Greenhouse Dehumidification in Cold Regions

Abstract

One major challenge greenhouse producers face is the excessively high relative humidity (RH) during mild and cold seasons which result in fungi diseases and reduction in yield and quality. Conventional dehumidification by increasing ventilation rate is either costly because of the resultant heat loss or ineffective in spring or fall when outside RH is high. In this study, two dehumidification technologies, i.e. air to air heat exchangers and mechanical dehumidifiers, were evaluated in a Saskatchewan tomato greenhouse. In addition to the heating and ventilation system based on temperature control, two heat exchangers were installed in the south wall and two mechanical dehumidifiers were set up at diagonal corners inside the greenhouse, both controlled by RH setpoint of 75%. Eight days were designed to be one experiment cycle: three days for only heat exchangers running, three for only dehumidifiers running, and the left two for the existing conventional temperature control method (no additional humidity control). The experiment was conducted for a year and the greenhouse environmental parameters and weather conditions were monitored. The three treatments were compared based on RH control ability, moisture removal efficiency (MRE) as well as the energy cost. The heat exchangers controlled the RH better than the other two methods. The dehumidifiers used had lower capacity than the heat exchangers and resulted in slightly higher RH than that of the heat exchanger treatment. However, it is the most energy efficient based on MRE and had the lowest overall energy cost, thus is the most promising method for greenhouse dehumidification in greenhouses in cold regions.