Air distribution system for an insect housing module

Abstract

An air processing and distribution system for use in insect farming inside a chamber which may be a transportable container unit. There is a primary duct unit 10 with a first air flow channel 12 suppl

Description

FIELD OF THE INVENTION The present invention relates to the field of insect farming, and in particular to climate control for insect farming. BACKGROUND OF THE INVENTION Black soldier fly farming is a form of insect farming, focusing on the cultivation of black soldier flies and their larvae. The main objective is to utilize these insects in sustainable waste management and the production of animal feed. The inputs to black soldier fly farming are: black soldier fly larvae, and organic waste for the larvae to feed on. This may range from kitchen waste such as vegetables, fruits, coffee grounds, and so on, to agricultural waste, such as crop residues, or even manure. BSF larvae can consume almost any type of organic matter. The outputs of BSF farming include at least: biofertilizer and sustainable animal feed. In particular, the residual waste from BSF larvae, also known as frass, is a nutrient-rich organic material that can be used as a biofertilizer. Further to this, the larvae themselves, once matured, are an excellent source of protein and fats. They can be used as a sustainable, cost-effective feed for poultry, fish, and other livestock. A further benefit of BSF farming is efficient waste management. The BSF larvae provide a means for disposing of organic waste and in a way that is convenient, environmentally sound, and which yields a useful agricultural output as byproduct. As will be apparent, there are numerous environmental benefits to BSF farming. A first environmental benefit is waste reduction. BSF larvae can consume significant amounts of organic waste, thereby reducing the overall waste that ends up in landfill or other disposal sites. This, in turn, can help decrease greenhouse gas emissions. A further environmental benefit is the provision of a sustainable protein source. By providing a sustainable source of protein for animal feed, BSF farming can reduce the environmental impact of other protein sources, such as soy or fishmeal, which often involve deforestation and overfishing. A further environmental benefit is soil improvement. The frass produced by BSF larvae is a high-quality compost that can enhance soil health and productivity, reducing the need for chemical fertilizers. A further environmental benefit is reduction of methane emissions. Organic waste, especially food waste, produces methane—a potent greenhouse gas—when it decomposes in landfills. By consuming this waste, BSF larvae help reduce methane production. A further environmental benefit is conservation of resources. Traditional livestock feed sources such as soy and fishmeal require large amounts of water, land, and other resources. BSF farming, however, requires comparatively fewer resources, making it a more sustainable option. The conventional approach to insect farming is to farm insects at large scale inside at one or more central locations, and wherein the outputs of the farming (fertilizer and animal feed) may then be distributed to customers. Of growing interest in the field is the concept of modular insect farming. In modular farming, the farming process is done instead at small scale, on-site at individual locations. Of particular interest is enabling localized insect rearing on site at livestock or arable farms. This would provide farmers a way to dispose of organic waste while at the same time yielding a source of fertilizer for crop growth and / or animal feed for livestock. The modular approach enables small and medium scale farmers to upcycle waste and produce a sustainable source of feed for their farm with an organic fertilizer as a by-product. SUMMARY OF THE INVENTION The invention is defined by the claims. It is the recognition of the applicant that there would be benefit in providing a fully modular insect farming solution. As one part of this solution, the applicant proposes a modular insect housing chamber / unit for housing insects during one or more phases of their life cycle, for example during rearing of the insects. A challenge in providing a fully self-contained modular insect housing unit is facilitating efficient and reliable air distribution and conditioning within the unit in a way that will optimize air conditions for insect growth within the tight constraints of a small internal volume of the unit, and ideally tight packing of insect carrying trays / containers. This balance of space constraints with air distribution optimization is a challenging problem. The inventor has devised an air distribution and conditioning system incorporating a number of technical developments which help address this problem. According to examples in accordance with an aspect of the invention, there is provided an air distribution and / or conditioning system for an insect housing chamber defined by an interior of a walled unit or box, such as a transportable container unit. The transportable container unit may for example be a shipping container. The system comprises a primary duct unit for location inside the chamber, and for extending along at least a portion of (e.g. a length of) the chamber. The primary duct unit comprises at least a first air flow channel, wherein the first airflow channel comprises a plurality of air inflow vents distributed along a length of the channel for drawing air in from an interior of the chamber / container. The system further comprises an air processing unit having an inlet and outlet, and adapted to process air received at the inlet. The air processing unit may process received air to modify at least one characteristic of the air, for example temperature. The air processing unit may be an air conditioning unit. The system further comprises a controllable air extraction unit having an inlet and outlet, the air extraction unit for extracting air received at the inlet to outside of the chamber / container via the outlet, preferably at a controllable (flow) rate. The first air flow channel is fluidly connected to both the inlet of the air processing unit and the inlet of the air extraction unit. It provides a fluid feed for both the air processing unit and the air extraction unit. Thus, at least one aspect of the invention relates to air distribution in the context of insect farming, and with particular advantage in containerized insect farming. In such systems, effective air flow and space efficiency are two major challenges in view of the small internal volume of the container and the need to tightly stack larvae trays within the container. The present invention relates to an air distribution system aimed at optimizing space efficiency and air flow. As outlined above, the proposed air distribution and / or conditioning system is configured so that a single air flow channel is connected fluidly to both the air processing unit, for processing and returning air to the chamber, and the air extraction unit, for extracting air from the chamber. In other words, there is provided a shared duct for extract and return air. This is an unorthodox configuration for an HVAC system, where it is standard practice to provide separate ducts for carrying the return air to the air conditioning unit and the extract air to the extract fan. This orthodox configuration provides greater control over air distribution and improves homogeneity of air processing and air extraction across the chamber. However, it is the realization of the inventor that significant space saving can be gained by combining the extract and return flows into a single duct channel. This runs contrary to the prevailing assumption in the art that separate return and extract ducts are essential. However, it has been found in testing that, due in part to the relatively small internal volume of the insect housing chamber, there is in fact relatively little adverse effect on homogeneity of air extraction and processing when this adaptation is made. Indeed, it has been the realization of the inventor that providing a single set of inflow grilles for both return and extract can provide a positive benefit to air flow patterns. In particular, when used in practice, all air leaving the space can be drawn along a single vertical air flow path, or a single pair of such paths, rather than a multiplicity of split air flow paths. This allows for establishing a stable cyclical air current which can, for example, be drawn around the side edges of a set of larvae tray stacks loaded in the chamber. Stable air flow patterns are important in the context of insect farming. The air processing unit may be an air conditioning unit. The air processing unit may be controlled in dependence upon a temperature inside the chamber, as measured by one or more temperature sensors for disposal inside the chamber. The air extraction unit may be controlled at least in part in dependence upon a CO2 concentration of air inside the chamber, as measured by one or more CO2 sensors for disposal inside the chamber. The first air flow channel of the primary duct unit may be otherwise closed / sealed. The first airflow channel of the primary duct unit may provide the sole air feed / supply to each of the air processing unit and the air extraction unit. The chamber has a length, width and height, and the primary duct unit may be structured and arranged such that the plurality of air inflow vents of the primary duct unit are disposed at a plurality of different length and / or width positions, and optionally all may be disposed at a same height position. The primary duct unit and the first air flow channel may extend linearly along at least a portion of a length and / or width of the chamber The primary duct unit may be suspended from or coupled to a ceiling of the chamber / container. The primary duct unit may be disposed centrally with respect to a width of the chamber. The primary duct unit may be for extending from a first location on the ceiling to a second location on the ceiling. It may be for extending from a location proximal to one end of the container to a further location proximal to the opposite end of the container. In some embodiments, the system further comprises a controller, operatively coupled to the air processing unit and the air extraction unit, for example for controlling an air condition inside the chamber. In some embodiments, the plurality of air inflow vents are distributed along a section of the first air flow channel extending between the air processing unit and the air extraction unit. In other words, they may be disposed between a fluid connection of the first air flow channel to the air processing unit and a fluid connection of the first air flow channel to the air extraction unit. In some embodiments, the first air flow channel has a first and second end, and wherein the first end of the first air flow channel is fluidly connected to the inlet of the air processing unit and the second end of the first air flow channel is fluidly connected to the inlet of the air extraction unit. This provides a space efficient arrangement. The air extraction unit is preferably controllable to provide a variable rate of air extraction. A rate of air extraction means a flow rate of air extracted from inside the chamber to outside the chamber. In some embodiments, the air extraction unit comprises a controllable air flow driver (e.g. a fan) disposed between the inlet and outlet of the extraction unit for drawing a flow of air toward the outlet at a controllable flow rate. The controller may be adapted to control the air extraction rate of the air extraction unit, e.g. by adjusting a power level. The air processing unit may also have an air driving function, and, when active, draws air in through the inlet. The through-flow rate of the air processing unit may be operated at a fixed level, or may be controllable. In some embodiments, the system further comprises a first non-retum damper, disposed at a fluid connection or interface between the first air flow channel and the air processing unit, for impeding air passage from the first air flow channel to the inlet of the air processing unit when the air processing unit is inactive. For example, it may be disposed at a first end of the first air flow channel. In some embodiments, the system comprises a second non-retum damper, disposed at a fluid connection or interface between the first air flow channel and the air extraction unit, for impeding air passage from the first air flow channel to the inlet of the air extraction unit when the air extraction unit is inactive. For example, it may be disposed at a second end of the first air flow channel. The function of the non-retum dampers is to close off or intermpt an air path or air flow route from the first air flow channel to the extraction unit or the air processing unit when these components are switched off. The non-retum dampers may be gravity driven, such that their open / close state is determined according to whether the component to which they are adjacent is on or off. In some embodiments, the primary duct unit further comprises a second air flow channel, for example running in parallel with and fluidly separated / isolated from the first air flow channel. In some embodiments, the second airflow channel comprised a plurality of air outflow vents distributed along a length of the channel. In some embodiments, the second airflow channel is fluidly connected to the outlet of the air processing unit. Thus, a same primary air duct structure carries both the return air to the air processing unit and the processed air from the air processing unit. This is spatially and functionally efficient. The second air flow may extend spatially parallel with the first air flow channel. The air flow direction in the first air flow channel may be opposite to that in the second air flow channel. The first air flow channel may be defined by the lumen of a first duct portion of the primary duct unit and the second air flow channel defined by the lumen of a second duct portion of the primary duct unit, and wherein the first and second duct portions are physically coupled to one another, for example adjacent one another, for example contiguously adjacent to one another, for example touching one another. The two may be formed by separate channels in a unitary duct structure, for example fluidly separated by a barrier element. In some embodiments, the first air flow channel is stacked above the second air flow channel or vice versa. This is a space efficient arrangement. Preferably, it is the first air flow channel which is stacked about the second air flow channel. By having the conditioned air flow channel below the retum / extract flow channel, the processed air can fall freely down into the chamber without being drawn into the air inflow vents. In some embodiments, the air outflow vents of the second airflow channel are arranged for facing toward a floor of the chamber and the air inflow vents of the first airflow channel are arranged for facing sides of the chamber, or vice versa. This helps to avoid interference of the two flows, i.e. avoids the conditioned air being drawn up directly into the return duct. In some embodiments, the primary duct unit is for mounting to a ceiling of the container unit. In this way, it is disposed suspended above the insect containers, e.g. larvae trays, when these are loaded in the chamber. In some embodiments, the system further comprises an air supply sub-system, for supplying fresh air from outside of the chamber to an interior of the chamber. In some embodiments, the air supply subsystem is fluidically independent / separate from the primary duct unit, the air processing unit and the air extraction unit. In this way, fresh air supply can be controlled fully independently from conditioned air supply and air extraction. This adds an extra degree of freedom to the climate regulation. In some embodiments, the air supply subsystem comprises one or more secondary duct units, each comprising at least one air flow channel for extending along at least a portion of a length of the container and having a plurality of air outflow vents distributed along the length of the channel for venting air into an interior of the container. Each of the one or more secondary duct units may be for connection to a fresh air inlet of the container for receiving air from an environment outside of the container. The air supply sub-system may further comprise one or more controllable air flow drivers being arranged for drawing air into the one or more secondary duct units from a fresh air inlet at a controllable flow rate. In some embodiments, each of the one or more secondary duct units is spaced from the primary duct unit. In some embodiments, each of the one or more secondary duct units is spaced from the primary duct unit along a width dimension of the chamber / container, the width dimension being perpendicular to the length dimension of the chamber / container. In some embodiments, a proximal end of each of the one or more secondary duct units is for connection to a fresh air inlet of the container for drawing in air from an environment outside of the container. The one or more secondary duct units preferably extend spatially parallel with the primary duct unit, and particularly the second flow channel of the primary duct unit. Both the primary duct unit and each of the one or more secondary duct units are preferably suspended from, or coupled to, the ceiling, so that the airflow vents are all suspended above the insect containers when the containers are loaded into the chamber. The air outflow vents of each secondary duct unit may be arranged in a linear pattern. The air outflow vents of the primary duct unit may also be arranged in a linear pattern. The air inflow vents of the primary duct unit may also be arranged in one or more linear patterns. All of these linear patterns may extend spatially parallel to one another. The linear pattern of air inflow vents of the primary duct unit may be arranged, relative to a width of the chamber, in-between the linear pattern of outflow vents of at least one of the one or more secondary duct units and the linear