Coolant Application; Definition; Requirement - Danfoss MCHE Installation And Maintenance Manual

Service guide | Application, Installation and Maintenance Manual MCHE
7.

Coolant Application

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7.1 Definition
7.1.1 Water: treated water without any chemical compound added.
7.1.2 Glycol Solution: Refers to commercially available glycol coolants that include inhibitors, pH
buffers, and compounds for biological integrity. It is not a pure glycol solution.
7.1.3 Coolant: refer to:
7.1.3.1 Water solution: Treated water with added inhibitors, pH buffers, and compounds
for biological integrity.
7.1.3.2 Glycol solution: As defined above.
7.2

Requirement:

7.2.1 For coolant:
To ensure the long operating lifespan for microchannel coil, the following conditions for
coolant shall be in place:
- PH: Ideal case pH neutral at 20-25°C (7.5 < pH < 8.5).
- Ammonium NH4+< 2 mg/L.
- Cl- chloride ions < 10 mg/L. (water temp. < 65°C)
- Sulfate ions SO4-2 < 30 mg/L.
- Fluoride ions < 0.1 mg/L.
- No Fe2+ and Fe3+ ions if non negligible levels of dissolved oxygen present (>5mg/L) ,
Fe2+ and Fe3+ ions < 5mg/L if dissolved oxygen < 5mg/L.
- Zn ions is not allowed (ethylene glycol solution application).
- Dissolved silicon < 1mg/L
- Water hardness: > 0.5 mmol/L. Value between 1 and 2.5 mmol/L is recommended.
- Total alkalimetric title (TAC) 100 mg/L.
- Specific resistance – electric conductivity: > 30 Ohm.m is expected. For electric
conductivity value in the order of 20 to 60 mS/m is expected.
Notes:
• Dissolved Oxygen: No sudden changes in water oxygenation conditions are expected.
• Corrosion Inhibitor: Adding a corrosion inhibitor is necessary to ensure coil protection, such as
those based on monopropylene glycol or sodium molybdate.
• High coolant velocity may cause corrosion of microchannel tubes. It is
Coolant Velocity:
recommended that the tube-side coolant velocity not exceed 1.5 m/s to
prevent this issue.
• Filtration: A filter with greater than 20 mesh is recommended to prevent tube
blockages.
7.2.1.1 Specific notes for water solution
• Treated water with the appropriate inhibitor is an acceptable solution. The inhibitor should
provide protection for the entire material system.
Different material systems may require different inhibitors. For instance, inhibitors for
copper and iron systems will differ from those needed for systems containing aluminum,
copper, and iron.
• In addition to inhibitors, pH buffers and compounds for biological integrity should also be
added.
• Before mixing with inhibitors, pH buffers, and compounds for biological integrity, the
water should meet or exceed the 3rd-grade water quality requirements as per ISO
3696-1995. Reverse osmosis water can achieve this quality. It is advisable to consult a local
water treatment company for expertise.
7.2.1.2 Specific notes for glycol solution
7.2.1.2.1 Glycol solution concentration:
Glycol solution concentration is determined by the minimum freeze temperature of the
mixture, but other factors should also be considered to define the "right" glycol
concentration in a closed loop. Increasing glycol solution concentration reduces heat
transfer, so a comprehensive approach is necessary. The following guidelines apply to all
glycol circuits:
• The suggested minimum glycol concentration is always above 20%, even if not required
by the freezing temperature.
• A suitable inhibitor should be chosen for the entire material system. For instance,
inhibitors for copper and iron systems will differ from those needed for systems
containing aluminum, copper, and iron.
Reasons for these guidelines:
• Corrosion Protection: Glycol solution is not a corrosion inhibitor at low concentrations.
Below 20%, there are not enough inhibitors to preserve pipe integrity. Glycol solutions
are designed to guarantee corrosion protection at concentrations above 20%.
• pH Buffering: Oxidation of glycol (e.g., exposure to high temperatures) forms acids that
can potentially damage pipes. The correct minimum glycol concentration will buffer the
solution against these acids by increasing its pH.
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