Development and testing of a low-cost condensation detection system

A condensation sensing and control system was design to detect condensation using a commercially available leaf wetness sensor (LWS). The leaf wetness sensor was a variable resistance grid-type that responded to moisture on the surface. A circuit was developed to compare the LWS voltage output to a user specified reference voltage, and operate a relay for possible switching of a humidity control device (for example a fan and or heater). The condensation detection system operation was validated in an environmental chamber in the laboratory using a heat exchanger and water bath. Condensate was immediately detected when the plate was cooled below the dew point temperature of the chamber. When the water temperature increased above the dew point temperature, there was a delay as the moisture evaporated from the plate. Soil and other foreign material were added to the leaf wetness sensor with little effect on system performance. The soil acted to further delay the sensor from drying and predicted slightly longer condensation and recovery periods. The condensation detection system was tested in a transplant growing greenhouse and a grain bin, with operation verified by simultaneously measuring the relative humidity and dry bulb temperature. There were frequent periods of condensation in the greenhouse and the system accurately predicted them. Condensation did not occur in the grain bin, as was verified using the relative humidity and dry bulb temperature. The condensation detection system can provide a low-cost, rugged method for determining periods of condensation without the need for routine maintenance and calibration.