EuroFresh Tinkers With Greenhouse Design
Research shows fruit yields in the modified greenhouse have been consistently higher
Jelle Schoonderbeek has described a new greenhouse design concept in which conditioned (heated or cooled) air is prepared prior to its entry into the greenhouse in an adjacent attached chamber.
An experimental greenhouse with this design feature is being tested at the EuroFresh tomato greenhouse complex located at Willcox, Ariz. So far, tomatoes growing inside seem to like the change. Fruit yields in this modified greenhouse have been consistently higher (+20%) than those obtained in the initially designed greenhouses.
Schoonderbeek made his remarks at the recent Greenhouse Crop Production and Engineering Design Short Course, sponsored by the Controlled Environment Agriculture Center in Tucson, Ariz.
In my view, this newly designed system by Schoonderbeek is a major breakthrough that will change how greenhouses are constructed and operated. Although the cost of construction is high, the increase in crop productivity will quickly compensate in terms of higher fruit yields and quality. In addition, the energy costs will be substantially lower than that required for convention heating and cooling greenhouse systems. The ability to maintain constant carbon dioxide concentration in the greenhouse air and the ability to keep pests out also will be major advantages.
The basic design for most greenhouses has not substantially changed for several decades. When the greenhouse requires heating, a hot air furnace distributes heated air into a gable positioned plastic holed-tube that runs the length of the greenhouse. For mixing, fans are periodically placed in the gable structure, pushing air down into the body of the greenhouse. For cooling, ventilation fans are placed either at one end of the greenhouse or along one side, the size and capacity being sufficient to evacuate the air in the greenhouse at a designated turn-over rate.
Air is brought into the greenhouse from either open vents or through a cooling pad or pads located across from the ventilation fans. Depending on the greenhouse design and glazing, the greenhouse may be equipped with panels at the ridge line that can be opened, exhausting warm (hot) air that accumulates in the gable space. Through any opening into the greenhouse, suspended particles, disease organisms, or insects can enter. Screening openings can significantly reduce such entrance, but not entirely, and, in addition, screening (depending on mess size) restricts airflow, requiring the use of larger and higher capacity ventilation fans.
The Difference
The greenhouse design described by Schoonderbeek is a "closed" system. Outside air is introduced only when needed into the attached chamber, keeping the greenhouse air environment from contact with the outside. With this system, the air within the greenhouse is constantly maintained as to its temperature, relative humidity, carbon dioxide content, etc., using less energy and low quality of heat. In addition, having no openings (vents, fan and cooling pad fittings, etc.) to the outside environment, the entry of disease organisms, insects, and other substances can not occur.
The heating and cooling devices are located in a room next to the greenhouse. Conditioned air is introduced into the greenhouse through large plastic tubes placed under each row of rockwool slabs, the rooting medium for the tomato plants. The conditioned air is vented through four rows of small holes near the top of the large tubes, producing a gentle flow of air. For the return, air is taken from the end of the roof gable and drawn back into the adjacent room for conditioning and re-circulation.
Walking into this newly designed greenhouse, the air felt cool and low in humidity, quite different from most greenhouses in which the air feels warm and humid.
This newly designed system had to conform to what already existed. Therefore, the large air distribution tubes have to be placed under each crop row. For a new greenhouse employing this system, the incoming ventilation air distribution system would be under the greenhouse, with air coming up through openings in the greenhouse floor. The size of the ventilation ducts and capacity of the air-moving fans would be such that air movement up through the canopy would be a gentle flow.
By having conditioned air constantly moving slowly up through the plant canopy, the air characteristics within the canopy, such as temperature, humidity, and carbon dioxide content, can be held constant within set parameters. Upward air movement over the plant leaf surfaces keeps them dry, while disease organisms and insects, if present, would have difficulty attaching themselves to the plant. Constantly moving air over the leaf surfaces promotes water movement up through the plant's vascular (xylem and phloem vessels) system, keeping the plant fully turgid as well as distributing nutrient elements required for sufficiency, thereby sustaining vigorous plant growth, including fruit set and development.
In a greenhouse with tomato (would also apply to cucumber and possibly pepper) as the crop, there are essentially three atmospheric entities that interact with each other. There exists an exchange process that establishes an equilibrium between the environment surrounding the greenhouse, that within the greenhouse structure, and that within the plant canopy. Each has its own characteristics, established and maintained by the interaction of both internal and external forces. The plant canopy is that portion of the system that is most resistant to change, as well as being affected by plant functions. Forcing air from outside the canopy into it is extremely difficult as the canopy acts like a "box", causing air directed at the canopy to either go around or up over it. The only efficient way to exchange the air within the canopy is to introduce air at its base.
