Comprehensive review on dehumidification strategies for agricultural greenhouse applications

Humidity is one of the important climate parameters in greenhouse food production. Maintaining humidity levels within the optimal growth range enhances yield. Moreover, excessively high relative humidity leads to diseases and deterioration of the crops. This paper presents a state-of-the-art review of the various dehumidification technologies available in the agricultural industry. Several novel conceptual designs from the literature are also discussed. The principal humidity control approaches utilized in greenhouses are ventilation (natural and forced), maintaining a high temperature, condensation on a cold surface, and adsorption by hygroscopic materials. The most common method for dehumidification is ventilation due to its minimal infrastructure. Although this method is considered the simplest, it causes additional sensible heating loads, particularly in colder climates. The added heating load can be reduced, ideally eliminated, by employing heat recovery systems. Furthermore, dehumidification by controlled condensation on a cold surface enables the capture and re-use of the latent energy released in condensation. By adsorption of water vapor using hygroscopic material, the latent heat of condensation is converted to sensible heat, which can be used for space heating in the greenhouse. Such a system can reduce the greenhouse humidity while maintaining a more uniform temperature profile over the crop canopy and reducing energy consumption. Finally, it is essential to emphasize that an appropriate dehumidification method should prevent condensation on plant surfaces, and also its operational cost should be as low as reasonably achievable to remain beneficial for growers.