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Use care when selecting heat transfer fluids

When choosing a heating or cooling system a key factor to consider is the composition and quality of the heat transfer fluid used in cooling or heating, ventilation and air conditioning applications.

Despite the relatively low initial cost to the customer, a heat transfer fluid can become the most expensive aspect of a cooling or heating system if it has been sourced or used incorrectly. While it is also important to abide by an efficient and rigorous maintenance regime, the lifespan of a system also depends on the quality of the heat transfer fluid used.

Glycol, which is used to transfer heat through the system, is not particularly corrosive in concentrate form. However, when it is diluted with water to achieve the required frost protection, system corrosion becomes a real problem for the installer and ultimately the end user. Bacterial growth and scaling within the system can also become an issue.

It is easy to assume that all glycol-based fluids are the same but it is vital to select a heat transfer fluid that has advanced glycol inhibitors in order to prevent corrosion, scale and other harmful fouling within a system. To prevent rust within the systems and increase their longevity, it is best to use a less corrosive heat transfer fluid, ie inhibited glycol mixed with water of a sufficient quality.

As the industry recognises the importance of corrosion prevention, an international standard, known as the ASTM D 1384 corrosion test standard, is playing an increasingly important role. This involves immersing metals commonly used in heat transfer systems, such as aluminium, iron, steel, brass, solder and copper in an inhibited glycol/water mixture and analysing them in laboratory conditions for signs of corrosion.

The test is carried out over a period of four weeks and is important as it demonstrates how the fluid protects sufficiently against corrosion. Any fluid can claim to contain corrosion inhibitors but without the presence of a test standard, the extent of protection is impossible to gauge accurately.

There is still a lack of understanding of this standard in the industry. Some heat transfer fluid manufacturers have chosen to embrace the standard. However, the test remains voluntary.

In summary, it is essential to evaluate both the initial cost of installation and the ongoing maintenance and repair costs. An efficient inhibited heat transfer fluid gives the installer and the end user greater peace of mind. Careful and rigorous selection of heat transfer fluids can reduce the need for maintenance and system repairs, in turn extending the life of equipment and maximising the investment that has been made.

Andrew Murray is senior manager at Kilfrost’s speciality fluids division

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