Drip Tray Icing Up

[Refrigerologist]

Hi Guys. I have a low temp freezer operating a -29degC.
2No. Friga Bohn LUC435 Evaporators installed. I should addd that even running the room at -24deg C same problem occurs only a bit slower.

The drip trays ice up every 5 to 6 monthshttp://www.refrigeration-engineer.com/forums/images/icons/icon8.gif. All heaters are working correctly, including the drain heater tapes. The drain remains clear, but a film of ice builds up beneath the coil just above the drain outlet. Then of course when it builds over the drain outlet it completely fills with ice.

There is only 1No. Drain pan heater installed and this runs more or less around the perimeter of the drain tray.

I have the folowing ideas for solving the problem:
1. Install a second drain pan heater and fit it just below the coil and as near as possible to the drain outlet.
2. Insulate the drain pans with sheet close cell insulation.
3. A combination of 1 & 2.

Is this a common problem with the Friga Bohn Evap?
Does anyone have any better ideas?

[taz24]

Hi Guys. I have a low temp freezer operating a -29degC.
2No. Friga Bohn LUC435 Evaporators installed. I should addd that even running the room at -24deg C same problem occurs only a bit slower.

The drip trays ice up every 5 to 6 monthshttp://www.refrigeration-engineer.com/forums/images/icons/icon8.gif. All heaters are working correctly, including the drain heater tapes. The drain remains clear, but a film of ice builds up beneath the coil just above the drain outlet. Then of course when it builds over the drain outlet it completely fills with ice.

There is only 1No. Drain pan heater installed and this runs more or less around the perimeter of the drain tray.

I have the folowing ideas for solving the problem:
1. Install a second drain pan heater and fit it just below the coil and as near as possible to the drain outlet.
2. Insulate the drain pans with sheet closed cell insulation.
3. A combination of 1 & 2.

Is this a common problem with the Friga Bohn Evap?
Does anyone have any better ideas?


Does the drain have the heater tape wraped around it or through it?

I would put a thin short heater tape running from the evap through the drain past the first bend.
Wire the heater to be on continuasly and see what happens.
I dont think it is just a problem with Friga Bohn evaps, most suffer from the same problem at those temps.

Cheers taz.

[Refrigerologist]

Does the drain have the heater tape wraped around it or through it?

I would put a thin short heater tape running from the evap through the drain past the first bend.
Wire the heater to be on continuasly and see what happens.
I dont think it is just a problem with Friga Bohn evaps, most suffer from the same problem at those temps.

Cheers taz.
Taz. the drain actually remains clear. The ice forms in the tray and causes a dam around the drain outlet, then later the ice builds up and forms a thin film over the hole.

The heater tape is wrapped on the outside of the tube and around the drain connection, it is permanently on. I know what you are saying about installing a heater throught the drain, but I don't think it applies in this case.

[taz24]

Taz. the drain actually remains clear. The ice forms in the tray and causes a dam around the drain outlet, then later the ice builds up and forms a thin film over the hole.

The heater tape is wrapped on the outside of the tube and around the drain connection. I know what you are saying about installing a heater throught the drain, but I don't think it applies in this case.

Ok.
Test the drain it may have a resriction. It allows the water to drain but it keeps it in the pan long enough to frost up and start the ice above the drain.


Go inside and pour a bucket of water down both evaps.
If the blockage is comon the water can come back from one evap to the other.
Prove the drains are spotless.

Cheers taz

[750 Valve]

Are the drain connections in the centre of the evaps or at one end?
Is there adequate fall in the pan?
How long is your drip time?
What temp are you terminating at on defrost or is it time terminated?
How long does the defrost run for and what is the temp of the pan in the affected region at the end of defrost?

[Refrigerologist]

Ok.
Test the drain it may have a resriction. It allows the water to drain but it keeps it in the pan long enough to frost up and start the ice above the drain.


Go inside and pour a bucket of water down both evaps.
If the blockage is comon the water can come back from one evap to the other.
Prove the drains are spotless.

Cheers taz

No restrictions in the drain line. 2 feet of fall from first evap drain before it enters common drain. Second evap drain 4 feet of fall before it enters common drain. And when I say fall I mean vertical:D Ths is a problem that started day 1 with new drains, new install!

I should also add that this is a run and standby set up. So each system runs alternately. So we there will be no issues of water coming back up the line from the other evaporator.

[Refrigerologist]

Are the drain connections in the centre of the evaps or at one end?
Is there adequate fall in the pan?
How long is your drip time?
What temp are you terminating at on defrost or is it time terminated?
How long does the defrost run for and what is the temp of the pan in the affected region at the end of defrost?

