Temperature controlled storage and retrieval system

Abstract

A temperature controlled automated storage and retrieval system comprising a tracked 46 and grided arrangement on which at least one robotic load handling device 30 operates, comprises container stora

Description

TECHNICAL FIELD The present invention relates to the field of an automated storage and retrieval system, more specifically to a temperature controlled automated storage and retrieval system comprising a storage area for the storage of storage containers and robotic load handling devices operative in the storage area for handling the storage containers. BACKGROUND Some commercial and industrial activities require systems that enable the storage and retrieval of a large number of different products. One known type of an automated storage and retrieval system (ASRS) for the storage and retrieval of items in multiple product lines is a grid-based storage and retrieval system in which storage containers (also known as bins or totes) are arranged in stacks on top of one another, the stacks being arranged in rows. The storage containers are removed from the stacks and accessed from above by load handling devices, removing the need for aisles between the rows and thereby allowing a large number of containers to be stored in a given space. As shown in Figures 1 and 2, the storage containers 10, also known as bins or totes, are stacked on top of one another to form stacks 12. The stacks 12 are arranged in a grid framework structure 14 in a warehousing or manufacturing environment. The grid framework is made up of a plurality of storage columns or grid columns 11. Each grid in the grid framework structure has at least one storage column 11 for storage of a stack of containers. Figure lisa schematic perspective view of the grid framework structure 14, and Figure 2 is a top-down view showing a single stack 12 of containers 10 arranged within the framework structure 14. Each container or tote 10 typically holds a plurality of product items (not shown), and the product items within the storage container 10 may be identical, or may be of different product types depending on the application. Each storage container 10 may be used to store grocery items (i.e. food items), for example. Furthermore, the storage containers 10 may be physically subdivided to accommodate a plurality of different inventory items. The grid framework structure 14 comprises a plurality of upright members or upright columns 16 that support horizontal members 18, 20. A first set of parallel horizontal grid members 18 is arranged perpendicularly to a second set of parallel horizontal grid members 20 to form a grid structure lying in a substantially horizontal plane and supported by the upright members 16. The members 16, 18, 20 are typically manufactured from metal and typically welded or bolted together or a combination of both. The storage containers 10 are stacked between the upright members 16 of the grid framework structure 14, so that the grid framework structure 14 guards against horizontal movement of the stacks 12 of the storage containers 10, and guides vertical movement of the storage containers 10. The top level of the grid framework structure 14 includes a track system 15 comprising a plurality of rails or tracks 22 arranged in a grid pattern across the top of the stacks 12. Referring additionally to Figure 3, the rails 22 support a plurality of load handling devices or robotic load handling devices 30. A first set 22a of parallel rails 22 guide movement of the robotic load handling devices 30 in a first direction (for example, an X-direction) across the top of the grid framework structure 14, and a second set 22b of parallel rails 22, arranged perpendicular to the first set 22a, guide movement of the load handling devices 30 in a second direction (for example, a Y-direction), perpendicular to the first direction. In this way, the rails 22 allow movement of the robotic load handling devices 30 laterally in two dimensions in the horizontal X-Y plane, so that a load handling device 30 can be moved into position above any of the stacks 12. The track system 15 can be integrated into the grid structure in the sense that the first and second sets of tracks are respectively integrated into the first and second set of grid members. Alternatively, the track system 15 can be separate to the grid structure in the sense that the first and second sets of tracks are respectively mounted to the first and second sets of grid members. Each load handling device 30 comprises a vehicle body 32 which is arranged to travel in the X and Y directions on the tracks or rails 22 of the grid frame structure 14, above the stacks 12 (see Figure 4). Figures 4 and 5 shows a load handling device 30 described in PCT Patent Publication No. WO2015 / 019055 (Ocado Innovation Limited) and International patent application WO 2015 / 140216 (Ocado Innovation Limited) comprising a vehicle body 32 equipped with a lifting mechanism 33 comprising a winch or a crane mechanism 35 to lift a storage container or bin 10, also known as a tote, from above. The crane mechanism 35 comprises a winch cable 38 wound on a spool or reel and a grabber device 39. Typically, the lifting device comprises a set of lifting tethers 38 extending in a vertical direction and connected nearby or at the four corners of the grabber device 39 (one tether near each of the four comers of the grabber device) for releasable connection to a storage container 10. The grabber device 39 is configured to grip the top of the storage container 10 and lift it from a stack of containers in a storage system of the type shown in Figures 1 and 2. Typically, the grabber device 39 is configured as a lifting frame. To grab a container 10, the grabber device 39 comprises four locating pins or guide pins nearby or at each corner of the grabber device 39 which mate with corresponding cut outs or holes formed at four corners of the storage container 10 and four gripper elements arranged at the bottom side of the grabber device 39 to engage with the rim of the storage container 10. The locating pins help to properly align the gripper elements with corresponding holes in the rim of the container. Each of the gripper elements comprises a pair of wings or legs that are collapsible to be receivable in corresponding holes in the rim of the storage container and an open enlarged configuration having a size greater than the holes in the rim of the storage container 10 in at least one dimension so as to lock onto the storage container 10. The wings are driven into the open configuration by a drive gear (not shown). More specifically, the head of at least one of the wings comprises a plurality of teeth that mesh with the drive gear such that when the gripper elements are actuated, rotation of the drive gear causes the pair of wings to rotate from a collapsed configuration to an open enlarged configuration. The vehicle body 32 comprises an upper part and a lower part (see Figure 5 (a and b)). The lower part is fitted with two sets of wheels 34, 36, which run on rails at the top of the framework structure of the storage system. The upper part of the vehicle body 32 may house a majority of the bulky components of the load handling device. Typically, the upper part of the vehicle body houses a driving mechanism for driving both the wheels and the lifting mechanism together with an on-board rechargeable power source for providing the power to the driving mechanism and the lifting mechanism. The lower part of the vehicle body 32 comprises a wheel assembly that is are driven to enable movement of the vehicle in X and Y directions respectively along the rails. A first set of wheels 34, consisting of a pair of wheels 34 on the front of the vehicle 32 and a pair of wheels 34 on the back of the vehicle 32, are arranged to engage with two adjacent rails of the first set 22a of rails 22. Similarly, a second set of wheels 36, consisting of a pair of wheels 36 on each side of the vehicle 32, are arranged to engage with two adjacent rails of the second set 22b of rails 22. One or both sets of wheels can be moved vertically to lift each set of wheels clear of the respective rails, thereby allowing the vehicle to move in the desired direction. When the first set of wheels 34 is engaged with the first set of tracks or rails 22a and the second set of wheels 36 are lifted clear from the tracks or rails 22, the wheels 34 can be driven, by way of a drive mechanism (not shown) housed in the vehicle 32, to move the load handling device 30 in the X direction. To move the load handling device 30 in the Y direction, the first set of wheels 34 are lifted clear of the tracks or rails 22, and the second set of wheels 36 are lowered into engagement with the second set of tracks or rails 22a. The drive mechanism can then be used to drive the second set of wheels 36 to achieve movement in the Y direction. One or both sets of wheels can be moved vertically to lift each set of wheels clear of the respective rails, thereby allowing the vehicle to move in the desired direction on the track system. The wheels are arranged around the periphery of a cavity or recess, known as a containerreceiving recess 40, in the lower part. The recess 40 is sized to accommodate the storage container or bin 10 when it is lifted by the crane mechanism comprising a winch, as shown in Figure 5 (a and b). When in the recess, the container is lifted clear of the rails beneath, so that the load handling device can move laterally to a different location. Whilst the container receiving space 40 is shown in Figure 4 arranged within the vehicle body 32, the container receiving space can be located below a cantilever as described in WO2019 / 23 8702 (Autostore Technology AS). Upon receipt of a customer order, a robotic load handling device operative to move on the tracks is instructed to pick up a storage bin containing the item of the order from a stack in the grid framework structure and transport the storage bin to a pick station whereupon the item can be retrieved from the storage bin. Typically, the load handling device transports the storage bin or container to a bin lift device that is integrated into the grid framework structure. A mechanism of the bin lift device lowers the storage bin or container to a pick station. Alternatively, the storage bin is lowered by the lifting mechanism of the robotic load handling device to the pick station. A grid framework structure normally has at least one grid cell or storage column which is used not for storing storage containers, but which comprises a location where the load handling devices can drop off and / or pick up storage containers so that they can be transported to a second location (not shown in the prior art figures) where the storage containers can be accessed from outside of the grid framework structure or transferred out of or into the grid framework structure. Within the art, such a location is normally referred to as a “port” and the grid cell or storage column in which the port is located may be referred to as a “delivery column”. The storage columns typically comprise two delivery columns. A first delivery column may, for example, comprise a dedicated drop-off port where the robotic load handling vehicles or load handling vehicles can drop off storage containers to be transported through the delivery column and further to the pick station, and a second delivery column may comprise a dedicated pick-up port where the robotic load handling vehicles can pick up storage containers that have been transported through the second delivery column from the pick station, i.e. storage containers are fed into the pick station via the first delivery column and exit the access station via the second delivery column. At the pick station, the item is retrieved from the storage bin. Picking can done manually by hand or by a robot. After retrieval from the storage bin, the storage bin is transported to a second bin lift device whereupon it is lifted to grid level to be retrieved by a load handling device and transported back into its location within the grid framework structure. Alternatively, the storage bin can be picked up by the lifting mechanism of the robotic load handling device through the pick-up port. A control system and a communication system keeps track of the location of the storage bins and their contents within the grid framework structure. As individual storage containers are stacked in vertical layers in storage columns, their locations in the grid framework structure or “hive” may be indicated using co-ordinates in three dimensions to represent the load handling device or a container’s position and a container depth (e.g. container at (X, Y, Z), depth W). Equally, locations in the grid framework structure may be indicated in two dimensions to represent the load handling device or a container’s position and a container depth (e.g. container depth (e.g. container at (X, Y), depth Z). For example, Z=1 identifies the uppermost layer of the grid, i.e. the layer immediately below the rail system, Z=2 is the second layer below the rail system and so on to the lowermost, bottom layer of the grid. To erect the grid framework structure in the art, a plurality of vertical uprights are individually positioned one piece at a time in a grid-like pattern on the ground. The assembling of individual vertical uprights together one piece at a time is sometimes referred to as a “stick-built” structure. The “stick-built” approach of the assembling the grid framework structure requires numerous time-consuming adjustments to be made for reliable operation of the robotic load handling devices on the tracks. The height of the vertical uprights and thus the level of the grid mounted thereon is adjusted by one or more adjustable feet at the base or bottom end of each of the vertical uprights. A sub-group of the vertical uprights are braced together to provide structural stability to the grid framework structure. The vertical uprights are interconnected at their top ends by grid members so that the grid members adopt the same grid pattern as the vertical uprights, i.e. the vertical uprights support the grid members at the point or node where each of the grid members intersect in the grid pattern. For the purpose of explanation of the present invention, the points or junctions where the grid members intersect or are interconnected constitute the nodes of the track system and correspond to the area where the track system is supported by a vertical upright. The resultant grid framework structure can be considered as a free standing rectilinear assemblage of upright columns supporting the grid formed from intersecting horizontal grid members, i.e. a four wall shaped framework. The arrangement of the vertical uprights provides multiple vertical storage columns for the storage of one or more containers in a stack. The vertical uprights help to guide the grabber device of the lifting mechanism as the grabber device engages with a container within the grid framework structure and is lifted towards the load handling device operative on the grid. The size of the grid framework structure and thus the ability to store containers containing different items or stock keeping units (SKUs) is largely dependent on the number of vertical uprights spanning over a given footprint of the grid framework structure. However, one of the biggest bottlenecks in the building of a fulfilment or distribution centre is the erection of the grid framework structure. The time and cost to assemble the grid framework structure represents a huge proportion of the time and cost to build a fulfilment or distribution centre. The biggest and the most time consuming operation involves erecting the vertical uprights individually and fixing the track system to the vertical uprights. As electronic commerce (e-commerce) continues to grow and overtake conventional brick and mortar retail practices, many businesses are facing challenges of maintaining or gaining relevance in an online marketplace and being able to compete with prominent players in the space. A typical supply chain involves the storage and retrieval of a large number of different products. For example, e-commerce and retail platforms that sell multiple product lines require systems that are able to provide a storage area where hundreds of thousands of different product lines having different temperature storage requirements may be stored. Different product items need to be maintained at different prescribed temperatures within the storage area, while the product items are stored and / or transported, and / or while orders are fulfilled. Some product items need to be maintained in a chilled or frozen environment to ensure freshness, while other product items can be stored or transported at ambient temperature. For example, where an order of one or more items involves the delivery of food and grocery goods that are of a perishable nature, storage of goods must adhere to strict temperature and environmental requirements, e.g. chilled or frozen temperature. For example, some types of food require a chilled temperature environment (typically temperatures between 1°C to 8°C), some types of food require an even colder temperature environment (typically temperatures lower than -15°C), and other types of food require a higher temperature environment (typically temperatures above 10 °C). Conventional multi-temperature storage and retrieval systems typically require a separate walk-in cooler or freezer to be pre-constructed or additional components to be installed around the existing storage and retrieval system discussed above, which substantially expands the footprint of the storage and retrieval system and increases the cost and complexity of installing and operating the storage and retrieval system across multiple environmentally controlled zones. As a result, there has been a need for a freestanding, high density, automated storage and retrieval system with multiple integrated, environmentally controlled zones that removes the need of separate walk-in, environmentally controlled zones that operate independently of the storage and retrieval system. In an attempt to adapt an existing automated grid based storage and retrieval system to provide storage for temperature sensitive items, e.g. chilled or frozen items, WO2015124610 (Autostore Tech AS) relates to a storage system for receiving and storing processed refrigerated and frozen food products where there is provided thermal insulation