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?
◦ 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
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.