Daikin VRV II Series Design, Installation & Testing Instructions page 152

Appendix
7.12.3 Example 3:
Situation
Indoor unit was fitted with a drain trap but a leak occurred during subsequent operation.
Source of
The trap was not properly shaped thus preventing it from functioning effectively as a trap and resulting in
Problem and drain leakage. The trap was reshaped and the fault disappeared.
Remedial Action
!
Main Points
Reason:There is resistance on the air inlet side caused by the heat exchanger and air filter and this in turn
creates negative pressure in relation to the atmospheric pressure on the discharge side. If there is no drain
trap then air will be drawn in from the drain pipe and the waste water splashed around giving rise to the risk
of water overflowing from the drain pan. To avoid this problem it is therefore necessary to design a trap
which takes account of the maximum negative pressure which is likely to be created on the suction side.
146
Drain pipe trap shape defective
Duct types (40~125) require a drain trap.
Si39-303
General Information