between at least a section of the grid structure and the remotely operated vehicle. The system comprises insulating covers arranged in the top level of the grid structure. The insulating covers provide a thermal barrier towards the remotely operated vehicle as well as contributing to maintaining the desired temperature in the bins in the grid structure. The insulating covers are arranged to be movable by means of the remotely operated vehicle. The vehicle can move one insulating cover to another cell in the grid, or hold it temporarily while a bin is removed from the stack. WO2021198170 (Autostore Tech AS) relates to an automated storage and retrieval system for storing specialized goods in storage containers in an isolating housing, having walls and a roof. Openable and closable hatches are arranged in the roof. A storage tower is arranged inside the isolating housing such that the storage tower being accessible to a container handling vehicle though the hatch. The storage tower has a number of vertically stacked, horizontally movable container supports in the form of shelves upon which may rest a plurality of storage containers and one or more openings corresponding in size to a storage container such that storage containers may pass therethrough. The container supports may align their openings to form a tower port beneath a hatch, through which the container handling vehicle may lower its lifting device though the hatch, down the tower port, and access the target container. In both teachings, there is a requirement that the thermal insulation covering of the grid cell has to be removed or moved aside so that a container handling vehicle operating on the grid structure is able to gain access to one or more storage containers in storage. Not only does this introduce an additional step when retrieving storage containers from the storage system but there is no guarantee that the thermal insulation covers of the grid cells will provide adequate insulation to prevent the ingress of warmer air into the grid structure from the ambient region above the grid structure. However, the use of thermal insulation covers for each of the grid cells introduces an additional complexity of the need to be easily removal in order to gain access to one or more storage container in storage in the grid structure. To mitigate this problem, a fleet of robotic load handling devices are disposed in a chilled, or freezer environment. In these facilities, the robotic load handling devices reside and operate in the chilled or freezer environment on a full-time basis. Whilst having a fleet of load handling devices operating in the chilled or freezer environment on a full-time basis automates the storage and retrieval of storage containers from the storage system, there will be occasions where one or more load handling devices would have to be taken out service. This could be as a result of a breakdown or malfunction of the load handling device or simply the need to service the load handling device. In both cases, access to the load handling device would be required by maintenance personnel. However, in the case where the load handling device resides in the freezer environment, which can be low as -30°C, this introduces another problem of the health and safety of the maintenance personnel working at such low temperatures. WO2021209648 (Ocado Innovation Ltd) teaches a multi-temperature storage system comprising temperature-control means configured to maintain a first-temperature region within the storage structure at a first temperature and a second-temperature region within the storage structure at a second temperature. The temperature-control means includes a temperaturecontrol plant or chill plant and tubing providing a closed loop along which temperature-control fluid is configured to flow from the temperature-control plant to the first- temperature region within the storage structure and from the first-temperature region within the storage structure to the temperature-control plant. In an embodiment of WO2021209648 (Ocado Innovation Ltd), the tubing comprises outbound ducting having multiple branches which diverge from a single outlet of the chill plant that direct chilled air from the chill plant to different regions in the storage structure. For example, one branch of the outbound ducting may direct chilled air from the chill plant to the top of a stack of containers via an outlet of the ducting. The chilled air may then descend to the bottom of the stack, chilling the products in the containers in the stack. Multiple branches of the ducting may in some examples be directed to the same region. To accommodate the tubing within the grid framework, the tubing is arranged to extend through 5 one or more storage columns reducing the storage capacity of the grid framework structure. To mitigate occupying valuable storage space in the grid framework structure, in another embodiment of WO2021209648 (Ocado Innovation Ltd), the tubing is located within and extends along the vertical uprights which support the track system to transfer a chilled fluid from the chill plant to one or more regions of the storage structure. However, locating the 10 tubing within the vertical uprights not only limits the exposure of the tubing within the storage structure but also limits the flexibility of distributing the chilled fluid within the storage structure to the warmer regions of the storage structure. In an attempt to mitigate this problem, it is necessary that the tubing has a complicated arrangement of straight sections and helical sections, the helical sections providing a greater exposure of the chilled fluid. 15 Thus, there is a need for an automated storage and retrieval system for storing frozen or chilled items without the shortcomings discussed above. SUMMARY OF THE INVENTION In comparison to a forced convention type cooling system in which cool air from a chill plant is blown into the storage area of an automated storage and retrieval system, cooling within the storage area according to the present invention is largely by radiant cooling. Radiant cooling is the use of cooled surfaces in the form of a network of tubes or tubing carrying a heat transfer fluid or refrigerant to remove heat primarily by thermal radiation and only secondarily by other methods such as convection. Radiant cooling systems remove the need for a blower and therefore, offers the potential of lower energy consumption than conventional cooling systems known in the art such as forced convection type cooling systems. The cooled surfaces are largely provided by a network of tubes carrying a heat transfer fluid or refrigerant coupled to a cooling unit such as a refrigerator comprising a compressor, a condenser, a refrigerant expansion element and an evaporator. The evaporator is in form of the network of tubing extending through the storage area of the ASRS to exchange heat with the surrounding air in the storage area. It will be appreciated that the storage area in the ASRS is not limited to a gridbased framework structure discussed above, the present disclosure can be adapted to interact with other forms of ASRSs. These include but is not limited to an aisle-based storage and retrieval systems, a rack-based storage and retrieval system operated with an automatic guided vehicle (AGVs) or autonomous mobile robot (AMR) or other material handling system known in the art. As the environment within the storage area is largely static and is primarily disrupted by the movement of the storage containers within the storage area, any forced movement of air besides convection within the storage area is usually minimum. Air cooled by radiant cooling in the upper portion of the storage area is denser and sinks towards the lower portion of the storage area to be replaced by the raising warmer air. This process continues, creating convection air currents that transfers heat through the air within the storage area. Thus, the one or more storage containers and their contents in the lower portion of the storage area are kept cool by the cool air descending from the upper portion to the lower portion of the storage area. However, as the temperature of the air surrounding the cooling surfaces, namely, the network of tubes drops below the dew point temperature of the surrounding air in the storage area, moisture in the air has a tendency to condense on the network of tubes. The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point, the air cannot hold more water in the gas or vapour form and result in the condensation of water vapour in the air. To achieve a chilled temperature which is typically operates in the region of 1°C to 8°C or freezing temperature which is typically operates in the region -30°C to -18°C, the heat transfer fluid in the tubes flows at a temperature below the freezing point of water. As a result, water vapour in the air that has condensed on the surface of the cooling tubes has a tendency to freeze to the extent that ice builds up on the surface of the tubes. Since ice is a relatively good heat insulator, ice and frost accumulated on the network of tubes carrying the heat transfer fluid reduces the efficiency and effectiveness of the network of tubes to further cool the surrounding air by radiant cooling. Since water vapour in the air is carried by the convective air currents, the build-up of ice largely occurs on the cooling tubes in the upper portion of the storage area resulting in a disproportionate amount of ice building up on the network of tubes in the upper portion than in the lower portion of the storage area. Moreover, heat and therefore, moisture, can also enter the storage area, particularly in the upper portion of the storage area external of the storage area which is subsequently exchanged by the network of tubing carrying the heat transfer fluid extending within the storage area. To mitigate this problem in the present disclosure, a defrost system or heating system is provided to defrost ice that has accumulated on at least a portion of the cooling tubes and the melted ice is drained away. To melt at least portion of the ice accumulated on the at least portion of the network of tubing, the present disclosure applies a defrost cycle to the at least portion of the network of tubing. In one example of the defrost cycle, feeding of the compressed refrigerant to the network of tubing can be temporarily interrupted and hot heat transfer fluid or refrigerant is directed to the at least portion of the network of tubing to defrost ice that has accumulated on the surface of the at least portion of the network of tubing. The flow of the warmer heat transfer fluid is subsequently stopped and the circulation of the compressed heat transfer fluid is continued through the condenser and the refrigerator can continue to operate in a refrigeration mode. Alternatively, or in addition to feeding a hot heat transfer fluid in the network of tubing, a defrost electric heater can be employed to thaw or defrost the ice that has accumulated on the at least portion of the network of tubing. To enable a defrost cycle to be incorporated into the cooling cycle of the network of tubing, the present disclosure provides a temperature controlled automated storage and retrieval system, comprising:- A) a storage area for the storage of a plurality of storage containers and one or more robotic load handling devices for moving one or more of the plurality of storage containers through the storage area; B) a cooling system comprising at least one cooling unit and a closed network of tubing in fluid communication with the at least one cooling unit to circulate the heat transfer fluid from the at least one cooling unit to the closed network of tubing via a common feed inlet and back to the at least one cooling unit via a common return inlet, at least a portion of the closed network of tubing extends in the storage area for circulating a heat transfer fluid to exchange heat with a portion (e.g. surrounding air) of the storage area; wherein the cooling system further comprises a defrost system and a controller operatively coupled to the defrost system to control the temperature of the at least portion of the closed network of tubing in response to the thickness of ice on the at least portion of the network of tubing being equal to or above a predetermined thickness. By controlling the temperature of the at least portion of the network of tubing in the storage area, the system can improve the effectiveness of the cooling system to adequately cool the air in the storage area to a predetermined storage temperature. For the purpose of definition of the present invention, the predetermined temperature can be a chilled temperature zone which operates in the temperature range 1°C to 8°C or a freezer temperature zone which operates in the temperature range -30°C to -18°C. Moreover, as ice accumulates onto at least portion of the network of tubing, moisture is taken away from the air in the storage area. To mitigate the build-up of ice on at least portion of the network of tubing and thereby, control the temperature of the storage area, the cooling system comprises a defrost system and a controller operatively coupled to the a defrost system to control the temperature of the at least portion of the network of tubing in response to the thickness of ice on at least a portion of the network of tubing being equal to or above a predetermined thickness. For the purpose of definition of the present disclosure, the thickness of the ice can be construed to mean the cross-sectional thickness of the ice on the tube carrying the heat transfer fluid. Considering that the storage area typically operates in an enclosed environment at a substantially constant pressure, moisture that is taken away from the surrounding air results in the absolute humidity expressed as a measure of the actual amount of water vapour in the air in the storage area to begin to fall. Since warmer air tend to carry more moisture due to convective air currents, moisture that is taken out of the surrounding air in the storage area sinks to the lower portion of the storage area. At any given time, the absolute humidity in the lower portion of the storage area will be different to the absolute humidity in the upper portion of the storage area. As moisture is largely taken out of the air in the upper portion of the storage area, the upper portion of the storage area can be defined as the dehumidifying zone and the lower portion of the storage area can be defined as the storage zone suitable to store one or more storage containers at the predetermined temperature. Optionally, the at least portion of the network of tubing comprises at least one distribution circuit comprising a first branch of tubes and a second branch of tubes, said first branch of tubes extends in the upper portion of the storage area and the second branch of tubes extends in the lower portion of the storage area, said defrost system being operable to independently control the temperature of the first branch of tubes or second branch of tubes. Optionally, the defrost system further comprises a control valve operatively coupled to the controller to independently control the flow of the heat transfer fluid to the first or second branch of tubes. By independently controlling the temperature of the first branch of tubes or the second branch of tubes the cooling system can operate as a dehumidifier without the need for a separate dehumidifier. As a result, one or more robotic load handling devices can operate in a relatively stable temperature environment in comparison to the environment when moving across different temperature zones to and from the storage area and yet be able to access storage containers stored in the storage area. This increases the longevity of the one or more load handling devices operative in the storage area at low temperatures, in particular the charge held by the battery. Other benefits include preventing one or more areas of the robotic load handling device suffering from the effects of condensation when moving from a cold environment to a warmer environment when trying to access storage containers stored in the storage area. In some instances, the condensation risk of moving a robotic load handling device from a cold area to a warmer area may affect one or more electrical components of the robotic load handling device. For example, condensation can lead to electrical shorting and / or bad electrical contacts. Both effects can compromise the reliability of the respective circuitry and / or can even lead to the destruction of the circuitry or at least one of components of the circuitry. Furthermore, condensation will lead to corrosion effects, shortening the lifetime of the circuitry and / or the build-up of moisture on the robotic load handling devices. The controller can comprise one or more processors and memory storing instructions that when executed by the one or more processors cause the one or more processors to actuate the defrost system to independently control the temperature of the at least portion of the network of tubing. There are numerous ways according to the present disclosure in which the temperature of at least portion of the network of tubing can be changed. One approach would be to operate the at least one cooling unit under an off-cycle defrost or an air defrost cycle and involves switching off the power to the compressor for a predetermined duration of time removing any refrigeration in the storage area and causing the temperature of the heat transfer fluid to increase, thereby allowing the surrounding air to naturally melt the ice accumulated on the at least portion of the network of tubing. This process is effective if the ambient temperature is above the freezing point of water. Optionally, the temperature of at least portion of the network of tubing can be increased by applying one or more electric heating elements to the at least portion of the network of tubing, i.e., the defrost system comprises one or more electric heating elements. Electric power is supplied to the one or more electric heating elements to increase the temperature of at least a portion of network of tubing. Optionally, the at least one cooling unit comprises a compressor and a condenser coil in fluid communication with said compressor, said network of tubing is in fluid communication with the condenser coil through a refrigerant expansion element and the compressor via a compressor return line, wherein the heat transfer fluid is circulatable to at least portion of