Feasibility of winter cultivation of fruit vegetables in a solar greenhouse in temperate zone; experimental and numerical study

Feasibility of winter-cultivation of fruit vegetables was studied in a solar double plastic covered greenhouse in a temperate zone. An experment for 24-hour-course including a cold night was performed and an unsteady numerical model was developed to predict microclimate in the greenhouse. Sensible heat term with separated air and leaf temperatures was applied to energy equation. Modeling of plant transpiration and outside boundary conditions were accomplished by applying a user defined function added to FLUENT. Comparisons between measured and simulated air/leaf temperatures showed a good agreement for the 24-hour-course. Simulations were performed to examine the feasibility of ensuring the inside air temperature higher than 12 degrees C (the lowest temperature limit for fruit vegetables) in inner greenhouse during the coldest winter night. When covering both the outer and inner films with quilts, it could overcome the night with the lowest outside air temperature of -18.6 degrees C. A necessity of heat shield for north wall outside surface was confirmed. Results show that the double plastic covered greenhouse can be a good passive solar system for winter-cultivating the fruit vegetables in some temperate zones.