The Importance of Heat Transfer Fluids in Solar Thermal Systems Explained

Heat transfer fluids are a critical element across a range of industries; and particularly those where solar thermal systems are used. Aside from absorbing solar radiation and transferring that heat to an exchanger, these versatile fluids also guarantee freeze protection at cold temperatures. By considering factors such as thermal stability, non-toxicity, corrosion protection and pH buffering ability, you can make an informed decision that ensures optimal efficiency and system performance.

Heat Transfer Fluids for Solar Thermal Systems: Available Options

• Water

Thanks to its high heat capacity and low cost, water is one of the most popular Heat Transfer Fluids used in solar thermal systems. It efficiently absorbs and transfers heat, making it suitable for moderate temperature applications due to its natural ability to absorb and transfer heat. However, this low cost option has its drawbacks, often requiring additional preventative measures such as freeze, burst and corrosion protection using various chemicals such as antifreeze solutions.

• Inhibited Propylene Glycol

It is important to consider that in the likely event your solar thermal system’s glycol bulk temperature reaches a range of 250°F, residual glycol can become acidic and increase the likelihood of component corrosion. This makes inhibited propylene glycol a popular Heat Transfer Fluid for solar applications, which can be mixed with inhibitors that add to alkaline reserves to greatly reduce that likelihood of corrosion.

This solution is among the safest and easiest to handle and pump into solar thermal systems, with its non-toxicity making it the antifreeze of choice across a range of industries, from HVAC to domestic hot water supply. However, its lower heat conductivity and higher viscosity may require adjustments to your solar thermal system depending on your working climate.

• Inhibited Ethylene Glycol

Ethylene glycol is similar to propylene glycol in terms of providing exceptional freeze protection for solar thermal systems, with a lower viscosity than propylene glycol which typically enhances its heat transfer properties. Ethylene glycol is commonly used in applications where a lower freeze point is required. However, it is important to note that ethylene glycol is more toxic than propylene glycol and requires careful handling and disposal measures to ensure environmental safety.

An important point to bear in mind with propylene glycol is its lower level of performance when subjected to high temperatures. Propylene glycol degrades much faster than its ethylene counterpart, particularly within the higher operating temperatures seen in solar thermal systems. This will require more regular system maintenance, and the costs that are associated with it.

Choosing the Ideal Heat Transfer Fluid for Your Solar Thermal System

Selecting the ideal Heat Transfer Fluid for your solar thermal system involves considering various factors. To simplify this process, CORECHEM has identified some of key criteria:

• Coefficient of thermal expansion: The proportionate change in length or volume of a material in response to a temperature variation.
• Viscous properties: The resistance of a liquid to internal friction, impacting its flow characteristics.
• Thermal storage capacity: The capacity of a substance to retain and store heat energy.
• Solidification temperature: The critical temperature at which a liquid transitions into a solid state.
• Vaporization temperature: The temperature at which a liquid starts to boil and transform into a gas.
• Ignition temperature: The minimum temperature required to cause the vapor above a liquid to ignite in the presence of air.
• Compatibility with materials: The ability of a fluid to interact favorably with other substances and additives, minimizing the risk of corrosion.
• Safety considerations: The assessment of a fluid’s non-toxicity for use in systems involving potable water.
• Long term maintenance and operational costs: The cost-effectiveness of maintaining your solar thermal system long-term using your chosen Heat Transfer Fluid.

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Maintenance and Troubleshooting Tips

Regular maintenance and monitoring of the Heat Transfer Fluid in your solar thermal system is essential for optimal system performance. It is important to inspect the fluid regularly for signs of degradation, contamination, or leaks that can affect system efficiency. 

CORECHEM recommends proactive troubleshooting and appropriate corrective measures to address common issues related to Heat Transfer Fluids by engaging field experts – taking these preventative steps will help ensure the smooth operation of your solar thermal system.

Speak to a member of the CORECHEM team