How To Choose the Best Heat Transfer Fluid

 

Heat transfer fluid (HTF) comes in many different forms, each with its own unique properties and performance characteristics. HTF can have major impacts on the efficiency, safety, and longevity of your system, so it's critical to choose the ideal option for your use case. 

 

Old World Industries (OWI) senior account manager Vache Soghomoian has deep knowledge in this area. Vache is a heat transfer fluid expert specializing in glycol-based HTFs and their applications in various industries. 

 

Vache sat down with us to talk about heat transfer fluid systems and the variables you should evaluate when selecting an HTF. We covered: 

 

• Essential basics of heat transfer fluids 
• Heat transfer fluid types and their unique characteristics 
• 7 Factors to consider when choosing a heat transfer fluid 

 

If you're not sure what kind of heat transfer fluid to use, Vache's insights can help you identify the product that best suits your needs. 

 

Essential basics of heat transfer fluids 

First, let's review what heat transfer fluids are and why they're important. 

 

HTFs are specialized fluids used to transfer heat in systems where direct exchange isn't a practical option. Examples of direct heat exchange include: 

 

• Using an electric element to heat liquid directly 
• Heating a surface with a live flame 
• Cooling a product with cold blown air 

 

Direct heat exchange can be difficult to control, especially if temperatures must remain within very narrow or specific ranges. Substances can also degrade or react when exposed to direct heating or cooling. Safety is another issue, since direct heat exchange can increase explosion, fire, and contamination risks. 

 

Heat transfer fluids solve these challenges by using engineered fluids as a heat exchange medium. They safely absorb, dissipate, and transfer heat within thermal systems without any direct exchange. This makes them ideal for applications that use heating and cooling agents to keep systems within specific temperature ranges. 

 

 

Types and unique characteristics of heat transfer fluids  

The four major categories of engineered heat transfer fluids include: 

 

Glycol-based heat transfer fluids 

Glycol-based heat transfer fluids combine glycol, a type of alcohol, with water. OWI's industry-leading Thermal Charge^Ⓡ line of glycol HTFs add state-of-the-art inhibitor packages that also protect against corrosion while reducing your system's maintenance needs. 

 

Here's an at-a-glance overview of glycol heat transfer fluids: 

 

Glycol-Based Heat Transfer Fluids
Operating temperature range	-60°F to 250°F
Thermal stability	Good
Viscosity	Low
Heat transfer properties	Very good
Cost	Low

 

Glycol heat transfer fluids come in two main forms: 

 

• Ethylene glycol (EG) 
• Propylene glycol (PG) 

 

EG and PG heat transfer fluids function similarly, but some of their performance characteristics vary slightly. They also have specific use-case recommendations due to their differing toxicity profiles: 

 

Type	Heat Transfer Properties	Freezing Point	Toxicity	Usage Recommendations
Ethylene glycol	Highly efficient	Slightly lower	Toxic if ingested	Systems where toxicity can be controlled
Propylene glycol	Slightly less efficient	Slightly higher	Lower toxicity*	Systems with the potential for human or environmental exposure

*As compared to ethylene glycol-based formulas. 

 

"With ethylene glycol, heat moves a little better throughout the system," Vache says. "On the flip side, propylene glycol is less toxic than ethylene glycol.”  

 

For a complete breakdown of OWI's glycol-based heat transfer fluids and their distinct performance specifications, consult our Thermal ChargeⓇ product catalog. 

 

Synthetic heat transfer fluids 

Synthetic heat transfer fluids are derived from synthetic base stocks and combined with engineered additives. They have excellent oxidation stability and are mainly used for high-temperature applications in chemical processing and manufacturing. 

 

Their main performance characteristics break down as follows: 

 

Synthetic Heat Transfer Fluids
Operating temperature range	-75°F to 750°F
Thermal stability	Excellent
Viscosity	Varies across a wide range
Heat transfer properties	Excellent
Cost	High

 

Mineral oil-based heat transfer fluids 

Petroleum-based crude is the base ingredient in mineral oil-based heat transfer fluids. These HTFs have only moderate thermal stability, but they're usually pretty cost-effective. They're also quite popular in the food and textile manufacturing industries. 

 

Here are the details: 

 

Mineral Oil-Based Heat Transfer Fluids
Operating temperature range	0°F to 575°F
Thermal stability	Moderate
Viscosity	Moderate
Heat transfer properties	Good
Cost	Varies

 

Silicone Heat Transfer Fluids 

Siloxane-based compounds form the basis of silicone heat transfer fluids, which have lower toxicity with high thermal stability. These features make them ideal for applications in the medical and pharmaceutical industries. 

