Mitsubishi Electric CAHV-P500YB-HPB Service Handbook page 34

[ II Restrictions ]
(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.
(6) Connecting pipes made from different materials
If different types of metals are placed in direct contact with each other, the contact surface will corrode.
Install an insulating material between pipes that are made of different materials to keep them out of direct
contact with each other.
(7) In the case that the unit is installed in higher than storage tank
Note the following. Air pockets inside of heat exchanger will cause to corrode or scale up.
( Refer to the lower diagram.)
1) Provide air vent valve at the unit outlet to let the air certainly go through.
2) Keep the height differences between the unit and storage tank within 7 m.
3) Note the following not to become negative pressure.
a) Continuously operate the pump not to become negative pressure.
(Reference Boiling point : -70 kPaG, 70°C)
When the pump is not continuously operated, provide pressure holding valve to prevent air mixing.
b) Provide vacuum valve or use sealed tank not to become negative pressure.
Height differences
Within 7 m
HWE15070
Air conditioning unit
Heat pump unit
Strainer (20 mesh or its equivalent)
Automatic air vent valve
Unit
Check valve
Water pump
Bypass strainer
Vacuum valve
Pressure holding valve
Storage tank
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GB