Vitovent 300-W Frostschutz

[AFercec]

Hi!
At first, I am sorry that I am writing in English. I am struggling to find any good answer to my problem and this forum is the only place I have seen that some answers are being provided. I hope it is not too much of a problem.

I have a Vitovent 300-W (serial number: 7372260101628104) connected and controlled via a Vitocal 222-g (serial number: 7956893101126125). I also replaced the original heat exchanger with the enthalpy one. The setup works mostly fine, but the heater in the Vitovent seems to have a slight issue. For some reason, I am not able to read the incoming air temperature to the Vitovent, so I placed a Bluetooth thermometer inside (between the heater and the filter).

I observed, that when the incoming air temperature drops to -1,5°C, the snowflake is indicated on the display. However, the heater is not turned on. The heater only turns on, when the incoming air temperature gets to -6,0°C. It then starts to work at around 47% (with an air volume of 200m3/h) and works normally (gradually decreasing the percentages to 0%) until the incoming air temperature gets back to 0,0°C. In case the morning temperatures are not as low and the incoming air temperature does drop only to for example -5,5°C, the heat exchanger freezes and the fan blowing air out of the house starts to gradually increase the RPM. If I take the heat exchanger out for a few hours, it seems to be back to normal.

Additionally, if the daily temperatures are so low, that the snowflake indicator remains on (even if the heater turns off - to 0% activation), the heater will normally start to work when the air temperatures start to drop again - starting with 1% activation and gradually increasing through the night.

I cannot imagine that this is a normal behaviour of the device. Or is it? If it is not, does anyone know what I can do to make it work better? Official Viessmann serviceman is saying he does not know what to do. I tried a full reset of the Vitovent, but it did nothing.

[Flo_Schneider]

Hello AFercec,

The fact that not all temperatures can be queried in the ventilation overview is normal for your system and cannot be changed.

Frost protection function:

If the outside temperature falls below -1.5 °C for more than 5 minutes, the factory-installed electric preheater switches on. The pressure on the exhaust air side is monitored as an additional switch-on criterion. The output of the factory-installed electric preheating coil is regulated so that the exhaust air temperature reaches 0 °C.

If the output of the factory-installed preheating coil is not sufficient to reach the respective exhaust air temperature, the additional electric preheating coil is switched on.

If the exhaust air temperature is not reached at maximum heating output, the supply air volume flow is also reduced to protect the heat exchanger.

Best regards
Flo

[AFercec]

Hi Flo!

Thank you for your answer. It is much appreciated.

If I understand correctly, only the exhaust temperature is measured and electrical heating is regulated in a way that it never reaches below zero. As I installed a less efficient heat exchanger (to increase humidity in the house), the difference between intake and exhaust temperatures got bigger, so the intake temperature can effectively go much lower, as the exhaust temperature will still be positive.

I will monitor the system some more (but now more warm weather is coming), to see if it behaves as you described. The heat exchanger somehow gets slightly blocked sometimes (at about 3070 RPM only 265 m3/h of exhaust airflow, intake is not affected), but if I take it out for some amount of time, it gets better again. Maybe something else is causing this behaviour. Currently, it is 12°C outside and the system is running great. I will see if it happens again and at what temperatures.

Best regards,

Anze

[Flo_Schneider · Accepted solution]

What do you mean that it is sometimes clogged? It is normal for it to clog easily due to ice formation.

Best regards
Flo

[AFercec]

OK. Now I get it. I thought that the system was designed in such a way as to fully prevent any formation of ice in the heat exchanger. If this is normal and allowed, everything is fine and the system works as intended (I only wasted money on two sets of filters as at first I thought that they were the issue 🙂 ).

Thank you very much!

Best regards,

Anze