NL1042086B1 - Assimilation lamp device - Google Patents

Abstract

An assimilation lamp device (1) for stimulating plant and crop growth comprises a central lamp unit (10), comprising a body (14) and a plurality of LEDs (12) mounted to an under surface of the body ( 14 ), wherein the body ( 14) is made of a thermally well conducting material, for instance aluminum, and acts as a heat sink for the heat generated by the LEDs. The body (14) is provided with cooling fins or lamellae (41). The assimilation lamp device further comprises air stream generating means (42) such as a fan for generating a downward air stream (43) in heat exchanging contact with the cooling fins or lamellae, so that heat is removed from the respective cooling block and used to increase the temperature of said downward air stream (43). The air stream generating means ( 42) such as a fan is controllable independently from the lamp operation.

Description

FIELD OF THE INVENTION

The present invention relates in general to the field of plant growth, specifically but not exclusively the field of large-scale commercially growing plants for production. The invention contributes to enhance the micro climate in greenhouses in a controlled manner.

BACKGROUND OF THE INVENTION

In greenhouses, crop like tomatoes, cucumber, pepper, flowers, or more in general plants, are cultivated for an optimal yield. It is a general desire that crop grows as fast as possible in order to be able to harvest as early as possible and to obtain a commercial value as high as possible. Crop growth and the enhancement of crop growth is dependent on many factors. Apart from nutrients, the most important growth factors are water, air (with a substantial percentage of carbon dioxide), temperature, and light, and a commercial plant grower will try to control these factors to some optimum values. Crop growth is basically dependent on the photosynthesis of the plant. Photosynthesis is basically the conversion of carbon dioxide into sugar and oxygen stimulated by photons (light). This process can be optimized (or hindered) by the adjustment of specific environmental parameters. Known factors influencing the photosynthesis are the (leaf) temperature, concentration of carbon dioxide, light spectrum, availability of water and nutrients, humidity, etcetera.

During daytime, when photosynthesis takes place, carbon dioxide is typically blown into the greenhouse. However, the resulting temperature and carbon dioxide distribution is mainly determined by coincidence rather than controlled and is unstable, among other things due to natural convection and vertical air flow. The instability of temperature and carbon dioxide distribution in a greenhouse is a continuous concern in terms of crop yield.

SUMMARY OF THE INVENTION

In modern greenhouses, artificial illumination as part of creating an optimal set of conditions for the stimulation of crop or ornamental plant growth is quite common. Especially when sun light is fading and/or periods of daylight are getting shorter, like in autumn and winter season, artificial illumination of plants is essential for obtaining good growth. Such artificial illumination is also indicated as assimilation lighting.

Light sources can be considered as sources of energy. This energy is emitted by means of photons with different wavelengths (blue to red, respectively 400 - 700 nanometres), which are used by plants for photosynthesis. However, not every wavelength is efficient for crop growth. The photosynthesis creates nutrients required for growth.

The type of artificial illumination depends on the application, e.g. stimulation of crop growth, ripening of crop fruits, root stimulation etc, or simply type of crop.

Mostly, high or low pressure gas discharge lamps (sodium lamps) are used for assimilation lighting. However, these lamps have a limited lifespan of typical 6 months to one year and therefore need regular replacement. Further, these lamps consume a lot of energy, typically 600 W to 1000 W for approximately 10 square meters of crop. Unfortunately, the energy to light conversion rate is quite low: about 30 percent of the energy input is converted into usable light (photons), and the remaining energy is converted into heat and usually lost in the ridge of the greenhouse where it is of no use for crop. The excess heat must be discharged by ventilating the greenhouse in order to keep temperature at a optimal level.

This waste of energy (heat and energy consumption) is not acceptable anymore for economic, environmental and sustainability reasons. Also the limited lifetime of gas discharge lamps puts an economic pressure on business, mainly, but not only, because of labour costs for replacement.

