Plants release water vapour as they grow. Inside a greenhouse, this creates a challenge that becomes particularly noticeable during cooler months: how can growers remove excess humidity without losing valuable heat?<\/p>\n\n\n\n
The European research project TheGreefa<\/strong> explored an unusual answer \u2014 using a salt solution to absorb moisture from greenhouse air while releasing heat. An article published by the European Commission\u2019s CORDIS service describes how this approach was demonstrated in Switzerland and Tunisia.<\/p>\n\n\n\n Why humidity deserves as much attention as temperature<\/strong><\/p>\n\n\n\n A warm greenhouse can still provide favourable conditions for plant disease. As temperatures fall overnight, moisture can condense on cooler leaves and covering materials. Wet plant surfaces encourage diseases such as grey mould caused by Botrytis.<\/p>\n\n\n\n University of Massachusetts Extension identifies keeping the plant canopy dry, especially between dusk and dawn, as an important part of disease prevention. Watering early enough for foliage to dry, avoiding standing water and maintaining adequate plant spacing can all help reduce the problem.<\/p>\n\n\n\n Removing moisture through ventilation, however, introduces another challenge. During cold weather, exchanging indoor air with outdoor air also releases heat, which can increase the energy needed to maintain growing conditions.<\/p>\n\n\n\n How a salt solution captures moisture<\/strong><\/p>\n\n\n\n TheGreefa investigated thermochemical fluids: salt solutions with the ability to attract and absorb water vapour.<\/p>\n\n\n\n When concentrated solution comes into contact with humid air, it absorbs moisture and releases heat. As it takes up water, the solution becomes diluted. Restoring its concentration requires energy to drive that water out again, allowing the fluid to be reused.<\/p>\n\n\n\n The project\u2019s technical concept explains that regeneration can use heat at temperatures below 60\u00b0C, depending on operating conditions. This creates opportunities to use low-temperature heat sources within greenhouse climate management.<\/p>\n\n\n\n What the demonstrations showed<\/strong><\/p>\n\n\n\n According to the CORDIS article, the Swiss demonstration operated automatically for a year. The project team reported that the system removed the need for outdoor ventilation for humidity control in that demonstration, reducing associated thermal losses.<\/p>\n\n\n\n The process also released heat that could be used inside the greenhouse. Solar heat and waste heat were identified as possible sources of energy for regenerating the solution. These findings demonstrate a promising approach, although they do not establish a universal energy-saving figure for every greenhouse.<\/p>\n\n\n\n A useful perspective for passive greenhouse design<\/strong><\/p>\n\n\n\n For passive greenhouse development, this research raises a practical design question: how can moisture management work together with heat conservation?<\/strong><\/p>\n\n\n\n Our interpretation is that humidity should be considered from the beginning, alongside insulation, solar gains and heat storage. A greenhouse needs a way to manage the moisture continuously produced by its crops, and that choice influences its overall energy balance.<\/p>\n\n\n\n TheGreefa offers a specific example of how these functions can be connected. Its approach invites designers to consider the heat carried by water vapour as a resource worth recovering \u2014 and to assess temperature, moisture and energy as parts of the same growing environment.<\/p>\n\n\n\n Sources<\/strong>:<\/p>\n\n\n\n Plants release water vapour as they grow. Inside a greenhouse, this creates a challenge that becomes particularly noticeable during cooler months: how can growers remove excess humidity without losing valuable<\/p>\n\n