the network of tubing via the condenser coil and the refrigerant expansion element to define a refrigeration mode. To defrost ice that has accumulated on at least portion of the network of tubing, the at least one cooling unit can operate in reverse mode otherwise known as the hot gas defrost cycle. In the hot gas defrost cycle, the defrost system further comprises a defrost circuit line in which the heat transfer fluid is directly circulatable to the at least portion of the network of tubing by the compressor to define a defrost mode for defrosting the at least portion of the network of tubing. The change in temperature of the at least portion of the network of tubing can be automated in response to a control signal indicative of the thickness of ice on at least portion of the network of tubing being equal to or above a predetermined thickness. For example, a predetermined thickness of greater than 1mm can trigger the defrost cycle of at least portion of the network of tubing. Optionally, 1mm <R >20mm. Optionally, the cooling system further comprises at least one sensor for determining the thickness of ice on the at least a portion of the network of tubing, said controller being configured to actuate the defrost system to control the temperature of the at least portion of the network of tubing in response to a signal from the sensor indicative of the thickness of the ice on the at least portion of the network of tubing being equal to or above a predetermined thickness. Since ice has a tendency to initially accumulate on the first branch of tubing extending in the upper portion of the storage area, the sensor is configured to determine the thickness of ice on the first branch of tubes. Optionally, the sensor could be a photoelectric sensor comprising a transmitter and a receiver. The signal from the transmitter is interrupted as a result of the thickness of ice on the tubing being above a predetermined thickness. Alternatively, or in addition to the photelectric sensor, the thickness of the ice can be determined by use of an ultrasonic sensor through the time taken for an ultrasonic wave transmitted by a transmitter through the ice to be received by a receiver of the ultrasonic sensor. To independently control the temperature of the first and second branch of tubes, the cooling system can be configured to bypass the second branch of tubes to the at least one cooling unit. For example, the bypass enables warmer heat transfer fluid to flow through the first branch of tubes prior to returning to the at least one cooling unit via the common return inlet. Optionally, the defrost system comprise a control valve interposed between the first branch of tubes extending the upper portion of the storage area and the second branch of tubes extending in the lower portion of the storage area, said control valve being configured to independently control the flow of the heat transfer fluid in the first or the second branch of tubes. For example, the controller can be configured to actuate the control valve to bypass the second branch of tubes to the cooling unit. The control valve separates the first branch of tubes from the second branch of tubes. To bypass the second branch of tubes, optionally, the network of tubing comprises a bypass portion in fluid communication with the control valve, said bypass portion being configured to bypass the second branch of tubes to the at least one cooling unit via the common return inlet. To switch between the heat transfer fluid flowing through the second branch of tubes or the bypass portion, optionally, the control valve is a three-way valve having a first open state to permit the flow of the heat transfer fluid to the second branch of tubes and a second open state to permit the flow of the heat transfer fluid to the at least one cooling unit via the bypass portion. The different open states of the three-way valve can be actuated by the controller to allow the heat transfer fluid to flow in the second branch of tubes when returning to the at least one cooling unit or the bypass the second branch of tubes when in the second open state. To prevent heat transfer fluid flowing into the at least one cooling unit when in the second open state of the three-way valve, optionally, the defrost system comprises a second control value fluidly connected to the control valve, said second control valve being operable to control the return flow of the heat transfer fluid to the at least one cooling unit from the second branch of tubes via the common return inlet. Like the control valve, the second control valve can optionally comprise a three-way valve having a first open state to permit the heat transfer fluid to flow to the at least one cooling unit via the second branch of tube and a second open state to permit the heat transfer fluid to flow to the at least one cooling unit via the bypass portion such that in the second open state of the control valve and the second control valve, the network of tubing bypasses the second branch of tubes to the at least one cooling unit. To distribute the network of tubing within the storage area and thereby, improve the cooling capacity of the cooling system to cool the environment within the storage area, optionally, the at least one distribution circuit comprises a plurality of distribution circuits, each of the plurality of the distribution circuits comprising a respective first branch of tubes extending in the upper portion of the storage area and a respective second branch of tubes extending in the lower portion of the storage area. To circulate the heat transfer fluid from the at least one cooling unit to each of the plurality of distribution circuits via the common feed inlet and back to the at least one cooling unit via the common return inlet, optionally, the plurality of the distribution circuits are connected in parallel, and wherein the first branch of tubes of each of the plurality of circuits are fluidly connected to the common feed inlet by an infeed manifold and second branch of tubes of each of the plurality of circuits are fluidly connected to the common return inlet by a return manifold. In another optional aspect of the present disclosure, the at least one cooling unit comprises a first cooling unit and a second cooling unit, the closed network of tubing comprising a first closed branch of tubing in fluid communication with the first cooling unit and a second closed branch of tubing in fluid communication with the second cooling unit, at least a portion of the first closed branch of tubing extending in the upper portion of the storage area and at least a portion of the second closed branch of tubing extending in the lower portion of the storage area. Independent control of the temperature of the first and second closed branch of tubing can be achieved by having separate cooling units rather than a single cooling unit, wherein each of the first and second cooling units being configurable to supply the heat transfer fluid to their respective first and second closed branch of tubing at different temperatures. Optionally, the defrost system comprises a first control valve and a second control valve, said controller being operable to selectively actuate the first control valve independently of the second control valve so as to independently control the flow of the heat transfer fluid in the first closed branch of tubing and the second closed branch of tubing. The first and second control valves can be controlled by the controller to separately allow the heat transfer fluid to flow in the first or the second closed branch of tubing at different temperatures, thereby, allowing the temperature of the first or the second closed branch of tubing to be independently controlled. To increase the cooling surface area of the network of tubing to exchange heat with the surrounding air in the storage area, optionally, at least portion of the network of tubing comprises a plurality of sets of parallel tubes, each set of the plurality of sets of parallel tubes extending substantially horizontally in the storage area. As warmer air rises in the storage area due to convective air currents, to regulate the temperature of the air in the storage area according to the present disclosure, ideally the cooling capacity of the first branch of tubing extending in the upper portion of the storage area is greater than the cooling capacity of the second branch of tubing extending in the lower portion of the storage area. To increase the cooling capacity in the upper portion of the storage area, optionally, the cooling surface area of the first branch of tubing is greater than the cooling surface area of the second branch of tubing. There are various ways to increase the cooling surface area of the least portion of the network of tubing in the storage area. The simplest approach would be to increase the proportion of the network of the tubing in the storage area. Another approach according to the present disclosure would be to, optionally, have at least a portion of the network of tubing comprise one or more finned tubes, each of the one or more finned tubes comprises a plurality of spaced apart fins extending longitudinally along an outer surface of at least portion of the networking of tubing. The one or more fins extends outwardly from the surface of the tube provides an additional cooling surface in addition to the cooling surface of the tube. Moreover, the use of the finned tube reduces the number of tubing required to provide the same cooling capacity as conventional non-finned tubes. As less tubing is required to provide the same cooling capacity, the storage capacity of the storage area is increased. To capture the water melted on at least portion of the network of tubing when the cooling system is operated in the defrost mode, the cooling system further comprises a run-off system, said run-off system comprising a network of gutters extending substantially longitudinally along the at least portion of the network of tubing. Water captured by the run-off system when operating the cooling system in the defrost mode is taken to a location external of the storage area. Optionally, the run-off system comprises a downpipe having an inlet opening for capturing fluid from the network of gutters and an outlet opening external of the storage area. Whilst cooling by radiant cooling can operate in a static system, to increase the convective air currents and thus, the rate of heat exchange of heat in the storage area with the network of tubing extending in the storage area, optionally, the cooling system further comprises an air circulating system to create a degree of air turbulence in the storage area. Optionally, the air circulating system comprises at least one fan for circulating air from the lower portion of the storage area to the upper portion of the storage area. Optionally, the cooling system according to the present disclosure can be used in a grid based ASRS comprising a grid framework structure to define the storage area, said grid framework structure compri sing:- a) a supporting framework structure comprising a plurality of storage columns to define the storage area, each of the plurality of storage columns being arranged to accommodate the plurality of storage containers in one or more stack of storage containers, wherein at least a portion of the closed network of tubing is arranged to extend between two or more storage columns; b) a track system for guiding the movement of the one or more robotic load handling devices on the grid framework structure, the track system being mounted to the supporting framework structure and comprising a plurality of tracks arranged in a grid pattern to form a plurality of grid cells extending across the plurality of the storage columns. Optionally, the supporting framework structure comprises a load bearing assembly of supporting walls arranged in a three-dimensional grid pattern comprising a plurality of modular storage cells for the storage of a plurality of stacks of storage containers, said at least one of the supporting walls is a thermally insulating panel. In comparison to a “stick-built” approach of constructing the supporting framework structure, the supporting framework structure according to the present invention is formed from a load bearing assembly of supporting walls that are arranged in a three-dimensional grid pattern comprising a plurality of modular storage cells. Each of the plurality of modular cells provided by the three-dimensional grid pattern defines a storage space for storing one or more stacks of storage containers. Optionally, the load bearing assembly of supporting walls comprises a plurality of prefabricated frames. Thus, the supporting framework structure is formed from an assembly of prefabricated frames and at least one thermally insulating panel. The supporting walls are load bearing in the sense that, when assembled together to form the supporting framework structure, they provide a load bearing structure to support one or more robotic load handling devices moving on the track system mounted to the supporting framework structure. As a result, the modular storage cells provide sufficient spacing within the grid framework structure to accommodate at least a portion of the network of tubing carrying the heat transfer fluid without affecting the storage capacity of the plurality of storage columns. The size of the modular storage cells is such that each of the plurality of modular storage cells supports a subgroup of two or more grid cells of the track system. For example, each of the modular storage cells is sized to accommodate an array of 4 by 4 grid cells of the track system and therefore is able to accommodate 16 stacks of storage containers. The arrangement of the prefabricated frames permits at least a portion of the network of tubing to be fed through the supporting framework structure without affecting the storage capacity of the grid framework structure. At least one of the plurality of supporting walls is a thermally insulating panel that can be arranged in the supporting framework structure to separate the plurality of storage columns into a first group of storage columns to define a first temperature storage zone and a second group of storage locations to define a second temperature storage zone. The network of tubing according to the present disclosure extends in the first storage zone for circulating the heat transfer fluid to exchange heat with at least a portion of the first temperature storage zone such that the first temperature storage zone is at a lower temperature than the second temperature storage zone. To support the network of tubing in the grid framework structure, optionally, the grid framework structure further comprises a plurality of tote guides for guiding the plurality of storage containers through the grid cells of the track system, wherein at least portion of the network of tubing extends through a portion of the plurality of tote guides. For example, each of the plurality of sets of tote guides comprises a plurality of openings that are spaced apart, and wherein at least a portion of the network of tubing extends through the plurality of openings. The present disclosure provides a method of controlling the environmental state in a temperature-controlled storage and retrieval system as defined in any of the preceding claims, the method comprising the step of controlling the temperature of the at least portion of the closed network of tubing in response to the thickness of ice on the at least portion of the closed network of tubing being equal to or greater than a predetermined thickness. BRIEF DESCRIPTION OF THE DRAWINGS Further features and aspects of the present invention will be apparent from the following detailed description of an illustrative embodiment made with reference to the drawings, in which: Figure 1 is an illustration of an automated storage and retrieval system according to an exemplary embodiment of the present invention. Figure 2 is a schematic diagram of a top down view showing a stack of bins arranged within the framework structure of Figure 1. Figure 3 is a schematic diagram of a system of a known robotic load handling device operating on the grid framework structure. Figure 4 is a schematic perspective view of the load handling device showing the container receiving space within the body of the load handling device. Figure 5(a) and 5(b) are schematic perspective cut away views of the load handling device of Figure 4 showing (a) a container accommodating a container receiving space of the load handling device and (b) the container receiving space of the load handling device. Figure 6 is an isometric view of the grid framework structure according to an embodiment of the present invention. Figure 7 is a perspective view of the prefabricated braced frame used to assemble the grid framework structure shown in Figure 6. Figure 8 is a perspective overhead view of the grid framework structure showing the track system extending across the supporting framework structure. Figure 9 is a perspective side view of a temperature controlled automated storage and retrieval system comprising a cooling system according to an exemplary embodiment of the present disclosure. Figure 10 is an isometric view of a dual temperature grid framework structure showing the first temperature storage zone enclosed in a thermally insulating enclosure comprising the temperature controlled automated storage and retrieval system shown in Figure 9 and a second temperature zone in an ambient environment. Figure 11 is a schematic view showing a cut-away of the temperature controlled automated storage and retrieval system enclosed by the thermally insulating enclosure extending below and above the track system. Figure 12(a and b) are schematic views of the arrangement of the network of tubes in the storage area; where (a) shows the status of the cooling system in a partial defrost mode; and (b) shows the status of the cooling system in a full refrigeration mode. Figure 13(a, b, c and d) are isometric views of the temperature controlled automated storage and retrieval system, where (a) show the distribution of the network of tubing of the cooling system comprising three distribution circuits of tubing in the supporting framework structure, (b) show the three distribution circuits of tubing of the network of tubing between the stacks of storage containers, (c) show the network of tubing between the stacks of storage containers for another perspective angle; and (d) is a front view of