In order to avoid these disadvantages, a system for stimulating plant growth has been developed that comprises light sources based on a different technology,

i.e. LEDs. Light Emitting Diodes (LEDs) have all kinds of advantages, including compact size, high efficiency, and long life expectancy. In principle, an LED generates light within a narrow spectral range only but, in contrast to the sodium lamp whose narrow spectral range is fixed, it is possible to design an LED such that it generates its light output in a desired spectral range. Of course, it is possible to combine LEDs of different types, each generating light in mutually different spectral ranges, to obtain an overall light output having a certain desired spectral distribution.

The present invention aims to further elaborate on the LED technology to optimize an illumination system for stimulating plant growth.

Especially when compared to incandescent lamps, which generate much light in non-useful spectral regions including infrared, LEDs are very efficient light generators. Nevertheless, the LED bodies dissipate energy, and especially in the case of high-power LEDs, cooling of the LEDs is necessary in order to prevent damage of the LEDs.

Dutch patent application 1040116 describes a lamp device that comprises one or more LEDs, a heat sink for the LEDs, and at least one fan system for generating a downward air stream that is in heat exchange with the heat sink such that the heat sink is sufficiently cooled while at the same time the air stream is warmed up. A fan controller controls the operation of the fan. In a greenhouse, a system of a plurality of such lamp devices is arranged. In practice, all controllers operate independently from each other, and all fans in the system are controlled in the same manner: each fan is operated in a constant power mode, and blows heat generated by the LEDs downwards into the direction of the crop.

The present invention aims to further elaborate on this system.

According to the invention, the system is provided with a common system controller that supervises the operation of all fans in the system. This may either be implemented in the form of one common controller that replaces all individual controllers to directly control the operation of each individual fan system, or one common controller that is hierarchially higher than individual controllers and controls the operation of the respective fan controllers. The system controls the fans such that groups of fans cooperate to create a large-scale air stream which enhances the business and climate control of the greenhouse. This reduces operational costs in terms of additional vent systems, use of carbon dioxide and heating.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the present invention will be further explained by the following description of one or more preferred embodiments with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which:

figure 1 schematically shows a longitudinal cross section of an exemplary embodiment of an assimilation lamp device according to the present invention; figure 2 schematically shows a row of assimilation lamp devices for illustrating the induction of a horizontal air flow by a plurality of vertically operating fans; figure 3 schematically shows an illumination and air flow system that comprises an array of assimilation lamp devices;

figure 4 schematically shows a top view of an array of assimilation lamp devices; figure 5 schematically shows a greenhouse with an array of assimilation lamp devices.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 schematically shows an exemplary embodiment of a compact and relatively low cost assimilation lamp device 101 useful for application in the present invention. The lamp device 101 comprises a central lamp unit 10 which includes a body 14 of a general rectangular block shape. The lamp device 101 further comprises a plurality of LEDs 12 mounted to the bottom surface of the body 14, preferably in a recessed portion 11 thereof. The body 14 has a cabinet 15 accomodating driving and control circuitry 17 for the LEDs. The cabinet 15 will receive an electric supply cable for electrical supply, but this is not shown for sake of simplicity. The driving and control circuitry 17 generates driving current for the LEDs 12, which current is transported to the LEDs via conductors extending through the body 14, but this too is not shown for sake of simplicity.

The LEDs may be selected to emit light in (different) parts of the 400 - 700 nm spectrum.

The LEDs 12 are mounted to have a good thermal conduction towards the body 14. The body 14 is made of a thermally well conducting material, for instance aluminum. Thus, the body 14 acts as a heat sink for the heat generated by the LEDs. This in any case has the effect that the temperature of the LED’s remains at such a level that the lifetime of the LED’s is not affected.

The lamp device 101 comprises a fan 42 or any other type of air stream generating means for generating a downward air stream 43, as well as heat transfer and exchange means 20 for transferring heat from the body 14 to the air stream 43, so that the air stream cools the body 14 and the heat from the LEDs 12 is used to warm said downward air stream 43. This warm air stream 43 ultimately reaches the plants, so that all in all the heat generated by the LEDs is not a loss any more but is advantageously used to warm the environment of the plants.

