EFFECT OF AERIAL CONDITIONS ON HEAT AND MASS-EXCHANGE BETWEEN PLANTS AND AIR IN GREENHOUSES

Experiments and analysis were conducted to examine the effects of aero dynamic and thermal conditions of greenhouse air on estimation of heat and mass fluxes from a uniform canopy, and the 'aerodynamic resistanc e' formulations in delineating the aerial effects by using similarity numbers or via calibration procedures. The airflow mode in greenhouses was found to be complex, variable, and largely in mixed mode. The dif ferences of air temperature and velocity between above- and within-can opy were so significant that use of different reference values may cau se different classifications of the air flow mode. it was shown that t he resistance determined using similarity numbers is locally defined, must be calculated from within-canopy aerial parameters, and has no po wer in explaining the vertical transport processes in the air column. The aerodynamic resistance calibrated from the sensible heat flux and the temperature difference between leaves and above-canopy air was sho wn to be conceptually different from that determined using similarity numbers, and deficient in describing the exchange processes between pl ants and the greenhouse air. Differentiation between the aerial condit ions within a canopy from those above the canopy was strongly recommen ded for future studies on greenhouse microclimate and transport proces ses.