USING THERMODYNAMIC DEHUMIDIFICATION IN SOILLESS TOMATO CROP IN GREENHOUSE: APPLICATION IN THE WEST OF FRANCE

In the perspective to reduce the energy costs in heated glasshouses, the research works at the Ctifl Center in Carquefou focused on the air processing techniques such as the thermodynamic dehumidification as an alternative to the conventional and expensive dehumidification both based on heating and aeration. Following an experi¬ment conducted in 2011 and targeted on fruit yield improvement to secure the technical and economic viability of this new system, the investigation in 2012 was about the specific management of humidity during the early-morning increase of temperature, with a view to limit the sanitary risks linked to Botrytis cinerea and to optimize energy consumption by providing an alternative heating source. The objective of this study was therefore to characterize the impact of the use of thermo¬dynamic dehumidification for that purpose on glasshouse climate, plant development and microclimate, agronomic yield and energy balance. The results demonstrated that: i) there is no risk of condensation on the tomato fruit in the crop treatment with a dehumidifier, that leads to a perfect sanitary control towards Botrytis despite the absence of heating and slightly lower temperatures of air and fruit compared to the control compartment with classic heating network; ii) plant growth and development and cumulated yield on the whole campaign scale are generally similar between both treatments; iii) the energy saving with thermodynamic dehumidification reaches 16% compared to the control. However, when considering the costs for additional electric consumption and liquid CO₂ supply, the economic balance of the use of a dehumidifier is negative even before taking the investment cost into account. As a consequence, the thermodynamic dehumidification showed not enough advantages to be kept in the French western conditions of soilless tomato crop in glasshouse.