The global demand for industrial process cooling remains at a steady high. Reliability and minimal downtime are key to consistent and profitable industrial and commercial processes.
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This article will consider the best methods to attain the optimal temperatures required to operate production processes in the metal finishing, medical, brewing, and agricultural industries.
So, how does a chiller work? The process works in a loop, but we will start where the cooling medium interfaces with your process equipment.
The system's coolant absorbs thermal energy from your process, typically causing a phase change into a gas. The gaseous refrigerant is then circulated to a condenser which expels the heat through evaporative condensation or a cooling tower. This heat exchange condenses the cooling medium back into a cooler liquid that is sent back to process heating source to begin the cycle again.
The type of coolant utilized in a chiller is based on process needs and cost considerations. The most popular coolants used are either water or a mixture of water and another substance with suitable heat conduction properties ' like glycol compounds.
The use of water as chiller fluid is an economical one as in most cases the water can be easily sourced with minimal costs. Alternatively, purified (deionized water, reverse osmosis) water can be used in a water-based chiller to achieve a higher cooling efficiency.
Glycol based coolants are either composed of ethylene glycol or propylene glycol. While these two variants have similar physical properties, they should never be mixed. The major advantages which glycol coolants confer are an improved resistance to corrosion as well as antifreeze properties.
Using a glycol-water mix as a chiller coolant has various benefits over the use of plain water as a chiller fluid. These advantages are due to its unique physical properties which include a lower freezing point than water.
For water free of impurities, the freezing point is 32°F which is much higher compared to pure ethylene glycol which changes to its solid-state at 8.9°F. When a glycol-water mixture is altered, the freezing point of the coolant also changes. To cite an example, 10% ethylene glycol will freeze at 25.9°F while a 60% glycol solution will freeze at -63°F.
From the above analysis, it's clear that glycol has refrigerant properties that are more suited for use in chillers expected to function in low-temperature environments. In these thermal conditions, a water coolant will freeze and obstruct chiller circulation while diminishing overall efficiency.
By contrast, utilizing a glycol-based chiller will take advantage of its antifreeze properties ensuring the coolant remains in a desirable fluid state.
Both glycol and water chillers can be used to satisfactorily dissipate the heat being generated by your production process. The fundamental difference between both chiller types lies in variations in their freezing points as well as their heat conduction capacities.
Pure glycol or a mix of glycol and water has a much lower freezing point than that of pure water. By implication, glycol-based chillers are better suited to low-temp environments. Conversely, water has a better ability to retain and conduct heat from an associated process than a glycol mixture can. As a result, the efficiency of heat transfer for a water chiller will be higher than that of a glycol chiller.
Overall, operators need to consider the ambient temperatures for the siting environment before choosing a chiller type.
A glycol chiller plant is composed of a refrigeration component and tubing containing a glycol-water mixture as coolant. Chilled fluid from the refrigeration unit is channeled through the piping associated with a thermal exchanger surrounding a heated process. After absorbing heat from the associated process, the warmed coolant is returned to the refrigeration unit for cooling after which the process is repeated.
For many chiller types, ethylene glycol is mixed with water at a ratio of 60/40. This higher percentage of glycol boosts the mixture's antifreeze properties significantly. This is useful in cases where rapid cooling is required. In these situations, a process can be cooled to very low temperatures without freezing the coolant within its piping.
A conventional water chiller works on the principles of heat transmission between various mediums both fluid and solid. These cooling systems work either by heat absorption or vapor compression. The basic components of a water chiller system include a refrigeration unit and a piping system that circulated chilled coolant.
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Automotive antifreezes are not formulated for complex mixed metal chillers, or any other low temperature industrial applications. Many automotive antifreezes are not glycol based and contain silicate-based inhibitors (necessary to protect automotive engines), that can cause serious issues for chiller systems, including:
Regular drain and refill required
Automotive antifreezes generally have a short lifespan and require more frequent draining and refilling than inhibited glycols. Over the long-term, the cost of draining and refilling a system regularly with auto antifreeze will be far greater than the initial cost of inhibited glycol.
