Mitsubishi Electric E Series Data Book page 61

4. System Design
4-1-4. Notes on pipe corrosion
Water processing and water quality control
Poor-quality circulating water can cause the water-side heat exchanger to scale up or corrode, reducing heat-exchange per-
formance. 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.
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
Items
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 an air conditioner (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.
(5) Suspended solids in the water
Sand, pebbles, suspended solids, and corrosion products in water can damage the heating surface of the heat
exchanger and cause corrosion. Install a good quality strainer (20 mesh or better) at the inlet of the unit to filter out
suspended solids.
Removing foreign substances from the water system
Consider installing a settlement tank or a bypass strainer to remove foreign substances from the water system.
Select a strainer capable of handling two to three percent of the circulating water. The figure below shows a sample
system with a bypass strainer.
Strainer (20 mesh or its equivalent)
MEES19K040
Lower mid-range temperature water system
Water Temp. ≤ 60ºC
Recirculating water
7.0 ~ 8.0
(mS/m) (25 ˚C)
30 or less
(μs/cm) (25 ˚C) [300 or less]
-
(mg Cl /ℓ) 50 or less
(mg SO4 2- /ℓ) 50 or less
50 or less
(pH4.8) (mg CaCO /ℓ)
3
(mg CaCO /ℓ) 70 or less
3
50 or less
(mg CaCO /ℓ)
3
(mg SiO /ℓ) 30 or less
2
(mg Fe/ℓ)
1.0 or less
(mg Cu/ℓ) 1.0 or less
(mg S 2- /ℓ) Not to be detected
(mg NH + /ℓ)
0.3 or less
4
(mg Cl/ℓ)
0.25 or less
(mg CO /ℓ)
0.4 or less
2
-
Load system unit
Heat pump unit
Higher mid-range temperature water system
Water Temp. > 60ºC
Make-up water Recirculating water
7.0 ~ 8.0 7.0 ~ 8.0
30 or less
30 or less
[300 or less] [300 or less]
50 or less 30 or less
50 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
0.3 or less 1.0 or less
1.0 or less 1.0 or less
Not to be detected Not to be detected
0.1 or less 0.1 or less
0.3 or less 0.1 or less
4.0 or less 0.4 or less
- -
pump
Bypass strainer (100 mesh or its equivalent)
Tendency
Scale-
Make-up water Corrosive
forming
7.0 ~ 8.0
30 or less
[300 or less]
30 or less
30 or less
50 or less
70 or less
50 or less
30 or less
0.3 or less
1.0 or less
Not to be detected
0.1 or less
0.3 or less
4.0 or less
-
Tank
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