Solar greenhouses can be considered as efficient places for biological CO2 capture and utilization if CO2 enrichment becomes a common practice there. As CO2 enrichment is applied only when greenhouses are closed, ventilated greenhouses - which represent a large percentage of greenhouses all over the world - cannot be considered for this practice, consequently cannot be available for CO2
capture and utilization. The aim this paper is to show-through modeling and simulation-that these
ventilated greenhouses can be activated for serving as efficient CO2 capture and utilization places if
they are kept closed (to apply CO2 enrichment) and used microclimate control methods alternative to
ventilation. The paper introduces a realistic mathematical model in which all the processes and
phenomena associated with the biological CO2 capture and utilization by photosynthesis inside
greenhouses are considered. The model considers solar radiation attenuation through the atmosphere
and absorption by the greenhouse components. It also accounts for the estimation of radiative heat exchange between the various surfaces inside the greenhouse. The realistic photosynthesis
sub model selected in the present work is a mechanistic one applicable to the commonly planted C3 species. The model also provides a strategy for CO2 enrichment and microclimate
control. In these strategies, the CO2 injection specific rate for enriching the greenhouse air to a
specific concentration, and the cooling and dehumidification specific rates required to be keep the microclimate temperature and relative humidity within the favorable limits, are estimated. The
model validity and accuracy were ensured through the good agreement of its numerical
predictions with the available experimental results in the literature. The effect of different environmental conditions and planting conditions on the CO2 capturing process (the
photosynthesis process) is investigated. Finally, a case study was chosen to investigate the
effects of the cooling method, cooling temperature, planting conditions, and CO2 concentration level on the cumulative amount of captured CO2 considered to represent the greenhouse capturing
performance. The results show that the capturing performance of greenhouse can be enhanced from
value as low as 1.0 g CO2/m
2.day for ventilated greenhouses to value as high as 52 g CO2/m
2.day when alternative microclimate control methods and CO2 enrichment are used. In addition, the
greenhouse has extended ability to capture as high as 140 g CO2/m2.day within its growing period
considering the appropriate plant type. Furthermore, additional benefits besides CO2 capture are
reported for the possible increase of the plant productivity and possible lowering of water
consumption by plants.