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Glycol and Your Chilling System Explained
Glycol is a class of organic compounds that belong to the alcohol family. When mixed with water and pumped through the pipes of a chilling system, glycol serves to slow the rate of freezing. It helps maintain temperature consistency in the application. Some glycol products also work to inhibit corrosion and bacterial growth within the pipes of the chilling system.
The Two Types of Glycol Compared
Glycol comes in two varieties that should never be mixed together: ethylene glycol and propylene glycol. Both types offer the same relative level of freeze protection. Both also help to guard against corrosion. Some grades of both types of glycol also help to prevent the growth of algae and bacteria within the chiller.
Ethylene Glycol
Ethylene glycol is a moderately toxic chemical that has a sweet taste and can be harmful if swallowed. For this reason, it should not be used in potable water or
Propylene Glycol
Propylene glycol has a lower level of toxicity and is considered to be a food grade antifreeze. This type of glycol is safer to handle than ethylene and can be more easily disposed of.
Mixing Water with Glycol in Your Industrial Refrigeration System
Although you should never mix glycol types there is something that should always be added: water. As mentioned, glycol must be mixed with water to function properly. The type and amount of water to use are key factors to consider.
Type of Water to Use
Each glycol chiller comes with its own set of manufacturer recommendations for the best type of water to use for that system. Although city water may be acceptable initially, it is almost never recommended that de-ionized water be maintained for the long term as it could have adverse affects on certain metals in the chiller. Sometimes manufactures require the chiller to use distilled or reverse-osmosis water. The key is to check with the manufacturer for the particular needs of your refrigeration system.
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Ratio of Water to Glycol to Use
Calculating the proper ratio of glycol to water in your chilling system depends on the coldest temperature that the glycol solution will reach during operation. If a chilling system is used indoors where there is no chance of freezing, the amount of glycol needed would be significantly less than required by a glycol chiller used outdoors where temperatures are prone to drop below freezing.
Also, if an application requires a very low temperature to operate it should use a glycol mixture similar to that of an outdoor system.
In a chilling system, this temperature is normally the saturated suction temperature in the evaporator, and normally this temperature is 10°F below the chiller set point temperature.
Using the proper ratio of glycol and water in your chilling system is very important. Adding too much to your chiller system will cause it to become inefficient. However, not enough glycol could cause the system to freeze up, potentially bursting pipes or even rupturing the chiller evaporator.
Learn More About Glycol Chilling Systems
To learn more about how a glycol chiller works or to find out if this system is right for your application,
Berg manufactures glycol chilling systems for a wide variety of industries ranging from food and beverage processing to. Yet, what makes these systems unique and how they operate remains a mystery to many of our current and potential clients. Glycol chillers are industrial refrigeration systems that use a type of antifreeze called glycol, mixed with water, to lower the freezing point in the application of the chilling system. Here are the top three things you should know about glycol chillers.Glycol is a class of organic compounds that belong to the alcohol family. When mixed with water and pumped through the pipes of a chilling system, glycol serves to slow the rate of freezing. It helps maintain temperature consistency in the application. Some glycol products also work to inhibit corrosion and bacterial growth within the pipes of the chilling system.Glycol comes in two varieties that should never be mixed together: ethylene glycol and propylene glycol. Both types offer the same relative level of freeze protection. Both also help to guard against corrosion. Some grades of both types of glycol also help to prevent the growth of algae and bacteria within the chiller.Ethylene glycol is a moderately toxic chemical that has a sweet taste and can be harmful if swallowed. For this reason, it should not be used in potable water ors when leakage is a possibility. Ethylene glycol has more widespread use due to its lower purchase price. Industrial applications likeandrequiring large volumes of the coolant find this to be the most economical choice of glycol.Propylene glycol has a lower level of toxicity and is considered to be a food grade antifreeze. This type of glycol is safer to handle than ethylene and can be more easily disposed of. Propylene glycol is commonly used inor in industrial refrigeration systems where people may come into contact with fluid. Propylene glycol can also become more viscous than ethylene, even slightly affecting the heat exchange rate when used at very low temperatures. It is important to note that you should never mix different types or brand names of glycol, as this leads to the product congealing and the clogging of filters in the refrigeration system 'potentially causing problems with heat transfer and fluid flow.Although you should never mix glycol types there is something that should always be added: water. As mentioned, glycol must be mixed with water to function properly. The type and amount of water to use are key factors to consider.Each glycol chiller comes with its own set of manufacturer recommendations for the best type of water to use for that system. Although city water may be acceptable initially, it is almost never recommended that de-ionized water be maintained for the long term as it could have adverse affects on certain metals in the chiller. Sometimes manufactures require the chiller to use distilled or reverse-osmosis water. The key is to check with the manufacturer for the particular needs of your refrigeration system. Read more about how process water can affect a chilling system's performance Calculating the proper ratio of glycol to water in your chilling system depends on the coldest temperature that the glycol solution will reach during operation. If a chilling system is used indoors where there is no chance of freezing, the amount of glycol needed would be significantly less than required by a glycol chiller used outdoors where temperatures are prone to drop below freezing. Also, if an application requires a very low temperature to operate it should use a glycol mixture similar to that of an outdoor system. In a chilling system, this temperature is normally the saturated suction temperature in the evaporator, and normally this temperature is 10°F below the chiller set point temperature. Using the proper ratio of glycol and water in your chilling system is very important. Adding too much to your chiller system will cause it to become inefficient. However, not enough glycol could cause the system to freeze up, potentially bursting pipes or even rupturing the chiller evaporator.To learn more about how a glycol chiller works or to find out if this system is right for your application,
This article has been updated. It is accurate as of Feb. 8,
For low-temperature hydronic systems, systems in which chillers and AHUs are located outdoors, or other equipment used in low-temperature processes, some form of glycol is a critical ingredient. It works to lower the fluid's freezing temperature, enabling lower-temperature operation and preventing freezing.
