Humidity Control Chamber

Hi everyone,

For my research project I need to build a small box where I can monitor and control the humidity percentage inside, maybe programmatically (I should type the desired value and the system reaches it). Any ideas?

I have seen other posts about using a sensor and a humidifier, but I was unsure of how to control it in a programming environment.

Do I need an arduino, connected to a PID and to a humidifier and a sensor? And how would I change the RH% from the computer? Also, what kind of humidifer do I need? Shall I take into consideration the efficiency aswell? My chamber should be like 3x3 cm.

Any help would be appreciated.

Also, what kind of humidifer do I need?

That’s the tricky part, and the dehumidifier too…

It depends on the humidity-range, temperature, and the ambient humidity range. i.e. If you need to go below ambient humidity you’ll need a dehumidifier. If you don’t need to go below ambient you can simply blow the humidity out of your chamber and blow-in fresh “dry” air.

And it depends on how fast it has to work. It’s easy to get to 100% if you add water and wait long enough.

Most people don’t understand what humidity is - It’s water vapor, which is water in the gaseous state… It’s actually “dry”. i.e. Fog/mist is not humidity but you can get fog/mist/rain when you exceed 100% relative humidity.

I assume most “industrial” humidifiers generate steam* (which is also H2O gas), and then possibly the humidified air is cooled. Or, if you have (enough) liquid water in a closed environment it will eventually evaporate 'till you get 100% humidity.

Dehumidifiers usually work by refrigeration. When the air cools the relative humidity goes up and as you “try” to go over 100% the water turns to liquid and “falls out” of the air (less absolute humidity). Then when the air is re-heated with less water vaper you have lower relative humidity. At freezing you have a discontinuity with zero humidity (relative and absolute) so you can extract all of the H2O from the air.

The “control” is simple. It’s just like a heater/cooler. When humidity is below target, you turn-on the humidifier. If the humidity is above target, you turn-on the de-humidifier.

  • When you “see” steam, you are aren’t actually seeing the steam. You are seeing some of the H2O gas that’s cooled enough to convert back to liquid.

I have done some measurements under different humidity conditions in the past in a small box not too different to what you are suggesting, we had no feedback system though. The way that we did it was with a dry air line, that we split into two, the first side went directly into the box and gave us a dry component, the second went into a bubbler (flask with water in) which added moisture to the air that came out, we used two (manual) valves to balance the system between the extremes, this was sufficient for low humidity. You could heat up the water in the bubbler to get to higher humidities (as it is a closed system make sure you use a suitable material). You can use the dry air to clear it out, it would just take a fair bit of time to clear out from a high to low humidity.

Have a look at the results of using your favorite internet search engine and the using the words "diy electronic humidor."

No the Arduino can do PID. Start by researching environmental ovens to get some background. Determine if you want laminar or turblent air flow or not. Laminar flow occurs when air can flow smoothly, and exhibits a parabolic velocity profile; turbulent flow occurs when there is an irregularity (such as a disruption in the surface across which the fluid is flowing), which alters the direction of movement.Next determine how you are going to put the humidity into your chamber. Get the Arduino cookbook and read it. Also on line there are many videos etc showing the Arduino and how to do what you want. This additional information will go a long way in getting your problem solved.

Thank you all, I think I have figured out what sensor, arduino + (de/)humidifier need I to use, however, a small problem has come up.
A humidifier works by spraying water molecules in my chamber. These molecules might absorb the surrounding temperature to turn into vapour, meaning that the temperature inside the chamber will decrease (if correct so far). I need to work in a constant temperature, is this even possible?

souk99:
A humidifier works by spraying water molecules in my chamber. These molecules might absorb the surrounding temperature to turn into vapour, meaning that the temperature inside the chamber will decrease (if correct so far). I need to work in a constant temperature, is this even possible?

It will not be as easy but you can use a Peltier device with a high current motor driver to heat and cool.

If the temp starts to go down, why not just regulate the temp back up?