Blast Evap Fan Ice Build Up In Cowling

[matt watson]

Recently our company insltalled a large blast freezer the evap fans are high flow with 11kw motors we have a problem of ice droplets building up on the inside of the cowling which the fan blades nearly touch or rub on which inceases the load on the motor and trips the overload. Thankfully no blades have smashed yet! Just wondering if this has been a problem for anyone else? It has a water defrost but is not to long have looked at that and has an adequate dripping period. The ice droplets seem to form during the frezzing cycle.

Thanks for any replies

[N.Lewis]

Hi matt, i have come across this prob before working at a site with several large cold rooms, to combat this we had to increase the number of hot gas de-frosts to about four a day, also being site based we had the luxury of doing weekly maintenance IE: getting in there and chipping the ice of, i know you can get heaters for this prob but don't know where, this has been raised before on this site so i'm sure someone will give you a better reply...Good luck mate..

[US Iceman]

The ice droplets seem to form during the freezing cycle.

Is the water collecting on the cowling after defrost or during defrost?

If you start off with a clean coil and cowling and then right after defrost the ice starts to accumulate in the cowling, it's usually due to the water droplets being pulled off of the coil (immediately after defrost when the fan starts).

If this is the case, then the post defrost time for cooling the coil back down to operating temperature needs to be longer.

Blast freezers operate with very high air velocities and they can certainly pull water that is not frozen off of the coil.

[chemi-cool]

ITs all in the defrost cycle. Myself, I dont like water defrost in blast freezers from the point mentioned by US iceman.
Try to increas the dripping time or run the fans backwards for a minut to dry the coils before it gets into cooling cycle again.
Adjust the fans starting temp a few ° lower.

[casstrig]

When you experience this problem what type of ice is there ie flaky ice,as I had a similar problem and it was due to air infiltration which I solved with an air curtain.

[GXMPLX]

Check with the manufacturer if there is an option of defrost heaters for the fans cowling!

[US Iceman]

Check with the manufacturer if there is an option of defrost heaters for the fans cowling!

That's a band-aid for a something else being wrong, in my opinion. To me this is almost like saying; if the fan cowling has ice on it the unit capacity is increased.

[Magoo]

Matt.
I aree with USIceman , extend drip time and coil chill time before fans start, what water is left on coil will freeze and not be dragged of by high velocity airflow, and attach to fan cowls.
PS.. how did assignment go.
magoo

[GXMPLX]

That's a band-aid for a something else being wrong, in my opinion. To me this is almost like saying; if the fan cowling has ice on it the unit capacity is increased.

Not if ice buildup occurs during defrost!

[GXMPLX]

I would also check if the evap has fan delays, or they are working correctly because you could get water spray that quickly freezes when fans start.

[matt watson]

Thanks for the replies guys
The defrost period is for 8 mins and i have watched it defrost and the fan blades do not sweat or defrost.
The dripping period is for ten mins which i thought would be ample.
I will clear the cowling amd monitor the build up.
Thanks for the help

Assessment went well cheers grunta!

[Peter_1]

Inform us about your progress so that we can learn from you

[750 Valve]

Thanks for the replies guys
The defrost period is for 8 mins and i have watched it defrost and the fan blades do not sweat or defrost.
The dripping period is for ten mins which i thought would be ample.
I will clear the cowling amd monitor the build up.
Thanks for the help

Assessment went well cheers grunta!

you have mentioned the drip time, and the fact the moisture does not form on defrost, but you have failed to mention the fan delay that the evap has, is it time or temp initiated? how long/what temp? is it controlled by a klixon or a probe? what is its location?

[Peter_1]

750 Valve made the same assumption I made, you better to it in my opinion temperature controlled and start the fans as soon you're sure they're completely frosted.