Propylene glycol vs ethylene glycol | The best choice for HVAC systems?
Looking to use glycols in your HVAC system but unsure whether to opt for propylene glycol or ethylene glycol? It’s a common conundrum. But, while the two chemical compounds are from the same family, they’re definitely not interchangeable. In fact, using the wrong glycol will almost certainly impact the effectiveness of your system and could even prove hazardous. Here, we’ll delve into the differences between the two chemical compounds. Read on to learn more about their divergent characteristics and discover which is best for your HVAC system.
Want to speak to an expert about which glycol is most effective for your HVAC system? Get in touch, today.
What is glycol?
Let’s start at the very beginning – glycol is a term used to describe the class of organic compounds that contain multiple hydroxyl groups attached to carbon atoms. Part of the alcohol family, glycol is widely used as antifreeze. Glycol lowers the freezing point and changes the boiling point of a solution, making it an important element of any heating and cooling system. It is usually a clear, viscous liquid with a very mild odor. Ethylene glycol (1,2-ethanediol) is the simplest member of the class and is extensively used in antifreeze and brake fluids. Propylene glycol (1,2-propanediol) is also widely used and is popular in cosmetic, food and beverage and refrigeration industries.
What are the main differences between ethylene and propylene glycol?
While propylene and ethylene glycol both present as colorless and largely odorless liquids, there are some major differences between the two, differences that are important to understand if you work within the HVAC industry.
Ethylene Glycol
Ethylene glycol has great heat transferability and is often used in HVAC systems. The number one thing to note is that ethylene glycol and its derivatives may be toxic so are not suitable for use where incidental contact with nature is possible. Those working with open-loop or geothermal HVAC systems, for instance, should choose to avoid using ethylene glycol.
Propylene Glycol
Propylene glycol shares many of the characteristics of ethylene glycol. It is effective at a wider range of operational temperatures but doesn’t possess the same level of heat transferability as ethylene glycol. The payoff is that propylene glycol is less toxic so can be used in open-loop systems and places where contact with humans or nature is possible. Additionally, propylene glycol can be derived from renewable plant sources, unlike ethylene glycol, which is only refined from crude oil or natural gas.
Which is better ethylene or propylene glycol?
In terms of which of the two is “better”, it largely comes down to how you intend to use the compound. Ethylene glycol has better heat transferability meaning it will be more effective at transmitting heat, it also has a higher boiling point than propylene glycol and its low viscosity means it may outperform propylene glycol at lower temperatures. Combined, these characteristics make it a great choice for closed-loop HVAC systems. However, ethylene glycol is considered toxic and harmful to marine life.
Propylene glycol, by contrast, has a higher viscosity and lower heat transferability. To put it simply, it’s unlikely to be the choice for those who value thermal performance above all else. But, given ethylene glycol’s toxicity, propylene glycol still has an important place in the HVAC industry. Propylene glycol is considered safe for humans and is used in the food and beverage industry as well as in various pharmaceuticals and cosmetics. It is the safer choice for open-loop or geothermal HVAC systems where contact with nature is possible.
Can I use propylene glycol instead of ethylene glycol?
Propylene and ethylene glycol cannot be used interchangeably. While both are glycol compounds, they have differing characteristics and differing toxicity levels so will not be suitable for the same applications.
Do I have propylene or ethylene glycol in my HVAC system?
Both propylene and ethylene glycol present in a similar way but there are two tests to separate propylene from ethylene glycol: a specific gravity test and a refractive index. In a specific gravity test, a hydrometer will be used to assess the liquid’s density. If the value recorded is more than 1.05 then the heat transfer fluid is ethylene-glycol-based – propylene glycol solutions will have a gravity below 1.045. If the results of this test are within the margin of error, then a refractometer should be used and the liquid assessed via the refractive index.
Get in touch to learn more about the fluid testing services CORECHEM offers.
Which is less toxic – ethylene or propylene glycol?
Propylene glycol is considered less toxic than ethylene glycol. Propylene glycol is biodegradable and available as a food-grade antifreeze making this the safer choice for open-loop, geothermal, or food-grade systems. It is “generally recognized as safe” by the Food and Drug Administration (FDA).
Propylene vs ethylene – which glycol is best for your HTF system?
When it comes to which of the two glycols is best for a HVAC system, it really is dependent on the type of system you have and your heat transfer requirements. Generally speaking, ethylene glycol is an ideal choice if thermal performance is important and there is no possibility of contact with humans. If toxicity is your number one concern, then propylene glycol is likely to be the safest choice.
Need more information on which glycol is the right choice for your HVAC system? Get in touch with a member of the CORCHEM team today.
