Patent Description:
Greenhouses have been used for hundreds of years to grow different varieties of plants, including ornamental plants and fruit/vegetable producing plants. Greenhouses typically comprise a structure with a plastic or glass roof and frequently glass or plastic walls. The interior of the greenhouse can be heated by incoming solar radiation that warms the plants and soil therein. The closed environment of a greenhouse has its own unique requirements compared with outdoor production. Pests and diseases need to be controlled and irrigation is necessary to provide water. Of equal importance, greenhouses can also be arranged to compensate for extreme highs and lows of heat and humidity, and to generally control the environmental conditions such as the level of carbon dioxide (CO<NUM>).

Different greenhouses have been developed to control the environmental conditions in a greenhouse. <CIT>describes a method and structure for environmental control of plant growth in greenhouse conditions. The structure comprises a translucent stressed fabric shell on a base, with which to grow plants, the shell and base sealing the environment within the space against external environmental conditions. The temperature and relative humidity within the production areas are generally controlled by a microprocessor based series of spray systems, along with a furnace. The spray systems can lower the temperature in the space while at the same time increasing humidity, and the furnace can be utilized to increase the temperature within the space.

<CIT>describes a greenhouse and a method for controlling the environment of the interior space of the greenhouse. The greenhouse includes an interior insulating panel and a movable exterior reflective panel capable of both insulating the interior of the greenhouse and reflecting sunlight into the interior. The greenhouse also includes a closed-system heat exchanger having a plurality of spaced water-impermeable water flow passageways through which water flows by gravitational forces and having a means for blowing air between the water flow passageways such that the air does not contact the water and such that the air is either heated or cooled by the water. In addition, the heat exchanger may include a water discharge and/or a gas discharge for the control of humidity and gas levels within the greenhouse. Finally, the greenhouse includes hydroponic plant beds disposed on top of the heat exchangers and hydroponic solution tanks along the outer interior walls of the greenhouse.

<CIT>discloses a greenhouse for providing environmental control for growing plants comprising a frame defining a structure forming an interior region for holding plants. A flexible cover is positioned over the frame for providing a roof enclosure for the structure, and an elongate roller extends along the length of the structure secured to a lengthwise edge of the cover. A power source is coupled to the roller driving the roller about its longitudinal axis to retract or extend the cover relative to the frame. The greenhouse also includes a water distribution system that includes a distribution conduit with spaced-apart spray nozzles positioned adjacent the top interior of the greenhouse. A power drive system oscillates the conduit through a defined arc to distribute water downwardly to plants growing in the greenhouse. A timing means is associated with the power drive for delaying the return rotation of the conduit to ensure that the outside edges of the spray pattern will be watered evenly.

<CIT>et al. discloses a greenhouse having an exterior curtain wall structure formed by spaced tubular posts carrying external transparent panels and bottom non-transparent wall panels below a sill with the panels spanning the posts. A plurality of elongate benches is located within the interior at spaced positions along one side wall with the width of the benches being equal to the post spacing to form an expandable construction. Each bench has associated with it a respective air handling system for conditioning including a duct which is located partly under the respective bench and a fan in a fan housing at the side wall. From the fan a vertical duct section extends to a flexible tube extending over the bench. Air dehumidification, fogging, heating and cooling are provided in the duct under the bench. An alley is arranged along the opposite wall containing electrical controls mounted in cabinets forming panels for mounting in the span between posts.

European Patent Application No. <CIT> discloses a method for growing crops arranged in a greenhouse that is closed off from the environment and wherein the climate is regulated and watering of the crop is controlled within by a watering device. The photosynthesis and yield of the crop is regulated by controlling, independent of the outside conditions, the CO<NUM> concentration in the greenhouse and the transpiration by regulation of the temperature and air movements around the crop. Air regulating means can be utilized such as partitions, screens and the like, and outlet openings for air at different heights near the crop are provided so that the climate near the crop, and in particular the microclimate near the leaves of the crop, can be regulated and monitored.

