Glycol Chilling Systems

Propylene glycol and ethylene glycol solutions are widely used in industrial chilling applications, but why?  The primary answer is due to the freeze protection provided by adding either of these glycols to water.  As we all know, water freezes at 32°F (0°C), and there are many applications that require chilling something down to near that temperature, or have outdoor equipment placements in environments that can get well below that temperature.  For this reason, we need to use a fluid other than pure water to ensure that it doesn’t freeze inside the chiller or piping causing equipment damage and down time.  Adding just about anything to water will reduce the freezing point of it, this is why we salt roads during ice storms and why you can put vodka in the freezer without worry of it freezing in the bottle.  So why can’t we use salt brines or ethanol solutions as heat transfer fluids?  The short answer is that you can and in some instances we do, but for many applications they present more problems than they solve.  Salt brines are often very corrosive causing the need for more robust materials of construction and ethanol is flammable causing explosion proof construction of the chiller unit.  Glycol solutions present a happy medium in that they provide excellent antifreeze capabilities while remaining relatively benign on the equipment itself and presenting few handling hazards.  Ethylene glycol does have a relatively high toxicity so its use in food applications (like beverage production) is often frowned upon.  Propylene glycol has a much lower toxicity and still has relatively good heat transfer qualities and low viscosity (which makes pumping easier) so it is the chemical of choice for many of these applications.  Another benefit of propylene glycol is its availability and ease of production which means it is relatively cheap to utilize!

Almost all chilling systems utilize mild steel or even iron as a material of construction for a handful of items within the chiller.  These items will easily rust using water or glycol solutions so we do recommend a rust inhibited glycol solution be used to prevent rust build up and eventual equipment failure.  The majority of these inhibitors work by forming a passive layer on the surfaces within the system which prevents oxygen from being able to react with it and cause rust to develop over time.

There are many manufacturers of inhibited propylene glycol and here at G&D we don’t play favorites.  We tend to recommend purchasing a 95%+ solution of inhibited propylene glycol and then diluting it down to the required mixture (which for the majority of our systems is 35%).  This is more economical as you are not buying water and then paying for it to be shipped to you.

We recommend using glycol solutions up to ~50% to operate chilling systems down to -4F (-20C), but for operating temperatures below this we tend to recommend moving away from glycols to other heat transfer fluids.  This is mainly due to the high viscosities that come about from increasing glycol mixture percentages and reduced operating temperatures.  Pumping of these fluids becomes difficult and fluid dynamics inside of heat exchangers and elsewhere cause a handful of operational difficulties that outweigh the benefits of low cost that come about from simple glycol solutions.

As always, here at G&D we deal with these types of issues day in and day out, so if you have any questions about what heat transfer/glycol solution is best for your application please feel free to reach out and we will be more than happy to point you in the right direction!