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. The high humidity that surrounds crop plants, aggravated in mild weather greenhouses by high transpiration and lack of ventilation, encourages plant diseases and physiological disorders. A heat pump dehumidifier (HPD) has been installed in a mild weather greenhouse. Its development and the characteristics of the dehumidification process have been studied. The results indicate that the HPD reduced the risk of crop damage caused by humidity. Its effectiveness was related to the temperature value and the air humidity inside the greenhouse. HPD operation was not suitable under dry weather conditions. Conversely, when humidity was excessive, the HPD did not eliminate the risk of moisture damage. The appropiate conditions for using an HPD to eliminate humidity damage risk are relative humidity between 84% and 88%, and air temperature higher than 15.0 °C. Under these conditions, the condensed steam production value was 14.2 kg h−1, the specific moisture extraction rate was 2.3 kg (kW h−1), and the coefficient of performance was 2.5.