Heat transfer, mass transport and horticultural commodity water loss during hypobaric storage

- Hypobaric storage promotes capillary water condensation in non-waxed cardboard boxes.
- Capillary water condensation does not occur in cardboard boxes at atmospheric pressure.
- Heat released when water condenses in a cardboard box radiates to the commodity and warms it.
- The warm commodity can only dispel the acquired heat by evaporative cooling, causing an extra water loss.
- CA and NA cause a larger commodity water loss than LP performed in a water-proof box.

Freedom red roses stored in a hypobaric warehouse at 11.1 mmHg, 2 °C, lost 6.78% of their water in 35 days. Respiratory heat only evaporated enough water from the flowers to cause a 2.5% weight loss. The low storage pressure promoted capillary water condensation in the non-waxed cardboard boxes used for flower distribution, increasing the cardboard's weight by 20%. Radiation and convection transferred the heat of capillary water condensation from the cardboard to the roses, and evaporative cooling caused the extra water loss moving heat from the roses to the chamber air. A weight increase due to capillary water condensation did not occur in cardboard boxes at atmospheric pressure, 85-90% RH, or in waterproof plastic boxes at 11.1 mmHg, 99.8% RH. Horticultural commodities lose more water during controlled atmosphere (CA) or normal atmosphere storage (NA) than during hypobaric storage (LP) in waterproof boxes because more respiratory heat is produced in CA and NA. Non waxed cardboard boxes should not be used for hypobaric storage.