Notes On Pipe Corrosion - Mitsubishi Electric CAHV-R450YA-HPB Installation & Operation Manual

[2] Notes on Pipe Corrosion

Water treatment and water quality control
Poor-quality circulating water can cause the water-side heat exchanger to scale up or corrode, reducing heat-
exchange performance. Properly control the quality of the circulating water.
• Removing foreign objects and impurities in the pipes
During installation, keep foreign objects, such as welding and sealant fragments and rust, out of the pipes.
• Water Quality Control
(1) Poor-quality water can corrode or scale up the heat exchanger. Regular water treatment is recommended.
Water circulation systems using open heat storage tanks are particularly prone to corrosion.
When using an open heat storage tank, install a water-to-water heat exchanger, and use a closed-loop circuit
on the hot water heat pump unit side. If a water supply tank is installed, keep contact with air to a minimum, and
keep the level of dissolved oxygen in the water no higher than 1 mg/ℓ.
(2) Water quality standard
pH (25˚C)
Electric conductivity
Chloride ion
Sulfate ion
Standard
items
Acid consumption
Total hardness
Calcium hardness
Ionic silica
Iron
Copper
Sulfide ion
Reference
Ammonium ion
items
Residual chlorine
Free carbon dioxide
Ryzner stability index
Reference: Guideline of Water Quality for Refrigeration and Air Conditioning Equipment. (JRA GL02E-1994)
(3) Please consult with a water quality control specialist about water quality control methods and water quality
calculations before using anti-corrosive solutions for water quality management.
(4) When replacing a hot water heat pump unit (including when only the heat exchanger is replaced), first analyze
the water quality and check for possible corrosion.
Corrosion can occur in water systems in which there has been no signs of corrosion. If the water quality level
has dropped, adjust the water quality before replacing the unit.
Lower mid-range temperature water system
Items
Recirculating water
(mS/m) (25˚C)
(µs/cm) (25˚C) [300 or less]
-
(mg Cl /ℓ)
2-
(mg SO4 /ℓ)
(pH4.8) (mg CaCO /ℓ)
3
(mg CaCO /ℓ)
3
(mg CaCO /ℓ)
3
(mg SiO /ℓ)
2
(mg Fe/ℓ)
(mg Cu/ℓ)
2-
/ℓ) Not to be detected Not to be detected Not to be detected Not to be detected
(mg S
+
(mg NH /ℓ)
4
(mg Cl/ℓ) 0.25 or less
(mg CO /ℓ)
2
Water Temp. ≤ 60ºC
Make-up water
7.0 ~ 8.0 7.0 ~ 8.0
30 or less
30 or less
[300 or less]
50 or less 50 or less
50 or less 50 or less
50 or less 50 or less
70 or less 70 or less
50 or less 50 or less
30 or less 30 or less
1.0 or less 0.3 or less
1.0 or less 0.1 or less
0.3 or less 0.1 or less
0.3 or less
0.4 or less 4.0 or less
— —
13
Higher mid-range temperature water system
Water Temp. > 60ºC
Recirculating water Make-up water
7.0 ~ 8.0 7.0 ~ 8.0
30 or less 30 or less
[300 or less] [300 or less]
30 or less 30 or less
30 or less 30 or less
50 or less 50 or less
70 or less 70 or less
50 or less 50 or less
30 or less 30 or less
1.0 or less 0.3 or less
1.0 or less 0.1 or less
0.1 or less 0.1 or less
0.1 or less 0.3 or less
0.4 or less 4.0 or less
— —
Tendency
Scale-
Corrosive
forming