the storage area showing the arrangement of the three distribution circuits extending between the stacks of storage containers. Figure 14 (a, b and c) are isometric views of the temperature controlled automated storage and retrieval system according to another example of the present disclosure, where (a) show the distribution of the network of tubing; (b) show the distribution of the network of tubing in the storage area; and (c) show the distribution of the network of tubing in the storage area from another perspective angle. Figure 15 is a schematic view of a finned cooling tube for increasing the cooling capacity of the network of tubing. Figure 16 are schematic drawings of a photoelectric sensor for triggering the defrost cycle when the thickness of the ice on the tubes reaches a predetermined thickness, where (a) show the photoelectric sensor in an inactive state; and (b) show the active state of the photoelectric sensor by the thickness of the ice. Figure 17 is a block diagram showing the main components of the defrost system according to an exemplary embodiment of the present disclosure. Figure 18 is a magnified view of a portion of the closed network of tubing forming parallel circulation loops in the upper portion of the first temperature storage zone. Figure 19 is a perspective view of a portion of the closed network of tubing showing an array of parallel tubes extending through the tote guides. Figure 20 is a flowchart showing the process to defrost at least a portion of the network of tubing extending in the storage area. DETAILED DESCRIPTION The present invention provides a cooling system for an automate storage and retrieval system comprising a storage area for the storage of temperature sensitive items, e.g., grocery items and various temperature sensitive pharmaceutical items. Typically, to retrieve the one or more temperature sensitive items from the storage area, the temperature sensitive items are stored in one or more storage containers (otherwise known as “totes”). One or more robotic load handling devices are operative in the storage area to move one or more of the storage containers in the storage area. In the illustrative examples shown in Figures 6 to 19, the automated storage and retrieval system is based on a grid-based storage and retrieval system; wherein the storage area comprises a grid framework structure for the storage of a plurality of totes. It will be appreciated that while the ASRS is described as a grid-based storage and retrieval system, the temperature control system can be adapted to operate with other forms of ASRSs. These include but is not limited to an aisle-based storage and retrieval systems, a rack-based storage and retrieval system operated with an automatic guided vehicle (AGVs) or autonomous mobile robot (AMR) or other material handling system known in the art. In all cases, one or more totes stored in the storage area are handled by one or more robotic load handling devices operative in the storage area. However, for ease of explanation of the present invention, the cooling system is described with reference to a grid-based storage and retrieval system comprising a grid framework as shown in Figures 6 to 8. An example of a grid framework structure 42 according to an embodiment of the present invention comprises a support framework 44 structure comprising a plurality of storage columns 11 and a track system 46 for guiding the movement of one or more robotic load handling devices on the grid framework structure 42 is shown in Figure 6. Each of the plurality of storage columns 11 being arranged to store a plurality of storage containers as a stack of storage containers. In contrast to the existing grid framework structure described in the introductory section of the description, the supporting framework structure 44 according to the illustrative example of the present disclosure is erected from a plurality of supporting or load bearing walls 48 arranged in a grid pattern to define a three dimensional supporting framework structure 44 comprising a plurality of modular storage cells 50, each of the modular storage cells 50 being sized to accommodate two or more storage columns 21, i.e. two or more stacks of storage containers. In the particular embodiment of the present invention, the plurality of supporting walls 48 comprises a plurality of prefabricated frames 48. Prefabrication of the frames 48 involves assembling and fixing separate components of the supporting framework structure 44 together prior to erecting the supporting framework structure 44. The prefabricated frames 48 can be envisaged to be planar. This allows ease of assembly of the supporting framework structure 44 since the use of prefabricated frames 48 greatly reduces the time and effort to assemble the supporting framework structure 44 rather than erecting a plurality of vertical uprights one by one in a “stick by stick” approach and then mounting the track system to the supporting framework structure as currently practised in the art. The prefabricated frames 48 forming the supporting framework structure according to the particular example of the present invention shown in Figure 7 are each configured as prefabricated braced frames or panels 48 comprising a plurality of uprights 52 braced together by one or more bracing members 54, 56 extending between the plurality of uprights 52. The plurality of uprights 52 of each of the prefabricated braced frames 48 making up the supporting framework structure 44 can be braced by horizontal 54 and diagonal bracing members 56. To enable the prefabricated braced frames 48 to be flat packed to facilitate transport, the plurality of uprights 52 of each of the prefabricated braced frames 48 extend in a common plane and are secured together by one or more of the bracing members 54, 56. The one or more bracing members connecting the plurality of uprights lie in the same plane as the plurality of the uprights such that each of the prefabricated braced frames is planar. Each upright 52 of the plurality of uprights can be a solid support beam of I-shape or H-shape or U shaped comprising opposing beam flanges or C shaped or L shaped to enable the uprights to be braced together by the one or more bracing members. The bracing allows a sub-group of uprights 52 to be pre-assembled together prior to being assembled in the supporting framework structure 44. In the particular example shown in Figure 7, the plurality of horizontal bracing members 54 extend between the upper and middle regions of the plurality of uprights 52. Each horizontal bracing member 54 functions as a load bearing beam extending between the uprights 52. The horizontal bracing element 54 braces at least two of the uprights 52 at their upper and / or middle regions. The horizontal bracing element 54 therefore acts as a drag strut or collector, as commonly known in the art. A drag strut or collector is a structural element (for example, a truss) installed parallel to an applied load that collects and transfers diaphragm shear forces to vertical elements, in this case the uprights 52. In addition to at least one horizontal bracing member 54 extending between the plurality of uprights 52 of each of the prefabricated brace frames 48 at least one diagonal bracing member 56 can be connected to the uprights to provide additional stability to the prefabricated braced frame. The bracing members 54, 56 extending between the plurality of uprights 52 are designed to work in tension and compression similar to a truss. The bracing between the plurality of uprights can be designed in different patterns including cross-bracing, K-bracing, V-bracing and / or eccentric bracing. Cross-bracing, also known as X-bracing, is made of two diagonal bracing members crossing each other. The bracing members in K bracing are arranged to form a K shape between the plurality of uprights. In the particular embodiment of the present invention shown in Figure 7, the pattern of the bracing members 54, 56 connecting the plurality of uprights 52 of each of the prefabricated braced frames 48 shown in Figure 7 adopts a K bracing pattern providing an A frame. The bracing members 54, 56 are fixedly connected to the uprights 52 by fasteners commonly known in the art. These include but are not limited to welding, bolts, rivets, or a combination thereof. Various lightweight materials can be used in the prefabrication of the frames. These include but are not limited to metal, plastic, or a fibre reinforced composite material. To reduce cost of manufacture of the grid framework structure, each of the uprights 52 and / or the bracing members 54, 56 can be formed from a folded sheet metal blank having one or more fold lines. Examples of folding the sheet metal blank to form the upright 88 include but is not limited to cold rolling. The plurality of the prefabricated frames 48 are arranged in a three-dimensional grid pattern as shown in Figure 6 in the sense that the prefabricated frames comprises a first set of parallel prefabricated frames and a second set of parallel prefabricated frames. The first set of parallel prefabricated frames extend in a first direction and the second set of parallel prefabricated frames extend in a second direction, the second direction being substantially perpendicular to the first direction such that the plurality of the prefabricated frames are arranged in a grid pattern comprising a plurality of modular storage cells or spaces 50. The first and second directions can represent X and Y axes of a Cartesian coordinate system. Each of the plurality of prefabricated frames 48 are sized such that each of the modular storage cells 50 generate storage spaces for the storage of a plurality of stacks of storage containers within the supporting framework structure, i.e. an open storage space for the storage of a plurality of stacks of storage containers. Connection of adjacent prefabricated frames 48 in the supporting framework structure 44 involves connecting one of the plurality of uprights 52 of a prefabricated frame 48 extending in the first direction to one of the plurality of uprights 52 of an adjacent prefabricated frame 48 extending in the second direction. Various fasteners or fixtures known in the art can be used to connect adjacent prefabricated frames together. These include but are not limited to bolts, riveting, welding or even the use of a suitable adhesive. To guide one or more of the storage containers in a vertical direction along a storage column and through a grid cell of the track system, the grid framework structure comprises a plurality of tote guides arranged around a storage column. The plurality of tote guides 88 can extend from one or more nodes 90 where the plurality of tracks intersects in the track system to the floor such that the storage containers are guided along the tote guides and through a grid cell of the track system. The plurality of the tote guides are arranged in each of the modular storage cells 50 of the supporting framework structure to form a plurality of storage columns for the storage of a plurality of stacks of storage containers within each of the plurality of the modular storage cells. To guide one or more storage containers along a given storage column, each tote guide of the plurality of tote guides comprises two perpendicular bin guiding plates 92(a and b) extending between the track system and the floor for accommodating a corner of a storage container. The two perpendicular bin guiding plates are configured to accommodate a corner section of a grabber device and / or storage container. For maximum stability of the storage containers as they are guided along the storage columns, four tote guides for a given storage column would be necessary to accommodate the four comer sections of a standard storage container, which is generally rectilinear in shape. However, it is not necessary to engage or accommodate all four corners of a storage container along the tote guides as the container is hoisted towards the track system by the lifting mechanism of the load handling device. In another embodiment of the present invention, the plurality of tote guides are arranged for guiding one or more containers in a stack along only a pair of diagonally opposed corners of the one or more containers. This gives the grabber device and / or the storage containers a level of lateral stability in the X and Y direction as the storage container is hoisted along diagonally opposed guides. By guiding the grabber device and / or the storage container attached thereto by only diagonally opposed tote guides, the number of tote guides necessary to guide the grabber device and / or the storage container attached thereto is reduced. In fact, the plurality of tote guides can be arranged at alternate nodes 90 in the first direction (e.g. X direction) and in the second direction (e.g. Y direction), the second direction being substantially perpendicular to the first direction, such that the one or more containers are guided along their diagonally opposed corners. As it is not necessary for each of the plurality of tote guides to be load bearing, lower cost manufacturing methods can be used to fabricate the tote guides 88. Optionally, the plurality of tote guides are formed from a sheet metal blank folded along parallel fold lines and extend longitudinally along the sheet metal blank to form two substantially perpendicular bin guiding plates defining two tote guides. The sheet metal blank is folded along the fold lines to form two substantially perpendicular bin guiding plates defining two tote guides. As the grid framework structure is primarily used to store grocery items, the metal type used in the fabrication of the tote guide should be sufficiently corrosion resistant. Examples of metal types of the sheet metal blank used to form the tote guide include but is not limited to stainless steel or galvanised steel. To guide one or more robotic load handling devices 30 on the grid framework structure 42, the track system 46 is mounted to the supporting framework structure 44 such that the track system 46 extends across the plurality of storage columns in the storage area. The track system 46 comprises a plurality of tracks arranged in a grid pattern comprising a plurality of grid cells 58 (see Figure 8). More specifically, a first set of parallel tracks 22a extending in the first direction and a second set of parallel tracks 22b extending in the second direction, the second direction being substantially perpendicular to the first direction to adopt a grid like pattern (see Figure 8). The track system further comprises a track support structure (not shown) comprising a plurality of track supports arranged in a grid pattern corresponding to the grid pattern of the plurality of tracks. More specifically, the plurality of track supports comprises a first set of track supports extending in the first direction and a second set of track supports extending in the second direction, the second direction being substantially perpendicular to the first direction. The plurality of tracks are mounted to the track support structure. Whilst not shown in Figure 6, the track system 46 can be assembled from a plurality of prefabricated modular sub-track support structures, wherein each of the plurality of prefabricated modular sub-track support structures comprises a portion of the first set of parallel tracks and a portion of the second set of parallel tracks so providing two or more grid cells. Further detail of the track system comprising the track support structure is discussed in WO2022 / 034195 (Ocado Innovation Limited), the details of which are herein incorporated by reference. The plurality of storage columns 11 provides a storage area 60 for the storage of the plurality of storage containers (see Figure 9). With reference to the grid framework structure 42 shown in Figure 6, the storage area corresponds to the volume or space provided by the supporting framework structure 44. As each of the plurality of modular storage cells 50 of the supporting framework structure 44 is sized to accommodate a plurality of stacks of storage containers, each modular storage cell 50 of the supporting framework structure 44 is sized to accommodate a sub-group of two or more grid cells of the track system 46 shown in Figure 8. In the particular embodiment of the present disclosure showing a top plan view of the grid framework structure in Figure 8, each of the plurality of the modular storage cells 50 of the supporting framework structure 82, shown as a dashed box for illustration purposes, is sized to accommodate sixteen grid cells 66 of the track system 46. Thus, each of the modular storage cells 50 of the supporting framework structure 44 provides a storage space for the storage of sixteen stacks of storage containers. The size of each of the plurality of modular storage cells is not limited to accommodating sixteen grid cells of the track system 46 and can be a plurality of grid cells of the track system. In other words, the ratio of the number of grid cells 58 of the track system 46 per grid cell of the modular storage cell 50 of the supporting framework structure 44 can be equated to X: 1, where X is any integer greater than one, i.e. each of the plurality of modular storage cells 50 of the supporting framework structure 44 is sized to support a subset of the plurality of grid cells 58 of the track system 46, said subset comprising two or more grid cells 66 of the track system 46. In the particular example shown in Figure 8, X equates to sixteen which means that the grid cells of the track system per modular storage cell is in the ratio 16:1. For grocery items and temperature sensitive pharmaceutical items, the present disclosure provides a cooling system 62 operable in the storage area 60 to regulate the temperature to within a predefined temperature. The storage area 60 can include the area or volume within the supporting framework structure 44 and / or additionally the area or volume above the track system 46 where the one or more of the robotic load handling devices 30 operate on the grid framework structure 42. To prevent heat loss from the storage area, the external walls around the periphery of the supporting framework structure can be enclosed by one or more thermally insulating solid walled panels 64 to define a thermally insulating enclosure 65, i.e., the storage area is enclosed in a thermally insulating enclosure. Figure 10 is an example of a grid framework structure 42 where at least a portion of the storage area 60 of