Drain oulets are in the centre, towards the rear of the tray beneath the evaporator coil. Defrost is terminated at a 5 deg C coil temp. Failsafe termination time is an old Marks and Spencer spec of 28minutes. Drip time is 3 minutes. The coils are clear, only the trays ice up, the drains are clear and run freely. In an earlier post you will see that I stated that a thin layer of ice forms in the tray after a few defrosts and fails to clear, this builds a dam around the drain outlet and eventually the whole tray fills with ice and then it bridges over the outlet. I have already tried higher termination temperatures, but of course this leads to steaming and the forming of "hoare frost" on the ceiling and panels.

My theory is that due to the very low temperature, the tray heater element has insufficient output to warm the tray for long enough to allow the water to escape. So, if I insulate the tray, I will cut down the heat loss and the tray should stay a little warmer for longer, and hopefully the water will drain before refreezing.

[Chunk]

Is it a moulded drain fitting on the pan or is it just a hole where you put your own fitting into it?

I have had on one set of blowers before where i had put my own fittings on,a small gap between fitting an pan,which holds a small amount of water,which then freezes and gets larger and stops any more flow.

The only other solution is as Taz said is to run a small peice of heater tape near drain outlet.:)

[Refrigerologist]

Is it a moulded drain fitting on the pan or is it just a hole where you put your own fitting into it?

I have had on one set of blowers before where i had put my own fittings on,a small gap between fitting an pan,which holds a small amount of water,which then freezes and gets larger and stops any more flow.

The only other solution is as Taz said is to run a small peice of heater tape near drain outlet.:)

It is the recessed fitting that came with the blower.

Is there anything that will stick some self terminating heater tape to the tray?

[Chunk]

It is the recessed fitting that came with the blower.

Is there anything that will stick some self terminating heater tape to the tray?

You can use the foil type ducting tape,most suppliers stock it.

If you have a small ridge around the drain outlet,i have used a gel called LSX that you can pack into the recess.It is a waterproof gel that is maliable and sets like mastik and can be used in freezers.You can buy it in tubes from plumbers merchants or B&Q for about £5.

[Chunk]

Hi

Just to give you an idea about the tape

http://www.tapes-direct.co.uk

Click on foil tapes.It is the standard type that i normally use.

[taz24]

I would just put a 1 mtr internal heater tape through the bottom of the evap and into the drain past the fitting.
This will always keep a route open for the water to flow and it should be ok.


Cheers taz.

[Chunk]

I`ve put heater tape underneath the pan before,just to keep the pan slightly warm,but it did look awfull.

It worked though.:)

[philfridge]

Hi I have overcome this problem in the past by using a isopad 2m KDL/SL nrs 678918 drain heater tape .Fit it inside the drainline .Run some done the start of the drain and leave the rest laying in the drainpan. This should keep it clear .

[andywill]

Hi Refrigerologist
I think you are going down the wrong route with more heater tapes. Firstly is your tray heater on for the full duration of the defrost cycle including drain down and secondly i think your drain down period is too short at 3 min. I would have this at about 8-10 min. coil heaters off after defrost, pan heater on until after drain down period. Had same problem once and this worked for me.

[Refrigerologist]

Hi Refrigerologist
I think you are going down the wrong route with more heater tapes. Firstly is your tray heater on for the full duration of the defrost cycle including drain down and secondly i think your drain down period is too short at 3 min. I would have this at about 8-10 min. coil heaters off after defrost, pan heater on until after drain down period. Had same problem once and this worked for me.

Andy, Good idea!

I must admit that the drain pan heater is fed off of the same supply as the coil heaters. So a bit of rewiring will be required. I do seem to remember doing what you say in the past, but I have not really been doing much fridging in the last 15 years. Nearly all A/C. The memories are dimming:eek:


Thanks for that, I will give it a tryhttp://www.refrigeration-engineer.com/forums/images/icons/icon14.gif I am sure it will work as it will warm the tray through.

[philfridge]

Hi Refrigerologist
I think you are going down the wrong route with more heater tapes. Firstly is your tray heater on for the full duration of the defrost cycle including drain down and secondly i think your drain down period is too short at 3 min. I would have this at about 8-10 min. coil heaters off after defrost, pan heater on until after drain down period. Had same problem once and this worked for me.
This will do nothing to solve the problem of ice build up . Having a drip time of 8 to 10 mins :confused: will do nothing and is not a solution to stop the drainhole in the coil pan freezing up . A thick internal heater wired in permanent is the answer :D:D trust me.

[Refrigerologist]

This will do nothing to solve the problem of ice build up . Having a drip time of 8 to 10 mins :confused: will do nothing and is not a solution to stop the drainhole in the coil pan freezing up . A thick internal heater wired in permanent is the answer :D:D trust me.

