Greenhouses allow horticulturists to better control the growing environment, making more efficient use of water and energy. However the air in greenhouses needs to be refreshed during the day to avoid overheating, and during the night to lower air humidity. This causes respectively water loss through plant transpiration during the day, and nightly loss of heat accumulated in the greenhouse during the day. Installing heat exchangers in solar towers allows taking advantage of natural air circulation in greenhouses to refresh the air without incurring extra energy expenses. In addition, the heat exchanger regulates the greenhouse environment and recovers water and heat which can later be re-used.

The sun heats the air in the solar tower, making it rise and creating a draft that sucks air from the greenhouse. This air is then passed through the coil of a condenser which is cooled with water. The cool coil reduces air temperature and condenses air humidity recovering the water which the plants had lost tthrough transpiration. The cooler and drier air is then sent back to the greenhouse, improving humidity and temperature conditions. The water inside the coil which has been heated by the hot air can be stored in a tank and it can be used later to heat the greenhouse during night. The system avoids having to open the greenhouse to refresh the air, thus minimising heat and humidity losses. In addition it recovers water and heat, improving energy and water efficiency.



The solar tower and the condenser have proven to be very efficient in arid areas. Tests in Almería (Spain) showed that around 85% of irrigation water can be recovered. The recovered water combined with rainwater harvested from the greenhouse roofs made the test self-sufficient as regards to water. In addition, the system offers potential to be used for recycling grey or low quality water to later use it for irrigation.