the grid framework structure is enclosed by the thermally insulating solid walled panels 64 to form a multitemperature storage system having a first temperature zone 66 for storing the temperature sensitive items and a second temperature zone 68 for storage the less temperature sensitive items, e.g., in an ambient environment. The temperature inside the first temperature zone 66 can be regulated to chilled or frozen temperatures by the cooling system according to the present disclosure. The track system 46 is shown in Figure 10 extending across the first temperature zone 66 and the second temperature zone 68 to enable one or more robotic load handling devices to retrieve and store one or more totes from both temperature zones 66, 68. The thermal insulating solid walled panels can be a load bearing wall. The advantage of assembling the grid framework structure from a plurality of prefabricated frames in a grid pattern to form one or more modular storage cells discussed above is not only allows the one or more modular storage cells to accommodate the cooling system comprising a network of tubing 70 but the prefabricated frames can be replaced by a load bearing wall without affecting the structural integrity of the gid framework structure. Examples of a load bearing wall include but is not limited to a structural insulation panel (otherwise known as a SIP panel) comprising a thermal insulation core sandwiched between at least two layers of structural board. An example of a structural board that is load bearing include but is not limited to magnesium oxide. The load bearing walls can be configured to interlock with each other, e.g., tongue and groove, in the supporting framework structure. One or more fasteners discussed above can optionally be used to fix adjacent load bearing walls together or to an adjacent prefabricated frame in the supporting framework structure. The temperature inside the thermally insulating enclosure 65 is regulated to a temperature lower than the ambient temperature by the cooling system 62 according to the present disclosure. For example, the cooling system can maintain the temperature inside the enclosure to provide a chilled zone, e.g., in the temperature range of 4°C to 8°C. Equally, the cooling system can maintain the temperature inside the enclosure to provide a freezer zone, e.g., in the temperature range -18°C to -30°C. The ambient temperature can include the temperature of the external environment that is not regulated by the cooling system and is largely dependent on the seasonal temperature which can range from 0°C in the winter months to 30°C in the summer months. Optionally, the thermally insulating solid wall panels can extend above the track system such that the environment in which one or more of the robotic load handling devices operate on the track system can also be regulated to a chilled or freezer temperature. To mitigate excessive heat in the region above the track system transferring into the storage area below the track system, the environment above the track system can optionally be shielded by a thermally insulating roof 72 formed from the one or more load bearing walls extending above the track system as systematically shown in Figure 11. The roof 72 is sufficiently spaced apart from the track system 46 to provide an opening 74 for one or more robotic load handling devices 30 to move on the track system 46. The roof 72 provides shading or screening from the heat effect of direct sunlight onto the tracks. Preventing heat loss above the track system to the ambient environment can also mitigate the ingress of warm, moist air below the track system and into the storage area. In comparison to a forced air-cooling system, the cooling system 62 according to the present disclosure is very much focused on radiant cooling wherein cooled surfaces in the storage area are used to remove heat radiating from warm bodies largely by radiant exchange and secondary by other methods such as convection. Warmer bodies in the storage area can include but are not limited to the storage containers and their contents. The benefit of radiant cooling over other cooling systems is that heat exchange can be concentrated to a particular region of the grid framework structure. In the present disclosure, radiant cooling is concentrated in the region largely below the track system 46 (see Figures 9 and 11). This has the advantage of keeping the environment outside of the storage area at the ambient temperature which will have a positive impact on the robotic load handling devices operating on the track system 46. The robotic load handling devices 30 operating on the track system 46 can operate at ambient temperatures. As a result, the robotic load handling devices operating on the track system will not be negatively impacted by the effects of the cooler temperatures, e.g., chilled temperatures or frozen temperatures, in the storage area. The functionality of various components of the robotic load handling device such as the rechargeable power source, e.g., battery, and / or other electrical components may be compromised at low temperatures and in a worst-case scenario function improperly. In the particular embodiment of the present disclosure shown in Figures 13(a to d), the cooled surfaces to exchange heat radiated from bodies in the storage area is provided by a closed network of tubing or pipes 70 carrying a heat transfer fluid or refrigerant in fluid communication with a cooling unit 76 extending through the storage area 60. The heat transfer fluid can be a gas or a liquid and is maintained at a temperature below the surrounding temperature in the storage area by exchanging heat with the cooling unit 76. The cooling unit 76 can be a refrigeration unit comprising a compressor, a condenser, an expansion valve and an evaporator. In the present disclosure, the evaporator is formed as the network of tubing 70 that is in fluid communication with the cooling unit 76, namely the compressor and the condenser. The heat transfer fluid can be a refrigerant, e.g., comprising glycol. In the particular example of the present disclosure, the heat transfer fluid is an ethylene glycol under the tradename Coolflow DTX ® from Hydratech (United Kingdom). As is commonly known in art, when operating in a refrigeration mode, the heat transfer fluid or refrigerant enters the compressor at low pressure where it is compressed to a high pressure, high temperature gas. Heat is removed from the high temperature, high pressure gas in the condenser to a high pressure to form a low temperature liquid. The low temperature liquid is subsequently fed into the expansion valve which reduces the pressure abruptly causing the temperature to drop dramatically. The cold low-pressure mixture of liquid and vapor travels through the evaporator where it vaporizes completely as it accepts heat from the surroundings before returning to the compressor as a low-pressure low temperature gas to start the cycle again. The network of tubing 70 distributes the heat transfer fluid within at least a portion of the storage area 60. Heat absorbed by the heat transfer fluid within the storage area is exchanged by the cooling unit or refrigeration unit 76. The storage area shown in Figures 13(a to d) is below the track system 46. However, the storage area 60 can also extend above the track system such that at least a portion of the network of tubes can extend above the track system as well as below the track system 46 as shown in Figures 14(a and b). To maximise the cooling capacity of the radiant cooling system in the grid framework structure, the network of tubing 70 shown in Figures 13(a and d) can be sub-divided into a plurality of distribution circuits 78, each of the plurality of distribution circuits 78 comprise a plurality of parallel tubes 80 extending substantially horizontally in the storage area 60. The parallel tubes 80 in the storage area are sufficiently spaced apart to allow air to circulate between the tubes and exchange heat with the heat transfer fluid carried by the tubes. In the particular example shown in Figures 13(a and d), each of the plurality of distribution circuits 78 comprise a plurality of parallel circulation loops 82 (see Figure 18) that lie in a single vertical plane such that the plurality of distribution circuits lies in multiple vertical planes. Each of the plurality of distribution circuits lying in their respective vertical planes is separated by one or more storage columns or stacks of storage containers such that the plurality of distribution circuits extends between two or more storage columns in the storage area (see Figure 13(d)). The parallel circulation loops 82 of each of the distribution circuits 78 lying in their respective vertical planes exchange heat with the air in the upper portion and the lower portion of the storage area such that each of the distribution circuits in a given vertical plane extend along at least a portion of the height of the grid framework structure. The heat transfer fluid in the upper portion of the storage area is independently controllable relative to the lower portion of the storage area. Further detail of the arrangement of the parallel circulation loops in each of the plurality of distribution circuits is discussed below. The parallel circulation loops 82 of the network of tubing 70 extend between two or more storage columns or stack of storage containers as shown in Figures 13(d). Each storage column 11 in the storage area is, thus, adjacent to a plurality of parallel circulation loops so that each of the plurality of distribution circuits provide radiant cooling along a given row of stacks of storage containers 12. In the particular example shown in Figures 13(a to d), the plurality of distribution circuits 78 comprises three distribution circuits that lie in three different vertical planes spaced apart by one or more storage columns within the storage area. However, the present invention is not limited to the plurality of distribution circuits being adjacent each of the storage columns in the storage area. The plurality of distribution circuits can also be distributed between any numbers of the storage columns in the storage area. An example of the arrangement of the network of tubing in a given distribution circuit lying in a single vertical plane is shown by a section of the storage area 60 in Figures 12(a and b). The network of tubing 70 is arranged as a closed network of tubing in fluid communication with the cooling unit 76 having an inlet for feeding the heat transfer fluid at a supplied temperature and pressure to the network of tubing and a return for returning the heat transfer fluid back to the cooling unit. In the particular disclosure shown in Figures 12(a and b), the inlet is common to the network of tubing and is herewith defined as a common feed inlet 84. Equally, the return is common to the network of tubing and is herewith defined as a common return inlet 86. To distribute the heat transfer fluid to each of the distribution circuits 78 in their respective vertical planes, the network of tubing further comprises at least one common distribution system for distributing the heat transfer fluid from the cooling unit to each of the plurality of distribution circuits. Heat transfer fluid distributed to each of the plurality of distribution circuits is returned to the cooling unit by at least one common return system in fluid communication with the cooling unit. The at least one common distribution system comprises an infeed manifold 88 to fluidly connect each of the plurality of distribution circuits to the cooling unit and a return manifold 90 for returning the heat transfer fluid to the cooling unit. As shown in Figure 13(a), the feed from the cooling unit 76 to the infeed manifold 88 is connected via the common feed inlet 84 and the return from the return manifold 90 to the cooling unit 76 is connected via the common return inlet 86. The plurality of distribution circuits are shown connected in parallel by the infeed manifold 88 and the return manifold 90. The parallel arrangement of the distribution circuits 78 allows the heat transfer fluid to be independently circulated to any one of the plurality of distribution circuits and thus, cooling to the different rows of the stacks of storage containers in the storage area. The infeed manifold 88 is shown connected to the cooling unit 76 via the common feed inlet 84 by a first joint 92 and the return manifold 90 is connected to the cooling unit via the common return inlet 86 by a second joint 94. The first joint 92 can be a connecting joint for distributing the heat transfer fluid via the common feed inlet 84 to the plurality of distribution circuits. In the particular example shown in Figures 13(a to d), the common feed inlet 84 is fluidly connected to three distribution circuits by a three-way connecting joint, i.e., the connecting joint 92 comprises a three-way connecting joint. To independently control the flow of the heat transfer fluid to the different portions of the network of tubing extending in the storage area, the cooling system 62 comprises a defrost system that is configured to apply heat to at least portion of the network of tubing. To apply the defrost system to the network of tubing, the network of tubing 70 in a given distribution circuit 78 can be divided into having an upper portion 96 and a lower portion 98. The upper portion 96 is fluidly connected to the lower portion 98 by a first control valve 100 and the lower portion is fluidly connected to the cooling unit 76 by a second control valve 102. Thus, the defrost system comprises the first and second control valve 100, 102. Each of the first and second control valves 92, 94 controls the flow of the heat transfer fluid to the different portions of the network of tubing. To ensure that the heat transfer fluid is distributed uniformly throughout the plurality of distribution circuits, the first joint 92 is fluidly connected substantially at the centre of the infeed manifold 88. Similarly, the second joint 94 is fluidly connected substantially at the centre of the return manifold 90. Further detail of the control of the heat transfer fluid in each of the distribution circuits is discussed below. To establish a chilled or frozen temperature in the storage area, the heat transfer fluid flowing in the network of tubing is usually at a sub-zero temperature, i.e., below 0°C. This results in the temperature of the network of tubing being at the sub-zero temperature. The temperature of the heat transfer fluid flowing in the network of tubes is largely dependent on the ambient temperature or ambient air temperature. In both cases, the temperature of the heat transfer fluid is at sub-zero temperatures in order to provide the necessary cooling in the storage area. However, if the temperature of at least a portion of the network of tubing extending in the storage area is below the dew point temperature of the surrounding air, the relatively humidity of the surrounding air would reach 100% resulting in moisture in the air condensing on the at least a portion of the network of tubes. Water that has condensed on the surface of the tubes have a tendency to freeze to the extent that ice builds up on the surface of the tubes. Since ice is a relatively good heat insulator, ice and frost accumulated on the network of tubes carrying the heat transfer fluid reduces the efficiency and effectiveness of the network of tubes to further cool the surrounding air by radiant cooling. To prevent the build of ice on the tubes and thereby, affecting the cooling capacity of the network of tubes, the present disclosure applies the defrost system to at least portion of the network of tubes when the cross-sectional thickness, R, of the ice on the at least portion of the network of tubing is equal to or exceeds a predetermined thickness (see Figure 16). For the purpose of the present disclosure, the cooling capacity is defined as the ability of the heat transfer fluid in the network of tubing to exchange heat with the surrounding air in the storage area. The predetermined thickness of the ice, R, is determined by the impact the ice has on the cooling capacity of the network of tubing. Tests have shown that a predetermined thickness of equal to or greater than 1mm has an impact on the cooling capacity of the network of tubing to provide radiant cooling. The great the value R, the greater the impact on the cooling capacity of the network of tubes. Preferably, the value of R to actuate the defrost system is equal to or greater than 1mm. Optionally, 1mm <R >20mm. The defrost system can apply various defrost mechanisms according to the present disclosure to thaw or defrost ice that has accumulated on the at least portion of the network tubing. These include but is not limited to applying heat to the at least portion of the network of tubing. In one example, the defrost system comprises mounting one or more electrical heating elements to the at least portion of the network of tubing that is actuated to supply power to the one or more heating elements when the thickness of the ice accumulated on the at least portion of the network of tubing is equal to or exceeds the predetermined thickness, R. In the present disclosure, the defrost system configures the cooling unit to apply a hot-gas process to the refrigeration cycle so that ice accumulated on the at least portion of the network of tubing melts and the resultant water is drained away. In the hot-gas defrost method, the feed of the compressed refrigerant or heat transfer fluid to the at least portion of the network of tubing in the refrigeration mode is temporarily interrupted and the hot refrigerant is re-directed via a defrost circuit line to the at least portion of the network of tubing to cause the temperature of the at least portion of the network of tubing to be raised to the temperature of the hot refrigerant. As the temperature of the hot refrigerant from the compressor is above the freezing point of water, ice that has accumulated on the at least portion of the network of tubing melts and the resultant water is drained away. A drainage system comprising a network of gutters 104 can be used to capture the melted ice and transport the water to a location outside of the storage area. Further detail of the drainage system is discussed below (see Figure 18). In both defrost modes discussed, the at least portion of the network of tubing is raised above the freezing point of water to cause the ice that has accumulated on the