6 minute read
FREEZE PROTECTION
By Jonathon Harp
Part I of this primer, in the November/December 2020 issue, dealt with glycol types, uses and mixtures. In Part II, we review how glycol affects the operation of HVAC systems and provide tips for contractors on key factors, that can ensure systems perform well throughout their usable lives.
“Contractors play an important role in the use of glycol systems,” said Neil Bingham of Hood Chemical, a manufacturer of glycol. “Building owners know very little about glycol and its value to their equipment. Contractors who work with glycol systems can act as an information bridge and educate customers about the importance of protecting their investments.”
Glycol can have significant effect on performance and potential need for maintenance. The typical concerns are freezing and bursting of pipes in water-based systems; however, glycol also affects the way pumps, pipes and other components operate in systems. Consider the following when looking at system operations:
•While the right mixture of glycol in a system can prevent freezing and bursting, too much glycol can affect its performance, efficiency and longevity. From a performance standpoint, it is important to understand that water is a much better heat transfer fluid than glycol. For example, a 50-50 water/glycol mixture has 16 per cent lower heat transfer capacity than water alone.
•Performance and efficiency are going to decrease as the amount of glycol in the system increases, and the ambient temperature at which the system is operating decreases. The glycol mixture must be carefully determined to ensure freezing and bursting will not occur and the glycol percentage used is not excessive, which can cause performance to drop unnecessarily. Excessive glycol in a system increases costs and may increase maintenance requirements.
This glycol primer is a general overview of the key factors associated with the use of glycol in waterbased HVAC systems. These articles are not intended as exhaustive field guides. The objective is to help contractors better understand glycol use and prompt you to obtain more specific technical information from wholesalers and/or glycol suppliers about specific systems. The more information you have, the better your design decisions will be.
glycol A primer on Part II
Keeping it clean
Photo Adey Innovation, Morrison Mechanical, BC Cleaning and flushing are essential when adding glycol to both new and existing systems. Existing systems accumulate a number of contaminants such as rust, scale and sediment that must be removed before glycol is introduced. In the case of large systems, professional industrial cleaning companies may be needed to ensure the cleaning process is done correctly. With new systems, there are typically contaminants such as oil, grease and protective substances, as well as welding and pipe scale, that remain in the system from the fabrication or construction processes. Again, a thorough cleaning and flushing is needed to remove these contaminants. There are a variety of commercial cleaning products available to accomplish this task. To protect against corrosion and degradation, glycol systems require inhibitors and buffers to be added to the mixture. These inhibitors are usually
As evidenced by the magnetite premixed with the glycol by capture here, installing a magnetic the supplier. Inhibited glycol dirt filter is a vital step in protecting system components. typically contains four to six per cent inhibitors. Many suppliers
Tips and cautions for contractors
Keep the following advice provided by the glycol supply chain in mind:
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Properly design the HVAC system, and determine the proper mixture of glycol to provide the necessary freeze and burst protection. Remember, wholesalers and glycol suppliers can help with system design.
Choose a reputable glycol supplier and determine the proper fluid specification for the design and use of the system. Again, your wholesaler can typically assist with this process.
Be cautious of using recycled glycol. It is sometimes difficult to determine the specs on recycled product and this could cause system problems down the road.
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A number of boilers have aluminum heat exchangers with special glycol requirements. Be sure to check with the boiler manufacturer’s specifications for using glycol with this type of equipment.
Unless you have experience putting together glycol/water mixtures for HVAC systems, contractors should obtain glycol products already mixed to the levels determined for the system. This will ensure the glycol concentration, water purity, and inhibitors are all at proper levels when added to the system.
Take the time to determine the fluid mixture for the system accurately. Don’t take shortcuts. Do not mix different types or brands of glycol in the same system whether it is the initial fill or a top up. When filling or refilling a system, remember to eliminate any air that has entered the system during this step.
Have regular maintenance checks of the glycol/water concentration in HVAC systems (at least annually). These “checkups” should establish that the concentration, including inhibitors, is at the designed levels and the pH level remains within the range specified by the equipment manufacturer.
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recommend a minimum of 25 per cent glycol be used to ensure proper inhibitor levels are achieved in the mixture. Uninhibited glycol mixtures are extremely corrosive and need additional maintenance of the inhibitor and buffer levels to prevent corrosion and degradation. For example, an uninhibited ethylene glycol solution is nearly five times more corrosive towards carbon steel than water. As glycol degradation increases, corrosion and associated issues become more severe. Contractors who decide to go the uninhibited mixture route must carefully take into account the introduction of inhibitors and buffers throughout the life of the system. Without proper treatment measures, the systems can have serious and long-term maintenance problems. Proper maintenance of glycol-water mixtures requires regular testing of glycol mixtures as well as pH, reserve alkalinity, inhibitor and contamination levels. Glycol degradation is a serious problem that can be difficult to address once it has begun; regular testing of glycol mixtures will assist in identifying degradation symptoms such as pH reduction, presence of a septic odour and severe steel corrosion. A laboratory analysis of the glycol mixtures at regular intervals is also recommended. Periodic testing and monitoring of the inhibited glycol solution will keep the system’s operating maintenance at a minimum.
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Readers can reach Jonathon Harp at editorial@mechanicalbusiness.com.
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