pattern of outflow vents of the primary duct unit. This optimizes air mixing. In some embodiments, the air supply subsystem comprises at least two secondary duct units, arranged either side of the primary duct unit across a width of the container. Each may extend along a length of the container. Each may extend spatially parallel with an extension of the primary duct unit. The primary duct unit may extend along the chamber at a central width position, and the two secondary duct units may extend along a length of the chamber adjacent opposite side edges of the chamber. The air extraction unit may be arranged having an air flow direction which is nonparallel with, e.g. perpendicular to, an air flow direction of the first air flow channel of the primary duct unit, and arranged in the chamber offset with respect to the first air flow channel along the width direction and wherein the primary duct unit includes a comer section to fluidly connect the first air flow channel to the air extraction unit. The air extraction unit may for example be arranged to output air to an outside of the chamber through an outflow vent formed through a side wall of the chamber. By orienting the air extraction unit perpendicular to the primary duct unit, and offsetting it laterally relative to the primary duct unit, this allows the length of the primary duct to be maximized. This also allows for fitting the extract unit at an end of the container carrying the doors without the extract vent needing to be formed through the doors. In some embodiments, at least one secondary duct unit extends spatially parallel to the primary duct unit from a first end of the chamber to a terminal point spaced from a second end of the chamber by a clearance space, and wherein at least a section of the air extraction unit is disposed in said clearance space. This is space efficient. In some embodiments, the one or more fresh air inlets are each disposed at an opposite end of the container to the extraction unit outlet. According to an advantageous set of embodiments, the air extraction unit and the air supply subsystem are configured such that a maximum flow rate of fresh air into the chamber achievable by the air supply subsystem is greater than a maximum extraction rate of air from the chamber achievable by the air extraction unit, and preferably wherein the maximum air inflow rate of the air supply subsystem is at least 50% greater, more preferably at least 100% greater, than the maximum air outflow rate of the air extraction unit. In other words, the maximum fresh air supply capacity is greater than the maximum air extraction capacity, e.g. 50% greater, e.g. 100% greater (i.e. double). In some embodiments, as explained above, this may be achieved by providing an air supply subsystem with two or more ducts (e.g. at least two secondary duct units mentioned previously), each being fluidly supplied by a respective air inflow vent and air flow driver, while providing only a single air extraction duct (e.g. the first air flow channel of the primary duct unit mentioned above), coupled to a single air extraction unit (e.g. having a single air flow driver, e.g. fan) extracting air through a single outflow vent of the chamber. In some embodiments, the system includes a controller, operatively coupled to the air supply subsystem and the air extraction unit, and wherein, in at least a first control mode, the controller is adapted to control the air supply subsystem and the air extraction unit in co-ordination such that a flow rate of fresh air into the chamber provided by the air supply subsystem exceeds a flow rate of air extracted from the chamber by the air extraction unit. Due to the tight packing of trays within the container during operation, maintaining continuous air flow is a challenge. It is the realization of the inventor that this can be partially addressed by drawing in air to the container at a greater rate than it is extracted, thereby effectively establishing a positive air pressure inside the container. This helps overcome the problem of the trays impeding air flow and helps to promote air mixing and air distribution. Furthermore, under some conditions, it may be preferable for reasons of climate conditioning inside the chamber to draw in large volumes of fresh outside air. Due to space constraints inside the chamber, the air extraction unit may have a maximum air extraction rate which is less than the maximum possible air inflow rate of the air supply subsystem. For example, as explained above, in preferred embodiments, to save space and to optimize air flows, a single duct (the first air flow channel of the primary duct unit) is provided for extract and return air. This limits the total extract rate at any given time. To overcome the limitations imposed by this, providing extra fresh air inflow capacity means that a high rate of air changes can still be achieved despite limited extract capacity. In some embodiments, the container comprises one or more pressure relief dampers permitting outflow of air from the interior of the container to outside the container, for example responsive to an air pressure inside the container exceeding a threshold. This may advantageously complement the feature outlined above, wherein fresh air is drawn in at a greater rate than air is extracted by the extract unit. In such circumstances, the excess air inside the chamber can be vented via the pressure relief dampers. Thus, in effect, the more limited air extraction capacity available due to the shared primary duct unit is counterbalanced by the extra (driven) fresh air inflow capacity in combination with pressure relief dampers which act as a passive supplement to the driven air extraction of the air extraction unit. The pressure relief dampers may prevent air flow from outside the container to inside. The pressure relief dampers may be closed in absence of pressure applied on them by air. These would not typically be needed in conventional HVAC systems as there is generally always somewhere for air to escape unless it is a strictly controlled environment. It is proposed according to this embodiment to draw in more air in than is extracted, and thus pressure relief vents are provided to allow for the over-air to escape. In some embodiments, the controller may be configurable in at least a further control mode in which the controller is adapted to control the air extraction unit and the air supply subsystem in co-ordination such that a flow rate of air extracted from the chamber (volume / time) by the air extraction unit exceeds a flow rate of fresh air provided into the chamber by the air supply subsystem. In some embodiments, the flow rate of fresh air provided into the chamber may be set to zero. The above further control option might be implemented for example in cases where low power consumption is required, for example where there is an interruption in the power supply or power availability is low. For example, in some instances, mains supply power might fail, and the system may operate using a backup power supply system. In this event, power may be prioritized to the air extraction unit, leaving the air supply subsystem deactivated. The remainder of the air supply may be provided passively through the non-retum dampers. The container may comprise one or more non-retum dampers permitting inflow of air from outside the container to inside the container, for example responsive to a pressure inside the container falling below a threshold. This may help balance air pressure for example in the case outlined above wherein more air is being extracted than drawn into the chamber. In an advantageous set of embodiments, the air outflow vents of the primary duct unit may be positioned at intervals along a length of the container unit, and the air outflow vents of at least one of the one or more the secondary duct units may be positioned at intervals along the length of the container, and wherein the positions of the air outflow vents of the primary duct unit are interspaced with those of at least one of the one or more the secondary duct units along the length dimension of the chamber. In other words, positions of the air outflow vents of the primary duct unit alternate with those of the secondary duct unit along the length dimension of the container. The positions of the fresh air outlets are thus arranged in-between, or interleaved with, the positions of the conditioned air outlets. For example, a periodic spacing of the air outflow vents of the primary duct unit is offset with respect to a periodic spacing of the air outflow vents of the secondary duct unit along the length dimension of the container. As will become clearer with reference to the drawings, this can provide an efficient air mixing arrangement. In particular, it advantageously allows for positioning insect container stacks beneath the ducts in such a way that each container stack is supplied on one side by a fresh air flow from the secondary duct vents and on the other side by a conditioned air flow from the primary duct vents. In some embodiments, in at least one control mode, the controller is adapted to control the air supply subsystem in co-ordination with the air extraction unit such that the air within the chamber is fully replaced at a rate of at least 15 air changes per hour. In some embodiments, the air extraction unit and / or the air supply sub-system are each configured to drive air out and / or in to the chamber at a flow rate of at least 300 liters per second, for example at least 350 liters per second, for example 375 liters per second. In some embodiments, the system further comprises a plurality of insect container stacks, each stack comprising a plurality of containers stacked vertically atop one another, the container stacks for being supported by a floor of the container. The insect containers may be larvae containers, for example larvae trays. The insect containers may be for holding black soldier fly, for example for holding black solider fly larvae. The container may include visual alignment markings or physical locating / alignment members to denote target positionings of containers. In some embodiments, an interval spacing between the outflow vents of the primary duct unit and / or an interval spacing between the outflow vents of at least one of the one or more secondary duct units is greater than or equal to a width of a single insect container stack. In some embodiments, a spacing (separation), along the length of the container, between each air outflow vent of the primary duct unit and a next neighboring (along the length of the container) air outflow vent of at least one of the secondary duct units may be greater than or equal to the width of a single insect container stack intended for use. This allows each insect container stack to be positioned, length-wise, between one fresh airvent and one conditioned air vent. In some embodiments, each insect container stack is aligned along the length dimension of the container with a point disposed in-between a primary duct outflow vent and a secondary duct outflow vent. This way, one side of each stack is aligned, lengthwise, with a downflowing air supply from the fresh air duct and one side of each stack is aligned, lengthwise, with a downflowing air supply from the conditioned air supply. In some embodiments, the system comprises a controller, operably coupled to at least the air processing unit and the air extraction unit, for controlling an air condition in the module. In some embodiments, the system further comprises a set of air sensors for sensing one or more characteristics of an air inside the chamber. The controller may be configured to regulate an air condition inside the chamber based on control of at least an air extraction rate of the air extraction unit and control of the air conditioning unit, and based on input signals received from the one or more sensors. The sensors may include one or more CO2 sensors, one or more temperature sensors, and / or one or more humidity sensors. In some embodiments, the system may further comprise one or more temperature sensors for disposal within one or more of the insect containers for measuring a temperature of organic matter in the containers, and wherein the controller is communicatively coupled with the one or more temperature sensors. In some embodiments, the controller is configured to regulate an air condition inside the chamber based in addition on control of a flow rate of fresh air supplied into the chamber by of the air supply sub-system. In some embodiments, the system comprises a set of outdoor air sensors for sensing one or more characteristics of an air outside the chamber, and wherein the regulation of the air condition is performed further dependent upon input signals from the set of outdoor air sensors. In some embodiments, the controller is configured to determine a target internal temperature for air inside the chamber, obtain a measurement of a temperature of an environment outside of the chamber, compare the target internal temperature with the measurement of the temperature outside of the chamber to determine a difference between the two temperatures, and set an air inflow rate of the air supply subsystem in dependence upon a result of said comparison, wherein the air inflow rate of the air supply subsystem is set at a greater level where the difference between the temperatures is less, and is set at a lower level where the difference between the temperatures is greater. In other words, the air inflow rate of the air supply subsystem is increased as a function of increasing similarity (decreasing difference) between the outside temperature and the target inside temperature of the chamber. This is energy efficient since it minimizes use of the air processing unit (air conditioning unit) to configure the temperature inside the chamber. Where air outside the chamber is close to the target temperature inside the chamber, the outside air can be used to condition the temperature inside the chamber, in preference to use of the (energy expensive) air processing unit. Another aspect of the invention is a kit of parts, comprising: a transportable container unit; and the air distribution system in accordance with any example or embodiment outlined in this document or in accordance with any claim of the application, in an unassembled or partially assembled state, for installation in the container unit. The transportable container unit is for example a shipping container. In some embodiments, the transportable container unit is a high cube shipping container. Another aspect of the invention is an insect housing module, comprising: a transportable container unit, an interior thereof defining an insect housing chamber; and an air distribution system in accordance with any example or embodiment outlined in this document or in accordance with any claim of the application assembled within the insect housing chamber. The transportable container unit is for example a shipping container. In some embodiments, the transportable container unit is a high cube shipping container. The container unit may have at least one extract outlet for expelling air to an environment outside the container. The outlet of the air extraction unit may be fluidly connected to the extract outlet of the container. A ceiling of the container unit has a length and a width, and the primary duct unit may extend along at least a portion of the length of the container unit ceiling. Another aspect of the invention is the use of an air distribution system in accordance with any embodiment disclosed herein or any claim of the application for insect farming purposes, for example for black soldier fly (BSF) farming purposes. Another aspect of the invention is the use of an air distribution system in accordance with any embodiment disclosed herein or any claim of the application, installed within a walled unit defining an interior chamber, for example a transportable container unit. Another aspect of the invention is a method, comprising assembling an air distribution system in accordance with any embodiment disclosed herein or any claim of the application within a walled unit defining an interior chamber, for example within a transportable container unit. An independent aspect of the invention is an air distribution system for an insect housing chamber defined by an interior of a transportable container unit, comprising: a controllable air supply sub-system for drawing in fresh air from an environment outside of the container and venting the air into an interior of the container at a controllable rate; a controllable air extraction unit for extracting air from inside the container to outside the container at a controllable rate; and a controller operatively coupled to the air supply subsystem and the air extraction unit. In some embodiments, a maximum air inflow rate of fresh air into the chamber achievable by the air supply subsystem is greater than a maximum air outflow rate achievable by the air extraction unit, and preferably wherein the maximum air inflow rate of the air supply subsystem is at least 50% greater, more preferably at least 100% greater, than the maximum air outflow rate of the air extraction unit. Additionally or alternatively, in some embodiments, in at least a first control mode, the controller is adapted to control the air supply subsystem and the air extraction unit in coordination such that a flow rate of fresh air supplied into the chamber by the air supply subsystem exceeds a flow rate of air extracted from the chamber by the air extraction unit. This aspect of the invention independently provides a technical benefit in effectively providing a novel degree of freedom in the air distribution system which can allow for accelerating a required change in a condition of the air in a way that is not possible using the standard components of the system in their normal state. Due to the tight packing of trays within the container during operation, maintaining continuous air flow is a challenge. It is the realization of the inventor that this can be partially addressed by drawing in air to the container at a greater rate than it is extracted, thereby effectively establishing a positive air pressure inside the container. This helps overcome the problem