International Application No. <CIT> (Publication No. <CIT>) discloses a market garden greenhouse system in which plant products can be cultivated. The market greenhouse is closed in that it is substantially not provided with ventilating openings or ventilating windows that can be opened. The greenhouse comprises heat regulating means for regulating heat therein, with heat generating from solar energy and a heating system. The greenhouse can also comprise an air humidity regulating means and surplus heat is removed from the greenhouse to an aquifer in the summer. <CIT> attempts to uniformize a heat radiating quantity in the longitudinal direction of a duct, in the duct and a green house system.

The invention consists in a greenhouse according to claim <NUM>, comprising a growing section with an air or gas distribution system within said growing section. The distribution system comprises one or more conduits for distributing air or gas within the greenhouse with conduits carrying air or gas having different pressures along the length of the conduits. The conduits are arranged to provide substantially equal distribution of air or gas throughout the growing section.

The invention consists in a greenhouse air distribution system according to claim <NUM>, comprising a plurality of tubes to distribute air within a greenhouse. A system is included for providing a main air flow to the interior of at least one of the tubes, the air pressure within the tubes varying along its length. The tubes have holes to allow air to exit from the tubes with the holes formed to compensate for the pressure variations to allow the tubes to provide for a substantially uniform air distribution along their lengths.

These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings which illustrate by way of example the features of the invention.

The present invention generally relates to improved greenhouses and forced greenhouse climate control systems that are arranged to operate in different modes to control the temperature and environmental conditions within the greenhouse. In one mode ambient air is drawn into the greenhouse, and in other modes air from within the greenhouse is re-circulated. In still other modes, the system can draw ambient air in combination with recirculation of air, and when ambient air is drawn in, it can also be cooled. This arrangement provides for control of the greenhouse climate using a simple and cost effective system.

In one embodiment of a greenhouse and greenhouse climate control system according to the present invention, tubes are provided along the full length of the greenhouse growing section. Ambient and or re-circulated air is drawn into the tubes and each of the tubes has a means for allowing air to exit along its length, such as through holes along the length of the tubes. The number and size of holes is arranged to promote even distribution of air from the tubes throughout the greenhouse structure. It is understood that other devices can be used beyond tubes for flowing air into the greenhouse, and different means for allowing air to exit from the tubes can be used. The separation (spacing) between the tubes can vary and the diameter of the tubes can vary depending on the particular circumstances including but not limited to the surrounding climate, or crops being grown. In different embodiments the tubes can also be above the greenhouse crop or below gutters tables or other systems in the greenhouse.

Fans or other mechanisms for drawing air are arranged on the tubes to supply a flow of air volume to the tubes to cool the greenhouse during the expected elevated outside (external) temperatures and to heat the greenhouse during expected low temperatures. In one embodiment, a respective one of fans is located at one end of each of the tubes and flows air into and along the length of the tubes. It is understood, however, that the fans can be located in other positions on the tubes and a single fan can be used to flow air into more than one of the tubes.

The climate control system according to the present invention is also arranged to efficiently flow air of different temperatures into the tubes to control the temperature in the greenhouse during temperature cycles of the surrounding climate. When the temperature within the greenhouse rises, cooler gasses are provided to the greenhouse tubes, and in one embodiment the cooler air is provided from the ambient air outside the greenhouse. Systems can also be used to further cool the ambient air as it enters the greenhouse, if necessary. When the temperature in the greenhouse is at or near the desired level air from within the greenhouse can be circulated into the tubes. When the temperature within the greenhouse falls, known internal heater systems can be used to heat the air in the greenhouse with the heated air re-circulated to the tubes. To achieve the desired temperature within the greenhouse a controller can be employed to automatically provide for the different modes above or provide a combination of the modes. The systems according to the present invention can also control the pressure within the greenhouse and the level of certain gases such as carbon dioxide (CO<NUM>).

Conventional greenhouse air distribution systems can distribute unequal amounts of gas along the length of the greenhouse. In the case of tubes provided along the length of the greenhouse, equally spaced perforations are provided along the tube to allow air or gas to pass from within the tube to the interior of the greenhouse. The air or gas is typically supplied to the tube from one end, and as a result of pressure differences and turbulence along the length of the tube, an unequal distribution of air can exit from the tube at different points along its length.

