Humidity control apparatus

An apparatus for controlling a humidity in an enclosure including duct means having an outlet opening into the enclosure, a recirculated air inlet communicating with the enclosure and an outside air inlet, proportioning means for controlling a proportion of air entering the duct means from the outside air inlet relative to air entering the duct means from the recirculated air inlet and humidifier means for, when energized, increasing a humidity in the enclosure, characterized by comprising:

• humidity sensor means for sensing the humidity in the enclosure;
• and
• control means responsive to the humidity sensor means and constructed to, when the humidity drops below a first predetermined value, control the proportioning means to set said proportion to a predetermined low value and, after a predetermined length of time has subsequently elapsed and only if the humidity is below a second predetermined value, energize the humidifier means, and;
• when the humidity rises above a third predetermined value which is higher than the first predetermined value, de-energize the humidifier means and, after a predetermined length of time has subsequently elapsed and only if the humidity is above a fourth predetermined value, control the proportioning means to set said proportion to a predetermined high value.