Evaporator Drain Trays Choked; Dripping water and Icing

[haris]

Dear All,

I am an instrumentation engineer and have to look after a cold storage as well. This is an Ammonia unit with both freezer and chiller operations. I have an issue - there is a lot of icing right under the evaporators - they drip and eventually form ice on the floor which makes operations very difficult.

I got the evaporators checked, the drain trays were misaligned and also - there was icing on the drains. I believe it has to do with the drain heaters - they were 20Watts/M self regulating at 10C. My concern is, the room temperature stays between -18 or -26 C - wouldn't the drain heaters remain ON considering they are regulated at 10C.

Should I use non regulated heaters and control their switching using timers and contactors?

Also, I have started noticing ICE on the panel walls and ceiling - right where the blast hits; is it due to moisture?

Regards,

Haris

[RANGER1]

haris,
I think drain heaters are on all the time, if closely wrapped around drain pipe & then insulated or run heater in drain itself.
Should also have a "P" trap outside of room to stop ingress of warm moist air on coil face.

Other reasons for drips & ice build up might be unit near a door opening.leaking penetrations or seal in panels, leaking drain tray ,no air curtain or strip curtain on door, doors left open to long, defrost to long.
You can also insulate drain trays

[Rob White]

.

Drain heater of this type would normally be on continuously.

I have found though with self regulating heater tapes, that they
can develop cool spots on the tape. Small areas that do not work
correctly and therefor they are cooler around that area. If this happens
then the chances of an ice build up is possible.

I have stopped using self regulating tapes and only fit pre made internal
heater tapes down the inside of the drain.

As for the ice build up on the wall, you have a moisture ingress problem.
Somehow moist air is getting into the rooms and is freezing on the evaps
and walls in the area of the evap.

You need to check all the door seals and make sure there are no faults in the
room alowing air in. Door opening times are critical.

It might be worth fitting door air curtains or air lock chambers if it is coming in
through the doors.

[mikeref]

As Ranger mentioned above, + make sure the evaporator fans don't start up straight after a defrost.
There has to be a fan delay thermostat, or sensor that won't allow evap fans to restart until coil temperature is several degrees below zero.
Self regulating heater cable is fine and running inside the condensate drain is not a problem if left on continuously, and insulated. Cycling that heater with defrost times will cause a problem.