Another problem that may be encountered is a temperature difference over the length of the tube due to radiation and convection from or into the air tube, resulting in unequal temperatures. While still other challenges in providing homogeneous air distribution can result from air exiting the tube at an angle corresponding to the direction of airflow through the tube. In areas of turbulence, the air can emit at different directions from the holes, contributing to non-homogeneous air distribution along the tube.

As further described below, these problems can be minimized or eliminated by utilizing an air distribution system arranged according to the present invention. The distribution systems can be arranged to distribute equal amounts of air of a substantial homogeneous quality of the entire length of the greenhouse. In some embodiments the distance between perforations can be varied along the length to compensate for the pressure differences and turbulence. In other embodiments, the tubes can be arranged with compartments along its length that provide a barrier between the main flow in the tube and air exiting from the tube. This not only reduces the effects of the turbulence, but also provides and insulation barrier to reduce unequal temperatures along the length of the tube.

The present invention is described herein with reference to certain embodiments but it is understood that the invention can be embodied in many different ways and should not be construed as limited to the embodiments set forth herein. In particular, the present invention is described below in regards to greenhouse features arranged in a particular way but it is understood that these features can be arranged in different ways and can be used in other applications.

It is also understood that when an element or feature is referred to as being "on" or "adjacent" another element or feature, it can be directly on or adjacent the other element or feature or intervening elements or features may also be present. Furthermore, relative terms such as "outer", "above", "lower", "below", and similar terms, may be used herein to describe a relationship of one feature to another. It is understood that these terms are intended to encompass different orientations in addition to the orientation depicted in the figures.

Although the terms first, second, etc. may be used herein to describe various elements or components, these elements or components should not be limited by these terms. These terms are only used to distinguish one element or component from another element or component. Thus, a first element or component discussed below could be termed a second element or component without departing from the teachings of the present invention.

Embodiments of the invention are described herein with reference to different views and illustrations that are schematic illustrations of idealized embodiments of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances are expected. Embodiments of the invention should not be construed as limited to the particular shapes of the regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing.

<FIG> show one embodiment of greenhouse <NUM> utilizing a forced greenhouse climate control system <NUM> according to the present invention. The greenhouse <NUM> has a gabled end <NUM> that is separated from the crop growing section <NUM> of the greenhouse by partition <NUM>. The majority of the climate control system <NUM> is housed within the gabled end <NUM> with a portion of the system continuing into the crop growing section <NUM>. The crop section <NUM> comprises a portion of the system comprising devices for distributing air from the gabled end <NUM> throughout the crop growing section <NUM>. Many different distribution devices can be used, with a suitable device being a plurality of tubes <NUM> running the length of the crop section. As mentioned above, different numbers of tubes can be used with greenhouse <NUM> shown having five (<NUM>) tubes <NUM>. The tubes <NUM> open through the partition <NUM> such that air from the gabled end <NUM> can flow into the tubes <NUM> and pass into the growing end through tube holes. Different numbers and sizes of holes can be included along the length of the tubes <NUM> to insure even distribution.

Fans <NUM> can be placed on or close to the bottom of the partition <NUM> between the gabled end <NUM> and the section <NUM> each at a respective one of the tubes <NUM>. The fans <NUM> are arranged to pull or flow air into its respective one of the tubes <NUM> from in the gabled end <NUM>. The air in the gabled end <NUM> can include ambient air from outside the greenhouse <NUM> or air from inside the crop section <NUM> during recirculation, or combination of the two. As more fully described below, this is accomplished by a louver and vent system within the greenhouse <NUM>.

The greenhouse <NUM> further comprises a first vent/opening <NUM> ("first vent") in the outside gable wall <NUM> through which ambient air can enter the gabled end <NUM>. The first vent <NUM> can be arranged in many different locations, with a suitable location as shown being on the lower portion of the outside gable wall. In the embodiment shown, one first vent <NUM> is shown, but it is understood that more than one vent can be included. The first vent <NUM> can be arranged in many different ways, with the preferred vent running substantially the length of the outside gable wall <NUM>.

