I recently took on the challenge of automating my basement ventilation system, and I thought I’d share my experience and setup with the community. My goal was to ensure that the basement remains dry and comfortable without constant manual intervention.
The problem I faced was determining the optimal times to open or close the basement windows. I realized that relying solely on a fixed schedule wasn’t effective, as weather conditions can vary significantly. Instead, I decided to base the automation on environmental data: outdoor and indoor temperature and humidity levels.
I set up Homematic sensors to monitor both the outdoor and indoor conditions. Using the outdoor sensor, I track the temperature (Ta) and relative humidity (rFa). Similarly, the indoor sensor provides the basement temperature (Tk) and relative humidity (rFk). With these values, I calculate the saturation vapor pressure both outside (Sa) and inside (Sk) using the formula:
Sa = 6.112 * exp((17.62 * Ta) / (243.12 + Ta))
Sk = 6.112 * exp((17.62 * Tk) / (243.12 + Tk))
Next, I calculate the absolute humidity outside (aFa) and inside (aFk) using:
aFa = Sa * (rFa / 100)
aFk = Sk * (rFk / 100)
The automation rule is straightforward: if the absolute humidity outside (aFa) is lower than inside (aFk), the basement windows open to allow fresh air in. Conversely, if aFa is higher, the windows close to prevent moisture from entering.
I implemented this logic using Home Assistant, leveraging its powerful automation capabilities. The system has been running smoothly, and I’m thrilled with the results. It’s been a great learning experience, and I’d love to hear how others have approached similar projects or if there are alternative methods you’d recommend!
Feel free to share your thoughts or ask questions—I’m happy to discuss further!