A frozen room at -22 °C will rise about one degree an hour with the doors shut and the power off. That sounds slow, until you remember that grid supply in Ilorin can be off for twelve hours at a time. So we built our hub on the assumption that the grid will fail, often.
Three layers
The first layer is the grid. The second is a gas generator sized to run every cold room at once, which starts automatically within thirty seconds. The third is a solar array with batteries that carries the pharma room, the alarms and the control room on its own for eight hours. Behind all three sits 72 hours of diesel for a backup generator.
The plan is only real if it has been tried on a Monday morning.
The Monday drill
Every Monday at 7 am we switch off the grid supply on purpose and watch. The controller logs how long each layer takes to pick up, the engineer checks every room, and the readings go into the same logs our customers see. If a layer is slow, it is fixed that week.
Doors matter more than power
Most temperature rises in a cold room come from doors, not power cuts. Our docks open directly onto the van, rooms have strip curtains, and loaders work to a twenty-minute limit for any cross-dock. These are our own practices, shared as general information.