Fan controlled by humidity sensor – pre implementation data gathering

This article documents measurements of temperature and relative humidity (RH) over 10 days prior to implementing the fan solution to provide a baseline for designing the Fan controlled by humidity sensor.

A RC-4HC datalogger was used to collect temperature and RH measurements over 10 days which included a range of late winter weather, some rain, some fine clear days. The logger was located at 1.5m above floor level in the shed in a relatively clear spot in the middle of the area..

Screenshot - 22_08_16 , 15_53_17

Above is a chart of temperature and RH. The daily RH peaks are typically between 08:00 and 09:30, and pretty much coincide with the minimum observed temperature. There is clearly a lag from outside temperature which would tend to be minimum a few hours earlier, and a lower minimum (there were plenty of frosty days in the sample set).

Screenshot - 22_08_16 , 15_57_01

Above is the RH chart alone with expanded scale.

The total time where RH approaches condensing conditions is relatively small, but occurs on quite a few days.

The original design criteria of setpoint=70%, differential=10%, alarm=90%, and minimum run time of 1h seem ok, but in the light of the measurements I am inclined to revise it to setpoint=75%, differential=5%, alarm=90%.

Screenshot - 22_08_16 , 17_39_44

Above, the revised EEPROM contents for the new criteria.

A trial will be conducted with the RH controlled fan and similar measurements taken along with visual observation of evidence of condensing.