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. jeudi 19 janvier 2012
In North Africa, temperatures can range from 43 deg C in summer to near freezing during the winter. Is this a hot, temperate or moderate zone? Perhaps it would be most beneficial for the purchaser to know at what temperature range the refrigerators will provide proper storage conditions. For example, the range for good vaccine storage may be 15 deg C to 43 deg C. If the unit has a water pack freezer, ice making capabilities could be given at various temperatures. For example, 1.2 kg/day at 15 deg C and 20 deg C, 2.5 kg/day at 32 deg C and 2 kg/day at 43 deg C. If this hypothetical refrigerator had a 60 liter freezer, PQS specifications require it to make 2.4 kg of ice per day. This unit would fail at 15 deg C and 20 deg C even though it kept the vaccines at the proper storage temperature. The ability of the refrigerator to maintain proper storage temperature at 15 deg C and 20 deg C would not be revealed to the purchaser in the PQS sheet, although this would be a valuable piece of information. Actual ice making capabilities for that refrigerator will be more closely correlated to the average daily temperatures, not the minimum daily temperature. If daily temperatures varied from 15 deg C to 32 deg C the ice making capabilities may not be diminished. If ice making capabilities were given at different temperatures the purchaser could judge if ice production was adequate. If ice making capabilities are reduced when temperatures are statistically uncommon the consequences would be small. Ice stored in the freezer could make up for temporarily reduced production. With the performance data suggested here, Mujtaba’s would be able to make a more informed decision on how a refrigerator would perform in Ethiopia’s micro climates. In summary we suggest the ambient temperature range for which the refrigerator compartment provides safe storage be listed. The ice making capabilities could be measured and presented over the range of temperatures the refrigerator compartment provides safe storage.
Toryalai Hart Réponse acceptée
Thanks Larry for your excellent portrayal of operating conditions in Marrakech - which is a great example since it gets very hot in summer and freezing in winter. The building in which equipment is housed is a critical variable that needs to be taken into account in order to truly equate manufacturer specifications to the end user operating environment. Country / city climate data alone is insufficient to correctly predict the operating conditions for equipment. In an ideal world, the ambient temperature of vaccine storage facilities in a country would be sampled and recorded over an entire 12 month cycle, and this data would be used as the basis for equipment selection. Alternatively, building types could be classified and given standardized temperature modifiers that procurement people could then apply to the low and high ranges of a city/country's climate data to make them equatable to manufacturer specified operating conditions. Although both of these scenarios help to more accurately place equipment, ultimately, the buildings in which equipment gets installed need to be designed to mitigate climatic extremes (hot or cold).
Larry Schlussler Réponse acceptée
There are several points I was trying to make which I would like to clarify. According to my interpretation of the PQS test results, if a tested refrigerator which passes the stable run test for 43 deg C, but can not make a sufficient amount of ice to pass the water-pack freezing test at 43 deg C it would fail the 43 deg C test. Published PQS test results would then not show that vaccines could be safely stored at 43 deg C, which I think is a valuable piece of information. Picking climate zones can be ambiguous; what climate zone would you put Marrakech, Morocco? Marrakech can experience temperatures from 43 deg C to 0 deg C. If the clinic was located in a well designed traditional building interior, high temperatures could be kept below 32 deg in summer and above 20 deg C in winter. The refrigerator would then be in a temperate environment. If the clinic had a tin roof and temperatures climbed to over 43 deg C would that put it in a hot climate? In the winter if the temperatures in the clinic dropped below 10 deg C would that make Marrakech a cold climate? I think it would be more straight forward for system sizing to just give the range of temperatures for which the refrigerator will store vaccines properly.
Denis Réponse acceptée
There are three main reasons why PQS has defined different climate zones: 1. Establish the temperature range at which an appliance works properly 2. Use this range as a criterion for purchasers to make their choice according to their need, mainly in terms of climate, location, characteristics of the room where the appliance will be installed. 3. Allow designers to develop appliances in accordance with these criteria. This includes the determination of energy requirements for batteries or solar arrays for operation at a given temperature It is to be noted that the domestic refrigeration industry uses a somewhat similar approach. This is defined in the IEC 62552:2007 - Household refrigerating appliances - characteristics and test methods. This standard uses the following temperature ranges: * Extended temperate +10°C to +32°C * Temperate +16°C to +32°C * Subtropical +16°C to +38°C * Tropical +16°C to +43°C The PQS testing process tries to establish the temperature range in which the fridges can store vaccines safely. Each pre-qualified appliance is listed in the PQS catalogue showing the climate zone against which it has been tested - the maximum figure in the top (red) half of the circular climate zone sticker - and a minimum rated ambient temperature - the figure in the lower blue half of the climate zone sticker. Some products have a very wide safe operating temperature range, some have quite a narrow range. We do recognize that the data provided by manufacturers too often cover only one climate zone - in other words products are fully tested for only one of the three PQS climate ranges. For this reason we do encourage manufacturers to provide complete data for more than one temperature zone because this gives the buyer/user better information for product selection; however we have to recognize that laboratory testing is expensive and time consuming. We strongly encourage end users to report any cases of unacceptable temperature control which may result from incomplete testing and/or improper product selection. Purchasers should note that appliances may not control temperatures correctly if they are required to operate outside their tested upper and lower temperature range. The production capacity of ice is an important criteria to be considered. We do concur with Larry's idea to have the freezing capacity at different temperatures - up to now there is no restriction in doing so as long as the minimum information is provided according to WHO requirements. Denis Maire
Larry Schlussler Réponse acceptée
Some Suggestions for control of solar gain in clinics Toryalai Hart had a good point, controlling the temperature of a clinic would help both the performance of the refrigerator and the occupants. Near the equator most solar gain will occur on the east/west walls and the roof. Solar heating on east and west walls could be minimized by vegetation and exterior window shades; exterior shades are more effective than interior. Over hangs are not effective on east/west windows. For a new building east/west facing windows should be minimized. An inexpensive way to minimize heat gain though the roof is the use of a radiant barrier. A radiant barrier would be installed inside. It is either aluminum foil or aluminum coated plastic film. The principle means of heat transfer from the roof is by radiation. Convection is minor since hot air stays near the ceiling. The aluminum surface minimizes radiant heat transfer. Painting the outside roof surface and east/west walls white would also be helpful. As Toryalai Hart points out traditional building materials produced more comfortable buildings. Poor architecture designs could produce hot conditions when outside temperatures are temperate. While effective traditional architecture could on the other hand produce temperate conditions on a hot day. It would be easier to pick an appropriate refrigerator if performance figures are based on temperature, not climate zones.
Toryalai Hart Réponse acceptée
A country climatic zone alone for equipment selection has never made much sense to me since the true operating conditions for a fridge are also a function of the passive solar thermal architectural properties of the room in which it is installed. Perhaps if we invested some time into developing some passive solar thermal cooling architectural standards for vaccine storage rooms using local materials to compliment the more durable modern ones, and then promoted the use of these designs, we could: a. use a broader range of refrigerator models in hot zones b. benefit from products installed in hot zones performing more reliably and lasting longer c. reduce the energy requirements of refrigerators in hot zones (major cost saving) d. potentially benefit from cool chain / out of the cold chain / controlled temperature chain storage for vaccines in hot zones Sadly, in W-Africa at least, we tend towards modern materials = concrete blocks + zinc roof instead of incorporating traditional materials = mudbrick + thatch into modern health center design, and too often lean towards new technology to solve our problems instead of taking advantage of what we already have in country.


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