AHU drains

[R1976]

Hi all,

Can anyone explain to me how to work out the size of a trap off of a ducted AHU. The trap should be equal to the suction pressure, what does this mean?

thanks

[The Viking]

The pressure on the suction side of the fan must not be greater than the "lock" created by the water inside the trap.

First you have to decide what this pressure is likely to be, then convert it in to something useful like "mm of Water column" (Hint: 1 bar = 10 meter of WC).

Say that you have designed the AHU and it's ductwork to operate with a pressure of -10mBar, then:
0.01 x 10 = 0.1 meter or 100 mm
In this example, 100 mm would be the MINIMUM height of the water in the trap.

In real life,
Make the trap as big as you can, also remember to put 2 unions in it so it can be taken apart for cleaning purposes.

[Brian_UK]

And don't forget to fill it with water when it is installed.

If not then the suction pressure can keep it dry and allow the coil drain pan to overflow.

[Freecool]

Viking is right make the as big as you can, You dont want a call back and the evaporator tray is full of water, and its leaked all into the ceiling or floor.

Freecool

[R1976]

Thanks guys

I'll give em some depth as I think calculating precise measurements will be a bit of a bore, no pun intended.

[wambat]

This is an excellent article on the subject.
http://hvacindia.org.in/journals/2002oct/article05.html