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. Moderator
  2. équipement de la chaîne du froid
  3. vendredi 9 décembre 2011
With many thanks to John Lloyd for this post. Countries that currently use absorption refrigeration (gas, electric or kerosene-powered) are facing increasing pressure to switch to solar photovoltaic-powered refrigeration for vaccine as manufacture of absorption equipment shrinks. We have a substantial evidence from the field on the success of solar refrigeration systems that point to a few critical success factors: ? Systems designed rigorously to match climatic and irradiation, site-specific data ? Installation following standard procedures and quality norms of WHO ? Commitment and budgeting for routine maintenance (including battery replacement) and timely repair The stakeholders of immunization are the lead position to assure systematic procedures in the field, thus assuring future success. Plans are in process for a major new field assessment of solar ‘direct drive’ refrigerators (four models that do not depend on battery systems) that have already been prequalified by WHO/PQS. Procurement by countries will proceed in parallel to this assessment and pending the results the following criteria for successful implementation of solar refrigeration should be pursued: • Solar refrigeration is now the preferred option where grid electricity is not available or is available less than 4 hours per day and where sufficient solar radiation exists to permit a reliable and affordable system design (See figure 1) ? Kerosene/electric absorption options for areas without electricity have a lower performance, are less reliable and more costly to operate then solar refrigerators ? Direct drive solar refrigerators are more reliable than battery based solar refrigerators because they rely less on battery systems and have simpler control equipment and have less electrical connections ? No direct drive solar refrigerators available at this time include icepack freezers, so they are only suitable where water packs or Phase Change Materials (PCM) packs are used for outreach immunization – or where there is no outreach immunization • Solar refrigerators should be selected from the WHO/PQS list of pre-qualified products and the Qualified Suppliers responsible for supply and contractors/technicians (could be MOH techs) responsible for installation should conform to WHO/PQS (ref) norms. The process of procurement and installation should include the following main steps: ? Identify appropriate sites GPS data (country desk study) o No prolonged cloud (> 1 week continuous) o No shading between 9AM and 3PM o Electricity less than 4-8 hours / day o Solar technical service is, or can be, available ? System design (solar technician site visit) o Review climate data for temperature, solar radiation and to determine autonomy needed o Site visit to determine shading, panel support structure, fridge location, cable routing, etc. ? Documents assembled for open tender: o System design documents (technician) o Site visit reports (technician) o Installation procedures o Maintenance and repair plan and commitment ? Bidding and adjudication o Technical review bidding documentation o Send out request for bids to Qualified Suppliers. o Technical review of bids to ensure appropriate specifications proposed. o Award, installation and acceptance • Resources will be needed to follow the process described above including: ? Technical staff or consultants, training: o to visit each candidate site for solar PV refrigerators and collect data o to assemble system design briefing documents for tender o to install or supervise installation of solar PV equipment ? Guide materials: o WHO PQS solar refrigeration (E3) documents o Refrigerator manual in appropriate language o Copy of the Markvart system design tool ? Multi-year Plan: o Budgeting, maintenance and repair of solar refrigerators ? Need for consultants, training, guide materials, software tools etc. Figure 1: Decision chart for selection of power source for vaccine refrigeration equipment: http://www.technet21.org/components/com_agora/img/members/3149/mini_Decision-chart-for-selection-of-power-source-for-vaccine-refrigeration-equipment.png (Please click on the image for a bigger picture.)
Alejo Bejemino Réponse acceptée
Fully agree with Steve that the sustainability of the good performance of solar powered vaccine refrigerator is its long term maintenance. Many of the solar powered vaccine refrigerators both with battery and direct driven that were installed without regular preventive maintenance were already not working. Contributing factors to these non-working units are: incorrect installation, absence of regular maintenance and unavailability of spares to replace the defective parts. Since solar powered units were mostly installed in remote health centers, its maintenance is really crucial and also a challenge. It is therefore recommended that health staff in the health center responsible for the solar powered unit should be provided with the following: a) hands on training on the preventive maintenance; b) basic tools and training on how to use them correctly (particularly a multi-tester); and c) consumables and spare parts. These should be immediately provided during the installation and commissioning work of the solar powered unit. Additional costs for these provisions are less significant compared to the amount of free, environmental friendly and non-stop energy availed from the sun. Regarding Abdul Mateen's request, I suggest to kindly check WHO PQS website for the latest update on the pre-qualified solar powered vaccine fridges.
