Selecting and sizing a chiller requires knowing the process fluid so the best design can be used for the application.

The fluids used most with chillers are the following:

  • Water
  • Oil
  • Water Soluble Oil
  • Special Fluids

What are the Different Types of Water and How to Maintain it?

Most industrial processes today utilize a process fluid to cool the equipment by moving heat away from the operation. An industrial chiller is a cooling system designed to remove heat from that process fluid, transfer the heat to another medium (ambient air or water), and return cool fluid to the process to begin the cycle again. One of the critical maintenance issues with process chillers is understanding what is in your water.

When it comes to process cooling fluids, water is commonly used. Knowing the difference between the different types of water helps the overall performance of the chiller and the process being cooled. Most equipment manufacturers have recommendations on what kind of water should be used in their equipment, which would enhance the overall production uptime as well as the service life of the equipment.

In some applications, like cooling laser equipment, the water conductivity is vital to the performance of the equipment.  These commonly use deionized water (DI) which resists the flow of electrical current.  In other applications water glycol is required to protect from freezing and bacterial growth.

Process chillers usually use four main types of water.

Depending on the application, some chillers use tap or city water. While using tap or city water may seem like an easy option for manufacturing processes, it is not a recommended one because it can damage the equipment, leading to costly repairs and downtime. Tap or city water contains impurities that can damage components so an industrial inhibited glycol is recommended to add to the water. Tap or city water is also a conductor of electricity.

Steam distilled water is the result of when some of the impurities are removed from the water through the steam distillation process. While this process has less buildup of scale and minerals, it is still recommended to add an industrial inhibited glycol to add to the water. Steam distilled water is also a conductor of electricity.

Whether the equipment is using tap, city or steam distilled water, the use of industrial inhibited glycol and water mixture is recommended. Ethylene and Propylene are the two standard types of inhibited glycols commonly used.

The main job of glycol is to prevent freezing of the process fluid and ensure consistent flow at the operating temperature. Industrial glycols have inhibitors which will also prevent formation of scale and corrosion while protecting metals such as brass, copper, steel, cast iron and aluminum. Water systems treated with an inhibited glycol will also be protected from algae and bacteria that can grow and degrade the fluid system performance.

There are a few tips to consider when using glycol.

Don’t Mix Glycols — Do NOT mix different types or brand names of glycol. This can result in some inhibitors precipitating out of the solution. Mixing glycols will also gel and clog filters and prevent proper flow rates. If switching glycol types, it will be necessary to run a thorough flush and clean of the fluid system. Once that’s done, it’s okay to change over.

Don’t Use Automotive Grade Anti-Freeze — Do not use automotive grade anti-freeze in the chiller process. These types of glycols do not have the right type of inhibitors and are not designed for industrial applications and may cause problems with heat transfer or fluid flow. Many automotive glycols contain silicate-based inhibitors that can coat heat exchangers, attack pump seals, or form a flow restricting gel.

Check Local Environmental Regulations — Check state and local codes when selecting the process fluid. Certain areas may have environmental regulations concerning the use and disposal of glycol or other additives.

Ethylene Glycol for Most Standard Industrial Applications — Ethylene glycol is the standard heat-transfer fluid for most industrial applications. This type of glycol can be used in any application where a low-toxicity content is not required. Ethylene glycol has moderately acute oral toxicity and should not be used in processes where the fluid could come in contact with potable water, food, or beverage products.

Propylene Glycol for User-Contact Applications — Propylene glycol maintains generally the same freeze protection and corrosion/algae prevention levels as ethylene glycol – but has a lower level of toxicity. This type of glycol is more readily disposable than ethylene and safer to handle. Propylene glycol is commonly used in the food industry and in applications where the user may come in frequent contact with the fluid.

Difference Between Ethylene and Propylene Glycol — At very cold temperatures, propylene glycol become more viscous, changing the heat exchange rate slightly. Some chillers are designed for that compensation so that either glycol type can be used. Ethylene is more widely used due to its lower purchase price, making it more economically feasible for factories with significant purchasing volumes.

Applications Drive Water/Glycol Mix Percentages — The location of the chiller and environmental concerns must be taken into account when selecting the proper mixture of glycol and water for the chiller process. A process located completely indoors, with no chance of freezing, will require less glycol than a system located outdoors where low temperatures can cause the fluid to freeze and piping to burst. Applications with a very low operating temperature (below 20 F) should use a glycol mixture equivalent to an outdoor system. After selecting the proper glycol and water types, use the following chart to determine the recommended mixture depending on the application and location of the process. The glycol percentage figures in the chart below will apply to any brand of ethylene or propylene glycol.

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*Figures based on the performance of Koolant Koolers K-Kool-E brand of ethylene glycol

Deionized water (DI) is the result after the removal of the mineral ions, such as cations like sodium, calcium, iron, and copper, and anions such as chloride and sulfate. This type of water is commonly used with cooling laser equipment. Deionizing the water can be a costly process but it cannot be substituted because deionized water is required in some applications where the water conductivity is important.  This is a measure of the purity of the water which correlates to its conductivity.  It indicates the resistance to the flow of electrical current which is measured in ohms.  Conductivity is the inverse of resistance and is measured in mhos or Micro Siemens indicating how much electrical current flow.

Each application typically has specific requirements for the allowable conductivity level of the DI water used. 

The chiller must be properly designed to operate with the DI water required since at low DI conductivity levels it will actually attack certain metals and cause damage to some components. The purity of deionized water can vary and should be measured against the conductivity scale. Pure deionized water is a poor conductor of electricity. If it is pure enough, inhibitors are not necessary.

Not to be confused with demineralized water, deionized water is very corrosive because it pulls any impurities from the metal piping and atmosphere into it. In its purest form, it is not safe to drink since this can cause internal bleeding.

The water used is important to consider with chillers. Using the wrong type of water can affect the performance as well as the life of the chiller components. The chiller manufacturer should be informed of the application and the equipment manufacturer’s specifications so the proper components and design are used for the water or cooling fluid being used.