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  1. Larry Schlussler
  2. Cold chain equipment
  3. Thursday, 13 June 2013
The data given for solar-powered refrigerators in the PQS sheets is not given consistently enough so that comparisons of various models can be made. The data needed for a fair comparison most often is energy consumption at 32 deg C without ice making, energy use with ice making and quantity of ice made. It would also be useful to know the number of days of autonomy time for direct-drive refrigerators. Looking at the PQS sheets it is not always clear how to obtain total energy consumption when refrigerator and freezer consumption are given separately. Perhaps it should state whether or not it is a two compressor model and if the refrigerator and freezer consumption should be added together to obtain the total energy consumption. Another confusing point on the PQS sheets is that the solar radiation reference period is often given without energy consumption data or recommended solar array size. Without this information the radiation reference period has little meaning. There are few places in the world where average daily temperatures are over 32 deg C. It is important to know if afternoon temperatures peak at 43 deg C that the vaccines will be safely stored and remain between 2 deg C and 8 deg C. However, the average ambient temperature will probably be at 32 deg C or below and the stable running consumption at 32 deg C will be used for system sizing. The latest data I received for a direct drive refrigerator E003/037, for example, gives no energy consumption at any temperatures or any recommendations on a array sizing, it does however give the solar radiation reference period, which alone would be no help judging efficiency or in sizing a system. When the compressor for this model (E003/037) was switched to an AC model so that it could be transformed into an ice lined refrigerator (E003/036) for some reason stable run energy consumption at 43 deg C was given in addition the cool down energy consumption was listed. If the pertinent data is not consistently published there is no incentive for a manufacture to build a more efficient product and no way for a buyer to make an intelligent purchasing decision. I hope the PQS sheets can be transformed into a more useful document.
Larry Schlussler Accepted Answer
I recently came across the PQS tests for long term vaccine cold boxes (WHO/PQS/E004/CR03-VP.1). I was glad to see that the hot zone and temperate zone tests did not keep the temperature at 43 deg C and 32 deg C respectively for 24 hours. During the day temperatures were kept at 43 deg C and 32 deg C then reduced to simulate night time temperatures. This more realistic temperature profiles could be used for testing direct drive, battery powered refrigerators and smaller vaccine carriers. The result would be less expensive and better performing refrigerators and freezers. -Larry Schlussler PhD. Sun Frost
  1. more than a month ago
  2. Cold chain equipment
  3. # 1
Larry Schlussler Accepted Answer
Denis, Thanks for your reply. In your reply you pose the question “It is correct that in most part of the world +32°C data is the most used design value; however should we leave aside more extreme conditions?” In my opinion, this dilemma could be resolved by looking at climate data more closely; and considering which refrigerator characteristics are affected by average daily temperatures, and which are affected by peak temperatures. For example, for direct drive system and ice pack carriers the number of days of autonomy are primarily dependent on the average daily temperature. For a battery powered system the ice making capabilities are also mainly dependent on the average daily temperature. For both direct drive and battery powered the energy use is also dependent on average daily temperature. Since it is extremely rare to experience average temperatures which are above 32 deg C we have the following suggestions. If the installation is to be placed in a location where daytime temperatures approach 43 deg C, I suggest using the “Stable Run Test” data at 43 deg C, to make sure the vaccines stay at an acceptable temperature. Then use the 32 deg C data to indicate the number of days of autonomy for a direct drive system, the ice making capabilities for a battery powered system, and their energy consumption. This method has a built-in safety factor. When the temperature extremes are experienced, the sun will be bright and the need for a large number of days of autonomy will be decreased. For a battery powered system more energy will be available for ice making. Requiring ice making tests and the measurement of autonomy time at 43 deg C will have a negative impact on performance. As a consequence of the way a compressor powered system incorporating a capillary tube work, having to make ice at 43 deg C will lower the evaporator temperature at cooler temperatures. This would result in decreased efficiency, increased system costs, and on some models, greater temperature swings. In a direct drive system, efficiency would be reduced at 32 deg C and below. I propose new testing procedures to assure that vaccines are stored safely when ambient daytime temperatures approach 43 deg C. They would be similar to the day/night test already in use. Vaccines would be kept at 32 deg