A cooling mechanism <NUM> can be included at the first vent <NUM> to cool air being pulled into the gabled end <NUM>, and/or to control the humidity within the air. In one embodiment the cooling mechanism <NUM> is a conventional pad cooling system that is known in the art and not described in detail herein. A screen can also be included over the vent <NUM> to prevent insects and other pests from entering the greenhouse <NUM>.

In some embodiments, a heat exchanger <NUM> can be included at or near the fans <NUM> to further heat or cool the air passing into the tubes <NUM>. Heat exchangers are generally known in the art and the basic operation is only briefly discussed herein. According to the present invention, the greenhouse <NUM> can be arranged to store heated water from the heat exchanger for use in heating the greenhouse at a later time.

The heat exchanger <NUM> relies on a flow of water to cool air passing through the fan <NUM> as it enters the tube <NUM>. The cooling of the air by the water passing though the heat exchanger can result in the warming of the water flowing through the heat exchanger. In some embodiments, this warmed water can be stored in a separate storage tank for later use in warming the air in the crop section <NUM>. For example, warm water can fill the storage tank when the temperature of the air is high, such as during the day. The warmed water can be stored and at night, when the temperature dips, the warm water can be flowed into the heat exchanger <NUM> to warm the air passing into the tubes.

A first louver <NUM> can be included at the outside gable wall <NUM> that is movable in the directions of arrow <NUM> to control the amount of air entering the end gable <NUM>. When operating in the mode to block air from entering the end gable <NUM> the louver is lowered to cover the first vent <NUM>. When operating in the mode to allow air to enter the end gable <NUM>, the louver <NUM> can be raised so that it is not blocking air from entering or can be partially raised such that it is partially blocking air from entering. As shown, the first louver <NUM> can be a planar shield that can slide down to fully or partially cover the first vent <NUM> depending on the desired amount of air to pass through the vent <NUM>. It is understood that many different mechanisms can be used beyond the first louver <NUM> described above and the second louver described below.

The partition <NUM> comprises a second vent <NUM> that is located near the top of the partition <NUM>, although the vent <NUM> can be in many different locations. A second louver <NUM> can be included at the partition <NUM> that operates similar to the first louver <NUM>. The second louver <NUM> can be moved in the direction of arrow <NUM> to block air from entering through the second vent <NUM>, or can be moved so that it is not blocking air from entering or is partially blocking air from entering. Like the first louver, the second louver <NUM> can be a planar shield that can slide down to fully or partially cover the second vent <NUM> depending on the desired amount of air to pass through the vent <NUM>.

The crop section <NUM> of the greenhouse <NUM> can also comprise one or more conventional greenhouse vents (not shown) to allow excess air to be released from the greenhouse <NUM>. This is particularly useful when ambient air is being drawn into the greenhouse. The release of air through the vents releases excess air that can build up in the crop section <NUM>. These vents are generally known in the art and are not described herein. It is understood that these vents can also include screens to prevent insects from entering and the vents are preferably located at or near the greenhouse roof. In some embodiments, the vents can include fans to assist in the release of air, and it is understood that air can be released from the greenhouse using many different mechanisms beyond conventional vents.

In operation, when the air temperature within the crop section <NUM> rises it may be desirable to pull cooler air into the section <NUM>. This is referred to as the cooling mode and is illustrated by the first airflow <NUM> shown in <FIG>. The second louver <NUM> can be closed and the first louver <NUM> can be at least partially opened to allow air to pass through the first vent <NUM>. Fans <NUM> can be activated to pull greenhouse ambient air through the first vent <NUM> and in those embodiments where additional cooling of the air is desired, the cooling mechanism <NUM> can be activated to cool the air pulled through the vent <NUM>. The cooled air enters the gabled end <NUM> and is pulled into the tubes <NUM> by the fans <NUM>. The cooled air is then distributed evenly throughout the crop section <NUM> through the holes in the tubes <NUM>. The heat exchanger <NUM> can also contain a flow of water to further cool water entering the tubes <NUM>. As additional ambient air is pulled into the greenhouse, excess air can be released from the greenhouse through roof vents.

