When dealing with expensive equipment, selecting the process cooling fluid is probably not a high priority. However, the adverse effects of the wrong fluid can be devastating to the equipment as well as the process itself. Proper fluid selection and maintenance will ensure the best results.
Ethylene Glycol vs. Propylene Glycol
Strict attention to the freezing point of fluids is imperative when dealing with process chillers. Chiller manufacturers consider this — as well as the specific application requirements — before designing a system and recommending a water/glycol ratio for its use.
Whether the chiller is designed for indoor or outdoor use, the manufacturer’s recommendation should be strictly adhered to because the type of glycol and the glycol ratio have a dramatic effect on operation. If not protected, low ambient temperatures on outdoor chillers can cause the fluid to freeze and piping to burst.
Chillers located indoors with ambient temperatures above freezing will require less glycol than a system located outdoors. However, whether indoors or out, most chillers are designed for use with a designated mixture of water and inhibited glycol. Maintaining the correct percentage also is important for reasons beyond freeze protection.
A proper glycol concentration will help ensure the correct level of inhibitors for rust protection, lubrication and anti-bacterial growth. All are important aspects in ensuring that the unit’s life expectancy is maintained. Additionally, in an open-to-atmosphere chiller system, operating outside the recommended glycol ratios presents a significantly increased risk for biological growth.
One of the most common types of biological fouling is fungal colonies. Fungi can wreak havoc on a system and be costly and difficult to eradicate. While inadequate inhibitor levels can slow fungi growth, a fungus is a living organism and will continue to spread. If you do not eliminate it, the problem will most likely return. In addition, if your glycol levels are too low, eventually the fungi will feed on the available glycol and continue to spread throughout the system. This will have a substantial impact on system flow, resulting in, at best, a loss of cooling capacity or, at worst, system shutdown. An extremely contaminated machine appears as though there is a large, fibrous rag inside the machine constricting the flow.
Once in a system, fungi can only be removed through the use of a good, strong biocide that is both safe for the chiller and safe for the process. After treating with biocides, the operator must follow up with significant efforts in cleaning and flushing the entire system.
A common mistake regarding glycol is substituting automotive antifreeze for industrial inhibited glycol. It is true that automotive antifreeze is inexpensive, easily accessed, and — yes — glycol-based, but it is missing the necessary level of inhibitors for process chillers, causing similar issues to those described above.
Additionally, automotive antifreeze is specifically designed to operate at high temperatures. When the antifreeze gets cold, it begins to break down, and silicates segregate and begin to coat the internal system. This will have a negative impact on the system components, interfering with heat transfer. Once a system has been contaminated with automotive antifreeze, it must be flushed and cleaned prior to filling it with industrial inhibited glycol. It is important to note that mixing various types of glycol presents additional problems and is never recommended.
Straight Water as the Cooling Fluid?
If an application such as a welding requires operation with straight water, there are alternate measures to ensure both the chiller and the process are protected. Every chiller manufacturer will have water quality standards for each application as well as the equipment. Inhibitors should be added in order to protect the system from corrosion and biological fouling. It is imperative that ongoing testing of water quality takes place every four to six weeks, which will ensure that any impurities from city water do not contaminate the system. Finally, the chiller must be designed to operate with straight water and have integrated freeze protection, including a low pressure switch, flow switch, hot gas protection or freeze stat.
There is no doubt that the selection and maintenance of fluid is crucial to uptime.
Web Exclusive: Selecting the Chiller Type for the Fluid Process