Controlling RH

Humidifiers and dehumidifiers can be used to control and/or maintain RH levels. The most straightforward method is to use heat.
By increasing the temperature the RH goes down - the size of the "sponge" has been increased and it can hold more water.

By decreasing the temperature the RH goes up - the size of the "sponge" has been decreased and it can hold less water.

Any method of controlling the RH requires the RH to be monitored so that the control method can be adjusted as the conditions change.