When the air within the greenhouse is at the desired temperature or needs to be increased, the greenhouse enters the recycle mode as shown by second airflow <NUM> is <FIG>. The first louver <NUM> can be closed and the second louver <NUM> opened. The fans <NUM> can then be activated to pull air from within the greenhouse section <NUM> into the gabled end <NUM>. The air is then pulled into the tubes <NUM> and the air is distributed throughout the greenhouse through holes in the tubes <NUM>. This circulation can continue as the temperature is maintained at its desired level. If the air needs to be heated, known heating systems can be employed within the greenhouse with one such system supplying heated water to rails or pipes in the greenhouse floor. Alternatively, heated water can be supplied to the heat exchanger <NUM> from the supply of heated water as described above. Air heated by this system can then be circulated until the desired temperature is achieved within the greenhouse <NUM>. Alternatively, the growing section can rely on the heat generated from sunlight passing into the growing section through the transparent roof or sidewalls.

As mentioned above, the system <NUM> can also be operated to supply a combination of air to the tubes <NUM> from a combination of airflows <NUM> and <NUM>. This can be accomplished by controlling the opening of the first and second louvers <NUM> and <NUM> while the fans <NUM> are operating. The fans <NUM>, first and second louvers <NUM>, <NUM> and the heat exchanger <NUM>, are preferably operated under computer control using various known sensors and hardware/software combinations.

The greenhouse <NUM> and its forced greenhouse climate control system <NUM> provide for improved and cost effective control of the greenhouse climate compared to conventional systems. It is particularly useful in desert climates where it is useful to provide cost effective systems for minimizing the maximum heat experienced by crops within a greenhouse. For example, one embodiment of the greenhouse <NUM> can reduce what would typically be <NUM> temperature in greenhouse to <NUM> without employing expensive cooling systems. This reduction in temperature can have a dramatic impact on the improved health and growth of crops within the greenhouse.

<FIG> show another embodiment of greenhouse <NUM> that is similar to the greenhouse <NUM> described above and shown in <FIG>. The greenhouse <NUM> also utilizing a forced greenhouse climate control system <NUM> according to the present invention. The greenhouse <NUM> has a gabled end <NUM> that is separated from the crop holding section <NUM> of the greenhouse <NUM> by partition <NUM>. The crop section <NUM> comprises an air distributing device to distribute air from the gabled end <NUM> throughout the crop section <NUM>. Many different distribution devices can be used, with a suitable device being a plurality of tubes <NUM> running the length of the crop section <NUM> similar to the tubes <NUM> in greenhouse <NUM>. As mentioned above, different numbers of tubes can be used with greenhouse <NUM> shown having ten (<NUM>) tubes <NUM> as best shown in <FIG>. Referring again to <FIG> and <FIG> the tubes <NUM> open through the partition <NUM> such that air from the gabled end <NUM> can flow into the tubes <NUM>.

Fans <NUM> can placed in or close to the partition <NUM> between. Each of the tubes <NUM> are connected to an opening in the partition lower portion of the partition <NUM>. A respective fan <NUM> is then arranged over each of the openings and air from each of the fans <NUM> flows into its respective one of the tubes <NUM>. The fans <NUM> are arranged with the ability to pull ambient air from in the gabled end <NUM> into the tubes during operation. This can either be ambient air or re-circulated air, or combination of the two.

The greenhouse <NUM> further comprises a vent/opening <NUM> ("vent") in the outside gable wall <NUM> through which ambient air can enter the gabled end <NUM>. The vent <NUM> is similar to the opening <NUM> in greenhouse <NUM> described above but is located near the center of the gabled wall <NUM>, as shown. The vent <NUM> preferably runs the length of the gabled wall and although one vent <NUM> is shown it is understood that more than one opening can be included.

A cooling mechanism <NUM> can also be included at the vent <NUM> to cool air being pulled in into the gabled end <NUM>, and/or to control the humidity within the air. In one embodiment the cooling mechanism <NUM> is a conventional pad cooling system that also runs the length of and is included over the vent <NUM>. A screen <NUM> can also be included over the vent <NUM> to prevent insects and other pests from entering the greenhouse <NUM>. A heat exchanger <NUM> can also be included at or near the fans <NUM> that is arranged and operates similar to the heat exchanger <NUM> shown in <FIG> and described above. The heat exchanger <NUM> can further heat or cool air entering the tubes <NUM> as described above.