of the trays impeding air flow and helps to promote air mixing and air distribution. In addition, under some conditions, it may be preferable for reasons of climate conditioning inside the chamber to draw in large volumes of fresh outside air. Due to space constraints inside the chamber, the air extraction unit may have a maximum air extraction rate which is less than the maximum possible air inflow rate of the air supply subsystem. For example, as explained above, in preferred embodiments, to save space and to optimize air flows, a single duct (the first air flow channel of the primary duct unit) is provided for extract and return air. This limits the total extract rate at any given time. To overcome the limitations imposed by this, providing extra fresh air inflow capacity means that a high rate of air changes can still be achieved despite limited extract capacity. In some embodiments, the system includes a container unit within which the system is to be assembled, and wherein the container unit comprises one or more pressure relief dampers permitting outflow of air from the interior of the container to outside the container, for example responsive to an air pressure inside the container exceeding a threshold. It is noted and it will be appreciated that this aspect of the invention may be combined with any of the features or options described in this document in relation to the first aspect of the invention or any other aspect of the invention. In particular, at least any of the dependent claims of another aspect of this invention can be combined with the present aspect of the invention to achieve a same technical effect. For example, this aspect of the invention may be combined with any of the features recited in at least any of claims 1-30 of the application. A further independent aspect of the invention is air distribution system for an insect housing chamber defined by an interior of a transportable container unit, comprising: a primary duct unit for location inside the chamber, and for extending along at least a portion of a length of the chamber, comprising at least one air flow channel, wherein the at least one airflow channel comprises a plurality of air outflow vents distributed along a length of the channel; an air processing unit having an inlet and outlet, and adapted to process air received at the inlet, wherein the outlet of the air processing unit is fluidly connected to the at least one air flow channel; and a fresh air supply subsystem, comprising one or more secondary duct units, each secondary duct unit comprising at least one air flow channel for extending along at least a portion of a length of the container and having a plurality of air outflow vents distributed along the length of the channel for venting air into an interior of the container, and wherein each of the one or more secondary duct units is spaced from the primary duct unit along the width dimension of the container, the width dimension being perpendicular to the length dimension of the container, and wherein the air outflow vents of the primary duct unit are positioned at intervals along a length of the container unit, and the air outflow vents of at least one of the one or more the secondary duct units are positioned at intervals along the length of the container, and wherein the positions of the air outflow vents of the primary duct unit are interspaced with those of the at least one secondary duct unit along the length dimension of the container. This aspect of the invention independently provides a beneficial technical effect in that this alternating spacing of the fresh air and processed air outflow vents allows for optimizing air supply to insect containers (e.g. larvae trays) when loaded into the chamber beneath the various ducts. In particular, it is the realization of the inventor that, by arranging the vents in this way, when the insect containers are loaded in the chamber, each insect container stack may be positioned (relative to a length of the chamber) in-between a fresh air vent and a conditioned air vent, and thus supplied on one side with a fresh air flow, and one the other side with a conditioned air flow. In preferred embodiments, a spacing (separation), along the length of the container, between each air outflow vent of the primary duct unit and a next neighboring (along the length of the container) air outflow vent of at least one of the secondary duct units may be greater than or equal to the width of a single container stack intended for use. It some embodiments, it may be substantially equal to the width of a single tray stack intended for use. The width of a tray stack may be between 600 mm and 400 mm in some examples. In preferred embodiments, an interval spacing between the outflow vents of the primary duct unit and / or an interval spacing between the outflow vents of at least one of the one or more secondary duct units is greater than or equal to a width of a single container stack which is intended to be used. The provided system may further include one or more of the insect container stacks for loading in the chamber in use. In some embodiments, each insect container stack may be aligned along the length dimension of the container with a point disposed in-between a primary duct outflow vent and a secondary duct outflow vent. In some embodiments, the insect container stacks may be loaded in the container in three rows, each row extending along a length of the container, each row extending parallel with both the primary duct unit and each of the secondary duct units, and wherein each row is situated beneath a respective one of the first secondary duct unit, the primary duct unit and the second secondary duct unit. In some embodiments, the container may include visual alignment markings or physical locating / alignment members to denote target positionings of containers. The insect containers may be larvae trays in some embodiments. The insect container stacks may be larvae tray stacks in some embodiments. It is noted and it will be appreciated that this aspect of the invention may be combined with any of the features or options described in this document in relation to the first aspect of the invention or any other aspect of the invention. In particular, at least any of the dependent claims of another aspect of this invention can be combined with the present aspect of the invention to achieve a same technical effect. For example, this aspect of the invention may be combined with any of the features recited in at least any of claims 1-30 of the application. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Fig. 1 shows a schematic plan view diagram of an example system in accordance with one or more embodiments; Fig. 2 shows a view of a system according to one or more embodiments, installed in a container unit, viewed from one end of the container unit; Fig. 3 shows a view of the system of Fig. 2, installed in a container unit, viewed from an opposite end of the container unit; Figs. 4-5 show schematic cross-section views from opposite ends of the container of an example system installed in a container unit in combination with a set of larvae container stacks, and illustrates air flow patterns induced; Fig. 6 shows a schematic plan view of the system, illustrating placement of larvae container stacks according to one or more embodiments; Figs. 7-8 illustrates exterior perspective views of an example container unit of installation of a system according to one or more embodiments; Figs 9-10 illustrate elevation views of opposite ends of the example container unit of Fig. 7-8; and Fig. 11 illustrates an example placement for a set of air sensors of the system. DETAILED DESCRIPTION OF THE EMBODIMENTS The invention will be described with reference to the Figures. It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts. The invention provides an air processing and distribution system for use in insect farming, for example for use in a chamber defined by an interior of a walled unit such as a transportable container unit. Adaptations are made for optimizing space constraints and air flow patterns. In at least some embodiments, it is proposed to use a single shared duct unit, with a common set of air inflow vents, to carry both return air (to an air processing / conditioning unit within the chamber) and extract air (to an air extraction unit for expelling outside). This saves space and makes air flow patterns more stable. The correct climate is fundamental for insects to complete their life cycle efficiently. According to embodiments of the present invention, a dedicated heating, ventilation & air conditioning ( HVAC ) design has been developed to manage the conditions within insect housing modules to optimize the insects performance and efficiency. The use of sensing instrumentation coupled with control logic may be used to drive fans and air conditioning to maintain optimum conditions. Local outdoor conditions may be compared with live indoor conditions so that HVAC equipment can be optimized for most energy efficient operation. For example, a rate of fresh air supplied to the chamber may be increased as a function of greater similarity between outside air temperature and a target inside air temperature, thereby reducing demand on the air conditioning unit and thus reducing power consumption. The purpose of a climate control system is to stabilize climate conditions within the chamber. For example, it has been found that the biological process may be inconsistent if the climate conditions for the Black Soldier Fly’s life cycle are not stable. Introducing climate control solves this issue and allows for stable and efficient egg and larvae production. Fig. 1 shows a schematic diagram of the air distribution system 6 in accordance with one or more embodiments of the invention. It will be appreciated that this represents one advantageous implementation of the proposed system and not all illustrated components are essential to the more general inventive concepts discussed above and hereafter. The system 6 is intended for use assembled or installed inside an insect housing module or chamber. The insect housing module or chamber may be formed by an interior of a walled unit or box 8. For example, in a preferred set of embodiments, the air distribution system is for installation in an insect housing chamber defined by an interior of a transportable container unit. In the example of Fig. 1, the air distribution system is installed inside the interior of a container unit. The outline of the container unit is indicated by arrow 8, and the chamber is defined by the interior of this unit. By ‘insect housing chamber’ is meant a space in which insects are contained as part of an insect farming operation. For example, in some embodiments, the insect housing chamber is an insect rearing or growing chamber. The insects may be held in containers such as trays which may be stacked inside the chamber. The insects may be black soldier fly in some embodiments. The assembled air distribution system represents an aspect of the invention alone. The unassembled air distribution system as a kit of parts represents another aspect of the invention. An insect housing module comprising the air distribution system assembled in a walled unit or box such as a transportable container unit and including the walled unit or box represents another aspect of the invention. The system 6 comprises a primary duct unit 10 for location inside the chamber, and for extending along at least a portion of a length of the chamber. A length dimension, I, of the chamber is indicated in Fig. 1. It represents the longer dimension of the chamber. The primary duct unit 10 comprises at least a first air flow channel 12, wherein the first airflow channel comprises a plurality of air inflow vents 18 distributed along a length of the channel for drawing air in from an interior of the chamber. The system further comprises an air processing unit 20 having an inlet and outlet, and adapted to process air received at the inlet. The air processing unit may be an air conditioning unit. The air processing unit may be adapted to process air to controllably modify or configure a temperature of the air. The air processing unit in some embodiments may comprise an inverter heat pump, which has the advantage of enabling a controllable air processing rate and a variable speed compressor in the outdoor unit, which allows for variable refrigerant flow inside the system. In the case where the air processing unit comprises an inverter heat pump, this may comprise an outdoor unit and an indoor unit. The outdoor unit may be mounted outside of the chamber, for example mounted to a roof of the container unit. The outside unit may include the following components: a compressor: compresses the refrigerant and pushes it through the system. In an inverter heat pump, the compressor can vary its speed to match the heating or cooling needs. A condenser coil: either absorbs heat from the outside air (in heating mode) or absorbs heat from the inside air (in cooling mode); expansion valve: lowers the pressure of the refrigerant, causing it to expand and cool down; fan: this helps move air across the condenser coil to facilitate heat transfer. The inside unit may comprise the following components: evaporator coil: where the refrigerant evaporates, absorbing heat from the indoor air (in cooling mode) or releasing heat to the indoor air (in heating mode); air handler: the fan that moves the air across the evaporator coil and pushes the air out of the outlet to the conditioner air duct (e.g. the second air flow channel 14 (to be discussed later); optional filter: removes particulates from the air during processing. The air processing unit may further comprise a thermostat or controller, permitting control of the temperature settings and operation mode of the heat pump. The system further comprises a controllable air extraction unit 32 having an inlet and outlet. The outlet is coupled to an extract vent 36 formed through a wall of the container unit 8. The air extraction unit 32 is for extracting air received at its inlet to outside of the container 8 via the outlet and through the extract vent 36 in the wall. An air extraction rate (volume per unit time) of the air extraction unit is controllable / configurable. In other words, the flow rate of air extracted from the chamber by the air extraction unit is controllable. The air extraction unit may include an air flow driver, such as a fan, to drive the air extraction at a controllable rate. The air extraction unit may consist of an extract fan unit. As illustrated in Fig. 1, the arrangement is characterized particularly in that the first air flow channel 12 is fluidly connected to both the inlet of the air processing unit 20 and the inlet of the air extraction unit 32 so that it provides a fluid feed for both the air processing unit and air extraction unit. In other words, a single duct charnel doubles as both an extract duct and return duct for the system. This makes the arrangement space efficient, since it avoids a need to provide a separate return and extract duct, as would be the usual practice. This configuration is available as an efficient option in the present case in part because of the relatively small internal volume of the chamber. For example, if the chamber is formed by an interior of a shipping container, a typical internal volume of the chamber may be between 20 m3 and 100 m3, for example between 30 m3 and 80 m3. For example, a 20 foot long high cube shipping container has an internal volume of approximately 33.2 m3, while a 40 foot long high cube shipping container has an internal volume of approximately 75.3 m3. Given the small internal volume, there is relatively good level of internal diffusive mixing of air, meaning that it is not essential to provide an extract ducting and a return ducting which each extend independently along the entire extent of the chamber. It is sufficient that each of the air processing unit 20 and the air extraction unit 32 are able to draw air from at least a section of the chamber. When both units are running for example, the air extraction unit might tend to draw air more from one half of the first air flow channel 12 and the air processing unit might tend to draw air more from the other half of the first air flow channel 12. However, by using a single continuous duct to which both units are connected, it means that, if one of the units is inactive, the other of the units is advantageously able to draw air from the whole of the length of the first air flow channel. For example, if the air processing unit is deactivated for power saving, the air extraction unit 32 can draw air from the whole length of the air flow channel 12. In preferred embodiments, and as illustrated in Fig. 1, the plurality of air inflow vents 18 of the first air flow channel 12 are distributed along a section of the first air flow channel 12 extending between the air processing unit 20 and the air extraction unit 32. In other words, the air inflow vents to the first air flow channel are disposed between a fluid connection of the first air flow channel to the air processing unit and a fluid connection of the first air flow channel to the air extraction unit. More particularly, in the illustrated example, the air processing unit 20 and air extraction unit 32 are disposed at opposite ends of the first air flow channel 12, with the inflow vents distributed along the channel in-between. In other words, the first air flow channel 12 has a first and second end, and wherein the first end of the first air flow channel is fluidly connected to the inlet of the air processing unit 20 and the second end of the first air flow channel is fluid connected to the inlet of the air extraction unit 32. This is both space efficient and airflow efficient. In the illustrated example, aside from the two ends connected to the air processing unit and the air extraction unit, and the air inflow vents, the first air flow channel is otherwise closed / sealed. The first airflow channel of the primary duct unit preferably provides the sole air feed / supply to each of the air processing unit 20 and the air extraction unit 32. The chamber has a length (L), width (W) and height (H) (see e.g. Fig. 7-8). The