Glycol is fundamental to the smooth operation of any chiller system. But if it is specified incorrectly it can cause expensive problems including reduced heat transfer and corrosion. Brent Hall, technical manager at ICS Cool Energy, gives his tips for using glycol in chillers and chilled water systems.
15 September 2016 | By Brent Hall
8 point plan
1. Never use automotive antifreeze
Automotive antifreeze is formulated for engine cooling rather than process or industrial cooling applications, so when it is used for the wrong applications, it can cause problems with flow rates/pressures and reduced heat transfer. Many automotive antifreezes are not glycol-based and contain other alcohols or glycerine, as well as silicate-based inhibitors, which can coat heat exchangers, attack pump seals, and form a gel, significantly affecting flow rates.
2. Only use inhibited glycol
Uninhibited glycol and water mixtures are very corrosive, often even more than mains water. Modern process and industrial glycols contain inhibitors alongside a pH buffer and biocide to protect against corrosion, scale formation, and rust. For a system to be contamination-free, it needs to be properly flushed, cleaned, and sanitised before the addition of a suitable inhibited glycol and water mixture. Don't mix different types and brands of glycol. Modern glycols contain inhibitors and are dyed for identification. If mixed, their incompatibilities can lead to separation and/or reaction, resulting in gel formation clogging filters, strainers, and pump suctions, as well as a deterioration in heat carrying and transfer properties.
3. Checking your local environmental rules
Some areas have regulations on the use and disposal of particular glycols and antifreeze solutions, concerning things such as ground structure, the water table, and drainage. Check with your local authority. Businesses should also consider using a bio-glycol derived from a sustainable source. These are non-toxic, non-flammable, non-hazardous, and biodegradable.
4. Be aware of the effects of antifreeze on a system
Plain water is one of the most efficient pumped fluids for absorbing and carrying heat. But when any other chemical is added to it, this ability is affected. Adding glycol will cause an increase in the fluid's viscosity and density, and decrease its heat transfer and heat carrying properties. These changes will not affect the overall functionality of your chilling plant and system as long as they are understood and discussed beforehand as they will result in a slightly reduced cooling capacity, an increased pumping power consumption and an increased fluid temperature difference (or an increased fluid flow).
5. Use the correct water
Most systems use mains tap water, which can be damaging to any chiller and its associated machinery and systems. The relative hardness (and mineral content) varies from region to region, so applying the appropriate inhibitors and biocide is vital. Even microbiological contaminants vary, giving a degree of unpredictability to using town mains water or any other uninhibited water source. Using distilled, dematerialised, de-ionised or reverse osmosis water will remove this unpredictability.
Pure water can be damaging to heat exchangers as it tends to attack certain metals in the chiller and water circuit. It also has low conductivity, which can be a problem with some chillers. We recommend the use of pure water with a suitable (minimum 20 per cent) inhibited glycol mix to give the ultimate protection. The added glycol will increase the solution's conductivity to a level compatible with both the system materials and any conductivity-based instrumentation.
6. Consider ethylene glycol in process/industrial applications
Ethylene-based glycol is the standard process/industrial antifreeze additive and can be used in any application where low toxicity is not a requirement. In terms of efficiency losses, ethylene glycol has the least effect on flow rate, heat transfer capability, and pressure loss. But ethylene glycol has moderate acute oral toxicity so should not be used in applications where it may come into contact with potable water and food.
7. Consider propylene-based glycol for food applications
Propylene-based glycols have low toxicity and are the ideal antifreeze additives for applications in the food and beverage industry, and where user contact occurs frequently. Make sure it has been tested by the National Sanitary Foundation, and bears the NSF mark. This means the product is approved by an independent certification body and regulatory agencies worldwide.
8. Maintain the system's hygiene and fluid
Filters/strainers should be installed and checked regularly. The chilled water system must be flushed and sanitised before adding a new solution. It must also be regularly tested to ensure there is no underlying or progressive contamination. For recently cleaned and dosed systems, we recommend a test after three months of operation, including a full sample analysis, then six-monthly tests thereafter.
Brent Hall is technical manager at ICS Cool Energy