Super­mar­kets have not sold by the season for a long time. Fresh and crispy toma­toes, peppers, and other produce are avail­able in the produce section throughout the year, regard­less of the season. By providing summery condi­tions during the winter, green­houses are one of the things making this possible (Fig. 1). The situ­a­tion has bene­fits for both consumers and farmers. The latter can use green­houses to harvest more crops and mini­mize risk in the process: under a protec­tive roof, weather-related crop fail­ures and hail damage are not an issue. In prin­ciple, with smart irri­ga­tion systems and air condi­tioners, plants can even thrive in places where nature would not normally allow it, such as deserts or cold regions.

A ques­tion of distri­b­u­tion

Unfor­tu­nately, cold or hot spots may arise over the entire green­house area. Only limited plant growth is possible in such places, and the plants are more suscep­tible to disease there. Photo­syn­thesis and plant growth are strongly depen­dent on the temper­a­ture. If it is too cold, photo­syn­thesis proceeds very slowly; if it is too warm, it comes to a stop very quickly.

AxiCool fans from ebm-papst enable precise control of the air flow.

On the one hand, the optimum temper­a­ture that needs to be evenly distrib­uted throughout the green­house depends on the type of plant. And on the other hand, a good supply of fresh air and air circu­la­tion are the keys to a good harvest – along­side the right temper­a­ture and humidity. This is why the goal is to create uniform climatic condi­tions with a roaming air flow by evenly distrib­uting the air at a constant speed over the entire green­house.

Hori­zontal venti­lation is a common method of evenly distrib­uting the air in green­houses (Fig. 2). In this method, the air is guided above the plants in the hori­zontal direc­tion. As a rule, fresh air is supplied through the sides of the green­house. A highly inno­v­a­tive air supply method is the use of venti­lation tubes from below (Fig. 3). This process ensures that suffi­cient CO₂ reaches the plants. This is partic­u­larly impor­tant since CO₂ is the base substance for photo­syn­thesis in plants.

Figure 2: With hori­zontal venti­lation, the air in the green­house is circu­lated so as to ensure a uniform temper­a­ture around the plants. (Graphic | ebm-papst)

Figure 3: With venti­lation tubes, the air is supplied under­neath the plants, providing an optimum supply of CO₂ to the under­sides of their leaves. (Graphic | ebm-papst)

Solu­tion from refrig­er­a­tion tech­nology

Green­house oper­a­tors have the option to use a venti­lation system that meets all of the plants’ needs and is also easy to install. The solu­tion uses AxiCool axial fans from ebm-papst (Fig. 4).

Figure 4: AxiCool fans with guide vanes on the outlet side are used for hori­zontal venti­lation. They have a white housing to reflect as much of the inci­dent light (impor­tant for plant growth) as possible. (Photo | ebm-papst)

They were orig­i­nally devel­oped for refrig­er­a­tion tech­nology since even temper­a­ture distri­b­u­tion is also impor­tant to keep goods fresh in cold storage rooms. That also makes them ideal for green­houses. They feature high air throw and enable precise control of the air flow.

Guide vanes are also installed on the outlet side of AxiCool fans to improve overall effi­ciency (Fig. 5). The housing and mounting are white in order to reflect as much inci­dent sunlight from the green­house as possible. To meet the service life require­ments, the fans are specially equipped for use in the high humidity of green­houses, and their plastic compo­nents are made of UV-resis­tant mate­rials that are also easy to clean. With their aero­dy­namic blade design, axial fans also run very quietly – a major improve­ment in working condi­tions for the employees.

ebm-papst Inc. in Farm­ington, U.S.A. devel­oped a height-adjustable mounting system for the AxiCool fans that is easy to install. It allows the fan posi­tion to be adjusted to the plant height, which changes as the plants grow. This adds up to a customized, high-power air guiding system that opti­mally simu­lates the natural move­ment of air.

Figure 5: Air flow for AxiCool without guide vanes ...

... Opti­mized air flow with guide vanes, doubling the air throw. (Graphic | ebm-papst)

Inno­v­a­tive: Air supply from below

Energy-effi­cient back­ward-curved centrifugal fans or espe­cially high-pres­sure axial fans from ebm-papst are used for the tube venti­lation system (Fig. 6). The air is supplied through a perfo­rated tube installed under the plants. The axial fans intake air that has usually been condi­tioned (temper­a­ture-controlled and humidified/dehumidified) from the air treat­ment chamber of “semi-closed” green­houses.

The air is first pressed into the tube, flows upward through holes past the plants, and is then guided back into the intake air flow. The result is a defined circuit of air flow. With this type of air supply, the under­sides of the leaves are opti­mally supplied with CO₂. This is espe­cially effi­cient, since that is where the intake for photo­syn­thesis occurs. Thanks to the high-powered fans, espe­cially long tubes can be used. Such systems enable the imple­men­ta­tion of effi­cient venti­lation solu­tions for maximum yield in large-scale green­house instal­la­tions such as those in the United States and also in Euro­pean coun­tries such as Spain and the Nether­lands.

Figure 6: High-pres­sure axial fans for tube venti­lation that supplies the plants with CO2 from below. (Photo | ebm-papst)

Energy saving made easy

It is also impor­tant to have energy-saving EC motors drive the fans. These grid-fed, perma­nently ener­gized, synchro­nous motors with elec­tronic commu­ta­tion, also called BLDC (brush­less DC) motors, boast effi­cien­cies that are far above effi­ciency class IE4. An inno­v­a­tive green­house design in Canada uses ebm-papst AxiCool fans and its elec­tricity bills were reduced by more than 70% in compar­ison to the venti­lation tech­nology previ­ously used.

EC motors have another advan­tage: their control char­ac­ter­is­tics. They can be controlled across the entire speed range while retaining their high effi­ciency in partial-load oper­a­tion. This means that fans on smooth walls can be set to a higher speed than fans on walls with protru­sions or obsta­cles. Air flow effec­tive­ness can be opti­mized with this precise tuning. Digital MODBUS-RTU, which use the 4–20 mA or 0–10 V inter­face, can be used to control the fans as needed. The MODBUS commu­ni­ca­tion inter­face can be used to configure and monitor the fans according to the situ­a­tion in the green­house with utmost preci­sion.