primary duct unit is structured and arranged such that plurality of air inflow vents 18 of the primary duct unit 10 are disposed at a plurality of different length and / or width positions. Preferably, all of the air inflow vents 18 of the primary duct unit 10 are disposed at a same height level in the chamber. The primary duct unit 10 and the first air flow channel 12 extend linearly along at least a portion of a length and / or width of the chamber. In the illustrated example, the primary duct unit 10 and first air flow channel 12 extend along a majority of the length of the chamber. In the illustrated example, the primary duct unit 10 is suspended from or coupled to a ceiling of the chamber / container. This allows for air to be distributed using the system around an arrangement of insect containers (e.g. trays) stacked on the floor of the chamber. . Preferably, the primary duct unit 10 is disposed centrally relative to a dimension of the chamber perpendicular to a direction of extension of the first air flow channel 12, for example centrally relative to a width dimension, w, of the chamber. In general, the primary duct unit 10 may be configured for extending from a first location on the ceiling to a second location on the ceiling, for example from a location proximal to one end of the chamber to a location proximal to an opposite end of the chamber. The air processing unit 20 is or comprises an air conditioning unit. The air processing unit 20 may be controlled in dependence upon a temperature inside the chamber, as measured by one or more temperature sensors for disposal inside the chamber. The air extraction 32 unit may be controlled at least in part in dependence upon a CO2 concentration of air inside the chamber, as measured by one or more CO2 sensors for disposal inside the chamber. The air processing unit 20 may comprise an inverter heat pump. An inverter heat pump is a specific type of heat pump that uses inverter technology to control the speed of the compressor motor, thereby regulating the temperature continuously. In a standard heat pump, the compressor is either on (working at 100% capacity) or off, resulting in a more dramatic fluctuation in temperature and a less efficient system. When the compressor is on, it is using maximum electricity, and when it is off, no heating or cooling is happening. On the other hand, an inverter heat pump can adjust the speed of the compressor to exactly match the heating or cooling needs at a given moment. With reference to the air extraction unit 32, this may comprise a controllable air flow driver disposed between the inlet and outlet of the extraction unit 32 for drawing a flow of air toward the outlet 36, preferably at a controllable air flow rate. The air flow driver in some embodiments is an air fan. In other words, the air extraction unit comprises an extract fan. A controller may be provided which is adapted to control the air outflow rate of the air extraction unit to thereby control a rate of air extraction from the chamber, e.g. by adjusting a power level to the fan. The air processing unit 20 also has an air circulating function, and, when active, draws air in through the inlet. The through-flow rate of the air processing unit may be operated at a fixed level, or may be controllable. Advantageously, in preferred embodiments, and as illustrated in Fig. 1, a first nonreturn damper 24 is provided disposed at a fluid connection / interface between the first air flow path 12 and the air processing unit 20, for impeding air passage from the first air flow channel 12 to the inlet of the air processing unit 20 when the air processing unit is inactive. A second non-retum damper 26 is also disposed at a fluid connection / interface between the first air flow path 12 and the air extraction unit 32, for impeding air passage from the first air flow channel 12 to the inlet of the air extraction unit 32 when the air extraction unit is inactive. Since the air processing unit and air extraction unit are disposed at opposite ends of the first air flow channel 12 in this example, the first and second non-retum dampers are likewise disposed at the two opposite ends of the first air flow channel 12. These dampers allow for maximally efficient utilization of the whole length of the first air flow channel 12 in the event that one of the air processing unit 20 and air extraction unit 32 is inactive, while the other is active. By closing off the fluid connection to the inactive unit, this means that the other unit is able to efficiently draw air from air inflow vents 18 along the whole length of the air flow channel 12. Without the damper, there would remain a semi-open air flow path through the inactive unit, impeding the efficient drawing of air along the air flow channel. This therefore means that both the air extraction unit or the air processing unit can each independently draw air from the whole length of the chamber (or at least the portion spanned by the primary duct unit 10) in the event that only one of the two units is operating, but without having to provide each one a separate air flow duct, thereby saving space. The non-retum dampers may be gravity driven, such that their open / close state is determined according to whether the component to which they are adjacent is on or off. A further advantageous feature of at least some embodiments, and as illustrated in the figures, is the provision of a second airflow channel 14 integrated in the same primary duct unit 10 for purposes of distributing air processed by the air processing unit. It is noted that this feature is not inextricably linked with the feature already described of the shared use of the first air flow channel for extract and return, but, if applied, combines synergistically with this feature is further improving space efficiency as well as airflow efficiency. In particular, in some embodiments, the primary duct unit 10 further comprises a second air flow channel 14, fluidly separated / isolated from the first air flow channel 12. It preferably runs parallel with the first air flow channel, fluidically and / or spatially. The duct portion which carries the second air flow channel is preferably solidly coupled with or mounted to the first air flow channel, for example so that the two extend together as a common structural unit. The second airflow channel 14 comprises a plurality of air outflow vents 16 distributed along at least a portion of the length of the channel. The second airflow channel 14 is fluidly connected to the outlet of the air processing unit 20. Thus the second air flow channel 14 acts to carry processed air from the air processing unit 20 and distribute it via the air outflow vents 16 into the interior space of the chamber. For the illustrated example shown in the figures, the second air flow channel 14 is not visible in the plan view of Fig. 1 because it is situated underneath the first air flow channel 12. However, the positions of the air outflow vents 16 of the second airflow channel are indicated in the plan view of Fig. 1. It is noted that the relative spatial arrangement of the first and second airflow channels shown in the illustrated example is not essential to the general inventive principles, but, as explained later, does carry some technical advantages in terms of space efficiency and air distribution. The second air flow channel 14 is visible in the projection views of Figs. 2-5. Fig. 2 shows a view of a system according to one or more embodiments, installed in a container unit, viewed from one end of the container unit. Fig. 3 shows a view of the system of Fig. 2, installed in a container unit, viewed from an opposite end of the container unit. In particular, Fig. 2 shows a view down the length of the container, viewed from the end labelled 64 in Fig. 1. Fig. 3 shows a view down the length of the container, viewed from the end labelled 62 in Fig. 1. The second air flow channel 14 can be seen in these views. Thus, according to the presently described set of embodiments, the same common primary air duct 10 carries both the return air to the air processing unit 10 and the processed air from the air processing unit 20. This is structurally and functionally efficient. The second air flow channel 14 may be fluidly parallel with the first air flow channel 12. The second air flow channel may extend spatially parallel with the first air flow channel. The air flow direction in the first air flow channel 12 may be opposite to that in the second air flow channel 14. The first air flow channel 12 may be defined by the lumen of a first duct portion of the primary duct unit 10 and the second air flow channel 14 defined by the lumen of a second duct portion of the primary duct unit 10, and wherein the first and second duct portions are physically coupled to one another, for example solidly mounted to one another, for example adjacent one another, for example contiguously adjacent to one another, for example touching one another. The 22 two may be formed by separate channels in a unitary duct structure, for example fluidly separated by a barrier element. Advantageously, in some embodiments, and as illustrated in Fig. 2-Fig. 5, the first air flow channel 12 is stacked above the second air flow channel 14 (in a height direction of the chamber) or vice versa. The height direction means for example a direction parallel with the direction of gravity. It is most preferably the first air flow channel 12 above the second airflow channel 14. This is because, by having the air flow channel carrying conditioned air below the air flow channel drawing in return air, the processed air can fall freely down into the chamber without being drawn immediately back into the air inflow vents 18. In some embodiments, and as illustrated in Figs. 2-5, the air outflow vents 16 of the second airflow channel 14 are arranged for facing toward a floor of the chamber and the air inflow vents 18 of the first airflow channel are arranged for facing sides of the chamber, or vice versa. This helps to avoid interference of the two flows, i.e. avoids the conditioned air being drawn up directly into the retum / extract duct 12. As illustrated in the example, advantageously, the primary duct unit 10 is for mounting to a ceiling of the chamber (i.e. a ceiling of the container unit in the present example). In this way it may be disposed suspended above the larvae trays when these are loaded in the chamber. Descriptions above have related to the inventive principle of the common first air flow channel for carrying return and extract air, and the spatially efficient integration of a second airflow channel into the same duct unit for carrying processed air back into the chamber along a spatial path parallel with that of the first air flow channel. According to a preferred set of embodiments, and as illustrated in the example shown in the figures, the air distribution system further includes a fresh air supply sub-system (44, 42). The fresh air supply subsystem may be fluidically separate / isolated from the air processing and extract subsystem previously discussed. In the context of insect housing, a separate fresh air supply is valuable for purposes of regulating CO2 levels, among other things. By providing a fresh air supply subsystem which is fluidically independent of the air processing subsystem (meaning the air processing unit 20 and the air flow channels 12, 14 leading to and from it), this advantageously allows for greater control over air conditions inside the chamber. By way of example, it allows for independently regulating CO2 levels (by adjusting a rate of fresh air supply into the chamber) and temperature levels (e.g. by adjusting a temperature setting or activation / deactivation of the air processing unit). In some examples, and as illustrated in the figures, the air supply sub-system, comprises one or more secondary duct units 42a, 42b, each comprising at least one air flow channel for extending along at least a portion of a length of the chamber / container and having a plurality of air outflow vents 46 distributed along the length of the channel for venting air into an interior of the chamber. In the particular example shown in the figures, the air supply subsystem comprises two secondary duct units 42a, 42b, which are arranged on alternate sides (relative to a width dimension of the chamber) of the primary duct 10. Each secondary duct unit extends along at least a portion of the length of the chamber in this example. Each of the one or more secondary duct units is spaced from the primary duct unit across a width dimension of the container. Furthermore, each extends spatially parallel with the primary duct unit 10. As will be explained later, not only is this a spatially efficient configuration, it is also efficient from the point of view of inducing mixing of fresh air and conditioned air in the chamber volume. In the illustrated example, the primary duct unit 10 extends along the chamber at a central width position, and the two secondary duct units 42a, 42b extend along a length of the chamber on alternate sides of the primary duct unit, for example running adjacent opposite side edges of the chamber. Each of the secondary duct units 42a, 42b is connected, for example at one end, to a fresh air inlet 44a, 44b of the container for receiving air from an environment outside of the container. A first secondary duct unit 42a is connected to a first fresh air inlet 44a, and a second secondary duct unit 42b is connected to a second fresh air inlet 44b. At the fluid interface between each fresh air inlet 44 and the respective secondary duct unit 42 to which it is connected may be included a controllable air flow driver arranged for drawing air into the respective secondary duct unit from a fresh air inlet 44. Each air flow driver may be connected to the same controller to which the air processing unit 20 and air extraction unit 32 are connected. As illustrated in Fig. 3, preferably the air outflow vents 46 of each of the one or more secondary duct units 42 is disposed at a height (vertical) level which is below a height level of the air inflow vents 18 of the first air flow channel 12. This is so that the fresh air can fall into the chamber beneath without being drawn into an inflow path of the air inflow vents 18 en route. As illustrated, both the air outflow vents 46 of the secondary duct units 42 and the air outflow vents 16 of the primary duct unit are disposed at a height level below the air inflow vents 18 of the primary duct unit. As illustrated in Fig. 1, in some embodiments, the air flow channels of each of the one or more secondary duct units 42a, 42b may transition from a first cross-sectional area to a second, smaller cross-sectional area part way along the length of the channel, for example approximately half way along. This helps to maintain velocity of the air as the volume of air reduces as it is discharged through the first subset of the air outflow grilles 46. As illustrated, the one or more secondary duct units 42a, 42b preferably extend spatially parallel with the primary duct unit 10, and particularly the first 12 and / or second 14 air flow channel of the primary duct unit 10. Both the primary duct unit 10 and each of the secondary duct units 42a, 42b are preferably suspended from, or coupled to, the ceiling, so that the airflow vents 46, 16 are all suspended above the larvae trays when the trays are loaded into the chamber. In the illustrated example, the air outflow vents 46 of each secondary duct unit are arranged in a linear pattern. The air outflow vents 16 of the primary duct unit 10 are also arranged in a linear pattern. The air inflow vents 18 of the primary duct unit 10 are also arranged in one or more linear patterns. In the illustrated example, there are two linear rows of air inflow channels 18, one on either side of the first airflow channel 12. All of these linear pattems / paths may extend spatially parallel to one another. In the illustrated example, each of the two linear patterns of air inflow vents 18 of the primary duct unit 10 are disposed, relative to a width of the chamber, in-between a linear patten of outflow vents of the secondary duct and the linear pattern of outflow vents of the primary duct unit. This optimizes air mixing. Effectively, the air distribution system is configured to provide air mixing along an air mixing corridor extending along at least a portion of the length of the chamber. Along the corridor, air outflow and inflow vents of the primary and secondary duct units are distributed at intervals. The proposed configuration synergistically balances space efficiency with air mixing efficiency. This is schematically illustrated for example in Fig. 4 and Fig. 5. These schematically show a view along a length of the chamber, from one end 64 of the chamber in Fig. 4 and from an opposite end 62 of the chamber in Fig. 5. In these depictions, the intended loading positions for a set of larvae trays 72 are further shown. Each larvae tray holds insect larvae which are to be reared or grown while housed in the chamber. For example, these may be black soldier fly larvae. Although trays are referred to in the present descriptions, any other insect container may be used, preferably containers which are vertically stackable, or which have a vertical extension, may be used instead. Thus ‘larvae tray’ or ‘insect tray’ may be replaced throughout in this disclosure by ‘larvae container’ or ‘insect container’ / Illustrated in the figures are a plurality of larvae tray stacks 74, each stack comprising a plurality of trays 72 stacked vertically atop one another, the tray stacks for being supported by a floor of the container. As will be explained with greater clarity later, these larvae tray stacks may be arranged in repeating rows, e.g. of three, as shown in Fig. 4 and Fig. 5 along a major portion of the length of the chamber. An example set of positions of the larvae tray stacks 74 along the chamber is indicated in Fig. 6. Returning to Fig. 4 and Fig. 5, it can be seen that the proposed configuration achieves a stable cyclical air flow pattern. When all three of the air processing unit 20, the air extraction unit 32 and the fresh air supply subsystem 44, 42 are running, the air flow pattern in the chamber may be as