for 12 hours and then 43 deg C for 12 hours. The MKT temperature could then be used to verify that vaccines were safely stored. Attached is some temperature data I extracted from a report you coauthored, “Use of Cool Water Packs to Prevent Freezing During Vaccine Transportation at the Country Level”. The graphs are for a location in Myanmar and Zimbabwe. At both locations peak temperatures are around 40 deg C, however, average daily temperature are about 32 deg C or below. Temperature drops into the mid 20’s are common where temperatures peaks near 43 deg C. This could easily be verified by a statistical search of hot spots on the NASA website or data compiled on the BBC weather website. Another related point I would like to address is we often get RFQ’s for projects in the tropics where hot zone PQS rating is required, however some of these areas are actually in a temperate zone. I have a feeling in these instances climatic data was never examined. Here are some examples of some equatorial locations that are actually in a temperate cool climate zone: Location: Average High (Hottest Month) Average Low (Hottest Month) Record High Kinshasa, Congo 32 deg C 22 deg C 36 deg C Manaus, Brazil 32 deg C 24 deg C 38 deg C Port Moresby,New Guinea 32 deg C 24 deg C 37 deg C Monrovia, Liberia 31 deg C 23 deg C 34 deg C Quito, Ecuador 23 deg C 7 deg C 30 deg C http://www.technet-21.org/images/agorapro/attachments/2724/mini_graph-Myanmar.jpg http://www.technet-21.org/images/agorapro/attachments/2724/mini_graph-zimbabwe.jpg In summary here are my suggestions: - Use records of ambient temperatures to determine climate zones - If daytime temperatures can approach 43 deg C use 43 deg C stable run test results to determine if vaccines will be safely stored. Use 32 deg C test data to determine energy consumption, autonomy time, ice making capabilities and storage times for ice pack carries. - Incorporate a day/night test for hot climates where daytime temperatures are 43 deg C and nighttime temperatures are 32 deg C. A more realistic test such as this could improve system costs and performance.
  1. more than a month ago
  2. Cold chain equipment
  3. # 2
Denis Accepted Answer
Thanks to Larry for his always appreciated comments. In the name of PQS I would like to bring the following points to the discussion: 1. PQS strongly agree that having appliances tested at different climate zones is an impediment to the comparison between various models. On the other hand, it is to be recognized that requesting manufacturers to have the tests repeated three times is time consuming and represents a substantial investment. Among the 13 solar fridges with PQS prequalification all but 3 solar fridges were tested at +43°C. Nevertheless, this is something we need to tackle and it might be time for us to think of eventual solutions. PQS will engage into an evaluation of its testing procedures for this type of equipment after the summer. This will start in collaboration with various stakeholders by an exercise of collecting information from the field where such equipment has been installed. Manufacturers and laboratories will also be given the opportunity to provide their opinion/contribution. The objective of the review will be to explore the possibility to simplify our requirements while trying to have a set of specifications that would cover the widest range of conditions. 2. We do not publish energy consumption data of SDD as we realized that it might be confusing and/or misleading for the sizing of the solar systems. We have intentionally chosen to insert a warning in the products data sheets, requesting manufacturers be involved in this task as too many variables come into play to properly size the system. It is to be noted that the first intention of the PQS data sheets publication is to target purchasers and procurement agencies. In that intent PQS is trying to provide enough information for the purchaser to choose among the proposed products. Prices coupled with key specifications should cover most of what buyers are looking for. 3. It is correct that in most part of the world +32°C data is the most used design value; however should we leave aside more extreme conditions? 4. Autonomy data is supplied for all SDD (It is noted that BLF100DC and ZLF100DC both only report 72 hours of autonomy when they actually have better results). 5. Solar array capacity is noted for all SDD but the ZLF100DC (will be corrected in the database – in fact it is the same than for the BLF100DC). 6. As mentioned earlier, buyers can compare between the standard specifications shown on the data sheets and bottom line price. Therefore, if all other factors are equal, then an efficient product theoretically will cost less and buyers will see the price as the advantage. In that sense manufacturers do have an incentive to build a more efficient product. 7. It is a good suggestion to note in the datasheet when an appliance is with dual compressor systems. 8. Test 3 - Stable running and power consumption test: does measure total energy consumption. 9. Test 4 - Water-pack freezing capacity and power consumption test: does measure total energy consumption, refrigerator + freezer Hoping that this will be helpful, Denis MAIRE, WHO PQS
  1. more than a month ago
  2. Cold chain equipment
  3. # 3


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