A first louver <NUM> can be included inside of gable wall <NUM> that is movable in the directions of arrows <NUM> to control the amount of ambient air entering the end gable <NUM>. When operating in the mode to block air from entering the end gable <NUM> the louver <NUM> is closed to cover the vent <NUM>. When operating in the mode to allow air to enter the end gable <NUM>, the louver <NUM> can be swing open so that it is not blocking air from entering or can be partially opened such that it is partially blocking air from entering. As the louver <NUM> swings from its closed and fully blocking position over the first vent/opening <NUM> it also blocks re-circulating air that would otherwise be pulled into the tubes <NUM> by the fans <NUM>. The greenhouse further comprises a shelf <NUM> on the inside surface of the partition <NUM>. When the louver <NUM> is fully opened its lower surface abuts the shelf <NUM> to fully block re-circulating air from being drawn by the fans <NUM>. Instead, in this position the fans <NUM> draw primarily ambient air that can be cooled by cooling mechanism <NUM>. It is understood that many different mechanisms can be used beyond the first louver <NUM> described above.

The partition <NUM> comprises a second vent/opening <NUM> that is located near the top of the partition <NUM>, although the vent <NUM> can be in many different locations. Unlike the vent <NUM> described above in greenhouse <NUM>, the vent <NUM> does not have a second louver and remains open through operation. The amount of air from the crop section <NUM> drawn through by the fans and re-circulated into the tubes is controlled by the extent to which the louver <NUM> is opened. If the louver <NUM> is fully closed all of the air drawn through the fans <NUM> comes through vent <NUM> for re-circulating. When the louver <NUM> is fully open no air through the vent is drawn by the fans. When the louver is at different positions between fully open and closed, the fans draw a combination of ambient and air through the vent <NUM>.

The crop section <NUM> can also comprise one or more conventional greenhouse vents (not shown) to allow excess air to be released from the greenhouse <NUM>. These vents are generally known in the art and are not described herein. The greenhouse vents are preferably located at or near the greenhouse roof and can include fans to assist in the release of air. It is understood that air can be released from the greenhouse using many different mechanisms beyond conventional vents.

The greenhouse <NUM> operates similar to the greenhouse <NUM>. In operation, when the air temperature within the crop section <NUM> rises it may be desirable to pull cooler air into the section <NUM>. This is referred to as the cooling mode and is illustrated by the first airflow <NUM> shown in <FIG>. The louver <NUM> can be at least partially opened to allow ambient air to pass through the first vent <NUM>. Fans <NUM> can be activated to pull ambient air through the vent <NUM> and in those embodiments where additional cooling of the air is desired, the cooling mechanism <NUM> can be activated to cool the air pulled through the vent <NUM>. The cooled air enters the gabled end <NUM> and is pulled into the tubes <NUM> by the fans <NUM>. The cooled air can be further cooled by heat exchanger <NUM> and the cooled air is then distributed evenly throughout the crop section <NUM> through the holes in the tubes <NUM>. As additional ambient air is pulled into the greenhouse, excess air can be released from the greenhouse through roof vents.

When the air within the greenhouse is at the desired temperature the greenhouse enters the recycle mode as shown by second airflow <NUM> in <FIG>. The first louver <NUM> can be closed and the fans <NUM> can then be activated to pull air from within the greenhouse section <NUM> into the gabled end <NUM> through the second vent <NUM>. This circulation can continue as the temperature is maintained at its desired level. If the air needs to be heated, known heating systems can be employed within the greenhouse with one such system supplying heated water to rails in the greenhouse floor as described above. Alternatively, warm water can be supplied to the heat exchanger <NUM> from the separate heated water supply as described above with reference to heat exchanger <NUM>. As ambient or recycled air passes through the fans <NUM> it is heated and passed into tubes <NUM>. As the heated air exits the tubes it heats the air within the crop section. Air heated by this system can then be circulated until the desired temperature is achieved within the greenhouse <NUM>.