The precise structure of the heat transfer and exchange means 20 is not essential for understanding the present invention, and therefore this structure will not be discussed in detail here.

In this embodiment of the assimilation lamp 101, the fan 42 is arranged above the heat exchanger structure 20 to generate a vertical air flow towards the heat exchanger structure 20; the air flow is blocked by the body 14 and is deflected in a horizontal direction. The precise horizontal direction is determined by the design of the heat exchanger structure 20.

The heat exchanger structure 20 in this embodiment comprises a plurality of relatively thin cooling fins or lamellae 41 that in between them define flowing paths for the air. The fins or lamellae 41 are all mutually parallel and extend in XZ-planes, with the X-direction parallel to the longitudinal direction of the assimilation lamp 101. To assure the downwards air stream 43, this embodiment of the assimilation lamp 101 comprises a guiding hood 160 having a substantially inverse-U shaped profile with a top wall 161 and substantially vertical side walls 162. At its underside, the hood 160 is open. The top wall 161 has a raised portion 163 having a central opening

164, provided with a protective grating 165. Under the opening 164, surrounded and protected by the raised wall portion 163, the fan 42 is arranged. The top wall 161 lies in close proximity to the upper side of the fins or lamellae 41, so that in operation air is sucked in via the opening 164 and is forced to pass between the body 14 and the top wall 161 of the hood 160, following in X-direction the flow channels between the fins or lamellae 41. In this X-direction, the hood 160 is wider than the body 14, so that a collective flow path is defined between the side walls 162 and the body 14 where the air can do nothing else but flow down in vertical direction, to exit the device at the underside of the hood 160, which may be flush with or lower than the lower surface of body 14. It is noted that, in X-direction, the fins or lamellae 41 may have the same size as the body 14, as shown, but it is also possible that these fins or lamellae may extend as far as to meet the hood side walls 162.

It is to be noted that assimilation lamp devices of a different design may be used in the system of the present invention. It is further noted that, depending on climate conditions such as time of day and date of year, the illumination by the LEDs 12 is not needed and is therefore switched off, so that the air flow 43 is not heated. It is even possible that controllable downflow generators are used that comprise one or more fans but that do not include any LED or other heating means for the airflow.

In a normal greenhouse setup, each assimilation lamp illuminates approximately 10 square meters of crop. The crop illumination density is dependent on the type of crop, and the output power of the lamp. With this setup, each illuminated hectare (100 x 100 meters) is covered with a grid of 1000 assimilation lamps. In prior art, the incorporated cooling fan of each assimilation lamp device is autonomously driven at a constant speed in order to maintain the temperature of the heatsink and thus the LED temperature at a constant level. The downflow of air results in a slightly increased air pressure below the lamp, at plant level, and in a slightly decreased air pressure above the lamp. Vertical return flows will generally be created in between the lamps. Thus, each lamp device will typically be associated with a cell of vertical air circulation.

The present invention is based on the understanding that it is possible to obtain a large scale, well-controlled horizontal air flow in the greenhouse by a suitable control of the various assimilation lamp devices in combination.

Figure 2 shows a row of four identical lamps devices of figure 1, indicated by reference numerals 101(1), 101(2), 101(3), 101(4). The lamp devices will be attached to a structural beam of a greenhouse. In each of the lamp devices 101, the corresponding fan 42 can be individually controlled, i.e. the rotational speed of the fans 42 can be controlled. Assume that the rotational speed of the fan 42 of the first lamp device 101(1) has a certain value, and that for each next lamp device in the row the rotational speed is always lower than the rotational speed of its corresponding previous neighbour. In formula: V(1) > V(2) > V(3) > V(4), in which V(i) indicates the rotational speed of lamp 101 (i). Each lamp device 101 (i) generates a downward airstream 43(i) (indicated by arrows) having an air speed (indicated by the length of the arrows) proportional to the fan speed V(i), which results in a local pressure level P(i) (indicated by the size of a star) proportional to the fan speed V(i), so that P(i) > P(i+1) for each i. These different pressures at different positions result in a large scale but decent horizontal air flow 243 at the level of the plants, from the first lamp device 101(1) to the last lamp device 101(4). In this respect, large scale means at a scale larger than the mutual distance between the respective lamp devices.

