Refrigerator – Fan Control

Reading time 5 minutes

Aktualisiert – May 18, 2024

Especially with absorption refrigerators, it is a problem to get the required cooling performance from the refrigerator in warm seasons, especially in southern and therefore warmer climes. A fan control can help.

Der Unterschied mit und ohne Ventilator ist deutlich: ohne beträgt die Temperatur im Gefrierfach zwischen 7 .. 11 °C, mit Lüfter nach kurzer Zeit -20 °C!

How absorbers work

An absorber, unlike a compressor, works with water and ammonia in a hydrogen atmosphere. Hydrogen acts as a pressure equalizer. Water and ammonia are heated in the so-called “cooker”, mainly using gas, 230 V AC or 12 V DC, but also petrol.

The ammonia becomes gaseous as a result of heating. It cools down via the condenser (located behind the upper vent in the caravan or motorhome wall) and, in turn, reaches the evaporator (located in the freezer compartment of the refrigerator) in a liquefied form, in which the hydrogen compensates for the pressure differences that arise when the ammonia evaporates again and produces the desired one Cold is generated. In the absorber, the ammonia dissolves again with the water and the cycle begins again.

A low cooling performance at higher outside temperatures is due to the fact that not enough ammonia in liquefied form can be fed into the evaporator because it cannot cool down sufficiently on the way through the condenser.

If the condenser is additionally cooled by fans with an increased air flow, more ammonia liquefies and the cooling performance increases accordingly.

Cooling for the condenser

Some absorption refrigerators already have one or two additional fans with temperature control. If this is not enough, you can remedy the situation yourself. SmartHome makes it possible.

First you need suitable fans, this are available in packs of three (360 x 120 x 25 mm). Together they have an air flow of 7 m³/H. They are designed for 12 V DC, but are supplied with a 230 V power supply. Of course a 12 V control would have been nicer. In order to be able to control the fans individually, the cable must be cut directly before the three individual lines are combined.

Installation is carried out using a 30 x 30 mm aluminum angle strip, which is held horizontally using a double-sided duct tape glued to the inside of the wall. The fans are also attached in the same way. The thick adhesive tape largely decouples running noises, although unfortunately not completely.

Fan control

Well, if the performance cannot be regulated via the speed, then by activating one, two or all three fans depending on the temperature difference in front of the condenser and after the evaporator.

A Homematic temperature difference sensor (Sensor 1 is attached to the top of the condenser using a cable tie, sensor 2 is attached to the lower pipe after the evaporator), determines the necessary values and is also attached to a free area behind the lower ventilation opening in the caravan or motorhome wall using double-sided adhesive tape.
Anyone who doesn't like batteries or accumulators (2x AA) but wants to use the 12 V DC on-board network will find this here instructions on how a DCDC converter 12 V / 3.3 V can be integrated into the temperature difference sensor for this purpose.

A Homematic 4-way switching actuator supplies the three individual fans with 12V via channels 1, 2 and 3.
Danger – There are different versions of the 4-way switching actuator: at the Version with mechanical relays you are free to choose the switching polarity (plus or minus), while the purely electronic ones, which switch via switching transistors, usually switch minus, i.e. here all plus lines must be connected directly to plus, while the minus lines are connected to the screw terminals of channels 1 .. 3 can be connected.
This can also be mounted in the same way.

programming

For the sake of simplicity, a separate program is created for each fan, which switches on the respective fan depending on the temperature difference threshold. also for the switch-off process when the switching threshold is undershot.

Here is an example for the fan on channel 1:

Legend:

KS_TDS_Diff_K3 -> Name* of channel 3 of the temperature difference sensor
KS_Lft -> created variable** (true or not true)
KS_SW_Lft1_K1 -> Name* of channel 1 of the switching actuator
KS_SW_Lft2_K2 -> Name* of channel 2 of the switching actuator
KS_SW_Lft3_K3 -> Name* of channel 3 of the switching actuator
KS_SW_Lft4_K4 -> Name* of channel 4 of the switching actuator

* will after Training of the device manually
** A variable to be checked is used to decide whether a subsequent action
    is initiated or not.
    (Here, for example, the fan should not be activated at night to create background noise.
     Consequently, the variable in the night time is set up in a separate program
     “not true”, set to “true” during the day)

• Turn on

Fan 2 is switched on when a differential temperature* of 16 °C is exceeded, fan 3 from 24 °C.

• Turn off

Fan 2 is switched off when the differential temperature* falls below 8 °C, fan 3 when the temperature drops below 16 °C.

A variable SV_KS_Lft can be used to make a decision that allows you to generally allow or prevent the action of the fans, for example if you are sensitive to noise at night and therefore the fans should not run.

*The difference temperature here is arbitrarily set to the values mentioned only as an example. In reality, at outside temperatures of around 5 to 10 °C, you should determine the temperature difference that occurs - without active ventilation. As the outside temperature rises, you monitor the change in this temperature difference and adjust the point of use of the fans accordingly.

• Manual control

• Manual and time-dependent control

Here the variable is either set manually to “false” in order to switch off all fans or automatically, depending on the selected time period, here daily from 10 p.m. to 7 a.m.

Temperatursensor im Gefrierfach

Wer auf Nummer Sicher gehen und die Lüfteraktion von der Temperatur im Gefrierfach abhängig gestalten möchte, bohrt ein Loch von etwa 5 mm (Durchmesser des Temperatursensors) oben links vom Wärmetauscher im Gefrierfach, steckt den Temperatursensor von hinten in dieses Loch, schiebt ihn soweit vor, dass er mit seiner Kabelzugentlastung gerade eben im Innern des Gefrierfachs erscheint und versiegelt von hinten die Bohrung samt Kabel mit Silikon.

Der Temperatursensor kann vom Typ HM-WDS30-T-O (1-Kanal) oder HM-WDS30-OT2-SM-2 (2-Kanal) sein.

Die Programmierung wird in dem Fall nicht über den Differenzkanal (K3), sondern den zugehörigen Sensorkanal (beim einkanaligen Sensor K1) vorgenommen, indem bei Unterschreiten der gemessenen Temperatur von z.B. -18 °C ein Lüfter eingeschaltet wird.

Der zweite Lüfter tritt in Aktion, wenn die Temperatur z.B. -16 °C, der dritte Lüfter bei -14 °C. Auf diese Weise kann sehr schnell die gewünschte Temperatur (hier z.B. -20 °C) wieder erreicht werden, gerade, wenn die Außentemperatur hoch ist.