Patent Publication Number: US-6666032-B1

Title: Thermally insulated container

Description:
The present invention relates to a thermally insulated container. In particular, but not exclusively, the invention relates to a transit container for transporting temperature sensitive items, that is equipped with “area-under-the curve” technology. 
     Thermally insulated containers are used to transport items that are sensitive to temperature and must therefore be maintained within predetermined temperature ranges. Such items include goods such as vaccines and drugs, human organs for transplant, tissue cultures, chilled and frozen foods and many other products, some of which have an extremely high value and are very sensitive to temperature changes. It is essential that such products are maintained within the appropriate temperature ranges during transportation. 
     This can, however, be a difficult task. Although such goods are normally transported within highly insulated containers, sometimes with hot or cold “dogs” (heat reservoirs) to provide additional heating or cooling, heat will still flow into or out of the container, according to the difference between the ambient temperature and the internal temperature of the container. It cannot always be predicted what temperatures will be experienced or how long they will last. If the container is exposed to excessively high or low temperatures for extended periods, the internal temperature may go outside the required range, causing damage to the contents. 
     A further problem arises in relation to certain live products, such as tissue cultures (for example artificial skin grafts) that are sustained on a nutrient-containing agar. Such products have to be maintained within a fairly narrow temperature range (typically 21-30C) to survive. However, the rate at which they consume the nutrients in the agar also depends on the temperature, increasing as the temperature rises. Therefore, if the temperature remains at the upper end of the acceptable range, the nutrients will be consumed more quickly than if it is at the lower end of that range. In fact, the nutrients may last twice as long at 21C than at 30C. Thus, for maximum life it is desirable to maintain the temperature as close as possible to the bottom end of the acceptable range, while always staying within that range. 
     A similar problem arises in relation to certain vaccines which degrade at a rate that depends on ambient temperature. As the rate of degradation increases with temperature. It is desirable to maintain the temperature as close as possible to the bottom end of the acceptable range (e.g. 2° C.-4° C.), while always staying within that range. In this way, the rate of degradation can be minimised. 
     Another problem with existing insulated containers is that they are generally extremely bulky and not reusable. Their use is not therefore environmentally sound and can lead to major storage and waste disposal problems. 
     One solution to this problem is of course to use a container that has a built in refrigeration or heating system that is operated by a thermostat to maintain the required internal temperature. However, running a refrigeration or heating system requires a large input of energy and generally such containers are only suitable for use where there is an external power supply They therefore require specialised handling and are not suitable for delivery by normal freight services or for delivering relatively small quantities of goods, such as drugs or vaccines to doctors. 
     GB2331938 describes a refrigerated container that uses a solid-state Peltier-effect thermoelectric nodule for cooling/heating which is controlled by solid-state temperature-sensing and control modules. 
     It is an object of the present invention to provide an insulated container that mitigates at least some of the aforementioned disadvantages. 
     According to the present invention there is provided a thermally insulated container including a payload volume that, in use is to be maintained within a predetermined temperature range it least one heat reservoir and a control device for controlling the flow of heat between the payload volume and the heat reservoir so as to maintain the temperature in the payload volume within the predetermined range. 
     The heat reservoir may be either hotter than the predetermined temperature range to serve as either a heat source compensating for heat lost to the surroundings or cooler than the predetermined temperature range to serve as a heat sink compensating for heat gained from the surroundings. 
     The Container automatically compensates for unexpected variations in the ambient temperature ensuring that the contents are maintained at the correct temperature. As it is entirely self-contained, an external power source is not required, allowing it to be delivered by normal delivery services. Nor is a large internal energy supply required, since the container is extremely well insulated to minimise heat transfer, and the heat reservoir or reservoirs have sufficient heat capacity to maintain the products at the required temperature for a considerable time. 
     Advantageously, the control device includes an external temperature sensor for measuring the ambient temperature. Advantageously, the control device includes an internal temperature sensor for measuring the temperature in the payload volume. Advantageously, the control device extrapolates for the measured temperature or temperatures the rate of transfer of heat to or from the container. By measuring the external and/or internal temperatures, the amount of heating/cooling required can be calculated. Preferably, the amount of heat transferred to and from the box is integrated over time, so that the heating/cooling capacity of the heat reservoir is used only when required. We refer to this as “area-under-the-curve” technology. 
