Filling a heat transfer system

Filling, preparing and starting up a new heat transfer system

Performing the planning, set up and maintenance of a newly installed heat transfer system according to best practice can improve the life span of a thermal fluid and ensure that a new system is a cost-effective investment.

Once the system is designed and built there are some actions you need to take because some components of a heat transfer system only perform functions during installation. For example, a strainer is added during installation to catch debris, such as metal shavings or bolts that enter the system during construction. General practice for engineers is to remove the strainer after the system has been up and running for around five working days. If the strainer is not removed, it can lead to carbon build up in the system and cause flow issues. Discuss with your system designer and installer to understand what components need to be removed or adapted after system installation.
All thermal fluid systems, new or recently drained, need cleaning and flushing prior to being filled with new heat transfer fluid. Flushing prior to filling or refills is an effective way of removing contaminants that accelerate the ageing of a fluid. After installation, for example, any welding slag, ferrous material or yellow metals that remain in the system after it is built, could accelerate fluid degradation and reduce the working life of a heat transfer fluid.
Contaminants can remain in the system even after draining the fluid. If they do, they can reduce the efficiency of the system and compromise the new fluid when it is introduced. Typically, up to 25 per cent of a system’s fluid volume can remain in the system after draining due to the physical attributes of some components, such as horizontal heater coils, meaning that not all fluid can be drained. So, after draining you still need to address the contaminants that remain in the system.
Circulating debris in any heat transfer system at any stage of its lifecycle is a cause for concern. High levels of debris can lead to the erosion of pipework and can also accelerate the wear of mechanical pump seals. Circulating debris can have other consequences if not managed properly. For instance, at low circulating speeds, larger particles settle out from the circulating thermal fluid. This leads to the formation of a sediment layer that will increase thermal resistance, reduce the efficiency of the fluid and can potentially form hot spots. In more extreme cases, contamination may even cause the clogging-up of the system. At high circulating speeds, large particles carry more momentum and kinetic energy and this can cause damage to the internal pipe work and accelerate erosion.
Once a new system is built or a current system is drained, engineers should refill the system with a cleaning and flushing fluid. Engineers should circulate the fluid in the system at 108-122 degrees Celsius (225-250 degrees Fahrenheit). This temperature range activates the detergent additives in the cleaning fluid so that it can mix with suspended loose particles. These particles will leave the system when draining the cleaning fluid.
After the system is cleaned, you can fill it with new fluid. Once the system is refilled and circulating at the proper levels in an expansion tank, heat can be applied in 15 degree increments until the heat transfer fluid reaches 105 degrees Celsius.
You should ensure you remove any water from a heat transfer system during start up. Increased water in the system often leads to contamination with larger particulate matter and iron, an indicator of rusting. One sign there is water in the system is if the primary pump starts to cavitate. To treat this issue, you can increase the temperature to 115 degrees to boil off the water, but this could take anywhere between a few hours and several days. Alternatively, installing a Light Ends Removal Kits (LERK) will remove water more efficiently. After all signs of water in the system have gone, the heat may be turned up to 125 degrees and gradually increased in steps to 140 degrees.
Once a system is up and running, manufacturers should establish a regular maintenance programme to maintain productivity. Regular and representative sampling and analysis of fluid when the system is hot, closed and circulating gives engineers an accurate representation of what’s happening in the system and means maintenance can be scheduled accordingly.
Global Heat Transfer engineers can help ensure that your new or existing systems are cleaned and ready for new heat transfer fluid. For support with filling heat transfer systems, call +44 (0)1785 760 555.