Uninhibited glycol/water solutions can be particularly corrosive and potentially more harmful to a chiller system than standard mains water. Inhibitors neutralise the natural tendency of water to corrode, scale and foul pipe-work systems and associated components.
To prevent internal corrosion, scaling and biological fouling all of Hydratech's heat transfer fluids are formulated with multi-metal and multi-function inhibitors, which exceed ASTM D standards.
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Ethylene glycol is used in most industrial applications where low toxicity is not required. It offers the best heat transfer rates of all glycols and is often selected ahead of propylene glycol for this reason. The main drawback associated to ethylene glycol is its toxicity to humans and animals, making it unsuitable for the food and beverage industry and frequent user contact.
Hydratech's IGE is an industrial grade secondary refrigerant antifreeze based on ethylene glycol for process cooling & AC systems - with proven corrosion, scale and biological inhibitors.
More information on Coolflow IGE here
Propylene glycol was developed to replace ethylene glycol for use in food and beverage processing systems or where there is a requirement for a non-toxic classification.
Characteristically, PG has a much lower capacity for efficient heat transfer, compared with ethylene glycol-based mixtures. It is also much more viscous at low temperatures and thus provides more of a challenge to pump.
Hydratech's Coolflow NTP is a non-toxic antifreeze and secondary refrigerant based on propylene glycol for process cooling & AC systems - with proven corrosion, scale and biological inhibitors.
More information on Coolflow NTP here
'
, a more efficient and cost effective alternative to PGCoolflow DTX' was introduced in as a high performance non-toxic secondary refrigerant, suitable for replacing propylene glycol in food and cold storage cooling systems.
The game-changing fluid combines the thermal efficiency and low viscosity associated to ethylene glycol, with the non-toxic rating of propylene glycol. The list of DTX adopters is now extensive and includes Arla Foods, Mϋller Dairy, Waitrose, Airbus, Siemens and BrewDog.
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It is important to check local environmental rules, as some areas have specific regulations regarding the disposal of working fluids. Your local authority will have all necessary guidelines.
If using regular tap water in a glycol/water solution, it is vitally important to apply the appropriate multi-metal and multi-function inhibitors. Mains water contains deposits and additives which can damage a chiller system and associated components.
An understanding of the local water's characteristics is also important, as mains water hardness varies from region to region. City or town mains water can be particularly problematic as their water properties can fluctuate.
Using water from a good quality, filtered source will eliminate any uncertainties.
For optimum system protection, Hydratech recommend a filtered water and 25% v/v inhibited glycol mix.
Selecting the correct type and concentration of glycol is very important. The glycol type should already be known and recorded in the commissioning documents or maintenance logs for your systems.
Hydratech Services can assist with glycol determination analysis if it is not known ' it is especially important to verify this for food or beverage process applications.
Too much glycol or too high a % will cause system inefficiencies through reduced heat transfer ability and pumping capacity. Not enough glycol or too low a % can lead to the expensive freeze-ups previously mentioned and can become susceptible to biological fouling.
Typically, external systems susceptible to freezing over winter months will need anti-freeze protection down to the lowest expected ambient temperature, with some margin advised for safety of +10%* (*Lowest temps ever recorded in UK -26.1°C - January ). To prevent internal corrosion, scaling and biological fouling year-round, it is recommended that the glycol is fully inhibited and monitored every 6 months. Hydratech recommend a minimum concentration for their inhibited glycols of 25% v/v ' this would provide a freeze protection average of -10°C.
Managing chiller working fluids is important if process efficiency is to be optimised and operating costs minimised. It is not uncommon for the maintenance of cooling and heating systems to be overlooked.
Under such circumstances various issues can develop, including; advanced corrosion, biological fouling and sediment formation. All of which will have a direct and negative impact on heat transfer, pumping performance and energy costs.
Often, cooling systems that have been altered or upgraded are topped up with uninhibited water, resulting in a dilution of the antifreeze and inhibitors.
To verify long-term condition of the fluid and system, Hydratech recommend periodic analysis of the heat transfer fluid. Hydratech provide a range of Fluid Management Services' to maximise thermal efficiency, minimise downtime and extend component life.
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