In Ethiopia almost most greenhouses are equipped with fixed ventilation owing to the fact that its influence on CO2 concentration, indoor temperature and RH% which affects plant growth is not clearly understood or due to lack of capacity. Particularly, relative humidity in the greenhouse not only affects plant growth but also major factor for pest-disease which should be maintained at the required range. In this study, the influences of fixed ventilation opening on indoor CO2 concentration, temperature and relative humidity which consequently affect yield were investigated. To execute simulation and examine the influence of ventilation opening on indoor climate and yield a generic tool or a model set up in Matlab software was employed. For the existing ventilation configuration, simulation of indoor climate was conducted and the result illustrated that low CO2 particularly during day time and high and low temperatures are major problems in the greenhouse. The observed indoor climate beyond the required range inhibits growth.
The result of the sensitivity analysis for summer period showed that one percent increase in ventilation opening increases the CO2 concentration by 0.013%, decreases canopy temperature and vapor concentration by 0.065% and 0.114% respectively and increases yield by 0.328%. During winter period, a percent increase in ventilation area resulted in 0.036% and 0.075% reduction in canopy temperature and vapor concentration respectively, 0.012% increased indoor CO2 concentration and 0.03% increment in dry matter harvest. A yearly base sensitivity analysis illustrated that, a percent increase in ventilation opening area increases the dry matter harvest and interior CO2 by 0.231% and 0.012% respectively and decreases the canopy temperature and vapor concentration by 0.057% and 0.102% respectively.
Thus, production in Ethiopian highland can be improved by providing better ventilation so as to increase the CO2 concentration and reducing extreme high temperature and vapor concentration in the greenhouse which influence the rate of photosynthesis. However, increased ventilation opening should be taken into consideration in relation to evapo-transpiration as a consequence of outdoor wind effect and the cost of insect screen to cover the larger ventilation opening.