some kind of fan to decrease humidity and temperature (like this??)
My biggest fear with the fan, would be that it changes both temperature and humidity, I don't want to get stocked in loop trying to correct both of them.
I was thinking to build a chamber of size (more or less) 18x18x18 centimeters. Any suggestion on the material i should use for the chamber?
Any advice about arduino needed, sensors, code, regulation, existing projects, how to connect it to a 220V plug, ... are well accepted.
Thank you
My boss is involved in repairing/servicing a local Uni environmental lab chamber, they complicate things with adding CO2 sensors.
A lot of work goes into considering how quick the heat or humidity will change when you turn a heater ON or OFF, or turn ON or OFF a humdifier, or open the chamber to admit dry air.
You may need to experiment to get the results you need.
One thing you will need to consider is small fans, rather than one fan.
You may have to consider using PID control if you have any over shoot problems.
The chamber would be 18x18x18 cm (~7.1x7.1x7.1 in).
I will consider multiple fans, thanks. Any suggestion on the model?
Considering that I am working in a room at 22°C and ~30-60%RH, it shouldn't be too complicated to condition it, if I create for example small opening to insert only my hand, avoiding to stress completely the internal conditioning. (At least I hope so xD)
Before starting to buy anything I want to be sure about all the details. I will give a look to tsome PID projects, thank you.
Sounds rather tricky to pull off - but that also depends on how close you want to keep to those values.
A dehumidifier may be needed - it seems your air is lot dryer than where I live (currently I'm reading 99.9% on my DHT22, it's not been much below 90% today) but even 60% is higher than your target 50% so venting doesn't do you any good.
A humidifier usually sprays small droplets of water, which then have to evaporate. This means you have the risk of droplets hitting your samples. It also means your temperature will drop when you humidify, and with RH depending on the air temperature that's getting complex.
Mind that the smaller the chamber, the harder it gets to be stable. It reacts much faster to changes in the environment. Your suggested size is really small.
I really like the BME280 as a temperature and humidity sensor. The other sensors are pretty good too but this puts it all in one package and it's extremely fast to react to changes in humidity.
One possible control method is, instead of controlling % humidity, you should control dew point. That way you won't get caught with changes in temperature also changing the humidity percentage.
I got the BMP280 here (same package but without the humidity part - the problem is that I can't expose them properly to the outside air) - one of the things I love most about them is how tiny they are. When I got my PCBs from the factory I really had to search for them Just 3x3 mm and barely 1 mm tall!
But they're not exactly cheap. Almost USD 4 a piece iirc for the BME280 vs just over USD 1 for the BMP280.
My main purpose would be to have them fixed at RH=50% and T=23°C...
...Considering that I am working in a room at 22°C and ~30-60%RH
Do you really need to heat by 1 degree? And if you do need heating, will you ever need cooling?
And, what about that 60% ambient? Are you just going to live with that?
As wvmarle says, that "humidifier" doesn't directly create humidity. Humidity is H2O in the gaseous state so you have to wait for the water droplets to evaporate.
And, those water droplets might confuse the humidity sensor.
My biggest fear with the fan, would be that it changes both temperature and humidity, I don't want to get stocked in loop trying to correct both of them.
I don't think that will be a problem, especially since you are holding a constant temperature and you're (probably) not dehumidifying.
As far as I know, you don't go into a "loop", but you can temporarily go in the wrong direction with humidity if your software isn't smart-enough to figure-out what the target-temperature changes are going to do to the humidity.
Any advice about arduino needed, sensors, code, regulation, existing projects, how to connect it to a 220V plug, ... are well accepted.
Everything looks like it will run from a 5V power supply, except if you need a heater. In a "real" environmental chamber you can get into trouble going over 100% humidity (well... you can't really go over 100%) and getting condensation, and/or if you go below freezing and you freeze the condensation.
How about having two small chambers, one with a layer of silica gel on the floor, one with water. And two fans sucking the air through these chambers into your chamber. This set would take care of the humidity. A similar set would take care of supplying warm and cool air. Some PID logic would keep everything in balance.
"React" is probably the wrong word. If you push air through a box filled with silica gel, it's going to come out drier at the other end. How much drier depends on how much time it has had to interact with the beads of silica. A "layer lying on the floor" won't touch most of the air travelling through the box so it won't be much drier.
You can get silica gel with a tell-tale colour. Some of the beads are blue and change as they absorb water. The best way is to weigh the silica gel. I don't have the numbers in front of me but I seem to remember that it can absorb 30% of its weight in water.
Well, of course it would be a sub-project to get the silica gel work in an optimal way. The air must get sucked through a filter like layer somehow. The air could rotate continuously through the filter, until it has reached a certain low level of humidity. After that the box could work as a magazine of dry air, which gets sucked into your chamber when needed. When that happens, more air from the room gets sucked into the air drying chamber.
what you ask is not hard, but what you are up against are the fundamentals of physics.
if you use a tiny CPU cooling fan, it will change all the air in your enclosure within a few minutes. that would mean that you would not only have no control, you would be running your system flat out to heat and cool.
Since the humidity is a ratio of moisture and air temperature, the easiest way to change humidity is to change air temperature.
this becomes a Catch-22 before you turn on your system. I would highly suggest you design and build a sketch that monitors both temperature and humidity and would know(predict) what the humidity would be in the chamber if you did nothing but raise the temperature 1 degree.
second, I would offer that in most cases one thing is more important than the other. fruits in cold storage start to ripen with a 1/4 deg F temperature change. humidity can be +/- 30% with little effect. in that case temperature control if far more important and humidity control follows temperature.
in your case, you should also be able to calculate the amount of heat needed to raise the temperature in your enclose by 1 degree. a 100 ohm resistor will heat it over X hours at 5 volts. what you should be looking for is a way to change the temperature over a period of a few minutes. if your heater could change temperature by 20 degrees in a few seconds, you will have a hard time controlling temperature.
as for humidity, a drop of water on a piece of cloth will allow for evaporation to create an equilibrium over time. the cloth will give up water, the air will take it until there is a balance. if your device is sealed, like a humidor, and is only opened rarely, then a very small change is needed. you could just open/close a door over the vial of water as needed.
and this brings me back to my main point. if you know that your air needs 1 gram of water to increase humidity by 10% ..... you have a basis of decision making.
if you know that at the present humidity, by cooling by 1 degree, you would raise the humidity by 2%, you have the ability to control without adding water.
all of this is readialy available knowledge and it has been done with Arduinos for humidors and incubators, so it is not out of reach.
as most of us ask "what were the results when you tried something ?"
get two chambers. use some plastic and some tape, put a sensor for temp and humidity in each. connect with a fan. increase temp and and watch humidity follow. put a bowl of water in one watch humidity rise over time. put on a lid with a hole, smaller hole, then larger hole.
bring in outside air in a long tube. monitor the inlet air temperature, calculate the air volume being moved. calculate the energy needed to increase that air by 1 degree. you will get watts or joules or Calories or calories, with that you can select a device, and control the heating by delivering that exact amount of heat into that air stream.
sorry for rambling on, still on my first cup of coffee and am not able to be simple and concise.