TechNet Admin Réponse acceptée
Admin
Dear Mr Al Bejemino A A I hop you are fine and healthy and how are your children  ,so i got your email addrass from Dr. Rafiqi let me introduce my self first I am Abdul Mateen National Cold chain Manager for  MOPH of Afghanistan, I need for  Solar Refrigeretor with Rechargible battry Brand name Price capacity of Solar No 2 Price with out Batrry with brand Thanks
Alejo Bejemino Réponse acceptée
Solar powered vaccine refrigerator with rechargeable battery and solar powered vaccine refrigerator direct drive can be compared as follows: 1. With rechargeable battery Refrigerant compressor runs during night and day. It has a refrigerator compartment for cooling and storing vaccines and freezer compartment for cooling, storing non-freeze sensitive vaccines and for freezing icepacks. Temperature control in the vaccine compartment is controlled by thermostat. Other model has two independent refrigeration systems: one for cooling and one for freezing. Refrigerant compressors are powered from the solar array, rechargeable battery and charge regulator. 2. Without rechargeable battery (Direct drive) Refrigerant compressor runs only during the day. It has a refrigerator vaccine compartment for cooling and storing vaccines and an ice bank compartment which keeps the cabinet at desired temperature during the night. Temperature in the ice bank compartment and vaccine compartment is controlled by thermostats. The unit has one refrigerant compressor motor, 3 circulating fans powered by an ancillary rechargeable battery and 3 thermostats. Refrigerant compressor is powered directly from the solar array. Some useful guides in selecting between a solar powered unit with rechargeable battery and a solar powered unit with direct drive are as follows: i. Vaccine storage capacity requirements of a health facility ii. Number of outreach immunization which requires frozen ice packs iii. Funding requirement (total capital cost and annual recurrent cost) Solar powered unit with rechargeable battery has more than 20 liters vaccine storage capacity and has an icepack freezer which could freeze more ice packs to cater to several outreach immunization sessions per day. However, the total capital and annual recurrent costs of a solar powered unit with rechargeable battery are higher compared to the direct drive solar powered unit. This is considering that there is no rechargeable battery and no charge regulator to replace and maintain in a direct drive solar powered unit. Direct drive has about 20 liters vaccine storage capacity with no ice pack freezer. It is economical and practical for use by a health facility with a vaccine storage capacity requirement of about 20 liters and one outreach immunization session per day. Solar chill by Vestfrost has an ice bank compartment which could accommodate and freeze four ice packs of 0.3 liter. These four frozen icepacks are enough for a small vaccine carrier and could be used by health worker for the outreach immunization session. Every time the four icepacks are removed and used these should be replaced by another four 0.3 liters icepacks to be frozen during daytime when the refrigerant compressor is fully operational. Summary of the field observations that need to be addressed to fully utilize the solar powered cold chain: i. Incorrect installation of solar array • Solar array not correctly installed. Incorrect tilt angle and/or direction (rechargeable battery & direct drive) • Solar array installations could not be easily maintained and repaired. No safe access for cleaning and checking of the wirings of the solar array (rechargeable & direct drive) • Solar array not correctly and strongly mounted on the roof of the building. There is not enough space to cool the solar array from the heat generated from the galvanized roofing material and not stable to withstand against the strong wind (rechargeable & direct drive) ii. User’s not briefed on the correct use of the solar powered refrigerator unit • Vaccine compartment not defrosted regularly (rechargeable battery & direct drive) • Blocked ventilation grill in the compressor compartment (direct drive) • Removal of vaccine baskets resulting to poor cool air circulation inside the vaccine compartment (direct drive) • Improper placement of ballast box in the vaccine compartment (direct drive) • Improper placement of internal lid in the ice bank compartment (direct drive) • Removal of some frozen ice packs from the ice bank compartment (direct drive) • Additional loads (light bulbs, radio, mobile charger etc.) are connected to the battery (rechargeable battery) • Poor ventilation of the condenser and compressor motor ( rechargeable battery & direct drive) • Users are not trained on how to clean and maintain the solar array and its wiring connections. Basic tools and consumables are not provided (rechargeable battery & direct drive) iii. Equipment failure (Manufacturer’s concern) • Undercharge refrigeration system (rechargeable battery) • Blocked or defective fan in the vaccine and compressor compartment (direct drive) • Damage or broken battery (rechargeable battery) • Broken refrigerator door hinges (rechargeable battery) • Three thermostats not fully sealed (direct drive) • Defective heating element (direct drive) • Defective thermostat for the heating element (direct drive) • Vaccine baskets not available (rechargeable battery) • Difficulty of removal of vaccine baskets from the vaccine compartment (direct drive) • Spare parts such as fan motors, fuses, heaters, ancillary battery, voltage regulator, solar thermometer, rubber gaskets, thermostats, starting device, diode are not provided (direct drive) Hope these are useful. Alejo H. Bejemino Cold Chain & Vaccine Management Consultant
Moderator Réponse acceptée
Admin