     Advantageously, the control device includes a thermoelectric device for controlling the flow of heat between the payload volume and the heat reservoir. The thermoelectric device may, for example, be a Peltier cell. Alternatively, a mechanical or electro-mechanical device may be used. 
     Advantageously, the heat reservoir includes a substance that changes state during use to liberate or absorb heat, thereby utilising the large latent heat capacity of the substance. 
     Advantageously, the heat reservoir includes a first substance for absorbing heat during use from the payload volume, and a second substance that liberates heat during use to the payload volume, so allowing for both heating and cooling as required. 
     Advantageously, the heat reservoir includes a first substance that changes state during use to liberate heat, and a second substance that chances state during use to absorb heat. 
     Advantageously, the control device is arranged to bias the temperature in the payload volume towards the lower end of the predetermined range, so maximising the lifetime of products such as live cultures that are sustained by a nutrient-containing agar, or temperature-sensitive vaccines. 
     Advantageously, the container includes a recording device for recording the temperature in the payload volume, thereby providing means for checking that the contents of the container have been maintained at the required temperature. The recording device may be arranged to calculate from the recorded temperature the remaining lifetime of products transported in the payload volume. 
     Advantageously, the container has the form of a sealable, thermally insulated box. Advantageously, the box is reusable, thereby reducing waste and alleviating storage problems, and may be substantially transparent to x-rays in at least one direction. 
    
    
     Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of a prior art insulated container; 
     FIG. 2 is a perspective view of an insulated container according to a first embodiment of the invention; 
     FIG. 3 is a cross-section through the container shown in FIG. 2; 
     FIG. 4 is a perspective view of an insulated container according to a second embodiment of the invention 
    
    
     The prior ant container shown in FIG. 1, which is known as an “SP box”, is the type that is currently used for transporting temperature sensitive goods. The container consists of an outer box  2  of double skinned cardboard, which is lined on five sides with a thick layer of foamed insulating material  4 . The bottom and the sides of the container are then lined with hot or cold “dogs”  6  which act as a heat reservoir and are designed to maintain the interior of the container at a predetermined temperature. There is an inner lining of thick cardboard  8 , into which the product is placed, which is held in a number of trays  10 . Further dogs  6  and card  8  are placed on top of the goods, followed by a thick foam lid  12 . The top flaps  14  of the box are then closed and sealed. 
     The box  2  is not very durable and can normally only be used once. This creates waste and storage problems. 
     The number of dogs placed in the box is arrived at by educated guesswork, based on the anticipated delivery time and the ambient temperature ranges likely to be experienced during transportation. However, as delivery can take longer than anticipated and the ambient temperatures may be much higher or lower than expected, the internal temperature may go outside the required range, causing damage to the contents. 
     An insulated container according to a first embodiment of the invention is shown in FIGS. 2 and 3. The container is in the form of a box  20  having a removable lid  2  and a set of castors  24  for ease of transport. A number of clips  26  are provided for securing the Lid  12  in place. 
     The components of the box are shown in cross section in FIG.  3 . This box  20  is designed specifically for use in transporting goods that must be maintained at a temperature of between +2° C. and +8° C., such as, for example, vaccines and transplant organs. Boxes for different temperatures will be generally similar in construction, but may be modified as described in more detail below to maintain the required temperatures. For example, for some applications the internal temperature must be maintained in the range +20° C. to +31° C. whereas for other applications, the internal temperature must be maintained at approximately −87° C. 
     The box consists of a casing  30  that includes an outer shell  32  of, for example, glass reinforced plastic (GRP), metal or a plastics material. The casino has an inner liner  34  of insulating materials with a very high K value, for example a foamed plastics material. The lid  22 , which has a sealing fit with the body of the box, has a similar construction. 