 

Here's how they perform: 

 

Silicone-Based Heat Transfer Fluids
Operating temperature range	0°F to 575°F
Thermal stability	High
Viscosity	Moderate
Heat transfer properties	Good
Cost	Varies

 

If you'd like to learn more about the different types of heat transfer fluid, review our complete guide to heat transfer fluids, their properties, and their use cases. 

 

 

Factors to consider when choosing a heat transfer fluid 

Vache suggests using a seven-point analysis to help you select the best heat transfer fluid for your application. These seven points cover: 

 

• Operating temperature range 
• Thermal stability 
• Compatibility 
• Safety and environmental considerations 
• Cost effectiveness 
• Viscosity 
• Application specifics 

 

Here's how to approach each of these considerations: 

 

Operating temperature range 

"You want to make sure the fluid's going to be stable at the temperature your system is operating at," Vache explains. "You don't want too many fluctuations, as they could degrade the fluid quite a bit." 

 

As a core piece of guidance, Vache tells customers to identify the lowest possible temperature their system will operate at. This allows you to identify a heat transfer fluid with precisely the right amount of freeze protection.  

 

With temperature ranges as low as -65°F to -75°F, glycol and synthetic heat transfer fluids perform best in this regard. 

 

Thermal stability 

"Choose a fluid that's going to maintain its properties throughout its lifespan," Vache says. "You should have a fluid with great oxidation resistance." Oxidation resistance describes a heat transfer fluid’s ability to resist chemical breakdown when exposed to oxygen, especially at higher temperatures. 

 

Oxidation resistance helps you avoid system downtime by preventing scaling, sludge formation, and thermal cracking. Glycol-based heat transfer fluids with corrosion inhibitors — like those found in OWI's Thermal ChargeⓇ products — perform very well in this regard. 

 

Compatibility 

"Check the fluid's compatibility with system materials and seals," Vache advises. Ensure your system's gaskets are up to date, and that they match current ASTM International standards. This ensures your system's compatibility with engineered heat transfer fluids, and it will also help prevent leaks and system failures. The manufacturer of the materials used in the system will have information on the fluid's compatibility with the system materials and seals. This allows them to provide recommendations on recommended types of Heat transfer fluids. 

 

Safety and environmental considerations 

"Opt for less-toxic, biodegradable, fire-resistant fluids whenever possible," Vache suggests. "This is especially important for applications involving food, or anywhere people could be present." 

 

Cost effectiveness 

As Vache explains, cost considerations have two sides. "First, understand the up-front costs of your heat transfer fluid, then consider long-term maintenance and replacement expenses. Some fluids are more cost-effective up front, but if they're not carefully maintained, your total costs could very quickly run up." 

 

Cheaper but lower-quality heat transfer fluids can degrade systems, leading to higher overall costs. As such, a heat transfer fluid’s initial cost is only part of the overall picture you should keep in mind when comparing products.  

 

Viscosity 

"Viscosity ties into the dilution of the fluid itself. The higher the fluid's concentration, the higher its viscosity," Vache notes. "High-viscosity fluids will have your pumps running a little harder, which will cause a higher energy bill for the building itself, especially when operated in a low temperature environment." 

 

Before switching to a lower-viscosity alternative, consider your system's operating temperature range. "Lower viscosity will have the pumps working easier, but you'll need to consider the freeze protection at the lower dilution percentage."  

 

The more diluted your heat transfer fluid is, the higher its freeze point becomes. This can create risks, including pipe or component damage and reduced safety margins when operating in cold weather. 

 

Application specifics 

"Food plants, hospitals, and anywhere human or environmental exposure is possible, you're going to want to have a GRAS-grade fluid," Vache emphasizes. "GRAS" stands for "Generally Recognized as Safe," which is a materials safety designation used by the U.S. Food and Drug Administration (FDA). 

 

In other cases, you'll need a heat transfer fluid with other specific performance capabilities. For example, heat transfer fluids used in chemical processing applications require fluids that can withstand continuous exposure to harsh or corrosive chemicals. 

 

Get deep, detailed insights into heat transfer fluids and their application-specific performance characteristics 

Choosing the right heat transfer fluid for your use case is a critical first step, but there's much more to consider when looking at HTFs and the systems that use them. Other key examples include: 

 

• Best practices for system maintenance and testing 
• Proper leak prevention and system flushing techniques 
• Safe storage guidelines for heat transfer fluids 

 

Vache explains these and many other critical considerations in Understanding Glycol-Based Heat Transfer Fluids, an informative webinar co-hosted by OWI and HPAC Engineering. To explore these and other topics in complete detail, access the full webinar for free on HPAC Engineering's website.