A method and a system for dehumidifying air in a greenhouse
The present invention relates to a method according to the preamble of claim 1.
Such a method is known from WO 00/76296. This publication describes with reference to Fig. 4 the use of a relatively large cooling heat exchanger, by means of which moisture present in the greenhouse is removed from the air by cooling down the air and subsequent condensation of that air. A heating heat exchanger is provided downstream. The air returned to the greenhouse is heated by the latter heat exchanger.
Although it has been found that this method is often satisfactory, in certain circumstances crop damage has been found. This results in a considerable reduction of the yield, with the result that such a method is not universally usable.
It is the object of the present invention to avoid this disadvantage and to provide a method by means of which it is possible in an expedient manner to dehumidify air without damage being caused to the crop. This object is realised in a method of the type described above with the characterizing measures of claim 1.
According to the present invention, the temperature of the air blown out of the dehumidification system is precisely controlled. This air is at most 10°C colder than the air taken out of the greenhouse into the system, in other words than the "ambient air" prevailing in the greenhouse. It has been found that crop damage can be prevented in the case of such a temperature difference. More particularly, the temperature difference between the air emerging from the dehumidification system and the air prevailing in the greenhouse is less than 8°C, and more particularly 3°C. It has been found that with the precise control of the temperature of the air coming out of the dehumidification system, apart from the abovementioned limitation of crop damage, a higher yield of the crop can even be obtained. This has been found, inter alia, in the growing of tomatoes, but it must be understood that the invention is not limited to growing tomatoes. It is assumed that this is due to the fact that the air blown out causes the microclimate to be refreshed. This applies in particular if the air blown out of the dehumidification system passes close to the leaves of the crop. This can be achieved, for example, by blowing out this air at a relatively low level, and as it rises this air will rise along the leaves and remove moisture there. Such a precisely directed airflow is in particular combined with growth occurring at a higher level, such as in gutters. However, it should be understood that the above is only a theory for explaining the advantageous effects achieved with the
invention. As described above, the term ambient should be understood as being the environment inside the greenhouse, and more particularly the crop or fruits in it. Circulating air gives an advantageous microclimate with optimum (relative) air humidity, temperature and CO2%. More particularly, according to the present invention, the air is blown into an air distribution system. Such an air distribution system can be connected to one or more of the systems for achieving the method described above.
According to the invention, before being blown into the air distribution system, the air is brought to a temperature that is such that even in the most unfavorable conditions no damage can occur in the crops during the outflow of this air from the air distribution system. From research it has been found that to that end the temperature difference in relation to the ambient air, in other words the untreated air present around the crop, should be less than 10°C, preferably less than 8°C, and more particularly 3°C or less. The above is dependent, inter alia, upon the crop being grown and the way in which it is being grown. In this case there is a difference between growing with growing tables and with hanging or other gutters and crops grown on the ground. The airflow from the air distribution system is different in all three of the situations.
According to an advantageous embodiment of the method, carbon dioxide is added to the air coming out of the air distribution system. The carbon dioxide is preferably fed in downstream of the heating heat exchanger. The terms upstream/downstream here refer to the direction of movement of the air through the air distribution system.
In principle, the position of the fan or other blowing device relative to the two heat exchangers can be freely selected. In other words, the fan can be placed upstream of, downstream of or between the two heat exchangers. According to an advantageous embodiment of the invention, it is, however, placed downstream of the heat exchangers.
The air that is displaced can be either air coming from the greenhouse or from the environment, in other words from outside the greenhouse. The invention also relates to a system for dehumidifying air in a greenhouse, comprising a cooling heat exchanger placed in said greenhouse as the dehumidifier for the air flowing through from the greenhouse or environment, and also a fan, both provided in a pipe system connected to said greenhouse, which pipe system comprises
an air distribution system for dehumidified air, a heating heat exchanger being provided downstream of said cooling heat exchanger.
Heating or cooling takes place in a heat exchanger. Water or any other heating/cooling agent can preferably be used for the other medium. Both cooling and heating can be achieved in any way known in the prior art. Underground cold-heat storage and also heat pumps are used in preferred variants of the invention, but electric heating or cooling is not excluded.
The air distribution system, as described above, is preferably a flexible pipe of at least 20 m. According to the invention, the length of such a pipe can be up to hundreds of meters. Such a pipe preferably has a relatively large diameter (tens of centimeters) and is provided with a large number of air outflow apertures distributed along its length. According to an advantageous preferred embodiment of the invention, these apertures are provided on the upper side of the pipe. In a greenhouse all this is set up in such a way that a number of such systems, comprising a dehumidification/heating part and an air distribution system, are disposed parallel to each other.
