You probably calculated the amount of anti-freeze you required using the theoretical volume of your installation as the basis. Our experience shows that in large volume systems, from 5 or 6m3 upwards, the theoretical calculation of the volume of the installation is always about 10% less than the real volume.
The glycols used in the manufacture of anti-freeze do not disappear over time. The only possible chemical explanation is that water has been added to the circuit.
Two possible explanations:
- The freezing temperature of the glycolated water is too close to the evaporation temperature. As it approaches its freezing point, glycolated water undergoes a very significant increase in viscosity and "layers" of glycolated water stop flowing. The heat exchange drops and the glycolated water slowly freezes in the heat exchanger. The freezing point of glycolated water must be at least 5 degrees lower than the lowest temperature likely to be reached in the exchanger. Increasing the glycol concentration will solve this issue.
- The circuit contains a lot of sludge. This sludge will settle in the areas where there are the greatest losses of load and the coldest areas, so generally in the exchanger. In this case the only solutions are either to drain and clean out the system or to mount a bypass filter to remove the sludge.
If you put water into your system which is mainly steel, when you drain the system it will corrode on the surface. The glycolated water will then remove this thin layer of rust and sludge will form. The quantity of sludge will be directly proportional to the size of the system. When cleaning with water, it is important that the time between draining the water and filling back up with glycolated water is as short as possible. If you need to leave the system with water in it for several days or leave it in the open air for cleaning, ensure you mount a by-pass filter to remove the oxides that the glycolated water will inevitably remove.
Anti-freezes are generally miscible, meaning that if you mix them you get a homogeneous solution, unless they are heat transfer fluids using different glycols (MEG, MPG etc). However, this does not mean that the anti-freezes are compatible. Two different anti-freezes will have different formulations in terms of corrosion inhibitors.
Mixing them together will result in a blend of corrosion inhibitors, the effectiveness of which cannot be determined. Before adding anything, we recommend that you check the glycolated water present in the circuit to assess whether it might not be better to undertake a complete renewal.