A greenhouse with a phase change material (PCM) heat storage system containing a quasi-eutectic
mixture was tested with a classical lettuce-tomato rotation. Measurements on the greenhouse microclimate
and assessment of the thermal storage performances were carried out during two heating seasons,
with special attention paid to evapo-condensative processes.
It is concluded that such a heat storage system, when used in the South of France, can keep a greenhouse
roughly 10 °C higher than outside during typical nights of March or April. It appears however
that the present phase change storage medium, with a transition point as high as 22 ° C, is not adequate
for periods with low solar gains (January or February). On the other hand, when the greenhouse
temperature exceeds the melting point of the PCM (in late winter ), the present ( 1.6 MJ m-2) storage
capacity was found to be too low to cope with actual solar gains. Humidity measurements showed the
positive effect of condensation on the storage. At night, as most of the condensates are drained away,
the purely convective and weaker heat transfers from the storage contribute to keep the greenhouse
humidity below saturation and preserve the crops from fungal diseases.