follows. Air is drawn into the first flow channel 12 through the air inflow vents 18 on either side of the first air flow channel 12. Within the first air flow channel 12, some air is drawn toward the air extraction unit 32 and some air is drawn toward the air processing unit 20. The air reaching the air extraction unit is extracted to an outside of the chamber, i.e. outside of the container. The air reaching the air processing unit 20 is processed by the air processing unit, e.g. conditioned so as to modify its temperature, and output by the processing unit into the second air flow channel 14 which is connected to the outlet of the air processing unit. This processed air is then discharged into the chamber via the air outflow vents 16 of the second airflow channel 14. At the same time, and fluidly independently, each of the one or more (two in this case) secondary duct units 42a, 42b of the air supply subsystem is supplied with an inflow of fresh air from outside the chamber / container. This fresh air flows along each secondary duct unit 42a, 42b and is discharged into the container via the air outflow vents 46 of the respective secondary duct unit. As illustrated in Fig. 4, this creates a stable airflow current or pattern on each side of the primary duct unit 10 within the chamber in which processed air and fresh air each fall in a respective vertical path down into the chamber, and wherein, in-between these two downward air flows, a single upward air flow current extends up toward the inflow vents 18 of the first air flow channel 12. There is thus established a stable cyclical pattern. For ease of viewing, Fig. 4 shows the airflow cycle on only one side of the chamber, but a corresponding air flow pattern is also established of the other side. This air flow pattern is advantageous since it allows for efficient mixing of the fresh air and the processed air, and allows for the fresh air and processed air to dissipate a significant way down the vertical height of the chamber before being interrupted by the retum / extract flow current. This is furthermore achieved in a small space setting where provision of widely spaced ducts for discharging and drawing in air respectively is not possible. When the trays are loaded in the container, the air flow pattern advantageously establishes an air flow which cycles around the borders of the tray stacks 74 as illustrated in Fig. 4, effectively supplying a mix of fresh and processed air to all of the trays. The particular pattern illustrated arises in part because, relative to a width of the chamber, each air inflow vent 18 of the first air flow channel 12 is disposed in-between an air outflow vent 16 of the second airflow channel 14 and an air outflow vent 46 of one of the secondary duct units 42a, 52b. A further particularly advantageous feature in accordance with at least some embodiments, is the relative placement of the fresh air outflow vents 42 and the processed air outflow vents 16 along the length of the chamber. In particular, in some embodiments, and as illustrated in Fig. 1, the air outflow vents 16 of the primary duct unit 10 are positioned at intervals along a length of the container unit, and the air outflow vents 46 of each of the one or more the secondary duct units 42a, 42b are positioned at intervals along the length of the container, and wherein the positions of the air outflow vents 16 of the primary duct unit 10 (i.e. of the second airflow channel 14) are interspaced / interleaved with those of at least one of the one or more the secondary duct units 42a, 42b along the length dimension of the container. In the illustrated example, the outflow vents 46 of the first 42a and second 42b secondary duct units are arranged in alignment with one another relative to a length dimension of the container, and thus the positions of the air outflow vents 16 of the primary duct unit 10 are interspaced / interleaved with those of the two secondary duct units 42a, 42b. The advantage of this alternating spacing of the fresh air and processed air outflow vents is to optimize air supply to larvae trays when loaded into the container beneath the various ducts. In particular, it is the realization of the inventor that, by arranging the vents in this way, when the larvae trays are loaded in the chamber, each tray stack may be positioned (relative to a length of the chamber) in-between a fresh air vent 46 and a conditioned air vent 16, and thus supplied on one side with a fresh air flow, and one the other side with a conditioned air flow. This is perhaps easiest to see from Fig. 6, which shows the same plan view as Fig. 1, but additionally indicates, with dashed-outline boxes, the intended positions for the larvae tray stacks 74 when loaded into the container. It can be seen that each tray stack is located so that its position along a length of the container is disposed in-between a fresh air outflow vent 46 on one side and a conditioned air outflow vent 16 on the other side. In this way, one side of each tray stack is supplied with a column of fresh air and the other side of each tray stack is supplied with a column of conditioned air. Thus each tray receives a mix of the two air inflows. To facilitate this, preferably an interval spacing between each neighboring pair of outflow vents 16 of the primary duct unit 10 and / or an interval spacing between each neighboring pair of outflow vents 46 of at least one of the one or more secondary duct units 42a, 42b is greater than or equal to a width of a single tray stack which is intended to be used. In fact, as shown in Fig. 6, preferably this interval spacing in both cases is greater than or equal to the width of two of the larvae tray stacks. Indeed, preferably, this interval spacing in both cases is greater than or equal to a sum of: the width of two of the larvae tray stacks and a length (along the length dimension of the chamber) of one of the air outflow vents of the primary duct unit or secondary duct unit. The typical width of a larvae tray stack may be between 400 mm and 600 mm in some examples. Furthermore, preferably a spacing (separation), along the length of the container, between each air outflow vent of the primary duct unit 10 and a next neighboring (along the length of the container) air outflow vent 46 of at least one of the secondary duct units 42a, 42b should be greater than or equal to the width of a single tray stack intended for use. In practice, the tray stacks may be loaded in the container in three rows, each row extending along a length of the container, each row extending parallel with both the primary duct unit and each of the secondary duct units, and wherein each row is situated beneath a respective one of the first secondary duct unit 42a, the primary duct unit 10 and the second secondary duct unit 42b. This is illustrated in Fig. 6 and Figs. 4-5. The air distribution system can be provided as an aspect of the invention without the trays themselves. However, in some embodiments, a complete kit or module may be provided which includes the trays. For example in some embodiments, there may be provided a plurality of larvae trays for forming a plurality of larvae tray stacks, each stack comprising a plurality of trays stacked vertically atop one another, the tray stacks for being supported by a floor of the container. Instead of trays, any other insect container may be used. In some embodiments, the container may include visual alignment markings or physical locating / alignment members to denote target positionings of trays. A further space saving feature of the present invention is that the air extraction unit 32 is provided extending with air flow direction which is perpendicular to an air flow direction of the first air flow channel 12 of the primary duct unit. The advantage of this will be recognized from the plan view of Fig. 1 for example. The air extraction unit 32 is arranged in the chamber offset with respect to the first air flow channel along the width direction and wherein the primary duct unit 10 includes a comer section to fluidly connect the first air flow channel 12 to the air extraction unit 32. Thus, the air extraction unit 32 in the illustrated example extends cross-ways relative to the path of the first air flow channel 12 and is arranged to output air to an outside of the chamber through an outflow vent 36 formed through a side wall of the chamber. By orienting the air extraction unit perpendicular to the primary duct unit, and offsetting it laterally relative to the primary duct, this avoids the air extraction unit having to take up some of the length of the container that could otherwise be occupied by first and second air flow channels. It thus allows a length of these channels to be maximized, which is optimal for airflow. In some embodiments, and as is illustrated in the figures, at least one secondary duct unit 42a extends spatially parallel to the primary duct unit 10 from one first end 64 of the chamber to a terminal point spaced from a further end 62 of the chamber by a clearance space, and wherein at least a section of the air extraction unit 32 is disposed in said clearance space. In other words, and as illustrated in Fig. 1, the air extraction unit is fitted into a space between an end of one of the fresh air ducts 42a and an end of the container, thus optimizing space usage. In preferred embodiments, the fresh air inlet(s) 44a, 44b to the one or more secondary duct units 42a, 42b are preferably disposed at an opposite end of the container to the outlet 36 of the air extraction unit. This is optimal for minimizing interaction between the two flows, to avoid extracted air being recycled into the chamber as fresh air. As mentioned briefly above, in some embodiments, the system comprises a controller operatively coupled at least the air processing unit 20 and the air extraction unit 32 (e.g. the air flow driver in the air extraction unit), for controlling an air condition in the module. In an advantageous set of embodiments, a maximum air supply rate of fresh air into the chamber achievable by the air supply subsystem is greater than a maximum air extraction rate of air from the chamber achievable by the air extraction unit. For example, preferably the maximum air inflow rate of the air supply subsystem is at least 50% greater, more preferably at least 100% greater, than the maximum possible air outflow rate of the air extraction unit. In other words, the system is weighted with greater fresh air supply capacity than air extraction capacity. This may be achieved in some embodiments by providing two secondary duct units, each with a respective fresh air supply vent and air driver unit, while providing only a single air extraction unit coupled to the single first airflow channel of the primary duct unit. Thus, in some embodiments, there is provided approximately double the air supply flow capacity to air extraction flow capacity. Due to the tight packing of trays within the container during operation, maintaining continuous air flow is a challenge. It is the realization of the inventor that this can be partially addressed by drawing in air to the container at a greater rate than it is extracted, thereby effectively establishing a positive air pressure inside the container. This helps overcome the problem of the trays impeding air flow and helps to promote air mixing and air distribution. Furthermore, the proposed imbalance of fresh air supply to air extraction rate is also based on a need to optimize space usage. It is the realization of the inventorthat space can be saved by providing only half the extraction capacity to fresh air supply capacity, but to compensate for this under-extraction by additionally providing pressure relief dampers in walls of the container unit. Thus, in some embodiments, the container defining the chamber may comprise one or more pressure relief dampers permitting outflow of air from the interior of the container to outside the container, for example responsive to an air pressure inside the container acting on the damper exceeding a threshold. These one or more pressure relief dampers may be formed in walls of the container. The pressure relief dampers may be passively driven. The pressure relief dampers allow for implementing the over-pressuring control mode mentioned above without the pressure in the container becoming too high. As pressure rises, air can be vented out through the dampers. In other words, the pressure relief dampers supplement the driven air extraction capacity of the air extraction unit, but with a passive mode of operation. Positions of an example set of pressure relief dampers 52a-52f are schematically indicated in Fig. 1. The exact positions are not essential. However, it will be recognized that they can be positioned as desired to create desired air flow patterns. For example, Fig. 7 - Fig. 10 show example positionings of the pressure relief dampers 5 2a-52f located at a similar or same height level as the air inflow vents 18 of the first air flow channel 12 which supplies the air extraction unit. Thus, when there is a greater rate of fresh air supply into the chamber than rate of air extraction from the chamber by the air extraction unit 32, the pressure relief dampers 52 effectively provide supplementary air extraction capacity. The pressure relief vents 52a-52f may include passive, pressure-responsive dampers. The pressure relief dampers may prevent air flow from outside the container to inside. The pressure relief dampers may be closed in absence of pressure applied by air. These would not typically be need in conventional HVAC systems as there is generally always somewhere for air to escape unless it is a strictly controlled environment. It is proposed according to this embodiment to draw in more air in than is extracted, and thus pressure relief vents are provided to allow for the over-air to escape. In some embodiments, the system includes a controller, operatively coupled to the air supply subsystem 42, 44 and the air extraction unit 32, and wherein, in at least a first control mode, the controller is adapted to control the air supply subsystem and the air extraction unit in coordination such that a flow rate of fresh air into the chamber provided by the air supply subsystem exceeds a flow rate of air extracted from the chamber by the air extraction unit. Excess fresh air may in some embodiments be vented through a set of pressure-relief dampers. In some embodiments, the controller may be configurable in at least a further control mode in which the controller is adapted to control the air extraction unit and the air supply subsystem in co-ordination such that a flow rate of air extracted from the chamber (volume / time) by the air extraction unit exceeds a flow rate of fresh air provided into the chamber by the air supply subsystem. In some embodiments, the flow rate of fresh air provided into the chamber may be set to zero. To complement this possible feature, in some embodiments, the container may additionally comprise one or more non-retum dampers 54 permitting inflow of air from outside the container to insider the container, for example responsive to a pressure inside the container falling below a threshold. The above control option may be implemented in cases where low power consumption is required, for example where there is an interruption in the power supply or power availability is low. For example, in some instances, mains supply power might fail, and the system may operate using a backup power supply system. In this event, power may be prioritized to the air extraction unit, leaving the air supply subsystem deactivated. The remainder of the air supply may be provided passively through the non-retum dampers. These may be formed in a one or more walls of the container. The non return dampers 54 may prevent air flow from inside the container to outside. The non return dampers may be closed in absence of pressure applied by air. They may permit flow of air only in the condition of a negative pressure inside the container relative to outside air pressure. In some embodiments, both pressure relief dampers 52 and non-retum dampers 54 may be formed in walls of the container. This is schematically illustrated in the exterior perspective views of the container presented in Figs. 7-8 and the elevation views of the ends of the container shown in Figs. 9-10. These show possible positions of pressure relief dampers 52 and non-retum dampers 54 in walls of the container. In some embodiments, there may be provided a same number of pressure relief dampers 52 as non-retum dampers 54. In some embodiments, the set of pressure relief dampers 52 may be located at positions elevated relative to the non-retum dampers 54. In some embodiments, the controller is adapted to set / control a target ratio between: a flow rate (volume / time) of fresh air supplied into the chamber and a flow rate of air extracted from the chamber, and wherein the controller is adapted control the air supply sub-system in co-ordination with the air extraction unit 32 in accordance with said target ratio. In at least one control mode, the controller is adapted to control the air supply subsystem in co-ordination with the air extraction unit 32 such that the air within the chamber is fully replaced at a rate of at least 15 air changes per hour. In the context of insect farming, higher frequency of air changes per unit time is needed than in typical applications of HVAC systems, due at least in part to the need to efficiently vent carbon dioxide. In some embodiments, the air extraction unit 32 and / or the air supply sub-system 42, 44 are each configured to drive air out and / or in to the chamber at a flow rate of at least 300 liters per second, for example at least 350 liters per second, for example 375 liters per second. To complement the views of the system shown in Figs. 1-6, Fig. 7 and Fig. 8 illustrate exterior perspective views of an example container unit within which the system might be assembled in operation. Fig. 9 and Fig. 10 show elevation views of a respective first 62 and second 64 end of the container. The first end 62 of the unit carries the cargo doors for access to the interior chamber defined inside the unit. The second end 64 may be closed. Alternatively, and as illustrated in Fig. 