Efficient cooling of strawberries: From model calculation to implementation in a commercial greenhouse

Growing strawberries in autumn and spring crop cycle in greenhouses requires a start in the first week of August. Light intensity in this period ensures a good quality of crop with enough flower capacity for the spring crop cycle. A disadvantage of this early start is the almost non controllability of the start of harvest in autumn. An early start of harvest results in low prices and a low production. To control this, cooling of the greenhouse is required. Using a greenhouse climate model the effects on green¬house climate of a number of cooling methods such as mechanical cooling, misting, misting with forced ventilation and insulation of the greenhouse soil were calculated. The most promising solutions were implemented in a greenhouse with four sections of a commercial grower. One section was used as reference. All sections were equipped with a misting system and vertical fans to improve air movement around the crop. The model predicted that the best solution was mechanical cooling in combination with insulation of the soil. Results of the autumn crop showed good agreement of the model calculations with the measured data. A reduction in growing degree hours of more than 10% by beginning of November was achieved. Night time temperature dropped up to 4°C compared with the reference. The start of the harvest was delayed by 10 days. Initially, a higher average fruit weight was achieved, but the overall production was not influenced. The overall energy use of the different treatments was reduced by 30% compared to the standard due to the use of several energy saving techniques.