Application of the constant soil temperature layer for energy-saving control of the local environment of greenhouse crops. I. Local control of the ambient environment of strawberry

In a farmer's strawberry greenhouse, seasonal changes in solar radiation and air conditions (temperature, humidity, and CO₂ concentration) were measured, and it became clear that the stable year-round production of strawberry was depressed by low temperature and low solar radiation in the cold season and by excessively high temperature in early autumn. Furthermore, dew formations during the nighttime and inappropriate application of CO₂ enrichment were also related to the depression of stable production. Therefore, a local environmental control system was newly developed for strawberry crops based on air circulation and heat exchange between the constant soil temperature layer and the ambient air. The system consisted of an underground air pipe (UAP) and perforated inter-row air ducts (IAD) connected to the UAP; the UAP was set at a depth of 1.5 m, where soil temperature remained suitable for year-round strawberry growth. The greenhouse air was drawn into the UAP, and the air flowing through the UAP exchanged heat with the constant soil temperature layer and was dispersed to the ambient environment of the strawberry crops through the perforated IAD. In the nighttime during the cold season, air flowing through the system was heated by 8°C, and a heating effect of 3°C was observed in the ambient air. The proposed system of applying the constant soil temperature layer can be expected to reduce the nighttime heating load by 50% and enable energy-saving environmental control.