As mentioned above, the system <NUM> can also be operated to supply a combination of air to the tubes <NUM> from a combination of airflows <NUM> and <NUM>. This can be accomplished by controlling the opening of the louver <NUM> while the fans <NUM> are operating. Like the embodiment above, the fans <NUM>, louver <NUM>, heat exchanger <NUM> are preferably operated under computer control using various known sensors and hardware/software combinations.

It is understood that there are many additional advantages and alternative arrangements provided by the present invention. One advantage is that the crop section <NUM> can be over-pressurized by the system <NUM>, which can prevent undesired insects. The invention further provides for enhanced crop yields by allowing for greater levels of radiation to reach the plants by eliminating conventional roof vent superstructures and accompanying insect netting. The crop section <NUM> can also be arranged so that a gas, such as CO<NUM> can be fed into and more efficiently maintained within the section <NUM>. The gas feed systems are known in the art and not discussed in detail herein. These gasses can further enhance the health and growth of the crop within section <NUM>.

In alternative embodiments, the fans <NUM> can be controlled and operated as variable drive fans to provide additional control over airflow. The vents can be different sizes and more vents can be included in many different locations.

In still other embodiments, the greenhouse can be arranged without a gabled end. For example, the first louver can be arranged over the fans with the cooling mechanism located at the fans such that ambient air can be pulled directly into the tubes with the air passing the cooling mechanism for additional cooling. Pipes can be included and arranged to provide an air passageway between the second vent and the fans during the mode when air from within the crop section is to be recycled. This is only one of the many alternative arrangements for greenhouses and forced greenhouse climate control systems according to present invention.

As discussed above, one air distribution according to the present invention can comprise tubes running the length of the crop section of the greenhouse. It is understood, however, that the present invention can also comprise any other mechanism that can distribute air in a controlled fashion, including but not limited to different types of conduits. As mentioned above, in greenhouse <NUM> different numbers of tubes <NUM> and different numbers and sizes of holes can be included along the length of the tubes to provide even distribution. <FIG> show one embodiment of an air distribution tube <NUM> according to the present invention comprising an outer tube <NUM> and an inner tube <NUM>. The inner and outer tubes <NUM>, <NUM> can be made of many different materials such as known polymer materials.

Outer tube holes <NUM> are provided in the outer tube <NUM>, and inner tube holes <NUM> are included in the inner tube <NUM>. By changing the pattern of the outer tube holes <NUM>, the inner tube holes <NUM>, or both, different amounts of air are allowed to pass out of the tube <NUM> at different locations along the tube <NUM>. In different embodiments the pattern of holes can vary in different ways along the length of the tube <NUM> to compensate for pressure variations, with the appropriate pattern can be determined during design of the air distribution system and greenhouse arrangement.

In one embodiment according to the present invention, the first outer tube section <NUM> can have holes 110a that are further apart compared to other tube sections, with section <NUM> corresponding to a tube section with higher pressure passing through it. By having holes further apart, less air passes from the tube in section <NUM>, allowing for a more equal distribution of air along all the sections of the tube. The holes can be changed in other ways to compensate for different pressures along the tube. The second outer tube section <NUM> can also have second tube holes 112a that are larger than the holes in other sections. Second tube section <NUM> can correspond to a tube section with lower pressure, with the larger holes allowing more air out in those sections, to equalize the air exiting along the outer tube <NUM>. Different size and spacing arrangements can be provided along the length of the tube, and although the holes are shown in outer tube <NUM> as being in straight line, it is understood that the holes can be provided in many different arrangements such as staggered, wavy, zigzag, random, etc. The changes in the hole size and arrangement are shown in outer tube <NUM>, but it is understood that the holes can also be varied in the inner tube <NUM>, or in both the outer tube <NUM> and inner tube <NUM>.

For tube <NUM>, the inner tube <NUM> can have a smaller diameter than the outer tube <NUM>, at least along some sections of the tube. In the embodiment shown the outer tube <NUM> has a diameter that varies slightly along its length between a diameter that is the same as the inner tube <NUM> and a diameter that is slightly larger than the inner tube <NUM>. In some embodiments where the inner tube <NUM> and outer tube <NUM> have the same diameter, the two can be bonded together, although in other embodiments the two may not bonded together. In still other embodiments the inner tube <NUM> can have a diameter that varies within the other tube to form the compartments. In all these embodiments, compartments <NUM> are formed between the inner tube <NUM> and the outer tube <NUM>, and in the embodiment shown, multiple compartments <NUM> are formed along the length of the tube <NUM>. It is understood, however, that other embodiments can have larger or smaller compartments and can also be arranged with a single compartment along the length of the tube <NUM>, between the inner tube <NUM> and outer tube <NUM>.