Basically, if there's any risk of your fluid-containing equipment being exposed to freezing temperatures, it needs some form of glycol. There are two main types of glycol used for this function: ethylene and propylene. Some important differences exist between the two, and they should be understood before making a decision.
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What is ethylene glycol?
Ethylene glycol (CH'OH'), also known as 1,2-ethanediol, is an alcohol-based organic compound often used as an anti-freezing agent in HVAC equipment and vehicle systems, among others. Its an odorless, colorless, viscous liquid, known to have a sweet taste.
In its pure form, ethylene glycol freezes at around -10°F, but when mixed with water, it can remain liquid at much lower temperatures. For example, a mixture consisting of 40% water and 60% glycol can withstand temperatures close to -50°F before freezing.[1]
For glycols used as heat transfer media, viscosity ' a fluid's resistance to flow ' is a critical property, affecting flow rate, friction loss, and ultimately thermal performance. Relative to propylene glycol, which we'll cover later in this post, ethylene glycol is less viscous. For heat transfer applications, lower viscosity is beneficial. Higher viscosity means higher friction loss ' i.e. more energy is required to move a more viscous substance through the system. Applications that require glycol also often include turbulators as well, which help minimize the impact of glycol's viscosity by creating turbulent flow.
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When should I use ethylene glycol?
Between ethylene and propylene glycol, ethylene glycol is the more thermally conductive of the two (see table below). Therefore, ethylene glycol is a good choice for applications in which thermal performance is the top priority.
Essentially, if none of the circumstances in the next section describe your application, ethylene glycol is likely the better option.
If you want to learn more, please visit our website Glycol for Chiller Systems.
When shouldn't I use ethylene glycol?
Ethylene glycol is toxic to humans, causing a number of physiological issues when ingested, including death (the Centers for Disease Control estimate a lethal dose to be between 1,400 and 1,600 mg/kg). As a result, ethylene glycol should not be used in applications in which contamination of drinking water is possible. It should also not be used for heating or cooling systems at facilities like food processing plants or other operations creating products for consumption.
The reason for this is two-fold. Ethylene glycol is harmful to terrestrial and aquatic animals, and when deposited into waterways, takes roughly 10 to 30 days to biodegrade. Glycols biodegrade through aerobic biodegradation, during which the breakdown of glycols is enacted by bacteria, which require oxygen to perform this function. This action depletes the oxygen levels of the effected waterways, which can have devastating effects if the amount of glycol and rate of biodegradation are great enough.
What is propylene glycol?
Propylene glycol (C'H'O'), also called Propane-1,2-diol, is a synthetic liquid used for a litany of purposes across dozens of industries. It's a viscous, colorless, nearly odorless liquid that possesses a faintly sweet taste.
Like ethylene glycol, propylene glycol is combined with water in variable concentrations to depress the freezing temperature of a working fluid in heat transfer applications.
The eutectic temperature, or the lowest possible freezing temperature attainable by any ratio of the two substances (propylene glycol + water) is -76°F at a concentration of 60% propylene glycol and 40% water. However, commercial products typically have that ratio inverted, at 40% propylene glycol and 60% water, the freezing point of which is roughly -7°F.[2]
When should I use propylene glycol?
The answer to this question also answers the question of 'when shouldn't I use propylene glycol?' as well. Relative to ethylene glycol, propylene glycol's higher viscosity and friction loss combined with its lower heat capacity typically limit its usage to applications with safety concerns.
There are extremely few, if any, instances where propylene glycol would be chosen for its thermal performance. It's simply less effective than ethylene glycol for its intended function. But given ethylene glycol's toxicity, several applications exist for which propylene glycol must be used, such as those we covered earlier in this post, namely food production, applications in which water contamination is possible, and the HVAC systems at facilities of these types.
Propylene glycol is considered to be relatively safe for humans. It's a common ingredient in a variety of beauty products, pharmaceuticals, and indirect food additives. While less toxic than ethylene glycol, propylene glycol can pose some environmental concerns.
Propylene ' like ethylene glycol ' is broken down by aerobic means, but where ethylene takes approximately 10 to 30 days to biodegrade, propylene glycol does so in 20 to 30 days or more.
Still not sure which type of glycol is best for your application? Give Super Radiator Coils a call, and let's talk.
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[1] Siegfried Rebsdat; Dieter Mayer. "Ethylene Glycol". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH
[2] 'Properties of Some Particular Solutions' (PDF). Portal del DMT. Retrieved -09-22
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