     The lid and the box are transparent to x-rays, at least in the vertical direction, allowing the box and its contents to be checked for security purposes at airports Without opening the box. 
     In the centre of the casing  30  there is provided a payload volume  36  which is defined by an inner shell  38  of for example stainless steel or aluminum. The bottom face  38   a  of the inner sheet may be made of a wire mesh, so that it is transparent to x-rays. The inner shell  38  is narrower than the internal width of the outer casing to provide on each side a space for a temperature control system  42 , which in operation maintains the temperature in the payload volume in the predetermined temperature range. 
     The temperature control system consists of two parts: a cold side  42   a  for reducing the temperature in the payload area, and a hot side  42   b  for increasing the payload temperature. These are located on opposite sides of the casing  30 . 
     The cold side of the system includes a cold dog  44  consisting of a frozen gel or similar material having a high value latent heat of fusion, which prior to use is frozen to a temperature of approximately −3° C. This cold dog serves as a heat sink for absorbing heat from the payload to reduce its temperature. 
     The cool side also includes a thermal gel  46  having a high specific heat capacity, which prior to use is heated or cooled to the desired temperature range. The thermal gel  46  is in thermal contact with the payload volume  36  and has an equal thermal mass to the cold dog  44 . The gel serves as a thermal buffer between the cold dog and the payload volume, preventing rapid or localised heating or cooling of the items in the payload volume. 
     Mounted between the thermal gel  46  and the cold dog  44  is a control device  48  for controlling the flow of heat from the gel to the cold do. The control device provides a thermal conduction path between the gel and the cold dog and, apart from this control device, the cold dog is thermally insulated from the gel and the payload volume by means of insulating layer  49 . The temperature control device nay, for example, be a Peltier cell having one junction in contact with the cold dog and the other in contact with the gel so that, by varying the current passed through the cell from a battery  50  the rate of heat flow into the cold dog can be increased or decreased. Alternatively, a mechanical temperature control device may be provided. 
     The hot side  42   b  of the temperature control system is similar to the cold side, and includes a hot dog  54  having a high specific heat capacity. The hot dog is heated or cooled to a temperature of +12° C. so that it acts as a heat reservoir that can provide heat to the cooler payload volume. The hot side of the system includes a thermal gel  56  which, before use, is heated or cooled to the desired payload temperature and a temperature control device  58  for controlling the flow of heat from the hot dog to the gel. This may be a Peltier cell, which is driven by a battery  60 , or a mechanical temperature control device may be provided. The control device  58  provides a thermal conduction path between the gel  56  and the hot dog  54  and, apart from this control device, the hot dog is thermally insulated from the gel and the payload volume by means of insulating layer  49 . 
     The box includes an external temperature sensor  52  mounted on the outside of the casing  30 , and an internal temperature sensor  54 , mounted inside the payload volume. These are connected to an electronic control unit (not shown), which controls the electric current flowing through the two temperature control devices  48 , 58  to control the rate of heat flow to and from the hot and cold dogs  54 , 44 . In use, the electronic control device determines from the sensed internal and external temperatures and the known K value of the box the rate of heat flow into or out of the box. It uses this information to activate either the hot side or the cold side of the temperature control system to increase or decrease the rate of heat flow into or out of the payload volume, so as to maintain the payload at a constant temperature. 
     For example, if the external ambient temperature is high, heat will flow into the box from the outside, increasing the payload temperature. The electronic control device will sense the high ambient temperature and activate the cold side of the temperature control system so that heat is allowed to flow from the payload into the cold dog  44 , thereby maintaining the payload in the desired temperature range. Conversely if the external temperature is low, heat will be lost from the box and the electronic control device will activate the hot side of the temperature control system, causing heat to flow from the hot dog  54  into the payload volume  36 , to maintain the payload at the required temperature. 
