material sufficiently hot to burn skin may result in absorption of
potentially lethal amounts.

 

[IRstuff]

One other hazard with EG from personal experience; DON'T EVER BOIL it, the fumes are NASTY. I had a sore throat for about 3 days after the incident; I don't know if PG is the same or not.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[EnergyProfessional]

I talked to our risk management and for PG they would require use of disposable gloves and glasses. For EG safety glasses, face shield, and chemical resistant gloves. and it also would require some added level of training. So there is a somewhat higher operating cost for EG.

I reached out to DOW to ask what life expectancy of their PG and EG are, what disposal requirements and cost, and if additives can be added instead of replacing the fluid (e.g. adding corrosion inhibitors like we do with water). Does anyone here have knowledge of those aspects?

I want to have a good overview about the entire life cycle before making a decision (or give the decision makers all information there is).

As for boiling, if you evaporate the glycol and inhale it, it would be like drinking it. so i see why you would avoid it. But I don't think that is an issue here since nothing in the boiler room would be hot enough to boil water or glycol. I guess if the boiler malfunctions and the relief valve releases stem it could happen. But that is routed to a drain. So really unlikely (hope so)

 

[IRstuff]

If you were to do a failure modes, effects, and criticality analysis (FMECA), that would be included, but the probability could be set very low.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[EnergyProfessional]

I talked to someone at DOW. They stated typical life before replacement is 20 years. That is if you test for pH, corrosion inhibitors etc and replace those if needed. DOW does the analysis for free if you have more than 250 gallons.

So I guess I have to add a chemical feeder for adding the inhibitors. Our existing glycol systems don't have feeders and only have a fill-station. I guess one could use that for feeding somehow. I once talked to the guy who tests our water systems, and he told me glycol doesn't need to be tested since the inhibitors "are so good". it seems he is wrong (or DOW is).

anyway, so after 20 years you have to find a way to dispose of thousands of gallons of glycol. Both EG and PG SDS state to not dump in the sewer.

Next, I try to find out if there is a difference in disposal cost.

 

[GT-EGR]

See attached, just came across this brief summary in ASHRAE journal last November article about runaround glycol heat recovery loops.

 

[EnergyProfessional]

Thanks, GT-ER. I'm surprised they state PG performs better in chilled water systems. If that is the case, there wouldn't really be a reason to use EG for chilled water systems.

edit: i did soem comparios on an example pipe. For 30% PG/EG system at a given flow the pressuredrop difference is:
- 8% more for PG in case of 40°F glycol
- 1% more for PG in case of 110°F glycol

so I'm not quite sure why ASHRAE says PG is recommended for chilled water systems since those show the biggest disadvantage for PG for pressuredrop. the warmer the fluid, the smaller the difference.

 

[mzgh]

EnergyProfessional, please see the attached. I think you were looking for this paper in your earlier comments "I swear I saw a Trane Engineer Newsletter where they compared EG vs. PG systems and had examples of the added pump energy for chilled water. But I can't find it right now."

 

[EnergyProfessional]

mzgh: thanks for posting. the one I meant was actually from Trane. but yours is good regardless.

I saw systems designed by someone only using the tables and charts and ignoring the fact it is glycol. So that paper really makes that point. i tget s abit conulated since the type of fluid not only changes the pressuredrop, but also the flowrate required.

I hope I'm using the correct methods:
- Revit takes into account type of fluid and temperature (it makes a difference)
- the manufacturer software makes adjustments for type of glycol (ad it changes capacity and pressuredrop)
- the pump sizing website asks for type of fluid and temperature, so I hope it takes that into account (but you never know!)
- the only device I'm manually adjusting is are the radiators. There the manufacturer doesn't have a software and just made a blanket statement by how much to adjust capacity for each 10% glycol. But they have really low pressure drop to begin with.

I have meanwhile tried to find some local glycol disposal places to find out how difficult and expensive it is to legally dispose off EG vs. PG. So far I haven't found any that would take thousands of gallons. Both PG and EG SDS state to not dispose into the sewer. I think a lot of the decision will be based on how to dispose of this if there is a significant difference.