Properly control ventilation

Hi there,

I’m trying to figure out how to properly control my Vallox MV350 ventilation. My goal is to achieve a stable humidity of ~50% as measured by my Homematic IP thermostats located in various rooms.

The valloxmv binding allows me to control the ventilation state (HOME, AWAY, …) as well as the associated fan speed. Does it make sense to set up a rule that changes the ventilation state based on the current humidity or should I rather change the fan speed of the current state?

As it takes some time to achieve measurable changes of the humidity, how can I prevent a rule (e.g. “increase fan speed by 5%”) from firing too often (e.g. “wait 30 minutes before triggering this rule again”)?

Are there any other (programmatically available) external factors that I should take into consideration?

Thanks a ton for any hint,

What does the different states do? Only change fan speed?

One possibility is to have a variable holding time value when last adjustment was made. I would use unix epoch but why not DateTime objects. Then when the rule triggers next time you compare if enough time has passed.

Calculating averages from humidity values using persistence could replace “time hysteresis” discussed above.

There’s no “right” answer to this. It’s all up to you.
You can make use of the Vallox-builtin capability to do the levelling based on humidity (AFAIK all MV350 have a builtin humidity sensor).
I’d untick that during wintertime though as ventilation tends to dry air more than you will feel comfortable with (< ~35%) anyway. I’d also get the enthalpy heat exchanger (it’ll keep most of the humidity inside in fact unless you tell the MV to bypass.)
Also, “local” maxima of humidity such as a steamy bathroom after taking an (excessive) shower will flatten out all by themselves as your ventilation will be constantly running and dispersing the “local” humid air all over the house, quickly flattening out the local maximum in the bathroom.
The best strategy in fact is to do - nothing.

A more useful idea of control is to switch between “home” and “away” modes based on OH presence detection.
I actually use OH to silence my ventilation (also a MV350-E) at bedtime (it’s located atop my bedroom and becomes perturbing when everything else around silences down at night) based on a motion detector in my bedroom. It returns to normal speed once I’ve fallen asleep and don’t move any more.

What does the different states do? Only change fan speed?

I think so, but that’s also what I’m trying to find out.

Thanks for your input! I’ve researched a bit on the enthalpy heat exchanger, however that seems to be a ~1000€ investment. But I’ll keep that in mind as a last resort.

Unfortunately, the built-in humidity sensor is somewhat off from the sensors in the most relevant rooms (living, sleeping) as it’s measuring the combined air flow of all rooms. The “do nothing” strategy is pretty much what I’m currently doing, however I’m suspecting the low humidity to cause health issues which is why I’m looking into alternatives.

Another idea I had is to measure the air quality, e.g. using Netatmo devices, reduce the fan speed as much as possible to increase humidity but make sure I sustain a certain air quality (e.g. by activating the boost mode or increasing fan speed if necessary). Would that make sense?

If you already experience that you would need to decrease ventilation. You can dry the air by increasing ventilation throughput but you cannot enrich air with humidity.

You could throttle down to keep humidity and add a VOC sensor somewhere to re-increase for a limited time if that goes atop say 1000 ppm. You can also add that to your MV unit which will automatically increase ventilation if you reach a certain threshold.
But it’s no good measure of “air quality” which is very much a perception thing.
I’d stick with ‘do nothing’ and use a physical button (or smartphone) to trigger boost ventilation when you (subjectively) feel air is not fresh enough.