     The electronic control device has a relatively long sampling interval of, for example 2 to 4 hours, so that it does not react immediately to sudden external temperature changes. This avoids wasting the heating and cooling effects of the hot and cold dogs when for example, the box is left in a warm or cold location for a relatively short time, which is insufficient to cause a large change in the payload temperature. This may occur for example when the container is placed in the hold of an aircraft that has to stand on a runway in full sun for some time before taking off. Since the effect of the high temperature experienced while the aircraft is standing on the runway is likely to be effectively cancelled by the much lower temperature experienced while the aircraft is flying at a high altitude, there is no need for the heating and cooling reserves of the dogs to be utilised to keep the internal temperature in the desired range. 
     The electronic control device operates by measuring the integrated rate of power transfer to and from the box, so that extra heating or cooling is provided only if heat lost or gained the box exceeds a predetermined amount, which will happen if the external temperature is very high or very low for prolonged periods. By integrating the rate of power transfer, the electronic control device takes account of both the magnitude of the temperature difference between the internal and external temperatures and also the time for which that external temperature is experienced. The energy transfer may be calculated in “units”, equal to the product of temperature difference and time. For example, an external temperature 10° above the internal temperature for five hours (50 “units”) will be cancelled out by an external temperature 5° below the internal temperature for ten hours (50 “units”), so requiring no use of the hot and cold dogs. On the other hand, an external temperature 20° above the internal temperature for ten hours (200 “units”), followed by 10° below for five hours (50 “units”) will result in a net heat gain of 150 units, requiring use of the cold dog to maintain the desired temperature range. 
     A modified operating method may be adopted when the device is used for transporting live products, such as tissue cultures that are sustained on a nutrient-containing agar. As mentioned above, such products have to be maintained within a fairly narrow temperature range (typically 21-30C) to survive, but the rate at which they consume the nutrients in the agar also depends on the temperature, increasing as the temperature rises. Similarly, certain vaccines can be affected by bacteria, which grow at a rate that increases with temperature. Therefore, for maximum life, it is desirable to maintain the temperature inside the container as close as possible to the bottom end of the acceptable range. In such a case, the control algorithms of the electronic control device may be modified, so as to bias the temperature towards the lower end of the acceptable ranges while always staying within that range. 
     A single or multi-channel data logger  56  may be provided to maintain a record of the payload temperature during the entire transit time. This may use the internal temperature sensor  54 , or a separate payload sensor may be provided. The temperature log may be kept in visual or electronic form, and in the latter case facilities may be provided for downloading the information telephonically or to a computer. The data logger may also record events such as the box being opened or tampered with. 
     In the case of a container that is to be used for transporting live cultures, the data logger may also be arranged to calculate from the temperatures recorded inside the container the rate at which the nutrients inside the agar have been consumed and, from that information, calculate and display the estimated remaining lifetime of the culture. Similarly, if the container is to be used for transporting vaccines, the data logger can calculate the rate of degradation, thereby increasing confidence that the vaccine will not have degraded unacceptably during transportation. 
     The heating or cooling capacity provided by the hot or cold dogs may be tailored according to the required internal temperature range and the anticipated external temperature range. For example, if the internal temperature must be maintained in the range +20° C. to +31° C. a larger heating capacity is likely to be required and it is possible that the cold dog may be omitted entirely. Conversely, if the internal temperature must be maintained at approximately −87° C., additional cooling capacity may be required and it may be possible to omit the hot dog entirely. 
     The substances chosen for the hot and cold dogs may also be tailored according to the desired temperature ranges so that their fusion temperatures are appropriate to the temperature range required. 
     An alternative embodiment of the in FIG. 4, in which the box has a hinged door  58  rather than a removable lid. Otherwise, the box is similar to the box shown in FIGS. 2 &amp; 3. 
     Various modifications of the invention are possible, some examples of which are discussed below. The inner payload container may include shock absorbing materials to prevent vibration and movement of the materials being carried. For example., the payload container may include an inner liner such as an air bag, or sprung shelving. The data logger may record events such as the box being inverted, subjected to shock or any other factor of interest to the user. The box may be bar coded to carry information such as the payload carried, transit dates and any other information that may be required. The box may also be provided with visual and/or audible warning devices, for example to warn that the required temperature range has not been maintained. The batteries  50 , 60  may be provided with Zener barriers, to prevent a current overload if they are short-circuited.