Dehumidifier NineSky Model CT2 . Very low effectiveness.

[OldBeginner]

Hi! Power: Max.85W It is built using Peltier elements.
Everything is working, but the room humidity hasn't changed after 24 hours of operation, and only 230 ml of water has collected in the tank. The device has been disassembled. No signs of origin were found. I realize that this is a cheap Chinese knockoff and that I shouldn't expect good results from it. However, there is a naive idea that its performance can be significantly improved through simple modifications. Perhaps someone has used a device like this, or maybe even tried to improve it. It would be interesting to hear their opinion.

Good luck

[dietert1]

I remember fixing a dehumidifier for a friend. It had a 600 W compressor similar to a refrigerator and an enourmous fan. It just needed cleaning of the dust filters. After that it would collect about 1 liter of water per hour running in a high humidity environment. So for your 85 W machine one would expect about 3 liters after 24 hours.
Important is reaching condensation at the low temperature surfaces. That may be difficult when the air has less than 50 % of humidity as the peltiers don't reach low enough temperature. Dehumidifiers are made to get from 100 % down to 50 % or so. My friend had several dehumidifiers to maintain a stock of carpets. They would pause once humidity became less than a certain limit.

Regards, Dieter

[Kean]

I've just been fixing one of mine at home.  It was pretty clogged up with dust.  I won't be able to evaluate it again for some months.

Extracting 230ml in a day may not be too bad depending on conditions.  A compressor based unit will easily do 10x that in the same conditions.

A lot depends on your environment.  They really struggle at lower temperatures, and work best in a well sealed room.

What is the ambient temperature and RH?
What kind of room is it in, and how big?

[OldBeginner]

Thank you for your attention.
 the ambient temperature is 70 and RH 68%
 room is 4m * 6m

[OldBeginner]

It occurred to me that the airflow is poorly organized—since there is only one fan, perhaps an additional one should be added, though I’m not entirely sure about that.

[Kean]

At that temperature (approx 21 Celsius), the effectiveness of a peltier dehumidifier will definitely be reduced.

The limitation is the physics of extraction, and the need to reduce the condensation plate below the dew point.  Keeping the delta between hot and cold sides of the peltier high is important, but also the cold side must be at or below the dew point.  I'd suggest measuring the condensation plate temperature to see how cool it gets, and if it can stay there.  If possible also measure the hot/cold side delta.

For that size room, you really need a compressor unit, as I'd guess that you'd need to remove about 2 litres per day to make a noticeable difference.

[OldBeginner]

I agree that a compressor-based dehumidifier is much more efficient, but it is much noisier. I don't have a suitable thermometer right now, but I think I'll have an infrared one soon and will take some temperature measurements.

[OldBeginner]

I took the measurements. The device has two modes: standard and quiet. In normal operating mode, the current of the elements in the string is 4.2 amperes at 17.6 volts. That is in silent mode 3A at a voltage of 13.77 volts. Efficiency testing was performed in quiet mode.
I have currently started the device in its disassembled state, in silent mode. After ten minutes of operation, the temperature of the hot radiator reached seventy-eight degrees, and that of the cold one, thirty-five degrees. The fan blew air only over the hot radiator, so the cold radiator became covered with frost. t hot 78, t cold 35, t room 73.
  The hot radiator is large and has a large surface area, with a fan mounted on it; however, the radiator temperature dropped by only a few degrees. The fan itself is very noisy.
  There is an idea to run the system at higher power but reduce the fan speed. I want to reduce the speed of this fan by connecting another, lower-capacity fan in series with it—a fan that will blow air over the cold side.

[dietert1]

I think in order to collect water you don't want to form ice but liquid water. So you may need a temperature sensor for the cold surface and some control loop that keeps that temperature slightly above 0 °C (and below Dew point).

Regards, Dieter

[helius]

Refrigerant-based dehumidifiers all have thermal sensors attached to their cold surface. But there is an engineering problem there, because sensors can fail and so must be a separable part, but that introduces a point of failure from the contact between the sensor and the evaporator coil assembly. Over time corrosion and/or scale can get into the contact and prevent the sensor from following the evaporator's true temperature. The result is icing of the evaporator coil. To fix it, the sensor can be removed and cleaned/decorroded and fitted back using dielectric grease together with extra pressure; you could use a lockwire for that.

[edavid]

The fan blew air only over the hot radiator, so the cold radiator became covered with frost. t hot 78, t cold 35, t room 73.

There's your problem - the cold side is getting too cold.   Perhaps the temperature sensor is broken.

P.S. Don't mess with the fan, that's not the issue.

[OldBeginner]

Thank you all. You are all right. Your advice is sound. This design is very simplified and does not have a single temperature sensor. I want to try out my upgrade idea involving the addition of an extra fan. My goal is to achieve slightly higher performance and, most importantly, reduce the noise.
   Regards, Serhii