Effect of Greenhouse Geometry on Greenhouse Performance in the Hot Humid Climatic Region of Kenya

Geometry is an integral part of greenhouse design. The Design of a greenhouse has a fundamental impact on its efficiency. Greenhouse designs must take into consideration the prevailing climatic conditions of the location, with special consideration to the most limiting climatic factor. There has been a general disregard for design consideration of greenhouses that are used in the hot humid coastal Kenya, thereby leading to underperformance of greenhouses in the region. In optimizing greenhouse designs for the study region, the Hortipro greenhouse model was modified to design nine greenhouse prototypes based on ventilation (25%, 50%, and 75% of floor area) and height (4 m, 4.5 m, and 5 m) variations. The nine prototypes were evaluated alongside the open field (the control) for their effect on the growth, yield, and quality of a tomato crop. The experiment was conducted at Mtwapa, in coastal Kenya, for two cropping cycles in 2018 using a randomized complete block design. The results of the study showed that tomato plants grown in the open field received significantly (p ≤0.05) higher radiation than those in the greenhouse prototypes. An increase in the size of greenhouse ventilation caused a significant (p ≤ 0.05) increase in the number of tomato fruit clusters per plant. An increase in greenhouse height caused a significant (p ≤ 0.05) increase in tomato fruit yield. Greenhouse prototypes expressed significant (p ≤ 0.05) yield differences owing to varying heights. Based on the results of this study, it can be recommended that a suitable greenhouse for the humid coastal region of Kenya should have a height of 4.5 m or 5 m and ventilation that is 50% or 75% of the floor area, which corresponds to a greenhouse geometry that allows between 31o and 38.7o angle of incidence.