at least portion of the network of tubing to thaw or melt. The defrost system can automatically apply a defrost cycle at specified intervals or periodically to prevent the thickness of the ice reaching the predetermined thickness, R. Alternatively, the defrost cycle can be applied automatically to the at least portion of the network of tubing in response to sensing the presence of or when the thickness of the ice that has accumulated on the at least portion of the network of tubing has reached the predetermined thickness, R. The defrost system can comprise a sensor that is responsive to the thickness of ice on the tubing. Figures 16(a and b) are examples of a type of sensor 106 that can be used to automatically actuate the defrost cycle when the thickness of the ice has reached the predetermined thickness, R. In the particular example shown in Figures 16(a and b), the sensor 106 is a photoelectric sensor, more specifically a photoelectric fork sensor, comprising a transmitter and a receiver. The sensor 106 can be configured to actuate the defrost cycle when the light transmitted by the transmitter is interrupted by the growing ice blocking the optical path to the receiver as shown in Figure 16(b). Various mountings can be used to mount the sensor to the tube. For example, the sensor can be mounted to the tube by an adjustable mount such that the thickness of the ice to actuate the sensor can be varied. Whilst the particular example of the sensor for sensing the presence of ice on the at least portion of the network of tubing is a photoelectric electric, the defrost system of the present disclosure is not limited to a photoelectric sensor and any type of sensor for sensing the presence of ice on the at least portion of the network of tubing can be used. These include but is not limited to an ultrasonic sensor that is configured to measure the time taken for sound pulses emitted from the ultrasonic sensor to travel through the ice. To facilitate the removal of ice that has accumulated on the tubes, the defrost system can optionally comprise a vibrator that is coupled to at least a portion of the network of tubing, e.g., an ultrasonic vibrator. Thus, ice that has partially thawed on the tubes can be removed from the tubes by vibrating the tubes resulting in the ice falling from the tubes and being captured by the network of gutters below. The process to automatically actuate the defrost system can be explained by the block diagram shown in Figure 17 and comprises a controller 108 in communication with the cooling system 62 (shown by the dashed box) comprising a control valve 110 and one or more sensors 106a,b for sensing the presence of ice on at least a portion of the network of tubing. As discussed above, the control valve is configured to redirect the hot heating transfer fluid or refrigerant from the cooling unit when operating in the refrigeration mode to a defrost mode so that different portions of the network of tubing that is susceptible to icing receive the hot refrigerant. The different portions of the network of tubing in a given distribution circuit 78 are shown in the block diagram comprising a 1st branch or first portion of the network of tubes 96 extending in the upper portion of the storage area and a 2nd branch or second portion of the network of tubes 98 extending in the lower portion of the storage area (see Figures 12(a and b)). The defrost system can involve supplying power to one or more electrical heating elements thermally coupled to the different portions of the network of tubing. In operation, the controller comprising one or more processors and memory storing instructions when executed by the one or more processors actuate the defrost cycle of the defrost system to at least a portion of the network of tubing in response to one or more signals from the sensor 106a, b indicative that the thickness of the ice has reached or exceeded the predetermined thickness. In the particular example of the present disclosure, the defrost cycle applies the hot-gas method discussed above. The number of sensors used to actuate the defrost cycle is not limited to one sensor and can be a plurality of sensors. One or more of the sensors can be used to sense the thickness of the ice at the different portions of the network of tubing. The sensor can comprise a first sensor 106a for sensing the presence of ice on the first branch of tubes 96 and a second sensor for sensing the presence of ice on the second branch of tubes 98. The controller 108 can instruct the cooling system to apply the defrost cycle to different portions of the network of tubing in response to the first and / or second sensor 106a,b sensing that the thickness of the ice on the different portions of the network of tubing being equal to or exceeds the predetermined thickness, R. During operation of the cooling system, convective air currents are generated as warmer air as a result of heat absorbed from the totes and their contents at the bottom of the storage area rises and cooler air descends towards the bottom of the supporting framework structure. Moisture carried by the warmer air has a tendency to condense on an upper portion of the network of tubes resulting in a disproportionate amount of ice accumulating on the surface of the tubes in the upper portion of the storage area. To cater for the accumulation of ice on different portions of the network of tubing, each of the plurality of distribution circuits lying in a given vertical plane is divided into the first branch of the network tubes 96 extending in the upper portion of the storage area and the second branch of the network of tubes 98 extending in the lower portion of the storage area. The plurality of parallel tubes carrying the heat transfer fluid in a given distribution circuit is shown in Figures 12(a and b). As shown in Figures 12(a and b), the first branch of the network of tubes 96 is closest to the track system 46 and extends a height Hi whereas, the second branch of tubes 98 is furthest away from the track system but closer to the floor of the storage area and extend a height H2. In a given distribution circuit, the first branch of tubes 96 is connected in series with the second branch of tubes 98 such that the refrigerant or heat transfer fluid circulates from the first branch of tubes to the second branch of tubes. The number of tubes and thus, density of the tubes in the upper portion and / or the lower portion can be varied depending on the cooling capacity of the cooling system in the upper and / or the lower portion. The network of tubing branches from the common feeding inlet 84 into a one or more parallel circulation loops extending in the upper portion of the storage area (herein referred to as the first branch of tubes). Likewise, the network of tubing branches from the first branch of tubes into one or more parallel circulation loops extending in the lower portion of the storage area (herein referred to as the second branch of tubes) and subsequently to the cooling unit via the common return inlet 86. The side view of the grid framework structure shown in Figures 12(a and b) show the network of parallel tubes comprising the first and second branch of tubing 96, 98 extending along a common vertical plane and represents a given distribution circuit discussed above. Since ice has a tendency to disproportionally accumulate on the first branch of tubes 96 in the upper portion of the storage area than the second branch of tubes 98 in the lower portion of the storage area, the defrost system is configured to preferentially apply the defrost cycle to the different portions of the network of tubing in response to the thickness of the ice exceeding the predetermined thickness. As ice has a tendency to accumulate on the first branch of tubes 96, the defrost cycle can be preferentially applied to the first branch of tubes. One or more sensors can be strategically placed on the different portions of the network of tubing to monitor the thickness of the ice that has accumulated on the tubes, namely the first branch of tubes in the upper portion of the storage area and / or the second branch of tubes in the lower portion of the storage area. The control valve in communication with the cooling unit is configured to apply the defrost cycle to the first branch of tubes extending in the upper portion of the storage area independently of the second branch of tubes extending in the lower portion of the storage area. The control valve in communication with the controller is configured to independently control the flow of the hot refrigerant from the cooling unit operating in the defrost mode to the first branch of tubes or the second branch of tubes to separately defrost the different portions of the network of tubing. To separately defrost the different portions of the network of tubing, the control valve 100 fluidly connects the first branch of tubes 96 to the second branch of tubes 98, i.e., the control valve is shown interposed between the first branch of tubes and the second branch of tubes. In communication with the controller, at least one control valve 100, 102 is configured to switch between directing the hot refrigerant to the first branch of tubes 96 or the second branch of tubes 98 in a given distribution circuit 78. To circulate the heat transfer fluid to the first branch of tubes 96 independently of the second branch of tubes 98, the at least one control valve comprises a first control valve 100 and a second control valve 102. The first control valve 100 is operable to bypass the second branch of tubing 98 and divert the heat transfer fluid to the cooling unit 76 via the common return inlet 86 and the second control valve 102 is operable to control the flow of the heat transfer fluid to the cooling unit 76 from the second branch of tubes 98 via the common return inlet 86. To bypass the second branch of tubes, the network of tubes comprises a bypass portion 110 fluidly connecting the first control valve 100 to the second control valve 102. To bypass the second branch of tubes, at least one connecting manifold 112 fluidly connects the first control valve 100 to the first branch of tubes 96 and the second branch of tubes 98 of each of the plurality of distribution circuits such that the first and second control valves are common to the plurality of parallel distribution circuits 78. The at least one connecting manifold 112 is shown in Figures 13a and 13b interposed between the first branch of tubes 96 and the second branch of tubes 98 of each of the plurality of distribution circuits 78. The at least one connecting manifold 112 comprises a connecting outfeed manifold 114 and a connecting infeed manifold 116. The first control valve 100 is interposed between the connecting outfeed manifold 114 and the connecting infeed manifold 116. The connecting outfeed manifold 114 directs the return flow of the heat transfer fluid from the first branch of tubes to the first control valve 100 and the connecting infeed manifold 116 receives the heat transfer fluid from the first control valve 100 and distributes the heat transfer fluid to the second branch of tube of each the plurality of distribution circuits. However, the present example is not limited to the first control valve and the second control valve being common to each of the plurality of distribution circuits, and the flow of the heat transfer fluid to each of the plurality of distribution can be controlled by separate first and second control valves. To bypass the second branch of tubes, each of the first and second control valves comprise a three-way valve. The three-way valve of the first control valve 100 has an inlet in fluid communication with the return flow of the heat transfer fluid from the first branch of tubes 96, a first outlet in fluid communication with the second branch of tubes 98 and a second outlet in fluid communication with the cooling unit via the bypass portion 110. In a first open state of the three-way valve of the first control valve 100, the return flow of the heat transfer fluid from the first branch of the tubes directly flows to the second branch of tubes and in a second open state, the return flow of the heat transfer fluid from the first branch of tubes bypasses the second branch of tubes and flows directly to the three-way valve of the second control valve 102 via the bypass portion 110. On the other hand, the three-way valve of the second control valve 102 has a first inlet in fluid communication with the second outlet of the three-way valve of the first control valve 100, a second inlet in fluid communication with the return flow of the heat transfer fluid from the second branch of tubes, and an outlet in fluid communication with the cooling unit 76 via the common return inlet 86. In a first open state of the second control valve 102, the heat transfer fluid flows to the cooling unit 76 via the second branch of tubes 98 and in a second open state of the second control valve 102, the heat transfer fluid flows directly to the cooling unit 76 via the bypass portion 110. Actuation of the first and second control valves 100, 102 by the controller control the flow of the heat transfer fluid through the first and second branch of tubes or bypass the second branch of tubes to the cooling unit 76 in response to sensing the thickness of the ice on the respective portion of the first and second branch of tubes exceeds or is equal to the predetermined thickness, R. In operation, the controller 108 in communication with the one or more sensors 106a, 106b is configured to control the operation of the first and second control valves 100, 102 to allow the heat transfer fluid to flow through the first branch of tubes 96 and bypass the second branch of tubes 98 or flow through both the first and second branch of tubes 96, 98. Thus, when defrosting ice that has accumulated on at least a portion of the first branch of tubes in a given distribution circuit in the upper portion of the storage area, the controller actuates the first and the second control valves to circulate the heat transfer fluid from the cooling unit, when operating in the defrost mode, to the first branch of tubes and directly to the cooling unit via the bypass portion 110. In this case, the three-way valves of the first and second control valves are actuated by the controller to the second open state. The flow of the heat transfer fluid to the first branch of tubes and bypassing the second branch of tubes is shown as a solid line in Figure 12(a). Equally, when defrosting ice that has accumulated on at least portion of the second branch of tubes in the lower portion of the storage area, the controller actuates the first and second control valves to circulate the heat transfer fluid from the cooling unit, when operating in the defrost mode, to the first and second branch of tubes and back to the cooling unit. In this case, the three-way valve of each of the first and second control valves are actuated by the controller to the first open state. The flow of the heat transfer fluid to the first and the second branch of tubes is shown as a solid line in Figure 12(b). As the plurality of grid cells 58 of the track system 46 are open to the plurality of storage columns below so as to enable a robotic load handling device 30 operable on the track system to lower and retrieve storage containers in storage in the storage columns via the grid cells, heat from above the track system can enter the storge area via the grid cells. Without any suitable cooling above the track system, there is a risk that air entering the uppermost portion of the storage area will displace the cool air in the storage area causing warming in the region around the uppermost portion of the storage area. This is exacerbated by the action of lowering a storage container through a grid cell forcing ambient air above the track system into the storage area. To mitigate the effect of heat entering the uppermost portion of the storage area via one or more grid cells and displacing the cool air, the cooling system, more specifically, at least a portion of the network of tubing carrying the heat transfer fluid can, optionally, extend above the track system as shown in Figures 12(a and b) and more clearly in Figures 14(a, b and c). To differentiate between the first and second branch of tubes 96, 98 in the storage area, the portion of the network of tubing extending above the track system can be defined as a third branch of tubes 118. Thus, instead of initially feeding the heat transfer fluid into the network of tubing via the first branch of tubes 96 discussed with reference to Figures 13(a to d), entry of the heat transfer fluid from the common feed inlet 84 into the network of tubing is via the third branch of tubes 118. As a result, the infeed manifold is fluidly connected to the third branch of tubes such that the heat transfer fluid from the common feed inlet 84 is distributed to the third branch of tubes 118 by the infeed manifold. By extending the network of tubing above the track system, the temperature above the track system can be maintained at the predetermined temperature, e.g., chilled or frozen temperature. Moreover, the delta (5) or difference in temperature between the air above and below the track system can be minimised by having additional radiant cooling above the track system. Like the first and second branch of tubes in the storage area, one or more sensors coupled to the controlled can monitor the thickness of the ice that has accumulated on at least portion of the third branch of tubes above the track system. The third branch of tubes 118 in a given distribution circuit can be fluidly connected in series with the first and / or second branch of tubes. As a result, heat transfer fluid enters the network of tubing from the common feed inlet 84 via the third branch of tubes and is circulated to the first and second branch of tubes before returning to the cooling unit via the common return inlet. Whilst not shown in Figures 14(a, b and c), one or more control valves in communication with the controller can, optionally, be configured to control the flow of the heat transfer fluid in the third branch of tubes independently of the first and / or second branch of tubes. For example, separate feeds from the cooling unit can feed the heat transfer fluid to the third branch of tubes above the track system independently of the first and / or second branch of tubes below the track system. Equally, a control valve can be interposed between the third and first and / or