In the example depicted in figure 2, an overall flow is directed to the right. It is also possible that for instance the third lamp device 101(3) has the fan 42(1) with the lowest speed V(3) and hence the lowest pressure P(3), so that at the left of this third lamp device 101(3) a flow is generated to the right while at the right of this third lamp device 101(3) a flow is generated to the left.

In the above explanation, only four lamps are involved. It should however be clear that the above explanation applies to any number of lamps in a row. It should further be clear that the above principle not only applies to fans that are placed in a row but also to fans that are arranged in a two-dimensional array: fans generating a larger downstream than their neighbours will generate a higher local pressure below themselves and will thus cause a horizontal air flow towards their neighbours, and oppositely, fans generating a lower downstream than their neighbours will generate a lower local pressure below themselves and will thus cause a horizontal air flow towards themselves.

It is noted that the pressure differences do not need to be large to induce the horizontal air flow, although larger pressure differences will indeed induce larger horizontal airflows. In any case, the induced horizontal airflow will result in a micro climate that is better controlled and more homogenous. This relates particularly to the temperature and moisture distribution, and to the distribution of carbon dioxide, which is blown into the greenhouse using fan systems and perforated hoses during daylight (when photosynthesis occurs).

Thus, with reference to figure 3, in accordance with the present invention, a greenhouse is equipped with an illumination and airflow system 300 that comprises an array 301 of assimilation lamp devices 101 that comprise air fans 42, and the air fans of those assimilation lamp devices are controlled individually such that at least two neighbouring fans have mutually different speeds. This control arrangement is schematically illustrated in figure 3, where reference numeral 142 indicates individual fan controllers of the individual assimilation lamp devices 101, and where reference numeral 310 indicates a common control device of higher hierarchy controlling the individual fan controllers 142. Alternatively, it is possible that common control device 310 directly controls the individual air fans 42 and that the individual fan controllers are omitted.

The common control device 310 may select a certain distribution of fan speed per lamp device to obtain a certain desired induced horizontal airflow. This distribution may be stationary, to obtain a stationary horizontal air flow pattern. However, in such case the LEDs of an assimilation lamp device 101 with lower air speed may receive insufficient cooling and become warmer than desired. It is desirable that all assimilation lamp devices 101 are subjected to the same average cooling, assuming that the assimilation lamp devices 101 are of mutually identical design. Therefore, according to a further aspect of the present invention, the distribution of the fan speed per lamp device is varied dynamically according to a predetermined schedule, such that the resulting horizontal airflow varies dynamically while the average cooling per lamp is the same. This is advantageous for the lamps but also for the crop. It is noted that the lowest fan speed in the array may be equal to zero and that the highest fan speed in the array may be 100%. It is further noted that the speed control may be a simple on/off control.

This aspect of the invention is illustrated in figure 4, which is a schematic top view of the array 301. The individual fans 42 are indicated by a circle. The figure shows an array of 8 rows of 5 devices each, but in practice the number of rows and the number of devices per row will be much larger. In this example, it will be assumed that a fan is controlled to either operate at full speed, which is shown as a large double circle, or at half speed, which is shown as a small single circle.

In this example, during a first phase, all fans of the first row and the fifth row are operated at full speed Vmax while all other fans are operated at half speed; this is illustrated at [A].

