Since early January the leaf, flower, greenhouse air and screen temperatures are monitored at Dutch gerbera growers Holstein Flowers and Zuijderwijk & Witzier. The aim is to better understand the individual temperatures in the nights in order to detect possible risks of condensation.
By using thermal imaging cameras, they are able to measure the temperature of each plant part separately. The research and the analysis is still ongoing, but initial results show that in a number of nights during the first two weeks of March the flower temperature at Holstein Flowers overnight could be 0 to a maximum of 0.5 ° C degrees colder than the leaf temperature.
In general, the leaf temperature was about 1 to 1.5 ° C colder than the ambient air temperature. At Zuijderwijk the flower temperature varied between 0.2 ° C colder and 0.2 ° C warmer than the leafs. The leaf temperature was about 0.5 - 1.0 ° C lower than the air temperature. At both growers the flower and leaf temperature almost always was at least 0.5 ° C above the dew point temperature of the air, which means that no leaf condensation occurred in this place.
Partially closed screens
The flowers get colder than the leaves because they protrude above the leaves and radiate to the colder screen. Both growers had their two screens partially closed. With one or two opened screens the flower temperature would even have been lower. With the radiation app the impact of the screens on plant temperature can be viewed in detail.
Differences
What causes the differences between flower and leaf temperature at both growers, is still unknown. These differences could possibly be explained by differences in the dehumidification system. Because of the circulation capacity at Zuijderwijk & Witzier, the air velocity in the greenhouse could be higher, so that the heat transfer between flower and air is higher. This is why the flower and plant temperature are closer to the ambient air temperature.
The differences between air, leaf and flower are very important parameters to avoid condensation in practice. In effect the flower and leaf temperature must be higher than the dew point temperature of the air. Of course the accuracy of the temperature/RH sensors must be taken into account and the fact that measuring is done at one place only.
Wageningen University and Research, Business Unit Greenhouse Horticulture, together with Inno-Agro and Flori Consult Group, intensively monitor the cultivation at Holstein Flowers and Zuijderwijk & Witzier so that maximum efficiency is obtained from their systems with the aim to further improve the quality of gerberas and reduce the energy consumption.
Source: Greenhouse as Energy Source (text: Bram Vanthoor, Wageningen University & Research, Business Unit Greenhouse Horticulture)