second branch of tubes to control the flow of the heat transfer fluid to the third branch of tubes independently of the first or second branch of tubes. Like the first and second control valves, the control valve interposed between the third branch of tubes and the first branch of tubes can be defined as a third control valve. The third control valve can be fluidly connected to the first and / or the second control valve. In response to instructions from the controller, the third control valve can be actuated to bypass the first and / or second branch of tubes when circulating the heat transfer fluid to the cooling unit via the common return inlet. Like the first and the second control valves, the third control valve can be a three-way valve having an inlet in fluid communication with the cooling unit, a first outlet in fluid communication with the first branch of tubes and / or a second outlet in fluid communication with the cooling unit. Thus, in a first open state of the three-way valve of the third control valve, the heat transfer fluid flows to the first branch of tubes in series with the third branch of tubes and in a second open state of the three-way valve of the third control valve, the network of tubing bypasses the first and / or the second branch of tubes to the cooling unit. One or more additional sensors can be used to monitor the thickness of the ice on at least portion of the third branch of tubes. Whilst not shown in Figures 14(a, b and c), the controller coupled to the one or more sensors can actuate the third control valve to selectively distribute the heat transfer fluid to the third branch of tubes in response to the thickness of ice exceeding or equal to a predetermined thickness. In addition to the third branch of tubes 118 extending above the track system 46, at least portion of the network of tubing can extend below the grid framework structure. As the floor 120 of the storage area is a large thermal mass, heat radiated from the floor may overwhelm the cooling unit. To differentiate between the third branch of tubes 118 extending above the track system 46, the at least portion of the network of tubing extending in the floor can be defined as a fourth branch of tubes 122. The fourth branch of tubes 122 extends into a screed 124 placed on top of a subfloor 126; the screed 124 and the subfloor 126 forming the floor 120 (see Figure 11). The screed 124 is insulated from the subfloor 126 by a layer of insulation or a damp-proof membrane 128. Examples of insulation separating the subfloor and the screed include but are not limited to polystyrene, polyurethane, mineral fibre etc. Consisting largely of gypsum, the fourth branch of tubes extends through the screed 124 and maintains the temperature of the screed at a predetermined temperature so as not to increase the temperature of the environment within the storage area. As opposed to heat radiating from the floor into the storage area, there may also be a transfer of heat from the storage area into the floor where it is absorbed by the fourth branch of tubes extending through the screed. In the particular example shown in Figures 14(a, b and c), the fourth branch of tubes 122 are arranged in a serpentine pattern in the screed 124 but other patterns for distributing the heat transfer fluid in the screed are applicable in the present invention. By maintaining the temperature of the screed at a predetermined temperature, the delta temperature (ST) between the temperature of the screed and the temperature of the environment in the storage area can be reduced to a minimum. Consequently, the efficiency of the cooling unit to exchange heat with the transfer fluid is improved and the ability of the radiant cooling system to effectively maintain the temperature of the environment within the storage area at the chilled temperature or the frozen temperature is greatly improved. Like the third branch of tubes 118, the fourth branch of tubes 122 in a given distribution circuit can be fluidly connected in series with the first and second and third branch of tubes. Again, a control valve (herein defined as a fourth control valve) in communication with the controller can be configured to control the flow of the heat transfer fluid to the fourth branch of tubes 122 independently of the first branch of tubes or the second branch of tubes or the third branch of tubes so as to preferentially feed the heat transfer fluid to the fourth branch of tubes. As shown in Figures 12(a and b), the control valve fluidly connecting the fourth branch of tubs 122 to the first and / or second and / or third branch of tubes is a two-way valve having an inlet in fluid communication with the outlet of the three-way valve of the first control valve 100 and an outlet in fluid communication with the three-way valve of the second control valve 102. This allows the return path of the heat transfer fluid from the first branch of the tubes 96 to bypass the second branch of tubes 98 to the fourth branch tube 122. Thus, in operation, when the three-way valve of the second control valve is in the second open state, the heat transfer fluid bypasses the second branch of tubes 98 and flows to the fourth branch of tubes 122 prior to returning to the cooling unit. In all cases, the first, second, third and / or the fourth control valves of the defrost system can be controlled by the controller to independently control the flow of the heat transfer fluid to any of the first and / or second and / or third and / or fourth branch of the tubes in a given distribution circuit of the network of tubing. Water that has accumulated or thawed on the surface of the network of tubing is taken away from the storage area to a region external of the grid framework structure by a run-off system comprising a network of gutters 104. In the particular embodiment of the present disclosure shown in Figure 18, the network of gutters 104 extends substantially longitudinally along a portion of the parallel circulation loops 80 for capturing water condensed on the parallel circulation loops. The network of gutters 104 can be arranged to extend below each of the plurality of circulation loops as shown in Figure 18 or a sub-group of the plurality of circulation loops. As shown in Figure 18, each of the network of gutters has a U-shaped cross-section extending below the network of tubing 70 for capturing water accumulated on the surface of network of tubing. The network of guttering is downwardly inclined towards one or more downpipes (not shown) having an inlet opening for the water to flow into the downpipe and an outlet opening external of the grid framework structure for releasing the water externally of the grid framework structure. One or more of the downpipes 132 extend vertically along at least portion of the height of the grid framework structure for taking away water captured from the network of gutters 104 (see Figure 10). To reduce the risk of water overfilling one or more gutters of the network of gutters, a pump (not shown) can be optionally installed to the run-off system to increase the flow rate of water through the downpipes. For example, a pump can be fitted to the outlet opening of the downpipe to increase the flowrate of water through the one or more of the downpipes. Each of the network of gutters extends longitudinally below the plurality of parallel tubes. One or more brackets (not shown) can be used to secure the network of gutters to the plurality of parallel tubes extending in the storage area and / or above the track system. For example, the network of gutters can comprise dedicated gutters for capturing water accumulated on the first and / or second and / or third and / or fourth branch of tubes. Since, warm air in the upper portion of the storage area is absorbed by the network of tubing carrying the heat transfer fluid, by concentrating the at least portion of the closed network of tubing 74 in the upper portion 96 of the storage area increases the effectiveness of the radiant cooling system to cool the environment within the storage area. As a result, the cooling capacity can be increased by increasing the cooling surface area of at least portion of the network of tubes extending in the upper portion of the storage area or the thermally insulated enclosure 65. The at least portion of the network of tubes in the upper portion of the storage area can include the first branch of tubes 96 below the track system and / or the third branch of tubes 118 above the track system. The cooling surface area in the upper portion can be increased by increasing the proportion of the parallel tubes in the upper portion or the depth, X of the parallel tubes. The greater the depth, X, of the parallel tubes 80, the greater is the height of the upper portion of the storage area and the more effective is the ability of the heat transfer fluid to exchange heat with the surrounding environment in the storage area, and vice versa. The upper portion of the network of tubes is shown separate from the lower portion of the network of tubing 98 by a gap or spacing to accommodate the first control valve 100. The lower portion of the tubes can include second branch of tubes 98 and / or the fourth branch of tubes 122. Alternatively, or in addition to increasing the depth of the parallel tubes to increase cooling surface area, one or more of the tubes can be a finned tube 134 as shown in Figure 15 comprising a plurality of fins 136 that extend outwardly from the exterior surface of the tube 138 and longitudinally along the length of the tube 138. The finned tubes reduces the number of tubes required to provide an equivalent cooing surface area to conventional non-finned tubes and thus, a reduction in costs to provide a network of parallel tubes extending in the storage area. Moisture removed from the air in the storage area as a result of condensation on the at least portion of the network of tubes also has the benefit of dehumidifying the air in the storage area. As a result, the cooling system not only offers the benefit of cooling the air by radiant cooling in the storage area but any portion of the network of tubing can also function as an integrated dehumidifier to remove moisture from the air. Lowering the total moisture content in the air in the storage area reduces the amount of moisture condensing on the items in storage in the storage area. This is particularly important where the items in storage are sensitive to moisture such as various food and pharmaceutical products. Over a period of time, the total moisture content of the air falls as moisture is continuously removed from the air by the cooling system. Taking the absolute humidity as a measure of the total amount of water vapour in a given volume of air in the storage area, the absolute humidity ranges from 4% to 6% at a temperature range of 8°C to 10°C in the upper portion of the storage area and 6% to 10% at a temperature range of 1°C to 3 °C in the lower portion of the storage area. For items to be stored at the chilled temperature of 4°C to 8°C, the lower portion of the storage area provides storage for chilled items. As a result, the lower portion of the storage area can be sized to occupy a greater proportion of the volume of the storage area than the upper portion. The lower portion of the storage area can be defined as the storage zone of the storage area. Since, water vapour preferentially condenses on the portion of the network of tubing extending in the upper portion of the storage area, the upper portion of the storage area can be defined as the dehumidifying zone of the storage area (see Figures 12(a and b)). The dehumidify zone can include the first branch of tubes 96 extending below the track system and / or the third branch of tubes 118 extending above the track system. The moisture content in the storage area can be regulated by increasing the cooling capacity of the network of tubing in the dehumidifying zone. For example, the cooling capacity in the upper zone can be increased by the use of one or more finned tubes discussed above in the dehumidifying zone. To accommodate the closed network of tubing within the storage area without affecting the storage capacity of the grid framework structure, the grid framework structure may further comprise a plurality of tote guides 140 for guiding the plurality of storage containers through the grid cells of the track system, wherein the closed network of tubing extends through a portion of the plurality of tote guides. The advantage of the grid framework structure assembled from a plurality of prefabricated frames in a grid pattern discussed above is that the load bearing capacity of the grid framework structure is largely borne by the plurality of prefabricated frames. As a result, the structural characteristics and thus, the load bearing capacity of the supporting framework structure is not greatly affected if the load bearing capacity of the tote guides is compromised by accommodating at least a portion of the network of tubes within the tote guides. As shown in Figure 19, the plurality of parallel tubes 80 extends through a plurality of holes or openings 142 formed in the plurality of tote guides 140. The plurality of holes or openings 142 are cut out in the sheet metal blank used to fabricate the tote guides 140. Not only does the plurality of holes in the tote guides allow the plurality of parallel tubes carrying the heat transfer fluid to be extended through the plurality of tote guides but the plurality of holes also provide support to the parallel tubing in a spaced apart relationship. The pattern of holes in the tote guides are arranged such that the plurality of parallel tubes form multiple single walled tubes between the storage columns. As discussed above, to increase the cooling capacity of the radiant cooling system, the pattern of holes in the tote guides can be arranged to accommodate an array of tubes of tubes through the plurality of tote guides as shown in Figure 19. Any number of tubes can extend through the tote guides as the structural integrity of the grid framework structure is not largely dictated by the tote guides but largely by the supporting framework structure 44. In addition to supporting the at least portion of the network of the tubes extending in the storage area, one or more of the plurality of totes can have one or more cut-outs to accommodate one or more of the plurality of the gutters 104 of the run-off system to capture water condensed on the network of tubes shown in Figure 19. Whilst, the cooling system in the particular example of the present disclosure discussed above comprises a closed network of tubing in cooperation with a single cooling unit, the present disclosure is not limited to a single cooling unit. The cooling system can comprise a plurality of cooling units for circulating the heat transfer fluid to different areas of the storage area by a plurality of closed network of tubing extending in the storage area. The plurality of cooling units can comprise a first cooling unit and a second cooling unit and each of the plurality of closed network of tubing can be fluidly connected to a respective cooling unit forming a plurality of closed cooling systems. Whilst not shown in the drawings, the defrost system can comprise a first cooling valve and a second cooling valve and the network of tubing can comprise a first closed branch of tubing in fluid communication with the first cooling unit and a second closed branch of tubing in fluid communication with the second cooling unit. Like the first and second branch of tubes discussed above, at least a portion of the first closed branch of tubes extends in the upper portion of the storage area and the second closed branch of tubes extends in the lower portion of the storage area. To control the flow of the heat transfer fluid to the different portions of the storage area, the first control valve in communication with the controller can be configured to control the flow of the heat transfer fluid in the first closed branch of tubes and the second control valve in communication with the controller can be configured to control the flow of the heat transfer fluid in the second closed branch of tubes. Having separate cooling units to independently control the flow of the heat transfer fluid and thus, temperature of the first branch of tubes extending in the upper portion of the storage area or the second branch of tubes extending in the lower portion of the storage area removes the need to have multiple control valves fluidly connecting the first branch of tubes to the second branch of tubes. The process of switching between the refrigeration mode and defrost mode of the cooling unit operable in the temperature controlled automated storage and retrieval system can be explained by the simplified flowchart shown in Figure 20. In operation 144, the cooling unit operates in the refrigeration mode to cool the surrounding air in the storage area to the chilled or frozen temperature 146. Over time, the thickness of ice on at least portion of the network of tubes extending in the storage area gradually increases. The controller determines whether the thickness of the ice on the at least portion of the tube has exceeded or equal to R 148. If the answer is ‘yes’, the controller actuates the defrost system to operate the cooling unit in the defrost mode. In the defrost mode, the hot refrigerant from the compressor is diverted directly to the at least portion of the network of tubing via a defrost circuit line and the hot refrigerant flows in the at least portion of the network of tubing 150. The controller actuates the control valve to divert the hot refrigerant to the at least portion of the network of tubing 152. Hot refrigerant continues to flow through the at least portion of the network of tubing until the thickness of the ice, R, falls below the predetermined thickness and the controller operates the 5 cooling unit in the refrigeration mode, i.e., the refrigerant continuing to flow through the condenser and expansion valve. The process of defrosting at least a portion of the network of tubing is repeated in a closed loop whenever the thickness of the ice on the tube, R, is equal or exceeds the predetermined thickness. Instead of or in addition to operating the cooling unit in the defrost mode, the controller can actuate the defrost system by applying heating to the at 10 least portion of the network of tubing by supplying power to the electric heating elements coupled to the at least portion of the network of tubing.