During a second phase, all fans of the second row and the sixth row are operated at full speed while all other fans are operated at half speed; this is illustrated at [B],

During a third phase, all fans of the third row and the seventh row are operated at full speed while all other fans are operated at half speed; this is illustrated at [C].

Etcetera. The pattern of full speed fans / half speed fans is gradually shifted. Open arrows indicate the horizontal and vertical air flow distribution. It will be seen that this flow distribution shifts with the subsequent phases.

Assume that each phase last a time duration Δ, and that there are N rows. It will be seen that operation is periodic, with an operation period T = Ν Δ.

Assume that the cooling power Q is proportional to fan speed V: Q = AV. It will be seen that, on average, the average cooling power Qav in each lamp is the same, because during each operation period each fan operates at full cooling capacity for 1χΔ time and operates at half cooling capacity for (Ν-1)χΔ time.

The above is just a simple example of a possible dynamic variation of fan speed; other settings and variations are also possible.

Since each individual fan can be individually controlled in speed, the number of patterns (defined by algorithms) in which the fans can be operated is very large.

An operator is free to define any pattern, on the basis of expected effect on the displacement of air and thus micro climate in the greenhouse, it is possible to aim at creating a constant air stream, but it is also possible to aim at a more turbulent micro climate which under certain circumstances may be desirable above a constant air stream.

Figure 5 shows a greenhouse arrangement 500 in which the lamps and the created airstream serve another purpose. Reference numeral 501 indicates a greenhouse, having a set of horizontal fabric screen 503 dividing the interior of the greenhouse 501 in an upper portion 502, also indicated as roof area, between the greenhouse roof and the screen 503, and a lower portion 504, also indicated as crop area, between the greenhouse ground and the screen 503. Due to the change of day to night and consequently the cooling down of the outside atmosphere, the temperature in the greenhouse will decrease. In order to temper a temperature drop at crop level, a common practice in greenhouses 501 is to shield the upper part of the greenhouse just above the crop with the fabric screens 503 at approximately sunset time. These flexible screens are normally located above lamp level. The screens prevent the rising of still present warm air to the roof of greenhouse 501, i.e. in the crop area 504 the warm air is trapped below the screens 503, so that the top of the crop is kept warmer at night than when the screens were absent. This enhances crop yield.

At night, the air trapped in the roof area 502 above the closed screens 503 will severely cool down. The temperature T502 of the air in the roof area 502 may approach the outside temperature and will definitely be considerably lower than the temperature T504 of the air in the crop area 504.

At dawn, the screens 503 must be opened in order to let daylight enter the greenhouse at crop area 504. However, if the screens would be opened completely at once, the cold air from the roof area 502 would drop down on the crop, causing a temperature shock in the crop and causing a hampering of crop growth. To prevent this, in practice the screens 503 are opened gradually step by step, e.g. every 30 minutes a passage opening in the screen 503 is increased. The cold air from the roof area 502 will fall gradually and mix in with the warmer air at crop level in the crop area 504. This procedure is time consuming and not ideal for crop growth and crop disease suppression.

In accordance with a further elaboration of the present invention, the migration at dawn of the trapped cold air from the roof area 502 to the crop area 504 is much more gentle and controlled. As shown in figure 5, each lamp device 101 is (or in any case one or more lamp devices are) aligned with a corresponding opening 505 in the screens 503, and may even be provided with a hose or tube or pipe 507 having an upper end projecting above the screens 503. When the lamp device 101 is operated, the fan 42 generates a downstream through the corresponding opening 505 and possibly guided by the pipe 507. The cold air in the crop area 504 with temperature Tlow is sucked down, and is guided along the fins of the heatsink of the operational and therefore hot lamp. The cold air is heated by the hot lamp to a higher temperature Thigh and then blown downwards to the crop; Thigh may be about 10 to 15 degrees Centigrade above Tlow. This has several advantages. The temperature shock of the crop, caused by a downflow of cold air, is prevented. The downflow of relatively warm air heats up the top of the crop and therefore enhances crop growth. Further it decreases the relative humidity of the air the crop area 504 surrounding the crop and contributes to the suppression of crop diseases.

