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De-Humidifier Coils Icing Up

03/06/2017 1:27 PM

I have a small homeowner type of a de-humidifier I use down in my clock shop spray booth. The finish I use needs to have humidity below 50% or it fogs all up.

I have a problem lately on very humid days of it frosting over so thick, that the ice is acting like an insulator and not taking any more water out of the air.

Any simple fix for this other than shutting the unit off,, let it melt, then start it up again?

I was thinking how about some of those super hydro phobic coatings? Like the Rustoleum never wet etc.

If the water cant stick to the coil, it cant freeze on it too.

But then if it cant stick, can the water still condence onto it so the water is removed from the air?

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#1

Re: De-Humidifier Coils Icing Up

03/06/2017 1:33 PM

My WAG is that your fan is not moving enough air across the cooling coils. ¯\_(ツ)_/¯

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#2
In reply to #1

Re: De-Humidifier Coils Icing Up

03/06/2017 1:39 PM

Yep. GA.

Some combination of blocked airway, fan damage/failure/speed.

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#4
In reply to #2

Re: De-Humidifier Coils Icing Up

03/06/2017 2:24 PM

I don't know how you are applying the finish on these clocks. If you are spraying them the filter could need replaced. As the the finish has adhered to the screen and reduced the pore size and the amount of air flow. Most are synthetic and will not hold up to the solvents to clean the finish out of them.

Even if not spraying the solvents could have a effect on the screen material and reduce the air flow.

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#5
In reply to #1

Re: De-Humidifier Coils Icing Up

03/06/2017 2:27 PM

I agree, the problem could be low air flow.

Another possible cause for icing is low refrigerant.

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#3

Re: De-Humidifier Coils Icing Up

03/06/2017 2:24 PM

There may be an evaporator pressure regulator in the system that is now allowing the evaporator pressure to go too low.

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#6

Re: De-Humidifier Coils Icing Up

03/06/2017 2:55 PM

The dehumidifier works by lowering the evaporator temperature below dew point...If the room temperature is too low(<65°F) or the airflow is restricted, this will cause the coil to ice up....When the coil is defrosted and the filter has been cleaned, you should be able to feel the exhausting air volume and temperature, it should be warm and have an adequate velocity....You might have to warm the area with a heater...

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#7

Re: De-Humidifier Coils Icing Up

03/06/2017 3:50 PM

Thanks guys for all the thoughts.

I'll check on the airflow next time.

I usually drag it down to 45% then shit it off before spraying, so none of the overspray goes into the unit.

But will still check on the airflow. Thanks!

Joe

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#8
In reply to #7

Re: De-Humidifier Coils Icing Up

03/07/2017 3:19 AM

Wow!

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#9
In reply to #7

Re: De-Humidifier Coils Icing Up

03/07/2017 6:34 AM

Aha, I think I see what might be restricting the airflow.

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#10

Re: De-Humidifier Coils Icing Up

03/07/2017 8:30 AM

Dehumidifiers are refrigeration units. The ice is the moisture it's collected. Larger units almost all have a defrost cycle and use hot gas from the compressor or a set of heating elements to melt the ice at either timed intervals or sensor triggered. And yes, the ice will act as an insulator and will no longer provide de-humidification. You said yours is a small household type but didn't specify the make and model, so I will assume yours doesn't have any defrost. In your case its a manual procedure of de-icing. I would suggest a regular shut-down. I do not recommend any coatings as this is not the larger problem. One solution may be to put the humidifier on a timer outlet so it's more automatic. Or, have a second humidifier and cycle between the two. Regards, JPS

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#11

Re: De-Humidifier Coils Icing Up

03/07/2017 8:58 AM

Thanks everyone.

I will take it apart shortly to see what it is like inside. I feel air moving, but it really never has for many years moved a LOT of air.

Joe

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#12
In reply to #11

Re: De-Humidifier Coils Icing Up

03/07/2017 9:32 AM

So probably as Troy36 mentions, low charge, not an unusual symptom or end for to a usually non-serviceable consumer product...

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#13
In reply to #12

Re: De-Humidifier Coils Icing Up

03/07/2017 9:42 AM

Plus it's I'm guessing really old too. I got it used, for Free, ohhh 10 years ago, and even then it looked old.

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#14
In reply to #13

Re: De-Humidifier Coils Icing Up

03/07/2017 9:51 AM

no insulating layer of dried paint on the evaporator fins...?

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#16
In reply to #14

Re: De-Humidifier Coils Icing Up

03/07/2017 10:42 AM

Actually surprisingly no,

Like I said I'll run it till I'm down to say 45% or so, then shut it off while actually spraying. So I am actually quite amazed that it actually is quite clean bare Alum tubing still.

Now a question,, this set of coils is obviously out in the open and clean. Now, the HOT side, Is deep inside the unit, what happens if it is clogged, or at least restricted?

My thoughts would be if anything the cold side would be hotter since the heat was not removed well enough by the hot coils.

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#17
In reply to #16

Re: De-Humidifier Coils Icing Up

03/07/2017 11:09 AM

If the charge is low, probably less heat because less vapor to compress in condenser section. I suppose if too hot in condenser, then the refrigerant wouldn't change state to liquid, but then wouldn't be able to freeze the coils by expanding to gas, just thinking out loud.

Usually you can feel some sensible temp rise from the condenser coils when the charge is good (feels warmer), but most dramatic is icing on evap when the charge is low.

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#15
In reply to #13

Re: De-Humidifier Coils Icing Up

03/07/2017 10:02 AM

Chances are, a new one would be more effective and probably more energy efficient...

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#18

Re: De-Humidifier Coils Icing Up

03/08/2017 6:17 AM

If RH is your only concern, then if you raise the ambient that will naturally lower the RH provided that there is no additional water getting into the air.

Second option is to reduce the total volume of air to be dealt with. Move to a smaller room or enclose the painting process in a smaller controlled space.

Third option is to move to a "slower" solvent. The evaporation speed of your solvent can cause localised cooling of your product, thus causing microcondensation on the paint causing the fogging outcome you describe.

Fourth option is to warm the product before painting to overcome the cooling caused by evaporation speed of the solvent. (also warming your air supply will have some impact.)

Fifth option is to set the heat exchanger temperature above freezing. If the condensed water can run off the coils, then the water can be collected on a continual basis rather than batch. If there is a way to wind down the cooling and run it for longer you will remove more water.

Sixth option is to monitor RH through the day. There will be times in the day where the RH will provide a lower (better) starting point.

We had moisture bloom problems on a large scale, using around 100L of paint per day at 50% solids. We learned a lot.

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#19

Re: De-Humidifier Coils Icing Up

03/09/2017 10:45 AM

One other thing comes to mind is the temperature of the room. You said lately and it winter here and don't know where you are. But if the temperature of the room drops too low they will ice up.

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Users who posted comments:

Crabtree (1); jpsherman1 (1); Just an Engineer (1); NSS (4); ozzb (2); PWSlack (1); Randall (1); rashavarek (1); redfred (1); rwilliams (3); SolarEagle (1); Tornado (1); Troy36 (1)

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