Claims

1. A temperature controlled automated storage and retrieval system, comprising:-A) a storage area for the storage of a plurality of storage containers and one or more robotic load handling devices for moving one or more of the plurality of storage containers through the storage area;B) a cooling system comprising at least one cooling unit and a closed network of tubing in fluid communication with the at least one cooling unit to circulate a heat transfer fluid from the at least one cooling unit to the closed network of tubing via a common feed inlet and back to the at least one cooling unit via a common return inlet, at least a portion of the closed network of tubing extends in the storage area for circulating the heat transfer fluid to exchange heat with the storage area;wherein the cooling system further comprises a defrost system and a controller operatively coupled to the defrost system to control the temperature of the at least portion of the closed network of tubing in response to the thickness of ice on the at least portion of the network of tubing being equal to or above a predetermined thickness.

2. The system of claim 1, wherein the cooling system further comprises at least one sensor for determining the thickness of ice on the at least portion of the network of tubing, said controller being configured to actuate the defrost system to control the temperature of the at least portion of the network of tubing in response to a signal from the sensor indicative of the thickness of the ice on the at least portion of the tubing being equal to or above a predetermined thickness.

3. The system of claim 1 or 2, wherein the at least portion of the network of tubing comprise at least one distribution circuit comprising a first branch of tubes and a second branch of tubes, at least portion of the first branch of tubes extends in an upper portion of the storage area and at least portion of the second branch of tubes extends in a lower portion of the storage area, said defrost system being operable to independently control the temperature of the first branch of tubes or second branch of tubes.

4. The system of claim 3, wherein said defrost system further comprises a control valve operatively coupled to the controller to independently control the flow of the heat transfer fluid to the first or second branch of tubes.

5. The system of claim 4, wherein the control valve is interposed between the first and the second branch of tubes, said control valve being configured to control the flow of the heat transfer fluid in the first branch of tubes independently of the second branch of tubes.

6. The system of the claim 4 or 5, wherein the network of tubing comprises a bypass portion in fluid communication with the control valve, said bypass portion being configured to bypass the second branch of tubes to the at least one cooling unit via the common return inlet.

7. The system of claim 6, wherein the control valve is a three-way valve having a first open state to permit the flow of the heat transfer fluid to the second branch of tubes and a second open state to permit the flow of the heat transfer fluid to the at least one cooling unit via the bypass portion.

8. The system of claim 7, wherein the defrost system comprises a second control value fluidly connected to the control valve, said second control valve being operable to control the return flow of the heat transfer fluid to the at least one cooling unit from the second branch of tubes via the common return inlet.

9. The system of claim 8, wherein the second control valve is a three-way valve having a first open state to permit the flow of the heat transfer fluid to the at least one cooling unit via the first branch of tubes and a second open state to permit the flow of the heat transfer fluid to the at least one cooling unit via the bypass portion such that in the second open state of the control valve and the second control valve, the network of tubing bypasses the second branch of tubes to the at least one cooling unit.

10. The system of any one of the claims 2 to 9, wherein the at least one distribution circuit comprises a plurality of distribution circuits, each of the plurality of the distribution circuits comprising a respective first branch of tubes extending in the upper portion of the storage area and a respective second branch of tubes extending in the lower portion of the storage area.

11. The system of claim 10, wherein the plurality of the distribution circuits are connected in parallel by an infeed manifold for feeding the heat transfer fluid to the first branch tubes of each of the plurality of distribution circuits and a return manifold for returning the heat transfer fluid from the second branch of tubes of each of the plurality of distribution circuits to the at least one cooling unit.

12. The system of claim 1 or 2, wherein the at least one cooling unit comprises a first cooling unit and a second cooling unit, the closed network of tubing comprising a first closed branch of tubing in fluid communication with the first cooling unit and a second branch of tubing in fluid communication with the second cooling unit, at least a portion of the first closed branch of tubing extending in the upper portion of the storage area and at least a portion of the second closed branch of tubing extending in the lower portion of the storage area.

13. The system of claim 12, wherein the defrost system comprises a first control valve and a second control valve, said controller being operable to selectively actuate the first control valve and the second control valve to independently control the flow of the heat transfer fluid in the first and the second closed network of tubing.

14. The system of any one of the preceding claims, wherein the at least a portion of the closed network of tubing comprises one or more finned tubes, each of the one or more finned tubes comprises a plurality of spaced apart fins extending outwardly from an outer surface of the tube.

15. The system of claim 14, wherein the at least portion of the first network of tubing comprises one or more of the finned tubes.

16. The system of any one of the preceding claims, wherein the at least one cooling unit comprises a compressor and a condenser coil in fluid communication with said compressor, said network of tubing is in fluid communication with the condenser coil through a refrigerant expansion element and the compressor via a compressor return line, wherein the heat transfer fluid is circulatable to at least portion of the network of tubing via the condenser coil and the refrigerant expansion element to define a refrigeration mode.

17. The system of claim 16, wherein the defrost system comprises a defrost circuit line in which the heat transfer fluid is directly circulatable to the at least portion of the network of tubing by the compressor to define a defrost mode for defrosting the at least portion of the network of tubing.

18. The system of claim 16 or 17, wherein the defrost system comprises one or more heating elements coupled to the at least portion of the network of tubing, said controller being operable to actuate the one or more heating elements to define a defrost mode.

19. The system of any one of the claims 16 to 18, wherein the at least one cooling system comprises a switching means configured to selectively switch between the refrigerant mode and the defrost mode.

20. The system of any one of the preceding claims, wherein the defrost system further comprises a vibrator, said vibrator being coupled to at least portion of the network of tubing.

21. The system of any one of the preceding claims, further comprises a run-off system for capturing condensation from the at least portion of the network of tubing, said run-off system comprising a network of gutters extending substantially longitudinally along the at least portion of the network of tubing.

22. The system of claim 21, wherein the run-off system comprises a downpipe having an inlet opening for capturing fluid from the network of gutters and an outlet opening external of the storage area.

23. The system of any one of the preceding claims, wherein the cooling system further comprises an air circulating system comprising at least one fan for circulating air within the storage area.

24. The system of any one of the preceding claims, wherein the storage area comprises a grid framework structure, said grid framework structure comprising:-a) a supporting framework structure comprising a plurality of storage columns to define the storage area, each of the plurality of storage columns being arranged to accommodate the plurality of storage containers in one or more stack of storage containers, wherein at least a portion of the closed network of tubing is arranged to extend between two or more storage columns;b) a track system for guiding the movement of the one or more robotic load handling devices on the grid framework structure, the track system being mounted to the supporting framework structure and comprising a plurality of tracks arranged in a grid pattern to form a plurality of grid cells extending across the plurality of the storage columns.

25. The system of claim 24, wherein the supporting framework structure comprises a load bearing assembly of supporting walls arranged in a three dimensional grid pattern comprising a plurality of modular storage cells for the storage of a plurality of stacks of storage containers, said at least one of the supporting walls is a thermally insulating panel.

26. The system of claim 24 or 25, wherein the grid framework structure further comprises a plurality of tote guides for guiding the plurality of storage containers through the grid cells of the track system, wherein at least portion of the network of tubing extends through a portion of the plurality of tote guides.

27. A method of controlling the environmental state in a temperature-controlled storage and retrieval system as defined in any of the preceding claims by the step of controlling the temperature of that at least portion of the closed network of tubing in response to the thickness 5 of ice on the at least portion of the closed network of tubing being equal to or greater than a predetermined thickness.

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