It should be clear to a person skilled in the art that the present invention is not limited to the exemplary embodiments discussed above, but that several variations and modifications are possible within the protective scope of the invention as defined in the appending claims.

For instance, while it is advantageous that the air stream generating means 42 can generate a downstream of air heated by the LEDs of the lamp device 101, and while it is advantageous that the flow speed of this air flow and consequently the temperature of this air flow can be adjusted independently from the operation of the LEDs, the operation of the LEDs is not a necessity. It is possible that the LEDs of a lamp device are off while the fan 42 is on.

Further, it is possible that the greenhouse is provided with a separate air flow regulating system. The airflow system according to the present invention can operate together with such separate air flow regulating system. It can add flexibility and variation to the air flow pattern, and/or it is possible to reduce the power of the separate air flow regulating system; it is even possible that the air flow system according to the present invention performs all functions of a standard separate air flow regulating system, so that the separate air flow regulating system can be omitted and the costs thereof can be avoided.

Even if certain features are recited in different dependent claims, the present invention also relates to an embodiment comprising these features in common. Any reference signs in a claim should not be construed as limiting the scope of that claim

Claims (8)

CONCLUSIONS An assimilation lamp device (101) for stimulating the growth of plants and crops, which lamp device comprises: a central lamp unit (10) comprising a body (14) and one or more LEDs (12) mounted on the bottom surface of the body (14), the body (14) being made of a thermally highly conductive material, for example aluminum, and acts as a heat sink for the heat generated by the LEDs; air flow generating means (42) for generating a downward directed air flow (43); heat transfer and exchange means (20; 30) for transferring heat from the body (14) to the air flow (43) so that heat from the LEDs (12) is used to increase the temperature of said downward air flow (43); wherein the air flow generating means (42) are controllable independently of the lamp operation. An air flow system (300) comprising an array (301) of assimilation lamp devices (101 (i)) according to claim 1, and a common control device (310) for controlling the operation of the individual air flow generating means (42 (i)), the common control device (310) is arranged to control at least one of said air flow generating means (42 (i)) at a speed different from the speed of at least one other of said air flow generating means (42 (i)) in order to have a controlled horizontal air flow to induce. The airflow system (300) according to claim 2, wherein the common control device (310) is arranged to vary the velocities of all airflow generation means (42 (i)) over time, such that a pattern of individual velocities is varied and consequently a resulting pattern of horizontal airflow is changed with time. The air flow system (300) according to claim 2, wherein the common control device (310) is arranged to vary the speeds of all air flow generating means (42 (i)) over time, such that a pattern of individual speeds is shifted and, consequently, a resulting pattern of horizontal airflow is shifted with time. The airflow system (300) according to claim 2 or 3 or 4, wherein the common control device (310) is adapted to vary the velocities of all airflow generating means (42 (i)) with time, such that a large-scale vertical flow pattern is obtained. A greenhouse assembly (500) comprising a greenhouse (501) with a system of controllable screens (503) that can subdivide the interior of the greenhouse into a crop area (504) and a roof area (502) above the crop area (504), wherein the assembly (500) further comprises at least one lamp device (101) according to claim 1 or an air flow system according to any one of claims 2-5; wherein at least one lamp device (101) is arranged in vertical alignment with an opening (505) of the controllable screens (503). The greenhouse assembly according to claim 6, wherein at least one lamp device (101) is provided with a vertical pipe (507), an upper end of which protrudes above the controllable screens (503). A method for operating a greenhouse assembly according to claim 6 or 7, wherein the screens are open during the day, wherein the screens are closed during the evening and / or night, and wherein in the morning before the screens are fully opened, cold air is sucked down from the roof area above the screens by the at least one lamp device (101) and is heated before being blown down to the crop area below the screens. 101 o CM CO