Almost ten years ago, we showed you how to combat humidity in a room using humidity-controlled ventilation. The system described had just then been installed in a cellar, where it worked efficiently until very recently. Unfortunately, the discovery of mold alerted us to a problem, and a quick check revealed that the system had broken down: the fan controlling the air intake had died.
Rather than simply replacing the damaged fan with an identical one, we wondered whether it might be possible to replace it with a more energy-efficient solution. In a ventilation system, air extraction is far more important than the introduction of outside air. For introduction, a simple controlled opening may suffice: if the air inlet is positioned at the right location, the negative pressure created by extraction is naturally compensated by an influx of outside air.
As it was the introduction fan that had died, our first idea was to remove the faulty motor, and keep only the blade opening device.
The original fan, with pivoting blades at the bottom to let air in during operation
Unfortunately, it turned out that the opening device was virtually non-functional. It was showing severe signs of overheating, and it is even probable that its malfunction was the cause of the motor failure:
Original fan blade opening device
This opening system is based on a part that expands with heat to push the lever that controls the blades. The part is heated electrically when the fan is powered. A little measure tells us that this system alone consumes almost 5 watts... we must be able to do better!
We therefore undertook a slightly more radical replacement of the fan's interior, while keeping the casing intact so as to be able to maintain it in the same window opening.
To drive the blades, we simply attached a model servo motor, connected to a Yocto-Servo:
Controlling the blades with a model servo motor and a Yocto-Servo
The faulty motor was removed. As we had plenty of room, we took the opportunity to fit an airflow sensor, which will enable us to detect any future failure of the exhaust fan. Just as well, we had just tested one a few weeks ago...
Replacing the motor with an airflow sensor
To facilitate airflow and measurement, we planed the central disc on both sides of the housing:
Modifications to the housing to allow air to pass through the center
There's plenty of room left in the housing for a PoE-powered YoctoHub-Ethernet, which will drive the Yoctopuce modules, and we can now close off our metering-controlled air intake:
Our controlled air opening with measuring device
And that's it, we've got our controlled air opening with flow measuring device, consuming less than 1 Watt!
