The percent difference between the gross refrigerator (ILRs and SDDs) volumes quoted in the PQS Catalogue and the net vaccine storage volume varies from 29.6% to 88.6 %. This is a wide variation for front opening fridges, due to space for air-circulation.
Increasingly, new models of ILR and SDD are emerging with cooled internal walls and cooled ceilings. Some of these models maintain a satisfactory internal temperature distribution whether they are packed according to the test procedure (with air spaces) or when the vaccine load fills the whole gross volume (without air spaces). The impact of this finding is that the storage capacity of a new model of ILR or SDD may be double or even treble the catalogue figure. The difference in capacity at intermediate levels of storage in-country will affect the economic decision to procure a cold room or maintain a bank of ILRs or SDDs. Running costs will be affected. Cold-chain equipment planners be made aware of this issue when they choose new equipment and when they re-equip stores. What about these next steps – just my own suggestion?
- we maintain the method of loading by the test laboratories that uses 1.0 and 0.5Lt. boxes and we maintain the 'net vaccine storage capacity' measured by the laboratory. But I suggest that this parameter be titled 'Minimum vaccine storage capacity'.
- we maintain the manufacturer's gross capacity, but we add a 'Maximum vaccine storage capacity' that is measured by the laboratory as the maximum vaccine load (represented by the dummy load) without airspaces, without baskets or shelves
- IF this extra loading step is done (Optional, requested by client) then:
◦ the Maximum vaccine storage capacity is reported by the lab. and entered in the catalogue
◦ the rest of the testing that requires a dummy load would be loaded according to the Maximum capacity
- IF it is not done, the Maximum capacity will be the same as the minimum and the Minimum capacity will be loaded for the rest of the testing.
- the country clients for cold chain equipment would be informed that the laboratory reports generate a range of capacity (Min./Max) for each refrigerator and that, within this range and according to the vaccines they use, the country managers can choose a value for the Vaccine storage capacity in that country.
The consequence of this approach is that ILRs and SDDs with satisfactory temperature disitribution performance even when fully loaded, will be more efficiently loaded, less numerous in larger stores and less energy and space consuming. Usually, this would result in lower cost of procurent and maintenance. Also, the coldchain manager has an opportunity, even an obligation, to check the capacity that he/she will use when equipping stores to better correspond to the vaccines in use. Finally, if an equipment model requires airspaces to assure a correct temperature range, then the manufacturer does not invoke the additional measuremnt during testing - the dummy vaccine load simply reverts to the current procedure.