I need to regulate temperature and humidity of a dryer wich has 0,5 cubic metres.
How can I regulate these parametres? My idea is that a fan is activated whenever relative humidity exceeds 65% or low than 55%... Is there any better idea?
Finally, How can I raise or lower the temperature of the dryer? I thought to put a resistor but i would like to know how to control it.
Thanks for your attention!
My idea is that a fan is activated whenever relative humidity exceeds 65% or low than 55%... Is there any better idea?
Just moving air around won't change the humidity. You need to add or remove moisture or heat to do that.
I thought to put a resistor but i would like to know how to control it.
A small resistor won't do much in a 1/2 cubic meter space. If you DID use one, though, you can't make the Arduino provide the needed current. You need to provide another source of power that can supply the needed current, and have the Arduino turn a transistor on or off to control the flow of current.
Controlling temperature and humidity is not as simple as it may sound. Test chambers for AC systems cost $100k+ for a reason... Now, you're not building a test chamber capable of handling a 5ton condenser but to get total control of te inside atmosphere, you will have to have the same tools available:
Humidity Control: a means to dry the air, a means to add moisture
Temperature Control: a means to heat, a means to cool
Then there is the very complex interaction between humidity and temperature that you have to watch / control for. Absolute humidity vs. relative.
This is likely a complex project. I'd love to hear you how made out in the end.
One way you could try is to have three air paths coming into and out of the box in a closed loop. Each air path would feature a small box fan to keep the air moving and each air path should feature a one-way valve/sock to prevent unwanted circulation.
Each path would address a different need. Small-scale drying can be done by passing air over a large dessicant bag (silica). Moistening can be achieved by running air over a humidifier wick sitting in a pool of water. A Peltier element could do the heating or cooling (they can heat or cool, depending on the direction of current). Now rig three 12VDC box fans and the Peltier on a PWM basis to an Arduino with a motor shield or somesuch. So, at minimum, you'll need 5 channels that you can control individually.
The Peltier may require some serious current capacity and massive heat shields inside the air channel and outside too. All depends on the loads imposed... but you would do well to have a second fan on the outside heat exchanger that ramps up and down with the Peltier element. So, you may need a 6-channel motor driver after all. Plus, the PWM driver on the Peltier has to be reversible (hence my recommendation re: a motor shield - they can usually handle high currents and reverse them too).
Next, you'll need to use multiple temperature/humidity sensors like the DHT22 series to see what the conditions are like in each tunnel as well as the box itself. Now it's time to implement PID control with a psychrometric chart. That should be fun.
The above rig will only work for small loads. For example, a dessicant bag can easily be overwhelmed if the load is very wet but it's cheap and easy to regenerate (i.e. throw it in an microwave oven). A humidifier sponge is easy to keep wet. Peltiers may be effective enough for your application and a lot cheaper than modifying an AC system to meet your needs. However, they are limited in terms of heat removal or addition.
The most effective and sustainable way to remove moisture is to take the air out to a chiller which cools it below the dew point so that water condenses out. The lower the temperature the drier the air will end up, but beware of trying to cooling down to freezing point as your chiller will ice up. Then warm it back up to your target temperature and return it to the drier. Some of the cooling/heating can be done using a counterflow heat exchange. If you need to drop it below the ambiant temperature then you would need something equivalent to a domestic fridge to cool one side and heat the other.
All true, but I was trying to avoid the need for an AC system if it could be avoided. They are IMO much more difficult to modify for non-intended uses than a Peltier, for example. That's not to say that it cannot be done.