Effect of covering materials on energy consumption and greenhouse microclimate

Abstract

The objective of the study was to conduct an extensive energy and microclimatic assessment of different greenhouse covering materials. Single glass (GL) and three types of double polyethylene (PE) claddings were compared. The double polyethylene cladding consisting of an anti-fog thermal film for the inner layer and a standard PE film for the outer layer was the most energy efficient. It had an average measured heat transfer coefficient ( U value) of 2.9 W m −2 K −1. The average U value for the other PE cladding was 3.4 W m −2 K −1. The use of thermal screens in the PE houses during the night reduced heat loss rates by 23–24%. The differences in climates under different claddings is presented in terms of PAR transmission and humidity levels. The measured average PAR transmission during the winter months (November–March) were 0.68, 0.62, 0.65 and 0.60 for glass, anti-fog 1-year, anti-fog 3-year and anti-fog thermal claddings, respectively. In the summer months (April–October) the values were higher. The average vapour pressure deficit in the double PE houses was found to be 0.2 kPa lower than under single glass during the winter season, but no significant difference was observed between various anti-fog films. The use of a thermal screen in a double PE houses caused only a slight increase in greenhouse humidity. The contribution of supplementary lighting to greenhouse heating demand is also presented and discussed.