Experimental evaluation of three different dehumidifiers for greenhouses in cold regions

Abstract

Selecting a dehumidifier is not easy for greenhouse growers because of its high capital and operation cost and new emerging technologies, besides selection variations with crop species, local weather climate, and greenhouse sizes. The technical performance evaluation of various dehumidification technologies in commercial-scale greenhouse settings and their comparative results can give growers the new information needed to select the best dehumidifier. In this study, the field performance of a newly developed state point liquid desiccant (SPLD) dehumidifier is compared with two other commercial dehumidification technologies; direct contact liquid desiccant (DCLD) dehumidifier, and heat recovery ventilator (HRV), in ornamental (rose) and tomato greenhouses. Under the test condition, among the three dehumidifiers, the HRV unit had the highest calculated moisture removal rate (MRR) of 189.1 kg hr-1, the lowest moisture removal cost of 0.022 $ kg−1, and the lowest electricity consumption (0.02 kWh kg−1 of moisture removal). The highest electrical consumption was found in the SPLD unit under the wet mode, with an average of 0.44 kWh kg−1. However, the SPLD-wet mode was the most efficient regarding net energy consumption (0.53 kWh kg−1). The DCLD showed a moderate performance on electrical energy (0.15 kWh kg−1) and net energy consumption (0.775 kWh kg−1) with good indoor humidity control. The SPLD unit under dry mode was similar to the HRV unit regarding moisture removal cost (0.026 $ kg−1) and electricity consumption (0.046 kWh kg−1). The comparative results of this study indicate that a single dehumidification technique cannot be both technically effective and economically cost-saving year-round. Thus, combining a low-cost technology, such as ventilation or a heat exchanger, and an internal dehumidification technology will be the most practical and feasible in cold regions.