TechNet-21 - Forum

Ce forum est un lieu d'échange où les membres peuvent poser des questions, partager leurs expériences, coordonner des activités, et discuter les récentes avancées en matière de vaccination.
  1. Larry Schlussler
  2. équipement de la chaîne du froid
  3. lundi 10 octobre 2011
Recently, I have seen a number of relatively large RFQ’s for direct drive refrigerators. These refrigerators do not have an ice pack freezer. From past feed back from our customers and WHO we have heard that ice packs are necessary to distribute vaccines to more remote areas. We are concerned that these remote clinics may not be getting a refrigerator, which fits all their needs. We would like to get feed back on this point.
Denis Réponse acceptée
Dear Ian, Thanks for this comprehensive answer. All comes down to the needs of health facilities and the sizing of the energy required. Normally there is no need of a vaccine freezer at the health facility level. What might be required is the possibility to cool waterpacks or to freeze them for outreach activities. Cool waterpacks can also be used during immunization sessions to avoid multiple refrigerator openings. It is interesting to know that the direct drive BLF100DC from True Energy would be suitable for the cooling of waterpacks. I would encourage all manufacturers to have an indication in their instruction manual on this as we have to recognize that users might instinctively put waterpacks in the compartment without realizing the impact it will have on the appliance. We would like to make a call to all manufacturers to make suggestions to the PQS on the best way to address this. Now that we see emerging technologies allowing the use of frozen waterpacks in vaccine carriers without the risk of freezing vaccines - Coldpack is the first one of this type - we do think that freezing waterpacks will remain important at the field level. A dedicated solar direct drive freezer ( with an eventual freezing compartment) might be an advantage if justified by the quantity of frozen waterpacks required. A combined refrigerator/freezer might be a sufficient solution in other circumstances. We do expect manufacturers to inform us on progress made towards the development of such appliances. Denis
ian.tansley Réponse acceptée
Larry & Denis, This is interesting as it highlights some of the problems experienced in the old type solar refrigerators that needed batteries. Clearly the cooling of water packs or feeezing of water packs will impact on the energy consumption of a refrigerator system. For instance in the old style PIS fridge freezers the ice pack freezing energy consumption often dominated the need for energy. In some of the better units it was possible to freeze the ice load (typically 2.4kg/24hrs) in much less time than one day and since all were capable of storing icepacks once frozen, you had to wonder how often they were being used to pull down large icepack volumes, soaking up the stored eneregy in the battery and risking starving the refrigerator compartment of energy. I'd say from my first hand experience this was highly likely to happen on a regular basis in the field. The other thing we used to see was manufacturers trying to use just one refrigeration circuit to cool both fridge and freezer. A tricky balance at the best of times but given the wide variation in ambient temperatures a system that is liable to catastrophic failure. Given the above it has become safer and more practical to manufacture fridge/freezers that have two separate and unconnected refrigeration circuits. One for refrigerator and one for freezer. The logical next step is to separate fridge and freezer allowing for greater flexibility in choice of ratio of sizes (some locations require no freezing, some the freezer volume is greater than the vaccine storage volume) and ensuring that the energy generated is more likely to keep the vaccines safe. Incidentally, the BLF100DC using Sure Chill technology is able to cool water packs in the same compartment as vaccines are stored without effecting the vaccine temperature if required although as Denis says we would need to re-size the solar power system to take account of this extra work load. Ian PQS-Sheet-True-Energy-E003-019-Solar.pdfPQS-Sheet-True-Energy-E003-019-Solar.pdfPQS-Sheet-True-Energy-E003-019-Solar.pdfPQS-Sheet-True-Energy-E003-019-Solar.pdf
Denis Réponse acceptée
Dear Larry, You have a very relevant point. Present SDD refrigerators have only one compartment meant to keep vaccines. Adding waterpacks in it would certainly effect the performance of the appliance. The amount of energy would increase with added load, possibly impacting vaccine temperature and autonomy. I do not think that any of the 4 existing direct drives have directly accomodated this idea of using chilled water packs and certainly they were not tested as such. Only the Vestfrost MKS044, with some removable icepacks, has indirectly approached coolant for outreach. I have to recognize however that this will need to be addressed by the PQS testing. In the meantime, manufacturers should indicate if their appliance would support such a load and in what limits. Denis
Larry Schlussler Réponse acceptée
Hi Denis, In your response, you mentioned the use of cold water packs. As far as I know, the direct drive refrigerators approved have a single storage compartment. If they were used to produce cold water, it would affect the temperature of the vaccines, the number of days of autonomy, and the amount of energy consumed. Are the cold water packs being produced in a way that avoids this? Please clarify. Larry Schlussler, Ph D
Denis Réponse acceptée
Dear Larry, Having direct drive solar refrigerators installed as near as possible from the end users was certainly a priority and the use of cool water packs allow them to get even further. However, in certain circumstances we do recognize that having a combined refrigerator/freezer might be necessary for longer distance outreach activities. Unfortunately, we haven't had yet a solar direct drive appliance PQS prequalified. As you know the technology is more complex than it seems and few manufacturers have already shared their work with us. We are quite confident that few appliances will be available in the near future. Denis

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