7 and Fig. 9, the container may be modified to include an additional personnel access door at the second end 64 of the container. This helps to gain access to components of the system when the container is fully loaded with trays. The positions of the first 62 and second ends 64 of the container relative to the air distribution system is also indicated in Fig. 1. The first end 62 is the end at which the air extract unit 32 and air extraction outlet 36 are disposed, and carries the cargo doors of the unit. The second end is the end at which the two fresh air inlets 44a, 44b are formed through the end wall of the unit. Dimensions of a height, H, length, L, and width, W, of the unit are indicated in the figures. In some embodiments, the system comprises a controller operatively coupled to the air extraction unit 32 and the air conditioning unit 20. Preferably, the controller is further operatively coupled with the fresh air supply subsystem, for example to the one or more air flow drivers 44a, 44b of the fresh air supply subsystem. In some embodiments, the system may comprise a set of air sensors for sensing one or more characteristics of an air inside the chamber. In some embodiments, the controller is configured to regulate an air condition inside the chamber based on control of at least the air extraction unit and the air conditioning unit and based on input signals received from the one or more sensors. It may further be based on control of the fresh air supply subsystem. In some embodiments, the controller is adapted to control a rate of fresh air supply by the fresh air supply subsystem in dependence upon a measured CO2 level and optionally in dependence upon temperature. In some embodiments, the air processing unit 20 is adapted to process air so as to modify a temperature of the air to a target air temperature, and wherein the controller is adapted to control at least one setting, e.g. activation / deactivation, of an air processing rate of the air processing unit 20 in dependence upon a measured temperature of air inside the chamber. The target air temperature may be pre-defined based on an optimal temperature for the biology of the insects, for example an optimal temperature for growth of the insects. In some embodiments, the set of air sensors comprised by the system for sensing one or more characteristics of an air inside the chamber may include one or more air temperature sensors for sensing a temperature of air inside the chamber. In some embodiments, the set of air sensors comprised by the system for sensing one or more characteristics of an air inside the chamber may include one or more carbon dioxide concentration sensors, for sensing a carbon dioxide concentration of air inside the chamber. In some embodiments, the system comprises a set of outdoor air sensors for sensing one or more characteristics of an air outside the chamber, and wherein the regulation of the air condition is performed further dependent upon signals from the set of outdoor air sensors. These may include one or more air temperature sensors, and optionally one or more humidity sensors. One example arrangement for the air sensors of the system is illustrated in Fig. 11. This shows the same plan view of the system as depicted in Fig. 1, but with positions of an example set of sensors indicated. In particular, in accordance with the illustrated example, there is provided a first 92a and second 92b internal air temperature sensor, each for sensing a temperature of air inside the chamber at a respective location. There is further provided a carbon dioxide sensor 94 for sensing a concentration of carbon dioxide in the chamber. The three sensors 92a, 94, 92b are spaced from one another. In the illustrated example, they are spaced from one another along a length dimension of the chamber. In some embodiments, the two temperature sensors are located at positions 1 / 3 and 2 / 3 of a way along the length of the chamber. The carbon dioxide sensor is positioned in-between the locations of the two temperature sensors, but this is not essential. All three of the sensors are positioned elevated above a floor of the chamber. For example, they may be mounted to an exterior surface of the primary duct unit 10 in some embodiments. At the top of the chamber is where temperature may be expected to be at a maximum. When measuring an internal air temperature of air inside the chamber, an average may be taken of the sensor readings of the first 92a and second 92b temperature sensors. It is anticipated that there may be a slight temperature gradient along the length of the chamber. Thus, providing two sensors allows for monitoring this temperature gradient and / or smoothing it out by taking an average. Furthermore, in some embodiments, by monitoring temperature at the two different locations, a real-time measure of air mixing efficiency can be derived. In some embodiments, the system comprises a set of outdoor air sensors for sensing one or more characteristics of an air outside the chamber, and wherein the regulation of the air condition is performed further dependent upon input signals from the set of outdoor air sensors. This is illustrated in Fig. 11, which shows a single external temperature sensor 96 for sensing a temperature of air in an environment outside of the chamber / container. In some embodiments, the controller is configured to determine a target internal temperature for air inside the chamber, obtain a measurement of a temperature of an environment outside of the chamber, compare the target internal temperature with the measurement of the temperature outside of the chamber to determine a difference between the two temperatures, and set an air inflow rate of the air supply subsystem in dependence upon a result of said comparison. For example, the air inflow rate of the air supply subsystem may be set at a greater level where the difference between the temperatures is less, and is set at a lower level where the difference between the temperatures is greater. In other words, the air inflow rate of the air supply subsystem is increased as a function of increasing similarity (decreasing difference) between the outside temperature and the target inside temperature of the chamber. This is energy efficient since it minimizes use of the air processing unit to configure the temperature inside the chamber. Where air outside the chamber is close to the target temperature inside the chamber, the outside air can be used to condition the temperature inside the chamber, in preference to use of the (energy expensive) air processing unit. The system may further comprise one or more temperature sensors for disposal within one or more of the larvae trays for measuring a temperature of organic matter in the trays, and wherein the controller is communicatively coupled with the one or more temperature sensors. The controller may be adapted to regulate the air condition inside the chamber further based on an output from these temperature sensors. Another aspect of the invention is a kit of parts, comprising: a transportable container unit; and the air distribution system in accordance with any example or embodiment outlined in this document or in accordance with any claim of the application, in an unassembled or partially assembled state. Another aspect of the invention is an insect housing module, comprising: a transportable container unit, an interior thereof defining an insect housing chamber; and an air distribution system in accordance with any example or embodiment outlined in this document or in accordance with any claim of the application assembled within the insect housing chamber. The transportable container unit may for example be a shipping container, for example a high cube shipping container. The container unit may have at least one extract outlet for expelling air to an environment outside the container. The outlet of the air extraction unit may be fluidly connected to the extract outlet of the container. A ceiling of the container unit has a length and a width, and the primary duct unit may extend along at least a portion of the length of the container unit ceiling. Another aspect of the invention is the use of an air distribution system in accordance with any embodiment disclosed herein or any claim of the application for insect farming purposes, Another aspect of the invention is the use of an air distribution system in accordance with any embodiment disclosed herein or any claim of the application, installed within a walled unit defining an interior chamber, for example a transportable container unit. Another aspect of the invention is a method, comprising assembling an air distribution system in accordance with any embodiment disclosed herein or any claim of the application within a walled unit defining an interior chamber, for example within a transportable container unit. As mentioned above, the control of the air supply subsystem and the air extraction unit to provide an imbalance of inflowing fresh air to extracted air is a particularly advantageous feature, offering additional control over the climate inside the chamber, and also providing airflow benefits in the context of chamber tightly packed with larvae trays. This feature in isolation provides an advantageous technical effect and represents a separate aspect of the invention. Accordingly, a further aspect of the invention is an air distribution system for an insect housing chamber defined by an interior of a transportable container unit, comprising: a controllable air supply sub-system for drawing in fresh air from an environment outside of the container and venting the air into an interior of the container at a controllable rate; and a controllable air extraction unit for extracting air from inside the container to outside the container at a controllable rate; and a controller operatively coupled to the air supply subsystem and the air extraction unit. In some embodiments, a maximum air inflow rate of fresh air into the chamber achievable by the air supply subsystem is greater than a maximum air outflow rate of air extracted from the chamber achievable by the air extraction unit, and preferably wherein the maximum air inflow rate of the air supply subsystem is at least 50% greater, more preferably at least 100% greater, than the maximum air outflow rate of the air extraction unit. Additionally or alternatively, in some embodiments, the system includes a controller, operatively coupled to the air supply subsystem and the air extraction unit, and wherein, in at least a first control mode, the controller is adapted to control the air supply subsystem and the air extraction unit in co-ordination such that a flow rate of fresh air into the chamber provided by the air supply subsystem exceeds a flow rate of air extracted from the chamber by the air extraction unit. In some embodiments, the system further includes the container in which the air distribution system is to be assembled, and wherein the container comprises one or more pressure relief dampers permitting outflow of air from the interior of the container to outside the container, for example responsive to an air pressure inside the container exceeding a threshold. It is noted and it will be appreciated that this aspect of the invention may be combined with any of the features or options described in this document in relation to the first aspect of the invention or any other aspect of the invention. In particular, at least any of the dependent claims of another aspect of this invention can be combined with the present aspect of the invention to achieve a same technical effect. As mentioned above, the interspacing of the air outflow vents to provide optimally balanced air supply to the trays is a particularly advantageous feature. This feature in isolation provides an advantageous technical effect and represents a separate aspect of the invention. . Accordingly, a further aspect of the invention is an air distribution system for an insect housing chamber defined by an interior of a transportable container unit, comprising: a primary duct unit 10 for location inside the chamber, and for extending along at least a portion of a length of the chamber, comprising at least one air flow channel 14, wherein the at least one airflow channel comprises a plurality of air outflow vents 16 distributed along a length of the channel. The system further comprises an air processing unit 20 having an inlet and outlet, and adapted to process air received at the inlet, wherein the outlet of the air processing unit is fluidly connected to the at least one air flow channel 14. The system further comprises a fresh air supply sub-system, comprising one or more secondary duct units 42a, 42b, each comprising at least one air flow channel for extending along at least a portion of a length of the container and having a plurality of air outflow vents 46 distributed along the length of the channel for venting air into an interior of the chamber. Each of the one or more secondary duct units 42a, 42b is spaced from the primary duct unit along the width dimension of the container, the width dimension being perpendicular to the length dimension of the container. The air outflow vents 16 of the primary duct unit are positioned at intervals along a length of the container unit, and the air outflow vents of the one or more secondary duct units 42a, 42b are positioned at intervals along the length of the container, and wherein the positions of the air outflow vents 16 of the primary duct unit 10 are interspaced with those of at least one of the one or more secondary duct units along the length dimension of the container. As discussed above, this alternating spacing of the fresh air and processed air outflow vents allows for optimizing air supply to larvae trays when loaded into the container beneath the various ducts. In particular, it is the realization of the inventorthat, by arranging the vents in this way, when the larvae trays are loaded in the chamber, each tray stack may be positioned (relative to a length of the chamber) in-between a fresh air vent 46 and a conditioned air vent 16, and thus supplied on one side with a fresh air flow, and one the other side with a conditioned air flow. In preferred embodiments, a spacing (separation), along the length of the container, between each air outflow vent of the primary duct unit and a next neighboring (along the length of the container) air outflow vent of at least one of the secondary duct units may be greater than or equal to the width of a single insect container stack intended for use. In some embodiments, it may be substantially equal to the width of a single insect container stack intended for use. In preferred embodiments, an interval spacing between the outflow vents of the primary duct unit and / or an interval spacing between the outflow vents of at least one of the one or more secondary duct units is greater than or equal to a width of a single tray stack which is intended to be used. The provided system may further include one or more of the insect container stacks for loading in the chamber in use. The insect containers may be larvae trays in some embodiments and the insect container stacks may be larvae tray stacks. In some embodiments, the insect container stacks may be loaded in the container in three rows, each row extending along a length of the container, each row extending parallel with both the primary duct unit and each of the secondary duct units, and wherein each row is situated beneath a respective one of the first secondary duct unit, the primary duct unit and the second secondary duct unit. In some embodiments, the chamber or container unit may include visual alignment markings or physical locating / alignment members to denote target positionings of trays. It is noted and it will be appreciated that this aspect of the invention may be combined with any of the features or options described in this document in relation to the first aspect of the invention or any other aspect of the invention. In particular, at least any of the dependent claims of another aspect of this invention can be combined with the present aspect of the invention to achieve a same technical effect. As discussed above, embodiments make use of a controller. The controller can be implemented in numerous ways, with software and / or hardware, to perform the various functions required. A processor is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the required functions. A controller may however be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs). In various implementations, a processor or controller may be associated with one or more storage media such as volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on one or more processors and / or controllers, perform the required functions. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. If the term “adapted to” is used in the claims or description, it is noted the term “adapted to” is intended to be equivalent to the term “configured to”. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An air distribution system (8) for an insect housing chamber defined by an interior ofa transportable container unit, comprising:a primary duct unit (10) for location inside the chamber, and for extending along at least a portion of a length of the chamber, comprising at least a first air flow channel (12), wherein the first airflow channel comprises a plurality of air inflow vents (18) distributed along a length of the channel for drawing air in from an interior of the chamber;an air processing unit (20) having an inlet and outlet, and adapted to process air received at the inlet;a controllable air extraction unit (32) having an inlet and outlet, the air extraction unit for extracting air received at the inlet to outside of the chamber via the outlet at a controllable flow5 rate;wherein the first air flow channel is fluidly connected to both the inlet of the air processing unit and the inlet of the air extraction unit so as to provide a fluid feed for both the air processing unit and air extraction unit.10    2.             The system of claim 1, further comprising a controller, operatively coupled to the airprocessing unit (20) and the air extraction unit (32), for controlling an air condition in the chamber.

