One of the problems that affect many houses is mould caused by condensation forming on the windows. This can affect bedrooms where the humidity level increases during the night due to the exhaustion of moist air and the window temperature decreasing during the night.

Last year I bought a dehumidifier to decrease the humidity levels at night but found that I was waking up with a dry mouth and headache.

After setting up a monitoring station to collect the necessary data I found that the dehumidifier was reducing the humidity levels well below what was necessary to stop condensation forming on the window. What was needed was a dehumidifier that used the window temperature and humidity to calculate the point at which condensation would form on the window and keep the humidity level slightly lower than that point. The point at which moist is release from the air is called the dew point and can be calculated using temperature and humidity.

This instructable details how to modify a dehumidifier so it keeps the dew point just slightly above the window temperature, stopping condensation form on windows and keeping mould at bay.

Step 1: Disassemble Dehumidifier

Start by removing screws from the base of Dehumidifier

Remove Filter Covers

Remove the screw behind the water tray and split the case in half

Step 2: Remove Vent Cover

Remove Vent Caps and Foam filters

Split the case into the two halves

Step 3: Remove Heat Exchanger

Remove the two screws and the Heat Exchanger

Disconnect the PCB and remove the Fan and PCB

Step 4: Drill Out Hole for Sensor

Drill the exisiting hole out to 8mm to the deep of 5mm

Drill all the way through the shell with a 3mm drill in the center of the 8mm hole.

Step 5: Fit the New Fan

Step 6: Fit New Fan and PCB

Fit the new smart PCB with the sensor through the hole drilled out in a previous step

Build details here Github link for PCB

Step 7:

Refit the heat exchanger and connect the PCB up, install the HTU21D humidity sensor board in the intake channel and connect to PCB.

HTU21D Sensor

Step 8: Reassemble the Two Halves of the Shell

Reassemble both halves back together and the dehumidifier is now ready for use, make sure that the window temperature sensor hole is facing the centre of the window pane.

Below shows that the dehumidifier keeps the dew point just above the temperature of the window.