Evaluation of a dehumidifier in a mild weather greenhouse

•The dehumidifier eliminated the risk of humidity damage in a mild weather greenhouse.•The external and internal climate influenced the efficacy of the dehumidifier.•The optimal climate was temperature of 15.0 °C and relative humidity between 84 and 88%.•When the weather was cold and dry, the dehumidifier was not efficient.•If the weather was cold and humid, the effect of HPD was not sufficient.