The compartments <NUM> encourage air exiting the tube <NUM> without being influenced by the direction of the main air flow or turbulence within the tube <NUM>. As best shown in <FIG>, the main air flow from the inner tube <NUM> passes through the inner tube holes <NUM> into the compartments <NUM>. The inner tube holes <NUM> are offset from the outer tube holes <NUM> such that much of the turbulence or directional nature of the air flow is dissipated in the compartments <NUM> before exiting from the tube <NUM> through outer tube holes <NUM>. This allows the air to exit the tube in a direction that is substantially perpendicular to the tube <NUM>. This allows for controlled dissipation of air from the tube <NUM> so that it enters the greenhouse at the desired location.

In some applications it may also be desirable to reduce the effects of the temperature difference between the man air flow within the tube <NUM> and the temperature of the air within the greenhouse. The compartments <NUM> along with the offset of the outer holes <NUM> and inner holes <NUM> and compartments <NUM>, provides for a double walled buffer zone that acts as an insulating barrier between the main air flow and the greenhouse. This arrangement of compartments <NUM> concentrates heat loss in air flow within the double walled buffer zone before the air is blown into the greenhouse environment. This helps equalize the temperature of the air entering the greenhouse from the tube <NUM>, even with a substantial difference in temperature between the main air flow and the greenhouse.

The inner and outer tube arrangement of tube <NUM> also provides the advantage of having no barriers or restrictions in the inner tube <NUM> to equalize pressure along the tube <NUM>. This results in an air distribution system that can consumes less energy in distributing air compared to systems having tubes with restrictions.

<FIG> show another embodiment of an air distribution tube <NUM> according to the present invention, also having an outer tube <NUM> and an inner tube <NUM> that can be arranged similar to those in tube <NUM> described above. The tube also comprises outer tube holes <NUM> and inner tube holes <NUM> that can have varying distances between adjacent holes and can have different sizes as discussed above to compensate for different air pressures and turbulence within the main air flow of the tube <NUM>. The tube <NUM> can also have compartments <NUM> that also allow air to exit the tube <NUM> without being influenced by the direction of the main air flow within the tube <NUM>. The compartment can also be arranged to reduce the effects of the temperature difference between the man air flow within the tube <NUM> and the temperature of the air within the greenhouse as described above.

Claim 1:
A greenhouse (<NUM>; <NUM>) comprising:
a growing section (<NUM>; <NUM>) with an air or gas distribution system within said growing section;
the distribution system comprising one or more conduits (<NUM>; <NUM>) for distributing air or gas within the greenhouse with the one or more conduits carrying air or gas having different pressures along the length of the one or more conduits, the one or more conduits being arranged to provide substantially equal distribution of air or gas throughout the growing section;
the one or more conduits comprising one or more air distribution tubes (<NUM>; <NUM>) each comprising an outer tube (<NUM>; <NUM>) and an inner tube (<NUM>; <NUM>);
outer tube holes (<NUM>; <NUM>) are provided in the outer tube and inner tube holes (<NUM>; <NUM>) are included in the inner tube;
the pattern of the outer tube holes (<NUM>; <NUM>) changing so that different amounts of air are allowed to pass out of the outer tube (<NUM>; <NUM>) at different locations along the outer tube (<NUM>; <NUM>), the pattern of holes varying along the length of the outer tube (<NUM>; <NUM>) to compensate for pressure variations;
one or more compartments (<NUM>; <NUM>) being formed between the inner tube and the outer tube;
a main air flow from the inner tube can pass through the inner tube holes into the one or more compartments;
the inner tube holes are offset from the outer tube holes such that much of the turbulence or directional nature of the air flow is dissipated in the one or more compartments before exiting from the air distribution tube through the outer tube holes.