An alternative to conventional fossil fuel heating systems: water filled passive NIR absorbing polyethylene sleeves
Mediterranean greenhouse horticulture must maintain yields and quality of the products during the cold period of the growing season, when theoretically it is more lucrative due to lower operations cost such as fossil fuel energy. However, the microclimate in low cost passive greenhouses that are majority in this region is not optimal for proper growth and productivity of the crops. Specifically the ambient and soil temperatures are sub-optimal, especially during the night, inducing direct damage as well as deterioration or early senescence of the plants. Conventional fossil heating is rarely used by growers in these areas because of costs. This work analysed the performance of an alternative, less expensive passive solar heating system, based on the use of 48 transparent NIR absorbing polyethylene sleeves filled with water (0,048 m3 water m-2 greenhouse soil). Both the water and the NIR absorbing material of the sleeves collected and stored heat during the daytime period inside the greenhouse which was then delivered to the greenhouse soil and the ambient during the night time period. The system was tested in a 1500 m2 Parral-type greenhouse with a soil grown bell pepper crop. An adjacent analogue greenhouse without any heat storage system other than the greenhouse soil itself was used as control. The average minimum air temperatures increases ranged between 1-2.5°C in relation to the reference greenhouse, depending on the radiation incident on the sleeves during the previous day. This temperature increase had a positive effect on the productivity of the pepper crop, with an increase of 13% in the total final marketable yield.
Baeza, E.J., Medrano, E., Sánchez-Guerrero, M.C., Sánchez-González, M.J., Porras, M.E., Giménez, M. and Lorenzo, P. 2017. An alternative to conventional fossil fuel heating systems: water filled passive NIR absorbing polyethylene sleeves. Acta Hort. (ISHS) 1170:765-772
passive greenhouse, pepper, intercepted radiation, temperature, yield