I recently built a humidifier I think others might find useful. This could be useful for cheese aging, meat curing, and storage of winter crops all of which require maintaining specific temperature and humidity. The details are available on the Tool Wiki at FarmHack. Take a look, and let me know if you find ways to improve it or if you have any questions. As part of this project I also developed this handy spreadsheet that calculates relative humidity based on dry-bulb and wet-bulb temperature and/or calculates wet-bulb temperature based on dry-bulb temperature and relative humidity. The spreadsheet also helps you tailor the humidifier design to your needs by estimating humidification capacity in gallons of water evaporated per 24 hours.
The idea was to turn a 5 gallon bucket into a high capacity (4 gal/day), automatic fill humidifier. The bucket serves as a reservoir for the water and also as a mounting platform for the parts required to operate the humidifier. Water heated to a know temperature will transfer a predictable amount of water vapor to an air stream of a known temperature and humidity (wet bulb temperature). We use this property to develop a highly controlled humidifier using a temperature control to sense water temperature and control the heater, tank deicer for heat, and a CPU fan for air flow. We also add a toilet fill valve to the assembly to allow for automatic fill of the humidifier.