Read my previous posts please:confused: The drain is not freezing up. It remains clear. A barrier of ice builds up in the tray and acts as a dam preventing the water from reaching the drain outlet. So the solution explained by Andy is pretty likely to work, whereas your idea will just keep the drain hole free but the tray will still ice up:D I WILL REPEAT IT FOR YOU: THE DRAIN OUTLET AND DRAIN DO NOT FREEZE UP!!!

[IceMan08]

Have you tried raising the defrost cut out temp? this could be raised if another unit takes the heat load? Just out of curiosity what type of material is used for the drain fitting + pipe is it copper?

[andywill]

Philfridge
I will explain what I mean. In a freezer room below -20 all the metal on the evaporator is below -20 and during a defrost cycle this takes some heating to get it above freezing point otherwise water that hits the drip tray wants to freeze right. As refrigerologist explained to you the drain is clear it is just not making it that far. Wet your finger on your tongue (body temp) and stick it to a freezer evap and see what happens. Hope this clarifies what i was saying.

[chillyblue]

This will do nothing to solve the problem of ice build up . Having a drip time of 8 to 10 mins :confused: will do nothing and is not a solution to stop the drainhole in the coil pan freezing up . A thick internal heater wired in permanent is the answer :D:D trust me.

Hi Refrigerologist

I think what he is trying to say here is that if you leave the heater tape in the drip tray (rather than in the drain line itself) it will keep the water around it from freezing which will leave a constant route unfrozen to the drain line, which will also be clear due to the heater which is already in the drain line heater.
I assume what is happenning here is that any water remaining in the tray even a slight amount is freezing and then building up over time.

Are you sure the LUC evap has enough heaters in it Friga bohn have a habit of suppling minimal heaters,(with options of additional heaters for low temp units) it may be that at your operating temperature they will advise more heaters or just tray heaters to be fitted.
The other item i familar with with Friga Bohn evaps is that you can get a baffle tray which fits between the bottom of the coil and the drain pan, the heaters are fitted to this and act as a heat sync.
1 system i worked on the fans when running were pulling water back up the drain line (even though it was trapped) back into the drip tray, after i fitted the baffle tray it stopped it happening.

Other things you can try

1. try giving the coil additional defrosts per day e.g. rather than 4 give it 6 (you said you have additional duty from the other system, so it won't matter.

2. also agree increase the termination temperature a little and give at least a 5 min drip poss 8 mins (drip down works 2 ways it continues to thaw the coil but also gives the coil time to coil down (removing load from the compressor at startup. too short and it will give excessive load to the comp and electricity.

CB

[SteinarN]

I would go for more heaters in the drip tray and/or insulation under the drip tray.

[KevinRPS]

Have had this fault before on frezer and chill rooms,
can be solved by moeving probe to top of evap and disconnecting the top heater (or top 2 heaters depends on size of coil and amount of heaters),this makes all the coil heat up to defrost stop temp not just top half.

[Refrigerologist]

Guys, no more please!! I know what you are all saying has merit. Steiner you have suggested something I thought about, it is a prety good solution. I think I will try Andy's idea first as it is the easiest to carry out. If that fails I will do as SteinerN says.

The Friga Bohn baffle is not something that I had heard of before so I may also check that one out.

As for the other ideas, I have tried the heated wire down the drain pipe before on other systems. The same scenario does not apply here. I have not misunderstood what any one is saying. It is just that I have the advantage of seeing the ice build up pattern and it has nothing to do with the drain outlet or drain pipe. It is due to lack of heat in the tray.

Thanks guys for all your ideas, not a single bad one!

[jstch00tme]

I have the exact same problem, but by the time they call me out the ice is up in the lower part of the coil as well as in the pan and i cant tell where it started to form? any ideas where i might start would be a great help. also should mention it formed the ice in only 4 days!

[jstch00tme]

I just got off the phone with Nor-Lake and was informed of the delay timer for the hot gas valve, supposed to give the pan heater 10 min to get good and hot, somthing to check!!

[Refrigerologist]

Hi guys, I thought I had better give you an update.

I have made the modifications as suggested by Andy. That is I have wired the drain pan heaters separately. These are now controlled via a second defrost contactor, which is energised, via an auxilliary contact, when the main defrost contactor pulls in. This second defrost contactor remains energised for a period of 10 minutes after defrost terminates. This is acheived by the use of a delay off timer which is installed in series with the control circuit to the second contactor. The defrost controller drain down time is also set for 10 minutes.

This has had three benefits:
1, the drip pan is staying clear of ice. 2, the amount of steaming, and hence hoare frost in the room has been reduce to almost zero! and 3, I have reduced the number of defrosts per day from 6 to 4.

Thanks for all the suggestions! Especially Andy's!

[Brian_UK]

Sounds like you've cracked it, good move.

[andywill]

Thanks for the update Refrigerologist glad i could be of help, we are all here to help each other out if we can. 24 years later and I'm still learning, this industry moves forward very fast.

[SteinarN]

Thanks for the update.