3. The system of claim 1 or 2, wherein the plurality of air inflow vents (18) of the firstairflow channel are distributed along a section of the first air flow channel (12) between the air 15 processing unit (20) and the air extraction unit (32).

4. The system of any of claims 1-3, wherein the first air flow channel (12) has a first andsecond end, and wherein the first end of the first air flow channel is fluidly connected to the inlet of the air processing unit (20) and the second end of the first air flow channel is fluid connected to the 20 inlet of the air extraction unit (32).

5. The system of any of claims 1-4, further comprisinga first non-retum damper (18), disposed at a fluid connection between the first air flow channel (12) and the air processing unit (20), for impeding air passage from the first air flow 25 channel to the inlet of the air processing unit (20) when tire air processing unit is inactive; anda second non-retum damper (26), disposed at a fluid connection between the first air flow channel (12) and the air extraction unit, for impeding air passage from the first air flow channel to the inlet of the air extraction unit (32) when the air extraction unit is inactive.02 01 246.             The system of any preceding claim,wherein the primary duct unit (10) further comprises a second air flow channel (14), parallel with and fluidly separated from the first air flow channel (12);5                   the second airflow channel (14) comprising a plurality of air outflow vents (16)distributed along a length of the second airflow channel; andthe second airflow channel (14) fluidly connected to the outlet of the air processing unit (20).10    7.             The system of claim 6, wherein the first air flow channel (12) is stacked above thesecond air flow channel (14) or vice versa.