Autonomy Tool background and Array Over Size Factor The Autonomy Tool was developed in 2008 by H. Toma and T. Markvart with the support of PATH. The tool calculates the number of days of autonomy required as a function of the Array Over Size Factor, CA. If the array is sized for average total daily insolation of the poorest solar month, CA would equal 1. If the array is increased 25% the array oversize factor would be CA=1.25. The largest CA results published was for CA=1.25. With PV decreasing in cost and the price of long life batteries high the required storage for larger CA’s (arrays) would be of value. We used an alternative method to calculate the amount of storage required. If for example, 15 years of solar data is available for a particular location. We assumed an array size and looked at deficit or excess solar collected each day using a spread sheet. We calculated the amount of storage needed each day in that 15 year period and based our storage needs on the maximum amount of storage needed during that period. Attached is the graph showing T. Markvart’s results for varying array oversize factors. Attached is “Days of Solar Autonomy for 132 Tropical Locations” Prepared for WHO by PATH, 2008 Sincerely, Larry Schlussler Sun Frost PO Box 1101 Arcata, CA 95518 (707) 822-9095 phone (707) 822-6213 fax larry@sunfrost.com http://www.sunfrost.com 14-Autonomy-tool-TM-Dec09.pdf FinalReport-SolarAutonomy-2.pdf
Moderator Réponse acceptée
Admin
Hi John, Sorry if my point was confusing and thank you for your efforts and excellent piece on implementing the solar cool chain. I was just pointing out that the current direct drive refrigerators are not in fact tested for cooling water packs or indeed PCM packs and users should take care as placing these in the vaccine compartment will push energy consumption up requiring a larger solar array. Guy Watson
John Lloyd Réponse acceptée
May I suggest that you check the following PQS specifications: Refrigerator or combined refrigerator-icepack freezer: compression-cycle. For solar direct drive without battery storage PQS performance specification WHO/PQS/E03/RF05.2 pdf, 166kb PQS independent type-testing protocol WHO/PQS/E03/RF05-VP.2 pdf, 149kb They can be found at the following link: http://www.who.int/immunization_standards/vaccine_quality/pqs_e03_fridges_freezers/en/index.html You should find references to icepack freezing in this specification; let me know if you are making a different point. John Lloyd
John Lloyd Réponse acceptée
Message posted by John Lloyd on behalf of Larry Schlussler: Quote: In the tropics, increasing the size of a solar array significantly reduces the number of days of storage required. This is illustrated in the attached graph produced by Tom Markvart. A PATH publication using the autonomy tool gives the required days of autonomy for 132 locations. We looked at the locations in Africa between +23.5 and –23.5 latitude, 71 locations. With an array over size factor of CA=1.25. The average number of days of autonomy is 2.1. Only one location required over 5 days of storage, Kigoma, Tanzania. Which required 6.4 days of storage. For Kigoma, when the CA was increased from CA 1.1 to CA 1.25 the number of days of days of autonomy decreased from 9.3 to 6.4 days. We are looking into building a more efficient refrigerator and increasing CA to at least CA=2. This should bring the number of days of autonomy required close to 1 in 95% of tropical Africa. These results are confirmed by spread sheets we previously ran for a several poor solar tropical locations. We plan on repeating this procedure for more locations. If for example 15 years of daily solar data is available. The performance for each day in that 15 years can easily be determined with a spread sheet, the process will show the correlation of the array size and storage requirements. This analysis could not be done for a direct drive system. Larry Schlussler Sun Frost PO Box 1101 Arcata, CA 95518 (707) 822-9095 phone (707) 822-6213 fax larry@sunfrost.com http://www.sunfrost.com
Guy Watson Réponse acceptée
Looking at the PQS sheets is is clear that direct drive refrigerators cannot freeze icepacks and they are not tested using water packs or PCM packs. If direct drive refrigerators are to be used for "freezing" phase change packs then a new test protocol will need to be developed to determine the number of packs to be loaded daily, the loading location in the refrigerator and the additional energy/solar system required to phase change the PCM packs. Or are we missing a trick here? "No direct drive solar refrigerators available at this time include icepack freezers, so they are only suitable where water packs or Phase Change Materials (PCM) packs are used for outreach immunization – or where there is no outreach immunization"
Mojtaba Haghgou Réponse acceptée
John’s informative and interesting post draws attention to the important field problem of replacing kerosene refrigerators with the alternative technology of solar chiller (battery less solar refrigerator). During the recent review of the vaccine management in Ethiopia we were faced with the logistical nightmare of provision of kerosene to remote areas of the country. The available information shows that battery-less solar refrigerators are used in Senegal and Vietnam, two countries with relatively hot climates. It is important to test this particular type of solar refrigerator in a country with Ethiopia’s cooler temperatures. UNICEF Ethiopia in collaboration with the Ethiopian Federal Ministry of Health and other partners is planning to purchase and test a limited number of solar chillers in different parts of the country for a period of one year. Positive results of the tests indicating that solar chillers are suitable for the cool ambient temperatures of Ethiopia could provide a potential solution for the phasing out of kerosene refrigerators. Hopefully, the economies of scale will also bring the capital cost of solar chillers to an affordable level.


Cette discussion ne contient encore aucune réponse.
Soyez le premier à y répondre !