According to an advantageous variant of the invention, a control is present, by means of which the outflow temperature of the air from the system is regulated. More particularly, such a control is designed in such a way that the outflowing air is at most 10° colder than the "ambient air" in the greenhouse. Such a control can influence the rate of flow of the air displaced by the fan and/or influence the effect of one or both of the heat exchangers.
It has been found that with the present invention it is possible in a simple manner to limit the moisture content in a greenhouse, with the result that fungal infections, pests and diseases are prevented or minimized, as does the damage arising from these. Furthermore, the crop does not suffer any damage from heating of the dried air. Finally, it is possible to feed ingredients into the outflowing air, such as CO2 and/or crop protection products (such as sulfur). The fan described above can be any fan known in the prior art, but preferably comprises a centrifugal or radial fan. Such a fan is preferably provided downstream of the heating heat exchanger. The invention will be explained in greater detail below with reference to an exemplary embodiment illustrated in the drawing, in which:
Fig. 1 shows very diagrammatically a greenhouse provided with the system according to the invention;
Fig. 2 shows in diagrammatic side view a system according to the invention;
Fig. 3 shows a variant of the system according to the invention; and
Fig. 4 shows in end view a part of the inside of a greenhouse.
In Fig. 1 reference numeral 1 indicates a greenhouse consisting of a number of bays. Two systems 2 are indicated diagrammatically.
Details of these systems 2 can be seen from Fig. 2. A housing 3 is present, in which housing a cooling heat exchanger 12 and a heating heat exchanger 13 are provided. The direction of flow of the air moving through the system 2 is indicated by arrows 15. It can be seen from this that the heating heat exchanger 13 is situated downstream of the cooling heat exchanger. A condensation collection facility can be present below/next to the cooling heat exchanger 12. Both heat exchangers are provided with diagrammatically illustrated connection sockets, which can be connected to a corresponding cooling/heating system.
Downstream of heating heat exchanger 13 a connection socket 11 is present for feeding in carbon dioxide and/or crop protection products and/or other gas. Reference numeral 14 indicates a fan, which draws in the air through the housing and through the heat exchangers 12 and 13 respectively and subsequently blows it out of the housing 3 into the flexible pipe 4. This flexible pipe or the air distribution system can be of a considerable length ranging from one meter to hundreds of meters. The flexible pipe 4 is provided with outflow apertures 5.
Fig. 3 shows a variant of the system shown in Fig. 2. The system is indicated in its entirety by 22 and comprises a housing 23, in which a cooling heat exchanger 32 and a heating heat exchanger 33 are accommodated. The airflow is indicated by arrows
35 and 36. The design of the flexible pipe 14 substantially corresponds to what is shown in Fig. 2. The same applies to the fan 34.
It can be seen from Fig. 3 that two airflows are drawn in by fan 34, one airflow being cooled and dehumidified by means of cooling heat exchanger 32, and the other airflow being only heated by means of the heating heat exchanger 33. These two airflows are subsequently mixed in fan 34, and the airflows 35, 36 flowing out of said fan have the same temperature and air humidity. In this case the air humidity will be lower than the air humidity in the greenhouse, and the temperature will be higher than that of the air coming out of the cooling heat exchanger 32. In this way a desired air velocity, relative humidity and temperature can also be achieved at the position of the
crop or its fruit.
Fig. 4 shows two air distribution systems or flexible pipes 4 situated next to each other. These systems are placed on ground 10. At some distance from the ground 10 a tubular rail network 6 is present. This serves for additional heating. In this example the crops are grown with the aid of gutters. The crop is indicated by 8 and the gutters by 7. Arrow 9 shows the airflow of the cold air coming out of aperture 5. Owing to its velocity, this air will move upwards in the first instance. However, owing to the small difference in temperature from that of the "ambient air", the subsequent downward movement of air observed in the case of very cold air will not be found. The positioning of flexible pipe 4 relative to the crop and the cooling down by heat exchanger 12, or heating by heat exchanger 13, are selected in such a way that if the air reaches the crop according to arrow 9, the temperature difference in relation to the environment is less than 10°C, and is preferably less than 8°C, and is more particularly less than approximately 3°C. In this way it can be ensured that no damage occurs in the crop.
The heating of the outflowing air described above can be carried out in any way known in the prior art. Use can be made of the same heat source as that by which the tubular rail network is operated. Combination with heat pumps/earth heat is likewise possible. These and similar variants will immediately spring to mind in the case of the person skilled in the art on reading of the above description, and lie within the scope of the appended claims.