8. The system of claim 6 or 7, wherein the air outflow vents (16) of the second airflowchannel (14) are arranged for facing toward a floor of the chamber, and the air inflow vents (18) of 15 the first airflow channel (14) are arranged for facing sides of the chamber, or vice versa.

9. The system of any preceding claim, wherein the primary duct unit (10) is formounting to a ceiling of the container unit.20    10.           The system of any of claims 1-9, further comprising an air supply sub-system(42, 44), for supplying fresh air from outside of the chamber to an interior of the chamber.

11. The system of claim 10, wherein the air supply subsystem is fluidically separate fromthe primary duct unit (10), the air processing unit (20) and the air extraction unit (32).2512.            The system of claim 10 or 11, wherein the air supply subsystem comprises:one or more secondary duct units (42a, 42b), each comprising at least one air flow channel for extending along at least a portion of a length of the chamber and having a plurality of air outflow vents (46) distributed along the length of the channel for venting air into an interior of the30 chamber;each of the one or more secondary duct units for connection to a fresh air inlet(44a, 44b) of the container for receiving air from an environment outside of the container;one or more controllable air flow drivers being arranged for drawing air into the one or more secondary duct units (42a, 42b) from a fresh air inlet at a controllable flow rate.3513.            The system of claim 12, wherein the system includes the transportable container unit,and wherein each of the one or more secondary duct units (42a, 42b) is spaced from the primary duct02 01 24unit (10) along a width dimension of the chamber, the width dimension being perpendicular to a length dimension of the chamber.

14. The system of claim 13, wherein the air supply subsystem comprises at least two5 secondary duct units (42a, 42b), arranged either side of the primary duct unit (10).

15. The system of any preceding claim, wherein the system includes the transportablecontainer unit, and wherein the air extraction unit (32) is arranged having an air flow direction which is perpendicular to an air flow direction of the first air flow channel (12) of the primary duct unit (10), 10 and arranged in the chamber offset with respect to the first air flow channel in the width direction and wherein the primary duct unit includes a comer section to fluidly connect the first air flow channel to the air extraction unit.

16. The system of claim 15, when dependent on any of claims 12-14, wherein at least one15 secondary duct unit (42a) extends spatially parallel to the primary duct unit (10) from a first end of the chamber to a terminal point spaced from a second end of the chamber by a clearance space, and wherein at least a section of the air extraction unit (32) is disposed in said clearance space.

17. The system of any of claims 10-16, wherein at least one fresh air inlet (44) of the air20 supply subsystem unit is disposed at an opposite end of the chamber to the extraction unit outlet (36).

18. The system of any of claims 10-17, wherein a maximum air inflow rate of fresh airinto the chamber achievable by the air supply subsystem is greater than a maximum air outflow rate from the chamber achievable by the air extraction unit, and preferably wherein the maximum air 25 inflow rate of the air supply subsystem is at least 50% greater, more preferably at least 100% greater, than the maximum air outflow rate of the air extraction unit.

19. The system of claim 18, wherein the system includes a controller, operatively coupledto the air supply subsystem and the air extraction unit, and wherein, in at least a first control mode, 30 the controller is adapted to control the air supply subsystem and the air extraction unit in coordination such that a flow rate of fresh air into the chamber provided by the air supply subsystem exceeds a flow rate of air extracted from the chamber by the air extraction unit.

20. The system of any of claims 10-19, wherein the system includes the transportable35 container unit, and wherein the container unit comprises one or more pressure relief dampers (52) permitting outflow of air from the interior of the container to outside the container.02 01 2421.            The system of any of claims 10-20, wherein the system includes the transportablecontainer unit, wherein the container unit comprises one or more non-retum dampers (54) permitting inflow of air from outside the container to insider the container.5   22.           The system of claim 12, or any of claims 13-21 when dependent on claim 12,wherein the system includes the transportable container unit, and wherein the air outflow vents (16) of the primary duct unit (10) are positioned at intervals along a length of the chamber, and the air outflow vents (46) of each of the one or more secondary duct units (52a, 42b) are positioned at intervals along the length of the chamber, and wherein the positions of the air outflow vents (16) of10 the primary duct unit are interspaced with the air outflow vents of at least one of the one or more secondary duct units (42a, 42b) along the length dimension of the chamber.

23. The system of any of claims 10-22, wherein, in at least one control mode, thecontroller is adapted to control the air supply subsystem in co-ordination with the air extraction unit15 such that the air within the chamber is fully replaced at a rate of at least 15 air changes per hour.

24. The system of any preceding claim, further comprising a plurality of insect containerstacks (64), each stack comprising a plurality of containers (72) stacked vertically atop one another, the container stacks for being supported by a floor of the container.2025.           The system of claim 24 when dependent on claim 12, wherein an interval spacingbetween the air outflow vents (16) of the primary duct unit (10) and / or an interval spacing between the air outflow vents (46) of at least one of the one or more secondary duct units (42a, 42b) is greater than or equal to a width of a single container stack (74).2526.           The system of claim 25 when dependent on claim 12, wherein the system includes thetransportable container unit, and wherein each insect container stack (74) is aligned along the length dimension of the chamber with a point disposed in-between a primary duct outflow vent (16) and a secondary duct outflow vent (46).3027.           The system of any of preceding claim, wherein:the system comprises a controller, operatively coupled to the air processing unit (20) and the air extraction unit (32);the system comprises a set of air sensors for sensing one or more characteristics of air 3 5 inside the chamber; and02 01 24wherein the controller is configured to regulate an air condition inside the chamber based on control of at least an extraction flow rate of the air extraction unit and control of the air processing unit, and based on input signals received from the one or more sensors.5   28.           The system of claim 27 when dependent on claim 10,wherein the controller is configured to regulate an air condition inside the chamber further based on control of a flow rate of fresh air supplied into the chamber by the air supply subsystem.10   29.           The system of claim 27 or 28, wherein the system comprises a set of outdoor airsensors for sensing one or more characteristics of an air outside the chamber, and wherein the regulation of the air condition inside the chamber is performed further dependent upon input signals from the set of outdoor air sensors.15    30.            The system of any of claims 10-29 , wherein the system includes a controller,operatively coupled to the air supply subsystem and the air extraction unit wherein the controller is configured to:determine a target internal temperature for air inside the chamber;obtain a measurement of a temperature of an environment outside of the chamber;20                  compare the target internal temperature with the measurement of the temperatureoutside of the chamber to determine a difference between the two temperatures; andset a flow rate of fresh air supplied into the chamber by the air supply subsystem in dependence upon a result of said comparison, wherein the air inflow rate of the air supply subsystem is set at a greater level where the difference between the temperatures is less, and is set at a lower25 level where the difference between the temperatures is greater.

31. A kit of parts, comprising:a transportable container unit; andthe system of any of claims 1-30 in an unassembled or partially assembled state.3032.           An insect housing module, comprising:a transportable container unit, an interior thereof defining an insect housing chamber; andan air distribution system of any of claims 1-30 assembled within the insect housing3 5 chamber.

33. Use of an air distribution system as claimed in any of claims 1-30 for insect farmingpurposes.

34. A method, comprising assembling an air distribution system as claimed in any of5 claims 1-30 within a transportable container unit.CXICXI